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HydrogenAn overview

ContentsArticlesOverview 1

Hydrogen 1Antihydrogen 18Hydrogen atom 20Hydrogen-like atom 26Hydrogen spectral series 29Liquid hydrogen 34Solid hydrogen 38Metallic hydrogen 39Nascent hydrogen 43

Isotopes 45

Isotopes of hydrogen 45Deuterium 49Tritium 59Hydrogen-4 69Hydrogen-5 70Spin isomers of hydrogen 71

Reactions 74

Bosch reaction 74Hydrogen cycle 75Hydrogenation 76Dehydrogenation 84Transfer hydrogenation 85Hydrogenolysis 89Hydron 90Sabatier reaction 91

Risks 93

Hydrogen damage 93Hydrogen embrittlement 96Hydrogen leak testing 99Hydrogen safety 100

Fuel 103

Timeline of hydrogen technologies 103Biohydrogen 107Hydrogen production 113Hydrogen infrastructure 118Hydrogen line 119Hydrogen purity 124

ReferencesArticle Sources and Contributors 125Image Sources, Licenses and Contributors 128

Article LicensesLicense 130

1

Overview

Hydrogen

Hydrogen

Appearance

Colorless gas with purple glow in its plasma state

Spectral lines of Hydrogen

General properties

Name, symbol, number hydrogen, H, 1

Pronunciation /ˈhaɪdrɵdʒɪn/[1] HYE-dro-jin

Element category nonmetal

Group, period, block 1, 1, s

Standard atomic weight 1.00794(7) g·mol−1

Electron configuration 1s1

Electrons per shell 1 (Image)

Physical properties

Color colorless

Phase gas

Density (0 °C, 101.325 kPa)0.08988 g/L

Liquid density at m.p. 0.07 (0.0763 solid)[2] g·cm−3

Melting point 14.01 K,-259.14 °C,-434.45 °F

Boiling point 20.28 K,-252.87 °C,-423.17 °F

Triple point 13.8033 K (-259°C), 7.042 kPa

Critical point 32.97 K, 1.293 MPa

Heat of fusion (H2) 0.117 kJ·mol−1

Heat of vaporization (H2) 0.904 kJ·mol−1

Specific heat capacity (25 °C) (H2) 28.836 J·mol−1·K−1

Vapor pressure

Hydrogen 2

P/Pa 1 10 100 1 k 10 k 100 k

at T/K 15 20

Atomic properties

Oxidation states 1, -1(amphoteric oxide)

Electronegativity 2.20 (Pauling scale)

Ionization energies 1st: 1312.0 kJ·mol−1

Covalent radius 31±5 pm

Van der Waals radius 120 pm

Miscellanea

Crystal structure hexagonal

Magnetic ordering diamagnetic[3]

Thermal conductivity (300 K) 0.1805 W·m−1·K−1

Speed of sound (gas, 27 °C) 1310 m/s

CAS registry number 1333-74-0

Most stable isotopes

Main article: Isotopes of hydrogen

iso NA half-life DM DE (MeV) DP

1H 99.985% 1H is stable with 0 neutron

2H 0.015% 2H is stable with 1 neutron

3H trace 12.32 y β− 0.01861 3He

Hydrogen ( /ˈhaɪdrɵdʒɪn/ HYE-dro-jin)[4] is the chemical element with atomic number 1. It is represented by thesymbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest andmost abundant chemical element, constituting roughly 75 % of the Universe's elemental mass.[5] Stars in the mainsequence are mainly composed of hydrogen in its plasma state. Naturally occurring elemental hydrogen is relativelyrare on Earth.The most common isotope of hydrogen is protium (name rarely used, symbol 1H) with a single proton and noneutrons. In ionic compounds it can take a negative charge (an anion known as a hydride and written as H−), or as apositively charged species H+. The latter cation is written as though composed of a bare proton, but in reality,hydrogen cations in ionic compounds always occur as more complex species. Hydrogen forms compounds with mostelements and is present in water and most organic compounds. It plays a particularly important role in acid-basechemistry with many reactions exchanging protons between soluble molecules. As the simplest atom known, thehydrogen atom has been of theoretical use. For example, as the only neutral atom with an analytic solution to theSchrödinger equation, the study of the energetics and bonding of the hydrogen atom played a key role in thedevelopment of quantum mechanics.Hydrogen gas (now known to be H2) was first artificially produced in the early 16th century, via the mixing of metals with strong acids. In 1766–81, Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance,[6] and that it produces water when burned, a property which later gave it its name, which in Greek means

Hydrogen 3

"water-former." At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless,highly combustible diatomic gas with the molecular formula H2.Industrial production is mainly from the steam reforming of natural gas, and less often from more energy-intensivehydrogen production methods like the electrolysis of water.[7] Most hydrogen is employed near its production site,with the two largest uses being fossil fuel processing (e.g., hydrocracking) and ammonia production, mostly for thefertilizer market.Hydrogen is a concern in metallurgy as it can embrittle many metals,[8] complicating the design of pipelines andstorage tanks.[9]

Properties

Combustion

The Space Shuttle Main Engineburns hydrogen with oxygen,

producing a nearly invisible flame atfull thrust.

Hydrogen gas (dihydrogen or molecular hydrogen)[10] is highly flammable andwill burn in air at a very wide range of concentrations between 4% and 75% byvolume.[11] The enthalpy of combustion for hydrogen is −286 kJ/mol:[12]

2 H2(g) + O2(g) → 2 H2O(l) + 572 kJ (286 kJ/mol)[13]

Hydrogen gas forms explosive mixtures with air in the concentration range4–74% (volume per cent of hydrogen in air) and with chlorine in the range5–95%. The mixtures spontaneously detonate by spark, heat or sunlight. Thehydrogen autoignition temperature, the temperature of spontaneous ignition inair, is 500 °C (932 °F).[14] Pure hydrogen-oxygen flames emit ultraviolet lightand are nearly invisible to the naked eye, as illustrated by the faint plume of theSpace Shuttle main engine compared to the highly visible plume of a SpaceShuttle Solid Rocket Booster. The detection of a burning hydrogen leak mayrequire a flame detector; such leaks can be very dangerous. The destruction of

the Hindenburg airship was an infamous example of hydrogen combustion; the cause is debated, but the visibleflames were the result of combustible materials in the ship's skin.[15] Because hydrogen is buoyant in air, hydrogenflames tend to ascend rapidly and cause less damage than hydrocarbon fires. Two-thirds of the Hindenburgpassengers survived the fire, and many deaths were instead the result of falls or burning diesel fuel.[16]

H2 reacts with every oxidizing element. Hydrogen can react spontaneously and violently at room temperature withchlorine and fluorine to form the corresponding hydrogen halides, hydrogen chloride and hydrogen fluoride, whichare also potentially dangerous acids.[17]

Hydrogen 4

Electron energy levels

Depiction of a hydrogen atom showing thediameter as about twice the Bohr model radius

(image not to scale).

The ground state energy level of the electron in a hydrogen atom is−13.6 eV, which is equivalent to an ultraviolet photon of roughly92 nm wavelength.[18]

The energy levels of hydrogen can be calculated fairly accurately usingthe Bohr model of the atom, which conceptualizes the electron as"orbiting" the proton in analogy to the Earth's orbit of the sun.However, the electromagnetic force attracts electrons and protons toone another, while planets and celestial objects are attracted to eachother by gravity. Because of the discretization of angular momentumpostulated in early quantum mechanics by Bohr, the electron in theBohr model can only occupy certain allowed distances from the proton,and therefore only certain allowed energies.[19]

A more accurate description of the hydrogen atom comes from a purelyquantum mechanical treatment that uses the Schrödinger equation or the equivalent Feynman path integralformulation to calculate the probability density of the electron around the proton.[20]

Elemental molecular forms

First tracks observed in liquid hydrogen bubblechamber at the Bevatron

There exist two different spin isomers of hydrogen diatomic moleculesthat differ by the relative spin of their nuclei.[21] In the orthohydrogenform, the spins of the two protons are parallel and form a triplet statewith a molecular spin quantum number of 1 (½+½); in theparahydrogen form the spins are antiparallel and form a singlet with amolecular spin quantum number of 0 (½-½). At standard temperatureand pressure, hydrogen gas contains about 25% of the para form and75% of the ortho form, also known as the "normal form".[22] Theequilibrium ratio of orthohydrogen to parahydrogen depends ontemperature, but because the ortho form is an excited state and has ahigher energy than the para form, it is unstable and cannot be purified.At very low temperatures, the equilibrium state is composed almostexclusively of the para form. The liquid and gas phase thermalproperties of pure parahydrogen differ significantly from those of thenormal form because of differences in rotational heat capacities, asdiscussed more fully in Spin isomers of hydrogen.[23] The ortho/paradistinction also occurs in other hydrogen-containing molecules orfunctional groups, such as water and methylene, but is of littlesignificance for their thermal properties.[24]

The uncatalyzed interconversion between para and ortho H2 increases with increasing temperature; thus rapidlycondensed H2 contains large quantities of the high-energy ortho form that converts to the para form very slowly.[25]

The ortho/para ratio in condensed H2 is an important consideration in the preparation and storage of liquid hydrogen:the conversion from ortho to para is exothermic and produces enough heat to evaporate some of the hydrogen liquid,leading to loss of liquefied material. Catalysts for the ortho-para interconversion, such as ferric oxide, activatedcarbon, platinized asbestos, rare earth metals, uranium compounds, chromic oxide, or some nickel[26] compounds,are used during hydrogen cooling.[27]

Hydrogen 5

A molecular form called protonated molecular hydrogen, or H , is found in the interstellar medium (ISM), where itis generated by ionization of molecular hydrogen from cosmic rays. It has also been observed in the upperatmosphere of the planet Jupiter. This molecule is relatively stable in the environment of outer space due to the lowtemperature and density. H is one of the most abundant ions in the Universe, and it plays a notable role in thechemistry of the interstellar medium.[28] Neutral triatomic hydrogen H3 can only exist in an excited from and isunstable.[29]

Compounds

Covalent and organic compounds

While H2 is not very reactive under standard conditions, it does form compounds with most elements. Millions ofhydrocarbons are known, but they are not formed by the direct reaction of elementary hydrogen and carbon.Hydrogen can form compounds with elements that are more electronegative, such as halogens (e.g., F, Cl, Br, I); inthese compounds hydrogen takes on a partial positive charge.[30] When bonded to fluorine, oxygen, or nitrogen,hydrogen can participate in a form of strong noncovalent bonding called hydrogen bonding, which is critical to thestability of many biological molecules.[31] [32] Hydrogen also forms compounds with less electronegative elements,such as the metals and metalloids, in which it takes on a partial negative charge. These compounds are often knownas hydrides.[33]

Hydrogen forms a vast array of compounds with carbon. Because of their general association with living things,these compounds came to be called organic compounds;[34] the study of their properties is known as organicchemistry[35] and their study in the context of living organisms is known as biochemistry.[36] By some definitions,"organic" compounds are only required to contain carbon. However, most of them also contain hydrogen, andbecause it is the carbon-hydrogen bond which gives this class of compounds most of its particular chemicalcharacteristics, carbon-hydrogen bonds are required in some definitions of the word "organic" in chemistry.[34]

In inorganic chemistry, hydrides can also serve as bridging ligands that link two metal centers in a coordinationcomplex. This function is particularly common in group 13 elements, especially in boranes (boron hydrides) andaluminium complexes, as well as in clustered carboranes.[37]

Hydrides

Compounds of hydrogen are often called hydrides, a term that is used fairly loosely. The term "hydride" suggeststhat the H atom has acquired a negative or anionic character, denoted H−, and is used when hydrogen forms acompound with a more electropositive element. The existence of the hydride anion, suggested by Gilbert N. Lewis in1916 for group I and II salt-like hydrides, was demonstrated by Moers in 1920 with the electrolysis of molten lithiumhydride (LiH), that produced a stoichiometric quantity of hydrogen at the anode.[38] For hydrides other than group Iand II metals, the term is quite misleading, considering the low electronegativity of hydrogen. An exception in groupII hydrides is BeH2, which is polymeric. In lithium aluminium hydride, the AlH anion carries hydridic centers firmlyattached to the Al(III). Although hydrides can be formed with almost all main-group elements, the number andcombination of possible compounds varies widely; for example, there are over 100 binary borane hydrides known,but only one binary aluminium hydride.[39] Binary indium hydride has not yet been identified, although largercomplexes exist.[40]

Hydrogen 6

Protons and acids

Oxidation of hydrogen, in the sense of removing its electron, formally gives H+, containing no electrons and anucleus which is usually composed of one proton. That is why H+ is often called a proton. This species is central todiscussion of acids. Under the Bronsted-Lowry theory, acids are proton donors, while bases are proton acceptors.A bare proton, H+, cannot exist in solution or in ionic crystals, because of its unstoppable attraction to other atoms ormolecules with electrons. Except at the high temperatures associated with plasmas, such protons cannot be removedfrom the electron clouds of atoms and molecules, and will remain attached to them. However, the term 'proton' issometimes used loosely and metaphorically to refer to positively charged or cationic hydrogen attached to otherspecies in this fashion, and as such is denoted "H+" without any implication that any single protons exist freely as aspecies.To avoid the implication of the naked "solvated proton" in solution, acidic aqueous solutions are sometimesconsidered to contain a less unlikely fictitious species, termed the "hydronium ion" (H3O+). However, even in thiscase, such solvated hydrogen cations are thought more realistically physically to be organized into clusters that formspecies closer to H9O .[41] Other oxonium ions are found when water is in solution with other solvents.[42]

Although exotic on earth, one of the most common ions in the universe is the H ion, known as protonatedmolecular hydrogen or the triatomic hydrogen cation.[43]

Isotopes

Hydrogen discharge (spectrum) tube

Deuterium discharge (spectrum) tube

Hydrogen has three naturally occurring isotopes, denoted 1H, 2H and3H. Other, highly unstable nuclei (4H to 7H) have been synthesized inthe laboratory but not observed in nature.[44] [45]

• 1H is the most common hydrogen isotope with an abundance ofmore than 99.98%. Because the nucleus of this isotope consists ofonly a single proton, it is given the descriptive but rarely usedformal name protium.[46]

• 2H, the other stable hydrogen isotope, is known as deuterium andcontains one proton and one neutron in its nucleus. Essentially alldeuterium in the universe is thought to have been produced at thetime of the Big Bang, and has endured since that time. Deuterium isnot radioactive, and does not represent a significant toxicity hazard.

Water enriched in molecules that include deuterium instead of normal hydrogen is called heavy water. Deuteriumand its compounds are used as a non-radioactive label in chemical experiments and in solvents for 1H-NMRspectroscopy.[47] Heavy water is used as a neutron moderator and coolant for nuclear reactors. Deuterium is also apotential fuel for commercial nuclear fusion.[48]

• 3H is known as tritium and contains one proton and two neutrons in its nucleus. It is radioactive, decaying intohelium-3 through beta decay with a half-life of 12.32 years.[37] Small amounts of tritium occur naturally becauseof the interaction of cosmic rays with atmospheric gases; tritium has also been released during nuclear weaponstests.[49] It is used in nuclear fusion reactions,[50] as a

Hydrogen 7

Protium, the most common isotope of hydrogen,has one proton and one electron. Unique among

all stable isotopes, it has no neutrons (seediproton for discussion of why others do not

exist).

tracer in isotope geochemistry,[51] and specialized in self-poweredlighting devices.[52] Tritium has also been used in chemical andbiological labeling experiments as a radiolabel.[53]

Hydrogen is the only element that has different names for its isotopesin common use today. (During the early study of radioactivity, variousheavy radioactive isotopes were given names, but such names are nolonger used). The symbols D and T (instead of 2H and 3H) aresometimes used for deuterium and tritium, but the correspondingsymbol P is already in use for phosphorus and thus is not available forprotium.[54] In its nomenclatural guidelines, the International Union ofPure and Applied Chemistry allows any of D, T, 2H, and 3H to be used,although 2H and 3H are preferred.[55]

History

Discovery and useHydrogen gas, H2, was first artificially produced and formally described by T. Von Hohenheim (also known asParacelsus, 1493–1541) via the mixing of metals with strong acids.[56] He was unaware that the flammable gasproduced by this chemical reaction was a new chemical element. In 1671, Robert Boyle rediscovered and describedthe reaction between iron filings and dilute acids, which results in the production of hydrogen gas.[57] [58] In 1766,Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by identifying the gas from ametal-acid reaction as "flammable air" and further finding in 1781 that the gas produces water when burned. He isusually given credit for its discovery as an element.[59] [60] In 1783, Antoine Lavoisier gave the element the namehydrogen (from the Greek ὕδρω hydro meaning water and γενῆς genes meaning creator)[61] when he and Laplacereproduced Cavendish's finding that water is produced when hydrogen is burned.[60]

Hydrogen was liquefied for the first time by James Dewar in 1898 by using regenerative cooling and his invention,the vacuum flask.[60] He produced solid hydrogen the next year.[60] Deuterium was discovered in December 1931 byHarold Urey, and tritium was prepared in 1934 by Ernest Rutherford, Mark Oliphant, and Paul Harteck.[59] Heavywater, which consists of deuterium in the place of regular hydrogen, was discovered by Urey's group in 1932.[60]

François Isaac de Rivaz built the first internal combustion engine powered by a mixture of hydrogen and oxygen in1806. Edward Daniel Clarke invented the hydrogen gas blowpipe in 1819. The Döbereiner's lamp and limelight wereinvented in 1823.[60]

The first hydrogen-filled balloon was invented by Jacques Charles in 1783.[60] Hydrogen provided the lift for thefirst reliable form of air-travel following the 1852 invention of the first hydrogen-lifted airship by Henri Giffard.[60]

German count Ferdinand von Zeppelin promoted the idea of rigid airships lifted by hydrogen that later were calledZeppelins; the first of which had its maiden flight in 1900.[60] Regularly scheduled flights started in 1910 and by theoutbreak of World War I in August 1914, they had carried 35,000 passengers without a serious incident.Hydrogen-lifted airships were used as observation platforms and bombers during the war.The first non-stop transatlantic crossing was made by the British airship R34 in 1919. Regular passenger service resumed in the 1920s and the discovery of helium reserves in the United States promised increased safety, but the U.S. government refused to sell the gas for this purpose. Therefore, H2 was used in the Hindenburg airship, which

Hydrogen 8

was destroyed in a midair fire over New Jersey on May 6, 1937.[60] The incident was broadcast live on radio andfilmed. Ignition of leaking hydrogen is widely assumed to be the cause, but later investigations pointed to theignition of the aluminized fabric coating by static electricity. But the damage to hydrogen's reputation as a lifting gaswas already done. In the same year the first hydrogen-cooled turbogenerator went into service with gaseoushydrogen as a coolant in the rotor and the stator in 1937 at Dayton, Ohio, by the Dayton Power & Light Co,[62]

because of the thermal conductivity of hydrogen gas this is the most common type in its field today. The nickelhydrogen battery was used for the first time in 1977 aboard the U.S. Navy's Navigation technology satellite-2(NTS-2).[63] For example, the ISS,[64] Mars Odyssey[65] and the Mars Global Surveyor[66] are equipped withnickel-hydrogen batteries. The Hubble Space Telescope, at the time its original batteries were finally changed inMay 2009, more than 19 years after launch, led with the highest number of charge/discharge cycles.

Role in quantum theory

Hydrogen emission spectrum lines in the visible range. These are the four visible lines ofthe Balmer series

Because of its relatively simple atomicstructure, consisting only of a protonand an electron, the hydrogen atom,together with the spectrum of lightproduced from it or absorbed by it, hasbeen central to the development of thetheory of atomic structure.[67] Furthermore, the corresponding simplicity of the hydrogen molecule and thecorresponding cation H2

+ allowed fuller understanding of the nature of the chemical bond, which followed shortlyafter the quantum mechanical treatment of the hydrogen atom had been developed in the mid-1920s.

One of the first quantum effects to be explicitly noticed (but not understood at the time) was a Maxwell observationinvolving hydrogen, half a century before full quantum mechanical theory arrived. Maxwell observed that thespecific heat capacity of H2 unaccountably departs from that of a diatomic gas below room temperature and begins toincreasingly resemble that of a monatomic gas at cryogenic temperatures. According to quantum theory, thisbehavior arises from the spacing of the (quantized) rotational energy levels, which are particularly wide-spaced in H2because of its low mass. These widely spaced levels inhibit equal partition of heat energy into rotational motion inhydrogen at low temperatures. Diatomic gases composed of heavier atoms do not have such widely spaced levelsand do not exhibit the same effect.[68]

Natural occurrence

Hydrogen 9

NGC 604, a giant region of ionized hydrogen inthe Triangulum Galaxy

Hydrogen is the most abundant element in the universe, making up75% of normal matter by mass and over 90% by number of atoms.[69]

This element is found in great abundance in stars and gas giant planets.Molecular clouds of H2 are associated with star formation. Hydrogenplays a vital role in powering stars through proton-proton reaction andCNO cycle nuclear fusion.[70]

Throughout the universe, hydrogen is mostly found in the atomic andplasma states whose properties are quite different from molecularhydrogen. As a plasma, hydrogen's electron and proton are not boundtogether, resulting in very high electrical conductivity and highemissivity (producing the light from the sun and other stars). Thecharged particles are highly influenced by magnetic and electric fields.For example, in the solar wind they interact with the Earth'smagnetosphere giving rise to Birkeland currents and the aurora.Hydrogen is found in the neutral atomic state in the Interstellar

medium. The large amount of neutral hydrogen found in the damped Lyman-alpha systems is thought to dominatethe cosmological baryonic density of the Universe up to redshift z=4.[71]

Under ordinary conditions on Earth, elemental hydrogen exists as the diatomic gas, H2 (for data see table). However,hydrogen gas is very rare in the Earth's atmosphere (1 ppm by volume) because of its light weight, which enables itto escape from Earth's gravity more easily than heavier gases. However, hydrogen is the third most abundant elementon the Earth's surface.[72] Most of the Earth's hydrogen is in the form of chemical compounds such as hydrocarbonsand water.[37] Hydrogen gas is produced by some bacteria and algae and is a natural component of flatus, as ismethane, itself a hydrogen source of increasing importance.[73]

ProductionH2 is produced in chemistry and biology laboratories, often as a by-product of other reactions; in industry for thehydrogenation of unsaturated substrates; and in nature as a means of expelling reducing equivalents in biochemicalreactions.

LaboratoryIn the laboratory, H2 is usually prepared by the reaction of acids on metals such as zinc with Kipp's apparatus.

Zn + 2 H+ → Zn2+ + H2Aluminium can also produce H2 upon treatment with bases:

2 Al + 6 H2O + 2 OH− → 2 Al(OH) + 3 H2The electrolysis of water is a simple method of producing hydrogen. A low voltage current is run through the water,and gaseous oxygen forms at the anode while gaseous hydrogen forms at the cathode. Typically the cathode is madefrom platinum or another inert metal when producing hydrogen for storage. If, however, the gas is to be burnt onsite, oxygen is desirable to assist the combustion, and so both electrodes would be made from inert metals. (Iron, forinstance, would oxidize, and thus decrease the amount of oxygen given off.) The theoretical maximum efficiency(electricity used vs. energetic value of hydrogen produced) is between 80–94%.[74]

2 H2O(aq) → 2 H2(g) + O2(g)In 2007, it was discovered that an alloy of aluminium and gallium in pellet form added to water could be used to generate hydrogen. The process also creates alumina, but the expensive gallium, which prevents the formation of an oxide skin on the pellets, can be re-used. This has important potential implications for a hydrogen economy, as

Hydrogen 10

hydrogen can be produced on-site and does not need to be transported.[75]

IndustrialHydrogen can be prepared in several different ways, but economically the most important processes involve removalof hydrogen from hydrocarbons. Commercial bulk hydrogen is usually produced by the steam reforming of naturalgas.[76] At high temperatures (1000–1400 K, 700–1100 °C or 1300–2000 °F), steam (water vapor) reacts withmethane to yield carbon monoxide and H2.

CH4 + H2O → CO + 3 H2This reaction is favored at low pressures but is nonetheless conducted at high pressures (2.0  MPa, 20 atm or600 inHg). This is because high-pressure H2 is the most marketable product and Pressure Swing Adsorption (PSA)purification systems work better at higher pressures. The product mixture is known as "synthesis gas" because it isoften used directly for the production of methanol and related compounds. Hydrocarbons other than methane can beused to produce synthesis gas with varying product ratios. One of the many complications to this highly optimizedtechnology is the formation of coke or carbon:

CH4 → C + 2 H2Consequently, steam reforming typically employs an excess of H2O. Additional hydrogen can be recovered from thesteam by use of carbon monoxide through the water gas shift reaction, especially with an iron oxide catalyst. Thisreaction is also a common industrial source of carbon dioxide:[76]

CO + H2O → CO2 + H2Other important methods for H2 production include partial oxidation of hydrocarbons:[77]

2 CH4 + O2 → 2 CO + 4 H2and the coal reaction, which can serve as a prelude to the shift reaction above:[76]

C + H2O → CO + H2Hydrogen is sometimes produced and consumed in the same industrial process, without being separated. In theHaber process for the production of ammonia, hydrogen is generated from natural gas.[78] Electrolysis of brine toyield chlorine also produces hydrogen as a co-product.[79]

ThermochemicalThere are more than 200 thermochemical cycles which can be used for water splitting, around a dozen of thesecycles such as the iron oxide cycle, cerium(IV) oxide-cerium(III) oxide cycle, zinc zinc-oxide cycle, sulfur-iodinecycle, copper-chlorine cycle and hybrid sulfur cycle are under research and in testing phase to produce hydrogen andoxygen from water and heat without using electricity.[80] A number of laboratories (including in France, Germany,Greece, Japan, and the USA) are developing thermochemical methods to produce hydrogen from solar energy andwater.[81]

Hydrogen 11

Anaerobic corrosionUnder anaerobic conditions, iron and steel alloys are slowly oxidized by the protons of water concomitantly reducedin molecular hydrogen (H2). The anaerobic corrosion of iron leads first to the formation of ferrous hydroxide (greenrust) and can be described by the following reaction:

Fe + 2 H2O → Fe(OH)2 + H2In its turn, under anaerobic conditions, the ferrous hydroxide (Fe(OH)2 ) can be oxidized by the protons of water toform magnetite and molecular hydrogen. This process is described by the Schikorr reaction:

3 Fe(OH)2 → Fe3O4 + 2 H2O + H2ferrous hydroxide → magnetite + water + hydrogen

The well crystallized magnetite (Fe3O4) is thermodynamically more stable than the ferrous hydroxide (Fe(OH)2 ).This process occurs during the anaerobic corrosion of iron and steel in oxygen-free groundwater and in reducingsoils below the water table.

Geological occurrence: the serpentinization reactionIn the absence of atmospheric oxygen (O2), in deep geological conditions prevailing far away from Earthatmosphere, hydrogen (H2) is produced during the process of serpentinization by the anaerobic oxidation by thewater protons (H+) of the ferrous (Fe2+) silicate present in the crystal lattice of the fayalite (Fe2SiO4, the olivineiron-endmember). The corresponding reaction leading to the formation of magnetite (Fe3O4), quartz (SiO2) andhydrogen (H2) is the following:

3 Fe2SiO4 + 2 H2O → 2 Fe3O4 + 3 SiO2 + 3 H2fayalite + water → magnetite + quartz + hydrogen

This reaction closely resembles the Schikorr reaction observed in the anaerobic oxidation of the ferrous hydroxide incontact with water.

ApplicationsLarge quantities of H2 are needed in the petroleum and chemical industries. The largest application of H2 is for theprocessing ("upgrading") of fossil fuels, and in the production of ammonia. The key consumers of H2 in thepetrochemical plant include hydrodealkylation, hydrodesulfurization, and hydrocracking. H2 has several otherimportant uses. H2 is used as a hydrogenating agent, particularly in increasing the level of saturation of unsaturatedfats and oils (found in items such as margarine), and in the production of methanol. It is similarly the source ofhydrogen in the manufacture of hydrochloric acid. H2 is also used as a reducing agent of metallic ores.[82]

Hydrogen is highly soluble in many rare earth and transition metals[83] and is soluble in both nanocrystalline andamorphous metals.[84] Hydrogen solubility in metals is influenced by local distortions or impurities in the crystallattice.[85] These properties may be useful when hydrogen is purified by passage through hot palladium disks, but thegas serves as a metallurgical problem as hydrogen solubility contributes in an unwanted way to embrittle manymetals,[8] complicating the design of pipelines and storage tanks.[9]

Apart from its use as a reactant, H2 has wide applications in physics and engineering. It is used as a shielding gas inwelding methods such as atomic hydrogen welding.[86] [87] H2 is used as the rotor coolant in electrical generators atpower stations, because it has the highest thermal conductivity of any gas. Liquid H2 is used in cryogenic research,including superconductivity studies.[88] Because H2 is lighter than air, having a little more than 1⁄15 of the density ofair, it was once widely used as a lifting gas in balloons and airships.[89]

In more recent applications, hydrogen is used pure or mixed with nitrogen (sometimes called forming gas) as a tracer gas for minute leak detection. Applications can be found in the automotive, chemical, power generation, aerospace, and telecommunications industries.[90] Hydrogen is an authorized food additive (E 949) that allows food package

Hydrogen 12

leak testing among other anti-oxidizing properties.[91]

Hydrogen's rarer isotopes also each have specific applications. Deuterium (hydrogen-2) is used in nuclear fissionapplications as a moderator to slow neutrons, and in nuclear fusion reactions.[60] Deuterium compounds haveapplications in chemistry and biology in studies of reaction isotope effects.[92] Tritium (hydrogen-3), produced innuclear reactors, is used in the production of hydrogen bombs,[93] as an isotopic label in the biosciences,[53] and as aradiation source in luminous paints.[94]

The triple point temperature of equilibrium hydrogen is a defining fixed point on the ITS-90 temperature scale at13.8033 kelvins.[95]

Energy carrierHydrogen is not an energy resource,[96] except in the hypothetical context of commercial nuclear fusion power plantsusing deuterium or tritium, a technology presently far from development.[97] The Sun's energy comes from nuclearfusion of hydrogen, but this process is difficult to achieve controllably on Earth.[98] Elemental hydrogen from solar,biological, or electrical sources require more energy to make it than is obtained by burning it, so in these caseshydrogen functions as an energy carrier, like a battery. Hydrogen may be obtained from fossil sources (such asmethane), but these sources are unsustainable.[96]

The energy density per unit volume of both liquid hydrogen and compressed hydrogen gas at any practicablepressure is significantly less than that of traditional fuel sources, although the energy density per unit fuel mass ishigher.[96] Nevertheless, elemental hydrogen has been widely discussed in the context of energy, as a possible futurecarrier of energy on an economy-wide scale.[99] For example, CO2 sequestration followed by carbon capture andstorage could be conducted at the point of H2 production from fossil fuels.[100] Hydrogen used in transportationwould burn relatively cleanly, with some NOx emissions,[101] but without carbon emissions.[100] However, theinfrastructure costs associated with full conversion to a hydrogen economy would be substantial.[102]

Semiconductor industryHydrogen is employed to saturate broken ("dangling") bonds of amorphous silicon and amorphous carbon that helpsstabilizing material properties.[103] It is also a potential electron donor in various oxide materials, including ZnO,[104]

[105] SnO2, CdO, MgO,[106] ZrO2, HfO2, La2O3, Y2O3, TiO2, SrTiO3, LaAlO3, SiO2, Al2O3, ZrSiO4, HfSiO4, andSrZrO3.[107]

Biological reactionsH2 is a product of some types of anaerobic metabolism and is produced by several microorganisms, usually viareactions catalyzed by iron- or nickel-containing enzymes called hydrogenases. These enzymes catalyze thereversible redox reaction between H2 and its component two protons and two electrons. Creation of hydrogen gasoccurs in the transfer of reducing equivalents produced during pyruvate fermentation to water.[108]

Water splitting, in which water is decomposed into its component protons, electrons, and oxygen, occurs in the lightreactions in all photosynthetic organisms. Some such organisms, including the alga Chlamydomonas reinhardtii andcyanobacteria, have evolved a second step in the dark reactions in which protons and electrons are reduced to formH2 gas by specialized hydrogenases in the chloroplast.[109] Efforts have been undertaken to genetically modifycyanobacterial hydrogenases to efficiently synthesize H2 gas even in the presence of oxygen.[110] Efforts have alsobeen undertaken with genetically modified alga in a bioreactor.[111]

Hydrogen 13

Safety and precautionsHydrogen poses a number of hazards to human safety, from potential detonations and fires when mixed with air tobeing an asphyxant in its pure, oxygen-free form.[112] In addition, liquid hydrogen is a cryogen and presents dangers(such as frostbite) associated with very cold liquids.[113] Hydrogen dissolves in many metals, and, in addition toleaking out, may have adverse effects on them, such as hydrogen embrittlement,[114] leading to cracks andexplosions.[115] Hydrogen gas leaking into external air may spontaneously ignite. Moreover, hydrogen fire, whilebeing extremely hot, is almost invisible, and thus can lead to accidental burns.[116]

Even interpreting the hydrogen data (including safety data) is confounded by a number of phenomena. Manyphysical and chemical properties of hydrogen depend on the parahydrogen/orthohydrogen ratio (it often takes daysor weeks at a given temperature to reach the equilibrium ratio, for which the data is usually given). Hydrogendetonation parameters, such as critical detonation pressure and temperature, strongly depend on the containergeometry.[112]

See also• Hydrogen atom• Hydrogen bond• Hydrogen ion• Hydrogen production• Isotopes of hydrogen• Liquid hydrogen• Metallic hydrogen• Solid hydrogen• Fuel cell

Notes[1] Simpson, J.A.; Weiner, E.S.C. (1989). "Hydrogen". Oxford English Dictionary. 7 (2nd ed.). Clarendon Press. ISBN 0-19-861219-2.[2] Wiberg, Egon; Wiberg, Nils; Holleman, Arnold Frederick (2001). Inorganic chemistry (http:/ / books. google. com/

books?id=vEwj1WZKThEC& pg=PA240). Academic Press. p. 240. ISBN 0123526515. .[3] Magnetic susceptibility of the elements and inorganic compounds (http:/ / www-d0. fnal. gov/ hardware/ cal/ lvps_info/ engineering/

elementmagn. pdf), in Handbook of Chemistry and Physics 81st edition, CRC press.[4] Simpson, J.A.; Weiner, E.S.C. (1989). "Hydrogen". Oxford English Dictionary. 7 (2nd ed.). Clarendon Press. ISBN 0-19-861219-2.[5] Palmer, D. (13 September 1997). "Hydrogen in the Universe" (http:/ / imagine. gsfc. nasa. gov/ docs/ ask_astro/ answers/ 971113i. html).

NASA. . Retrieved 2008-02-05.[6] " Discovering the Elements (http:/ / www. bbc. co. uk/ programmes/ b00q2mk5)". Presenter: Professor Jim Al-Khalili. Chemistry: A Volatile

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Center. 2007. . Retrieved 2008-02-05.[8] Rogers, H.C. (1999). "Hydrogen Embrittlement of Metals". Science 159 (3819): 1057–1064. doi:10.1126/science.159.3819.1057.

PMID 17775040.[9] Christensen, C.H.; Nørskov, J.K.; Johannessen, T. (9 July 2005). "Making society independent of fossil fuels — Danish researchers reveal

new technology" (http:/ / www. dtu. dk/ English/ About_DTU/ News. aspx?guid={E6FF7D39-1EDD-41A4-BC9A-20455C2CF1A7}).Technical University of Denmark. . Retrieved 2008-03-28.

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[12] Committee on Alternatives and Strategies for Future Hydrogen Production and Use, US National Research Council, US National Academyof Engineering (2004). The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs (http:/ / books. google. com/?id=ugniowznToAC& pg=PA240). National Academies Press. p. 240. ISBN 0309091632. .

[13] 286 kJ/mol: energy per mole of the combustible material (hydrogen)

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[109] Kruse, O.; Rupprecht, J.; Bader, K.-P.; Thomas-Hall, S.; Schenk, P. M.; Finazzi, G.; Hankamer, B (2005). "Improved photobiological H2production in engineered green algal cells". The Journal of Biological Chemistry 280 (40): 34170–7. doi:10.1074/jbc.M503840200.PMID 16100118.

[110] Smith, H. O.; Xu, Q (2005). "IV.E.6 Hydrogen from Water in a Novel Recombinant Oxygen-Tolerant Cyanobacteria System" (http:/ / ec.europa. eu/ food/ fs/ sfp/ addit_flavor/ flav15_en. pdf) (PDF). FY2005 Progress Report. United States Department of Energy. . Retrieved2008-02-05.

[111] Williams, Chris (2006-02-24). "Pond life: the future of energy" (http:/ / www. theregister. co. uk/ 2006/ 02/ 24/ pond_scum_breakthrough/). Science (The Register). . Retrieved 2008-03-24.

[112] Smith, H. O.; Xu, Q (1997). "Safety Standard for Hydrogen and Hydrogen Systems" (http:/ / www. hq. nasa. gov/ office/ codeq/ doctree/canceled/ 871916. pdf) (PDF). NASA. . Retrieved 2008-02-05.

[113] "Liquid Hydrogen MSDS" (http:/ / www. hydrogenandfuelcellsafety. info/ resources/ mdss/ Praxair-LH2. pdf) (PDF). Praxair, Inc..September 2004. . Retrieved 2008-04-16.

[114] "'Bugs' and hydrogen embrittlement" (http:/ / jstor. org/ stable/ 3970088). Science News (Washington D.C.) 128 (3): 41. 1985-07-20.doi:10.2307/3970088. .

[115] Hayes, B.. "Union Oil Amine Absorber Tower" (http:/ / www. twi. co. uk/ content/ oilgas_casedown29. html) (in en). TWI. . Retrieved 29January 2010.

[116] "Hydrogen Safety" (http:/ / www. schatzlab. org/ education/ h2safety. html). Humboldt State University. . Retrieved 2010-04-14.

References

Further reading• Chart of the Nuclides (http:/ / chartofthenuclides. com/ default. html). Fourteenth Edition. General Electric

Company. 1989.• Ferreira-Aparicio, P; M. J. Benito, J. L. Sanz (2005). "New Trends in Reforming Technologies: from Hydrogen

Industrial Plants to Multifuel Microreformers". Catalysis Reviews 47: 491–588.doi:10.1080/01614940500364958.

• Newton, David E. (1994). The Chemical Elements. New York, NY: Franklin Watts. ISBN 0-531-12501-7.• Rigden, John S. (2002). Hydrogen: The Essential Element. Cambridge, MA: Harvard University Press.

ISBN 0-531-12501-7.• Romm, Joseph, J. (2004). The Hype about Hydrogen, Fact and Fiction in the Race to Save the Climate. Island

Press. ISBN 1-55963-703-X. Author interview (http:/ / www. globalpublicmedia. com/ transcripts/ 635) at GlobalPublic Media.

• Scerri, Eric (2007). The Periodic System, Its Story and Its Significance,. New York, NY: Oxford University Press.ISBN 0-19-530573-6.

External links• Basic Hydrogen Calculations of Quantum Mechanics (http:/ / www. physics. drexel. edu/ ~tim/ open/ hydrofin/ )• Hydrogen phase diagram (http:/ / www. astro. washington. edu/ users/ larson/ Astro150b/ Lectures/

JupSatUraNep/ hydrogen_phase. gif)• Wavefunction of hydrogen (http:/ / hyperphysics. phy-astr. gsu. edu/ Hbase/ quantum/ hydwf. html#c3)koi:Ваувтыр

Antihydrogen 18

Antihydrogen

Antihydrogen consists of an antiproton and apositron

Antihydrogen is the antimatter counterpart of hydrogen. Whereas thecommon hydrogen atom is composed of an electron and proton, theantihydrogen atom is made up of a positron and antiproton.

The standard symbol for antihydrogen is H that is, H with an overbar(pronounced /ˌeɪtʃ ˈbɑr/ aitch-bar).

Characteristics

According to the CPT theorem of particle physics, antihydrogen atomsshould have many of the characteristics regular hydrogen atoms have,i.e. they should have the same mass, magnetic moment, and transitionfrequencies (see Atomic spectroscopy) between its atomic quantumstates. For example, excited antihydrogen atoms are expected to glow with the same color as that of regularhydrogen. Antihydrogen atoms should be attracted to other matter or antimatter gravitationally with a force of thesame magnitude as ordinary hydrogen atoms would experience. This would not be true if antimatter has negativegravitational mass, which is considered highly unlikely, though not yet empirically disproven.

When antihydrogen atoms come into contact with ordinary matter, their constituents quickly annihilate. Thepositron, which is an elementary particle, annihilates on electrons in ordinary matter and the rest mass of thepositrons and its annihilation partner is released as energy in the form of gamma rays. The antiproton on the otherhand is made up of antiquarks that combine with the quarks in either neutrons or protons in normal matter and theannihilation results in high-energy particles called pions. These pions in turn quickly decay into other particles calledmuons, neutrinos, positrons, and electrons, and these particles rapidly dissipate. If antihydrogen atoms were to besuspended in a perfect vacuum, however, they should survive indefinitely.

ProductionIn 1995, the first antihydrogen was produced by a team of researchers under the lead of Walter Oelert at the CERNlaboratory in Geneva.[1] The experiment took place in the LEAR, where antiprotons, which were produced in aparticle accelerator, were shot at xenon clusters[2] . When an antiproton gets close to a xenon nucleus, anelectron-positron-pair can be produced, and with some probability the positron will be captured by the antiproton toform antihydrogen. The probability for producing antihydrogen from one antiproton was only about  × 10−19, so thismethod is not well suited for the production of substantial amounts of antihydrogen, as detailed calculations hadshown before.[3]

The experiments done at CERN were later, in 1997, reproduced at Fermilab in the US where a somewhat differentcross section for the process was identified[4] . Both experiment resulted in highly energetic, or warm, antihydrogen,which were unsuitable for detailed study. Subsequently CERN build the Antiproton Decelerator in order to supportefforts towards creating low energy antihydrogen which could be used for tests of fundamental symmetries.

Antihydrogen 19

Low energy AntihydrogenIn experiments carried out by the ATRAP and ATHENA collaborations at CERN, positrons from a sodiumradioactive source and antiprotons were brought together in Penning traps, where synthesis took place at a typicalrate of 100 antihydrogen atoms per second. Antihydrogen was first produced by ATHENA[5] and subsequently byATRAP[6] in 2002, and by 2004 millions of antihydrogen atoms were produced in this way.The low energy antihydrogen atoms synthesized so far have had a relatively high temperature (a few thousandkelvins), thus hitting the walls of the experimental apparatus as a consequence and annihilating. A new experiment,ALPHA, a successor of the ATHENA collaboration, as well as ATRAP mentioned above, are pursuing the makingof antihydrogen at low enough kinetic energy to be magnetically confined[7] .Antimatter atoms such as antideuterium (D), antitritium (T), and antihelium (He) are much more difficult to producethan antihydrogen. Among these, only antideuterium nuclei have been produced so far, and these have such veryhigh velocities that synthesis of antideuterium atoms may still be many decades ahead.

Natural occurrenceToday, no conclusive spectral signature for the presence of antihydrogen could be reported, since measuring thespectrum of antihydrogen, especially the 1S-2S interval, is exactly the goal of these CERN located collaborations.

See also• Gravitational interaction of antimatter

References[1] Freedman, David H.. "Antiatoms: Here Today . . ." (http:/ / discovermagazine. com/ 1997/ jan/ antiatomsheretod1029). Discover Magazine. .[2] G.Baur, G.Boero, S.Brauksiepe, A.Buzzo, W.Eyrich, R.Geyer, D.Grzonka, J.Hauffe, K.Kilian, M.LoVetere, M. MacriM.Moosburger,

R.Nellen, W. Oelert, S.Passaggio, A.Pozzo, K.Röhrich, K.Sachs, G.Scheppers, T.Sefzick, R.S.Simon, R.Stratmann, F.Stinzing, M.Wolke(1996). "Production of Antihydrogen". Physics Letters B 368: 251ff.

[3] A. Aste; G.Baur, D. Trautmann, K. Hencken (1993). "Electromagnetic Pair Production with Capture". Physical Review A 50: 3980ff.[4] Blanford, G.; D.C. Christian, K. Gollwitzer, M. Mandelkern, C.T. Munger, J. Schultz, G. Zioulas (December 1997). "Observation of Atomic

Antihydrogen". Physical Review Letters (Fermi National Accelerator Laboratory). "FERMILAB-Pub-97/398-E E862 ... p and H experiments".[5] M. Amoretti, C. Amsler, G. Bonomi, A. Bouchta, P. Bowe, C. Carraro, C. L. Cesar, M. Charlton, M. J. T. Collier, M. Doser, V. Filippini, K.

S. Fine, A. Fontana, M. C. Fujiwara, R. Funakoshi, P. Genova, J. S. Hangst, R. S. Hayano, M. H. Holzscheiter, L. V. Jørgensen, V.Lagomarsino, R. Landua, D. Lindelöf, E. Lodi Rizzini, M. Macri, N. Madsen, G. Manuzio, M. Marchesotti, P. Montagna, H. Pruys, C.Regenfus, P. Riedler, J. Rochet, A. Rotondi, G. Rouleau, G. Testera, A. Variola, T. L. Watson and D. P. van der Werf (2002). "Production anddetection of cold antihydrogen atoms" (http:/ / www. nature. com/ nature/ journal/ v419/ n6906/ full/ nature01096. html). Nature 419 (6906):456ff. doi:10.1038/nature01096. PMID 12368849. .

[6] Gabrielse, G.; N. S. Bowden, P. Oxley, A. Speck, C. H. Storry, J. N. Tan, M.Wessels, D. Grzonka, W. Oelert, G. Schepers, T. Sefzick,J.Walz, H. Pittner, T.W. Ha¨nsch, and E. A. Hessels (2 DECEMBER 2002). "Driven Production of Cold Antihydrogen and the First MeasuredDistribution of Antihydrogen States". Ph Ysica L R Ev I Ew L et T Ers 89 (23): 233401. doi:10.1103/PhysRevLett.89.233401. "antihydrogen(H)".

[7] N. Madsen (2010). "Cold antihydrogen: a new frontier in fundamental physics" (http:/ / rsta. royalsocietypublishing. org/ content/ 368/ 1924/3671. full). Phil. Trans. R. Soc. A 368 (1924): 1924ff. doi:10.1098/rsta.2010.0026. PMID 20603376. .

Hydrogen atom 20

Hydrogen atom

Hydrogen-1

Full table

General

Name, symbol protium, 1H

Neutrons 0

Protons 1

Nuclide Data

Natural abundance 99.985%

Half-life Stable

Isotope mass 1.007825 u

Spin ½+

Excess energy 7288.969 ± 0.001 keV

Binding energy 0 ± 0 keV

Depiction of a hydrogen atom showing the diameter asabout twice the Bohr model radius. (Image not to scale)

A hydrogen atom is an atom of the chemical element hydrogen.The electrically neutral atom contains a single positively-chargedproton and a single negatively-charged electron bound to thenucleus by the Coulomb force. The most abundant isotope,hydrogen-1, protium, or light hydrogen, contains no neutrons;other isotopes of hydrogen, such as deuterium, contain one ormore neutrons. This article primarily concerns hydrogen-1.

The hydrogen atom has special significance in quantum mechanicsand quantum field theory as a simple two-body problem physicalsystem which has yielded many simple analytical solutions inclosed-form.

In 1914, Niels Bohr obtained the spectral frequencies of thehydrogen atom after making a number of simplifying assumptions.These assumptions, the cornerstones of the Bohr model, were notfully correct but did yield the correct energy answers. Bohr's results for the frequencies and underlying energy valueswere confirmed by the full quantum-mechanical analysis which uses the Schrödinger equation, as was shown in1925–1926. The solution to the Schrödinger equation for hydrogen is analytical. From this, the hydrogen energylevels and thus the frequencies of the hydrogen spectral lines can be calculated. The solution of the Schrödinger

equation goes much further than the Bohr model however, because it also yields the shape of the electron's wave function ("orbital") for the various possible quantum-mechanical states, thus explaining the anisotropic character of

Hydrogen atom 21

atomic bonds.The Schrödinger equation also applies to more complicated atoms and molecules. However, in most such cases thesolution is not analytical and either computer calculations are necessary or simplifying assumptions must be made.

Solution of Schrödinger equation: Overview of resultsThe solution of the Schrödinger equation (wave equations) for the hydrogen atom uses the fact that the Coulombpotential produced by the nucleus is isotropic (it is radially symmetric in space and only depends on the distance tothe nucleus). Although the resulting energy eigenfunctions (the orbitals) are not necessarily isotropic themselves,their dependence on the angular coordinates follows completely generally from this isotropy of the underlyingpotential: The eigenstates of the Hamiltonian (that is, the energy eigenstates) can be chosen as simultaneouseigenstates of the angular momentum operator. This corresponds to the fact that angular momentum is conserved inthe orbital motion of the electron around the nucleus. Therefore, the energy eigenstates may be classified by twoangular momentum quantum numbers, ℓ and m (both are integers). The angular momentum quantum number ℓ = 0,1, 2, ... determines the magnitude of the angular momentum. The magnetic quantum number m = −ℓ, ..., +ℓdetermines the projection of the angular momentum on the (arbitrarily chosen) z-axis.In addition to mathematical expressions for total angular momentum and angular momentum projection ofwavefunctions, an expression for the radial dependence of the wave functions must be found. It is only here that thedetails of the 1/r Coulomb potential enter (leading to Laguerre polynomials in r). This leads to a third quantumnumber, the principal quantum number n = 1, 2, 3, .... The principal quantum number in hydrogen is related to atom'stotal energy.Note that the maximum value of the angular momentum quantum number is limited by the principal quantumnumber: it can run only up to n − 1, i.e. ℓ = 0, 1, ..., n − 1.Due to angular momentum conservation, states of the same ℓ but different m have the same energy (this holds for allproblems with rotational symmetry). In addition, for the hydrogen atom, states of the same n but different ℓ are alsodegenerate (i.e. they have the same energy). However, this is a specific property of hydrogen and is no longer truefor more complicated atoms which have a (effective) potential differing from the form 1/r (due to the presence of theinner electrons shielding the nucleus potential).Taking into account the spin of the electron adds a last quantum number, the projection of the electron's spin angularmomentum along the z-axis, which can take on two values. Therefore, any eigenstate of the electron in the hydrogenatom is described fully by four quantum numbers. According to the usual rules of quantum mechanics, the actualstate of the electron may be any superposition of these states. This explains also why the choice of z-axis for thedirectional quantization of the angular momentum vector is immaterial: an orbital of given ℓ and m′ obtained foranother preferred axis z′ can always be represented as a suitable superposition of the various states of different m(but same l) that have been obtained for z.

Alternatives to the Schrödinger TheoryIn the language of Heisenberg's Matrix Mechanics, the hydrogen atom was first solved by Wolfgang Pauli[1] using arotational symmetry in four dimension [O(4)-symmetry] generated by the angular momentum and theLaplace–Runge–Lenz vector. By extending the symmetry group O(4) to the dynamical group O(4,2), the entirespectrum and all transitions were embedded in a single irreducible group representation.[2]

In 1979 the (non relativistic) hydrogen atom was solved for the first time within Feynman's path integral formulationof quantum mechanics.[3] [4] This work greatly extended the range of applicability of Feynman's method.

Hydrogen atom 22

Mathematical summary of eigenstates of hydrogen atom

Energy levelsThe energy levels of hydrogen, including fine structure are given by

where α is the fine-structure constant and j is a number which is the total angular momentum eigenvalue; that is, ℓ ±1/2 depending on the direction of the electron spin.The value of 13.6 eV is called the Rydberg constant and can be found from the Bohr model, and is given by

where me is the mass of the electron, qe is the charge of the electron, h is the Planck constant, and ε0 is the vacuumpermittivity.The Rydberg constant is connected to the fine-structure constant by the relation

Wavefunction

3D Image of the eigenstate wavefunction. The solid body contains 45% of the

electron's probability.

The normalized position wavefunctions, given in spherical coordinatesare:

where:

,

is the Bohr radius,

are the generalized Laguerre polynomials of degree n − ℓ − 1, andis a spherical harmonic function of degree ℓ and order m.

The quantum numbers can take the following values:

Additionally, these wavefunctions are orthogonal:

Hydrogen atom 23

where is the representation of the wavefunction in Dirac notation, and is the Kronecker deltafunction. [5]

Angular momentumThe eigenvalues for Angular momentum operator:

Visualizing the hydrogen electron orbitals

Probability densities through the xz-plane for theelectron at different quantum numbers (ℓ, across

top; n, down side; m = 0)

The image to the right shows the first few hydrogen atom orbitals(energy eigenfunctions). These are cross-sections of the probabilitydensity that are color-coded (black represents zero density and whiterepresents the highest density). The angular momentum (orbital)quantum number ℓ is denoted in each column, using the usualspectroscopic letter code (s means ℓ = 0, p means ℓ = 1, d means ℓ = 2).The main (principal) quantum number n (= 1, 2, 3, ...) is marked to theright of each row. For all pictures the magnetic quantum number m hasbeen set to 0, and the cross-sectional plane is the xz-plane (z is thevertical axis). The probability density in three-dimensional space isobtained by rotating the one shown here around the z-axis.

The "ground state", i.e. the state of lowest energy, in which the electronis usually found, is the first one, the 1s state (principal quantum level n= 1, ℓ = 0).

An image with more orbitals is also available (up to higher numbers n and ℓ).Black lines occur in each but the first orbital: these are the nodes of the wavefunction, i.e. where the probabilitydensity is zero. (More precisely, the nodes are Spherical harmonics that appear as a result of solving Schrodinger'sequation in polar coordinates.)

The quantum numbers determine the layout of these nodes.[6] There are:• total nodes,• of which are angular nodes:

• angular nodes go around the axis (in the xy plane). (The figure above does not show these nodes since it plots

cross-sections through the xz-plane.)• (the remaining angular nodes) occur on the (vertical) axis.

• (the remaining non-angular nodes) are radial nodes.

Hydrogen atom 24

Features going beyond the Schrödinger solutionThere are several important effects that are neglected by the Schrödinger equation and which are responsible forcertain small but measurable deviations of the real spectral lines from the predicted ones:• Although the mean speed of the electron in hydrogen is only 1/137th of the speed of light, many modern

experiments are sufficiently precise that a complete theoretical explanation requires a fully relativistic treatmentof the problem. A relativistic treatment results in a momentum increase of about one part in 37,000 for theelectron. Since the electron's wavelength is determined by its momentum, orbitals containing higher speedelectrons show contraction due to smaller wavelengths.

• Even when there is no external magnetic field, in the inertial frame of the moving electron, the electromagneticfield of the nucleus has a magnetic component. The spin of the electron has an associated magnetic momentwhich interacts with this magnetic field. This effect is also explained by special relativity, and it leads to theso-called spin-orbit coupling, i.e., an interaction between the electron's orbital motion around the nucleus, and itsspin.

Both of these features (and more) are incorporated in the relativistic Dirac equation, with predictions that come stillcloser to experiment. Again the Dirac equation may be solved analytically in the special case of a two-body system,such as the hydrogen atom. The resulting solution quantum states now must be classified by the total angularmomentum number j (arising through the coupling between electron spin and orbital angular momentum). States ofthe same j and the same n are still degenerate.• There are always vacuum fluctuations of the electromagnetic field, according to quantum mechanics. Due to such

fluctuations degeneracy between states of the same j but different l is lifted, giving them slightly differentenergies. This has been demonstrated in the famous Lamb-Retherford experiment and was the starting point forthe development of the theory of Quantum electrodynamics (which is able to deal with these vacuum fluctuationsand employs the famous Feynman diagrams for approximations using perturbation theory). This effect is nowcalled Lamb shift.

For these developments, it was essential that the solution of the Dirac equation for the hydrogen atom could beworked out exactly, such that any experimentally observed deviation had to be taken seriously as a signal of failureof the theory.Due to the high precision of the theory also very high precision for the experiments is needed, which utilize afrequency comb.

Hydrogen ionHydrogen is not found without its electron in ordinary chemistry (room temperatures and pressures), as ionizedhydrogen is highly chemically reactive. When ionized hydrogen is written as "H+" as in the solvation of classicalacids such hydrochloric acid, the hydronium ion, H3O+, is meant, not a literal ionized single hydrogen atom. In thatcase, the acid transfers the proton to H2O to form H3O+.Ionized hydrogen without its electron, or free protons, are common in the interstellar medium, and solar wind.

Hydrogen atom 25

See also• Atom• Balmer series• Bohr model• Deuterium• Helium atom• Isotopes of hydrogen• Proton decay• Quantum chemistry• Quantum field theory• Quantum mechanics• Quantum state• Theoretical and experimental justification for the Schrödinger equation• Trihydrogen cation• Tritium

References[1] Pauli, W (1926). "Über das Wasserstoffspektrum vom Standpunkt der neuen Quantenmechanik". Zeitschrift für Physik 36: 336–363.

doi:10.1007/BF01450175.[2] Kleinert H. (1968). "Group Dynamics of the Hydrogen Atom". Lectures in TheoreticalPhysics, edited by W.E. Brittin and A.O. Barut,

Gordon and Breach, N.Y. 1968: 427–482. .[3] Duru I.H., Kleinert H. (1979). "Solution of the path integral for the H-atom" (http:/ / www. physik. fu-berlin. de/ ~kleinert/ kleiner_re65/ 65.

pdf). Physics Letters B 84 (2): 185–188. doi:10.1016/0370-2693(79)90280-6. .[4] Duru I.H., Kleinert H. (1982). "Quantum Mechanics of H-Atom from Path Integrals" (http:/ / www. physik. fu-berlin. de/ ~kleinert/

kleiner_re83/ 83. pdf). Fortschr. Phys 30 (2): 401–435. doi:10.1002/prop.19820300802. .[5] Introduction to Quantum Mechanics, Griffiths 4.89[6] Lecture notes on quantum numbers (http:/ / www. physics. byu. edu/ faculty/ durfee/ courses/ Summer2009/ physics222/

AtomicQuantumNumbers. pdf)

Books• Griffiths, David J. (1995). Introduction to Quantum Mechanics. Prentice Hall. ISBN 0-13-111892-7.Section 4.2 deals with the hydrogen atom specifically, but all of Chapter 4 is relevant.• Bransden, B.H.; C.J. Joachain (1983). Physics of Atoms and Molecules. Longman. ISBN 0-582-44401-2.• Kleinert, H. (2009). Path Integrals in Quantum Mechanics, Statistics, Polymer Physics, and Financial Markets,

4th edition, Worldscibooks.com (http:/ / www. worldscibooks. com/ physics/ 7305. html), World Scientific,Singapore (also available online Physik.fi-berlin.de (http:/ / www. physik. fu-berlin. de/ ~kleinert/ re. html#B8)

External links• Physics of hydrogen atom on Scienceworld (http:/ / scienceworld. wolfram. com/ physics/ HydrogenAtom. html)• Interactive graphical representation of orbitals (http:/ / webphysics. davidson. edu/ faculty/ dmb/ hydrogen/ )• Applet which allows viewing of all sorts of hydrogenic orbitals (http:/ / www. falstad. com/ qmatom/ )• The Hydrogen Atom: Wave Functions, and Probability Density "pictures" (http:/ / panda. unm. edu/ courses/

finley/ P262/ Hydrogen/ WaveFcns. html)• Basic Quantum Mechanics of the Hydrogen Atom (http:/ / www. physics. drexel. edu/ ~tim/ open/ hydrofin)

Hydrogen-like atom 26

Hydrogen-like atomA hydrogen-like ion is any atomic nucleus with one electron and thus is isoelectronic with hydrogen. Except for thehydrogen atom itself (which is neutral) these ions carry the positive charge e(Z-1), where Z is the atomic number ofthe atom. Examples of hydrogen-like ions are He+, Li2+, Be3+ and B4+. Because hydrogen-like ions are two-particlesystems with an interaction depending only on the distance between the two particles, their (non-relativistic)Schrödinger equation can be solved in analytic form. The solutions are one-electron functions and are referred to ashydrogen-like atomic orbitals.[1]

Hydrogen-like atomic orbitals are eigenfunctions of the one-electron angular momentum operator L and its zcomponent Lz. The energy eigenvalues do not depend on the corresponding quantum numbers, but solely on theprincipal quantum number n. Hence, a hydrogen-like atomic orbital is uniquely identified by the values of: principalquantum number n, angular momentum quantum number l, and magnetic quantum number m. To this must be addedthe two-valued spin quantum number ms = ±½ in application of the Aufbau principle. This principle restricts theallowed values of the four quantum numbers in electron configurations of more-electron atoms. In hydrogen-likeatoms all degenerate orbitals of fixed n and l, m and s varying between certain values (see below) form an atomicshell.The Schrödinger equation of atoms or atomic ions with more than one electron has not been solved analytically,because of the computational difficulty imposed by the Coulomb interaction between the electrons. Numericalmethods must be applied in order to obtain (approximate) wavefunctions or other properties from quantummechanical calculations. Due to the spherical symmetry (of the Hamiltonian), the total angular momentum J of anatom is a conserved quantity. Many numerical procedures start from products of atomic orbitals that areeigenfunctions of the one-electron operators L and Lz. The radial parts of these atomic orbitals are sometimesnumerical tables or are sometimes Slater orbitals. By angular momentum coupling many-electron eigenfunctions ofJ2 (and possibly S2) are constructed.In quantum chemical calculations hydrogen-like atomic orbitals cannot serve as an expansion basis, because they arenot complete. The non-square-integrable continuum (E > 0) states must be included to obtain a complete set, i.e., tospan all of one-electron Hilbert space.[2]

Mathematical characterizationThe atomic orbitals of hydrogen-like ions are solutions to the Schrödinger equation in a spherically symmetricpotential. In this case, the potential term is the potential given by Coulomb's law:

where• ε0 is the permittivity of the vacuum,• Z is the atomic number (number of protons in the nucleus),• e is the elementary charge (charge of an electron),• r is the distance of the electron from the nucleus.After writing the wave function as a product of functions:

(in spherical coordinates), where are spherical harmonics, we arrive at the following Schrödinger equation:where is, approximately, the mass of the electron. More accurately, it is the reduced mass of the systemconsisting of the electron and the nucleus.

Hydrogen-like atom 27

Different values of l give solutions with different angular momentum, where l (a non-negative integer) is thequantum number of the orbital angular momentum. The magnetic quantum number m (satisfying ) isthe (quantized) projection of the orbital angular momentum on the z-axis. See here for the steps leading to thesolution of this equation.

Non-relativistic wavefunction and energyIn addition to l and m, a third integer n > 0, emerges from the boundary conditions placed on R. The functions R andY that solve the equations above depend on the values of these integers, called quantum numbers. It is customary tosubscript the wave functions with the values of the quantum numbers they depend on. The final expression for thenormalized wave function is:

where:

• are the generalized Laguerre polynomials in the definition given here.

•

Here, is the reduced mass of the nucleus-electron system, that is, where is the

mass of the nucleus. Typically, the nucleus is much more massive than the electron, so .

• .

• function is a spherical harmonic.parity due to angular wave function is -1 whole to the power l.

Quantum numbersThe quantum numbers n, l and m are integers and can have the following values:

See for a group theoretical interpretation of these quantum numbers this article. Among other things, this articlegives group theoretical reasons why and .

Angular momentumEach atomic orbital is associated with an angular momentum L. It is a vector operator, and the eigenvalues of itssquare L2 ≡ Lx

2 + Ly2 + Lz

2 are given by:

The projection of this vector onto an arbitrary direction is quantized. If the arbitrary direction is called z, thequantization is given by:

where m is restricted as described above. Note that L2 and Lz commute and have a common eigenstate, which is inaccordance with Heisenberg's uncertainty principle. Since Lx and Ly do not commute with Lz, it is not possible to finda state which is an eigenstate of all three components simultaneously. Hence the values of the x and y componentsare not sharp, but are given by a probability function of finite width. The fact that the x and y components are notwell-determined, implies that the direction of the angular momentum vector is not well determined either, althoughits component along the z-axis is sharp.

Hydrogen-like atom 28

These relations do not give the total angular momentum of the electron. For that, electron spin must be included.This quantization of angular momentum closely parallels that proposed by Niels Bohr (see Bohr model) in 1913,with no knowledge of wavefunctions.

Including spin-orbit interactionIn a real atom the spin interacts with the magnetic field created by the electron movement around the nucleus, aphenomenon known as spin-orbit interaction. When one takes this into account, the spin and angular momentum areno longer conserved, which can be pictured by the electron precessing. Therefore one has to replace the quantumnumbers l, m and the projection of the spin ms by quantum numbers which represent the total angular momentum(including spin), j and mj, as well as the quantum number of parity.

Notes[1] In quantum chemistry an orbital is synonymous with "a one-electron function", a square integrable function of x, y, and z.[2] This was observed as early as 1929 by E. A. Hylleraas, Z. f. Physik vol. 48, p. 469 (1929). English translation in H. Hettema, Quantum

Chemistry, Classic Scientific Papers, p. 81, World Scientific, Singapore (2000). Later it was pointed out again by H. Shull and P.-O. Löwdin,J. Chem. Phys. vol. 23, p. 1362 (1955).

See also• Rydberg atom• Positronium• Exotic atom• Two-electron atom

References• Tipler, Paul & Ralph Llewellyn (2003). Modern Physics (4th ed.). New York: W. H. Freeman and Company.

ISBN 0-7167-4345-0

Hydrogen spectral series 29

Hydrogen spectral series

The spectral series of hydrogen, on a logarithmicscale.

The emission spectrum of atomic hydrogen is divided into a number ofspectral series, with wavelengths given by the Rydberg formula.These observed spectral lines are due to electrons moving betweenenergy levels in the atom. The spectral series are important inastronomy for detecting the presence of hydrogen and calculating redshifts. Further series were discovered as spectroscopy techniquesdeveloped.

PhysicsIn physics, the spectral lines of hydrogen correspond to particular jumps of the electron between energy levels. Thesimplest model of the hydrogen atom is given by the Bohr model. When an electron jumps from a higher energy to alower, a photon of a specific wavelength is emitted.

Electron transitions and their resulting wavelengths for Hydrogen. Energy levels are notto scale.

The spectral lines are grouped intoseries according to n'. Lines are namedsequentially starting from the longestwavelength/lowest frequency of theseries, using Greek letters within eachseries. For example, the 2 → 1 line iscalled "Lyman-alpha" (Ly-α), whilethe 7 → 3 line is called"Paschen-delta" (Pa-δ). Somehydrogen spectral lines fall outsidethese series, such as the 21 cm line;these correspond to much rarer atomicevents such as hyperfine transitions.[1]

The fine structure also results in singlespectral lines appearing as two or moreclosely grouped thinner lines, due torelativistic corrections.[2] Typicallyone can only observe these series from

pure hydrogen samples in a lab. Many of the lines are very faint and additional lines can be caused by other elements(such as helium if using sunlight, or nitrogen in the air). Lines outside of the visible spectrum typically cannot beseen in observations of sunlight, as the atmosphere absorbs most infra-red and ultraviolet wavelengths.

Hydrogen spectral series 30

Rydberg formulaThe energy differences between levels in the Bohr model, and hence the wavelengths of emitted/absorbed photons, isgiven by the Rydberg formula[3] :

where n is the initial energy level, n′ is the final energy level, and R is the Rydberg constant.[4] Meaningful valuesare returned only when n is greater than n′ and the limit of one over infinity is taken to be zero.

SeriesAll wavelengths are given to 3 significant figures.

Lyman series (n′ = 1)

λ (nm)

2 122

3 103

4 97.2

5 94.9

6 93.7

91.1

The series is named after its discoverer, Theodore Lyman, who discovered the spectral lines from 1906-1914. All thewavelengths in the Lyman series are in the ultraviolet band.[5] [6]

Balmer series (n′ = 2)

λ (nm)

3 656

4 486

5 434

6 410

7 397

365

Named after Johann Balmer, who discovered the Balmer formula, an empirical equation to predict the Balmerseries, in 1885. Balmer lines are historically referred to as "H-alpha", "H-beta", "H-gamma" and so on, where H isthe element hydrogen.[7] Four of the Balmer lines are in the technically "visible" part of the spectrum, withwavelengths longer than 400 nm. Parts of the Balmer series can be seen in the solar spectrum. H-alpha is animportant line used in astronomy to detect the presence of hydrogen.

The four visible hydrogen emission spectrumlines in the Balmer series. H-alpha is the red line

at the right.

Hydrogen spectral series 31

Paschen series (n′ = 3)

λ (nm)

4 1870

5 1280

6 1090

7 1000

8 954

820

Named after the Austro-German physicist Friedrich Paschen who first observed them in 1908. The Paschen lines alllie in the infrared band.[8]

Brackett series (n′ = 4 )

λ (nm)

5 4050

6 2630

7 2170

8 1940

9 1820

1460

Named after the American physicist Frederick Sumner Brackett who first observed the spectral lines in 1922.[9]

Pfund series (n′ = 5)

λ (nm)

6 7460

7 4650

8 3740

9 3300

10 3040

2280

Experimentally discovered in 1924 by August Herman Pfund.[10]

Humphreys series (n′ = 6)

Hydrogen spectral series 32

λ (nm)

7 12400

8 7500

9 5910

10 5130

11 4670

3280

Discovered by American physicist Curtis J. Humphreys.[11]

Further (n′ > 6)Further series are unnamed, but follow exactly the same pattern as dictated by the Rydberg equation. Series areincreasingly spread out and occur in increasing wavelengths. The lines are also increasingly faint, corresponding toincreasingly rare atomic events.

Extension to other systemsThe concepts of the Rydberg formula can be applied to any system with a single particle orbiting a nucleus, forexample a He+ ion or a muonium particle. The equation must be modified based on the system's Bohr radius;emissions will be of a similar character but at a different range of energies.All other atoms possess at least two electrons in their unionized form and the interactions between these electronsmakes analysis of the spectrum by such simple methods as described here impractical. The deduction of the Rydbergformula was a major step in physics, but it was long before an extension to the spectra of other elements could beaccomplished.

See also• Astronomical spectroscopy• Bohr Theory and Balmer-Rydberg Equation• Moseley's law• Theoretical and experimental justification for the Schrödinger equation

References[1] "The Hydrogen 21-cm Line" (http:/ / hyperphysics. phy-astr. gsu. edu/ hbase/ quantum/ h21. html). Hyperphysics. Georgia State University.

2004-10-30. . Retrieved 2009-03-18.[2] Liboff, Richard L. (2002). Introductory Quantum Mechanics. Addison-Wesley. ISBN 0-8053-8714-5.[3] Bohr, Niels (1985), "Rydberg's discovery of the spectral laws", in Kalckar, J., N. Bohr: Collected Works, 10, Amsterdam: North-Holland

Publ., pp. 373–9[4] "CODATA Recommended Values of the Fundamental Physical Constants: 2006" (http:/ / physics. nist. gov/ cuu/ Constants/ codata. pdf)

(PDF). Committee on Data for Science and Technology (CODATA). NIST. .[5] Lyman, Theodore (1906), "The Spectrum of Hydrogen in the Region of Extremely Short Wave-Length" (http:/ / www. jstor. org/ stable/

25058084), Memoirs of the American Academy of Arts and Sciences, New Series 13 (3): 125–146, ISSN 00966134,[6] Lyman, Theodore (1914), "An Extension of the Spectrum in the Extreme Ultra-Violet", Nature 93: 241, doi:10.1038/093241a0[7] Balmer, J. J. (1885), "Notiz uber die Spectrallinien des Wasserstoffs" (http:/ / www3. interscience. wiley. com/ journal/ 112487600/ abstract),

Annalen der Physik 261 (5): 80–87, doi:10.1002/andp.18852610506,[8] Paschen, Friedrich (1908), "Zur Kenntnis ultraroter Linienspektra. I. (Normalwellenlängen bis 27000 Å.-E.)" (http:/ / www3. interscience.

wiley. com/ journal/ 112500956/ abstract), Annalen der Physik 332 (13): 537–570, doi:10.1002/andp.19083321303,[9] Brackett, Frederick Sumner (1922), "Visible and infra-red radiation of hydrogen", Astrophysical Journal 56: 154, doi:10.1086/142697[10] Pfund, A. H. (1924), "The emission of nitrogen and hydrogen in infrared", J. Opt. Soc. Am. 9 (3): 193–196, doi:10.1364/JOSA.9.000193

Hydrogen spectral series 33

[11] Humphreys, C.J. (1953), "Humphreys Series", J. Research Natl. Bur. Standards 50

External links• Spectral series of hydrogen animation (http:/ / www. bigs. de/ BLH/ en/ index. php?option=com_content&

view=category& layout=blog& id=50& Itemid=221)

Liquid hydrogen 34

Liquid hydrogen

Liquid hydrogen

Identifiers

CAS number 1333-74-0 [1] 

PubChem 783 [2] 

ChemSpider 762 [3]  [chemspider]

UNII 7YNJ3PO35Z [4] 

UN number 1966

RTECS number MW8900000

SMILES

InChI

InChI key

Properties

Molecular formula H2

Molar mass 2.02 g mol−1

Appearance Colorless liquid

Density 67.8 kg·m-3 (4.23 lb./cu.ft)[5]

Melting point −259.14 °C (−434.45 °F, 14.01 K)[5]

Boiling point −252.87 °C (−423.17 °F, 20.28 K) [5]

Hazards

NFPA 704

Autoignitiontemperature

1060 °F = 571 °C[5]

Explosive limits LEL 4.0 %; UEL 74.2 % (in air)[5]

 (what is this?)   (verify) [6]

Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Infobox references

Liquid hydrogen 35

Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in themolecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point, however for hydrogento be in a full liquid state without boiling off it needs to be cooled to 20.28 K[7] (−423.17 °F/−252.87°C)[8] [9] whilestill pressurized. One common method of obtaining liquid hydrogen involves a compressor resembling a jet engine inboth appearance and principle. Liquid hydrogen is typically used as a concentrated form of hydrogen storage. As inany gas, storing it as liquid takes less space than storing it as a gas at normal temperature and pressure. Onceliquefied it can be maintained as a liquid in pressurized and thermally insulated containers.Liquid hydrogen consists of 99.79% parahydrogen, 0.21% orthohydrogen.[10]

History1756 - The first documented public demonstration of artificial refrigeration by William Cullen[11] , Gaspard Mongeliquefied the first gas producing liquid sulfur dioxide in 1784. Michael Faraday liquefied ammonia to cause cooling,Oliver Evans designed the first closed circuit refrigeration machine in 1805, Jacob Perkins patented the firstrefrigerating machine in 1834 and John Gorrie patented his mechanical refrigeration machine in 1851 in the US tomake ice to cool the air[12] [13] , Siemens introduced the Regenerative cooling concept in 1857, Carl von Lindepatented equipment to liquefy air using tile Joule Thomson expansion process and regenerative cooling[14] in 1876,in 1885 Zygmunt Florenty Wróblewski published hydrogen's critical temperature as 33 K; critical pressure, 13.3atmospheres; and boiling point, 23 K.Hydrogen was liquefied for the first time by James Dewar in 1898 by using regenerative cooling and his invention,the vacuum flask. The first synthesis of the stable isomer form of liquid hydrogen, parahydrogen was achieved byPaul Harteck and Karl Friedrich Bonhoeffer in 1929.

Spin isomers of hydrogenRoom temperature hydrogen consists mostly of the orthohydrogen form. After production, liquid hydrogen is in ametastable state and must be converted into the parahydrogen isomer form to avoid the exothermic reaction thatoccurs when it changes at low temperatures, this is usually performed using a catalyst like ferric oxide, activatedcarbon, platinized asbestos, rare earth metals, uranium compounds, chromic oxide, or some nickel compounds[15] .

UsesIt is a common liquid rocket fuel for rocket applications. In most rocket engines fueled by liquid hydrogen, it firstcools the nozzle and other parts before being mixed with the oxidizer (usually liquid oxygen (LOX)) and burned toproduce water with traces of ozone and hydrogen peroxide. Practical H2/O2 rocket engines run fuel-rich so that theexhaust contains some unburned hydrogen. This reduces combustion chamber and nozzle erosion. It also reduces themolecular weight of the exhaust that can actually increase specific impulse despite the incomplete combustion.

Liquid hydrogen 36

RTECS MW8900000

PEL-OSHA Simple asphyxiant

ACGIH TLV-TWA Simple asphyxiant

Liquid hydrogen can be used as the fuel storage in an internal combustion engine or fuel cell. Various submarines(Type 212 submarine, Type 214 submarine) and concept hydrogen vehicles have been built using this form ofhydrogen (see DeepC, BMW H2R). Due to its similarity, builders can sometimes modify and share equipment withsystems designed for LNG. However, because of the lower volumetric energy, the hydrogen volumes needed forcombustion are large. Unless LH2 is injected instead of gas, hydrogen-fueled piston engines usually require largerfuel systems. Unless direct injection is used, a severe gas-displacement effect also hampers maximum breathing andincreases pumping losses.Liquid hydrogen is also used to cool neutrons to be used in neutron scattering. Since neutrons and hydrogen nucleihave similar masses, kinetic energy exchange per interaction is maximum (elastic collision).

AdvantagesThe byproduct of its combustion with oxygen alone is water vapor(although if its combustion is with oxygen andnitrogen it can form toxic chemicals), which can be cooled with the some of liquid hydrogen. Since water isconsidered harmless to the environment, the engine is considered "zero emissions." Liquid hydrogen also has a muchhigher specific energy than gasoline, natural gas, or diesel[16] .

DrawbacksThe density of liquid hydrogen is only 70.99 g/L (at 20 K). Liquid hydrogen requires cryogenic storage technologysuch as special thermally insulated containers and requires special handling common to all cryogenic fuels. This issimilar to, but more severe than liquid oxygen. Even with thermally insulated containers it is difficult to keep such alow temperature, and the hydrogen will gradually leak away (Typically it will evaporate at a rate of 1% per day[17] ).It also shares many of the same safety issues as other forms of hydrogen, as well as being cold enough to liquefy(and possibly solidify) atmospheric oxygen which can be an explosion hazard.

Liquid hydrogen 37

See also

Tank for liquid hydrogen of Linde, Museum Autovision,Altlußheim, Germany

• Hydrogen safety• Compressed hydrogen• Cryo-adsorption• Expansion ratio• Gasoline gallon equivalent• industrial gas• Slush hydrogen• Solid hydrogen• Metallic hydrogen• Hydrogen infrastructure• Liquid hydrogen tank car• Liquid hydrogen tanktainer• Liquid hydrogen tank truck• Liquefaction of gases

References[1] http:/ / www. commonchemistry. org/ ChemicalDetail. aspx?ref=1333-74-0[2] http:/ / pubchem. ncbi. nlm. nih. gov/ summary/ summary. cgi?cid=783[3] http:/ / www. chemspider. com/ 762[4] http:/ / fdasis. nlm. nih. gov/ srs/ srsdirect. jsp?regno=7YNJ3PO35Z[5] Information specific to liquid hydrogen (http:/ / www. safety. seas. harvard. edu/ services/ hydrogen. html), harvard.edu, accessed 2009-06-12[6] http:/ / en. wikipedia. org/ wiki/ %3Aliquid_hydrogen[7] IPTS-1968 (http:/ / media. iupac. org/ publications/ pac/ 1970/ pdf/ 2203x0555. pdf), iupac.org, accessed 2009-06-12[8] Chemical elements data references[9] Properties Of Gases (http:/ / www. roymech. co. uk/ Useful_Tables/ Matter/ Prop_Gas. htm)[10] Liquid Air/LH2 (http:/ / www. astronautix. com/ props/ liqirlh2. htm)[11] William Cullen, Of the Cold Produced by Evaporating Fluids and of Some Other Means of Producing Cold, in Essays and Observations

Physical and Literary Read Before a Society in Edinburgh and Published by Them, II, (Edinburgh 1756)[12] 1851 John Gorrie (http:/ / www. myoutbox. net/ popch20. htm)[13] 1851 Patent 8080 (http:/ / patimg2. uspto. gov/ . piw?Docid=00008080& homeurl=http:/ / patft. uspto. gov/ netacgi/

nph-Parser?Sect1=PTO1%26Sect2=HITOFF%26d=PALL%26p=1%26u=%252Fnetahtml%252FPTO%252Fsrchnum.htm%26r=1%26f=G%26l=50%26s1=0008,080. PN. %26OS=PN/ 0008,080%26RS=PN/ 0008,080& PageNum=& Rtype=& SectionNum=&idkey=NONE& Input=View+ first+ page)

[14] Hydrogen through the Nineteenth Century (http:/ / history. nasa. gov/ SP-4404/ app-a1. htm)[15] Ortho-Para conversion. Pag. 13 (http:/ / www. mae. ufl. edu/ NasaHydrogenResearch/ h2webcourse/ L11-liquefaction2. pdf)[16] http:/ / www. almc. army. mil/ alog/ issues/ MayJun00/ MS492. htm[17] http:/ / www. almc. army. mil/ alog/ issues/ MayJun00/ MS492. htm

Solid hydrogen 38

Solid hydrogenSolid hydrogen is the solid state of the element hydrogen, achieved by decreasing the temperature below hydrogen'smelting point of 14.01 K (−259.14 °C). It was collected for the first time by James Dewar in 1899 and publishedwith the title "Sur la solidification de l'hydrogène" in the Annales de Chimie et de Physique, 7th series, vol.18, Oct.1899.[1] [2]

Research• Solid-state physics• 1972: The experimental determination of the melting characteristics of solid hydrogen [3]

See also• Compressed hydrogen• Liquid hydrogen• Slush hydrogen• Metallic hydrogen• Timeline of hydrogen technologies

References[1] Correspondence and General A-I DEWAR/Box D I (http:/ / www. nationalarchives. gov. uk/ A2A/ records. aspx?cat=116-dewar_1&

cid=-1& Gsm=2008-06-18#-1)[2] Dewar, James (1899). "Sur la solidification de l'hydrogène" (http:/ / gallica. bnf. fr/ ark:/ 12148/ bpt6k349183/ f143. table). Annales de

Chimie et de Physique 18: 145–150. .[3] " Melting Characteristics and Bulk Thermophysical Properties of Solid Hydrogen (http:/ / oai. dtic. mil/ oai/ oai?verb=getRecord&

metadataPrefix=html& identifier=AD0748847)" (1972)

External links• " Properties of solid hydrogen at very low temperatures (http:/ / sciencelinks. jp/ j-east/ article/ 200211/

000020021102A0308056. php)" (2001)• " Solid hydrogen experiments for atomic propellants (http:/ / gltrs. grc. nasa. gov/ reports/ 2002/

TM-2002-211915. pdf)"

Metallic hydrogen 39

Metallic hydrogenMetallic hydrogen is a state of hydrogen which results when it is sufficiently compressed and undergoes a phasetransition; it is an example of degenerate matter. Solid metallic hydrogen is predicted to consist of a crystal lattice ofhydrogen nuclei (namely, protons), with a spacing which is significantly smaller than the Bohr radius. Indeed, thespacing is more comparable with the de Broglie wavelength of the electron. The electrons are unbound and behavelike the conduction electrons in a metal. In liquid metallic hydrogen, protons do not have lattice ordering; rather, it isa liquid system of protons and electrons.

History

Theoretical predictions

Metallization of hydrogen under pressure

Though at the top of the alkali metal column in the periodic table, hydrogen is not, under ordinary conditions, analkali metal. In 1935 however, physicists Eugene Wigner and Hillard Bell Huntington predicted that under animmense pressure of ~25 GPa (250000 atm or 3500000 psi), hydrogen atoms would display metallic properties,losing hold over their electrons.[1] Since then, metallic hydrogen has been described as "the holy grail ofhigh-pressure physics".[2]

The initial prediction about the amount of pressure needed was eventually proven to be too low.[3] Since the firstwork by Wigner and Huntington the more modern theoretical calculations were pointing toward higher butnonetheless potentially accessible metallization pressures. Techniques are being developed for creating pressures ofup to 500 GPa, higher than the pressure at the center of the Earth, in hopes of creating metallic hydrogen.[4]

Liquid metallic hydrogen

Helium-4 is a liquid at normal pressure and temperatures near absolute zero, a consequence of its high zero-pointenergy (ZPE). The ZPE of protons in a dense state is also high, and a decline in the ordering energy (relative to theZPE) is expected at high pressures. Arguments have been advanced by Neil Ashcroft and others that there is amelting point maximum in compressed hydrogen, but also that there may be a range of densities (at pressures around400 GPa) where hydrogen may be a liquid metal, even at low temperatures.[5] [6]

Superconductivity

In 1968, Ashcroft put forward that metallic hydrogen may be a superconductor, up to room temperature (~290 K),far higher than any other known candidate material. This stems from its extremely high speed of sound and theexpected strong coupling between the conduction electrons and the lattice vibrations.[7]

Possibility of novel types of quantum fluid

Presently known "super" states of matter are superconductors, superfluid liquids and gases, and supersolids. It waspredicted by Egor Babaev that, if hydrogen and deuterium have liquid metallic states, they may have ordered statesin quantum domains which cannot be classified as superconducting or superfluid in usual sense but represent twopossible novel types of quantum fluids: "superconducting superfluid" and "metallic superfluid". These were shown tohave highly unusual reactions to external magnetic fields and rotations, which might represent a route forexperimental verification of these possible new states of matter. It has also been suggested that, under the influenceof magnetic field, hydrogen may exhibit phase transitions from superconductivity to superfluidity and vice-versa.[8]

[9] [10]

Metallic hydrogen 40

Lithium doping reduces requisite pressure

In 2009, Zurek et al. predicted that the alloy LiH6 would be a stable metal at only 1⁄4 of the pressure required tometallize hydrogen, and that similar effects should hold for alloys of type LiHn and possibly other alloys of type?Lin.[11]

Experimental pursuit

Metallization of hydrogen in shock-wave compression

In March 1996, a group of scientists at Lawrence Livermore National Laboratory reported that they hadserendipitously produced, for about a microsecond and at temperatures of thousands of kelvins and pressures of overa million atmospheres (>100 GPa), the first identifiably metallic hydrogen.[12] The team did not expect to producemetallic hydrogen, as it was not using solid hydrogen, thought to be necessary, and was working at temperaturesabove those specified by metallization theory. Previous studies in which solid hydrogen was compressed insidediamond anvils to pressures of up to 2500000 atm (250 GPa), did not confirm detectable metallization. The team hadsought simply to measure the less extreme electrical conductivity changes which were expected to occur. Theresearchers used a 1960s-era light gas gun, originally employed in guided missile studies, to shoot an impactor plateinto a sealed container containing a half-millimeter thick sample of liquid hydrogen. The liquid hydrogen was incontact with wires leading to a device measuring electrical resistance. The scientists found that, as pressure rose to1400000 atm (140 GPa), the electronic energy band gap, a measure of electrical resistance, fell to almost zero. Theband-gap of hydrogen in its uncompressed state is about 15 eV, making it an insulator but, as the pressure increasessignificantly, the band-gap gradually fell to 0.3 eV. Because the thermal energy of the fluid (the temperature becameabout 3000 K due to compression of the sample) was above 0.3 eV, the hydrogen might be considered metallic.

Other experimental research since 1996

Many experiments are continuing in the production of metallic hydrogen in laboratory conditions at staticcompression and low temperature. Arthur Ruoff and Chandrabhas Narayana from Cornell University in 1998,[13] andlater Paul Loubeyre and René LeToullec from Commissariat à l'Énergie Atomique, France in 2002, have shown thatat pressures close to those at the center of the Earth (3.2 to 3.4 million atmospheres or 324 to 345 GPa) andtemperatures of 100–300 K, hydrogen is still not a true alkali metal, because of the non-zero band gap. The quest tosee metallic hydrogen in laboratory at low temperature and static compression continues. Studies are also undergoingon deuterium.[14] . Shahriar Badiei and Leif Holmlid from the University of Gothenburg have shown in 2004 thatcondensed metallic states made of excited hydrogen atoms (Rydberg matter) are effective promoters to metallichydrogen.[15]

Experimental breakthroughs in 2008

The theoretically predicted maximum of the melting curve (the prerequisite for the liquid metallic hydrogen) wasdiscovered by Shanti Deemyad and Isaac F. Silvera by using pulsed laser heating.[16] Hydrogen-rich alloy SiH4 wasmetalized and found to be superconducting by M.I. Eremets et al., confirming earlier theoretical prediction byAshcroft.[17] In this hydrogen rich alloy, even at moderate pressures (because of chemical precompression) thehydrogen forms a sub-lattice with density corresponding to metallic hydrogen.

Metallic hydrogen 41

Metallic hydrogen in other contexts

AstrophysicsMetallic hydrogen is thought to be present in large amounts in the gravitationally compressed interiors of Jupiter,Saturn, and some of the newly discovered extrasolar planets. Because previous predictions of the nature of thoseinteriors had taken for granted metallization at a higher pressure than the one at which we now know it to happen,those predictions must now be adjusted. The new data indicate much more metallic hydrogen must exist insideJupiter than previously thought, that it comes closer to the surface, and that therefore, Jupiter's tremendous magneticfield, the strongest of any planet in the solar system is, in turn, produced closer to the surface.

Hydrogen permeation of metalsAs mentioned earlier, pressurized SiH4 forms a metal alloy. It is well known that hydrogen can permeate to aremarkable extent various ordinary metals under conditions of ordinary pressure. In some metals (e.g., lithium) achemical reaction occurs that produces an ordinary non-metallic chemical compound (lithium hydride). In othercases it is possible that the hydrogen literally alloys itself with the metal (somewhat analogous to mercury amalgamformation). Certainly it is known that many metals remain metallic (e.g., palladium) after absorbing hydrogen—mostbecome brittle, but many ordinary alloys are brittle, too.

Applications

Nuclear powerOne method of producing nuclear fusion, called inertial confinement fusion, involves aiming laser beams at pelletsof hydrogen isotopes. The increased understanding of the behavior of hydrogen in extreme conditions could help toincrease energy yields.

FuelIt may be possible to produce substantial quantities of metallic hydrogen for practical purposes. The existence hasbeen theorized of a form called "Metastable Metallic Hydrogen", (abbreviated MSMH) which would not immediatelyrevert to ordinary hydrogen upon the release of pressure.In addition, MSMH would make an efficient fuel itself and also a clean one, with only water as an end product. Ninetimes as dense as standard hydrogen, it would give off considerable energy when reverting to standard hydrogen.Burned more quickly, it could be a propellant with up to five times the efficiency of liquid H2/O2, the current SpaceShuttle fuel.[18] Unfortunately, the above-mentioned Lawrence Livermore experiments produced metallic hydrogentoo briefly to determine whether or not metastability is possible.[19]

Metallic hydrogen 42

See also• Slush hydrogen• Solid hydrogen• Timeline of hydrogen technologies

References[1] Wigner, E.; Huntington, H.B. (1935). "On the possibility of a metallic modification of hydrogen". Journal of Chemical Physics 3: 764.

doi:10.1063/1.1749590.[2] Cornell News (6 May 1998). "High-pressure scientists 'journey' to the center of the Earth, but can't find elusive metallic hydrogen" (http:/ /

www. news. cornell. edu/ releases/ May98/ misbehaving. hydrogen. deb. html). Press release. . Retrieved 2010-01-02.[3] Loubeyre, P.; et al. (1996). "X-ray diffraction and equation of state of hydrogen at megabar pressures". Nature 383: 702.

doi:10.1038/383702a0.[4] "Peanut butter diamonds on display" (http:/ / news. bbc. co. uk/ 2/ hi/ uk_news/ scotland/ edinburgh_and_east/ 6244778. stm). BBC News. 27

June 2007. . Retrieved 2010-01-02.[5] Ashcroft, N.W. (2000). Journal of Physics: Condensed Matter 12: A129. doi:10.1088/0953-8984/12/8A/314.[6] Bonev, S.A.; et al. (2004). "A quantum fluid of metallic hydrogen suggested by first-principles calculations". Nature 431: 669.

doi:10.1038/nature02968.[7] Ashcroft, N.W. (1968). "Metallic Hydrogen: A High-Temperature Superconductor?". Physical Review Letters 21: 1748.

doi:10.1103/PhysRevLett.21.1748.[8] Babaev, E.; Ashcroft, N.W. (2007). "Violation of the London law and Onsager–Feynman quantization in multicomponent superconductors".

Nature Physics 3: 530. doi:10.1038/nphys646.[9] Babaev, E.; Sudbø, A.; Ashcroft, N.W. (2004). "A superconductor to superfluid phase transition in liquid metallic hydrogen". Nature 431:

666. doi:10.1038/nature02910.[10] Babaev; E. (2002). "Vortices with fractional flux in two-gap superconductors and in extended Faddeev model". Physical Review Letters 89:

067001. doi:10.1103/PhysRevLett.89.067001.[11] Zurek, E.; et al. (2009). "A little bit of lithium does a lot for hydrogen". Proceedings of the National Academy of Sciences.

doi:10.1073/pnas.0908262106.[12] Weir, S.T.; Mitchell, A.C.; Nellis, W. J. (1996). "Metallization of fluid molecular hydrogen at 140 GPa (1.4 Mbar)". Physical Review Letters

76: 1860. doi:10.1103/PhysRevLett.76.1860.[13] Ruoff, A.L.; et al. (1998). "Solid hydrogen at 342 GPa: No evidence for an alkali metal". Nature 393: 46. doi:10.1038/29949.[14] Baer, B.J.; Evans, W.J.; Yoo, C.-S. (2007). "Coherent anti-Stokes Raman spectroscopy of highly compressed solid deuterium at 300 K:

Evidence for a new phase and implications for the band gap". Physical Review Letters 98: 235503. doi:10.1103/PhysRevLett.98.235503.[15] Badiei, S.; Holmlid, L. (2004). "Experimental observation of an atomic hydrogen material with H–H bond distance of 150 pm suggesting

metallic hydrogen". Journal of Physics: Condensed Matter 16: 7017. doi:10.1088/0953-8984/16/39/034.[16] Deemyad, S.; Silvera, I.F (March 2008). "The melting line of hydrogen at high pressures". arΧiv:0803.2321.[17] Eremets, M.I.; et al. (2008). "Superconductivity in hydrogen dominant materials: Silane". Science 319: 1506. doi:10.1126/science.1153282.[18] Cole, I.F.; Silvera (2009). "Metallic Hydrogen Propelled Launch Vehicles for Lunar Missions" (http:/ / link. aip. org/ link/ ?APCPCS/ 1103/

117/ 1). AIP Conference Proceedings 1103: 117. doi:10.1063/1.3115485. .[19] Nellis, W.J. (2001), "Metastable Metallic Hydrogen Glass" (http:/ / www. llnl. gov/ tid/ lof/ documents/ pdf/ 244531. pdf), Lawrence

Livermore Preprint UCRL-JC-142360, OSTI 15005772 (http:/ / www. osti. gov/ energycitations/ product. biblio. jsp?osti_id=15005772),

Nascent hydrogen 43

Nascent hydrogenAtomic hydrogen (or nascent hydrogen)[1] is the species denoted by H (atomic), contrasted with dihydrogen, theusual 'hydrogen' (H2) commonly involved in chemical reactions. It is claimed to exist transiently but long enough toeffect chemical reactions. According to one claim, nascent hydrogen is generated in situ usually by the reaction ofzinc with an acid, aluminium (Devarda's alloy) with sodium hydroxide, or by electrolysis at the cathode. Beingmonoatomic, H atoms are much more reactive and thus a much more effective reducing agent than ordinary diatomicH2, but again the key question is whether H atoms exist in any chemically meaningful way under the conditionsclaimed. The concept is more popular in engineering and in older literature on catalysis. Atomic hydrogen is made ofindividual hydrogen atoms which are not bound together like ordinary hydrogen into molecules.

Making atomic hydrogenIt takes 4.476 eV to disassociate ordinary H2 hydrogen molecules. When they recombine, they liberate this energy.An electric arc or ultraviolet photon can generate atomic hydrogen.Atomic hydrogen can be formed under vacuum at temperatures high enough (> 2000 K) to thermally dissociate themolecule, or equivalent excitation in an electric discharge. Also, electromagnetic radiation above about 11 eV can beabsorbed by H2 and lead to its dissociation.

Uses of atomic hydrogenThe atomic hydrogen torch uses it to generate very high temperatures near 4,000°C for welding. Hydrogen is apowerful reducing agent which eliminates the need for flux to prevent oxidation of the weld.Atomic hydrogen determines the frequency of hydrogen masers which are used as precise frequency standards. Theyoperate at the 1420 MHz frequency corresponding to an absorption line in atomic hydrogen.NASA has investigated the use of atomic hydrogen as a rocket propellant. It could be stored in liquid helium toprevent it from recombining into molecular hydrogen. When the helium is vaporized, the atomic hydrogen would bereleased and combine back to molecular hydrogen. The result would be an intensely hot stream of hydrogen andhelium gas. The liftoff weight of rockets could be reduced by 50% by this method.[2]

Nascent hydrogen is claimed to reduce nitrites to ammonia, or arsenic to arsine even under mild conditions. Detailedscrutiny of such claims usually points to alternative pathways, not H atoms.

In natureMost interstellar hydrogen is in the form of atomic hydrogen because the atoms can seldom collide and combine.They are the source of the important 21 cm hydrogen line in astronomy at 1420 MHz.[3]

Another meaningOccasionally, hydrogen chemisorbed on metal surfaces is referred to as "nascent", although this terminology isfading with time. Other views hold that such chemisorbed hydrogen is "a bit less reactive than nascent hydrogenbecause of the bonds provided by the catalyst metal surface". Also, such catalyst provided atoms are not callednascent hydrogen, because they do not need to be captured and reacted in their instantaneous, temporary, "justgenerated" state, because the catalyst is able to reversibly generate them from the hydrogen gas supply at any time.

Nascent hydrogen 44

See also• Cold fusion• Devarda's alloy• Marsh test

• Arsine• Stibine• James Marsh

• Lithium aluminium hydride• Lithium borohydride• Sodium borohydride

References[1] Laborda, F.; E. Bolea, M. T. Baranguan, J. R. Castillo (2002). "Hydride generation in analytical chemistry and nascent hydrogen: when is it

going to be over?" (http:/ / www. sciencedirect. com/ science/ article/ B6THN-452FF7V-7/ 2/ 29eb1a70053dea76fb3ee7927530be6d).Spectrochimica Acta Part B: Atomic Spectroscopy 57 (4): 797–802. doi:10.1016/S0584-8547(02)00010-1. ISSN 0584-8547. . Retrieved2009-05-01.

[2] NASA/TM—2002-211915 : Solid Hydrogen Experiments for Atomic Propellants (http:/ / gltrs. grc. nasa. gov/ reports/ 2002/TM-2002-211915. pdf)

[3] 21 cm Line (http:/ / mysite. du. edu/ ~jcalvert/ phys/ hydrogen. htm)

Further reading• Tommasi, D. (1897). "Comment on the Note of R. Franchot entitled “Nascent Hydrogen”". The Journal of

Physical Chemistry 1 (9): 555. doi:10.1021/j150591a004. ISSN 1618-2642.• Meija, Juris; Alessandro D’Ulivo (2008). "Nascent hydrogen challenge". Analytical and Bioanalytical Chemistry

391 (5): 1475. doi:10.1007/s00216-008-2143-4. ISSN 1618-2642. PMID 18488209.• Meija, Juris; Alessandro D’Ulivo (2008). "Solution to nascent hydrogen challenge". Analytical and Bioanalytical

Chemistry 392 (5): 771–772. doi:10.1007/s00216-008-2356-6. ISSN 1618-2642. PMID 18795271.

45

Isotopes

Isotopes of hydrogen

Protium, the most common isotope of hydrogen,consists of one proton and one electron. Unique

among all stable isotopes, it has no neutrons. (seediproton for a discussion of why others do not

exist)

Hydrogen (H) (Standard atomic mass: 1.00782504(7) u) has threenaturally occurring isotopes, sometimes denoted 1H, 2H, and 3H.Other, highly unstable nuclei (4H to 7H) have been synthesized in thelaboratory but not observed in nature.[1] [2]

Hydrogen is the only element that has different names for its isotopesin common use today. The 2H (or H-2) isotope is usually calleddeuterium, while the 3H (or H-3) isotope is usually called tritium. Thesymbols D and T (instead of 2H and 3H) are sometimes used fordeuterium and tritium. The IUPAC states that while this use iscommon it is not preferred. The ordinary isotope of hydrogen, with noneutrons, is sometimes called "protium". (During the early study ofradioactivity, some other heavy radioactive isotopes were given names- but such names are rarely used today).

Hydrogen-1 (protium)1H is the most common hydrogen isotope with an abundance of more than 99.98%. Because the nucleus of thisisotope consists of only a single proton, it is given the descriptive but rarely used formal name protium.

Hydrogen-2 (deuterium)2H, the other stable hydrogen isotope, is known as deuterium and contains one proton and one neutron in its nucleus.Deuterium comprises 0.0026 – 0.0184% (by population, not by mass) of hydrogen samples on Earth, with the lowernumber tending to be found in samples of hydrogen gas and the higher enrichments (0.015% or 150 ppm) typical ofocean water. Deuterium is not radioactive, and does not represent a significant toxicity hazard. Water enriched inmolecules that include deuterium instead of normal hydrogen is called heavy water. Deuterium and its compoundsare used as a non-radioactive label in chemical experiments and in solvents for 1H-NMR spectroscopy. Heavy wateris used as a neutron moderator and coolant for nuclear reactors. Deuterium is also a potential fuel for commercialnuclear fusion.

Isotopes of hydrogen 46

Hydrogen-3 (tritium)3H is known as tritium and contains one proton and two neutrons in its nucleus. It is radioactive, decaying intohelium-3 through β− decay with a half-life of 12.32 years.[3] Small amounts of tritium occur naturally because of theinteraction of cosmic rays with atmospheric gases. Tritium has also been released during nuclear weapons tests. It isused in thermonuclear fusion weapons, as a tracer in isotope geochemistry, and specialized in self-powered lightingdevices.The most common method of producing tritium is by bombarding a natural isotope of lithium, lithium-6, withneutrons in a nuclear reactor.Tritium was once used routinely in chemical and biological labeling experiments as a radiolabel (this has becomeless common). D-T nuclear fusion uses tritium as its main reactant, along with deuterium, liberating energy throughthe loss of mass when the two nuclei collide and fuse under massive temperatures.

Hydrogen-4 (quadrium)4H is a highly unstable isotope of hydrogen. The nucleus consists of a proton and three neutrons. It has beensynthesised in the laboratory by bombarding tritium with fast-moving deuterium nuclei.[4] In this experiment, thetritium nuclei captured neutrons from the fast-moving deuterium nucleus. The presence of the hydrogen-4 wasdeduced by detecting the emitted protons. Its atomic mass is 4.02781 ± 0.00011.[5] It decays through neutronemission with a half-life of (1.39 ± 0.10) × 10−22 seconds.[6]

Hydrogen-55H is a highly unstable isotope of hydrogen. The nucleus consists of a proton and four neutrons. It has beensynthesised in the laboratory by bombarding tritium with fast-moving tritium nuclei.[4] [7] In this experiment, onetritium nucleus captures two neutrons from the other, becoming a nucleus with one proton and four neutrons. Theremaining proton may be detected, and the existence of hydrogen-5 deduced. It decays through double neutronemission and has a half-life of at least 9.1 × 10−22 seconds.[6]

Hydrogen-66H decays through triple neutron emission and has a half-life of 3×10−22 seconds. It consists of 1 proton and 5neutrons.

Hydrogen-77H consists of a proton and six neutrons. It was first synthesised in 2003 by a group of Russian, Japanese and Frenchscientists at RIKEN's RI Beam Science Laboratory by bombarding hydrogen with helium-8 atoms. In the resultingreaction, the helium-8's neutrons were donated to the hydrogen's nucleus. The two remaining protons were detectedby the "RIKEN telescope", a device composed of several layers of sensors, positioned behind the target of the RIBeam cyclotron.[2]

Isotopes of hydrogen 47

Table

Nuclide properties [8]

NuclideZ(p) N(n) mass (u)[9] half-life nuclear spin

( JP )[10]RIC [11]

(mole fraction)RNV [12]

(mole fraction)

1H 1 0 1.00782503207(10) Stable[13] 1⁄2+ 0.999885(70) 0.999816–0.999974

2H 1 1 2.0141017778(4) Stable 1+ 0.000115(70)[14] 0.000026–0.000184

3H 1 2 3.0160492777(25) 12.32(2) a 1⁄2+

4H 1 3 4.02781(11) 1.39(10) × 10−22 s[4.6(9) MeV]

2−

5H 1 4 5.03531(11) >9.1 × 10−22 s ? (1⁄2+)

6H 1 5 6.04494(28) 2.90(70) × 10−22 s[1.6(4) MeV]

2− [15]

7H 1 6 7.05275(108) [15] 2.3(6) × 10−23 s [15]

[20(5) MeV] [15]1/2+ [15]

See also• Isotopes of Helium

Notes[1] Y. B. Gurov et al. (2004). "Spectroscopy of superheavy hydrogen isotopes in stopped-pion absorption by nuclei". Physics of Atomic Nuclei 68

(3): 491–497. doi:10.1134/1.1891200.[2] A. A. Korsheninnikov et al. (2003). "Experimental Evidence for the Existence of 7H and for a Specific Structure of 8He". Physical Review

Letters 90: 082501. doi:10.1103/PhysRevLett.90.082501.[3] G. L. Miessler, D. A. Tarr (2004). Inorganic Chemistry (3rd ed.). Pearson Prentice Hall.[4] G. M. Ter-Akopian et al. (2002). "Hydrogen-4 and Hydrogen-5 from t+t and t+d transfer reactions studied with a 57.5-MeV triton beam".

AIP Conference Proceedings 610: 920. doi:10.1063/1.1470062.[5] "The 2003 Atomic Mass Evaluation" (http:/ / www. nndc. bnl. gov/ amdc/ web/ masseval. html). Atomic Mass Data Center. . Retrieved

2008-11-15.[6] G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (http:/ /

www. nndc. bnl. gov/ amdc/ nubase/ Nubase2003. pdf). Nuclear Physics A 729: 3–128. doi:10.1016/j.nuclphysa.2003.11.001. .[7] A. A. Korsheninnikov et al. (2001). "Superheavy Hydrogen 5H". Physical Review Letters 87: 92501. doi:10.1103/PhysRevLett.87.092501.[8] Commercially available materials may have been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations

from the given mass and composition can occur.[9] Uncertainties are given in concise form in parentheses after the corresponding last digits, and denote one standard deviation.[10] Spins with weak assignment arguments are enclosed in parentheses.[11] Representative isotopic composition (RIC): refers to that in water.[12] Range of natural variation (RNV): The precision of the isotope abundances and atomic mass is limited through variations. The given ranges

should be applicable to any normal terrestrial material.[13] Greater than 6.6 × 1033 a. See proton decay.[14] Tank hydrogen has a 2H abundance as low as 3.2 × 10−5 (mole fraction).[15] Value is not purely derived from experimental data, but at least partly from systematic trends.

Isotopes of hydrogen 48

References• Isotope masses from:

• G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclearand decay properties" (http:/ / www. nndc. bnl. gov/ amdc/ nubase/ Nubase2003. pdf). Nuclear Physics A 729:3–128. doi:10.1016/j.nuclphysa.2003.11.001.

• Isotopic compositions and standard atomic masses from:• J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor

(2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)" (http:/ / www. iupac. org/publications/ pac/ 75/ 6/ 0683/ pdf/ ). Pure and Applied Chemistry 75 (6): 683–800.doi:10.1351/pac200375060683.

• M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)" (http:/ / iupac. org/publications/ pac/ 78/ 11/ 2051/ pdf/ ). Pure and Applied Chemistry 78 (11): 2051–2066.doi:10.1351/pac200678112051. Lay summary (http:/ / old. iupac. org/ news/ archives/ 2005/atomic-weights_revised05. html).

• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.• G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear

and decay properties" (http:/ / www. nndc. bnl. gov/ amdc/ nubase/ Nubase2003. pdf). Nuclear Physics A 729:3–128. doi:10.1016/j.nuclphysa.2003.11.001.

• National Nuclear Data Center. "NuDat 2.1 database" (http:/ / www. nndc. bnl. gov/ nudat2/ ). BrookhavenNational Laboratory. Retrieved September 2005.

• N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85thed.). CRC Press. Section 11. ISBN 978-0849304859.

In fictionIn the 1955 satirical novel The Mouse That Roared, the name quadium was given to the hydrogen-4 isotope thatpowered the Q-bomb that the Duchy of Grand Fenwick captured from the United States.

External links• News of hydrogen-7 discovery (http:/ / physicsweb. org/ articles/ news/ 7/ 3/ 3)• Article on hydrogen-4 and hydrogen-5 (http:/ / content. aip. org/ APCPCS/ v610/ i1/ 920_1. html) (login required)

Deuterium 49

Deuterium

Hydrogen-2

Full table

General

Name, symbol deuterium, 2H or D

Neutrons 1

Protons 1

Nuclide Data

Natural abundance 0.015%

Half-life Stable

Isotope mass 2.01410178 u

Spin 1+

Excess energy 13135.720 ± 0.001 keV

Binding energy 2224.52 ± 0.20 keV

Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans ofEarth of approximately one atom in 6400 of hydrogen (156 ppm). Deuterium thus accounts for approximately0.0156% (alternately, on a mass basis: 0.0312%) of all naturally occurring hydrogen in the oceans on Earth (seeVSMOW; the abundance changes slightly from one kind of natural water to another).The nucleus of deuterium, called a deuteron, contains one proton and one neutron, whereas the far more commonhydrogen nucleus contains no neutron. The isotope name is formed from the Greek deuteros meaning "second", todenote the two particles composing the nucleus.[1]

Differences between deuterium and common hydrogen (protium)

Chemical symbol

Deuterium discharge (spectrum) tube

Deuterium is frequently represented by the chemical symbol D. Sinceit is an isotope of hydrogen with mass number 2, it is also representedby 2H. IUPAC allows both D and 2H, although 2H is preferred.[2] Adistinct chemical symbol is used for convenience because of theisotope's common use in various scientific processes. Also, its largemass difference with protium (1H) (deuterium has a mass of2.014102 u, compared to the mean hydrogen atomic weight of 1.007947 u, and protium's mass of 1.007825 u)confers non-negligible chemical dissimilarities with protium-containing compounds, whereas the isotope weightratios within other chemical elements are largely insignificant in this regard.

Deuterium 50

Natural abundanceDeuterium occurs in trace amounts naturally as deuterium gas, written 2H2 or D2, but most natural occurrence in theuniverse is bonded with a typical 1H atom, a gas called hydrogen deuteride (HD or 1H2H).[3]

The natural deuterium abundance seems to be a very similar fraction of hydrogen, wherever hydrogen is found.Thus, the existence of deuterium at a low but constant fraction in all hydrogen, is one of the arguments in favor ofthe Big Bang theory over the steady state theory of the universe. It is estimated that the abundances of deuteriumhave not evolved significantly since their production about 13.7 bya.[4]

Deuterium abundance on Jupiter is about 2.25 × 10−5 (roughly 22 atoms in a million, or 15% of the terrestrialdeuterium-to-hydrogen ratio);[5] these ratios presumably reflect the early solar nebula ratios, and those after the BigBang. However, other sources suggest a much higher abundance of e.g. 6 × 10−4 (6 atoms in 10000 or 0.06% atombasis).[6] There is thought to be little deuterium in the interior of the Sun and other stars, as at temperatures therenuclear fusion reactions that consume deuterium happen much faster than the proton-proton reaction that createsdeuterium. However, it continues to persist in the outer solar atmosphere at roughly the same concentration as inJupiter.The existence of deuterium on Earth, elsewhere in the solar system (as confirmed by planetary probes), and in thespectra of stars, is an important datum in cosmology. Gamma radiation from ordinary nuclear fusion dissociatesdeuterium into protons and neutrons, and there are no known natural processes other than the Big Bangnucleosynthesis, which might have produced deuterium at anything close to the observed natural abundance ofdeuterium (deuterium is produced by the rare cluster decay, and occasional absorption of naturally-occurringneutrons by light hydrogen, but these are trivial sources).

Concentrating natural abundance deuteriumDeuterium is concentrated for industrial, scientific and military purposes as heavy water from ordinary water. Theworld's leading supplier of deuterium was Atomic Energy of Canada Limited, in Canada, until 1997 when the lastplant was shut down. Canada uses heavy water as a neutron moderator for the operation of the CANDU reactordesign. India is now probably the world's largest concentrator of heavy water, also used in nuclear power reactors.

Properties

Physical propertiesThe physical properties of deuterium compounds can exhibit significant kinetic isotope effects and other physicaland chemical property differences from the hydrogen analogs; for example, D2O is more viscous than H2O.[7]

Chemically, deuterium behaves similarly to ordinary hydrogen, but there are differences in bond energy and lengthfor compounds of heavy hydrogen isotopes which are larger than the isotopic differences in any other element.Bonds involving deuterium and tritium are somewhat stronger than the corresponding bonds in hydrogen, and thesedifferences are enough to make significant changes in biological reactions.Deuterium can replace the normal hydrogen in water molecules to form heavy water (D2O), which is about 10.6%denser than normal water (enough that ice made from it sinks in ordinary water). Heavy water is slightly toxic ineukaryotic animals, with 25% substitution of the body water causing cell division problems and sterility, and 50%substitution causing death by cytotoxic syndrome (bone marrow failure and gastrointestinal lining failure).Prokaryotic organisms, however, can survive and grow in pure heavy water (though they grow more slowly).[8]

Consumption of heavy water would not pose a health threat to humans, it was estimated that a 70 kg person mightdrink 4.8 liters of heavy water without serious consequences.[9] Small doses of heavy water (a few grams in humans,containing an amount of deuterium comparable to that normally present in the body) are routinely used as harmlessmetabolic tracers in humans and animals.

Deuterium 51

Quantum propertiesThe deuteron has spin +1 ("triplet") and is thus a boson. The NMR frequency of deuterium is significantly differentfrom common light hydrogen. Infrared spectroscopy also easily differentiates many deuterated compounds, due tothe large difference in IR absorption frequency seen in the vibration of a chemical bond containing deuterium, versuslight hydrogen. The two stable isotopes of hydrogen can also be distinguished by using mass spectrometry.The triplet deuteron nucleon barely is bound at EB = 2.23 MeV, so all the higher energy states are not bound. Thesinglet deuteron is a virtual state, with a negative binding energy of 60 keV. There is no such stable particle, but thisvirtual particle transiently exists during neutron-proton inelastic scattering, accounting for the unusually largeneutron scattering cross-section of the proton.[10]

Nuclear properties (the deuteron)

Deuteron mass and radius

The nucleus of deuterium is called a deuteron. It has a mass of 2.013553212724(78) u [11] The charge radius of thedeuteron is 2.1402(28) fm [12]

Spin and energy

Deuterium is one of only four stable nuclides with an odd number of protons and odd number of neutrons. (2H, 6Li,10B, 14N; also, the long-lived radioactive nuclides 40K, 50V, 138La, 180mTa occur naturally.) Most odd-odd nuclei areunstable with respect to beta decay, because the decay products are even-even, and are therefore more stronglybound, due to nuclear pairing effects. Deuterium, however, benefits from having its proton and neutron coupled to aspin-1 state, which gives a stronger nuclear attraction; the corresponding spin-1 state does not exist in thetwo-neutron or two-proton system, due to the Pauli exclusion principle which would require one or the otheridentical particle with the same spin to have some other different quantum number, such as orbital angularmomentum. But orbital angular momentum of either particle gives a lower binding energy for the system, primarilydue to increasing distance of the particles in the steep gradient of the nuclear force. In both cases, this causes thediproton and dineutron nucleus to be unstable.The proton and neutron making up deuterium can be dissociated through neutral current interactions with neutrinos.The cross section for this interaction is comparatively large, and deuterium was successfully used as a neutrino targetin the Sudbury Neutrino Observatory experiment.

Isospin singlet state of the deuteron

Due to the similarity in mass and nuclear properties between the proton and neutron, they are sometimes consideredas two symmetric types of the same object, a nucleon. While only the proton has an electric charge, this is oftennegligible due of the weakness of the electromagnetic interaction relative to the strong nuclear interaction. Thesymmetry relating the proton and neutron is known as isospin and denoted I (or sometimes T).Isospin is an SU(2) symmetry, like ordinary spin, so is completely analogous to it. The proton and neutron form anisospin doublet, with a "down" state (↓) being a neutron, and an "up" state (↑) being a proton.A pair of nucleons can either be in an antisymmetric state of isospin called singlet, or in a symmetric state calledtriplet. In terms of the "down" state and "up" state, the singlet is

This is a nucleus with one proton and one neutron, i.e. a deuterium nucleus. The triplet is

Deuterium 52

and thus consists of three types of nuclei, which are supposed to be symmetric: a deuterium nucleus (actually ahighly excited state of it), a nucleus with two protons, and a nucleus with two neutrons. The latter two nuclei are notstable or nearly stable, and therefore so is this type of deuterium (meaning that it is indeed a highly excited state ofdeuterium).

Approximated wavefunction of the deuteron

The deuteron wavefunction must be antisymmetric if the isospin representation is used (since a proton and a neutronare not identical particles, the wavefunction need not be antisymmetric in general). Apart from their isospin, the twonucleons also have spin and spatial distributions of their wavefunction. The latter is symmetric if the deuteron issymmetric under parity (i.e. have an "even" or "positive" parity), and antisymmetric if the deuteron is antisymmetricunder parity (i.e. have an "odd" or "negative" parity). The parity is fully determined by the total orbital angularmomentum of the two nucleons: if it is even then the parity is even (positive), and if it is odd then the parity is odd(negative).The deuteron, being an isospin singlet, is antisymmetric under nucleons exchange due to isospin, and therefore mustbe symmetric under the double exchange of their spin and location. Therefore it can be in either of the following twodifferent states:• Symmetric spin and symmetric under parity. In this case, the exchange of the two nucleons will multiply the

deuterium wavefunction by (-1) from isospin exchange, (+1) from spin exchange and (+1) from parity (locationexchange), for a total of (-1) as needed for antisymmetry.

• Antisymmetric spin and antisymmetric under parity. In this case, the exchange of the two nucleons will multiplythe deuterium wavefunction by (-1) from isospin exchange, (-1) from spin exchange and (-1) from parity (locationexchange), again for a total of (-1) as needed for antisymmetry.

In the first case the deuteron is a spin triplet, so that its total spin s is 1. It also has an even parity and therefore evenorbital angular momentum l ; The lower its orbital angular momentum, the lower its energy. Therefore the lowestpossible energy state has s = 1, l = 0.In the second case the deuteron is a spin singlet, so that its total spin s is 0. It also has an odd parity and therefore oddorbital angular momentum l. Therefore the lowest possible energy state has s = 0, l = 1.Since s = 1 gives a stronger nuclear attraction, the deuterium ground state is in the s =1, l = 0 state.The same considerations lead to the possible states of an isospin triplet having s = 0, l = even or s = 1, l = odd. Thusthe state of lowest energy has s = 1, l = 1, higher than that of the isospin singlet.The analysis just given is in fact only approximate, both because isospin is not an exact symmetry, and moreimportantly because the strong nuclear interaction between the two nucleons is related to angular momentum inspin-orbit interaction that mixes different s and l states. That is, s and l are not constant in time (they do not commutewith the Hamiltonian), and over time a state such as s = 1, l = 0 may become a state of s = 1, l = 2. Parity is stillconstant in time so these do not mix with odd l states (such as s = 0, l = 1). Therefore the quantum state of thedeuterium is a superposition (a linear combination) of the s = 1, l = 0 state and the s = 1, l = 2 state, even though thefirst component is much bigger. Since the total angular momentum j is also a good quantum number (it is a constantin time), both components must have the same j, and therefore j = 1. This is the total spin of the deuterium nucleus.To summarize, the deuterium nucleus is antisymmetric in terms of isospin, and has spin 1 and even (+1) parity. Therelative angular momentum of its nucleons l is not well defined, and the deuteron is a superposition of mostly l = 0with some l = 2.

Deuterium 53

Magnetic and electric multipoles

In order to find theoretically the deuterium magnetic dipole moment µ, one uses the formula for a nuclear magneticmoment

with

g(l) and g(s) are g-factors of the nucleons.Since the proton and neutron have different values for g(l) and g(s), one must separate their contributions. Each getshalf of the deuterium orbital angular momentum and spin . One arrives at

where subscripts p and n stand for the proton and neutron, and g(l)n = 0.

By using the same identities as here and using the value g(l)p = 1 µN, we arrive at the following result, in nuclear

magneton unitsFor the s = 1, l = 0 state (j = 1), we obtain

For the s = 1, l = 2 state (j = 1), we obtain

The measured value of the deuterium magnetic dipole moment, is 0.857 µN. This suggests that the state of thedeuterium is indeed only approximately s = 1, l = 0 state, and is actually a linear combination of (mostly) this statewith s = 1, l = 2 state.The electric dipole is zero as usual.The measured electric quadrupole of the deuterium is 0.2859 e·fm2. While the order of magnitude is reasonable,since the deuterium radius is of order of 1 femtometer (see below) and its electric charge is e, the above model doesnot suffice for its computation. More specifically, the electric quadrupole does not get a contribution from the l =0state (which is the dominant one) and does get a contribution from a term mixing the l =0 and the l =2 states, becausethe electric quadrupole operator does not commute with angular momentum. The latter contribution is dominant inthe absence of a pure l = 0 contribution, but cannot be calculated without knowing the exact spatial form of thenucleons wavefunction inside the deuterium.Higher magnetic and electric multipole moments cannot be calculated by the above model, for similar reasons.

Deuterium 54

Applications

Ionized deuterium in an IEC fusion reactor giving off its characteristic pinkish-red glow.

Emission spectrum of an ultraviolet deuterium arc lamp.

Deuterium has a number ofcommercial and scientific uses. Theseinclude:

Nuclear reactors

Deuterium is useful in nuclear fusionreactions, especially in combinationwith tritium, because of the largereaction rate (or nuclear cross section)and high energy yield of the D–Treaction. There is an even higher-yieldD–3He fusion reaction, though thebreakeven point of D–3He is higherthan that of most other fusionreactions; together with the scarcity of3He, this makes it implausible as apractical power source until at leastD–T and D–D fusion reactions havebeen performed on a commercial scale.

Deuterium is used in heavy watermoderated fission reactors, usually asliquid D2O, to slow neutrons withouthigh neutron absorption of ordinaryhydrogen.

NMR spectroscopy

Deuterium NMR spectra are especiallyinformative in the solid state becauseof its relatively small quadrupolemoment in comparison with those ofbigger quadrupolar nuclei such aschlorine-35, for example.

Tracing

In chemistry, biochemistry and environmental sciences, deuterium is used as a non-radioactive, stable isotopic tracer,for example, in the doubly-labeled water test. In chemical reactions and metabolic pathways, deuterium behavessomewhat similarly to ordinary hydrogen (with a few chemical differences, as noted). It can be distinguished fromordinary hydrogen most easily by its mass, using mass spectrometry or infrared spectrometry. Deuterium can bedetected by femtosecond infrared spectroscopy, since the mass difference drastically affects the frequency ofmolecular vibrations; deuterium-carbon bond vibrations are found in locations free of other signals.

Measurements of small variations in the natural abundances of deuterium, along with those of the stable heavy oxygen isotopes 17O and 18O, are of importance in hydrology, to trace the geographic origin of Earth's waters. The heavy isotopes of hydrogen and oxygen in rainwater (so-called meteoric water) are enriched as a function of the

Deuterium 55

environmental temperature of the region in which the precipitation falls (and thus enrichment is related to meanlatitude). The relative enrichment of the heavy isotopes in rainwater (as referenced to mean ocean water), whenplotted against temperature falls predictably along a line called the global meteoric water line (GMWL). This plotallows samples of precipitation-originated water to be identified along with general information about the climate inwhich it originated. Evaporative and other processes in bodies of water, and also ground water processes, alsodifferentially alter the ratios of heavy hydrogen and oxygen isotopes in fresh and salt waters, in characteristic andoften regionally-distinctive ways.[13]

Contrast propertiesNeutron scattering techniques particularly profit from availability of deuterated samples: The H and D cross sectionsare very distinct and different in sign, which allows contrast variation in such experiments. Further, a nuisanceproblem of ordinary hydrogen is its large incoherent neutron cross section, which is nil for D. The substitution ofhydrogen atoms for deuterium atoms thus reduces scattering noise.Hydrogen is an important and major component in all materials of organic chemistry and life science, but is barelyinteracts with X-rays. As hydrogen (and deuterium) interact strongly with neutrons, neutron scattering techniques,together with a modern deuteration facility, fills a niche in many studies of macromolecules in biology and manyother areas.

Nuclear resonance spectroscopyDeuterium is useful in hydrogen nuclear magnetic resonance spectroscopy (proton NMR). NMR ordinarily requirescompounds of interest to be analyzed as dissolved in solution. Because of deuterium's nuclear spin properties whichdiffer from the light hydrogen usually present in organic molecules, NMR spectra of hydrogen/protium are highlydifferentiable from that of deuterium, and in practice deuterium is not "seen" by an NMR instrument tuned tolight-hydrogen. Deuterated solvents (including heavy water, but also compounds like deuterated chloroform, CDCl3)are therefore routinely used in NMR spectroscopy, in order to allow only the light-hydrogen spectra of thecompound of interest to be measured, without solvent-signal interference.

History

Suspicion of lighter element isotopesThe existence of nonradioactive isotopes of lighter elements had been suspected in studies of neon as early as 1913,and proven by mass spectroscopy of light elements in 1920. The prevailing theory at the time, however, was that theisotopes were due to the existence of differing numbers of "nuclear electrons" in different atoms of an element. Itwas expected that hydrogen, with a measured average atomic mass very close to 1 u, the known mass of the proton,always had a nucleus composed of a single proton (a known particle), and therefore could not contain any nuclearelectrons without losing its charge entirely. Thus, hydrogen could have no heavy isotopes.

Deuterium predicted and finally detectedDeuterium was predicted in 1926 by Walter Russell, using his "spiral" periodic table, and independently by CharlesJanet in 1928.It was first detected spectroscopically in late 1931 by Harold Urey, a chemist at Columbia University. Urey'scollaborator, Ferdinand Brickwedde, distilled five liters of cryogenically-produced liquid hydrogen to 1 mL ofliquid, using the low-temperature physics laboratory that had recently been established at the National Bureau ofStandards in Washington, D.C. (now the National Institute of Standards and Technology). This concentrated thefraction of the mass-2 isotope of hydrogen to a degree that made its spectroscopic identification unambiguous.

Deuterium 56

NameUrey called the new isotope "deuterium", from the Greek deuteros (second), and the nucleus to be called "deuteron"or "deuton". Isotopes and new elements were traditionally given the name that their discoverer decided, but someBritish chemists, like Ernest Rutherford, wanted the isotope to be called "diplogen", from the Greek diploos(double), and the nucleus to be called diplon. The British magazine Nature also published a letter where only thedenomination "diplogen" was used, perhaps annunciating that British could prefer that name over the name given byits discoverer. Urey and his two co-discoverers sent a letter to Nature saying that they had already considered thatname and they had rejected it because "The compound NH1H2/2 would be called di-diplogen mono-hydrogennitride", which would repeat the syllable "di." They also said that the British seemed to object on the basis that"neutron" and "deuton" could be confused with each other, and Urey pointed out that American workers were usingthe terms and they didn't seem to be having any such confusion.[1]

Abundance, purification, and impactThe amount inferred for normal abundance of this heavy isotope of hydrogen was so small (only about 1 atom in6400 hydrogen atoms in ocean water) that it had not noticeably affected previous measurements of (average)hydrogen atomic mass. This explained why it hadn't been experimentally suspected before. Urey was able toconcentrate water to show partial enrichment of deuterium. Gilbert Newton Lewis prepared the first samples of pureheavy water in 1933.The discovery of deuterium, coming before the discovery of the neutron in 1932, was an experimental shock totheory, but when the neutron was reported, making deuterium's existence more explainable, deuterium won Urey theNobel Prize in chemistry in 1934.

"Heavy water" experiments in World War IIShortly before the war, Hans von Halban and Lew Kowarski moved their research on neutron moderation fromFrance to England, smuggling the entire global supply of heavy water (which had been made in Norway) across intwenty-six steel drums.[14] [15]

During World War II, Nazi Germany was known to be conducting experiments using heavy water as moderator for anuclear reactor design. Such experiments were a source of concern because they might allow them to produceplutonium for an atomic bomb. Ultimately it led to the Allied operation called the "Norwegian heavy watersabotage", the purpose of which was to destroy the Vemork deuterium production/enrichment facility in Norway. Atthe time this was considered important to the potential progress of the war.After World War II ended, the Allies discovered that Germany was not putting as much serious effort into theprogram as had been previously thought. The Germans had completed only a small, partly-built experimental reactor(which had been hidden away). By the end of the war, the Germans did not even have a fifth of the amount of heavywater needed to run the reactor, partially due to the Norwegian heavy water sabotage operation. However, even hadthe Germans succeeded in getting a reactor operational (as the U.S. did with a graphite reactor in late 1942), theywould still have been at least several years away from development of an atomic bomb with maximal effort. Theengineering process, even with maximal effort and funding, required about two and a half years (from first criticalreactor to bomb) in both the U.S. and U.S.S.R, for example.

Deuterium 57

Data• Density: 0.180 kg/m3 at STP (0 °C, 101.325 kPa).• Atomic weight: 2.0141017926 u.• Mean abundance in ocean water (see VSMOW) about 0.0156 of H atoms = 1/6400 H atoms.Data at approximately 18 K for D2 (triple point):• Density:

• Liquid: 162.4 kg/m3

• Gas: 0.452 kg/m3

• Viscosity: 12.6 µPa·s at 300 K (gas phase)• Specific heat capacity at constant pressure cp:

• Solid: 2950 J/(kg·K)• Gas: 5200 J/(kg·K)

Anti-deuteriumAn antideuteron is the antiparticle of the nucleus of deuterium, consisting of an antiproton and an antineutron. Theantideuteron was first produced in 1965 at the Proton Synchrotron at CERN[16] and the Alternating GradientSynchrotron [17] at Brookhaven National Laboratory.[18] A complete atom, with a positron orbiting the nucleus,would be called antideuterium, but as of 2005 antideuterium has not yet been created. The proposed symbol forantideuterium is D, that is, D with an overbar.[19]

PycnodeuteriumDeuterium atoms can be absorbed into a palladium (Pd) lattice. They are effectively solidified as an ultrahigh densitydeuterium lump (Pycnodeuterium) inside each octahedral space within the unit cell of the palladium host lattice. Itwas once reported that deuterium absorbed into palladium enabled nuclear cold fusion.[20] However, cold fusion bythis mechanism has not been generally accepted by the scientific community.[21]

Ultra-dense deuteriumThe existence of ultra-dense deuterium is suggested by experiment. If its existence is confirmed, this material, atdensity of 140 kg/cm3, would be a million times more dense than regular deuterium, denser than the core of the Sun.This ultra-dense form of deuterium may facilitate achieving laser-induced fusion.[22] Only minute amounts ofultra-dense deuterium have been produced thus far.[23] [24]

See also• Isotopes of hydrogen• Nuclear fusion• Tokamak• Tritium• Heavy water

Deuterium 58

References[1] "Science: Deuterium v. Diplogen" (http:/ / www. time. com/ time/ magazine/ article/ 0,9171,746988,00. html). Time. 1934-02-19. .[2] "§ IR-3.3.2 Provisional Recommendations" (http:/ / www. iupac. org/ reports/ provisional/ abstract04/ connelly_310804. html). Nomenclature

of Inorganic Chemistry. Chemical Nomenclature and Structure Representation Division, IUPAC. . Retrieved 2007-10-03.[3] IUPAC Commission on Nomenclature of Inorganic Chemistry (2001). "Names for Muonium and Hydrogen Atoms and their Ions" (http:/ /

www. iupac. org/ publications/ pac/ 2001/ pdf/ 7302x0377. pdf) (PDF). Pure and Applied Chemistry 73: 377–380.doi:10.1351/pac200173020377. .

[4] The End of Cosmology?: Scientific American (http:/ / www. sciam. com/ article. cfm?id=the-end-of-cosmology& print=true)[5] Lellouch, E; Bézard, B.; Fouchet, T.; Feuchtgruber, H.; Encrenaz, T.; De Graauw, T. (2001). "The deuterium abundance in Jupiter and Saturn

from ISO-SWS observations". Astronomy & Astrophysics 670: 610–622. doi:10.1051/0004-6361:20010259.[6] "Hubble measures deuterium on Jupiter" (http:/ / findarticles. com/ p/ articles/ mi_m1200/ is_n14_v150/ ai_18757250). Science News – Find

Articles. 5 October 1996. . Retrieved 2007-09-10. As mentioned in this article, this value also agrees with the Galileo entry probemeasurement for Jupiter

[7] Lide, D. R., ed. (2005), CRC Handbook of Chemistry and Physics (86th ed.), Boca Raton (FL): CRC Press, ISBN 0-8493-0486-5[8] D. J. Kushner, Alison Baker, and T. G. Dunstall (1999). "Pharmacological uses and perspectives of heavy water and deuterated compounds".

Can. J. Physiol. Pharmacol. 77 (2): 79–88. doi:10.1139/cjpp-77-2-79. PMID 10535697.[9] ed. by Attila Vertes .... (2003). "Physiological effect of heavy water" (http:/ / books. google. com/ ?id=nQh7iGX1geIC& pg=PA111).

Elements and isotopes : formation, transformation, distribution.. Dordrecht: Kluwer Acad. Publ.. pp. 111– 112. ISBN 9781402013140. .[10] Neutron-Proton Scattering (http:/ / mightylib. mit. edu/ Course Materials/ 22. 101/ Fall 2004/ Notes/ Part3. pdf)[11] 2002 CODATA recommended value (http:/ / physics. nist. gov/ cgi-bin/ cuu/ Value?mdu)[12] 2006 CODATA recommended value Mohr, Peter J.; Taylor, Barry N.; Newell, David B. (2008). "CODATA Recommended Values of the

Fundamental Physical Constants: 2006" (http:/ / physics. nist. gov/ cuu/ Constants/ codata. pdf). Rev. Mod. Phys. 80: 633–730.doi:10.1103/RevModPhys.80.633. .

[13] "Oxygen – Isotopes and Hydrology" (http:/ / www. sahra. arizona. edu/ programs/ isotopes/ oxygen. html). SAHRA. . Retrieved2007-09-10.

[14] Sherriff, Lucy (2007-06-01). "Royal Society unearths top secret nuclear research" (http:/ / www. theregister. co. uk/ 2007/ 06/ 01/royal_soc_secret_physics/ ). The Register. Situation Publishing Ltd.. . Retrieved 2007-06-03.

[15] "The Battle for Heavy Water Three physicists' heroic exploits" (http:/ / bulletin. cern. ch/ eng/ articles. php?bullno=14/ 2002& base=art).CERN Bulletin. European Organization for Nuclear Research. 2002-04-01. . Retrieved 2007-06-03.

[16] Massam, T; Muller, Th.; Righini, B.; Schneegans, M.; Zichichi, A. (1965). "Experimental observation of antideuteron production". Il NuovoCimento 39: 10–14. doi:10.1007/BF02814251.

[17] http:/ / www. bnl. gov/ bnlweb/ facilities/ AGS. asp[18] Dorfan, D. E; Eades, J.; Lederman, L. M.; Lee, W.; Ting, C. C. (June 1965). "Observation of Antideuterons". Phys. Rev. Lett. 14 (24):

1003–1006. doi:10.1103/PhysRevLett.14.1003.[19] Chardonnet, P (1997). "The production of anti-matter in our galaxy" (http:/ / arxiv. org/ abs/ astro-ph/ 9705110v1). Physics Letters B 409:

313. doi:10.1016/S0370-2693(97)00870-8. .[20] Arata Y, Zhang Y-C, Fujita H, Inoue A; Koon Gakkaishi 29(2) (2003). "Discovery of solid deuterium nuclear fusion of

pycnodeuterium-lumps solidified locally within nano-Pd particles". Formation of condensed metallic deuterium lattice and nuclear fusion(2006/10/17) (http:/ / www. journalarchive. jst. go. jp/ english/ jnlabstract_en. php?cdjournal=pjab1977& cdvol=78& noissue=3&startpage=57).

[21] Feder, Toni (2005). "Cold Fusion Gets Chilly Encore" (http:/ / scitation. aip. org/ journals/ doc/ PHTOAD-ft/ vol_58/ iss_1/ 31_1. shtml).Physics Today 58 (January): 31. doi:10.1063/1.1881896. . Retrieved 2008-05-28.

[22] Andersson, Patrik U.; Holmlid, Leif (2009). "Ultra-dense deuterium: A possible nuclear fuel for inertial confinement fusion (ICF)". PhysicsLetters A 373: 3067–3070. doi:10.1016/j.physleta.2009.06.046.

[23] Badiei, S; Andersson, P; Holmlid, L (2009). "Fusion reactions in high-density hydrogen: A fast route to small-scale fusion?". InternationalJournal of Hydrogen Energy 34: 487–495. doi:10.1016/j.ijhydene.2008.10.024.

[24] Badiei, Shahriar; Andersson, Patrik U.; Holmlid, Leif (2009). "High-energy Coulomb explosions in ultra-dense deuterium:Time-of-flight-mass spectrometry with variable energy and flight length". International Journal of Mass Spectrometry 282: 70–76.doi:10.1016/j.ijms.2009.02.014.

Deuterium 59

External links• Nuclear Data Evaluation Lab (http:/ / atom. kaeri. re. kr/ )• Mullins, Justin (27 April 2005). "Desktop nuclear fusion demonstrated with deuterium gas" (http:/ / www.

newscientist. com/ article. ns?id=dn7315). New Scientist. Retrieved 2007-09-10.• Annotated bibliography for Deuterium from the Alsos Digital Library for Nuclear Issues (http:/ / alsos. wlu. edu/

qsearch. aspx?browse=science/ Deuterium)• Missing Gas Found in Milky Way (http:/ / space. com/ scienceastronomy/ 060821_mystery_monday. html).

Space.com

Tritium

Tritium

TritiumFull table

General

Name, symbol tritium, triton,3H

Neutrons 2

Protons 1

Nuclide data

Natural abundance trace

Half-life 12.32 years

Decay products 3He

Isotope mass 3.0160492 u

Spin 1⁄2+

Excess energy 14,949.794± 0.001 keV

Binding energy 8,481.821± 0.004 keV

Decay mode Decay energy

Beta emission 0.018590 MeV

Tritium (pronounced /ˈtrɪtiəm/ or English pronunciation: /ˈtrɪʃiəm/, symbol T or 3H, also known as hydrogen-3) is aradioactive isotope of hydrogen. The nucleus of tritium (sometimes called a triton) contains one proton and twoneutrons, whereas the nucleus of protium (by far the most abundant hydrogen isotope) contains one proton and noneutrons. Naturally-occurring tritium is extremely rare on Earth, where trace amounts are formed by the interactionof the atmosphere with cosmic rays. The name of this isotope is formed from the Greek word "tritos" meaning"third".

Tritium 60

DecayWhile tritium has several different experimentally-determined values of its half-life, the National Institute ofStandards and Technology lists 4,500±8 days (approximately 12.32 years).[1] It decays into helium-3 by beta decayas in this nuclear equation:

T → He1+ + e− + νe

and it releases 18.6 keV of energy in the process. The electron's kinetic energy varies, with an average of 5.7 keV,while the remaining energy is carried off by the nearly-undetectable electron antineutrino. Beta particles from tritiumcan penetrate only about 6.0 mm of air, and they are incapable of passing through the dead outermost layer of humanskin.[2]

Tritium is potentially dangerous if inhaled or ingested. It can combine with oxygen to form tritiated water molecules,and those can be absorbed through pores in the skin.The low energy of tritium's radiation makes it difficult to detect tritium-labelled compounds except by using liquidscintillation counting.

Production

LithiumTritium is produced in nuclear reactors by neutron activation of lithium-6. This is possible with neutrons of anyenergy, and is an exothermic reaction yielding 4.8 MeV. In comparison, the fusion of deuterium with tritium releasesabout 17.6 MeV of energy.

Li + n → He ( 2.05 MeV ) + T ( 2.75 MeV )

High-energy neutrons can also produce tritium from lithium-7 in an endothermic reaction, consuming 2.466 MeV.This was discovered when the 1954 Castle Bravo nuclear test produced an unexpectedly high yield.[3]

Li + n → He + T + n

High-energy neutrons irradiating boron-10 will also occasionally produce tritium.[4] The more common result ofboron-10 neutron capture is 7Li and a single alpha particle.[5]

B + n → 2  He + T

The reactions requiring high neutron energies are not attractive production methods.

DeuteriumTritium is also produced in heavy water-moderated reactors whenever a deuterium nucleus captures a neutron. Thisreaction has a quite small cross section, making heavy water a good neutron moderator, and relatively little tritium isproduced. Even so, cleaning tritium from the moderator may be desirable after several years to reduce the risk of itsescaping to the environment. The Ontario Power Generation's "Tritium Removal Facility" processes up to 2500 longtons ( kg) of heavy water a year, and it separates out about 2.5 kg (5.5 lb) of tritium, making it available for otheruses.[6]

Deuterium's absorption cross section for thermal neutrons is about 0.52 millibarns, whereas that of oxygen-16 ( O) is about 0.19 millibarns and that of oxygen-17 ( O) is about 0.24 barn. O makes up about 0.038% of all naturally-occurring oxygen, hence oxygen has an overall absorption cross section of about 0.28 millibarns. Therefore, in deuterium oxide made with natural oxygen, 21% of neutron captures are by oxygen nuclei, a

Tritium 61

proportion that may rise further since the percentage of O increases from neutron captures by O. Also, O splits whenbombarded by the alpha particles emitted by decaying uranium, producing radioactive carbon-14 ( C), a dangerousby-product, by the equation.

O + He → C + assorted smalled products

FissionTritium is an uncommon product of the nuclear fission of uranium-235, plutonium-239, and uranium-233, with aproduction of about one per each 10,000 fissions.[7] [8] This means that the release or recovery of tritium needs to beconsidered in the operation of nuclear reactors, especially in the reprocessing of nuclear fuels and in the storage ofspent nuclear fuel. The production of tritium was not a goal, but rather, it is just a side-effect.

Helium-3 and tritiumTritium's decay product, helium-3, has a very large cross section for reacting with thermal neutrons, expelling aproton, hence it is rapidly converted back to tritium in nuclear reactors.[9]

He + n --> H + H

Cosmic raysTritium occurs naturally due to cosmic rays interacting with atmospheric gases. In the most important reaction fornatural production, a fast neutron (which must have energy greater than 4.0 MeV[10] ) interacts with atmosphericnitrogen:

N + n → C + T

Because of tritium's relatively short half-life, tritium produced in this manner does not accumulate over geologicaltimescales, and thus it occurs only in negligible quantities in nature.

Production historyAccording to the Institute for Energy and Environmental Research report in 1996 about the U.S. Department ofEnergy, only 225 kg (500 lb) of tritium has been produced in the United States since 1955. Since it continuallydecays into helium-3, the total amount remaining was about 75 kg (170 lb) at the time of the report.[3]

Tritium for American nuclear weapons was produced in special heavy water reactors at the Savannah River Site untiltheir close-downs in 1988. With the Strategic Arms Reduction Treaty (SALT) after the end of the Cold War, theexisting supplies were sufficient for the new, smaller number of nuclear weapons for some time.The production of tritium was resumed with irradiation of rods containing lithium (replacing the usual control rodscontaining boron, cadmium, or hafnium), at the reactors of the commercial Watts Bar Nuclear Generating Station in2003 - 05 followed by extraction of tritium from the rods at the new Tritium Extraction Facility[11] at the SavannahRiver Site beginning in November 2006.[12]

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PropertiesTritium has an atomic mass of 3.0160492. It is a gas (T2 or 3H2) at standard temperature and pressure. It combineswith oxygen to form a liquid called tritiated water, T2O, or partially tritiated water, THO.Tritium figures prominently in studies of nuclear fusion because of its favorable reaction cross section and the largeamount of energy (17.6 MeV) produced through its reaction with deuterium:

T + D → He + n

All atomic nuclei, being composed of protons and neutrons, repel one another because of their positive charge.However, if the atoms have a high enough temperature and pressure (for example, in the core of the Sun), then theirrandom motions can overcome such electrical repulsion (called the Coulomb force), and they can come close enoughfor the strong nuclear force to take effect, fusing them into heavier atoms.The tritium nucleus, containing one proton and two neutrons[7] , has the same charge as the nucleus of ordinaryhydrogen, and it experiences the same electrostatic repulsive force when brought close to another atomic nucleus.However, the neutrons in the tritium nucleus increase the attractive strong nuclear force when brought close enoughto another atomic nucleus. As a result, tritium can more easily fuse with other light atoms, compared with the abilityof ordinary hydrogen to do so.The same is true, albeit to a lesser extent, of deuterium. This is why brown dwarfs (so-called failed stars) cannotutilize ordinary hydrogen, but they do fuse the small minority of deuterium nuclei together.

Radioluminescent 1.2 curie 4" × .2" tritium vials are simply tritium gas-filled glassvials, the inner surfaces of which are coated with a phosphor. The "gaseous tritium

light source" vial shown here is 1.5 years old.

Like hydrogen, tritium is difficult toconfine. Rubber, plastic, and some kinds ofsteel are all somewhat permeable. This hasraised concerns that if tritium were used inlarge quantities, in particular for fusionreactors, it may contribute to radioactivecontamination, although its short half-lifeshould prevent significant long-termaccumulation in the atmosphere.

The high levels atmospheric nuclearweapons testing that took place prior to theenactment of the Partial Test Ban Treatyproved to be unexpectedly useful tooceanographers. The high levels of tritiumoxide introduced into upper layers of theoceans have been used in the years sincethen to measure the rate of mixing of theupper layers of the oceans with their lowerlevels.

Health risks

Tritium is an isotope of hydrogen, which makes it bind to hydroxyl radicals to form tritiated water (HTO), and that itcan bind with carbon atoms readily (C-T). The HTO and the carbon-tritium compounds are easily ingested bydrinking, or by eating organic or water-containing foodstuffs. Since tritium is not a very active beta emitter, it is not

dangerous externally, but it is a radiation hazard when inhaled, ingested via food, water, or absorbed through the skin.[13] [14] [15] [16] HTO has a short biological half life in the human body of seven to 14 days, which both reduces

Tritium 63

the total effects of single-incident ingestion and precludes long-term bioaccumulation of HTO from the environment.

Regulatory limitsThe legal limits for tritium in drinking water vary from country-to-country and from continent-to-continent. Somefigures are given below.• Canada: 7,000 becquerel per liter (Bq/L).• United States: 740 Bq/L or 20,000 picocurie per liter (pCi/L) (Safe Drinking Water Act)• World Health Organization: 10,000 Bq/L.• European Union: "investigative" limit of 100 Bq/L.The American limit is calculated to yield a dose of 4.0 millirems (or 40 microsieverts in SI units) per year. This isabout 1.3% of the natural background radiation (roughly 3000 microsieverts).

Usage

Self-powered lighting

Commander Analog Date tritium-illuminatedwatch face

The emitted electrons from the radioactive decay of small amounts oftritium cause phosphors to glow so as to make self-powered lightingdevices called betalights, which are now used in Firearms night sights,watches (See Luminox for example), exit signs, map lights, and avariety of other devices. This takes the place of radium, which cancause bone cancer and has been banned in most countries for decades.Commercial demand for tritium is 400 grams per year[3] and costsapproximately $US30,000 per gram[17]

Nuclear weapons

Tritium is widely used in multi-stage hydrogen bombs for boosting thefission primary explosion of a thermonuclear weapon (It can besimilarly used for fission bombs.) as well as in external neutroninitiators.

Neutron initiator

Actuated by an ultrafast switch like a krytron, a small particleaccelerator accelerates ions of tritium and deuterium to energies abovethe 15 kilo-electron-volts or so needed for deuterium-tritium fusion anddirects them into a metal target where the tritium and deuterium are adsorbed as hydrides. High-energy fusionneutrons from the resulting fusion radiate in all directions. Some of these strike plutonium or uranium nuclei in theprimary's pit, initiating nuclear chain reaction. The quantity of neutrons produced is large in absolute numbers,allowing the pit to quickly achieve neutron levels that would otherwise need many more generations of chainreaction, though still small compared to the total number of nuclei in the pit.

Tritium 64

Boosting

Before detonation, a few grams of tritium-deuterium gas are injected into the hollow "pit" of fissile plutonium oruranium. The early stages of the fission chain reaction supply enough heat and compression to startdeuterium-tritium fusion, then both fission and fusion proceed in parallel, the fission assisting the fusion bycontinuing heating and compression, and the fusion assisting the fission with highly energetic (14.1 MeV) neutrons.As the fission fuel depletes and also explodes outward, it falls below the density needed to stay critical by itself, butthe fusion neutrons make the fission process progress faster and continue longer than it would without boosting.Increased yield comes overwhelmingly from the increase in fission. The energy released by the fusion itself is muchsmaller because the amount of fusion fuel is so much smaller. The effects of boosting include:• increased yield (for the same amount of fission fuel, compared to detonation without boosting)• the possibility of variable yield by varying the amount of fusion fuel• allowing the bomb to require a smaller amount of the very expensive fissile material - and also eliminating the

risk of predetonation by nearby nuclear explosions• allowing the primary to quickly release most of its power before it has expanded to a larger size difficult to retain

within a so-called "radiation case" (??).• not so stringent requirements on the implosion setup, allowing for a smaller and lighter amount of high-explosives

to be usedThe tritium in a warhead is continually undergoing radioactive decay, hence becoming unavailable for fusion.Furthermore its decay product, helium-3, absorbs neutrons if exposed to the ones emitted by nuclear fission. Thispotentially offsets or reverses the intended effect of the tritium, which was to generate many free neutrons, if toomuch helium-3 has accumulated from the decay of tritium. Therefore, it is necessary to replenish tritium in boostedbombs periodically. The estimated quantity needed is 4 grams per warhead.[3] To maintain constant levels of tritium,about 0.20 grams per warhead per year must be suppiled to the bomb.One mole of deuterium-tritium gas would contain about 3.0 grams of tritium and 2.0 grams of deuterium. Incomparison, the plutonium-239 of a 4.5 kilograms of a nuclear bomb contains about 20 moles of plutonium.

Tritium in hydrogen bomb secondaries

Since tritium undergoes radioactive decay, and it is also difficult to confine physically, the much-larger secondarycharge of heavy hydrogen isotopes needed in a true hydrogen bomb uses solid lithium deuteride as its source ofdeuterium and tritium, where the lithium is all in the form of the lithium-6 isotope.During the detonation of the primary fission bomb stage, excesss neutrons released by the chain reaction splitlithium-6 into tritium plus helium-4. In the extreme heat and pressure of the explosion, some of the tritium is thenforced into fusion with deuterium, and that reaction releases even more neutrons.Since this fusion process requires an extremely-higher temperature for ignition, and it produces fewer and lessenergetic neutrons (only fission, deuterium-tritium fusion, and Li splitting are net neutron producers), lithiumdeuteride is not used in boosted bombs, but rather, for multistage hydrogen bombs.

Controlled nuclear fusionTritium is an important fuel for controlled nuclear fusion in both magnetic confinement and inertial confinementfusion reactor designs. The experimental fusion reactor ITER and the National Ignition Facility (NIF) will usedeuterium-tritium fuel. The deuterium-tritium reaction is favorable since it has the largest fusion cross-section (about5.0 barns) and it reaches this maximum cross-section at the lowest energy (about 65 keV center-of-mass) of anypotential fusion fuel.The Tritium Systems Test Assembly (TSTA) was a facility at the Los Alamos National Laboratory dedicated to thedevelopment and demonstration of technologies required for fusion-relevant deuterium-tritium processing.

Tritium 65

Analytical chemistryTritium is sometimes used as a radiolabel. It has the advantage that hydrogen appears in almost all organic chemicalsmaking it easy to find a place to put tritium on the molecule under investigation. It has the disadvantage of producinga comparatively weak signal.

Use as an oceanic transient tracerAside from chlorofluorocarbons, tritium can act as a transient tracer and has the ability to “outline” the biological,chemical, and physical paths (along with climate change) throughout the world oceans because of its evolvingdistribution.[18] Tritium can thus be used as a tool to examine ocean circulation and ventilation and, foroceanographic and atmospheric science interests, is usually measured in Tritium Units where 1 TU is defined as theratio of 1 tritium atom to 1018 hydrogen atoms.[18] As noted earlier, nuclear weapons testing, primarily in thehigh-latitude regions of the Northern Hemisphere, throughout the late 1950s and early 1960s introduced largeamounts of tritium into the atmosphere, especially the stratosphere. Before these nuclear tests, there were only about3 to 4 kilograms of tritium on the Earth’s surface; but these amounts rose by 2 or 3 orders of magnitude during thepost-test period.[18]

Water samples taken must typically undergo the following procedure (generally-speaking) and significant testingbefore the tritium can officially and successfully be utilized as a tracer:1. Desalting via vacuum distillation;2. Electrolysis and volume reduction to effect enrichment of the tritium;3. Reduction of the electrolyzed sample to hydrogen in a super-heated furnace;4. Tritium labeling by catalytic hydrogenation of tank ethylene; and5. Gas-proportional counting of tritiated ethane[19]

In an attempt to examine the downward transport of tritium into the ocean via the use of a cloud model, it isnecessary and customary to use the following model structure:1) Inelastic continuity equation; 2) momentum equation – includes pressure gradient term, Newtonian damping term,buoyancy term, and turbulent mixing terms; 3) thermodynamic energy equation; 4) conservation of water vapor; 5)bulk cloud physics – includes the Kessler parameterization (conservation equations for cloud water and rainwater);and 6) tritium budget equations – includes tritium for water vapor, cloud water, and rainwater; rate of change oftritium concentration as a function of decay rate[20]

North Atlantic OceanWhile in the stratosphere (post-test period), the tritium interacted with and oxidized to water molecules and waspresent in much of the rapidly-produced rainfall, making tritium a prognostic tool for studying the evolution andstructure of the hydrologic cycle as well as the ventilation and formation of water masses in the North AtlanticOcean.[18] In fact, bomb-tritium data were utilized from the Transient Tracers in the Ocean (TTO) program in orderto quantify the replenishment and overturning rates for deep water located in the North Atlantic.[21] Most of thebomb tritiated water (HTO) throughout the atmosphere can enter the ocean through the following processes: a)precipitation, b) vapor exchange, and c) river runoff – these processes make HTO a great tracer for time-scales up toa few decades.[21] Using the data from these processes for the year 1981, the 1 TU isosurface lies between 500 and1,000 meters deep in the subtropical regions and then extends to 1,500-2,000 meters south of the Gulf Stream due torecirculation and ventilation in the upper portion of the Atlantic Ocean.[18] To the north, the isosurface deepens andreaches the floor of the abyssal plain which is directly related to the ventilation of the ocean floor over 10 to 20 yeartime-scales.[18]

Also evident in the Atlantic Ocean is the tritium profile near Bermuda between the late 1960s and late 1980s. There is a downward propagation of the tritium maximum from the surface (1960s) to 400 meters (1980s), which

Tritium 66

corresponds to a deepening rate of approximately 18 meters per year.[18] There are also tritium increases at 1,500meters depth in the late 1970s and 2,500 meters in the middle of the 1980s, both of which correspond to coolingevents in the deep water and associated deep water ventilation.[18]

From a study in 1991, the tritium profile was used as a tool for studying the mixing and spreading of newly-formedNorth Atlantic Deep Water (NADW), corresponding to tritium increases to 4 TU.[21] This NADW tends to spill oversills that divide the Norwegian Sea from the North Atlantic Ocean and then flows to the west and equatorward indeep boundary currents. This process was explained via the large-scale tritium distribution in the deep North Atlanticbetween 1981 and 1983.[21] The sub-polar gyre tends to be freshened (ventilated) by the NADW and is directlyrelated to the high tritium values (> 1.5 TU). Also evident was the decrease in tritium in the deep western boundarycurrent by a factor of 10 from the Labrador Sea to the Tropics, which is indicative of loss to ocean interior due toturbulent mixing and recirculation.[21]

Pacific and Indian OceansIn a 1998 study, tritium concentrations in surface seawater and atmospheric water vapor (10 meters above thesurface) were sampled at the following locations: the Sulu Sea, the Fremantle Bay, the Bay of Bengal, the PenangBay, and the Strait of Malacca.[22] Results indicated that the tritium concentration in surface seawater was highest atthe Fremantle Bay (approximately 0.40 Bq/liter), which could be accredited to the mixing of runoff of freshwaterfrom nearby lands due to large amounts found in coastal waters.[22] Typically, lower concentrations were foundbetween 35 and 45 degrees south latitude and near the equator. Results also indicated that (in general) tritium hasdecreased over the years (up to 1997) due to the physical decay of bomb tritium in the Indian Ocean. As for watervapor, the tritium concentration was approximately one order of magnitude greater than surface seawaterconcentrations (ranging from 0.46 to 1.15 Bq/liter).[22] Therefore, the water vapor tritium is not affected by thesurface seawater concentration; thus, the high tritium concentrations in the vapor were concluded to be a directconsequence of the downward movement of natural tritium from the stratosphere to the troposphere (therefore, theocean air showed a dependence on latitudinal change)[22]

In the North Pacific Ocean, the tritium (introduced as bomb tritium in the Northern Hemisphere) spread in threedimensions. There were subsurface maxima in the middle and low latitude regions, which is indicative of lateralmixing (advection) and diffusion processes along lines of constant potential density (isopycnals) in the upperocean.[23] Some of these maxima even correlate well with salinity extrema.[23] In order to obtain the structure forocean circulation, the tritium concentrations were mapped on 3 surfaces of constant potential density (23.90, 26.02,and 26.81).[23] Results indicated that the tritium was well-mixed (at 6 to 7 TU) on the 26.81 isopycnal in thesubarctic cyclonic gyre and there appeared to be a slow exchange of tritium (relative to shallower isopycnals)between this gyre and the anticyclonic gyre to the south; also, the tritium on the 23.90 and 26.02 surfaces appeared tobe exchanged at a slower rate between the central gyre of the North Pacific and the equatorial regions.[23]

The depth penetration of bomb tritium can be separated into 3 distinct layers. Layer 1 is the shallowest layer andincludes the deepest, ventilated layer in winter; it has received tritium via radioactive fallout and lost some due toadvection and/or vertical diffusion and contains approximately 28 % of the total amount of tritium.[23] Layer 2 isbelow the first layer but above the 26.81 isopycnal and is no longer part of the mixed layer. Its 2 sources arediffusion downward from the mixed layer and lateral expansions outcropping strata (poleward); it contains about 58% of the total tritium.[23] Layer 3 is representative of waters that are deeper than the outcrop isopycnal and can onlyreceive tritium via vertical diffusion; it contains the remaining 14 % of the total tritium.[23]

Tritium 67

Mississippi River SystemThe impacts of the nuclear fallout were even felt in the United States throughout the Mississippi River System.Tritium concentrations can be used to understand the residence times of continental hydrologic systems (as opposedto the usual oceanic hydrologic systems) which include surface waters such as lakes, streams, and rivers.[24]

Studying these systems can also provide societies and municipals with information for agricultural purposes andoverall river water quality.In a 2004 study, several rivers were taken into account during the examination of tritium concentrations (starting inthe 1960s) throughout the Mississippi River Basin: Ohio River (largest input to the Mississippi River flow), MissouriRiver, and Arkansas River.[24] The largest tritium concentrations were found in 1963 at all the sampled locationsthroughout these rivers and correlate well with the peak concentrations in precipitation due to the nuclear bomb testsin 1962. The overall highest concentrations occurred in the Missouri River (1963) and were greater than 1,200 TUwhile the lowest concentrations were found in the Arkansas River (never greater than 850 TU and less than 10 TU inthe mid-1980s).[24]

Several processes can be identified using the tritium data from the rivers: direct runoff and outflow of water fromgroundwater reservoirs.[24] Using these processes, it becomes possible to model the response of the river basins tothe transient tritium tracer. Two of the most common models are the following:• Piston-flow approach – tritium signal appears immediately; and• Well-mixed reservoir approach – outflow concentration depends upon the residence time of the basin water[24]

Unfortunately, both models fail to reproduce the tritium in river waters; thus, a two-member mixing model wasdeveloped that consists of 2 components: a prompt-flow component (recent precipitation – “piston”) and acomponent where waters reside in the basin for longer than 1 year (“well-mixed reservoir”).[24] Therefore, the basintritium concentration becomes a function of the residence times within the basin, sinks (radioactive decay) or sourcesof tritium, and the input function.For the Ohio River, the tritium data indicated that about 40% of the flow was composed of precipitation withresidence times of less than 1 year (in the Ohio basin) and older waters consisted of residence times of about 10years.[24] Thus, the short residence times (less than 1 year) corresponded to the “prompt-flow” component of thetwo-member mixing model. As for the Missouri River, results indicated that residence times were approximately 4years with the prompt-flow component being around 10% (these results are due to the series of dams in the area ofthe Missouri River).[24]

As for the mass flux of tritium through the main stem of the Mississippi River into the Gulf of Mexico, dataindicated that approximately 780 grams of tritium has flowed out of the River and into the Gulf between 1961 and1997.[24] And current fluxes through the Mississippi River are about 1 to 2 grams per year as opposed to thepre-bomb period fluxes of roughly 0.4 grams per year.[24]

HistoryTritium was first predicted in the late 1920s by Walter Russell, using his "spiral" periodic table,[25] then produced in1934 from deuterium, another isotope of hydrogen, by Ernest Rutherford, working with Mark Oliphant and PaulHarteck. Rutherford was unable to isolate the tritium, a job that was left to Luis Alvarez and Robert Cornog, whocorrectly deduced that the substance was radioactive.[26] Willard F. Libby discovered that tritium could be used fordating water, and therefore wine.[27]

Tritium 68

See also• Hypertriton• Luminox

References[1] L. L. Lucas, M. P. Unterweger (2000). "Comprehensive Review and Critical Evaluation of the Half-Life of Tritium" (http:/ / nvl. nist. gov/

pub/ nistpubs/ jres/ 105/ 4/ j54luc2. pdf). Journal of Research of the National Institute of Standards and Technology 105 (4): 541. .[2] Nuclide safety data sheet: Hydrogen-3 (http:/ / www. ehso. emory. edu/ radiation/ Forms/ nuclide_data_safety_sheets. pdf)[3] Hisham Zerriffi (January 1996). "Tritium: The environmental, health, budgetary, and strategic effects of the Department of Energy's decision

to produce tritium" (http:/ / www. ieer. org/ reports/ tritium. html#(11)). Institute for Energy and Environmental Research. .[4] Greg Jones (2008). "Tritium Issues in Commercial Pressurized Water Reactors" (http:/ / www. new. ans. org/ store/ j_1824). Fusion Science

and Technology 54 (2): 329–332. .[5] Carey Sublette (2006-05-17). "Nuclear Weapons FAQ Section 12.0 Useful Tables" (http:/ / nuclearweaponarchive. org/ Nwfaq/ Nfaq12.

html). Nuclear Weapons Archive. . Retrieved 2010-09-19.[6] Dr. Jeremy Whitlock. "Section D: Safety and Liability - How does Ontario Power Generation manage tritium production in its CANDU

moderators?" (http:/ / www. nuclearfaq. ca/ cnf_sectionD. htm#x5). Canadian Nuclear FAQ. . Retrieved 2010-09-19.[7] "Tritium (Hydrogen-3) - Human Health Fact sheet" (http:/ / www. ead. anl. gov/ pub/ doc/ tritium. pdf). Argonne National Laboratory.

2005-08. . Retrieved 2010-09-19.[8] Serot, O.; Wagemans, C.; Heyse, J. (2005). "New Results on Helium and Tritium Gas Production From Ternary Fission". International

conference on nuclear data for science and technology. AIP Conference Proceedings 769: 857–860. doi:10.1063/1.1945141.[9] "Helium-3 Neutron Proportional Counters" (http:/ / web. mit. edu/ 8. 13/ www/ tgm-neutron-detectors. pdf). .[10] P.G Young and D.G Foster, Jr (1972-09). "An Evaluation of the Neutron and Gamma-ray Production Cross Sections for Nitrogen" (http:/ /

www. fas. org/ sgp/ othergov/ doe/ lanl/ lib-www/ la-pubs/ 00320217. pdf). Los Alamos Scientific Laboratory. . Retrieved 2010-09-19.[11] Defense Programs (http:/ / www. srs. gov/ general/ programs/ dp/ index. htm)[12] "Tritium Extraction Facility" (http:/ / www. srs. gov/ general/ news/ factsheets/ tef. pdf). Savannah River Site. 2007-12. . Retrieved

2010-09-19.[13] Tritium Hazard Report: Pollution and Radiation Risk from Canadian Nuclear Facilities (http:/ / www. greenpeace. org/ raw/ content/ canada/

en/ documents-and-links/ publications/ tritium-hazard-report-pollu. pdf), I. Fairlie, 2007 June[14] Review of the Greenpeace report: "Tritium Hazard Report: Pollution and Radiation Risk from Canadian Nuclear Facilities" (http:/ / www.

nuclearfaq. ca/ ReviewofGreenpeacereport_Final. pdf), R.V. Osborne, 2007 August[15] Fact Sheet on Tritium, Radiation Protection Limits, and Drinking Water Standards (http:/ / www. nrc. gov/ reading-rm/ doc-collections/

fact-sheets/ tritium-radiation-fs. html), U.S. Nuclear Regulatory Commission[16] Tritium Facts and Information (http:/ / www. dep. state. pa. us/ brp/ Radiation_Control_Division/ Tritium. htm), Pensilvania Department of

Environmental Protection[17] Scott Willms (2003-01-14). Tritium Supply Considerations (http:/ / fire. pppl. gov/ fesac_dp_ts_willms. pdf). Los Alamos National

Laboratory. . Retrieved 2010-08-01.[18] Jenkins, William J. et al, 1996: “Transient Tracers Track Ocean Climate Signals” (http:/ / www. whoi. edu/ oceanus/ viewArticle.

do?id=2330) Oceanus, Woods Hole Oceanographic Institution.[19] Tamuly, A. (2007). "Dispersal of Tritium in Southern Ocean Waters" (http:/ / pubs. aina. ucalgary. ca/ arctic/ Arctic27-1-27. pdf). Arctic

(Arctic Institute of North America) 27: 27–40. .[20] Lipps, Frank B. and Richard S. Hemler (1992). "On the Downward Transfer of Tritium to the Ocean by a Cloud Model" (http:/ / www. agu.

org/ pubs/ crossref/ 1992/ 92JD01062. shtml). Journal of Geophysical Research 97 (12): 12, 889–12, 900. .[21] Doney, Scott C.; Williams, P (1992). "Bomb Tritium in the Deep North Atlantic" (http:/ / www. tos. org/ oceanography/ issues/

issue_archive/ issue_pdfs/ 5_3/ 5. 3_doney. pdf). Oceanography 5: 169–170. doi:10.1016/0012-821X(73)90013-7. .[22] Kakiuchi, H.; Momoshima, N.; Okai, T.; Maeda, Y. (1999). "Tritium concentration in ocean". Journal of Radioanalytical and Nuclear

Chemistry 239: 523. doi:10.1007/BF02349062.[23] Fine, Rana A. et al. (1981). "Circulation of Tritium in the Pacific Ocean". Journal of Physical Oceanography 11: 3–14.

doi:10.1175/1520-0485(1981)011<0003:COTITP>2.0.CO;2.[24] Michel, Robert L. (2004). "Tritium hydrology of the Mississippi River basin". Hydrological Processes 18: 1255. doi:10.1002/hyp.1403.[25] Hartmann, Christian (2004). "Sutherland und das “flüssige Licht”". DO - Deutsche Zeitschrift für Osteopathie 2: 33.

doi:10.1055/s-2004-836019.[26] Alvarez, Luis W; Peter Trower, W (1987). Discovering Alvarez: selected works of Luis W. Alvarez, with commentary by his students and

colleagues (http:/ / books. google. com/ ?id=imidr-iFYCwC& pg=PA26). pp. 26–30. ISBN 9780226813042. .[27] Kaufman, Sheldon; Libby, W. (1954). "The Natural Distribution of Tritium". Physical Review 93: 1337. doi:10.1103/PhysRev.93.1337.

Tritium 69

External links• Annotated bibliography for tritium from the Alsos Digital Library (http:/ / alsos. wlu. edu/ qsearch.

aspx?browse=science/ Tritium)• NLM Hazardous Substances Databank – Tritium, Radioactive (http:/ / toxnet. nlm. nih. gov/ cgi-bin/ sis/ search/

r?dbs+ hsdb:@term+ @na+ @rel+ tritium,+ radioactive)• Nuclear Data Evaluation Lab (http:/ / atom. kaeri. re. kr/ )• Review of risks from tritium. Report of the independent Advisory Group on Ionising Radiation. (http:/ / www. hpa.

org. uk/ web/ HPAweb& HPAwebStandard/ HPAweb_C/ 1197382220012). Health Protection Agency.November 2007. RCE-4.

• Tritium on Ice: The Dangerous New Alliance of Nuclear Weapons and Nuclear Power by Kenneth D. Bergeron(http:/ / books. google. com/ books?id=sYKYZaxg0RUC)

Hydrogen-4

Hydrogen-4

Full table

General

Name, symbol Hydrogen-4,4H

Neutrons 3

Protons 1

Nuclide data

Half-life (1.39 ± 0.10) × 10−22 seconds[1]

Isotope mass 4.02781 ± 0.00011[2] u

Hydrogen-4 is a highly unstable isotope of hydrogen. The nucleus consists of a proton and three neutrons. It hasbeen synthesised in the laboratory by bombarding tritium with fast-moving deuterium nuclei.[3] In this experiment,the tritium nuclei captured neutrons from the fast-moving deuterium nucleus. The presence of the hydrogen-4 wasdeduced by detecting the emitted protons. Its atomic mass is 4.02781 ± 0.00011[2] . It decays through neutronemission and has a half-life of (1.39 ± 0.10) × 10−22 seconds.[1]

Hydrogen-4 70

QuadiumIn the 1955 satirical novel The Mouse That Roared, the name quadium was given to the hydrogen-4 isotope thatpowered the Q-bomb that the Duchy of Grand Fenwick captured from the United States.

See also• Isotopes of hydrogen

References[1] p. 27, The NUBASE evaluation of nuclear and decay properties (http:/ / amdc. in2p3. fr/ nubase/ Nubase2003. pdf), G. Audi, O. Bersillon, J.

Blachot, and A. H. Wapstra, Nuclear Physics A 729 (2003), pp. 3–128.[2] AME2003 atomic mass evaluation (http:/ / www. nndc. bnl. gov/ amdc/ web/ masseval. html), Atomic Mass Data Center. Accessed on line

November 15, 2008.[3] Hydrogen-4 and Hydrogen-5 from t+t and t+d transfer reactions studied with a 57.5-MeV triton beam, G. M. Ter-Akopian et al., Nuclear

Physics in the 21st Century: International Nuclear Physics Conference INPC 2001, American Institute of Physics Conference Proceedings610, pp. 920-924, doi:10.1063/1.1470062.

Hydrogen-5

Hydrogen-5

Full table

General

Name, symbol Hydrogen-5,5H

Neutrons 4

Protons 1

Nuclide data

Half-life >9.1 × 10−22 seconds[1]

Isotope mass 5.03531 ± 0.00011[2] u

Spin (1/2+)

Hydrogen-5 is a highly unstable isotope of hydrogen. The nucleus consists of a proton and four neutrons. It has beensynthesised in the laboratory by bombarding tritium with fast-moving tritium nuclei.[3] In this experiment, onetritium nucleus captures both neutrons from the other, becoming a nucleus with one proton and four neutrons. Theremaining proton may be detected, and the existence of hydrogen-5 deduced. It decays through emission of twoneutrons and has a half-life of more than 9.1 × 10−22 seconds.[1]

Hydrogen-5 71

See also• Isotopes of hydrogen

References[1] p. 27, The NUBASE evaluation of nuclear and decay properties (http:/ / amdc. in2p3. fr/ nubase/ Nubase2003. pdf), G. Audi, O. Bersillon, J.

Blachot, and A. H. Wapstra, Nuclear Physics A 729 (2003), pp. 3–128.[2] AME2003 atomic mass evaluation (http:/ / www. nndc. bnl. gov/ amdc/ web/ masseval. html), Atomic Mass Data Center. Accessed on line

November 15, 2008.[3] Hydrogen-4 and Hydrogen-5 from t+t and t+d transfer reactions studied with a 57.5-MeV triton beam, G. M. Ter-Akopian et al., Nuclear

Physics in the 21st Century: International Nuclear Physics Conference INPC 2001, American Institute of Physics Conference Proceedings610, pp. 920-924, doi:10.1063/1.1470062.

Spin isomers of hydrogen

Spin Isomers of Molecular Hydrogen

Molecular hydrogen occurs in two isomeric forms, one with its twoproton spins aligned parallel (orthohydrogen), the other with its twoproton spins aligned antiparallel (parahydrogen).[1] At roomtemperature and thermal equilibrium, hydrogen consists of 25%parahydrogen and 75% orthohydrogen.

Nuclear spin states of H2Each hydrogen molecule (H2) consists of two hydrogen atoms linkedby a covalent bond. If we neglect the small proportion of deuteriumand tritium which may be present, each hydrogen atom consists of oneproton and one electron. The proton has an associated magneticmoment, which is associated with the proton's spin. In the H2 molecule, the spins of the two hydrogen nuclei(protons) couple to form a triplet state (I = 1, α1α2, (α1β2 + β1α2)/21/2, or β1β2 for which MI = 1, 0, −1 respectively— this is orthohydrogen) or to form a singlet state (I = 0, (α1β2 – β1α2)/21/2 MI = 0 — this is parahydrogen). Theratio between the ortho and para forms is about 3:1 at standard temperature and pressure - a reflection of the spindegeneracy ratio, but if thermal equilibrium between the two forms is established, the para form dominates at lowtemperatures (approx. 99.8% at 20 K[2] ). Other molecules and functional groups containing two hydrogen atoms,such as water and methylene, also have ortho and para forms (e.g. orthowater and parawater), although their ratiosdiffer from that of the dihydrogen molecule.

Thermal propertiesThe permutational antisymmetry of the H2 wavefunction (protons are fermions) imposes restrictions on the possiblerotational states the two forms of H2 can adopt. Orthohydrogen, with symmetric nuclear spin functions, can onlyhave rotational wavefunctions that are antisymmetric with respect to permutation of the two protons. Conversely,parahydrogen with an antisymmetric nuclear spin function, can only have rotational wavefunctions that aresymmetric with respect to permutation of the two protons. Applying the rigid rotor approximation, the energies anddegeneracies of the rotational states are given by[3]

.

The rotational partition function is conventionally written as

Spin isomers of hydrogen 72

.

However, as long as these two spin isomers are not in equilibrium, it is more useful to write separate partitionfunctions for each,.The factor of 3 in the partition function for orthohydrogen accounts for the spin degeneracy associated with the +1spin state. When equilibrium between the spin isomers is possible, then a general partition function incorporatingthis degeneracy difference can be written as

The molar rotational energies and heat capacities are derived for any of these cases from

Molar Rotational Energies. Molar Heat Capacities.

Because of the antisymmetry-imposed restriction on possible rotational states, orthohydrogen has residual rotationalenergy at low temperature wherein nearly all the molecules are in the J = 1 state (molecules in the symmetricspin-triplet state can not fall into the lowest, symmetric rotational state) and possesses nuclear-spin entropy due tothe triplet state's threefold degeneracy. The residual energy is significant because the rotational energy levels arerelatively widely spaced in H2; the gap between the first two levels when expressed in temperature units is twice therotational temperature for H2,

.

This is the T = 0 intercept seen in the molar energy of orthohydrogen. This residual energy, 1091 J/mol, is somewhat larger than the enthalpy of vaporization of normal hydrogen, 904 J/mol at the boiling point, Tb = 20.369 K (this refers to the "normal", room-temperature, 3:1 ortho:para mixture).[4] Notably, the boiling points of parahydrogen and normal (3:1) hydrogen are nearly equal; for parahydrogen ∆Hvap = 898 J/mol at Tb = 20.277 K. It follows that nearly all the residual rotational energy of orthohydrogen is retained in the liquid state. Orthohydrogen is consequently unstable at low temperatures and spontaneously converts into parahydrogen, but the process is slow in

Spin isomers of hydrogen 73

the absence of a magnetic catalyst to facilitate interconversion of the singlet and triplet spin states. At roomtemperature, hydrogen contains 75% orthohydrogen, a proportion which the liquefaction process preserves if carriedout in the absence of a catalyst like ferric oxide, activated carbon, platinized asbestos, rare earth metals, uraniumcompounds, chromic oxide, or some nickel compounds[5] to accelerate the conversion of the liquid hydrogen intoparahydrogen, or supply additional refrigeration equipment to absorb the heat that the orthohydrogen fraction willrelease as it spontaneously converts into parahydrogen.The first synthesis of pure parahydrogen was achieved by Paul Harteck and Karl Friedrich Bonhoeffer in 1929.When used during hydrogenations, parahydrogen gives rise to hyperpolarized signals in the NMR spectrum. Thiseffect is called PHIP or PASADENA effect and was simultaneously discovered at two laboratories in Los Angeles(USA) and Bonn (Germany) in 1995. It was subsequently utilized to study the mechanism of hydrogenationreactions.Modern isolation of pure parahydrogen has been achieved utilizing rapid in-vacuum deposition of millimeters thicksolid parahydrogen (pH2) samples which are notable for their excellent optical qualities.[6]

Further research regarding parahydrogen thinfilm quantum state polarization matrices for computation seems a likelyfuture prospect for these material sets.

References[1] P. Atkins and J. de Paula, Atkins' Physical Chemistry, 8th edition (W.H.Freeman 2006), p.452[2] Rock, Peter A. "Chemical Thermodynamics", MacMillan 1969, p.478[3] F. T. Wall (1974). Chemical Thermodynamics, 3rd Edition. W. H. Freeman and Company.[4] http:/ / webbook. nist. gov/ chemistry/ fluid/[5] Ortho-Para conversion. Pag. 13 (http:/ / www. mae. ufl. edu/ NasaHydrogenResearch/ h2webcourse/ L11-liquefaction2. pdf)[6] Rapid Vapor Deposition of Millimeters Thick Optically Transparent Solid Parahydrogen Samples for Matrix Isolation Spectroscopy (http:/ /

www. stormingmedia. us/ 72/ 7208/ A720893. html)

1. Tikhonov V. I., Volkov A. A. (2002). "Separation of water into its ortho and para isomers". Science 296 (5577):2363. doi:10.1126/science.1069513. PMID 12089435.

2. Bonhoeffer KF, Harteck P (1929). "Para- and ortho hydrogen". Zeitschrift für Physikalische Chemie B 4 (1-2):113–141.

3. A. Farkas (1935). Orthohydrogen, parahydrogen and heavy hydrogen,. The Cambridge series of physicalchemistry.

4. Mario E. Fajardo; Simon Tam (1997). Rapid Vapor Deposition of Millimeters Thick Optically Transparent SolidParahydrogen Samples for Matrix Isolation Spectroscopy. AIR FORCE RESEARCH LAB EDWARDS AFB CAPROPULSION DIRECTORATE WEST.

74

Reactions

Bosch reactionThe Bosch reaction is a chemical reaction between carbon dioxide and hydrogen that produces elemental carbon(graphite), water and a 10% return of invested heat. This reaction requires the introduction of iron as a catalyst andrequires a temperature level of 530-730 degrees Celsius.[1]

The overall reaction is as follows:CO2(g) + 2 H2(g) → C(s) + 2 H2O(g)The above reaction is actually the result of two reactions. The first reaction, the reverse water gas shift reaction, is afast one.CO2 + H2 → CO + H2OThe second reaction controls the reaction rate.CO + H2 → C + H2OThe overall reaction produces 2.3×103 joules for every gram of carbon produced at 650 °C. Reaction temperaturesare in the range of 450 to 600 °C.The reaction can be accelerated in the presence of an iron, cobalt or nickel catalyst. Ruthenium also serves to speedup the reaction.Together with the Sabatier reaction the Bosch reaction is studied as a way to remove carbon dioxide and to generateclean water aboard a space station [2]

The reaction is also used to produce graphite for radiocarbon dating with Accelerator Mass Spectrometry.It is named after the German chemist Carl Bosch.The Bosch reaction is being investigated for use in maintaining space station life support. Though the Bosch reactionwould present a completely closed hydrogen and oxygen cycle which only produces atomic carbon as waste,difficulties maintaining its higher required temperature and properly handling carbon deposits mean significantlymore research will be required before a Bosch reactor could become a reality. One problem is that the production ofelemental carbon tends to foul the catalyst's surface, which is detrimental to the reaction's efficiency.

Notes[1] Messerschmid, Ernst and Reinhold Bertrand. Space Stations. Springer. 1999.[2] Methods of water production (http:/ / oregonstate. edu/ ~atwaterj/ h2o_gen. htm)

External links• A carbon dioxide reduction unit using Bosch reaction (http:/ / ntrs. nasa. gov/ archive/ nasa/ casi. ntrs. nasa. gov/

19710002858_1971002858. pdf)

Hydrogen cycle 75

Hydrogen cycleHydrogen is one of the constituents of water. It recycles as in other biogeochemical cycles. It is actively involvedwith the other cycles like the carbon cycle, nitrogen cycle, sulfur cycle and oxygen cycle as well.Anaerobic fermentation of organic substances to carbon dioxide and methane is a collaborative effort involvingmany different biochemical reactions, processes and species of microorganisms. One of these many processes thatoccur is termed "interspecies hydrogen transfer". This process has been described as integral to the symbiosisbetween certain methane-producing bacteria (methanogens) and nonmethanogenic anaerobes. In this symbiosis, thenonmethanogenic anaerobes degrade the organic substance and produce -among other things- molecular hydrogen(H2). This hydrogen is then taken up by methanogens and converted to methane via methanogenesis. One importantcharacteristic of interspecies hydrogen transfer is that the H2 concentration in the microbial environment is very low.Maintaining a low hydrogen concentration is important because the anaerobic fermentative process becomeincreasingly thermodynamically unfavorable as the partial pressure of hydrogen increases. A key differencecompared to other biogeochemical cycles is that because of its low molecular weight hydrogen can leave Earth'satmosphere. It has been suggested that this occurred on a grand scale in the past and that this is why today the Earthis mostly irreversibly oxidised.[1]

References[1] http:/ / www. sciencemag. org/ cgi/ content/ abstract/ 293/ 5531/ 839 Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of

Early Earth David C. Catling, Kevin J. Zahnle, and Christopher McKay (3 August 2001) Science 293 (5531), 839. [DOI:10.1126/science.1061976]

External links• A Lecture (http:/ / www. biosci. ohio-state. edu/ ~mgonzalez/ Micro521/ 19. html)

Bibliography• "Microbiology and Biochemistry of Strict Anaerobes Involved in Interspecies Hydrogen Transfer" by Jean-Pierre

Bélaich; Mireille Bruschi; Jean-Louis Garcia; Federation of European Microbiological Societies. Published Nov1990. ISBN 0306435179

• (http:/ / whitman. myweb. uga. edu/ coursedocs/ mibo8610/ de bok et al 04. pdf) F.A.M. de Bok, C.M. Plugge,and A.J.M. Stams; "Interspecies electron transfer in methanogenic proprionate degrading consortia". WaterResearch 38 (2004): 1368-1375

• (http:/ / www. ingentaconnect. com/ content/ bsc/ emi/ 2006/ 00000008/ 00000003/ art00001) A.J.M. Stams et al.,"Exocellular electron transfer in anaerobic microbial communities", Environmental Microbiology, 8(2006):371-382

Hydrogenation 76

Hydrogenation

Catalysed hydrogenationProcess type Chemical

Industrial sector(s) Food industry, petrochemical industry, pharmaceutical industry, agricultural industry

Main technologies or sub-processes Various transition metal catalysts, high-pressure technology

Feedstock Unsaturated substrates and hydrogen or hydrogen donors

Product(s) Saturated hydrocarbons and derivatives

Inventor Paul Sabatier

Year of invention 1897

Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecularhydrogen (H2) and another compound or element, usually in the presence of a catalyst. The process is commonlyemployed to reduce or saturate organic compounds. Hydrogenation typically constitutes the addition of pairs ofhydrogen atoms to a molecule, generally an alkene. Catalysts are required for the reaction to be usable; non-catalytichydrogenation takes place only at very high temperatures. Hydrogen adds to double and triple bonds inhydrocarbons.[1]

Because of the importance of hydrogen, many related reactions have been developed for its use. Mosthydrogenations use gaseous hydrogen (H2), but some involve the alternative sources of hydrogen, not H2: theseprocesses are called transfer hydrogenations. The reverse reaction, removal of hydrogen from a molecule, is calleddehydrogenation. A reaction where bonds are broken while hydrogen is added is called hydrogenolysis, a reactionthat may occur to carbon-carbon and carbon-heteroatom (O, N, X) bonds. Hydrogenation differs from protonation orhydride addition: in hydrogenation, the products have the same charge as the reactants.An illustrative example of a hydrogenation reaction is the addition of hydrogen to maleic acid to succinic aciddepicted on the right.[2] Numerous important applications are found in the petrochemical, pharmaceutical and foodindustries. Hydrogenation of unsaturated fats produces saturated fats and, in some cases, trans fats.

Process

Hydrogenation has three components,the unsaturated substrate, the hydrogen(or hydrogen source) and, invariably, acatalyst. The reaction is carried out atdifferent temperatures and pressures

depending upon the substrate and the activity of the catalyst.

Hydrogenation 77

SubstrateThe addition of H2 to an alkene affords an alkane in the protypical reaction:

RCH=CH2 + H2 → RCH2CH3 (R = alkyl, aryl)Hydrogenation is sensitive to steric hindrance explaining the selectivity for reaction with the exocyclic double bondbut not the internal double bond.An important characteristic of alkene and alkyne hydrogenations, both the homogeneously and heterogeneouslycatalyzed versions, is that hydrogen addition occurs with "syn addition", with hydrogen entering from the leasthindered side.[3] Typical substrates are listed in the table

Substrates for and products of hydrogenation

alkene, R2C=CR'2 alkane, R2CHCHR'2alkyne, RCCR alkene, cis-RHC=CHR'

aldehyde, RCHO primary alcohol, RCH2OH

ketone, R2CO secondary alcohol, R2CHOH

ester, RCO2R' two alcohols, RCH2OH, R'OH

imine, RR'CNR" amine, RR'CHNHR"

amide, RC(O)NR'2 amine, RCH2NR'2nitrile, RCN imine, RHCNH easily hydrogenated further

nitro, RNO2 amine, RNH2

CatalystsWith rare exception, no reaction below 480 °F occurs between H2 and organic compounds in the absence of metalcatalysts. The catalyst binds both the H2 and the unsaturated substrate and facilitates their union. Platinum groupmetals, particularly platinum, palladium, rhodium, and ruthenium, form highly active catalysts, which operate atlower temperatures and lower pressures of H2. Non-precious metal catalysts, especially those based on nickel (suchas Raney nickel and Urushibara nickel) have also been developed as economical alternatives, but they are oftenslower or require higher temperatures. The trade-off is activity (speed of reaction) vs. cost of the catalyst and cost ofthe apparatus required for use of high pressures. Notice that the Raney-nickel catalysed hydrogenations require highpressures:[4] [5]

Two broad families of catalysts areknown - homogeneous catalysts andheterogeneous catalysts. Homogeneouscatalysts dissolve in the solvent thatcontains the unsaturated substrate.Heterogeneous catalysts are solids thatare suspended in the same solvent withthe substrate or are treated withgaseous substrate.

Hydrogenation 78

Homogeneous catalysts

Illustrative homogeneous catalysts include the rhodium-based compound known as Wilkinson's catalyst and theiridium-based Crabtree's catalyst. An example is the hydrogenation of carvone:[6]

Hydrogenation is sensitive to sterichindrance explaining the selectivity forreaction with the exocyclic double bond butnot the internal double bond.

The activity and selectivity of homogeneouscatalysts is adjusted by changing theligands. For prochiral substrates, theselectivity of the catalyst can be adjusted

such that one enantiomeric product is favored. Asymmetric hydrogenation is also possible via heterogeneouscatalysis on a metal that is modified by a chiral ligand.[7]

Homogeneous catalysts are less active than heterogeneous catalysts.

Heterogeneous catalysts

Heterogeneous catalysts for hydrogenation are more common industrially. As in homogeneous catalysts, the activityis adjusted through changes in the environment around the metal, i.e. the coordination sphere. Different faces of acrystalline heterogeneous catalyst display distinct activities, for example. Similarly, heterogeneous catalysts areaffected by their supports, i.e. the material upon with the heterogeneous catalyst is bound. In many cases, highlyempirical modifications involve selective "poisons". Thus, a carefully chosen catalyst can be used to hydrogenatesome functional groups without affecting others, such as the hydrogenation of alkenes without touching aromaticrings, or the selective hydrogenation of alkynes to alkenes using Lindlar's catalyst. For example, when the catalystpalladium is placed on barium sulfate and then treated with quinoline, the resulting catalyst reduces alkynes only asfar as alkenes. The Lindlar catalyst has been applied to the conversion of phenylacetylene to styrene.[8]

Asymmetric hydrogenation is alsopossible via heterogeneous catalysis ona metal that is modified by a chiralligand.[7]

Hydrogen sources

For hydrogenation, the obvious source of hydrogen is H2 gas itself, which is typically available commercially withinthe storage medium of a pressurized cylinder. The hydrogenation process often uses greater than 1 atmosphere of H2,usually conveyed from the cylinders and sometimes augmented by "booster pumps". Gaseous hydrogen is producedindustrially from hydrocarbons by the process known as steam reforming.[9]

Hydrogen may, in specialised applications, also be extracted ("transferred") from "hydrogen-donors" in place of H2gas. Hydrogen donors, which often serve as solvents include hydrazine, dihydronaphthalene, dihydroanthracene,isopropanol, and formic acid.[10] In organic synthesis, transfer hydrogenation is useful for the reduction of polarunsaturated substrates, such as ketones, aldehydes, and imines.

Hydrogenation 79

Thermodynamics and mechanismHydrogenation is a strongly exothermic reaction. In the hydrogenation of vegetable oils and fatty acids, for example,the heat released is about 25 kcal per mole (105 kJ/mol), sufficient to raise the temperature of the oil by 1.6-1.7 °Cper iodine number drop. The mechanism of metal-catalyzed hydrogenation of alkenes and alkynes has beenextensively studied.[11] First of all isotope labeling using deuterium confirms the regiochemistry of the addition:

RCH=CH2 + D2 → RCHDCH2D

Heterogeneous catalysisOn solids, the accepted mechanism today is called the Horiuti-Polanyi mechanism.1. Binding of the unsaturated bond, and hydrogen dissociation into atomic hydrogen onto the catalyst2. Addition of one atom of hydrogen; this step is reversible3. Addition of the second atom; effectively irreversible under hydrogenating conditions.

Homogeneous catalysisIn many homogeneous hydrogenation processes,[12] the metal binds to both components to give an intermediatealkene-metal(H)2 complex. The general sequence of reactions is assumed to be as follows or a related sequence ofsteps:• binding of the hydrogen to give a dihydride complex ("oxidative addition"):

LnM + H2 → LnMH2• binding of alkene:

LnM(η2H2) + CH2=CHR → Ln-1MH2(CH2=CHR) + L• transfer of one hydrogen atom from the metal to carbon (migratory insertion)

Ln-1MH2(CH2=CHR) → Ln-1M(H)(CH2-CH2R)• transfer of the second hydrogen atom from the metal to the alkyl group with simultaneous dissociation of the

alkane ("reductive elimination")Ln-1M(H)(CH2-CH2R) → Ln-1M + CH3-CH2R

Preceding the oxidative addition of H2 is the formation of a dihydrogen complex.

Inorganic substratesThe hydrogenation of nitrogen to give ammonia is conducted on a vast scale by the Haber-Bosch process, consumingan estimated 1% of the world's energy supply.

Oxygen can be partially hydrogenated to give hydrogen peroxide,although this process has not been commercialized.

Industrial applications

Catalytic hydrogenation has diverse industrial uses.

In petrochemical processes, hydrogenation is used to convert alkenes and aromatics into saturated alkanes (paraffins)and cycloalkanes (napthenes). Hydrocracking of heavy residues into diesel is another application. In isomerizationand catalytic reforming processes, some hydrogen pressure is maintained to hydrogenolyze coke and prevent itsaccumulation.Xylitol, a polyol, is produced by hydrogenation of the sugar xylose, an aldehyde.

Hydrogenation 80

In the food industryHydrogenation is widely applied to the processing of vegetable oils and fats. Complete hydrogenation convertsunsaturated fatty acids to saturated ones. In practice the process is not usually carried to completion. Since theoriginal oils usually contain more than one double bond per molecule (that is, they are polyunsaturated), the result isusually described as partially hydrogenated vegetable oil; that is some, but usually not all, of the double bonds ineach molecule have been reduced. This is done by restricting the amount of hydrogen (or reducing agent) allowed toreact with the fat.Hydrogenation results in the conversion of liquid vegetable oils to solid or semi-solid fats, such as those present inmargarine. Changing the degree of saturation of the fat changes some important physical properties such as themelting point, which is why liquid oils become semi-solid. Semi-solid fats are preferred for baking because the waythe fat mixes with flour produces a more desirable texture in the baked product. Since partially hydrogenatedvegetable oils are cheaper than animal source fats, they are available in a wide range of consistencies, and have otherdesirable characteristics (e.g., increased oxidative stability (longer shelf life)), they are the predominant fats used inmost commercial baked goods. Fat blends formulated for this purpose are called shortenings.

Health implications

A side effect of incomplete hydrogenation having implications for human health is the isomerization of theremaining unsaturated carbon bonds. The cis configuration of these double bonds predominates in the unprocessedfats in most edible fat sources, but incomplete hydrogenation partially converts these molecules to trans isomers,which have been implicated in circulatory diseases including heart disease (see trans fats). The conversion from cisto trans bonds is favored because the trans configuration has lower energy than the natural cis one. At equilibrium,the trans/cis isomer ratio is about 2:1. Food legislation in the US and codes of practice in EU have long requiredlabels declaring the fat content of foods in retail trade and, more recently, have also required declaration of the transfat content. Furthermore, trans fats are banned in Denmark and New York City.[13] [14]

HistoryThe earliest hydrogenation is that of platinum catalyzed addition of hydrogen to oxygen in the Döbereiner's lamp, adevice commercialized as early as 1823. The French chemist Paul Sabatier is considered the father of thehydrogenation process. In 1897, building on the earlier work of James Boyce, an American chemist working in themanufacture of soap products, he discovered that the introduction of a trace of nickel as a catalyst facilitated theaddition of hydrogen to molecules of gaseous hydrocarbons in what is now known as the Sabatier process. For thiswork Sabatier shared the 1912 Nobel Prize in Chemistry. Wilhelm Normann was awarded a patent in Germany in1902 and in Britain in 1903 for the hydrogenation of liquid oils, which was the beginning of what is now a worldwide industry. The commercially important Haber-Bosch process, first described in 1905, involves hydrogenation ofnitrogen. In the Fischer-Tropsch process, reported in 1922 carbon monoxide, which is easily derived from coal, ishydrogenated to liquid fuels.Also in 1922, Voorhees and Adams described an apparatus for performing hydrogenation under pressures above oneatmosphere.[15] The Parr shaker, the first product to allow hydrogenation using elevated pressures and temperatures,was commercialized in 1926 based on Voorhees and Adams’ research and remains in widespread use. In 1924Murray Raney developed a nickel fine powder catalyst named after him which is still widely used in hydrogenationreactions such as conversion of nitriles to amines or the production of margarine. In 1938, Otto Roelen described theoxo process which involves the addition of both hydrogen and carbon monoxide to alkenes, giving aldehydes. Sincethis process entails C-C coupling, it and its many variations (see carbonylation) remains highly topical into the newdecade.[16] The 1960s witnessed the development of homogeneous catalysts, e.g., Wilkinson's catalyst. In the 1980s,the Noyori asymmetric hydrogenation represented one of the first applications of hydrogenation in asymmetricsynthesis, a growing application in the production of fine chemicals.

Hydrogenation 81

Metal-free hydrogenationFor all practical purposes, hydrogenation requires a metal catalyst. Hydrogenation can, however, proceed from somehydrogen donors without catalysts, illustrative hydrogen donors being diimide and aluminium isopropoxide. Somemetal-free catalytic systems have been investigated in academic research. One such system for reduction of ketonesconsists of tert-butanol and potassium tert-butoxide and very high temperatures.[17] The reaction depicted belowdescribes the hydrogenation of benzophenone:

A chemical kinetics study[18] found this reaction is first-order in all three reactants suggesting a cyclic 6-memberedtransition state.Another system for metal-free hydrogenation is based on the phosphine-borane, compound 1, which has been calleda frustrated Lewis pair. It reversibly accepts dihydrogen at relatively low temperatures to form the phosphoniumborate 2 which can reduce simple hindered imines.[19]

The reduction of nitrobenzene to aniline has been reported to be catalysed by fullerene , its mono-anion, atmospherichydrogen and UV light.[20]

Hydrogenation 82

Equipment used for hydrogenationToday’s bench chemist has three main choices of hydrogenation equipment:• Batch hydrogenation under atmospheric conditions• Batch hydrogenation at elevated temperature and/or pressure• Flow hydrogenation

Batch hydrogenation under atmospheric conditionsThe original and still a commonly practised form of hydrogenation in teaching laboratories, this process is usuallyeffected by adding solid catalyst to a round bottom flask of dissolved reactant which has been evacuated usingnitrogen or argon gas and sealing the mixture with a penetrable rubber seal. Hydrogen gas is then supplied from aH2-filled balloon. The resulting three phase mixture is agitated to promote mixing. Hydrogen uptake can bemonitored, which can be useful for monitoring progress of a hydrogenation. This is achieved by either using agraduated tube containing a coloured liquid, usually aqueous copper sulfate or with gauges for each reaction vessel.

Batch hydrogenation at elevated temperature and/or pressureSince many hydrogenation reactions such as hydrogenolysis of protecting groups and the reduction of aromaticsystems proceed extremely sluggishly at atmospheric temperature and pressure, pressurised systems are popular. Inthese cases, catalyst is added to a solution of reactant under an inert atmosphere in a pressure vessel. Hydrogen isadded directly from a cylinder or built in laboratory hydrogen source, and the pressurized slurry is mechanicallyrocked to provide agitation or a spinning basket is used. Heat may also be used, as the pressure compensates for theassociated reduction in gas solubility.

Flow hydrogenationFlow hydrogenation has become a popular technique at the bench and increasingly the process scale. This techniqueinvolves continuously flowing a dilute stream of dissolved reactant over a fixed bed catalyst in the presence ofhydrogen. Using established HPLC technology, this technique allows the application of pressures from atmosphericto 1,450 PSI. Elevated temperatures may also be used. At the bench scale, systems use a range of pre-packedcatalysts which eliminates the need for weighing and filtering pyrophoric catalysts.

Industrial reactorsCatalytic hydrogenation is done in a tubular plug-flow reactor (PFR) packed with a supported catalyst. The pressuresand temperatures are typically high, although this depends on the catalyst. Catalyst loading is typically much lowerthan in laboratory batch hydrogenation, and various promoters are added to the metal, or mixed metals are used, toimprove activity, selectivity and catalyst stability. The use of nickel is common despite its low activity, due to its lowcost compared to precious metals.

Hydrogenation 83

See also• Dehydrogenation• Transfer hydrogenation• Hydrogenolysis• Hydrodesulfurization, Hydrotreater and Oil desulfurization• Timeline of hydrogen technologies• Hydrogenated Oils-Silent Killers by columnist, David Lawrence Dewey. The first journalist in 1996 to warn

consumers about hydrogenated oils [21]

References[1] Hudlický, Miloš (1996). Reductions in Organic Chemistry. Washington, D.C.: American Chemical Society. pp. 429. ISBN 0-8412-3344-6.[2] Catalytic Hydrogenation of Maleic Acid at Moderate Pressures A Laboratory Demonstration Kwesi Amoa 1948 Journal of Chemical

Education • Vol. 84 No. 12 December 2007[3] Advanced Organic Chemistry Jerry March 2nd Edition[4] C. F. H. Allen and James VanAllan (1955), "m-Toylybenzylamine" (http:/ / www. orgsyn. org/ orgsyn/ orgsyn/ prepContent.

asp?prep=CV3P0827), Org. Synth., ; Coll. Vol. 3: 827[5] A. B. Mekler, S. Ramachandran, S. Swaminathan, and Melvin S. Newman (1973), "2-Methyl-1,3-Cyclohexanedione" (http:/ / www. orgsyn.

org/ orgsyn/ orgsyn/ prepContent. asp?prep=CV5P0567), Org. Synth., ; Coll. Vol. 5: 743[6] S. Robert E. Ireland and P. Bey (1988), "Homogeneous Catalytic Hydrogenation: Dihydrocarvone" (http:/ / www. orgsyn. org/ orgsyn/

orgsyn/ prepContent. asp?prep=CV6P0459), Org. Synth., ; Coll. Vol. 6: 459[7] T. Mallet, E. Orglmeister, A. Baiker" Chemical Reviews, 2007, 107, 4863-4890. DOI: 10.1021/cr0683663[8] H. Lindlar and R. Dubuis (1973), "Palladium Catalyst for Partial Reduction of Acetylenes" (http:/ / www. orgsyn. org/ orgsyn/ orgsyn/

prepContent. asp?prep=CV5P0880), Org. Synth., ; Coll. Vol. 5: 880[9] Paul N. Rylander, "Hydrogenation and Dehydrogenation" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.[10] van Es, T.; Staskun, B. "Aldehydes from Aromatic Nitriles: 4-Formylbenzenesulfonamide" Org. Syn., Coll. Vol. 6, p.631 (1988). ( Article

(http:/ / www. orgsyn. org/ orgsyn/ prep. asp?prep=cv6p0631))[11] Kubas, G. J., "Metal Dihydrogen and σ-Bond Complexes", Kluwer Academic/Plenum Publishers: New York, 2001[12] Johannes G. de Vries, Cornelis J. Elsevier, eds. The Handbook of Homogeneous Hydrogenation Wiley-VCH, Weinheim, 2007. ISBN

978-3-527-31161-3[13] "Deadly fats: why are we still eating them?" (http:/ / www. independent. co. uk/ life-style/ health-and-wellbeing/ healthy-living/

deadly-fats-why-are-we-still-eating-them-843400. html). The Independent. 2008-06-10. . Retrieved 2008-06-16.[14] "New York City passes trans fat ban" (http:/ / www. msnbc. msn. com/ id/ 16051436/ ). msnbc. 2006-12-05. . Retrieved 2010-01-09.[15] (http:/ / pubs. acs. org/ cgi-bin/ abstract. cgi/ jacsat/ 1922/ 44/ i06/ f-pdf/ f_ja01427a021. pdf)[16] Perspective: Hydrogen-Mediated C-C Bond Formation: A Broad New Concept in Catalytic C-C Coupling Ming-Yu Ngai, Jong-Rock Kong,

and Michael J. Krische J. Org. Chem.; 2007, 72, pp. 1063–1072. doi:10.1021/jo061895m[17] Homogeneous Hydrogenation in the Absence of Transition-Metal Catalysts Cheves Walling, Laszlo Bollyky J. Am. Chem. Soc.; 1964;

86(18); 3750–3752. doi:10.1021/ja01072a028[18] Hydrogenation without a Transition-Metal Catalyst: On the Mechanism of the Base-Catalyzed Hydrogenation of Ketones Albrecht

Berkessel, Thomas J. S. Schubert, and Thomas N. Muller J. Am. Chem. Soc. 2002, 124, 8693–8698 doi:10.1021/ja016152r[19] Metal-Free Catalytic Hydrogenation Preston A. Chase, Gregory C. Welch, Titel Jurca, and Douglas W. Stephan Angew. Chem. Int. Ed.

2007, 46, 8050–8053. doi:10.1002/anie.200702908[20] A Nonmetal Catalyst for Molecular Hydrogen Activation with Comparable Catalytic Hydrogenation Capability to Noble Metal Catalyst

Baojun Li and Zheng Xu J. Am. Chem. Soc., 2009, 131 (45), pp 16380–16382. doi:10.1021/ja9061097[21] http:/ / www. dldewey. com/ hydroil. htm

Hydrogenation 84

Further reading• Jang ES, Jung MY, Min DB (2005). "Hydrogenation for Low Trans and High Conjugated Fatty Acids" (http:/ /

members. ift. org/ NR/ rdonlyres/ 27B49B9B-EA63-4D73-BAB4-42FEFCD72C68/ 0/crfsfsv4n1p00220030ms20040577. pdf) (PDF). Comprehensive Reviews in Food Science and Food Safety 1.

• examples of hydrogenation from Organic Syntheses:• Organic Syntheses, Coll. Vol. 7, p.226 (1990). (http:/ / orgsynth. org/ orgsyn/ pdfs/ CV7P0226. pdf)• Organic Syntheses, Coll. Vol. 8, p.609 (1993). (http:/ / orgsynth. org/ orgsyn/ pdfs/ CV8P0609. pdf)• Organic Syntheses, Coll. Vol. 5, p.552 (1973). (http:/ / orgsynth. org/ orgsyn/ pdfs/ CV5P0552. pdf)• Organic Syntheses, Coll. Vol. 3, p.720 (1955). (http:/ / orgsynth. org/ orgsyn/ pdfs/ CV4P0603. pdf)• Organic Syntheses, Coll. Vol. 6, p.371 (1988). (http:/ / orgsynth. org/ orgsyn/ pdfs/ CV6P0371. pdf)

• early work on transfer hydrogenation: Davies, R. R.; Hodgson, H. H. J. Chem. Soc. 1943, 281. Leggether, B. E.;Brown, R. K. Can. J. Chem. 1960, 38, 2363. Kuhn, L. P. J. Am. Chem. Soc. 1951, 73, 1510.

• Fred A. Kummerow (2008). Cholesterol Won't Kill You, But Trans Fat Could. Trafford. ISBN 142513808.

DehydrogenationDehydrogenation is a chemical reaction that involves the elimination of hydrogen (H2). It is the reverse process ofhydrogenation. Dehydrogenation reactions may be either large scale industrial processes or smaller scale laboratoryprocedures.There are a variety of classes of dehydrogenations:• Aromatization - Six-membered alicyclic rings can be aromatized in the presence of hydrogenation catalysts, the

elements sulfur and selenium, or quinones (such as DDQ).• Oxidation - The conversion of alcohols to ketones or aldehydes can be effected by metal catalysts such as copper

chromite. In the Oppenauer oxidation, hydrogen is transferred from one alcohol to another to bring about theoxidation.

• Dehydrogenation of amines - amines can be converted to nitriles using a variety of reagents, such as IF5.• Dehydrogenation of paraffins and olefins - paraffins like n-pentane and isopentane can be converted to pentene

and isoprene using chromium (III) oxide as a catalyst at 500 degree C.Dehydrogenation converts saturated fats to unsaturated fats.Enzymes that catalyze dehydrogenation are called dehydrogenases.

References• Advanced Organic Chemistry, Jerry March, 1162-1173.

Transfer hydrogenation 85

Transfer hydrogenationTransfer hydrogenation is the addition of hydrogen (H2; dihydrogen in inorganic and organometallic chemistry) toa molecule from a source other than gaseous H2. It is applied in industry and in organic synthesis, in part because ofthe inconvenience and expense of using gaseous H2. One large scale application of transfer hydrogenation is coalliquefaction using "donor solvents" such as tetralin.[1] [2]

Organometallic catalystsIn the area of organic synthesis, a useful family of hydrogen-transfer catalysts have been developed based onruthenium and rhodium complexes with diamine and phosphine ligands.[3] A representative catalyst precursor isderived from (cymene)ruthenium dichloride dimer and the tosylated diphenylethylenediamine. These catalysts aremainly employed for the reduction of ketones and imines to alcohols and amines, respectively. The hydrogen-donor(transfer agent) is typically isopropanol, which coverts to acetone upon donation of hydrogen. Transferhydrogenations can proceed with high enantioselectivities when the starting material is prochiral:

RR'C=O + Me2CHOH → RR'C*H-OH + Me2C=Owhere RR'C*H-OH is a chiral product. A typical catalyst is (cymene(R,R-HNCHPhCHPhNTs), where Ts =SO2C6H4Me and R,R refers to the absolute configuration of the two chiral carbon centers. This work was recognizedwith the 2001 Nobel Prize in Chemistry to Ryōji Noyori. Another family of hydrogen-transfer agents are those basedon aluminium alkoxides, such as Aluminium isopropoxide.

Hydrogen donorsA historically prominent transfer hydrogenation agent is diimide, which becomes oxidized to the very stable N2:

The diimide is generated from hydrazine. Two hydrocarbons that can serve as hydrogen donors are cyclohexene orcyclohexadiene. In this case an alkane is formed along with the formation of benzene. The driving force of thereaction being the gain of aromatic stabilization energy when benzene is formed. Pd can be used as a catalyst and atemperature of 100 °C is employed. One limitation of using transfer hydrogenation for the production of alkane isthat it cannot be used to prepare methane as no unsaturated hydrocarbon contain only one carbon. More exotictransfer hydrogenations have been reported, including this intramolecular one:

Transfer hydrogenation 86

Many reactions exist with alcohol as the hydrogen donor. Examples are the sodium metal mediated Birch reduction(arenes) and the Bouveault-Blanc reduction (esters). The combination of magnesium and methanol is used in alkenereductions, e.g. the synthesis of asenapine:[4]

Organocatalytic transfer hydrogenationOrganocatalytic transfer hydrogenation has been described by the group of List in 2004 in a system with a Hantzschester as proton donor and an amine catalyst:[5]

In this particular reaction the substrate is an α,β-unsaturated carbonyl compound. The proton donor is oxidized to the pyridine form and resembles the biochemically relevant coenzyme NADH. In the catalytic cycle for this reaction the

Transfer hydrogenation 87

amine and the aldehyde first form an iminium ion, then proton transfer is followed by hydrolysis of the iminiumbond regenerating the catalyst. By adopting a chiral imidazolidinone MacMillan organocatalyst an enantioselectivityof 81% ee was obtained:

The group of MacMillan independently published a very similar asymmetric reaction in 2005 [6] :

In an interesting case of stereoconvergence, both the E-isomer and the Z-isomer in this reaction yield the(S)-enantiomer.Extending the scope of this reaction towards ketones or rather enones requires fine tuning of the catalyst (add abenzyl group and replace the t-butyl group by a furan) and of the Hantzsch ester (add more bulky t-butyl groups) [7] :

With a different organocatalyst altogether, hydrogenation can also be accomplished for imines. In one particularreaction the catalysts is a BINOL based phosphoric acid, the substrate a quinoline and the product a chiraltetradehydroquinoline in a 1,4-addition, isomerization and 1,2-addition cascade reaction [8] :

Transfer hydrogenation 88

The first step in this reaction is protonation of the quinoline nitrogen atom by the phosphoric acid forming a transientchiral iminium ion. It is noted that with most traditional metal based catalysts, hydrogenation of aromatic orheteroaromatic substrates tend to fail.

References[1] Speight, J. G. "The Chemistry and Technology of Coal" Marcel Dekker; New York, 1983; p. 226 ff. ISBN 0-8247-1915-8.[2] Muñiz, Kilian (2005). "Bifunctional Metal-Ligand Catalysis: Hydrogenations and New Reactions within the Metal-(Di)amine Scaffold13".

Angewandte Chemie International Edition 44 (41): 6622–6627. doi:10.1002/anie.200501787. PMID 16187395.[3] T. Ikariya, K. Murata, R. Noyori "Bifunctional Transition Metal-Based Molecular Catalysts for Asymmetric Syntheses" Org. Biomol. Chem.,

2006, volume 4, 393-406.[4] Linden, M. V. D.; Roeters, T.; Harting, R.; Stokkingreef, E.; Gelpke, A. S.; Kemperman, G. (2008). "Debottlenecking the Synthesis Route of

Asenapine". Organic Process Research & Development 12: 196–201. doi:10.1021/op700240c.[5] Yang; Hechavarria Fonseca, M.; List, B. (2004). "A metal-free transfer hydrogenation: organocatalytic conjugate reduction of

alpha,beta-unsaturated aldehydes". Angewandte Chemie (International ed. in English) 43 (48): 6660–6662. doi:10.1002/anie.200461816.PMID 15540245.

[6] Ouellet; Tuttle, J.; MacMillan, D. (2005). "Enantioselective organocatalytic hydride reduction". Journal of the American Chemical Society127 (1): 32–33. doi:10.1021/ja043834g. PMID 15631434.

[7] Tuttle; Ouellet, S.; MacMillan, D. (2006). "Organocatalytic transfer hydrogenation of cyclic enones". Journal of the American ChemicalSociety 128 (39): 12662–12663. doi:10.1021/ja0653066. PMID 17002356.

[8] Rueping; Antonchick, A.; Theissmann, T. (2006). "A highly enantioselective Brønsted acid catalyzed cascade reaction: organocatalytictransfer hydrogenation of quinolines and their application in the synthesis of alkaloids". Angewandte Chemie (International ed. in English) 45(22): 3683–3686. doi:10.1002/anie.200600191. PMID 16639754.

See also• Dehydrogenation• Hydrogenation• Hydrogenolysis

Hydrogenolysis 89

HydrogenolysisHydrogenolysis is a chemical reaction whereby a carbon-carbon or carbon-heteroatom single bond is cleaved orundergoes "lysis" by hydrogen.[1] The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. A relatedreaction is hydrogenation, where hydrogen is added to the molecule, without cleaving bonds. Usually hydrogenolysisis conducted catalytically using hydrogen gas.

HistoryThe term "hydrogenolysis" was coined by Carleton Ellis in reference to hydrogenolysis of carbon-carbon bonds.[1] [2]

Earlier, Sabatier had already observed the hydrogenolysis of benzyl alcohol to toluene,[3] and as early as 1906, Padoaand Ponti had observed the hydrogenolysis of furfuryl alcohol.[4] Adkins and Connors were the first to call thecarbon-oxygen bond cleavage "hydrogenolysis".[1]

In the petrochemical industryIn petroleum refineries, catalytic hydrogenolysis of feedstocks is conducted on a large scale to remove sulfur fromfeedstocks, releasing gaseous hydrogen sulfide (H2S). The hydrogen sulfide is subsequently recovered in an aminetreater and finally converted to elemental sulfur in a Claus process unit. In those industries, desulfurization processunits are often referred to as hydrodesulfurizers (HDS) or hydrotreaters (HDT). Catalysts are based on molybdenumsulfide containing smaller amounts of cobalt or nickel. Hydrogenolysis is accompanied by hydrogenation.[5]

Another hydrogenolysis reaction of commercial importance is the hydrogenolysis of esters into alcohols by catalystssuch as copper chromite.

In the laboratoryIn the laboratory, hydrogenolysis is used in organic synthesis. Debenzylation is most common and involves thecleavage of benzyl ethers:[6]

ROCH2C6H5 + H2 → ROH + CH3C6H5Thioketals undergo hydrogenolysis using Raney nickel, a catalyst that, conveniently, carries its own hydrogen.Laboratory hydrogenolysis is operationally similar to hydrogenation, and may be accomplished at atmosphericpressure by stirring the reaction mixture under a slight positive pressure of hydrogen gas, having flushed theapparatus with more of this gas. The hydrogen may be provided by attaching a balloon to a needle, filling it from abottle, and inserting the needle into the reaction flask via a rubber septum. At high pressure, a hydrogenationautoclave (i.e., a Parr hydrogenator) or similar piece of equipment is required.

References[1] Ralph Connor, Homer Adkins. Hydrogenolysis Of Oxygenated Organic Compounds. J. Am. Chem. Soc.; 1932; 54(12); 4678-4690. DOI:

10.1021/ja01351a026[2] Carleton Ellis. Hydrogenation of Organic Substances, 3rd ed., Van Nostrand Company, New York, 1930, p. 564 (as referred by Connor and

Adkins).[3] Sabatier and Murat. Ann. Chim. [9] 4, 258, (1915), according to Connor and Adkins.[4] Furfuryl alcohol hydrogenation is accompanied by hydrogenolysis into 2-methylfuran, which gives 2-methyltetrahydrofuran, and further

hydrogenolysis opens the ring to give 2-pentanol. Original: Padoa and Ponti. Atti. R. accad. Lincei, 15, [5] 610 (1906); Gazz. chim. ital. 37,[2] 105 (1907), according to Kaufmann: W. E. Kaufmann, Roger Adams. The Use Of Platinum Oxide As A Catalyst In The Reduction OfOrganic Compounds. Iv. Reduction Of Furfural And Its Derivatives. J. Am. Chem. Soc.; 1923; 45(12); 3029-3044. DOI:10.1021/ja01665a033

[5] Topsøe, H.; Clausen, B. S.; Massoth, F. E., Hydrotreating Catalysis, Science and Technology, Springer-Verlag: Berlin, 1996.

Hydrogenolysis 90

[6] For example Organic Syntheses, Coll. Vol. 7, p.386 (1990); Vol. 60, p.92 (1981). http:/ / orgsynth. org/ orgsyn/ pdfs/ CV7P0386. pdf. Forexample of C-N scission, see Organic Syntheses, Coll. Vol. 8, p.152 (1993); Vol. 68, p.227 (1990). http:/ / orgsynth. org/ orgsyn/ pdfs/CV8P0152. pdf

Hydron

3 types of hydron

In chemistry, hydron is the general name for the positive hydrogen H+ cation.The term is recommended by IUPAC to be used instead of proton if nodistinction is made between the isotopes proton, deuteron and triton, all foundin naturally occurring undifferentiated isotope mixtures. The name proton isprimarily used for isotopically pure 1H+. [1]

Hydron was defined by IUPAC in 1988.[2] [3] Traditionally, the term "proton"was and is used in place of "hydron". However, although 99.9 % of naturalhydrogen nuclei are protons, small amounts are deuterons and rare tritons.Hydron was located and identified by Walter Russell and documented in his1926 book "The Universal One".

The hydrated form of the hydrogen cation is the hydronium ion, H3O+(aq) Thenegatively-charged counterpart of the hydron is the hydride anion, H-.

Specific types of hydron

Proton, having the symbol p or 1H+, refers only to the +1 ion of protium, 1H.Deuteron, having the symbol 2H+ or D+, refers only to the +1 ion ofdeuterium, 2H or D.

Triton, having the symbol 3H+ or T+, refers only to the +1 ion of tritium, 3H or T.

See also• Hydrogen anion

References[1] Nomenclature of Inorganic Chemistry-IUPAC Recommendations 2005 Red Book 2005.pdf (http:/ / www. iupac. org/ publications/ books/

rbook/ Red_Book_2005. pdf) IR-3.3.2, p.48[2] IUPAC Gold Book internet edition: " hydron (http:/ / goldbook. iupac. org/ H02904. html)".[3] Bunnet, J.F.; Jones, R.A.Y. (1968). "Names for hydrogen atoms, ions, and groups, and for reactions involving them (Recommendations

1988)" (http:/ / www. iupac. org/ publications/ pac/ 1988/ pdf/ 6007x1115. pdf). Pure Appl. Chem. 60 (7): 1115–6.doi:10.1351/pac198860071115. .

Sabatier reaction 91

Sabatier reactionThe Sabatier reaction or Sabatier process involves the reaction of hydrogen with carbon dioxide at elevatedtemperatures and pressures in the presence of a nickel catalyst to produce methane and water. Optionally rutheniumon alumina (aluminum oxide) makes a more efficient catalyst. It is described by the following reaction:

CO2 + 4H2 → CH4 + 2H2OIt was discovered by the French chemist Paul Sabatier.

Space Station Life SupportCurrently, oxygen generators onboard the International Space Station produce oxygen from water using electrolysisand dump the hydrogen produced overboard. As astronauts consume oxygen, carbon dioxide is produced which mustthen be removed from the air and discarded as well. This approach requires copious amounts of water to be regularlytransported to the space station for oxygen generation in addition to that used for human consumption, hygiene, andother uses—a luxury that will not be available to future long duration missions beyond low Earth orbit.NASA is currently investigating the use of the Sabatier reaction to recover water from exhaled carbon dioxide, foruse on the International Space Station and future missions. (In April of 2010, Sabatier hardware was delivered to theInternational Space Station on the STS-131 shuttle mission.)[1] The other resulting chemical, methane, would mostlikely be dumped overboard. As half of the input hydrogen becomes wasted as methane, additional hydrogen wouldneed to be supplied from Earth to make up the difference. However, this creates a nearly closed cycle between water,oxygen, and carbon dioxide which only requires a relatively modest amount of imported hydrogen to maintain.Ignoring other results of respiration, this cycle would look like:

2H2O → O2 + 2H2 → (respiration) → CO2 + 2H2 + 2H2 (added) → 2H2O + CH4 (discarded)The loop could be completely closed if the waste methane was pyrolyzed into its component parts:

CH4 + heat → C + 2H2The released hydrogen would then be recycled back into the Sabatier reactor, leaving an easily removed deposit ofpyrolytic graphite. The reactor would be little more than a steel pipe, and could be periodically serviced by anastronaut where the deposit is chiselled out.The Bosch reaction is also being investigated for this purpose. Though the Bosch reaction would present acompletely closed hydrogen and oxygen cycle which only produces atomic carbon as waste, difficulties maintainingits higher required temperature and properly handling carbon deposits mean significantly more research will berequired before a Bosch reactor could become a reality. One problem is that the production of elemental carbon tendsto foul the catalyst's surface, which is detrimental to the reaction's efficiency.

Manufacturing Propellant on MarsThe Sabatier reaction has been proposed as a key step in reducing the cost of manned exploration of Mars (MarsDirect) through In-Situ Resource Utilization. Hydrogen is combined with CO2 from the atmosphere, with methanethen becoming a mars storable fuel and the water side product yielding oxygen to be liquefied for the oxidizer andhydrogen to be recycled back into the reactor. The original amount of hydrogen could be transported from Earth orseparated from martian sources of water [2] .The stoichiometric ratio of oxidizer and fuel is 3.5:1, for an oxygen:methane engine, however one pass through theSabatier reactor produces a ratio of only 2:1. More oxygen may be produced by running the water gas shift reactionin reverse. When the water is split, the extra oxygen needed is obtained.

Sabatier reaction 92

Another option is to make more methane than needed and pyrolyze the excess it into carbon and hydrogen (seeabove section) where the hydrogen is recycled back into the reactor to produce further methane and water. In anautomated system, the carbon deposit may be removed by blasting with hot Martian CO2, oxidizing the carbon intocarbon monoxide, which is vented.A fourth solution to the stoichiometry problem would be to combine the Sabatier reaction with the reverse watergas-shift reaction in a single reactor as follows:3CO2 + 6H2 → CH4 + 2CO + 4H2OThis reaction is slightly exothermic, and when the water is electrolyzed, an oxygen to methane ratio of 4:1 isobtained, resulting in a large backup supply of oxygen. With only the light hydrogen transported from Earth, and theheavy oxygen and carbon extracted locally, a mass leveraging of 18:1 is afforded with this scheme. This in-situresource utilization would result in massive weight and cost savings to any proposed manned Mars or sample returnmissions.

See also• In-Situ Resource Utilization• Timeline of hydrogen technologies

References[1] http:/ / www. nasaspaceflight. com/ 2010/ 10/ soyuz-01m-docking-iss-crews-conduct-hardware-installation/[2] Giant Pool of Water Ice at Mars' South Pole (http:/ / www. space. com/ scienceastronomy/ 070315_martian_beach. html) Space.com article

External links• A Crewed Mission to Mars (http:/ / nssdc. gsfc. nasa. gov/ planetary/ mars/ marssurf. html)• Development of an improved Sabatier reactor (http:/ / www. osti. gov/ energycitations/ product. biblio.

jsp?osti_id=5087687)• Improved Sabatier Reactions for In Situ Resource Utilization on Mars Missions (http:/ / www. isso. uh. edu/

publications/ A9900/ pdf/ rich84. pdf)

93

Risks

Hydrogen damageHydrogen damage is the generic name given to a large number of metal degradation processes due to interactionwith hydrogen.Hydrogen is present practically everywhere, in the atmosphere, several kilometres above the earth and inside theearth. Engineering materials are exposed to hydrogen and they may interact with it resulting in various kinds ofstructural damage. Damaging effects of hydrogen in metallic materials have been known since 1875 when W. H.Johnson reported[1] “some remarkable changes produced in iron by the action of hydrogen and acids”. During theintervening years many similar effects have been observed in different structural materials, such as steel, aluminium,titanium, and zirconium. Because of the technological importance of hydrogen damage, many people explored thenature, causes and control measures of hydrogen related degradation of metals. Hardening, embrittlement andinternal damage are the main hydrogen damage processes in metals. This article consists of a classification ofhydrogen damage, brief description of the various processes and their mechanisms, and some guidelines for thecontrol of hydrogen damage.

ImportanceWith advancing technology, use of high strength structural materials becomes a necessity. Depletion of fossil fuelsand the search for other sources of energy is a current activity of mankind. Hydrogen is believed to be a possiblefuture source of energy (Engineering note: Hydrogen could not be used as a "source" of energy but only as a meansto transport energy from one place to another) and a “hydrogen economy” is a strong possibility within the next 50years. In such a scenario, large scale production, storage, transportation and use of hydrogen becomes necessary[2] .Materials’ problems caused by hydrogen damage could limit the progress of such an economy. Hydrogen may bepicked up by metals during melting, casting, shaping and fabrication. They are also exposed to hydrogen during theirservice life. Materials susceptible to hydrogen damage have ample opportunities to be degraded during all thesestages.

ClassificationsHydrogen damage may be of four types: solid solution hardening, creation of internal defects, hydride embrittlement,and hydrogen embrittlement.[3] Each of these may further be classified into the various damaging processes.

Solid solution hardeningMetals like niobium and tantalum dissolve hydrogen and experience hardening and embrittlement at concentrationsmuch below their solid solubility limit[4] . The hardening and embrittlement are enhanced by increased rate ofstraining.

Hydride embrittlementIn hydride forming metals like titanium, zirconium and vanadium, hydrogen absorption causes severe embrittlement. At low concentrations of hydrogen, below the solid solubility limit, stress-assisted hydride formation causes the embrittlement which is enhanced by slow straining. At hydrogen concentrations above the solubility limit, brittle hydrides are precipitated on slip planes and cause severe embrittlement[5] . This latter kind of embrittlement is

Hydrogen damage 94

encouraged by increased strain-rates, decreased temperature and by the presence of notches in the material.

Creation of internal defectsHydrogen present in metals can produce several kinds of internal defects like blisters, shatter fracture, flakes,fish-eyes and porosity. Carbon steels exposed to hydrogen at high temperatures experience hydrogen attack whichleads to internal decarburization and weakening[6] .

BlisteringAtomic hydrogen diffusing through metals may collect at internal defects like inclusions and laminations and formmolecular hydrogen. High pressures may be built up at such locations due to continued absorption of hydrogenleading to blister formation, growth and eventual bursting of the blister. Such hydrogen induced blister cracking hasbeen observed in steels, aluminium alloys, titanium alloys and nuclear structural materials[3] .

Shatter cracks, flakes, fish-eyes and micro perforationsFlakes and shatter cracks are internal fissures seen in large forgings. Hydrogen picked up during melting and castingsegregates at internal voids and discontinuities and produces these defects during forging. Fish-eyes are brightpatches named for their appearance seen on fracture surfaces, generally of weldments. Hydrogen enters the metalduring fusion-welding and produces this defect during subsequent stressing. Steel containment vessels exposed toextremely high hydrogen pressures develop small fissures or micro perforations through which fluids may leak.[3]

PorosityIn metals like iron and steel, aluminium and magnesium whose hydrogen solubilities decrease with decreasingtemperature, liberation of excess hydrogen during cooling from the melt, (in ingots and castings) produces gasporosity.

Hydrogen embrittlementBy far, the most damaging effect of hydrogen in structural materials is hydrogen embrittlement. Materialssusceptible to this process exhibit a marked decrease in their energy absorption ability before fracture in the presenceof hydrogen. This phenomenon is also known as hydrogen-assisted cracking, hydrogen-induced blister cracking. Theembrittlement is enhanced by slow strain rates and low temperatures, near room temperature.

Hydrogen stress cracking

Brittle delayed failure of normally ductile materials when hydrogen is present within is called hydrogen stresscracking or internal hydrogen embrittlement. This effect is seen in high strength structural steels, titanium alloys andaluminium alloys.

Hydrogen environment embrittlement

Embrittlement of materials when tensile loaded in contact with gaseous hydrogen is known as hydrogen environmentembrittlement or external hydrogen embrittlement. It has been observed in alloy steels and alloys of nickel, titanium,uranium and niobium.

Hydrogen damage 95

Loss in tensile ductility

Hydrogen lowers tensile ductility in many materials. In ductile materials, like austenitic stainless steels andaluminium alloys, no marked embrittlement may occur, but may exhibit significant lowering in tensile ductility (%elongation or % reduction in area) in tensile tests.

Degradation of other mechanical properties

Hydrogen may also affect the plastic flow behaviour of metals. Increased or decreased yield strengths, serratedyielding, altered work hardening rates as well as lowered fatigue and creep properties have been reported.[3]

Control of hydrogen damageThe best method of controlling hydrogen damage is to control contact between the metal and hydrogen. Many stepscan be taken to reduce the entry of hydrogen into metals during critical operations like melting, casting, working(rolling, forging, etc.), welding, surface preparation, like chemical cleaning, electroplating, and corrosion duringtheir service life. Control of the environment and metallurgical control of the material to decrease its susceptibility tohydrogen are the two major approaches to reduce hydrogen damage.

Detection of hydrogen damageThere are various methods of adequately identifying and monitoring hydrogen damage, including ultrasonic echoattenuation method, amplitude-based backscatter, velocity ratio, creeping waves/time-of-flight measurement,pitch-catch mode shear wave velocity, advanced ultrasonic backscatter techniques (AUBT), time of flight diffraction(TOFD), thickness mapping and in-situ metallography – replicas.[7] .To inspect industrial facilities, such as a plant for the possible occurrence of hydrogen damage, an accurateinspection plan has to be made by combining advanced techniques like time of flight diffraction (TOFD), automatedbackscatter and velocity ratio measurements.[8]

The backscatter technique uses corroscan for the most critical areas, i.e., at highest temperature and/or highest partialhydrogen pressure. In order to discriminate between hydrogen damage and small inclusions, additionalmeasurements are taken with the Velocity Ratio Technique.

See also• Hydrogen piping

References[1] W. H. Johnson, Proc. Royal Soc. (London), 23 (1875), 168[2] J. O’M. Bockris, Int. J. Hydrogen Energy, 6 (1981), 223[3] T. K. G. Namboodhiri, Trans. Indian Inst. Metals, 37(1984), 764[4] B. A. Kolachev, Hydrogen embrittlement of non-ferrous metals, Translated from Russian, Israel Program for scientific translations, (1968)[5] W. J. Pardee and N. E. Paton, Metall. Trans. 11A (1980), 1391[6] G. A. Nelson, in Hydrogen Damage, C. D. Beachem (Ed.), American Society for Metals, Metals Park, Ohio, (1977), p. 377[7] The Australian Institute for Non Destructive Testing (AINDT), Detection and Quantification of Hydrogen Damage (http:/ / www. ndt. net/

apcndt2001/ papers/ 1154/ 1154. htm)[8] SGS Industrial Services, NDT-Hot Hydrogen Attack (http:/ / www. sgs. com/ ndt-hot-hydrogen-attack?serviceId=10149586& lobId=5550)

Hydrogen damage 96

External links• A 39-page paper on hydrogen damage of metals by M.R. Louthan, "Hydrogen Embrittlement of Metals: A Primer

for the Failure Analyst", 2008, from U.S. DOE OSTI, 3.4MB available here (http:/ / sti. srs. gov/ fulltext/WSRC-STI-2008-00062. pdf).

Hydrogen embrittlementHydrogen embrittlement is the process by which various metals, most importantly high-strength steel, becomebrittle and fracture following exposure to hydrogen. Hydrogen embrittlement is often the result of unintentionalintroduction of hydrogen into susceptible metals during forming or finishing operations.Hydrogen embrittlement is also used to describe the formation of zircaloy hydride. Use of the term in this context iscommon in the nuclear industry.

ProcessThe mechanism starts with lone hydrogen atoms diffusing through the metal. At high temperatures, the elevatedsolubility of hydrogen allows hydrogen to diffuse into the metal (or the hydrogen can diffuse in at a low temperature,assisted by a concentration gradient). When these hydrogen atoms re-combine in minuscule voids of the metal matrixto form hydrogen molecules, they create pressure from inside the cavity they are in. This pressure can increase tolevels where the metal has reduced ductility and tensile strength up to the point where it cracks open (hydrogeninduced cracking, or HIC). High-strength and low-alloy steels, nickel and titanium alloys are most susceptible.Austempered iron is also susceptible. Steel with an ultimate tensile strength of less than 1000 MPa or hardness ofless than 30 HRC are not generally considered susceptible to hydrogen embrittlement. Jewett et al.[1] reports theresults of tensile tests carried out on several structural metals under high-pressure molecular hydrogen environment.These tests have shown that austenitic stainless steels, aluminum (including alloys), copper (including alloys, e.g.beryllium copper) are not susceptible to hydrogen embrittlement along with few other metals[2] . For example of asevere embrittlement measured by Jewett, the elongation at failure of 17-4PH precipitation hardened stainless steelwas measured to drop from 17% to only 1.7% when smooth specimens were exposed to high-pressure hydrogen.Hydrogen embrittlement can occur during various manufacturing operations or operational use - anywhere that themetal comes into contact with atomic or molecular hydrogen. Processes that can lead to this include cathodicprotection, phosphating, pickling, and electroplating. A special case is arc welding, in which the hydrogen is releasedfrom moisture (for example in the coating of the welding electrodes; to minimize this, special low-hydrogenelectrodes are used for welding high-strength steels). Other mechanisms of introduction of hydrogen into metal aregalvanic corrosion, chemical reactions of metal with acids, or with other chemicals (notably hydrogen sulfide insulfide stress cracking, or SSC, a process of importance for the oil and gas industries).

CounteractionsIf the metal has not yet started to crack, the condition can be reversed by removing the hydrogen source and causingthe hydrogen within the metal to diffuse out, possibly at elevated temperatures. Susceptible alloys, after chemical orelectrochemical treatments where hydrogen is produced, are often subjected to heat treatment to remove absorbedhydrogen. There is a 4-hour time limit for baking out entrapped hydrogen after acid treating the parts. This is thetime between the end of acid exposure and the beginning of the heating cycle in the baking furnace. This per SAEAMS 2759/9 Section 3.3.3.1 which calls out the correct procedure for eliminating entrapped hydrogen.In the case of welding, often pre- and post-heating the metal is applied to allow the hydrogen to diffuse out before it can cause any damage. This is specifically done with high-strength steels and low alloy steel such as the

Hydrogen embrittlement 97

chrome/molybdenum/vanadium alloys. Due to the time needed to re-combine hydrogen atoms into the harmfulhydrogen molecules, hydrogen cracking due to welding can occur over 24 hours after the welding operation iscompleted.Products such as ferrosilicates can be used to treat surfaces normally subject to hydrogen embrittlement in order toprevent it from taking place.

Related phenomenaIf steel is exposed to hydrogen at high temperatures, hydrogen will diffuse into the alloy and combine with carbon toform tiny pockets of methane at internal surfaces like grain boundaries and voids. This methane does not diffuse outof the metal, and collects in the voids at high pressure and initiates cracks in the steel. This selective leaching processis known as hydrogen attack, or high temperature hydrogen attack and leads to decarburization of the steel and lossof strength and ductility.Copper alloys which contain oxygen can be embrittled if exposed to hot hydrogen. The hydrogen diffuses throughthe copper and reacts with inclusions of Cu2O, forming H2O (water), which then forms pressurized bubbles at thegrain boundaries. This process can cause the grains to literally be forced away from each other, and is known assteam embrittlement (because steam is produced, not because exposure to steam causes the problem).

TestingThere are two ASTM standards for testing embrittlement due to hydrogen gas. The standard ASTM F1459-06Standard Test Method for Determination of the Susceptibility of Metallic Materials to Hydrogen Gas Embrittlement(HGE) Test [3] uses a diaphragm loaded with a differential pressure. The test ASTM G142-98(2004) Standard TestMethod for Determination of Susceptibility of Metals to Embrittlement in Hydrogen Containing Environments atHigh Pressure, High Temperature, or Both [4] uses a cylindrical tensile specimen tested into an enclosure pressurizedwith hydrogen or helium.Another ASTM standard exists for quantitatively testing for the Hydrogen Embrittlement threshold stress for theonset of Hydrogen-Induced Cracking due to platings and coatings from Internal Hydrogen Embrittlement (IHE) andEnvironmental Hydrogen Embrittlement (EHE) [5] - F1624-06 Standard Test Method for Measurement of HydrogenEmbrittlement Threshold in Steel by the Incremental Step Loading Technique. References: ASTM STP543,"Hydrogen Embrittlement Testing" [6] and ASTM STP 962,"Hydrogen Embrittlement: Prevention and Control."[7]• NACE TM0284-2003 (NACE International) Resistance to Hydrogen-Induced Cracking• ISO 11114-4:2005 (ISO)Test methods for selecting metallic materials resistant to hydrogen embrittlement [8].• ASTM F1940-07a [9]- Standard Test Method for Process Control Verification to Prevent Hydrogen Embrittlement

in Plated or Coated Fasteners• ASTM F519-06e2 [10]-Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of

Plating/Coating Processes and Service Environments

Hydrogen embrittlement 98

See also• Hydrogen analyzer• Hydrogen damage• Hydrogen piping• Hydrogen safety• Low hydrogen annealing• Nascent hydrogen

References[1] Jewett, R.P. (1973). Hydrogen Environment Embrittlement of Metals. NASA CR-2163.[2] Overview of interstate hydrogen pipeline systems-Pag.13 (http:/ / corridoreis. anl. gov/ documents/ docs/ technical/

APT_61012_EVS_TM_08_2. pdf)[3] http:/ / www. astm. org/ Standards/ F1459. htm[4] http:/ / www. astm. org/ Standards/ G142. htm[5] http:/ / www. astm. org/ cgi-bin/ SoftCart. exe/ STORE/ filtrexx40. cgi?U+ mystore+ yvst4574+ -L+ ASTMF1624:06+ / usr6/ htdocs/ astm.

org/ DATABASE. CART/ REDLINE_PAGES/ F1624. htm[6] http:/ / www. astm. org/ cgi-bin/ SoftCart. exe/ DIGITAL_LIBRARY/ STP/ SOURCE_PAGES/ STP543. htm?L+ mystore+ hsjb1846+

1193986997[7] http:/ / www. astm. org/ cgi-bin/ SoftCart. exe/ BOOKSTORE/ PUBS/ 652. htm?E+ mystore[8] http:/ / www. iso. org/ iso/ en/ CatalogueDetailPage. CatalogueDetail?CSNUMBER=41281& ICS1=23& ICS2=20& ICS3=30[9] http:/ / www. astm. org/ cgi-bin/ SoftCart. exe/ DATABASE. CART/ REDLINE_PAGES/ F1940. htm?L+ mystore+ yvst4574+ 1196145312[10] http:/ / www. astm. org/ cgi-bin/ SoftCart. exe/ STORE/ filtrexx40. cgi?U+ mystore+ yvst4574+ -L+ F519+ / usr6/ htdocs/ astm. org/

DATABASE. CART/ REDLINE_PAGES/ F519. htm

Further reading• ASM international, ASM Handbook #13: Corrosion, ASM International, 1998

External links• Hydrogen embrittlement, revisited by in situ electrochemical nanoindentation (http:/ / www. shaker. de/

online-Gesamtkatalog/ details. asp?ID=8533580& CC=50968& ISBN=3-8322-7834-6)• Hydrogen embrittlement (http:/ / www. uni-saarland. de/ fak8/ wwm/ research/ phd_barnoush/ hydrogen. pdf)• Corrosion-Doctors.org Hydrogen embrittlement (http:/ / www. corrosion-doctors. org/ Forms-HIC/ embrittlement.

htm)• Hydrogen purity plays a critical role (http:/ / www. hydrogen. energy. gov/ pdfs/ progress05/ v_a_4_adams. pdf)• A Sandia National Lab technical reference manual. (http:/ / www. sandia. gov/ matlsTechRef/ )

Hydrogen leak testing 99

Hydrogen leak testingHydrogen leak testing is the normal way in which a hydrogen pressure vessel or installation is checked for leaks orflaws. There are various tests.• The Hydrostatic test, The vessel is filled with a nearly incompressible liquid - usually water or oil - and examined

for leaks or permanent changes in shape. The test pressure is always considerably more than the operatingpressure to give a margin for safety, typically 150% of the operating pressure.

• The Burst test, The vessel is filled with a gas and tested for leaks. The test pressure is always considerably morethan the operating pressure to give a margin for safety, typically 200% or more of the operating pressure.

• The Helium leak test, The leak detection method uses helium (the lightest inert gas) as a tracer gas and detects itin concentrations as small as one part in 10 million. The helium is selected primarily because it penetrates smallleaks readily.

• Usually a vacuum inside the object is created with an external pump connected to the instrument.• Alternatively helium can be injected inside the product while the product itself is enclosed in a vacuum chamber

connected to the instrument. In this case Burst and leakage tests can be combined in one operation.• The Hydrogen sensor, The object is filled with a mixture of 5% hydrogen/ 95% nitrogen, (below 5.7% hydrogen

is non-flammable (ISO-10156). This is called typically a sniffing test. The handprobe connected to themicroelectronic hydrogen sensors is used to check the object. An audiosignal increases in proximity of a leak.Detection of leaks go down to 5x10-7 cubic centimeters per second [1]. Compared to the helium test: hydrogen ischeaper than helium, no need for a vacuum, the instrument could be cheaper.

See also• Hydrogen analyzer• Hydrogen piping• Hydrogen safety• Tubing (material)• Hydrogen station• Tracer-gas leak testing method

External links• Fibre gratings for hydrogen sensing [2]

• Wide-Range Hydrogen Sensor [3]

• Wireless sensor [4]

• / Hydrogen leak tester [5]

References[1] http:/ / www. reedlink. com/ SingleArticle~ContentId~11957~pub~IA. html[2] http:/ / ej. iop. org/ links/ q63/ ,,,vhEqvhL1tjxru6ReiaQ/ mst6_5_s31. pdf[3] http:/ / www. sandia. gov/ mstc/ technologies/ microsensors/ hydrogensensor. html[4] http:/ / news. ufl. edu/ 2006/ 05/ 24/ hydrogen-sensor/[5] http:/ / www. directindustry. com/ prod/ ateq/ hydrogen-leak-detector-7689-258533. html

Hydrogen safety 100

Hydrogen safetyHydrogen safety covers the safe use and handling of hydrogen. Hydrogen poses unique challenges due to its ease ofleaking, low-energy ignition, wide range of combustible fuel-air mixtures, buoyancy, and its ability to embrittlemetals that must be accounted for to ensure safe operation. Liquid hydrogen poses additional challenges due to itsincreased density and extremely low temperatures.

Hydrogen codes and standardsHydrogen codes and standards are codes and standards (RCS) for hydrogen fuel cell vehicles, stationary fuel cellapplications and portable fuel cell applications.Additional to the codes and standards for hydrogen technology products, there are codes and standards for hydrogensafety, for the safe handling of hydrogen[1] and the storage of hydrogen.• Standard for the installation of stationary fuel cell power systems (National Fire Protection Association)

GuidelinesThe current ANSI/AIAA standard for hydrogen safety guidelines is AIAA G-095-2004, Guide to Safety ofHydrogen and Hydrogen Systems[2] . As NASA has been one of the world's largest users of hydrogen, this evolvedfrom NASA's earlier guidelines, NSS 1740.16 (8719.16).[3] These documents cover both the risks posed by hydrogenin its different forms and how to ameliorate them.

Ignition• "Hydrogen-air mixtures can ignite with very low energy input, 1/10th that required igniting a gasoline-air

mixture. For reference, an invisible spark or a static spark from a person can cause ignition."• "Although the autoignition temperature of hydrogen is higher than those for most hydrocarbons, hydrogen's lower

ignition energy makes the ignition of hydrogen–air mixtures more likely. The minimum energy for spark ignitionat atmospheric pressure is about 0.02 millijoules."

Mixtures• "The flammability limits based on the volume percent of hydrogen in air at 14.7 psia (1 atm, 101 kPa) are 4.0 and

75.0. The flammability limits based on the volume percent of hydrogen in oxygen at 14.7 psia (1 atm, 101 kPa)are 4.0 and 94.0."

• "Explosive limits of hydrogen in air are 18.3 to 59 percent by volume"• "Flames in and around a collection of pipes or structures can create turbulence that causes a deflagration to evolve

into a detonation, even in the absence of gross confinement."(For comparison: Deflagration limit of gasoline in air: 1.4–7.6%; of acetylene in air[4] , 2.5% to 82%)

Hydrogen safety 101

Leaks• Leakage, diffusion, and buoyancy: These hazards result from the difficulty in containing hydrogen. Hydrogen

diffuses extensively, and when a liquid spill or large gas release occurs, a combustible mixture can form over aconsiderable distance from the spill location.

• Hydrogen, in both the liquid and gaseous states, is particularly subject to leakage because of its low viscosity andlow molecular weight (leakage is inversely proportional to viscosity). Because of its low viscosity alone, theleakage rate of liquid hydrogen is roughly 100 times that of JP-4 fuel, 50 times that of water, and 10 times that ofliquid nitrogen.

• Hydrogen leaks can support combustion at very low flow rates, as low as 4 micrograms/s.[5]

Liquid hydrogen• "Condensed and solidified atmospheric air, or trace air accumulated in manufacturing, contaminates liquid

hydrogen, thereby forming an unstable mixture. This mixture may detonate with effects similar to those producedby trinitrotoluene (TNT) and other highly explosive materials"

Liquid Hydrogen requires complex storage technology such as the special thermally insulated containers andrequires special handling common to all cryogenic substances. This is similar to, but more severe than liquid oxygen.Even with thermally insulated containers it is difficult to keep such a low temperature, and the hydrogen willgradually leak away. (Typically it will evaporate at a rate of 1% per day.[6])

PreventionHydrogen collects under roofs and overhangs, where it forms an explosion hazard; any building that contains apotential source of hydrogen should have good ventillation, strong ignition suppression systems for all electricdevices, and preferably be designed to have a roof that can be safely blown away from the rest of the structure in anexplosion. It also enters pipes and can follow them to their destinations. Hydrogen pipes should be located aboveother pipes to prevent this occurrence. Hydrogen sensors allow for rapid detection of hydrogen leaks to ensure thatthe hydrogen can be vented and the source of the leak tracked down. As in natural gas, an odorant can be added tohydrogen sources to enable leaks to be detected by smell. While hydrogen flames can be hard to see with the nakedeye, they show up readily on UV/IR flame detectors.

AccidentsHydrogen has been feared in the popular press as a relatively more dangerous fuel, and hydrogen in fact has thewidest explosive/ignition mix range with air of all the gases except acetylene. However this can be mitigated by thefact that hydrogen rapidly rises and disperses before ignition. Unless the escape is in an enclosed, unventilated area,it is unlikely to be serious. Hydrogen also usually rapidly escapes after containment breach. Additionally, hydrogenflames are difficult to see, so may be difficult to fight. An experiment performed at the University of Miamiattempted to counter this by showing that hydrogen escapes while gasoline remains by setting alight hydrogen- andpetrol-fuelled vehicles.[7]

In a more recent event, an explosion of compressed hydrogen during delivery at the Muskingum River Coal Plant(owned and operated by AEP) caused significant damage and killed one person.[8] [9] For more information onincidents involving hydrogen, visit the US DOE's Hydrogen Incident Reporting and Lessons Learned page. [10]

Hydrogen safety 102

See also• Hydrogen embrittlement• Hydrogen economy• Compressed hydrogen• Liquid hydrogen• Slush hydrogen• Metallic hydrogen

References[1] HySafe Initial Guidance for Using Hydrogen in Confined Spaces (http:/ / www. hysafe. org/ download/ 1710/ HYSAFE_D113_version_1. 1.

pdf)[2] "AIAA G-095-2004, Guide to Safety of Hydrogen and Hydrogen Systems" (http:/ / aero-defense. ihs. com/ document/ abstract/

GFEIHBAAAAAAAAAA) (PDF). AIAA. . Retrieved 2008-07-28.[3] Gregory, Frederick D. (Feb. 12, 1997). "Safety Standard for Hydrogen and Hydrogen Systems" (http:/ / www. hq. nasa. gov/ office/ codeq/

doctree/ canceled/ 871916. pdf) (PDF). NASA. . Retrieved 2008-05-09.[4] http:/ / www. msha. gov/ alerts/ hazardsofacetylene. htm[5] M.S. Butler, C.W. Moran, Peter B. Sunderland, R.L. Axelbaum, Limits for Hydrogen Leaks that Can Support Stable Flames, International

Journal of Hydrogen Energy 34 (2009) 5174-5182.[6] http:/ / www. almc. army. mil/ alog/ issues/ MayJun00/ MS492. htm[7] "Hydrogen Car Fire Surprise" (http:/ / www. evworld. com/ article. cfm?storyid=482). January 18, 2003. . Retrieved 2008-05-09.[8] Williams, Mark (January 8, 2007). ""Ohio Power Plant Blast Kills 1, Hurts 9"" (http:/ / www. washingtonpost. com/ wp-dyn/ content/ article/

2007/ 01/ 08/ AR2007010800350. html). Associated Press. . Retrieved 2008-05-09.[9] "Muskingum River Plant Hydrogen Explosion January 8, 2007" (http:/ / web. archive. org/ web/ 20080409155509/ http:/ / www. eei. org/

meetings/ nonav_2007-04-29-cs/ Citations_Accident_Review. pdf) (PDF). American Electric Power. November 11, 2006. Archived from theoriginal (http:/ / www. eei. org/ meetings/ nonav_2007-04-29-cs/ Citations_Accident_Review. pdf) on 2008-04-09. . Retrieved 2008-05-09.

[10] ""Hydrogen Incident Reporting and Lessons Learned"" (http:/ / www. h2incidents. org/ ). .

External links• Hysafe (http:/ / www. hysafe. org/ )• Hydrogen and fuelcell safety (http:/ / www. hydrogenandfuelcellsafety. info)• DOE-Hydrogen safety for First Responders (http:/ / www. ehammertraining. us/ energy/ h2_login/ login. cfm)• First Responders - Emergency Response Guidebook - Guide 115 (http:/ / hazmat. dot. gov/ pubs/ erg/

erg2008_eng. pdf)• World's First Higher Educational Programme in Hydrogen Safety Engineering (http:/ / www. hysafe. org/

MScHSE)

103

Fuel

Timeline of hydrogen technologiesTimeline of hydrogen technologies A timeline of the history of hydrogen technology.

Timeline

1600s• 1625 - First description of hydrogen by Johann Baptista van Helmont. First to use the word "gas".• 1650 - Turquet de Mayerne obtained by the action of dilute sulphuric acid on iron a gas or "inflammable air".• 1662 - Boyle's law (gas law relating pressure and volume)• 1670 - Robert Boyle produced hydrogen by reacting metals with acid.• 1672 - "New Experiments touching the Relation between Flame and Air" by Robert Boyle.• 1679 - Denis Papin - safety valve

1700s• 1700 - Nicolas Lemery showed that the gas produced in the sulfuric acid/iron reaction was explosive in air• 1755 - Joseph Black confirmed that different gases exist. / Latent heat• 1766 - Henry Cavendish published in "On Factitious Airs" a description of "dephlogisticated air" by reacting zinc

metal with hydrochloric acid and isolated a gas 7 to 11 times lighter than air.• 1774 - Joseph Priestley isolated and categorized oxygen.• 1780 - Felice Fontana discovers the water gas shift reaction• 1783 - Antoine Lavoisier gave hydrogen its name (Gk: hydro = water, genes = born of)• 1783 - Jacques Charles made the first flight with his hydrogen balloon "La Charlière".• 1783 - Antoine Lavoisier and Pierre Laplace measured the heat of combustion of hydrogen using an ice

calorimeter.• 1784 - Jean-Pierre Blanchard, attempted a dirigible hydrogen balloon, but it would not steer.• 1784 - The invention of the Lavoisier Meusnier iron-steam process[1] , generating hydrogen by passing water

vapor over a bed of red-hot iron at 600 °Cdoi:10.1080/00033798300200381.• 1785 - Jean-François Pilâtre de Rozier built the hybrid Rozière balloon.• 1787 - Charles's law (Gas law, relating volume and temperature)• 1789 - Jan Rudolph Deiman and Adriaan Paets van Troostwijk using a electrostatic machine and a Leyden jar for

the first electrolysis of water.

Timeline of hydrogen technologies 104

1800s• 1800 - William Nicholson and Anthony Carlisle decomposed water into hydrogen and oxygen by electrolysis

with a voltaic pile.• 1800 - Johann Wilhelm Ritter duplicated the experiment with a rearranged set of electrodes to collect the two

gases separately.• 1806 - François Isaac de Rivaz built the first internal combustion engine powered by a mixture of hydrogen and

oxygen.• 1809 - Thomas Foster observed with a theodolite the drift of small free pilot balloons filled with "inflammable

gas"[2] [3]

• 1809 - Gay-Lussac's law (Gas law, relating temperature and pressure)• 1811 - Amedeo Avogadro - Avogadro's law a gas law• 1819 - Edward Daniel Clarke invented the hydrogen gas blowpipe.• 1820 - W. Cecil wrote a letter "On the application of hydrogen gas to produce a moving power in machinery"[4]

[5]

• 1823 - Goldsworthy Gurney demonstrated Limelight.• 1823 - Döbereiner's Lamp a lighter invented by Johann Wolfgang Döbereiner.• 1823 - Goldsworthy Gurney devised an oxy-hydrogen blowpipe.• 1824 - Michael Faraday invented the rubber balloon.• 1826 - Thomas Drummond built the Drummond Light.• 1826 - Samuel Brown tested his internal combustion engine by using it to propel a vehicle up Shooter's Hill• 1834 - Michael Faraday published Faraday's laws of electrolysis.• 1834 - Benoît Paul Émile Clapeyron - Ideal gas law• 1836 - John Frederic Daniell invented a primary cell in which hydrogen was eliminated in the generation of the

electricity.• 1839 - Christian Friedrich Schönbein published the principle of the fuel cell in the "Philosophical Magazine".• 1839 - William Robert Grove developed the Grove cell.• 1842 - William Robert Grove developed the first fuel cell (which he called the gas voltaic battery)• 1849 - Eugene Bourdon - Bourdon gauge (manometer)• 1863 - Etienne Lenoir made a test drive from Paris to Joinville-le-Pont with the 1-cylinder, 2-stroke Hippomobile.• 1866 - August Wilhelm von Hofmann invents the Hofmann voltameter for the electrolysis of water.• 1873 - Thaddeus S. C. Lowe - Water gas, the process used the water gas shift reaction.• 1874 - Jules Verne - The Mysterious Island, "water will one day be employed as fuel, that hydrogen and oxygen

of which it is constituted will be used"[6]

• 1884 - Charles Renard and Arthur Constantin Krebs launch the airship La France.• 1885 - Zygmunt Florenty Wróblewski published hydrogen's critical temperature as 33 K; critical pressure, 13.3

atmospheres; and boiling point, 23 K.• 1889 - Ludwig Mond and Carl Langer coined the name fuel cell and tried to build one running on air and Mond

gas.• 1893 - Friedrich Wilhelm Ostwald experimentally determined the interconnected roles of the various components

of the fuel cell.• 1895 - Hydrolysis• 1896 - Jackson D.D. and Ellms J.W., hydrogen production by microalgae (Anabaena)• 1896 - Leon Teisserenc de Bort carries out experiments with high flying instrumental weather balloons[7] .• 1897 - Paul Sabatier facilitated the use of hydrogenation with the discovery of the Sabatier reaction.• 1898 - James Dewar liquefied hydrogen by using regenerative cooling and his invention, the vacuum flask at the

Royal Institute of London.• 1899 - James Dewar collected solid hydrogen for the first time.

Timeline of hydrogen technologies 105

1900s• 1900 - Count Ferdinand von Zeppelin launched the first hydrogen-filled Zeppelin LZ1 airship.• 1901 - Wilhelm Normann introduced the hydrogenation of fats.• 1903 - Konstantin Eduardovich Tsiolkovskii published "The Exploration of Cosmic Space by Means of Reaction

Devices"[8]

• 1907 - Lane hydrogen producer• 1909 - Count Ferdinand Adolf August von Zeppelin made the first long distance flight with the Zeppelin LZ5.• 1909 - Linde-Frank-Caro process• 1910 - The first Zeppelin passenger flight with the Zeppelin LZ7.• 1910 - Fritz Haber patented the Haber process.• 1912 - The first scheduled international Zeppelin passenger flights with the Zeppelin LZ13.• 1919 - The first Atlantic crossing by airship with the Beardmore HMA R34.• 1920 - Hydrocracking, a plant for the commercial hydrogenation of brown coal is commissioned at Leuna in

Germany[9] .• 1923 - Steam reforming, the first synthetic methanol is produced by BASF in Leuna• 1923 - J. B. S. Haldane envisioned in Daedalus; or, Science and the Future "great power stations where during

windy weather the surplus power will be used for the electrolytic decomposition of water into oxygen andhydrogen."

• 1926 - Partial oxidation, Vandeveer and Parr at the University of Illinois used oxygen in the place of air for theproduction of syngas.

• 1926 - Cyril Norman Hinshelwood described the phenomenon of chain reaction.• 1926 - Umberto Nobile made the first flight over the north pole with the hydrogen airship Norge• 1929 - Paul Harteck and Karl Friedrich Bonhoeffer achieve the first synthesis of pure parahydrogen.• 1930 - Rudolf Erren - Erren engine - GB patent GB364180 - Improvements in and relating to internal combustion

engines using a mixture of hydrogen and oxygen as fuel[10]

• 1935 - Eugene Wigner and H.B. Huntington predicted metallic hydrogen.• 1937 - The Zeppelin LZ 129 Hindenburg was destroyed by fire.• 1937 - The Heinkel HeS 1 experimental gaseous hydrogen fueled centrifugal jet engine is tested at Hirth in

March- the first working jet engine• 1937 - The first hydrogen-cooled turbogenerator went into service at Dayton, Ohio.• 1938 - The first 240 km hydrogen pipeline Rhine-Ruhr [11] .• 1938 - Igor Sikorsky from Sikorsky Aircraft proposed liquid hydrogen as a fuel.• 1939 - Rudolf Erren - Erren engine - US patent 2,183,674 - Internal combustion engine using hydrogen as fuel• 1939 - Hans Gaffron discovered that algae can switch between producing oxygen and hydrogen.• 1943 - Liquid hydrogen is tested as rocket fuel at Ohio State University.• 1943 - Arne Zetterström describes hydrox• 1949 - Hydrodesulfurization (Catalytic reforming is commercialized under the name Platforming process)• 1952 - Hydrogen maser• 1952 - Non-Refrigerated transport Dewar• 1955 - W. Thomas Grubb modified the fuel cell design by using a sulphonated polystyrene ion-exchange

membrane as the electrolyte.• 1957 - Pratt & Whitney's model 304 jet engine using liquid hydrogen as fuel tested for the first time as part of the

Lockheed CL-400 Suntan project.[12]

• 1957 - The specifications for the U-2 a double axis liquid hydrogen semi-trailer were issued[13] .• 1958 - Leonard Niedrach devised a way of depositing platinum onto the membrane, this became known as the

Grubb-Niedrach fuel cell• 1958 - Allis-Chalmers demonstrated the D 12, the first 15 kW fuel cell tractor[14] .

Timeline of hydrogen technologies 106

• 1959 - Francis Thomas Bacon built the Bacon Cell, the first practical 5 kW hydrogen-air fuel cell to power awelding machine.

• 1960 - Allis-Chalmers builds the first fuel cell forklift[15]

• 1961 - RL-10 liquid hydrogen fuelled rocket engine first flight• 1964 - Allis-Chalmers built a 750-watt fuel cell to power a one-man underwater research vessel[16] .• 1965 - The first commercial use of a fuel cell in Project Gemini.• 1965 - Allis-Chalmers builds the first fuel cell golf carts.• 1966 - Slush hydrogen• 1966 - J-2 (rocket engine) liquid hydrogen rocket engine flies• 1967 - Akira Fujishima discovers the Honda-Fujishima effect which is used for photocatalysis in the

photoelectrochemical cell.• 1967 - Hydride compressor• 1970 - Nickel hydrogen battery [17]

• 1970 - John Bockris or Lawrence W. Jones coined the term hydrogen economy [18] [19]

• 1973 - The 30 km hydrogen pipeline in Isbergues• 1973 - Linear compressor• 1975 - John Bockris - Energy The Solar-Hydrogen Alternative - ISBN 0470084294• 1979 - HM7B rocket engine• 1981 - Space Shuttle main engine first flight• 1990 - The first solar-powered hydrogen production plant Solar-Wasserstoff-Bayern became operational.• 1996 - Vulcain rocket engine• 1997 - Anastasios Melis discovered that the deprivation of sulfur will cause algae to switch from producing

oxygen to producing hydrogen• 1998 - Type 212 submarine• 1999 - Hydrogen pinch

2000s• 2000 - Peter Toennies demonstrates superfluidity of hydrogen at 0.15 K• 2001 - The first type IV hydrogen tanks for compressed hydrogen at 700 Bar (10000 PSI) were demonstrated.• 2002 - Type 214 submarine• 2004 - DeepC• 2005 - Ionic liquid piston compressor

See also• Timeline of low-temperature technology• List of timelines

References[1] 1784 Experiments (http:/ / moro. imss. fi. it/ lavoisier/ Lavoisier_Experiments2Gb. asp?anno=1784)[2] 1809 - Fleming, History of Meteorology 25 Pag. 25 (http:/ / www. colby. edu/ sts/ st215/ history_of_meteorology. pdf)[3] 1809 - Pilot balloon resources (http:/ / www. csulb. edu/ ~mbrenner/ history. htm)[4] 1820 Cecil engine (http:/ / www. eng. cam. ac. uk/ DesignOffice/ projects/ cecil/ engine. html)[5] 1820 Cecil the letter (http:/ / www. eng. cam. ac. uk/ DesignOffice/ projects/ cecil/ cecil. pdf)[6] 1874 - Jules Verne, The Mysterious Island (http:/ / www. online-literature. com/ verne/ mysteriousisland/ 33/ )[7] 1896 Weather balloon (http:/ / www. metoffice. gov. uk/ corporate/ pressoffice/ anniversary/ balloon. html)[8] Tsiolkovsky's Исследование мировых пространств реактивными приборами - The Exploration of Cosmic Space by Means of Reaction

Devices (Russian paper) (http:/ / epizodsspace. testpilot. ru/ bibl/ dorev-knigi/ ciolkovskiy/ issl-03st. html)[9] 1920 - Hydrocracking (http:/ / www. cheresources. com/ refining5. shtml)

Timeline of hydrogen technologies 107

[10] Improvements in and relating to internal combustion engines using a mixture of hydrogen and oxygen as fuel (http:/ / www. wikipatents.com/ gb/ 0364180. html)

[11] The Technological Steps of Hydrogen Introduction - pag 24 (http:/ / www. storhy. net/ train-in/ PDF-TI/03_StorHy-Train-IN-Session-1_3_JToepler. pdf)

[12] Sloop, John L. (1978). Liquid hydrogen as a propulsion fuel, 1945-1959.(The NASA history series) (NASA SP-4404) (http:/ / www. hq. nasa.gov/ office/ pao/ History/ SP-4404/ ch8-9. htm). National Aeronautics and Space Administration. pp. 154–157. .

[13] NASA-LIQUID HYDROGEN AS A PROPULSION FUEL,1945-1959 (http:/ / history. nasa. gov/ SP-4404/ ch8-11. htm)[14] 1958 D 12 - Pag. 7 (http:/ / www. fuelcelltoday. com/ media/ pdf/ archive/ Article_1152_Fuel Cell History part 2 with illustrations. pdf)[15] 1960 -Fleet module Pag.3 (http:/ / www. hydrogenassociation. org/ general/ fleet_Module7. pdf)[16] 1964 Allis Chalmers Pag.1 (http:/ / www. aesc-inc. com/ download/ Ishii_Fuel_Cell_Paper. pdf)[17] Nickel-Hydrogen Battery Technology—Development and Status (http:/ / pdf. aiaa. org/ jaPreview/ JE/ 1982/ PVJAPRE62569. pdf)[18] History of Hydrogen (http:/ / www. getenergysmart. org/ Files/ Schools/ Hydrogen/ 3HistoryofHydrogen. pdf)[19] Lawrence W. Jones Toward a liquid hydrogen fuel economy (http:/ / deepblue. lib. umich. edu/ handle/ 2027. 42/ 5800), University of

Michigan Engineering Technical Report UMR2320, March 13, 1970

Biohydrogen

Microbial hydrogen production.

Biohydrogen is defined as hydrogen produced biologically, most commonlyby bacteria. Biohydrogen is a potential biofuel obtainable from waste organicmaterials.[1] More generally the term biohydrogen describes the hydrogenproduced via a number of biological processes.

Introduction

Currently, there is a huge demand of the chemical hydrogen. There is no logon the production volume and use of hydrogen world-wide. However theestimated consumption of hydrogen is expected to reach 900 billion cubicmeters in 2011[2]

Refineries are large-volume producers and consumers of hydrogen. Today96% of all hydrogen is derived from fossil fuels, with 48% from natural gas,30% from hydrocarbons, 18% from coal and about 4% from electrolysis.Oil-sands processing, gas-to-liquids and coal gasification projects that areongoing, require a huge amount of hydrogen and is expected to boost the requirement significantly within the nextfew years. Environmental regulations implemented in most countries, increase the hydrogen requirement at refineriesfor gas-line and diesel desulfurization[2] [3]

A important future application of hydrogen could be as an alternative for fossil fuels, once the oil deposits aredepleted.[4] This application is however dependent on the development of storage techniques to enable properstorage, distribution and combustion of hydrogen.[4] If the cost of hydrogen production, distribution, and end-usertechnologies decreases, hydrogen as a fuel could be entering the market in 2020.[5]

Industrial fermentation of hydrogen, or whole-cell catalysis, requires a limited amount of energy, since fission ofwater is achieved with whole cell catalysis, to lower the activation energy.[6] This allows hydrogen to be producedfrom any organic material that can be derived through whole cell catalysis since this process does not depend on theenergy of substrate.

Biohydrogen 108

Process requirementsIf hydrogen by fermentation is to be introduced as an industry, the fermentation process will dependent on organicacids as substrate for photo-fermentation. The organic acids are necessary for high hydrogen production rates.[6] [7]

The organic acids can be derived from any organic material source such as sewage waste waters or agriculturalwastes.[7] The most important organic acids are acetic acid (HAc), butyric acid (HBc) and propionic acid (HPc). Ahuge advantage is that production of hydrogen by fermentation does not require glucose as substrate.[7]

The fermentation of hydrogen has to be a continuous fermentation process, in order sustain high production rates,since the amount of time for the fermentation to enter high production rates are in days.[6]

FermentationSeveral strategies for the production of hydrogen by fermentation in lab-scale has been found in literature. Howeverno strategies for industrial-scale productions has been found. In order to define a industrial-scale production, theinformation from lab-scale experiments has been scaled to a industrial-size production on a theoretical basis. Ingeneral, the method of hydrogen fermentation are referred to in three main categories. The first category isdark-fermentation, which is fermentation, which does not involve light. The second category is photo-fermentation,which is fermentation, which require light as the source of energy. The third is combined-fermentation, which refersto the two fermentations combined.

Dark-fermentationThere are several bacteria with a potential for hydrogen production. The Gram-positive bacteria of the Clostridiumgenus, is promising because it has a natural high hydrogen production rate. In addition, it is fast growing and capableof forming spores, which make the bacteria easy to handle in industrial application.[8]

Species of the Clostridium genus allow hydrogen production in mixed cultures, under mesophilic or thermophilicconditions within a pH range of 5.0 to 6.5.[8] Dark-fermentation with mixed cultures seems promising since a mixedbacterial environment within the fermenter, allows cooperation of different species to efficiently degrade and convertorganic waste materials into hydrogen, accompanied by the formation of organic acids.[8]

For the fermentation to be sustainable in industrial-scale, we need to be able to control the bacterial environmentinside the fermenter. If the fermentation process is feed with sugar waste, we have a risk, that the feed will containmicro-organisms, which could change the bacterial environment inside the fermenter.[9] A way to prevent harmfulmicro-organisms from gaining control of the bacterial environment inside the fermenter could be through addition ofprobiotics which favors or promotes the intended bacterial environment and prevents harmful micro-organisms fromgaining control of the fermenter.[9]

The dilution rate has to ensure that the amount of biomass inside the fermenter is stable and that the organic acids areremoved properly with the outlet stream. The organic acids are toxic to the bacteria and huge amounts willinterrupted the fermentation process.[8] This fermentation of hydrogen is accompanied production of carbon-dioxidewhich can be separated from hydrogen with a passive separation process.[10]

The fermentation will convert some of the sugar waste into biomass instead of hydrogen.[8] The biomass is howevera carbohydrate-rich by-product which can be fed back into the fermenter, to ensure that the process is sustainable.[11]

Fermentation of hydrogen by dark-fermentation is restricted by incomplete degradation of organic material, intoorganic acids and this is why we need the photo-fermentation.[8]

The separation of organic acids from biomass in the outlet stream can be done with a settler tank in the outlet stream,where the sludge (biomass) is pumped back into the fermenter to increase the rate of hydrogen production.[11]

Biohydrogen 109

Photo-fermentationPhoto-fermentation refers to the method of fermentation where light is required as the source of energy. Thisfermentation relies on photosynthesis to maintain the cellular energy levels. Fermentation by photosynthesiscompared to other fermentations has the advantage of light as the source of energy instead of sugar. Sugars areusually available in limited quantities.All plants, algae and some bacteria are capable of utilizing light as the source of energy. Cyanobacteria which is analgae, is frequently mentioned capable of hydrogen production by photosynthesis.[12] However the purplenon-sulphur (PNS) bacteria genus Rhodobacter, holds significant promise for the production of hydrogen byfermentation.[6]

Studies have shown that Rhodobacter sphaeroides is highly capable of hydrogen production while feeding onorganic acids, consuming 98% to 99% of the organic acids during hydrogen production.[6]

As for the dark-fermentation the separation of biomass can be done with a settler tank in the outlet stream, where thesludge (biomass) is pumped back into the fermenter to increase the rate of hydrogen production .[11]

Currently there is limited experience with photo-fermentation at industrial-scale. Photo-fermentation require light inthe ultra-violet (UV) range up to 400 nm.[13] The distribution of light within the industrial scale photo-fermenter hasto be designed to prevent self-shading inside the fermenter and to ensure sustainable hydrogen production.A method to ensure proper light distribution and limit self-shading within the fermenter, could be to distribute thelight with an optic fiber where light is transferred into the fermenter and distributed from within the fermenter.[14]

Photo-fermentation with Rhodobacter sphaeroides require mesophilic conditions.[15] The optic fiber will transferlight and thus heat into the fermenter, but the heat transferred is limited.[14]

The design with an ultra-violent light-source has a huge advantage to other fermentations since ultra-violent light hasthe potential to eliminate foreign micro-organisms and to prevent contamination. This will limit the need of cleaningprocedures. However the production rates with photo-fermentation is not as high as with dark-fermentation.

Combined fermentationCombining dark- and photo-fermentation has shown to be the most efficient method to produce hydrogen throughfermentation.[16] The combined fermentation allows the organic acids produced during dark-fermentation of wastematerials, to be used as substrate in the photo-fermentation process.[6]

For industrial fermentation of hydrogen to be economical feasible, by-products of the fermentation process has to beminimized. Combined fermentation has the unique advantage of allowing reuse of the otherwise useless chemical,organic acids, through photosynthesis.As the method for hydrogen production, this method currently holds significant promise.[6]

Metabolic processesThe metabolic process for hydrogen production are dependent on the reduction of the metabolite ferredoxin.[17]

4H+ + ferredoxin(ox) → ferredoxin(red) + 2 H2

For this process to run, ferredoxin has to be recycled through oxidation. The recycling process is dependent on thetransfer of electrons from nicotinamide adenine dinucleotide (NADH) to ferredoxin.[17]

2 ferredoxin(red) + 2 NADH → 2 ferredoxin(ox) + H2

The enzymes that catalyse this recycling process are referred to as hydrogen-forming enzymes and have complexmetalloclusters in their active site and require several maturation proteins to attain their active form.[17] Thehydrogen-forming enzymes are inactivated by molecular oxygen and most be separated from oxygen, to producehydrogen.[17]

Biohydrogen 110

The three main classes of hydrogen-forming enzymes are [FeFe]-hydrogenase, [NiFe]-hydrogenase andnitrogenase.[17] These enzymes behaves differently in dark-fermentation with Clostridium and photo-fermentationwith Rhodobacter. The interplay of these enzymes are the key in hydrogen production by fermentation.

Clostridium

The interplay of the hydrogen-forming enzymes in Clostridium is very unique with little or no involvement ofnitrogenase. The hydrogen production in this bacteria is mostly due to [FeFe]-hydrogenase, which activity is ahundred times higher than [NiFe]-hydrogenase and a thousand times higher than nitrogenase. [FeFe]-hydrogenasehas a Fe-Fe catalytic core with a variety of electron donors and acceptors.[6] [17]

The enzyme [NiFe]-hydrogenase in Clostridium, catalyse a reversible oxidation of hydrogen. [NiFe]-hydrogenase isresponsible for hydrogen uptake, utilizing the electrons from hydrogen for cellular maintenance.[17]

In Clostridium, glucose is broken down into pyruvate and nicotinamide adenine dicleotide (NADH). The formedpyruvate is then further converted to acetyl-CoA and hydrogen by pyruvate ferredoxin oxidoreductase with thereduction of ferredoxin.[17] Acetyl-CoA is then converted to acetate, butyrate and propionate.[17] [18]

Acetate fermentation processes are well understood and have a maximum yield of 4 mol hydrogen pr. mol glucose.[6]

The yield of hydrogen from the conversion of acetyl-CoA to butyrate, has half the yield as the conversion toacetate.[6] [17] In mixed cultures of Clostridium the reaction is a combined production of acetate, butyrate andpropionate.[16] The organic acids which are the by-product of fermentation with Clostridium, can be furtherprocessed as substrate for hydrogen production with Rhodobacter.

Rhodobacter

The purple non-sulphur bacteria Rhodobacter spharoids is able to produce hydrogen from organic acids andultra-violet light.[17] The photo-system required for hydrogen production in Rhodobacter (PS-I), differ from itsoxygenic photosystem (PS-II) due to the requirement of organic acids and the inability to oxidize water.[17]

In Rhodobacter, the hydrogen production is due to catalysis by nitrogenase. The production of hydrogen by[FeFe]-hydrogenase is less than 10 times the hydrogen uptake by [NiFe]-hydrogenase.[19]

The interplay of hydrogenase and nitrogenase in this bacteria is responsible for the production of hydrogen andrequire nitrogen-deficient conditions to produce hydrogen.[17] [19]

Rhodobacter hydrogen metabolism

The main photosynthetic membrane complex is PS-I which accountsfor most of the light-harvest. The photosynthetic membrane complexPS-II produces oxygen, which inhibit hydrogen production and thuslow partial pressures of oxygen most be sustained duringfermentation.[17]

To attain high production rates of hydrogen, the hydrogen productionby nitrogenase has to exceed the hydrogen uptake by hydrogenase.[19]

The substrate is oxidized through the tricarboxylic acids circle and theproduced electrons are transferred to the nitrogenase catalysedreduction of protons to hydrogen, through the electron transport chain.[17] [19]

Biohydrogen 111

LED-fermenterA cheap way to build a industrial-size photo-fermenter could be to build a fermenter with ultra-violet light emittingdiodes (UV-LED) as light source. This design prevents self-shading within the fermenter, require limited energy tomaintain photosynthesis and has very low installation costs. This design would also allow cheap models to be builtfor educational purpose.

Metabolic engineeringThere is a huge potential for improving hydrogen yield by metabolic engineering. The bacteria Clostridium could beimproved for hydrogen production by disabling the uptake hydrogenase, or disabling the oxygen system. This willmake the hydrogen production robust and increase the hydrogen yield in the dark-fermentation step.The photo-fermentation step with Rhodobacter, is the step which is likely to gain the most from metabolicengineering. An option could be to disable the uptake-hydrogenase or to disable the photosynthetic membranesystem II (PS-II). Another improvement could be to decrease the expression of pigments, which shields of thephoto-system.

See also• Hyvolution• Biological hydrogen production (Algae)• Photobiology• Electrohydrogenesis• Microbial fuel cell• Caldicellulosiruptor saccharolyticus

References[1] Demirbas, A. (2009). Biohydrogen: For Future Engine Fuel Demands. Trabzon: Springer. ISBN 1848825102[2] Stefan Schlag, Bala Suresh, Masahiro Yoneyama (October 2007). "SRI Consulting CEH Report – Hydrogen" (http:/ / www. sriconsulting.

com/ CEH/ Public/ Reports/ 743. 5000/ ). SRI Consulting. . Retrieved 2010-07-01.[3] "The National Hydrogen Association" (http:/ / www. hydrogenassociation. org/ general/ faqs. asp#howmuchproduced).

Hydrogenassociation.org. 2004-08-13. . Retrieved 2010-07-01.[4] "Transport and the Hydrogen Economy" (http:/ / www. world-nuclear. org/ info/ inf70. html). World-nuclear.org. . Retrieved 2010-07-01.[5] The iea energy technology essentials are regularly-updated briefs that draw together the best-available, consolidated information on energy

technologies from the iea network, April 2007.[6] Tao, Yongzhen; Chen, Yang; Wu, Yongqiang; He, Yanling; Zhou, Zhihua (February 2007). "High hydrogen yield from a two-step process of

dark- and photo-fermentation of sucrose" (http:/ / www. sciencedirect. com/ science/ article/ B6V3F-4KGPP8H-1/ 2/a2e03311e524ba2baeb47e720d9c47e5). International Journal of Hydrogen Energy 32 (2): 200–206. doi:10.1016/j.ijhydene.2006.06.034.ISSN 0360-3199. .

[7] Kapdan, Ilgi Karapınar; Kargı, Fikret (2006). "Biohydrogen production from waste materials" (http:/ / www. ichet. org/ ihec2005/ files/manuscripts/ Kargi F. -Tr. pdf). Enzyme and Microbial Technology. .

[8] Krupp, M.; Widmann, R (May 2009). "Biohydrogen production by dark fermentation: Experiences of continuous operation in large labscale". International Journal of Hydrogen Energy 34 (10, Sp. Iss.SI): 4509–4516. doi:10.1016/j.ijhydene.2008.10.043.

[9] Verschuere, L; Rombaut,, G; Sorgeloos, P; Verstraete, W (December 2000). "Probiotic bacteria as biological control agents in aquaculture".Microbiology and Molecular Biology Reviews 64 (4): 655+. doi:10.1128/MMBR.64.4.655-671.2000.

[10] Watanabe, Hisanori; Yoshino, Hidekichi (May 2010). "Biohydrogen using leachate from an industrial waste landfill as inoculum".Renewable Energy 35 (5): 921–924. doi:10.1016/j.renene.2009.10.033.

[11] Villadsen, John; Nielsen, Jens Høiriis; Lidén, Gunnar (2003). Bioreaction Engineering Principles (http:/ / books. google. com/?id=htUeM34b7KgC& lpg=PP1& dq=Bioreaction Engineering Principles& pg=PP1#v=onepage& q) (2 ed.). Springer. ISBN 9780306473494..

[12] Lee, Jae-Hwa; Lee, Dong-Geun; Park, Jae-Il; Kim, Ji-Youn (JAN 2010). "Biohydrogen production from a marine brown algae and itsbacterial diversity". Korean Journal of Chemical Engineering 27 (1): 187–192. doi:10.1007/s11814-009-0300-x.

Biohydrogen 112

[13] Kahn, Amanda E.; Durako, Michael J. (October 2009). "Wavelength-specific photo-synthetic responses of Halophila johnsonii frommarine-influenced versus river-influenced habitats". Aquatic Botany 91 (3): 245–249. doi:10.1016/j.aquabot.2009.06.004.

[14] THE NORTH STATE, www.thenorthstate.com. "Sunlight Direct" (http:/ / www. sunlight-direct. com). Sunlight Direct. . Retrieved2010-07-01.

[15] Nath, K; Kumar, A; Das, D (September 2005). "Hydrogen production by Rhodobacter sphaeroides strain OU001 using spent media ofEnterobacter cloacae strain DM11". Applied Microbiology and Biotechnology 68 (4): 533–541. doi:10.1007/s00253-005-1887-4.PMID 15666144.

[16] Yang, Honghui; Guo,, Liejin; Liu, Fei (March 2010). "Enhanced bio-hydrogen production from corncob by a two-step process: Dark- andphoto-fermentation". Bioresource Technology 101 (6): 2049–2052. doi:10.1016/j.biortech.2009.10.078. PMID 19963373.

[17] Mathews, Juanita; Wang, Guangyi (September 2009). "Metabolic pathway engineering for enhanced biohydrogen production". InternationalJournal of Hydrogen Energy 34 (17, Sp. Iss. SI): 7404–7416. doi:10.1016/j.ijhydene.2009.05.078.

[18] "KEGG PATHWAY: Pyruvate metabolism - Clostridium acetobutylicum" (http:/ / www. genome. jp/ kegg-bin/ show_pathway?cac00620).Genome.jp. . Retrieved 2010-07-01.

[19] Koku, H; Eroglu, I; Gunduz, U; Yucel, M; Turker, L (2002). "Aspects of the metabolism of hydrogen production by Rhodobactersphaeroides". International Journal of Hydrogen Energy 27 (11-12): 1315–1329. doi:10.1016/S0360-3199(02)00127-1.

External links• Fermentation of hydrogen (http:/ / www. youtube. com/ watch?v=wKfx3-CpqTQ)• Production of hydrogen with bacteria (http:/ / www. youtube. com/ watch?v=n_h08Vbdjt4)• 1999 - Biohydrogen RITE Biological Hydrogen Program (http:/ / www. springerlink. com/ content/

p3u912048n600315/ )• GTL (http:/ / genomicsgtl. energy. gov/ benefits/ biohydrogen. shtml)• EU & Dutch Biohydrogen research page (http:/ / www. biohydrogen. nl)• wasteintoenergy.org (http:/ / www. wasteintoenergy. org)• University of California Davis -New Technology Turns Food Leftovers Into Electricity, Vehicle Fuels (http:/ /

www. news. ucdavis. edu/ search/ news_detail. lasso?id=7915)• Onsite Power Systems (http:/ / www. onsitepowersystems. com/ )• "Appendix 2: Biohydrogen" (http:/ / completebiogas. com/ BiogasHandbook_A02_biohydrogen. pdf) from The

Complete Biogas Handbook• BBSRC- Our Science- Bacteria Make Light Work of Hydrogen Production (http:/ / www. bbsrc. ac. uk/ science/

our_science_explained/ 0906_bacteria_make_light_work_of_hydrogen_production. html)• Biowaste2energy Ltd is applying biohydrogen (http:/ / www. bw2e. com)

Hydrogen production 113

Hydrogen productionHydrogen production is the industrial method for generating hydrogen. Currently the dominant technology fordirect production is steam reforming from hydrocarbons. Hydrogen is also produced as a byproduct of otherprocesses and managed with hydrogen pinch[1] . Many other methods are known including electrolysis andthermolysis. The discovery and development of less expensive methods of production of bulk hydrogen is relevant tothe establishment of a hydrogen economy.[2]

Hydrogen waste streamHydrogen is used for the creation of ammonia for fertilizer via the Haber process, converting heavy petroleumsources to lighter fractions via hydrocracking and petroleum fractions (dehydrocyclization and the aromatizationprocess). It was common to vent the surplus of hydrogen, nowadays the plants are balanced with hydrogen pinchwhich creates the possibility of collecting the hydrogen for further use.Hydrogen is also produced as a by-product of industrial chlorine production by electrolysis. It can be cooled,compressed and purified for use in other processes on site or sold to a customer via pipeline, cylinders or trucks.

From hydrocarbons

Steam reformingFossil fuel currently is the main source of hydrogen production[3] . Hydrogen can be generated from natural gas withapproximately 80% efficiency, or from other hydrocarbons to a varying degree of efficiency. Specifically, bulkhydrogen is usually produced by the steam reforming of methane or natural gas[4] At high temperatures(700–1100 °C), steam (H2O) reacts with methane (CH4) to yield syngas.

CH4 + H2O → CO + 3 H2 + 191.7 kJ/mol[5]

Gasification

In a second stage, further hydrogen is generated through thelower-temperature water gas shift reaction, performed at about 130 °C:

CO + H2O → CO2 + H2 - 40.4 kJ/molEssentially, the oxygen (O) atom is stripped from the additional water(steam) to oxidize CO to CO2. This oxidation also provides energy tomaintain the reaction. Additional heat required to drive the process isgenerally supplied by burning some portion of the methane.

Steam reforming generates carbon dioxide (CO2). Since the productionis concentrated in one facility, it is possible to separate the CO2 anddispose of it properly, for example by injecting it in an oil or gas reservoir (see carbon capture), although this is notcurrently done in most cases. A carbon dioxide injection project has been started by a Norwegian companyStatoilHydro in the North Sea, at the Sleipner field. However, even if the carbon dioxide is not sequestered, overallproducing hydrogen from natural gas and using it for a hydrogen vehicle only emits half the carbon dioxide that agasoline car would. (This is disputed in The Hype about Hydrogen: Fact and Fiction in the Race to Save theClimate, a book by Joseph J. Romm, published in 2004 by Island Press and updated in 2005. Romm says thatdirectly burning fossil fuels generates less CO2 than hydrogen production.)

Integrated steam reforming / co-generation - It is possible to combine steam reforming and co-generation of steamand power into a single plant. This can deliver benefits for an oil refinery because it is more efficient than separatehydrogen, steam and power plants. Air Products recently built an integrated steam reforming / co-generation plant inPort Arthur, Texas.[6]

Hydrogen production 114

Partial oxidationThe partial oxidation reaction occurs when a substoichiometric fuel-air mixture is partially combusted in a reformer,creating a hydrogen-rich syngas. A distinction is made between thermal partial oxidation (TPOX) and catalyticpartial oxidation (CPOX).

• General reaction equation: • Possible reaction equation (heating oil): • Possible reaction equation (coal):

Plasma reformingThe Kværner-process or Kvaerner carbon black & hydrogen process (CB&H)[3] is a plasma reforming method,developed in the 1980s by a Norwegian company of the same name, for the production of hydrogen and carbonblack from liquid hydrocarbons (CnHm). Of the available energy of the feed, approximately 48% is contained in thehydrogen, 40% is contained in activated carbon and 10% in superheated steam.[7] CO2 is not produced in the process.A variation of this process is presented in 2009 using plasma arc waste disposal technology for the creation ofhydrogen, heat and carbon from methane and natural gas in a plasma converter[8]

CoalCoal can be converted into syngas and methane, also known as town gas, via coal gasification. Syngas consists ofhydrogen and carbon monoxide.[9] . Another method for conversion is low temperature and high temperature coalcarbonization[10] .

From water

Electrolysis and thermolysisHydrogen is produced on an industrial scale by the electrolysis of water. While this can be done with a few volts in asimple apparatus like a Hofmann voltameter,[11] larger scale production usually relies on high-pressure andhigh-temperature systems to improve the energy efficiency of electrolysis. Experimental processes includeelectrolysis at very high temperatures (800 C), so that much of the energy required to release hydrogen is supplied asheat instead of electricity. Various catalytic agents are being studied to improve the efficiency of high-temperatureelectrolysis.Water spontaneously dissociates at around 2500 C, but this thermolysis occurs at temperatures too high for usualprocess piping and equipment. Catalysts are required to reduce the dissociation temperature.

Sulfur-Iodine CycleThe sulfur-iodine cycle (S-I cycle) is a thermochemical process which generates hydrogen from water, but at a muchhigher efficiency than water splitting. The sulfur and iodine used in the process are recovered and reused, and notconsumed by the process. It is well suited to production of hydrogen by high-temperature nuclear reactors.

From urineHydrogen can also be made from urine. Using urine, hydrogen production is 332% more energy efficient than usingwater.[12] [13] The research was conducted by Geraldine Botte from the Ohio University. Recently, Dr. Shanwen Taoof the Heriot-Watt University has invented a Carbamide Power System Fuel Cell that can immediatelly convert urineinto electricity.[14]

Hydrogen production 115

Biohydrogen routesBiomass and waste streams can be converted into biohydrogen with biomass gasification, steam reforming orbiological conversion like biocatalysed electrolysis or fermentative hydrogen production:

Fermentative hydrogen productionFermentative hydrogen production is the fermentative conversion of organic substrate to biohydrogen manifested bya diverse group bacteria using multi enzyme systems involving three steps similar to anaerobic conversion. Darkfermentation reactions do not require light energy, so they are capable of constantly producing hydrogen fromorganic compounds throughout the day and night. Photofermentation differs from dark fermentation because it onlyproceeds in the presence of light. For example photo-fermentation with Rhodobacter sphaeroides SH2C can beemployed to convert small molecular fatty acids into hydrogen.[15]

Biohydrogen can be produced in bioreactors that utilize feedstocks, the most common feedstock being wastestreams. The process involves bacteria feeding on hydrocarbons and exhaling hydrogen and CO2. The CO2 can besequestered successfully by several methods, leaving hydrogen gas. A prototype hydrogen bioreactor using waste asa feedstock is in operation at Welch's grape juice factory in North East, Pennsylvania (U.S.).

Enzymatic hydrogen generationDue to the Thauer limit (four H2/glucose) for dark fermentation, the biochemical engineer -- Y-H Percival Zhang,associate professor at Virginia Tech -- designed a non-natural enzymatic pathway that can generate 12 moles ofhydrogen per mole of glucose units of polysaccharides and water in 2007[16] . The stoichiometric reaction isC6H10O5+ 7 H2O --> 12 H2 + 6 CO2. The key technology is cell-free synthetic enzymatic pathwaybiotransformation (SyPaB)[17] [18] . A biochemist can understand it as "glucose oxidation by using water as oxidant".A chemist can describe it as "water splitting by energy in carbohydrate". A thermodynamics scientist can describe itas the first entropy-driving chemical reaction that can produce hydrogen by absorbing waste heat. In 2009, cellulosicmaterials were first used to generate high-yield hydrogen[19] . Furthermore, Dr. Zhang proposed the use ofcarbohydrate as a high-density hydrogen carrier so to solve the largest obstacle to the hydrogen economy andpropose the concept of sugar fuel cell vehicles[20] .

Biocatalysed electrolysis

A microbial electrolysis cell

Besides dark fermentation, electrohydrogenesis (electrolysis using microbes)is another possibility. Using microbial fuel cells, wastewater or plants can beused to generate power. Biocatalysed electrolysis should not be confused withbiological hydrogen production, as the latter only uses algae and with thelatter, the algae itself generates the hydrogen instantly, where withbiocatalysed electrolysis, this happens after running through the microbialfuel cell and a variety of aquatic plants[21] can be used. These include reedsweetgrass, cordgrass, rice, tomatoes, lupines, algae [22]

Hydrogen production 116

Other methods• Synthetic biology [23] [24] [25]

Renewable (or "Green") Hydrogen ProductionCurrently there are several practical ways of producing hydrogen in a renewable industrial process. One is to uselandfill gas to produce hydrogen in a steam reformer, and the other is to use renewable power to produce hydrogenfrom electrolysis. Hydrogen fuel, when produced by renewable sources of energy like wind or solar power, is arenewable fuel [26] .

See also• Ammonia production• Biological hydrogen production• Hydrogen• Hydrogen analyzer• Hydrogen compressor• Hydrogen economy• Hydrogen embrittlement• Hydrogen leak testing• Hydrogen pipeline transport• Hydrogen piping• Hydrogen purifier• Hydrogen purity• Hydrogen safety• Hydrogen sensor• Hydrogen storage• Hydrogen station• Hydrogen tank• Hydrogen tanker• Hydrogen technologies• Hydrogen valve• Industrial gas• Liquid Hydrogen• Next Generation Nuclear Plant (partly for hydrogen production)• The Phoenix Project: Shifting from Oil To Hydrogen (book)• Renewable energy• The Hype about Hydrogen• Lane hydrogen producer• Linde-Frank-Caro process• Liquid nitrogen production• Underground hydrogen storage

Hydrogen production 117

References[1] Waste hydrogen purification and supply (http:/ / www. hydrogenhighway. ca/ code/ navigate. asp?doi=224)[2] Peter Häussinger1, Reiner Lohmüller2, Allan M. Watson “Hydrogen” Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH,

Weinheim.[3] Bellona-HydrogenReport (http:/ / www. interstatetraveler. us/ Reference-Bibliography/ Bellona-HydrogenReport. html)[4] Fossil fuel processor (http:/ / auto. howstuffworks. com/ fuel-processor. htm)[5] "HFCIT Hydrogen Production: Natural Gas Reforming" (http:/ / www1. eere. energy. gov/ hydrogenandfuelcells/ production/ natural_gas.

html). U.S. Department of Energy. 2008-12-15. .[6] Port Arthur II Integrated Hydrogen/Cogeneration Facility, Port Arthur, Texas (http:/ / www. airproducts. com/ nr/ rdonlyres/

6226ec23-a536-4603-ab37-2b2ff3f9d45b/ 0/ port_arthur_122212258eprint. pdf) Power magazine, September 2007[7] https:/ / www. hfpeurope. org/ infotools/ energyinfos__e/ hydrogen/ main03. html[8] Kværner-process with plasma arc waste disposal technology (http:/ / fuelcellsworks. com/ news/ 2009/ 10/ 12/

hydrogen-breakthrough-for-norwegian-company/ )[9] "HFCIT Hydrogen Production: Coal Gasification" (http:/ / www1. eere. energy. gov/ hydrogenandfuelcells/ production/ coal_gasification.

html). U.S. Department of Energy. 2008-12-12. .[10] [pubs.acs.org/cgi-bin/jtext?enfuem/15/i03/abs/ef990178a Internal gas pressure characteristics generated during coal carbonization in a coke

oven][11] "Electrolysis of water and the concept of charge" (http:/ / www. practicalphysics. org/ go/ Experiment_677. html). .[12] Hydrogen from urine (http:/ / www. physorg. com/ news165836803. html)[13] 1,23V/0,37V[14] Carbamide Power System Fuel Cell (http:/ / www. outlookseries. com/ N8/ Science/

3753_Shanwen_Tao_Heriot-Watt_University_Carbamide_Power_System_Fuel_Cell_Turns_Urine_Electricity_Water_Shanwen_Tao. htm)[15] High hydrogen yield from a two-step process of dark-and photo-fermentation of sucrose (http:/ / cat. inist. fr/ ?aModele=afficheN&

cpsidt=18477081)[16] (http:/ / dx. doi. org/ 10. 1371/ journal. pone. 0000456)[17] (http:/ / dx. doi. org/ 10. 1002/ bit. 22630)[18] (http:/ / dx. doi. org/ 10. 1016/ j. copbio. 2010. 05. 005)[19] (http:/ / dx. doi. org/ 10. 1002/ cssc. 200900017)[20] (http:/ / dx. doi. org/ 10. 1039/ b818694d)[21] aquatic plants (http:/ / www. glastuinbouw. wur. nl/ UK/ expertise/ energy/ innovations/ plantenergy/ )[22] Power from plants using microbial fuel cell (http:/ / translate. google. com/ translate?js=n& prev=_t& hl=nl& ie=UTF-8& u=http:/ / www.

resource-online. nl/ achtergrond. php?id=147& sl=nl& tl=en& history_state0=)[23] Synthetic biology and hydrogen (http:/ / www. highbeam. com/ doc/ 1G1-163896478. html)[24] Synthetic biology to make hydrogen (http:/ / www. guardian. co. uk/ science/ 2008/ jun/ 19/ chemistry. agriculture)[25] Synthetic biology at Berkeley Lab (http:/ / pbd. lbl. gov/ synthbio/ aims. htm)[26] National Renewable Energy Laboratory 2003 Research Review: "New Horizons for Hydrogen." (http:/ / www. nrel. gov/ research_review/

pdfs/ 2003/ 36178b. pdf)

External links• U.S. DOE 2008-Technical progress in hydrogen production (http:/ / www. hydrogen. energy. gov/

annual_progress08_production. html)• U.S. NREL article on hydrogen production (http:/ / www. nrel. gov/ hydrogen/ proj_production_delivery. html)• Genetically engineered blood protein can be used to produce hydrogen gas from water (http:/ / www3. imperial.

ac. uk/ newsandeventspggrp/ imperialcollege/ newssummary/ news_1-12-2006-11-4-23?newsid=3016)

Hydrogen infrastructure 118

Hydrogen infrastructureA hydrogen infrastructure is the infrastructure of pipes and stations for distribution and sale of hydrogen fuel.

Network

Hydrogen pipeline transportHydrogen pipeline transport is a transportation of hydrogen through a pipe as part of the hydrogen infrastructure.Hydrogen pipeline transport is used to connect the point of hydrogen production or delivery of hydrogen with thepoint of demand, pipeline transport costs are similar to CNG[1] , the technology is proven[2] , however mosthydrogen is produced on the place of demand with every 50 to 100 miles an industrial production facility.[3] . As of2004 there are 900 miles (1450 km) of low pressure hydrogen pipelines in the USA and 930 miles in Europe.

Hydrogen highwayA hydrogen highway is a chain of hydrogen-equipped filling stations and other infrastructure along a road orhighway which allow hydrogen vehicles to travel.

Hydrogen stationsHydrogen stations which are not situated near a hydrogen pipeline get supply via hydrogen tanks, compressedhydrogen tube trailers, liquid hydrogen trailers, liquid hydrogen tank trucks or dedicated onsite production. Somefirms as ITM Power are also providing solutions to make your own hydrogen (for use in the car) at home.[4]

South Carolina also has a hydrogen freeway in the works. There are currently two hydrogen fueling stations, both inAiken and Columbia, SC. Additional stations are expected in places around South Carolina such as Charleston,Myrtle Beach, Greenville, and Florence. According to the South Carolina Hydrogen & Fuel Cell Alliance, theColumbia station has a current capacity of 120 kg a day, with future plans to develop on-site hydrogen productionfrom electrolysis and reformation. The Aiken station has a current capacity of 80 kg. There is extensive funding forHydrogen fuel cell research and infrastructure in South Carolina. The University of South Carolina, a foundingmember of the South Carolina Hydrogen & Fuel Cell Alliance, received 12.5 million dollars from the Department ofEnergy for its Future Fuels Program.[5]

The California Hydrogen Highway is an initiative by the California Governor to implement a series of hydrogenrefueling stations along that state. These stations are used to refuel hydrogen vehicles such as fuel cell vehicles andhydrogen combustion vehicles. As of July 2007 California had 179 fuel cell vehicles and twenty five stations were inoperation,[6] and ten more stations have been planned for assembly in California. However, there have already beenthree hydrogen fueling stations decommissioned.[7]

In May 2010, UNIDO has launched, on behalf of the International Centre for Hydrogen Energy Technologies, a callfor tender related to the supply and installation by the end of 2011 of a hydrogen production, storage and fillingfacility on the Golden Horn, in Istanbul. This station will be used for the refueling of a hydrogen fuel cell drivenpassenger boat as well as for that of a hydrogen internal combustion bus.[8]

Hydrogen infrastructure 119

See also• HCNG dispenser• Hydrogen piping• Hydrogen economy• Underground hydrogen storage

References[1] Compressorless Hydrogen Transmission Pipelines (http:/ / www. leightyfoundation. org/ files/ WHEC16-Lyon/ WHEC16-Ref022. pdf)[2] DOE Hydrogen Pipeline Working Group Workshop (http:/ / www1. eere. energy. gov/ hydrogenandfuelcells/ pdfs/ hpwgw_airprod_remp.

pdf)[3] Every 50 to 100 miles (http:/ / www. hydrogenforecast. com/ ArticleDetails. php?articleID=250)[4] Running on home-brewed hydrogen (http:/ / news. bbc. co. uk/ 2/ hi/ technology/ 7496644. stm)[5] Cluster Successes in South Carolina (http:/ / www. schydrogen. org/ documents/ Reports/ Cluster_Successes. pdf)[6] "California Fuel Cell Partnership" (http:/ / www. cafcp. org). .[7] "Hydrogen Fueling Stations" (http:/ / www. cafcp. org/ fuel-vehl_map. html). .[8] "Golden Horn Refuelling Station" (http:/ / www. unido-ichet. org. org/ index. php?lang=en& Itemid=42& option=com_content&

id=401:golden-horn-refuelling-station& view=article). .

External links• The Hydrogen Infrastructure Transition (HIT) Model (http:/ / pubs. its. ucdavis. edu/ publication_detail.

php?id=140)• Roads2HyCom Infrastructure (http:/ / www. ika. rwth-aachen. de/ r2h/ index. php/

European_Hydrogen_Infrastructure_and_Production)

Hydrogen lineThe hydrogen line, 21 centimeter line or HI line refers to the electromagnetic radiation spectral line that is createdby a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation is at the precise frequencyof 1420.40575177 MHz, which is equivalent to the vacuum wavelength of 21.10611405413 cm in free space. Thiswavelength or frequency falls within the microwave radio region of the electromagnetic spectrum, and it is observedfrequently in radio astronomy, since those radio waves can penetrate the large clouds of interstellar cosmic dust thatare opaque to visible light.Note that the relationship between the frequency and the wavelength is found from the simple equation that says thatthe wavelength equals c (the speed of light) divided by the frequency measured in hertz.The microwaves of the hydrogen line comes from the atomic transition between the two hyperfine levels of thehydrogen 1s ground state.[1] There is a difference in energy between these two hyperfine levels, and the frequency ofthe quanta that are emitted is given by Planck's equation.

Hydrogen line 120

Cause

Origin of Neutral Hydrogen Emission

An electron orbiting a proton with parallel spins (pictured) has higherenergy than if the spins were anti-parallel.

Fine and hyperfine structure inhydrogen. The hyperfine splittingof the ground 2S state is the source

of the 21 cm hydrogen line.

Electron transitions and their resulting wavelengths for Hydrogen.Energy levels are not to scale.

Neutral hydrogen consists of a single proton orbited by a single electron. As well as their orbital motion, the protonand electron also have spin. Classically, this is analogous to rotational motion (like the Earth rotating on its axis as itorbits the Sun), but as they are quantum particles the concept has a slightly different meaning.The spin of the electron and proton can be in either direction - in the classical analogy they are rotating clockwise oranticlockwise around a given axis. They may have their spin oriented in the same direction or in opposite directions.Because of magnetic interactions between the particles, a hydrogen atom that has the spins of the electron and protonaligned in the same direction (parallel) has slightly more energy than one where the spins of the electron and protonare in opposite directions (anti-parallel). The fact that the lowest-energy configuration arises in the anti-parallel spinconfiguration is an inherently quantum-mechanical result. A proton and electron with anti-parallel spins have parallelmagnetic moments owing to their opposite charge. Classical mechanics would predict that this configuration shouldhave higher energy, but a more detailed quantum mechanical analysis shows that the opposite is true.The lowest orbital energy state of atomic hydrogen has hyperfine splitting arising from the spins of the proton andelectron changing from a parallel to antiparallel configuration. This transition is highly forbidden with an extremelysmall probability of 2.9×10−15 s−1.This means that the time for a single isolated atom of neutral hydrogen to undergo this transition is around 10 million (107) years and so is unlikely to be seen in a laboratory on Earth. However, as the total number of atoms of neutral hydrogen in the interstellar medium is very large, this emission line is easily observed by radio telescopes. Also, the

Hydrogen line 121

lifetime can be considerably shortened by collisions with other hydrogen atoms and interaction with the cosmicmicrowave background.The line has an extremely small natural width because of its long lifetime, so most broadening is due to dopplershifts caused by the motion of the emitting regions relative to the observer.

DiscoveryDuring the 1930s, it was noticed that there was a radio 'hiss' that varied on a daily cycle and appeared to beextraterrestrial in origin. After initial suggestions that this was due to the Sun, it was observed that the radio wavesseemed to be coming from the centre of the Galaxy. These discoveries were published in 1940 and were seen byProfessor J.H. Oort who knew that significant advances could be made in astronomy if there were emission lines inthe radio part of the spectrum. He referred this to Dr Hendrik van de Hulst who, in 1944, predicted that neutralhydrogen could produce radiation at a frequency of 1420.4058 MHz due to two closely spaced energy levels in theground state of the hydrogen atom.The 21 cm line (1420.4 MHz) was first detected in 1951 by Ewen and Purcell at Harvard University,[2] andpublished after their data was corroborated by Dutch astronomers Muller and Oort,[3] and by Christiansen andHindman in Australia. After 1952 the first maps of the neutral hydrogen in the Galaxy were made and revealed, forthe first time, the spiral structure of the Milky Way.

Uses in radio astronomyLuckily, the spectral line appears within the radio spectrum (in the microwave window to be exact). Electromagneticenergy in this range can easily pass through the Earth's atmosphere and be observed from the Earth with littleinterference.Assuming that the hydrogen atoms are uniformly distributed throughout the galaxy, each line of sight through thegalaxy will reveal a hydrogen line. The only difference between each of these lines is the doppler shift that each ofthese lines has. Hence, one can calculate the relative speed of each arm of our galaxy. The rotation curve of ourgalaxy has also been calculated using the 21-cm hydrogen line. It is then possible to use the plot of the rotation curveand the velocity to determine the distance to a certain point within the galaxy.Hydrogen line observations have also been used indirectly to calculate the mass of galaxies, to put limits on anychanges over time of the universal gravitational constant and to study dynamics of individual galaxies.

Uses in cosmologyThe line is of great interest in big bang cosmology because it is the only known way to probe the "dark ages" fromrecombination to reionization. Including the redshift, this line will be observed at frequencies from 200 MHz toabout 9 MHz on Earth. It potentially has two applications. First, by mapping redshifted 21 centimeter radiation itcan, in principle, provide a very precise picture of the matter power spectrum in the period after recombination.Second, it can provide a picture of how the universe was reionized, as neutral hydrogen which has been ionized byradiation from stars or quasars will appear as holes in the 21 centimeter background.However, 21 centimeter experiments are very difficult. Ground based experiments to observe the faint signal areplagued by interference from television transmitters and the ionosphere, so they must be very secluded and carefulabout eliminating interference if they are to succeed. Space based experiments, even on the far side of the moon(which should not receive interference from terrestrial radio signals), have been proposed to compensate for this.Little is known about other effects, such as synchrotron emission and free-free emission on the galaxy. Despite theseproblems, 21 centimeter observations, along with space-based gravity wave observations, are generally viewed as thenext great frontier in observational cosmology, after the cosmic microwave background polarization.

Hydrogen line 122

Uses in terrestrial remote sensingThe Soil Moisture & Ocean Salinity (SMOS) satellite's main scientific instrument Microwave Imaging Radiometerwith Aperture Synthesis (MIRAS) uses the 1400-1427 MHz frequencies (including 1420.406 MHz) to monitor theocean surface salinity and the soil moisture of the Earth. The choice of HI band results from: 1) much better radiativesignature of salinity and moisture in microwave than in higher frequencies, 2) no electromagnetic interference fromanthropogenic sources, as HI is reserved for radioastronomy.

Possible uses for SETIThe Pioneer plaque, attached to the Pioneer 10 and Pioneer 11 spacecraft, portrays the hyperfine transition of neutralhydrogen and used the wavelength as a standard scale of measurement. For example the height of the woman in theimage is displayed as eight times 21 cm, or 168 cm. Similarly the frequency of the hydrogen spin-flip transition wasused for a unit of time in a map to Earth included on the Pioneer plaques and also the Voyager 1 and Voyager 2probes. On this map, the position of the Sun is portrayed relative to 14 pulsars whose rotation period circa 1977 isgiven as a multiple of the frequency of the hydrogen spin-flip transition. It is theorized by the plaque's creators thatan advanced civilization would then be able to use the locations of these pulsars to locate the Solar System at thetime the spacecraft were launched.The 21 cm hydrogen line is considered a favorable frequency by the SETI program in their search for signals frompotential extraterrestrial civilizations. In 1959, Italian physicist Giuseppe Cocconi and American physicist PhilipMorrison published "Searching for Interstellar Communications", a paper proposing the 21 cm hydrogen line and thepotential of microwaves in the search for interstellar communications. According to George Basalla, the paper byCocconi and Morrison "provided a reasonable theoretical basis" for the then nascent SETI program.[4]

Pyotr Makovetsky proposed to use for SETI a frequency which is equal to pi times 1420.4 MHz (pi times1420.40575177 megahertz = 4.46233627 gigahertz; (2 * pi) times 1420.40575177 megahertz = 8.92467255gigahertz). Since pi is a Transcendental number, such frequency couldn't possibly be produced in a natural way as aharmonic, and would clearly signify its artificial origin. Such signal would not be jammed by HI line itself, or any ofits harmonics.[5]

See also• H-alpha, the visible red spectral line with wavelength of 6562.8 Ångstroms• Hydrogen spectral series• Hydrogen Atom• Radio astronomy• Rydberg formula• Spectral line

References[1] "The Hydrogen 21-cm Line" (http:/ / hyperphysics. phy-astr. gsu. edu/ hbase/ quantum/ h21. html). Hyperphysics. Georgia State University.

2004-10-30. . Retrieved 2008-09-20.[2] Ewan, H.I.; E.M. Purcell (September 1951). "Observation of a line in the galactic radio spectrum" (http:/ / www. nature. com/ nature/ journal/

v168/ n4270/ pdf/ 168356a0. pdf). Nature 168 (4270): 356. doi:10.1038/168356a0. . Retrieved 2008-09-21.[3] Muller, C.A.; J.H. Oort (September 1951). "The Interstellar Hydrogen Line at 1,420 Mc./sec., and an Estimate of Galactic Rotation" (http:/ /

www. nature. com/ nature/ journal/ v168/ n4270/ pdf/ 168356a0. pdf). Nature 168 (4270): 357–358. doi:10.1038/168357a0. . Retrieved2008-09-21.

[4] {cite book |last=Basalla |first=George |date=2006 |title=Civilized Life in the Universe |publisher=Oxford University Press |isbn=0195171810|pages=133–135}}

[5] Makovetsky P. Smotri v koren' (http:/ / n-t. ru/ ri/ mk/ sk109-4. htm) (in Russian)

Hydrogen line 123

Cosmology• P. Madau, A. Meiksin and M. J. Rees, "21-cm Tomography of the Intergalactic Medium at High Redshift",

Astrophysical Journal 475, 429 (1997) arXiv:astro-ph/9608010.• B. Ciardi, P. Madau, "Probing Beyond the Epoch of Hydrogen Reionization with 21 Centimeter Radiation",

Astrophysical Journal 596, 1 (2003) arXiv:astro-ph/0303249.• M. Zaldarriaga, S. Furlanetto and L. Hernquist, "21 Centimeter Fluctuations from Cosmic Gas at High Redshifts",

Astrophysical Journal 608, (2004) 608 arXiv:astro-ph/0311514.• X. Chen and J. Miralda-Escudé, "Observing the Reionization Epoch Through 21 Centimeter Radiation", Mon.

Not. Roy. Astron. Soc. 347, 187 (2004) arXiv:astro-ph/0303395.• A. Loeb and M. Zaldarriaga, "Measuring the Small-Scale Power Spectrum of Cosmic Density Fluctuations

Through 21 cm Tomography Prior to the Epoch of Structure Formation", Phys. Rev. Lett. 92, 211301 (2004)arXiv:astro-ph/0312134.

• M. G. Santos, A. Cooray and L. Knox, "Multifrequency analysis of 21 cm fluctuations from the Era ofReionization", Astrophysical Journal 625, 575 (2005) arXiv:astro-ph/0408515.

• R. Barkana and A. Loeb, "Detecting the Earliest Galaxies Through Two New Sources of 21cm Fluctuations",Astrophysical Journal 626, 1 (2005) arXiv:astro-ph/0410129.

External links• The story of Ewen and Purcell's discovery of the 21 cm line (http:/ / www. nrao. edu/ whatisra/ hist_ewenpurcell.

shtml)• Ewen and Purcell's original paper in Nature (http:/ / www. nature. com/ physics/ looking-back/ ewen/ index. html)• PAST experiment, arXiv:astro-ph/0404083.• LOFAR experiment (http:/ / www. lofar. org/ )• Mileura Widefield Array experiment (http:/ / web. haystack. mit. edu/ MWA)• Square Kilometer Array experiment (http:/ / www. skatelescope. org/ )

Hydrogen purity 124

Hydrogen purityHydrogen purity or hydrogen quality is a term to describe the lack of impurities in hydrogen as a fuel gas. Thepurity requirement varies with the application, for example a H2 ICE can tolerate low hydrogen purity where ahydrogen fuel cell requires high hydrogen purity to prevent catalyst poisoning[1] .

High purity hydrogenIn the first generation of fuel cells catalysts like palladium, ruthenium and platinum are used in combination withhydrogen production from hydrocarbons which results in performance degradation. The catalyst poisoning inducedby carbon monoxide, formic acid, or formaldehyde can be reversed with a high purity hydrogen stream. Sulfurdioxide is problematic[2]

See also• Glossary of fuel cell terms• Katharometer

References[1] 2007-DOE-Hydrogen Fuel Quality (http:/ / www. nrel. gov/ docs/ fy07osti/ 41541. pdf)[2] Issues in hydrogen purity detection and monitoring (http:/ / www. ottawapolicyresearch. ca/ OPRA_Brief_H2PurityDetectionMonitoring.

pdf)

External links• H2 Quality (http:/ / www. fuelcellstandards. com/ H2Quality. ppt)• 2004-Hydrogen Purity Standard (http:/ / www1. eere. energy. gov/ hydrogenandfuelcells/ pdfs/

fp_workshop_smith. pdf)• 2004-Fuel Purity Specifications Workshop (http:/ / www1. eere. energy. gov/ hydrogenandfuelcells/ pdfs/

fuel_purity_notes. pdf)

Article Sources and Contributors 125

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Hydrogen-like atom  Source: http://en.wikipedia.org/w/index.php?oldid=386237051  Contributors: Achoo5000, Akesich, Barticus88, Bgamari, Chuunen Baka, Dan Gluck, Eequor, Eroica,Feezo, Fresheneesz, Granolanifa, GregRM, HappyCamper, Henrygb, Incnis Mrsi, Iridescent, Itub, Jacopo Werther, Jeppesn, JimR, John C PI, Karol Langner, Linas, Mion, Nergaal, OMCV, Outof Phase User, P.wormer, Paolo.dL, Pecos Joe, Pfalstad, Raghunathan, SPat, Sbandrews, Stereotonic24, Thurth, Trewesterre, Txomin, Xxanthippe, 39 anonymous edits

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Veraladeramanera, Vortexrealm, WAS 4.250, Wikibob, Wikiborg, Wolfkeeper, Woohookitty, 94 anonymous edits

Solid hydrogen  Source: http://en.wikipedia.org/w/index.php?oldid=336326340  Contributors: Carcharoth, Mion, Moralis, Nickosaurr, Pstanton, Skier Dude, Stone, Underpants, 2 anonymousedits

Metallic hydrogen  Source: http://en.wikipedia.org/w/index.php?oldid=383247016  Contributors: Aerobird, Agd1, Alan Peakall, AndrewBuck, Anthony Appleyard, Ary29, Ase1e1, Ataru,Attilios, Axl, BD2412, Barhamd, Bendzh, Bkell, Bryan Derksen, Calcwatch, Can't sleep, clown will eat me, CarlFeynman, Carlos84, Chemninja, CosineKitty, Crispmuncher, DMacks,Deanlsinclair, Dendropithecus, Doradus, DragonflySixtyseven, DryaUnda, Duncharris, Edgar181, Eleland, Emperorbma, Enochlau, EpiVictor, Fgb, FoeNyx, Fredrik, Gaius Cornelius, GeeJo,Gene Nygaard, Gene.arboit, GeorgeStepanek, Hair Commodore, HalfShadow, Hamiltondaniel, Headbomb, Headcreeps, Hibernian, Houston, Icairns, Igodard, Iknowyourider, Itub, Jaredroberts,Jfromcanada, JimScott, John, Julesd, Karl Andrews, Killing Vector, Kjkolb, Kmarinas86, Kymacpherson, LarryGilbert, Lord Snoeckx, LorenzoB, Lost tourist, LouI, Lovelac7, Mallorn,Materialscientist, Mazarin07, Michael Hardy, Mikeblas, Mikeo, Mion, Modify, Nbishop, Nergaal, Netrapt, Nihiltres, Nonagonal Spider, Novangelis, Objectivist, Ojovan, Omegatron, OrangeDog,Oroso, Pi.C.Noizecehx, Ponder, Quietust, Rich Farmbrough, RobChafer, RodC, Rossami, Salsa Shark, Schueltz 65, ScienceApologist, Serpent-A, Shalom Yechiel, Signalhead, Sinus, Slicky,Smack, Smyth, Stepa, Student1967-68, Swpb, ThAtSo, The Epopt, Thfledrich, Tlogmer, TutterMouse, Variable, Wikipediarules2221, Winiar, XJamRastafire, Youngjim, Zach4636, Zoicon5, 121anonymous edits

Nascent hydrogen  Source: http://en.wikipedia.org/w/index.php?oldid=357113164  Contributors: Abhishek191288, After Midnight, Cryptic C62, Doug butler, DragonflySixtyseven, Georgebts,Headbomb, Kbh3rd, Kku, Mac Davis, Michaf, Mion, Securiger, Shaddack, Shadowjams, Shinkolobwe, SiliconDioxide, Sillybilly, Smokefoot, The way, the truth, and the light, TubularWorld,X42bn6, 14 anonymous edits

Isotopes of hydrogen  Source: http://en.wikipedia.org/w/index.php?oldid=396800418  Contributors: (jarbarf), 13mullja, AdjustShift, Ardric47, BiT, Blacklemon67, Blue520, Castorquinn,DabMachine, Daigaku2051, Dirac66, Donarreiskoffer, Driedshroom, EdC, Eric119, Evil Monkey, Femto, Gamer007, Gene Nygaard, Glane23, Greater mind, Headbomb, JFreeman, Jared Preston,John, Julianonions, Karol Langner, Ketiltrout, Killing Vector, Larry R. Holmgren, LeonWhite, Mion, Muro de Aguas, Nergaal, Northfox, Oo64eva, OrangeDog, Oxymoron83, Philip Trueman,PoeticVerse, Pwjb, Retroneo, Reyk, Robbin' Knowledge, Spacepotato, Technopat, Thinking of England, Tide rolls, Tom harrison, V1adis1av, Vossman, Wisdom89, Wsiegmund, Xezbeth, Yerpo,आशीष भटनागर, 102 anonymous edits

Deuterium  Source: http://en.wikipedia.org/w/index.php?oldid=395716394  Contributors: 128.59.51.xxx, 130.225.29.xxx, 16@r, 203.109.250.xxx, A2-computist, Adam Conover, Agesworth,Ajaxkroon, An Unknown Person, Andre Engels, Andres, Andrewa, Anthony Appleyard, Ardric47, Ashmoo, AstroHurricane001, Awatral, Bambaiah, Barticus88, Bci2, Ben-Zin, Bender235,Benji9072, Bennish, BiT, BlueNovember, Brandonrush, Brichcja, BrokenSphere, Bryan Derksen, Btg2290, Byrial, C0nanPayne, CABAL, CCooke, Cadwaladr, Can't sleep, clown will eat me,Canderson7, Capricorn42, Ceyockey, Chan Yin Keen, Charles Clark, Chromaticity, Chutznik, Commander Nemet, Comte0, Conversion script, Crazy Fox, CuriousEric, Curps, Cyrek, DMacks,DV8 2XL, Daggerstab, Dan Gluck, DanGarb, Danelo, Davehi1, Deglr6328, Deuterium124, Discospinster, DocWatson42, Dryguy, E23, Edgar181, El C, Elroch, Enric Naval, Epiovesan, Ericwb,F-402, Flying fish, Frank Lofaro Jr., Freestyle-69, Gaius Cornelius, Gekritzl, Gene Nygaard, Geni, Giftlite, Gohmifune, Graham87, Gurch, Gzkn, Hadal, Harp, Hayter, Headbomb, Herbee,HereToHelp, Heron, Icairns, Ilmari Karonen, Infomaxim, JWB, Janke, Jclerman, Jerrykim, John, Juckum, Kainino, Kalamkaar, Karol Langner, Kazvorpal, Kbdank71, Kbh3rd, Kdliss, Keb25,Keenan Pepper, Keepingitfair, Ketiltrout, KhaLduNTR, Killing Vector, Kjkolb, KlaudiuMihaila, Klxmack, Kowey, Kristof vt, Kyle Barbour, LilHelpa, Looxix, Lupinoid, Lupo, Madbehemoth,Madmarigold, Magnus Manske, Malo, ManningBartlett, MarkS, Martianpenguin, Materialscientist, Mav, McSush, Melchoir, Mike40033, Modulatum, MonDroit, Mradigan, Mwoodman,Myasuda, NawlinWiki, Neurolysis, Nick, Nick Y., Nicolokyle, Nihiltres, Nonagonal Spider, OlEnglish, Oli Filth, Oliphaunt, Oo64eva, Oreo Priest, PC THE GREAT, Pakaran, Palica, Panoramix,Parksmp26, Patchouli, Pb30, Phasmatisnox, Phil Boswell, Physchim62, Physicistjedi, PierreAbbat, Piperh, Pjacobi, Pjstewart, ProfessorPaul, Prometheus235, RTC, Raeky, RainbowOfLight,Rebroad, Reyk, Rich Farmbrough, Rjwilmsi, Roadrunner, Rob Mahurin, Roo72, RoryReloaded, RoyBoy, Roycethevoice, Rwflammang, Rydel, SEWilco, SJP, SV Resolution, Salsa Shark, Salsb,Sarastro777, Sbharris, Sbyrnes321, ScAvenger lv, ScienceApologist, Sealpoint33, Securiger, Seth Ilys, Shaddack, Shalom Yechiel, SimonP, SiriusB, SkyLined, Sladen, Smithbrenon, Snigbrook,Spacepotato, Stokerm, Stone, Strait, Surly Dwarf, Takometer, Tapper of spines, Tarquin, Tempshill, That Guy, From That Show!, The ansible, TheTruthiness, Tide rolls, Toddst1, Toligalanis,Tristan Schmelcher, Tsuji, Urhixidur, VASANTH S.N., Vsmith, WFPM, WOSlinker, Warut, Webguy, WestA, WhiteDragon, Whitepaw, Wikisteff, Witan, WriterHound, Xerxes314,Yamaguchi先生, Zeimusu, 253 anonymous edits

Tritium  Source: http://en.wikipedia.org/w/index.php?oldid=396546936  Contributors: 128.59.51.xxx, 300840da, ARC Gritt, Aarchiba, Ahoerstemeier, Allissonn, Alvis, An Unknown Person,Andre Engels, Andrejj, Andres, Andrew c, Arbitrarily0, Ardric47, Arman94, Autopilot, Axd, BJ Axel, Bazonka, BlaiseFEgan, BlastOButter42, Bobo192, Borgx, Bornhj, Breakyunit, BryanDerksen, Cancun771, Capricorn42, Catgut, Cave troll, Cbrown1023, CharlesC, CheekyDreamer, Chyeburashka, Cip25, CipherZero, Conquerist, Conversion script, CosineKitty, DV8 2XL, DannyMiller, Debresser, Deglr6328, Deor, Dfeuer, Dinferno, DiverDave, Dod1, Dr U, Drewzkie, Dricherby, E23, ERcheck, Ebahe4, Edgar181, Eiland, Epbr123, Eric119, FDD, Favonian, FinlayMcWalter, FirefoxRocks, Flip 66, Fluzwup, Geni, Georgejmyersjr, Giftlite, Glenn, Graham87, Gypsydoctor, Happy-melon, Hashar, HazyM, Hcberkowitz, Headbomb, Hellbus, HenryLi, Herbee,Heron, Hibernian, HoodedMan, Icairns, IceKarma, Iridescent, Itub, J-Star, J.delanoy, JQF, JWB, JackMcJiggins, Jaganath, Jclerman, Jdforrester, Jimp, JoeBruno, Joelholdsworth, John,JohnDoe0007, JohnOwens, Jon513, Jotomicron, Julesd, KJG2007, KSmrq, Karol Langner, Kay Dekker, Kazvorpal, Kbdank71, Keegan, Keenan Pepper, KlaudiuMihaila, Knotnic, Knute, Kowey,Kwamikagami, Lee Daniel Crocker, Lee J Haywood, Leslie222, LichYoshi, LilHelpa, Looxix, LorenzoB, Luckrider7, Lunch, Mahboud, Malafaya, Malcolm Farmer, Markhurd, Materialscientist,Mattd4u2nv, Megansmith18, Mike Rosoft, Mike40033, Mintrick, Mion, Missy Pentney, Mmeijeri, Nafango2, Nathann sc, Nik42, Nknight, Nonagonal Spider, Novasource, Numbo3, OnePt618,Oo64eva, Open2universe, PJM, Palica, Peter todd, Petri Krohn, Pie4all88, PierreAbbat, Pikazilla, Pinethicket, Polpo, Pstudier, Pwjb, Quadrobyte, Qwertyus, RafaMolina, Rcingham, RichFarmbrough, Richard Arthur Norton (1958- ), Richards360, Rigosantana3, Ritalib, Rjwilmsi, Ronhjones, Rsquid, Rupertslander, Rursus, Rydel, SB Pete, SCStrikwerda, Sabo, Sam Hocevar,Sbharris, ScAvenger lv, Scog, Scoo, SeanNovack, Sfan00 IMG, Shaddack, Shane Lin, Shimmin, Sjc, SkyLined, Smappy, Smith609, Smurrayinchester, SoM, Spencer, SqueakBox, Stephan Leeds,Stone, Stormwriter, Suisui, Sunborn, SusanLesch, Tarquin, Taxman, Tedmund, The_ansible, Tide rolls, Trelvis, Trevor MacInnis, Tweenk, Tygrrr, Ubern00b, UltimatePyro, Vina, Viralmemesis,Vsmith, Walkinglikeahuricane, Wdsci, Whitepaw, Whitlock, Wiki Phantoms, WikiDao, Wikianon, Wimt, Wlipinski, Ziggaway, Zoidberg, आशीष भटनागर, 329 anonymous edits

Hydrogen-4  Source: http://en.wikipedia.org/w/index.php?oldid=384719175  Contributors: Antonio Lopez, DabMachine, Eric119, Gamer007, Headbomb, Ice Ardor, JWB, John, Karol Langner,Kbdank71, Keenan Pepper, LeonWhite, Mattd4u2nv, Maximaximax, Mewaqua, Mike Rosoft, Mike40033, Oo64eva, OrangeDog, Pamputt, Smith609, Spacepotato, Wang Ivan, 9 anonymousedits

Hydrogen-5  Source: http://en.wikipedia.org/w/index.php?oldid=296211195  Contributors: Ardric47, Bryan Derksen, DabMachine, Eric119, Hellbus, Ice Ardor, JWB, Karol Langner, Kbdank71,Keenan Pepper, Mattd4u2nv, Mike Rosoft, Mike40033, Mike4ty4, Oliphaunt, Oo64eva, Sceptre, Smith609, Spacepotato, Valodzka, 5 anonymous edits

Spin isomers of hydrogen  Source: http://en.wikipedia.org/w/index.php?oldid=395497029  Contributors: Aditya.m4, Ascentury, Dirac66, Doradus, Gadolinist, Headbomb, Hellbus, IceKarma,Jaeljojo, Mikespedia, Mion, Nergaal, Opabinia regalis, OrangeDog, Peregrinoerick, SilverStar, Stone, Terrek, Urhixidur, Vertovian, Whiner01, Wolfkeeper, Wyang, Xaa, 22 anonymous edits

Bosch reaction  Source: http://en.wikipedia.org/w/index.php?oldid=379704231  Contributors: CharlesC, Chem-awb, Choij, Headbomb, Icer CRO, Marcelo-Silva, Mion, Peter.steier, Silvonen,Tomasz Dolinowski, Treehill, V8rik, ~K, 18 anonymous edits

Hydrogen cycle  Source: http://en.wikipedia.org/w/index.php?oldid=379094852  Contributors: 1ForTheMoney, Anxietycello, Atif.t2, Conrad.Irwin, Cpl Syx, Dendlai, Discospinster,Hamburgerman, Headbomb, Jrockley, Karol Langner, Katoa, Keenan Pepper, Michael Hardy, Mikenorton, Onco p53, Orbst, Papodelwiken, Pb30, Poppy, Prashant.ashley, Shrumster, Skiff,Smartse, Snaxe920, Supten, TAS, The Thing That Should Not Be, Vortexrealm, Vsmith, Zawer, 27 anonymous edits

Hydrogenation  Source: http://en.wikipedia.org/w/index.php?oldid=396262832  Contributors: 168..., 19vwishart, 2261Daryl, AJim, AThing, Altenmann, AndrewHowse, Antandrus, Beagel,Bensaccount, Biscuittin, Bkell, Borgx, Cacycle, Calmer Waters, Calvero JP, CanadianLinuxUser, CatherineMunro, CerealBabyMilk, Christian75, Christopher Mann McKay, CommonsDelinker,Conortodd, CyclePat, DA3N, DTM, DabMachine, Dante Alighieri, David spector, Edgar181, Effeietsanders, El C, Erbaiwu, Erianna, EtienneCha, Fanghong, FayssalF, Flowchemguy, Forenti,Furrykef, Gareth McCaughan, GenQuest, Gene Nygaard, Gigemag76, Gioto, Guccililpiggy3, Gulliver001, Gökhan, Happyharris, Headbomb, Headius, Hermann Luyken, Hippolyte,Inoculatedcities, Iridescent, Isopropyl, Itub, J.delanoy, J0nokun, Jackfork, Janke, Jimp, Jmendez, Joshuapfohl, Julesd, Karol Langner, Karsten Adam, Kdevans, Keenan Pepper, Kenyon, Kostisl,LOL, LeadSongDog, Leslie Mateus, Loupeter, Lovecz, MER-C, MMS2013, Mausy5043, Mbeychok, Mdf, Michael Hardy, Mion, Mitchan, Mmmsnouts, Müslimix, NJA, Nevit, Nirvana2013,Notreallydavid, Novickas, OrangeDog, OverlordQ, PaperTruths, Physchim62, Picus viridis, Pinethicket, Poor Yorick, Qaddosh, RazorICE, RealGrouchy, RedHillian, Rhadamante, RickyWiki,SeventyThree, Shadow Puppet, Shawnc, Skittleys, Smokefoot, Soliloquial, Soyseñorsnibbles, Spalding, Stephenb, Stone, Tabledhote, Takometer, Tarotcards, Taurrandir, The Anome, TheMoUsY spell-checker, Tides, Trackbar, Turnstep, Tyciol, Tyler, V8rik, Vortexrealm, Vuo, Whosasking, Wimvandorst, Wjsams, Woohookitty, Wspencer11, Ww, ~K, 189 ,لیقع فشاکanonymous edits

Dehydrogenation  Source: http://en.wikipedia.org/w/index.php?oldid=395537881  Contributors: Bob, Bobo192, Carlog3, Craptree, Edgar181, Fermi121, Ideal gas equation, Itub, Jmendez,Keenan Pepper, Mion, Nirmos, Rifleman 82, Smaljers, Vortexrealm, 15 anonymous edits

Transfer hydrogenation  Source: http://en.wikipedia.org/w/index.php?oldid=396153470  Contributors: Andrewpmk, Beagel, Keenan Pepper, Mion, Nuklear, OMCV, Smokefoot, Stone,Takometer, V8rik, Vortexrealm, 10 anonymous edits

Hydrogenolysis  Source: http://en.wikipedia.org/w/index.php?oldid=376574197  Contributors: Adkins, CatherineMunro, Edgar181, Gnostic804, Kostisl, Mion, Nseidm1, Rifleman 82,Seansheep, Smokefoot, Stone, Tonyrex, Unara, V8rik, Vortexrealm, Vuo, Zotel, ~K, 5 anonymous edits

Article Sources and Contributors 127

Hydron  Source: http://en.wikipedia.org/w/index.php?oldid=381012749  Contributors: Armando-Martin, Chotu21, December21st2012Freak, Firq, Itub, Julianonions, Mikespedia, Okedem,Puppy8800, Reindra, Rifleman 82, Stone, Whiner01, Wickey-nl, 9 anonymous edits

Sabatier reaction  Source: http://en.wikipedia.org/w/index.php?oldid=391814198  Contributors: Antaeus Feldspar, Benjamindees, BiggKwell, Ceyockey, Charles Matthews, DanPope,Dlchambers, DonSiano, Headbomb, Itub, Jamelan, Ken g6, Leonard G., Like tears in rain, Mac, Marcelo-Silva, Mion, NickFr, Okedem, Onco p53, PigFlu Oink, Prari, Proximo.xv, Richcon,Sbandrews, Sdsds, Sillybilly, Toytoy, Ufinne, Vortexrealm, Who, 28 anonymous edits

Hydrogen damage  Source: http://en.wikipedia.org/w/index.php?oldid=393031210  Contributors: Bleh999, Craig Pemberton, Eastlaw, Edward, Element16, FCYTravis, Hkhenson, John, JohnQuiggin, Julesd, Mion, Peruvianllama, Portrino, Saimhe, Shaddack, Tkgnamboodhiri, Vortexrealm, Wildstar2501, Wizard191, 13 ,یکیو یلع anonymous edits

Hydrogen embrittlement  Source: http://en.wikipedia.org/w/index.php?oldid=395705728  Contributors: Abc root, Afroozpromethe, Anonymousphrase, Antiuser, Bernd in Japan, CraigPemberton, DRRLRA, Dagordon01, Diberri, DragonflySixtyseven, Eastlaw, Elektron, Element16, Equinox2, EricWesBrown, Fosnez, Gaius Cornelius, George Burgess, Gigemag76, Headbomb,Hooperbloob, Iain.mcclatchie, John, Ksuresh10, L.Raymond&Associates, LRA-FDI-RSL, LorenzoB, Mackay64, Michael Frind, Mikiemike, Mion, Orphan Wiki, Physchem, Radagast83, Rei,Rhun, Rudyh01, Shaddack, Snezzy, StaticGull, Stephenb, TheNewPhobia, Tkgnamboodhiri, Trisino, Turboragtop, Vortexrealm, Vsmith, Wavelength, Wizard191, ZorbaTHut, 51 ,یکیو یلعanonymous edits

Hydrogen leak testing  Source: http://en.wikipedia.org/w/index.php?oldid=351505588  Contributors: Aardvarktesting, Cgarber, FayssalF, Headbomb, Lambdacore, Maseracing, Mion, Nergaal,Quantumobserver, Trentool2, Vortexrealm, 11 anonymous edits

Hydrogen safety  Source: http://en.wikipedia.org/w/index.php?oldid=395812143  Contributors: Iridescent, Jjhamilton, Mion, Nergaal, NuclearWarfare, Pbspbs, R'n'B, Rei, Robbin' Knowledge,Sergey bloomkin, Shoefly, Tkma, Xenonice, 8 anonymous edits

Timeline of hydrogen technologies  Source: http://en.wikipedia.org/w/index.php?oldid=393572682  Contributors: Cromwellt, Daniel Christensen, FiggyBee, Gerhard51, Giovanni-P,Headbomb, Hibernian, Kingdon, Mild Bill Hiccup, Mion, Nergaal, OrangeDog, Ospalh, Wolfkeeper, 18 anonymous edits

Biohydrogen  Source: http://en.wikipedia.org/w/index.php?oldid=393581157  Contributors: 3l1t1st, Appeltree1, C777, ChildofMidnight, Dancter, Erud, Freewaay, Gmohanakrishna, Gobonobo,Green caterpillar, Headbomb, Hebrides, IstvanWolf, Jerome Charles Potts, KVDP, Kasjens, Mac, MarsInSVG, Mild Bill Hiccup, Mion, Mirgy, Morphriz, Nergaal, Rich Farmbrough, Rosenbluh,SebastianHelm, Smokefoot, Terjepetersen, Vortexrealm, Welsh, 22 anonymous edits

Hydrogen production  Source: http://en.wikipedia.org/w/index.php?oldid=396126029  Contributors: ABF, Aaadddaaammm, Acdx, Alagiah, Alan Liefting, Alansohn, AlexH555, AndrewBuck,Appeltree1, Armadillo1985, Ashmoo, Awotter, Balrog-kun, Barneca, Beagel, Behun, Bill W Ca, BlindEagle, Bobamnertiopsis, Bobblewik, CalumH93, CambridgeBayWeather, Casimirpo, Chemprof2000, Chris G, Closedmouth, CyclePat, Echo-cycle, Ehines99, Environnement2100, Equendil, EverGreg, Eyckfreymann, Eyrian, Falcon8765, FellGleaming, Gaius Cornelius, Greencaterpillar, Headbomb, Heron, Htomfields, Inwind, Iridescent, JForget, JHunterJ, Jandre680, Jerome Charles Potts, Jorfer, KVDP, Kaldosh, Klixovann, Koppas, L Kensington, LilHelpa,Loren.wilton, Margin1522, Materialscientist, Matrix452, Mattisse, Mbeychok, Megiddo1013, Mets501, MgW, Mion, MonoViejo, Mrz1818, NJGW, Nergaal, Nick2588, Nikolai Eroshenko,Nseidm1, OMCV, Olthebol, Petlif, Phantom25, Pinethicket, Pingpongpan, Pjacobi, Pserfass, Pstudier, Quasarstrider, RJHall, Robbin' Knowledge, Rocketere o1, SD5, Sbharris, Sequoian, Sergeybloomkin, Shaddack, Simesa, Skier Dude, Smokefoot, Ssilvers, Stan J Klimas, Stanislao Avogadro, Student050608, SudlonrA, SyntaxError55, Timberframe, Trekphiler, Virgofenix, Vortexrealm,Voyevoda, Vsmith, Wavelength, WereSpielChequers, Wikicali00, Woohookitty, Wtshymanski, Wwoods, 136 anonymous edits

Hydrogen infrastructure  Source: http://en.wikipedia.org/w/index.php?oldid=389491417  Contributors: Appeltree1, Daduck08, Geologyguy, Gregory Dziedzic, Headbomb, Hmains, KVDP,Mion, Nergaal, OrangeDog, RFerreira, Sergey bloomkin, Skierpage, Supaman89, 2 anonymous edits

Hydrogen line  Source: http://en.wikipedia.org/w/index.php?oldid=396203548  Contributors: 0xFFFF, 84user, Adaminstalbans, Binksternet, Bowlhover, Camouflage55, CapitalR, CharlesMatthews, Chekaz, Christopherlin, Commdor, Curps, DJIndica, Daveliney, Dina, Dmmaus, Eyreland, Gabodon, Giftlite, Gmaxwell, GregorB, Gurch, HairyDan, Headbomb, Hetar, Husond, IIMusLiM HyBRiD II, IRP, Iridescent, J.delanoy, JabberWok, Jacek Kendysz, Joke137, KJS77, Kaldosh, Karol Langner, Krash, Kvng, METIfan, Mcleodm, MichaelVernonDavis, Mike Peel,Mion, Mushin, Nergaal, Oliverkeenan, One-dimensional Tangent, OrangeDog, PhatSmurf, Phe, Phorse, Pjacobi, RJHall, RayTomes, Rykul, SDC, Sam Hocevar, Samw, Shortbread, Sirhulio,Smalljim, Spiderfrog, Steve Pucci, Stwalkerster, Sverdrup, THF, Ta bu shi da yu, Thingg, TimBentley, Tubbs334, Uhjoebilly, Viriditas, Vortexrealm, Zandperl, Zzuuzz, Δζ, 68 anonymous edits

Hydrogen purity  Source: http://en.wikipedia.org/w/index.php?oldid=372569471  Contributors: Benjah-bmm27, Mion, 1 anonymous edits

Image Sources, Licenses and Contributors 128

Image Sources, Licenses and Contributorsfile:Hydrogenglow.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogenglow.jpg  License: unknown  Contributors: User:Juriifile:Hydrogen Spectra.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen_Spectra.jpg  License: Public Domain  Contributors: User:teravoltFile:Loudspeaker.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Loudspeaker.svg  License: Public Domain  Contributors: Bayo, Gmaxwell, Husky, Iamunknown, Nethac DIU,Omegatron, Rocket000, The Evil IP address, 6 anonymous editsImage:Shuttle Main Engine Test Firing cropped edited and reduced.jpg  Source:http://en.wikipedia.org/w/index.php?title=File:Shuttle_Main_Engine_Test_Firing_cropped_edited_and_reduced.jpg  License: Public Domain  Contributors: Avron, WTCA, 1 anonymous editsImage:hydrogen atom.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen_atom.svg  License: Public Domain  Contributors: User:BensaccountImage:Liquid hydrogen bubblechamber.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Liquid_hydrogen_bubblechamber.jpg  License: Public Domain  Contributors: Lamiot,Pieter Kuiper, SaperaudFile:Hydrogen discharge tube.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen_discharge_tube.jpg  License: Attribution  Contributors: User:Alchemist-hpFile:Deuterium discharge tube.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Deuterium_discharge_tube.jpg  License: Attribution  Contributors: User:Alchemist-hpImage:Protium.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Protium.svg  License: Public Domain  Contributors: User:Blacklemon67Image:Emission spectrum-H.png  Source: http://en.wikipedia.org/w/index.php?title=File:Emission_spectrum-H.png  License: Public Domain  Contributors: user:MerikantoImage:Nursery of New Stars - GPN-2000-000972.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Nursery_of_New_Stars_-_GPN-2000-000972.jpg  License: Public Domain Contributors: NASA, Hui Yang University of Illinois ODNursery of New StarsFile:3D image of Antihydrogen.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:3D_image_of_Antihydrogen.jpg  License: Public Domain  Contributors: NSFImage:hydrogen-1.png  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen-1.png  License: GNU Free Documentation License  Contributors: user:Bryan_Derksen, user:oo64evaFile:hydrogen atom.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen_atom.svg  License: Public Domain  Contributors: User:BensaccountImage:Hydrogen eigenstate n4 l3 m1.png  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen_eigenstate_n4_l3_m1.png  License: GNU Free Documentation License Contributors: User:Geek3File:HAtomOrbitals.png  Source: http://en.wikipedia.org/w/index.php?title=File:HAtomOrbitals.png  License: GNU Free Documentation License  Contributors: Admrboltz, Benjah-bmm27,Dbc334, Dbenbenn, Ejdzej, Falcorian, Kborland, MichaelDiederich, Mion, Saperaud, 6 anonymous editsFile:Hydrogen spectrum.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen_spectrum.svg  License: Creative Commons Attribution-Sharealike 3.0  Contributors:User:OrangeDogFile:Hydrogen transitions.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen_transitions.svg  License: Creative Commons Attribution 2.5  Contributors: User:SzdoriFile:Dihydrogen-2D-dimensions.png  Source: http://en.wikipedia.org/w/index.php?title=File:Dihydrogen-2D-dimensions.png  License: Public Domain  Contributors: Benjah-bmm27, MionFile:Dihydrogen-3D-vdW.png  Source: http://en.wikipedia.org/w/index.php?title=File:Dihydrogen-3D-vdW.png  License: Public Domain  Contributors: Benjah-bmm27, Mion, Pieter Kuiper,ReguiieeeFile:Yes check.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Yes_check.svg  License: Public Domain  Contributors: User:Gmaxwell, User:WarXImage:DOT Hazardous Material Placard liquid hydrogen.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:DOT_Hazardous_Material_Placard_liquid_hydrogen.jpg  License:Public Domain  Contributors: http://www.hydrogen.energy.gov/Image:Linde-Wasserstofftank.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Linde-Wasserstofftank.JPG  License: GNU Free Documentation License  Contributors: User:ClausAbleiterImage:Hydrogen.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen.svg  License: GNU Free Documentation License  Contributors: Mets501, Mion, Soeb, Treisijs, Xxxx00, 5anonymous editsImage:hydrogen-2.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen-2.svg  License: GNU Free Documentation License  Contributors: User:McSushImage:Deuterium Ionized.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Deuterium_Ionized.JPG  License: Creative Commons Attribution-Sharealike 3.0  Contributors:User:Benji9072Image:Deuterium lamp 1.png  Source: http://en.wikipedia.org/w/index.php?title=File:Deuterium_lamp_1.png  License: unknown  Contributors: Deglr6328, QefImage:hydrogen-3.png  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen-3.png  License: GNU Free Documentation License  Contributors: user:oo64evaImage:TritiumLightTraser.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:TritiumLightTraser.jpg  License: Public Domain  Contributors: ViralmemesisImage:Tritium-watch.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Tritium-watch.jpg  License: Creative Commons Attribution 2.5  Contributors: User:AutopilotImage:Spinisomersofmolecularhydrogen.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Spinisomersofmolecularhydrogen.gif  License: Creative Commons Attribution-Sharealike3.0  Contributors: Xaa (Jim Farris)Image:ortho-para_H2_energies.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Ortho-para_H2_energies.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors:User:GadolinistImage:ortho-para_H2_Cvs.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Ortho-para_H2_Cvs.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors:User:GadolinistImage:SuccPdH2.png  Source: http://en.wikipedia.org/w/index.php?title=File:SuccPdH2.png  License: Public Domain  Contributors: User:SmokefootImage:ImineH2.png  Source: http://en.wikipedia.org/w/index.php?title=File:ImineH2.png  License: Public Domain  Contributors: User:SmokefootImage:ResorcinolH2.png  Source: http://en.wikipedia.org/w/index.php?title=File:ResorcinolH2.png  License: Public Domain  Contributors: User:SmokefootImage:CarvoneH2.png  Source: http://en.wikipedia.org/w/index.php?title=File:CarvoneH2.png  License: Public Domain  Contributors: User:SmokefootImage:PhC2HH2.png  Source: http://en.wikipedia.org/w/index.php?title=File:PhC2HH2.png  License: Public Domain  Contributors: User:SmokefootImage:N2H2.png  Source: http://en.wikipedia.org/w/index.php?title=File:N2H2.png  License: Public Domain  Contributors: User:SmokefootImage:BaseCatalyzedKetoneHydrogenation.svg  Source: http://en.wikipedia.org/w/index.php?title=File:BaseCatalyzedKetoneHydrogenation.svg  License: Creative CommonsAttribution-Sharealike 3.0  Contributors: V8rikImage:MetalfreehydrogenationPhosphineBorane.svg  Source: http://en.wikipedia.org/w/index.php?title=File:MetalfreehydrogenationPhosphineBorane.svg  License: Creative CommonsAttribution-Sharealike 3.0  Contributors: V8rikImage:Transfer1.png  Source: http://en.wikipedia.org/w/index.php?title=File:Transfer1.png  License: Creative Commons Attribution 2.5  Contributors: TakometerImage:Transfer2.png  Source: http://en.wikipedia.org/w/index.php?title=File:Transfer2.png  License: Creative Commons Attribution 2.5  Contributors: TakometerImage:AsenapineSynthreductionStep.svg  Source: http://en.wikipedia.org/w/index.php?title=File:AsenapineSynthreductionStep.svg  License: GNU Free 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Image Sources, Licenses and Contributors 129

File:Algae hydrogen production.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Algae_hydrogen_production.jpg  License: Public Domain  Contributors: EEREFile:Photo pathway draft.png  Source: http://en.wikipedia.org/w/index.php?title=File:Photo_pathway_draft.png  License: Free Art License  Contributors: Kasper JensenImage:Hydrogen.from.Coal.gasification tampa.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen.from.Coal.gasification_tampa.jpg  License: Public Domain  Contributors:MichaelFrey, Mion, Petri Krohn, SaupreißFile:Microbial electrolysis cell.png  Source: http://en.wikipedia.org/w/index.php?title=File:Microbial_electrolysis_cell.png  License: Public Domain  Contributors: User:KVDPImage:HydrogenLineAntiParallel.png  Source: http://en.wikipedia.org/w/index.php?title=File:HydrogenLineAntiParallel.png  License: Creative Commons Attribution-Sharealike 3.0 Contributors: Bender235, JabberWokImage:Fine hyperfine levels.png  Source: http://en.wikipedia.org/w/index.php?title=File:Fine_hyperfine_levels.png  License: Public Domain  Contributors: User:DJIndicaImage:Hydrogen transitions.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Hydrogen_transitions.svg  License: Creative Commons Attribution 2.5  Contributors: User:Szdori

License 130

LicenseCreative Commons Attribution-Share Alike 3.0 Unportedhttp:/ / creativecommons. org/ licenses/ by-sa/ 3. 0/