International Molybdenum Association · 4 Heathfield Terrace, London W4 4JE, United Kingdom · Tel: + 44 (0) 207 871 1580 · Fax: + 44 (0) 208 994 6067 · e-mail: info@imoa.info · www.imoa.info

Reducing energy consumption and improving sustainability have become primary goals for designers and building owners aroundthe world. Designs using a second outer façade layer, which may be movable (active) or immovable (passive) can help achievethese goals. Moly-containing Type 316 stainless steel is an excellent choice for these façades because it provides design flexibility,aesthetic appeal and corrosion resistance.

MOLYREVIEW

Article continued on page 6 �

January 2012

If reducing energy consumption and improving sustainability werethe only goals, the optimal building structure would have heavilyinsulated, windowless walls and would use recycled air. Of course,comfort, human health and productivity must also be considered.Balancing all these requirements while still producing beautifulbuildings can be quite a challenge.

Bioclimatic designs meet this challenge by making use of the en-vironment (for example, sun, air, wind, vegetation, water, soil andsky) for heating, cooling, and lighting. This concept is not new. Forhundreds or even thousands of years we have built houses adaptedto the local climate. Examples are thick-walled buildings with

small windows and shutters, typical in southern Europe that keepout the summer heat and maintain the warmth in winter, or thewind towers common in hot Arab countries, which catch the windabove the house and lead a breeze into the buildings.

But bioclimatic designs have been forgotten over the years withthe widespread use of central heating and air conditioning. Thenecessity of saving energy has lead to a renewed appreciation ofthese design principles. These new designs also seek to connectbuilding occupants with their surroundings through a maximumamount of natural lighting and green spaces such as atriums,courtyards, landscaping and green screens.

Energy-saving stainless steel façades

Content

Energy-saving stainless steel façades 1

Bubbling up with stainless 2

Molybdenum disulfide – a great lubricant 4

Atomistically molybdenum 8

Water – our most valuable resource 10

IMOA AGM 2011 12

Symposium on Mo in high performance steels 12

Moly Review

Publisher:International Molybdenum Association

4 Heathfield Terrace

London W4 4JE, United Kingdom

Editor in Chief:Nicole Kinsman

Managing Editor:Curtis Kovach

Contributing Writers:Catherine Houska (ch), James Fritz (jf),

Douglas Kulchar (dk), Philip Mitchell (pm),

Jan Post (jp)

Layout and Design:circa drei, Martina Helzel

The International Molybdenum Association (IMOA) has made every effort to ensure that

the information presented is technically correct. However, IMOA does not represent

or warrant the accuracy of the information contained in MolyReview or its suitability

for any general or specific use. The reader is advised that the material contained

herein is for information purposes only; it should not be used or relied upon for any

specific or general application without first obtaining competent advice. IMOA, its

members, staff and consultants specifically disclaim any and all liability or responsi-

bility of any kind for loss, damage, or injury resulting from the use of the information

contained in this publication.

Bubbling up with stainless

Fresh clean drinking water is something we all expect, including the citizens of Fairfax County near Washington, DC, USA. The localwater authority strives to both meet these expectations and enhance the environment. Their latest project will bubble oxygen gasinto the Occoquan water supply reservoir. This will achieve better oxygen distribution within the reservoir, improving its environ-mental, aquatic and recreational value. The project will also produce better manganese control and therefore better water qualityfor domestic consumption. Moly-containing Type 316 stainless steel components are an important part of the equipment requiredfor the project.

Exciting new things are bubbling up at the OccoquanReservoir in Fairfax, Virginia, where molybdenumstainless steels are helping to make drinking watersafer and better than ever. Dale Kovach, Manager of Construction for Fairfax Water, offered a briefoverview of both the project itself and molybdenum’scrucial role in it.

Stratification and water qualityA dam in the Occoquan River in southeastern Virginiahas created the Occoquan Reservoir with a currentcapacity of around 31 million cubic meter. Duringsummer months, the reservoir water can separateinto three temperature regions and the bottom of thereservoir becomes anaerobic (having low concen-trations of dissolved oxygen, or DO). The three tem-perature regions are the epilimnion (warm top), thehypolimnion (colder bottom) and the thermocline(middle region). Anaerobic conditions result when thecolder bottom becomes separated from the warmertop. This can suppress the fish and plant populationsthat require oxygen for life, and trigger the releaseof organic compounds containing manganese andphosphorous from ground sediment, further degrading

water quality. These minerals affect the taste andodor of drinking water and tend to accumulate asblack or orange build-up on plumbing fixtures. Aswater temperatures decline at the end of summer,the epilimnion cools and its water moves down intothe hypolimnion. This stirs and mixes the low-oxygenwater throughout the reservoir and restores theoxygen content of the hypolimnion. Fairfax Wateraims to preserve a minimum DO level of 5 mg/L, theminimum needed to prevent the release of the or-ganic compounds that affect water quality. This waspreviously achieved by a “destratification” systemthat used air compressors to mix oxygen-rich waterfrom the top with the oxygen-depleted water, similarto an aeration pump in a fish tank. However, recentstudies by Fairfax Water found that the system addedonly about half the required oxygen.

Hypolimnetic oxygenation systems and molybde-num’s key functionsThe destratification system is being replaced by a“hypolimnetic oxygenation system” (HOS), whichcan enhance natural aeration and prevent mineralrelease without having to mix the entire water �

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column. The HOS system aerates only the hypo -limnion waters that are susceptible to water qualityproblems due to low DO, since the warmer watersof the epilimnion layer are naturally aerated. Thesystem “works with Mother Nature” by bubbling pureoxygen from a porous hose into the water during thewarmer months. The porous hose (also called “linediffusor”) is positioned 20 meters below the surface,just above the floor of the reservoir with the help of a buoyancy system. The buoyancy pipe is tied tonumerous anchors, allowing it to float a specific dis-tance above the reservoir bottom. When the buoyancypipe is full of air, the line diffuser floats, and whenflooded with water, the diffuser sinks. The system is so effective that a single 800-meter long line dif-fuser, producing a curtain of rising bubbles, can dothe job. To put it simply, the HOS offers more “bangfor the buck” than the traditional method, increasingboth the quality and quantity of treated water.

Fairfax Water stores liquid oxygen for the system ina 49 cubic meter Type 304 stainless steel vacuum-enclosed tank. The liquid oxygen is carried through30 meters of Type 316 stainless steel pipes andvalves to two dedicated vaporizers which convert theliquid oxygen into gas. The 110-meter pipeline thatcarries the gas to the line diffuser and all the re-quired valves are made of Type 304 stainless steel.Although other pipe materials can be used for pro -jects of this kind, Mr. Kovach explains that Type 316stainless steel was chosen for handling the liquidoxygen due to its strength and high melting point

The Occoquan Dam and lowerreach provide plenty of action attimes of high water flow. Photo:Fairfax County Water Authority

Arrangement of major componentsof the oxygen bubbling system,not to scale.

The Occoquan Dam project in-cludes major dam rehabilitationas well as installation of thewater quality improvement system. Photo: Fairfax CountyWater Authority

compared to other materials. These are key advan-tages in this application because liquid oxygen sup-ports combustion. Stainless steel provides a marginof safety in an emergency and ensures safe, qualityperformance under normal operating conditions.Another key advantage of moly-grade stainless steelover competing materials is its resistance to atmos-pheric and aqueous corrosion, important becausethe gaseous oxygen pipe will be submerged in waterand mounted to the concrete dam. Fairfax Water optedfor Type 316 supports and anchors because they willnot corrode and discolor the dam face.

Molybdenum containing stainless steel pipe func-tions somewhat like blood vessels in this application,dependably carrying essential materials to theirdestinations. Type 316 stainless helps to ensure thenew HOS will be reliable and long lasting, and thatthe drinking water of over 1 million Fairfax Watercustomers will be cleaner and better tasting thanever. (dk)

Anchor Reservoirbottom

Stainlesssteel cable

Pipe teeconnection

Oxygen supply pipe

Saddle connection

Porous hose

Hypolimnion zone

Thermocline zone

Epilimnion zone

Buoyancypipe

4

Molybdenum disulfide with itslayered atom structure. Theblue spheres represent molyb-denum atoms and the yellowspheres sulfur atoms. Under asideways force the S-S layersslide before the S-Mo layersbreak or slide. Friction is muchreduced.

Molybdenum disulfide – a great lubricant

In 1860s Colorado, gold-rush miners lubricated wagon-wheel axles with molybdenum disulfide, prompting awriter of the time to say about the material, “It feelsmuch like soap, and its rubbing against solid bodiesrenders them slippery.” 1

A lubricant reduces friction and wear between mov-ing surfaces in contact with one another by producinga “slippery” film that separates them. Liquid oilsand greases are the most common basic lubricants.Molybdenum disulfide is used as an additive to im-prove the performance of lubricants under demandingconditions. For example, high pressure may squeezea liquid lubricant film out, but molybdenum disulfideadded to the liquid lubricant remains like a coatingon the surfaces to provide continued lubrication.Molybdenum disulfide may also be used alone as adry powder, or as an additive to composite materials.

Molybdenum disulfide structure and lubricityMolybdenum disulfide is a grey solid with a slipperytexture like graphite. It is extracted from the mineralmolybdenite, which contains about 0.25% molybde-num. It is marketed by many manufacturers as drypowder; standard grades have maximum particlesizes of 190, 36 and 7 microns. Lubricant gradeshave a molybdenum disulfide content greater than98%.

Molybdenum disulfide owes its lubricity to its struc-ture – layers of molybdenum atoms stacked be-tween layers of sulfur atoms. These SMoS layers arestacked with the sulfur atoms of each SMoS layerin contact, but they are not chemically bonded. Thisstructure has been compared to a deck of cards,each card representing a SMoS layer. The layers cansupport a downward force, but they slide easily whena sideways force is applied. Particles of molybde-num disulfide form an adherent coating on metalsurfaces that acts as a lubricating film between them.When the surfaces move relative to each other, slid-ing occurs between the SMoS layers and not themetals, reducing friction.

As a dry lubricantThe dry powder is applied to clean, degreased metalsurfaces by brushing or by applying a dispersion ofthe sulfide in a volatile solvent. Molybdenum disul-fide is typically used as a dry lubricant in difficultand extreme applications. Common uses are thebreak-in period of engines, metalworking operationssuch as pressing and bending, and brake linings.

Dry lubricant powder applications – Because it isa solid, molybdenum disulfide retains its lubricity ina vacuum. It is useful over the temperature range of

liquid nitrogen (-196°C) to 1200°C in a vacuum oran inert atmosphere. It oxidises in air above 400°C,losing its lubricity. It is non-volatile and does notoutgas, so it is an ideal lubricant for use in spaceapplications. Space vehicles use bearings with thinfilms of molybdenum disulfide sputtered on ball orroller cages.

Another high-vacuum application is for the movingparts in particle accelerators, for example, the accelerator at CERN, Geneva. Molybdenum disulfidedoes not emit particles and is stable under nuclearradiation, so it is the preferred lubricant for gearsin gas-cooled nuclear reactors where it will notcontaminate the helium cooling gas.

Molybdenum disulfide is used to lubricate the mov-ing parts of jet engines. An important attribute in thisapplication is that it is non-flammable.

As a solid or in solid composite applications Self-lubricating composites contain finely-dividedparticles of molybdenum disulfide suspended invarious plastics. They are used for gears, pulleysheaves, sprockets and custom parts. They can provide excellent performance as thin coatings forparts that have tight tolerances. Applications in-clude printers, scanners, jet engine parts andcomponents that are inaccessible after assembly.

Manufacturers of parts for the auto industry usemolybdenum disulfide coatings on parts like pistonrings. In this case, molybdenum disulfide is formedin situ from a molybdenum compound instead ofbeing applied as molybdenum disulfide. In a newly-developed process, the US Department of Energyhas demonstrated a self-lubricating coating �

Molybdenum disulfide is widelyused as a dry lubricant in bear-ing applications. Photo: istock-photo/frankright

Molybdenum disulfide is the preferred lubricant in many applications. It is used as a dry powder, a suspension in oils or greases,and an additive in plastic composites. It provides for the smooth functioning of machines, which translates into substantial world-wide material and energy savings.

5

by exposing a titanium alloy to a mixture of molyb-denum hexafluoride and other gases. The resultingcoating contains grains of molybdenum disulfidedispersed in titanium nitride. Tests show that thecomposite coating’s coefficient of friction is onlyone third that of a pure titanium nitride coating. 2

As an additive in oils and greasesThe largest commercial use for molybdenum disul-fide is as an additive to oils, emulsified oils, andgreases. Such “sulfurized lubricants” are consideredto be premium lubricants used under heavy loadingconditions, and are marketed by many specialtycompanies.

Automotive applications – In this large marketmany proprietary sulfurized oil and grease formula-tions are available and many claims are made, forexample:

• Molybdenum disulfide incorporated in a crank-case oil, replenished at six month intervals, willmaintain maximum engine protection againstdry and cold starts, wear and oil contamination.

• Molybdenum disulfide in the oil reacts with hotmetal surfaces.

• A solid molybdenum disulfide film plates out onthe surface.

• An engine so treated with molybdenum disulfideis said to be moly-plated.

• Molybdenum disulfide plating an engine providesprotection two to three times that of oil alone anddoubles the life of an engine.

While we should be wary of exaggerated claims, sub-stantial benefit cannot be denied.

General transportation – Molybdenum disulfidehelps with energy conservation in transport by reducing frictional losses in the engine and drivetrain. In fact, every time a lubricant is used in amachine the net result is a reduction in energy cost,which accumulates to being a significant factor interms of worldwide energy costs. Improvements of3% in engine efficiency and up to 4% in final driveefficiency are possible. 3

Metal working – The machining and shaping ofmetals requires lubricants that are effective underextreme pressure. High-performance sulfurized lubricants are standard in this large and importantapplication.

Summary and a word of caution Molybdenum disulfide is an effective and versatilelubricant providing for the efficient operation ofmany high-performance machines. Its wide use pro-duces many economic and sustainability benefits toour society. Proprietary lubricant formulations areavailable, but some carry claims that might not besubstantiated. Full descriptions, applications, andlimitations are available on manufacturers’ websites. (pm)

The lubricating qualities ofmolybdenum disulfide and itsresistance to high heat make ita preferred additive to race carengine oils and other lubricants.These lubricants reduce oil drag and prolong cylinder com-pression life. Photo: istock-photo/mevans

Wind turbines are enormousmachines weighing over 200tons. They have large bearingssubject to very high forces.These high forces and the rela-tive inaccessibility of wind turbines place high demand on their bearings. This in turnrequires special lubricants con-taining molybdenum disulfide.Photo: istockphoto/Baxternator

1 Molybdenum Disulphide Lubrication, A.R. Lansdown (Ed.)Elsevier, 1999, p.3

2 http://www.ornl.gov/info/press_releases/get_press_ release.cfm?ReleaseNumber=mr19950329-01

3 E.R. Braithwaite and A. B. Greene, A Critical Analysis of thePerformance of Molybdenum Compounds in Motor vehicles,“Wear”, 1978, 46,p. 405-4

Skiers go farther and faster whenmolybdenum disulfide is presentin their ski wax because it offersbetter glide and durability thangraphite. Photo: istockphoto/technotr

6

Energy-saving stainless steel façadesContinued from page 1

Stainless steel plays a large role in many of thesebioclimatic projects because of its longevity and lowmaintenance requirements. Many of these projectsare in more corrosive locations with industrial pol-lution or coastal salt exposure. Since the designsinherently create sheltered areas that are unlikely tobe washed by rain, more highly alloyed molybdenum-containing stainless steels are a logical choice, giventheir improved resistance to corrosion.

Double façade technologyThe double façade is a typical bioclimatic design element. Exterior building walls are no longer simpleclimate defense mechanisms. Two façade layers are used: an insulating wall, and a second “shading,”or sheltering, layer. The inner wall is shielded fromweather by the outer layer. Windows in the inner wallare operable and sometimes computer controlled tomaximize natural ventilation.

For the outer wall, a variety of technologies are used,including louvers, woven mesh, perforated screensand green (plant) screens. They may actively changewith varying conditions, or remain passively fixed.This great diversity of design options makes thebioclimatic style equally appropriate for state-of-the-art buildings or low technology/low maintenancedesigns.

Active second façade systemsHybrid systems, a type of active second-skin façade,employ an operable shading system over insulatedglass. The façade may be the outermost wall, orbe tween the inner and outer glass layers, which canbe from 0.2 to 2 meter apart, and incorporate inte-grated sunshades and natural ventilation.

Computer-controlled mechanical operating systemsthat work with the building’s heating and coolingsystems make it possible to respond dynamically tovarying conditions. By adjusting to the sun’s trajec-tory, they maximize the benefits of solar radiation

while minimizing heat gain. Although active systemsare highly adaptable, they are not suitable for allapplications, since energy is necessary to operatethese assemblies, and sensors and mechanics re-quire maintenance. The following are several exam-ples of highly successful active systems.

ThyssenKrupp AG Headquarters – TKQ architectconsortium, JSWD Architekten and Chaix & Morelteamed up with ThyssenKrupp AG to design their newseven-building corporate campus in Essen, Germany.All of the buildings are simple glazed structures, buttheir unique second façade sets them apart. Thebuildings are wrapped in automated sunshade sys-tems consisting of horizontal and vertical slats orcustom perforated sunscreens. These active systemshave moveable Type 316 (UNS S31603) stainlesssteel slats, which save energy by automatically ad-justing to changing conditions. This system, whenused in combination with natural ventilation, elimi-nates the need for air-conditioning. German Sus-tainable Building Council (DGNB) has awarded theproject a Pre-certificate in Gold based on the newGerman Certification for Sustainable Buildings. Energy requirements are expected to be as much as 20 to 30% below statutory requirements.

Council House No. 2 – Melbourne, Australia’smulti-award winning, ten-story Council House No. 2achieved the Green Building Council of Australia’shighest Green Star 6 rating. Compared to typicalconstruction methods, it uses 85% less electricity.Since half the energy consumption for typical Mel-bourne buildings is for traditional air conditioning,this is a great reduction. Additionally, the CouncilHouse uses 87% less gas and 72% less potable

The ThyssenKrupp Quarter cor-porate campus uses Type 316stainless steel exterior sun-screens in varying styles to actively adjust to seasonal andweather conditions to reduceenergy requirements. Photo: ThyssenKrupp AG

Plant screens were used alongthe balconies on the north sideof Council House No. 2 and overthe roof deck to shelter themfrom sun. Photo: Ronstan TensileArchitecture

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7

The perforated Type 316 screensaround 41 Cooper Square give ita sculptural appearance whilereducing the building’s energyconsumption. Photo: Iwan BaanStudio

water, and also reduces CO2 emissions by as muchas 60%. These great statistics are achieved throughthe use of active and passive sunscreens, conductivecooling of the ceiling, and also natural ventilation.

The west facing public façade is comprised of timberslat sunscreens, supported by a lightweight Type316 stainless steel tension cable system that allowsthem to be pivoted in response to the time of dayand angle of the sun. On the north side of the build-ing, passive green plant screens were used on thesides of balconies to screen low angle sun and filterglare. The whole structure, which is supported by aType 316 mesh and tension cable system, extendsover the roof and provides an arbor-like sunshade forthe rooftop terrace.

Passive second façade systems Second layer systems that do not move or adjustthemselves to climatic conditions are termed passivesystems. They use lightweight framing to supportwoven mesh or perforated panels, which allows thedesigner to anticipate changing climatic conditionsby varying the distance between the inner insulatedwall and the exterior hybrid second skin. These sun-shade systems can allow designers to create seam-lessly curving geometric and other shapes, whichcan dramatically change the appearance of a newor existing building at a much lower cost than in-stalling an undulating insulated curtain wall. Passivesystems also avoid the maintenance requirementsof automated systems while still improving energyefficiency, and are suitable for any environment.

41 Cooper Square – 41 Cooper Square is a new16,300 m2 university building at the Cooper Union,which was completed in 2009. It is the first USGreen Building Council LEED-certified educationalbuilding in New York City, and received a US LEEDPlatinum rating in recognition of its innovative design. A seemingly simple glass and aluminumbuilding was wrapped in a curving second facade of perforated Type 316 stainless steel panels. Thissemi-transparent layer gives the building a dramaticsculptural presence with areas of light and shadow.Functionally, the second layer reduces thermal radi-ation in the summer, shields the inner wall duringwinter, and allows natural light to enter. Additionally,seventy-five percent of the building’s regularly usedinterior spaces are lit with natural daylight. Whencombined with other design elements, the stainlesssteel panels help to reduce the building’s energyrequirements by 40%, relative to a standard build-ing of its type.

Guangzhou 2nd Children’s Activity Center – TheGuangzhou 2nd Children’s Activity Center (cover picture) in China provides teaching and performancespace for after-school and weekend arts educationfor primary and secondary school students. Designed �

by Steffian Bradley Architects (SBA) and completedin 2006, this 42,735 m2 concrete and glass buildinghas a capacity for 20,000.

The exterior’s dramatic and seamless compoundcurves were created by a Type 316 stainless steelmesh metal panel system, which eliminates the needfor air-conditioning in common spaces, substantiallyreducing energy requirements. The woven mesh alsomaximizes natural light inside the building, creatinga distinctive identity as well as excellent energysavings.

Stockholm Congress Centre – Designed by WhiteArkitekter of Stockholm and completed in 2011,Sweden’s new Congress Center, which is expectedto receive green building certification, is locatedalong the waterfront in the heart of the city. The con-toured, ribbon-like, softly reflective pieces of stain-less steel hover away from the structure, lending it a striking, undulating appearance, and excellentenergy efficiency.

8

Contoured, ribbon-like, softly re-flective pieces of stainless steelhover away from the StockholmCongress Centre, creating itsdistinctive appearance. Photo:Outokumpu

Atomistically molybdenum

Molybdenum is a transition element with an atomic number of 42 and an atomic mass of 95.96, located in Group 6 of the periodictable. While the preceding sentence may not make much sense to an uninitiated reader, a good chemist or physicist can tell youmore about molybdenum than you might imagine, just by knowing this much. It is a fascinating picture.

Molybdenum is used in a wide variety of ways: asan alloying element in other metals like iron, nickel,and titanium; in chemicals like catalysts, lubricants,corrosion inhibitors and agricultural chemicals; andeven in its pure state as a metal. The unique proper-ties that allow it to be used in so many ways are directly related to its atomic properties and the waysmolybdenum atoms interact with one another andother atoms. To understand why molybdenum be-haves this way, we have to understand the natureof an atom – the smallest quantity of any elementthat is still that element.

AtomsThe atom’s basic building blocks are protons, neu-trons and electrons. Protons are heavy particles(1.6726 × 10-27 kg) that carry a single positivecharge. Neutrons are only 0.14% heavier than protons (1.6749 × 10-27 kg) and are electricallyneutral, while electrons are very light particles(9.1094 × 10-31 kg, or 1/1836th the mass of a pro-ton) that carry a single negative charge. A simpleatomic model comprises a dense core (nucleus) ofneutrons and protons and shells that contain elec-trons, which surround the core.

The number of protons in the nucleus is the atom’satomic number. This number tells us the atom’s elemental identity. A given element may exist withvarious numbers of neutrons in the nucleus. Thesevariants are called isotopes, from the Greek iso(same) and topos (place). They still occupy the sameplace in the periodic table because they all

The passive sunscreen, which angles outward fromthe wall, used 3,500 Z-shaped duplex 2205 (UNSS32205) stainless steel sections, 3 to 16 meters inlength with a semi-reflective matte finish. The screenangle reflects away summer sun while still allowingnatural light to enter. Since the seasonal angle ofthe sun changes in winter, sunlight passes throughthe wall to passively heat the building.

ConclusionsSuccessful sustainable bioclimatic design requiresmaterials that can last the life of the structure orproject. Many of these designs inherently createsheltered environments that are visible from insidethe building. These areas naturally are more corro-sive because the washing action of wind and rain isnot available. Thus, corrosion-resistant molybdenum-containing stainless steel is often the best choicefor bioclimatic second-façade architecture. As themost corrosion resistant of the readily available architectural metal options, it contributes not only tothe functionality and efficiency of these structures,but also helps lend them their striking appearance.Molybdenum may soon be bringing cleaner, greenerbuildings to a corner near you. (ch)

42p54n

K L M N O

Schematic picture of the molybdenum atom showingthe electron shells surrounding the nucleus.

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9

have the same number of protons. For an atom to beneutral, its electron number must equal its protonnumber. If the atom has more or fewer electrons thanprotons, it is called an ion. The atomic mass of anatom is the sum of all its proton, neutron, and electronmasses, but the sum of its neutron and proton massesis a very good approximation to the atomic mass.

Electrons fill their shells according to well-definedrules that permit some elements to have the shellimmediately below the outermost shell (the penulti-mate shell) to be only partially filled. Elements withpartially filled penultimate shells are called transi-tion metals.

Each element’s arrangement of protons, neutrons,and electrons is unique. The arrangement determineshow the element behaves chemically. It also relatesdirectly to the physical properties observed in bulksamples of the element, and to the element’s nuclearstability. This short discussion focuses primarily onchemical behavior.

The periodic tableThe periodic table, devised by Dmitri Mendeleev in1869, displays the elements in an organized fashionthat illustrates their chemical nature. Many otherscientists have proposed alternative versions, butnearly all show the elements arranged in a two-dimensional grid. The table arranges elements inrows with atomic number increasing from left toright and top to bottom (see figure). Rows are de-signed so columns contain elements having similarchemical characteristics. Molybdenum and its com-panions are located in the center of the table withina group called transition elements – atoms withincomplete penultimate electron shells.

An element’s atomic mass and number of electronsare its most important characteristics. This arrange-ment plays a large part in determining how the atomsbond together and react with atoms of other elements.The periodic table gives a trained chemist a per-spective on each element at a glance. An excellentinteractive periodic table is available athttp://www.ptable.com.

The atomic makeup of molybdenumProtons – The enlarged illustration (see figure below)gives a closer look at molybdenum’s place in theperiodic table. The square’s upper left corner displaysmolybdenum’s atomic (proton) number 42.

Neutrons – Adding neutrons to the protons in themolybdenum nucleus gives molybdenum’s relativeatomic mass (95.96 unified atomic mass units) whichis in the lower left corner. The number of neutronsis variable, so several isotopes of molybdenum existin nature. This is one reason why the atomic massis not a whole number.

Electrons – The molybdenum atom contains 42electrons to balance the proton charge. The square’supper right corner shows how molybdenum’s elec-trons fill their shells. Thirteen are in the N shell,which chemists know has a capacity of eighteen.Since the O shell contains an electron, the (penulti-mate) N shell must be unfilled. Hence, molybdenumis a transition metal. The periodic table’s construc-tion places all the transition metals together. Thismakes it easier to identify them and helps us to un-derstand how they react with other elements. Thesepartially filled shells enable molybdenum to interactwith other metals and non-metals in many ways.

The molybdenum atom and chemical propertiesMolybdenum through its unfilled outermost electronshells can lose and gain electrons. This ability, totransfer and share electrons, is closely linked tocompound formation, which is why molybdenum ischemically versatile. Molybdenum is chameleon-like,forming alloys with metals, and compounds with, forexample, oxygen, sulfur, chlorine and carbon com-pounds. This versatility is why molybdenum is im-portant in catalysis, biology and human health, asprevious MolyReview articles have discussed.

SummaryThe structure of the molybdenum atom provides insight into why this element finds unique applica-tions in chemistry, biology and technology. A briefdiscussion cannot do justice to the exciting world of the molybdenum atom. (jp)

MoMolybdenum

2818131

KLMNO

42

95.96

Group 6

Group

Atomic weight

Shells Nand O unfilled(transitionelement)

No. elec-trons inshell

Electronshell

Atomic number (No. protons)

Period 5

Period

Molybdenum’s place in the periodic table –important descriptors

Simplified periodic system of the elements. For simplicity, the Lanthanide andActinide series are omitted.

H1

2

3

4

5

6

7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

*

**

* Lanthanide series; ** Actinide series; Transition elements blocked in yellow

Ti

Zr

Hf

Rf

V

Nb

Ta

Db

Cr

Mo

W

Sg

Mn

Tc

Re

Bh

Fe

Ru

Os

Hs

Co

Rh

Ir

Mt

Ni

Pd

Pt

Ds

Cu

Ag

Au

Rg

Zn

Cd

Hg

Cn

B

Al

Ga

In

Tl

Uut

C

Si

Ge

Sn

Pb

Fl

N

P

As

Sb

Bi

Uup

O

S

Se

Te

Po

Lv

F

Cl

Br

I

At

Uus

He

Ne

Ar

Kr

Xe

Rn

Uuo

10

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Water – our most valuable resource

A great challenge facing the world today is how to meet future fresh water needs. More fresh water will be needed but our resourcesare limited. Conservation will help, but the only real solution is to make fresh water from seawater. Moly-containing stainless steelsplay an important role in the desalination plants used to meet this challenge.

One day when one asks for a glass of water, willthe answer be “There is none”? We hope not. Thereis no doubt that clean fresh water is essential forhealthy living and thriving communities. What wouldwe do without it? Except for the commonly quotedfact that 70% of the earth’s surface is covered bywater, few of us know much about the statistics andtrends related to this vital resource. For example,did you know:

• 97% of the earth’s water is too salty for humanconsumption.

• Less than 1% of our accessible water is freshand safe.

• By 2025 the earth’s population is expected toincrease by 1 billion people, greatly increasingfresh water demand.

• With fixed supply and consumption increasingat its current rate, we will be consuming allavailable fresh water by 2025.

• Currently about 40% of the population, or 3 billion people, live in water-scarce regions.

• According to the United Nations, 1.1 billion people now have no access to a reliable watersupply, and 80% of the disease and deaths indeveloping countries are associated with un-sanitary water.

• Agriculture consumes 75% of our fresh waterresources to produce 40% of our food supply.

Questions about water supplyThe above statistics and projections produce twofundamental questions. Where will the needed extrasupply of fresh drinking water come from? Wherewill the needed extra agricultural water be found?Frighteningly, at our current per-capita consumptionlevel, the water supply will not be able to sustainthe expected population by 2025. The solution tothis problem will require a multipronged approachinvolving conservation, reuse, and development ofnew fresh water sources.

Reducing water consumptionPer-capita residential water consumption variessubstantially depending on cost and availability. Inthe United States, the average daily consumptionper person is 575 liters compared to 193 liters inGermany. This demonstrates that people can getalong with less water if necessary. Conservationworks in places where water is readily availableand where poor usage habits have lead to high consumption. It is far less likely to succeed whereconsumption is already low, such as in arid regions.Unfortunately, the population growth tends to behigh in exactly these arid third-world countrieswhere the water-saving potential is low.

Altering agricultural practices offers the greatestpotential for conservation because of the largeamount of water used and the inefficiency of its use.Currently, worldwide irrigation efficiency is onlyaround 35%, so even small improvements in effi-ciency will yield large savings because of the largeusage. Any solution to our pending water problemmust include more efficient irrigation methods.

Using wastewater (water reclaimed from one appli-cation) for another application can stretch scarcewater resources. The most common example isusing treated sewage water to irrigate golf coursesand other landscape applications. Reclaimed watersare also used to supplement in-stream flows duringdry periods, for wetland enhancement, and forcoastal ground water injection to minimize saltwater.Our reuse of wastewater must increase greatly inthe coming years. This will include the reuse of municipal wastewater as potable water, even thoughwe don’t like to think about this possibility.

Producing new fresh water – desalinationThe only way to increase our supply of fresh wateris to produce it from an abundant source, seawater.We can do this by various desalination (desalting)processes. Today desalination is widely performedby either thermal distillation technologies (TD), orreverse osmosis (RO). Thermal distillation

Summary of the per-capita water consumption for various countries. Source:Data360

100 200 300 400 500 600

Liters/day/person

China

India

Germany

France

Spain

Mexico

Japan

Italy

Australia

USA

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Solid 2205 duplex stainless steel evaporators used in a TDplant in Mellitah, Libya. Photo:Reggiane

evaporates seawater and collects the condensedvapor as fresh water. Reverse osmosis passes sea-water through a special membrane filter that re-moves the salt.

Global desalination capacity has increased exponen-tially since the early 1960s, and this rapid growth is expected to continue. There are about 14,400 desalination plants in operation around the world,having a total daily capacity of 62 million cubic me-ters of fresh water, or 16.3 billion gallons. This mayseem like a lot of water, but in reality it is only tentimes the amount of fresh water provided daily by theFairfax Water Authority to its 1,700,000 customers(see the article on page 2). You might say, “A dropin the bucket” compared to anticipated future needs.

Molybdenum plays a critical role in desalinationtechnology. The most cost-effective materials ofconstruction for desalination plants are molybdenum-bearing stainless steels because molybdenum pro-vides excellent corrosion resistance in seawater.Commonly used grades for brackish water RO plantsand for distillation chambers in thermal seawaterdesalination plants are Type 316L (S31603), 317L(S31703), and 2205 (S32205). These grades containbetween 2 and 3.5% molybdenum. The more highlyalloyed grades such as the 6% Mo super austeniticand 2507 (S32750) super duplex stainless steelsare commonly used for high-pressure piping appli-cations in seawater RO plants. These materials havean excellent performance record in both types ofplants.

Summarizing the future for molybdenumStatistics speak for themselves regarding future worldneeds for fresh water and new desalination plants.Every TD plant uses a large amount of molybdenum-grade stainless steel plate and tubing, while everyRO plant uses a large amount of moly-grade stain-less steel pipe. Mo-grade stainless steels have al-ready established themselves in an existing market

The Fujairah seawater RO plantin the United Arab Emirates,showing its 6% Mo stainlesssteel piping. Photo: Degremont

Stainless steels commonly used in brackish water treatment plants and seawater desalination plants (nominalcompositions in weight %, balance iron)

Grade UNS No. EN No. C (max.) Cr Ni Mo N Other

Austenitic Stainless Steels

316L S31603 1.4404 0.03 17 11 2.1 – –

317L S31703 1.4438 0.03 18 12 3.1 – –

904L N08904 1.4539 0.02 19.5 24.5 4.5 – –

6% Moly grades S31254 1.4547 0.02 20 18 6.1 0.20 Cu - 0.70

N08926 1.4529 0.02 19.5 24.5 6.1 0.20 Cu - 0.70

N08367 – 0.03 20.5 23 6.1 0.20 –

Duplex Stainless Steels

2205 S32205 1.4462 0.03 22 5 3.3 0.16 –

2507 S32750 1.4410 0.03 25 7 3.7 0.27 –

with a tremendous future growth potential. As ournatural fresh water resources become increasinglyscarce, molybdenum will play an ever-increasingand vital role in efforts to increase our fresh watersupply. (jf)

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IMOA AGM 2011

Symposium on Mo in high performance steels

“The Steel City” of Pittsburgh made an excellentbackdrop for IMOA’s 2011 AGM, thanks to generoushost, Thompson Creek Metals. Home to many titansof industry, like Andrew Carnegie and George Westinghouse, Pittsburgh once produced over halfof America’s total steel output, more than all of Europe combined. Today, the city is as well knownfor its educational, medical and cultural institutionsas it is for steel, and it is also a haven for financialand high-tech industries. Over 130 delegates from57 companies and 21 countries took advantage ofthe opportunity to visit Pittsburgh to meet and dis-cuss issues of concern to the molybdenum industry.

A full social program included gala dinners at theimpressive Phipps Conservatory and the spectacular“Music Hall Foyer” of the Carnegie Museum. A recordnumber of companies were in attendance and, wel-coming members and guests, IMOA President MarkWilson noted that such high levels of participationwere the essence of an industry association.

Expert speakers from both academia and industrygave presentations addressing markets, economyand sustainability. Appropriate to the location, therewere papers on developments in specialty steels,advanced high-strength steels and superalloys. Newresearch in the field of catalysis, funded in part by IMOA, was also featured and a paper on Health,Safety and Environment topics demonstrated IMOA’sapproach to regulatory matters: well-designed,sound scientific investigation and dialogue with rel-evant authorities. Members agreed that it was an-other successful and informative IMOA meeting.

IMOA’s next AGM will be held in September 2012 inthe Spanish capital, the vibrant and welcoming cityof Madrid.

The first Taiwan Symposium on “Fundamentals andApplications of Mo and Nb Alloying in High Perform-ance Steels” was held November 7–8, 2011 in theTaiwanese capital of Taipei. The symposium wasjointly organized by IMOA, CBMM, NiobelCon, ChinaSteel Corporation (CSC) and National Taiwan Univer-sity (NTU).

Leading research experts from both academia andindustry gathered to exchange ideas on the innova-tions in steel development necessary to improveenergy conservation, reduction of CO2 emissions, andother serious sustainability challenges facing today’ssteel-related industries. More than 80 delegatesgathered to hear 15 presentations from internation-ally renowned experts, focusing on “MetallurgicalFundamentals” and “Product Applications” of high-performance steels alloyed with Mo and Nb. Of particular interest were the synergies achieved by

alloying with these two elements and other micro -alloy constituents, which together create a moreprofound effect on the host metal’s properties thaneach element’s individual effect.

Line pipe, automotive, and structural applicationsprovide excellent examples where these effects leadto enhanced strength and toughness for a variety ofservice conditions. These better properties saveweight and improve performance and safety in end-use applications. Alloying can also be cost-effectivewhen processing and quality considerations areevaluated.

The symposium was judged a great success by itsparticipants and organizers, who are keen to repeatthe format in the future. The proceedings of thesymposium will be available on the IMOA website,www.imoa.info.

Pittsburgh presents a beautifulsight when viewed at dusk fromMount Washington. Photo: istock- photo.com/Andy445