skylab experiments. volume 3 materials science

8/8/2019 Skylab Experiments. Volume 3 Materials Science

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Source of AcquisitionNASA Washington, D. C.

Volume 3Materials Science

Information for Teachers, Including Suggestionson Relevance to School Curricula.

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qATIONAL AERONAUTICS AND SPACE ADMINISTRATION


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ExperimentsVolume 3MaterialsScience

Produced b y the Sky ab Program and NASA's Edueation ProgramsDivision in Cooperation with the University of Colorado

NATION AL AERONAUTICS AND SPACE ADM INISTRA TIONWashington, D.C. 20546, Ma y 1973

For snle by the Superintendentof Documents, W.8. Government Ph t l w Ofliw,Washington,D.C. !UMZ


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PREFACECharacteristically, new scientific knowledge reaches general application in classrooms yearsafter it has been obtained. This long delay stems, to a large extent, from a lack of awarenessthat information is available and that it has relevance to secondary school curricula. Toaccelerate this process, the National Aeronautics and Space Administration has prepared aseries of documents concerning Skylab experiments to apprise the educational communityin detail of the investigations being conducted in the Skylab Program, and the types ofinformation being produced.The objective is not to introduce the Skylab Program as a subject in the classroom, butrather to make certain that the educational community is aware of the information beinggenerated and that it will be available for use. Readers are urged to use these books as anaid in planning development of future curriculum supplement material to make the mostappropriate use of this source of scientific knowledge.

National Aeronautics and Space AdministrationWashington, D.C. 20546May 1973


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CONTENTSSECTION 1-INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1SECTION 2-PHYSICAL METALLURGY AND CRYSTAL MANUFACTURE .....Gallium Arsenide Crystal Growth (M555) . . . . . . . . . . . . . . . . . . . . . . . . . . . .Vapor Growth of IV-VI Compounds (M556) . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .mmiscible Alloy Compositions (M557)

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .adioactive Tracer Diffusion (M558) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .icrosegregation in Germanium (M559). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .rowth of Spherical Crystals (M560) . . . . . . . . . . . . . . . . . . . . . . . . . . . .hisker.. Reinforced Composites (M561)Indirum Antimonide Crystals (M562) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Mixed 111-V Crystal Growth (M563) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Halide Eutectecs (M564) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ilver Grids Melted in Space (M565) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .luminum.+ opper Eutectic (M566). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .lassroom DemonstrationsSECTION 3-SPACE OPERATIONS SUPPORT EXPERIMENT ...............

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ero-Gravity Flammability (M479)Metals Melting Experiment (M551) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .xothermic Brazing Experiment (M552)SECTION 4-EXPERIMENTAL PROGRAM SUPPORTING FACILITIES ........SECTION 5-APPENDIXES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .-Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .-Bibliography


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INTRODUCTIONThe Skylab Education ProgramThis year the United States' first manned scientific space station, Skylab, was launched intoorbit to be the facility in which successive crews of astronauts can perform more than 270scientific investigations in a variety of fields of interest. These investigations can be dividedinto four categories: physical sciences, biomedical sciences, earth applications, and spaceapplications.The Skylab Program will produce information tha t will enhance present scientific knowledgeand perhaps extend the frontiers of knowledge on subjects ranging from the nature of theuniverse to the structure of the single kiuman cell. It is the objective of the NationalAeronautics and Space Administration that the knowledge derived from the SkylabProgram's investigations be made available to the educational community for applications tohigh school education at the earliest possible date.For this reason, the Skylab Education Program was created to assure tha t maximumeducational benefits are obtained from the Skylab effort, documentation of Skylabactivities is adequately conducted, and understanding of scientific developments isenhanced.his document, one of several volumes prepared as part of the Skylab Education Program,has the dual purpose of (1) nforming high school teachers about the scientific investigationsperformed in Skylab, and (2) enabling teachers to evaluate the educational benefits theSkylab Program can provide.

These books will define the objectives of each experiment, describe the scientificbackground on which the experiment is based, outline the experimental procedures, andindicate the types of data anticipated.In preparing these documents an attempt has been made to illustrate relationships betweenthe planned Skylab investigations and high school science topics. Concepts for classroomactivities have been included that use specific elements of Skylab science as focal points fordemonstrations of selected subjects. In some areas these address current curriculum topicsby providing practical applications of relatively familiar, but sometimes abstract principles;in other areas the goal is to provide an introduction to phenomena rarely addressed in highschool science curricula.It is the hope of the National Aeronautics and Space Administration that these volumes willassist the high school teacher in recognizing the educational value of the informationresulting from the Skylab Program which is available to all who desire to make use of it.ApplicationReaders are asked to evaluate the investigations described herein in terms of the scientificsubjects taught in secondary schools. The related curriculum topics identified should serveas suggestions for the application of Skylab Program-generated information to classroomactivities. As information becomes available from the Skylab Program, announcements willbe distributed to members of the educational community on the NASA EducationalPrograms Division mailing list. To obtain these announcements send name, title, and fullschool mailing list (including zip code) to:

National Aeronautics and Space AdministrationWashington, D.C. 20546Mail Code FE


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This volume deals with the materials science and technology investigations conducted onSkylab. The thirteen experiments that support these investigations have been planned toevaluate the effect of a weightless environment on melting and resolidification of a varietyof metals and semiconductor crystals, and on combustion of solid flammable materials. Thefirst section of the book serves as an introduction to solidification and crystal growth andprovides a unifying background t o the experiments. Section 2 discusses experiments relatedto crystal growth and solidification of metals. Section 3 discusses experiments in weldingand brazing, and flammability; and Section 4 contains a description of the materials scienceexperiment facilities on Skylab. Appendix A contains a glossary and Appendix B abibliography.Attempts have been made to identify relationships between the Skylab science andclassroom science curricula. These are discussed in Sections 1,2 and 3 and are summarizedin Table 1.

Acknowledgments

Table 1 Related Curriculum Topics

Valuable guidance was provided in the area of relevance to high school curricula by Dr.James R. Wailes, Professor of Science Education, School of Education, University ofColorado; assisted by Mr. Kenneth C. Jacknicke, Research Associate on leave from the

SECTION 2PHYSICAL METALLURGY &CRYSTAL MANUFACTURE(M553, M555, M556, M557, M558, M559,M560, M561, M562, M563, M564, M565,M566)

SECTION 3SPACE OPERATIONS - SUPPORTEXPERIMENTS(M479, M551, M552)

CHEMISTRYComposition, crystal growth, crystal structurealloys, electrical conductivity, IV-VI compounds,111-V compounds, phase diagrams, whisker growth,supercooling, semiconductors, properties of mate-rials in vacuum, surface tension, radioactive tracertechniques, zone refining, ultrafiltration porosity,flame tests, and spectroscopy

Combustion, explosive mixture ranges, com-position, oxidation-reduction, alloys, flashpoint and flammability, phase changes;con-vection and buoyancy, specific heat, electronmicroscopy, adhesion, and cohesion

INDUSTRIAL ARTSFinishes, metal forming, reinforced materials Welding, brazingMETALLURGYStructure, nucleation crystals, alloys, tensilestrength, ductility, malleability, sphericity,zone refining

Microstructure alloys

PHYSICSHeat, vacuum, electrical properties, zero gravity,strength of materials, semiconductors, phasechanges, droplet formation, surface tension,radioactive tracer techniques

Convection, heat transfer, ignition and flashpoint buoyancy, diffusion, electron micro-scopy, surface properties, adhesion andcohesion, heat of fusion, and vaporization

GENERAL SCIENCECrystal growth, flame tes ts, phase changes,diffusion

Kindling temperature, combustion, flameextinguishing, flame proofing, dust explo-sion demonstrations: explosive mixturerange, heat transfer, convection currents,crystal growth, purification by crysta llization


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University of Alberta, Edmonton, Alberta, Canada; Mr Russel Yeany, Jr., ResearchAssociate, on leave from the Armstrong School District, Pennsylvania; and Dr. Harry Herzerand Mr. Duane Houston, Education and Research Foundation, Oklahoma State University.The Skylab ProgramThe Skylab orbiting space station will serve as a workshop and living quarters for astronautsas they perform investigations in the following broad categories: physical sciences,biomedical sciences, Earth applications, and space applications.The spacecraft will remain operational for an eight-month period, manned on threeoccasions and unmanned during intervening periods of operation. Each manned flight willhave a crew of three different astronauts. The three flights are planned for durations of onemonth, two months, and two months, respectively.A summary of objectives of each of the categories of investigation follows.Physical ScienceObservations free of filtering and obscuring effects of the Earth's atmosphere will beperformed to increase man's knowledge of (1)he sun and of its importance to Earth andmankind, and (2) the radiation and particulate environment in near-Earth space and thesources from which these phenomena emanate.Biomedical ScienceObservations under conditions different from those on Earth will be made to increase man's 'knowledge of the biological functions of living organisms, and of the capabilities of man tolive and work for prolonged periods in the orbital environment.Earth ApplicationsTechniques will be developed for observing from space and interpreting (1) Earthphenomena in the areas of agriculture, forestry, geology, geography, air and water pollution,land use and meteorology, and ( 2) the influence of man on these elements.Space ApplicationsTechniques for adapting to and using the unique properties of space flight will be developed.The Skylab SpacecraftThe Skylab cluster contains five modules (see illustration).1) The orbital workshop is the prime living and working area for the Skylab crews. Itcontains living and sleeping quarters, food preparation and eating areas, and personalhygiene equipment. It also contains the equipment for the biomedical science experimentsand for some of the physical science and space applications experiments. Solar arrays forgeneration of electrical power are mounted outside this module.2) The uirlock module contains the airlock through which suited astronauts emerge toperform activities outside the cluster. It also contains equipment used to control thecluster's internal environment and the workshop electrical power and communicationssystems.

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3) The multiple docking adapter provides the docking port for t he arriving and departingcommand and service modules, and contains the control center for the telescope mountexperiments and systems. It also houses the Earth applications experiments and materialsscience and technology experiments.4) The Apollo telescope mount houses a sophisticated solar observatory having eighttelescopes observing varying wavelengths from visible, through near and far ultraviolet, toX-ray. It contains the gyroscopes and computers by which the flight attitude of Skylab iscontrolled. Solar arrays mounted on this module generate about hdf of the electrical poweravailable t o the cluster.5) The command and service module is the vehicle in which the crew travels from Earth t oSkylab and back to Earth, and in which supplies are conveyed to Skylab, and experimentspecimens and film are returned to Earth.Skylab will fly in a circular orbit about 436 kilometers (235 nautical miles) above thesurface of the Earth, and is planned to pass over any given point within latitudes 50" northand 50" south of the equator every five days. In its orbital configuration, Skylab will weighover 91,000 kilograms (200,000 pounds) and will contain nearly 370 cubic meters (13,000cubic feet) for work and living space (about the size of a three bedroom house).

1 Apollo telescope mount 5 Biomedical science experiment 9 Airlock module2 Solar arrays 6 Ward room 10 Airlock external hatch3 Sleeping quarters 7 Orbital workshop 11 Multiple docking adapter4 Personal hygiene 8 Experiment compartment 12 Earth resources experiments13 Command and service moduleSkylab Orbiting Station

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Section 1Introduction


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BACKGROUNDSince the Industrial Revolution, progress made in metals de-velopment has undergone significant acceleration. For exam-ple, in the past 20 years, improvements in alloying have al-most doubled the strength of steels and other structuralmetals. Research in other fields has improved other physicalproperties such as corrosion resistance, thermal and electricalconductivity, stability, workability, and tolerance to extremetemperatures, and has brought "new" metals such as titaniuminto commercial usage.The processing of metals is influenced by the Earth's environ-mental characteristics such as the atmosphere in which theprocessing occurs and gravity. The former can introduce ad-verse contaminating influences, but these can be minimizedby use of artificial atmospheres such as inert gases. Nothingpractical can be done about gravitational effects, at least noton Earth. These gravitational effects include separation ofliquid metals of different densities, uneven cooling character-istics and possible chemical contamination from the vessel inwhich the metal must be contained.These undesirable gravity-related effects may be minimized inthe weightless environment of orbital flight where differencesin density have little significance and solidification withoutcontact with a container is possible. Within the orbitingSkylab, experiments will be performed to provide researchdata with respect to the effect of weightlessness on metalprocessing.A few of the basic principles of metallurgy are presented asbackground information in support of the processes involvedin the experiments. For more detailed data, refer to the Bibli-ographyMATERIALSThe Skylab materials science and technology investigationsdeal mainly with metallic materials. The metals studied in-clude the familiar steel, aluminum, copper, nickel, and silverand the less familiar gallium, germanium, indium, and tellu-rium which may not be commonly recognized as metals:The shaded area of the periodic table shown in Figure 1-1identifies those elements that have the metallic characteris-tics, including those elements in the borderline region thathave aspects of both metals and nonmetals.CHARACTERISTICS OF METALSMost substances that are classified as metals have commonphysical characteristics. They are generally light in color and


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Nonmetals

Increasing electronegativityrDecreasing metallic character

. :...:......+: (Borderline 2~: ; ;~ ;~ :. . . . . Metals. ....................Figure 1-1 Periodic Table


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have a lustrous appearance; they have high tensile strength,elasticity, and ductility; they combine with oxygen to formoxides; they have electrical and thermal conductivity; andthey may be manipulated by machining, forming, and extru-sion. The different metals in their pure state have these char-acteristics in varying combinations and degrees; i.e., copperhas high electrical and thermal conductivity, but low tensilestrength; iron has high tensile strength, but low conductivity.

Change in The characteristics of a metal can be selectively changed byCharacteristics the addition of other elements. This combination of otherof Metal chemical elements is called an alloy. Some of the variations in

physical properties obtainable by alloying are (1) he addi-tion of less then 1% arbon to iron produces steel havinggreatly increased tensile strength; (2) the introduction of asmall quant ity of vanadium to a steel alloy increases the hard-ness potential so that it can be used for cutting other steelalloys; and (3 ) adding 2% thorium oxide t o nickel produces amarked increase in high temperature strength.Many important alloy combinations have properties whichcould not be predicted on the basis of the properties of theconstituent metals. For example, copper and nickel, bothhaving good electrical conductivity, form alloys having verylow conductivity, or high resistivity, making them useful aselectrical resistance wire.SEMICONDUCTORSA semiconductor is a material that has electrical conductivitycharacteristics that range between that of a good conductorand an insulator. Pure silicon and germanium function assemiconductors because the electrons in these crystals are notas free to move as in good conductors such as copper oraluminum. In order to make the semiconductors useful astransistors, small traces of another element are added to thecrystal t o provide the excess of positive or negative chargesnecessary for a specific degree of conduction. The process ofadding the substance is called doping the crystal and thesubstance added is called the dopant. The addition of the Dopant-a small quantity of adopant enhances conductivity of the semiconductor crystal; substance added to anotheri.e., if boron is added t o pure silicon at the ratio of one part substance the latter'^boron per million parts silicon, the conductivity is increased propertiesby a factor of about one hundred thousand.Electronic circuitry today is made mostly with semicon-ductor material. The state of the art in semiconductor devel-opment has evolved to the point where microminiature cir-cuits are now widely used. A typical silicon semiconductorchip that measures only a few millimeters across can incorpo-rate 200 devices (such as transistors and diodes) on its surfaceto perform a complex function, such as running a pocketcalculator.


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The density of 200 devices on a single chip could be in-creased about a hundred times if a perfect semiconductorcrystal could be manufactured. On a piece of silicon less thanone inch in diameter, 750,000 devices could be incorporatedto serve as a photocathode of a television camera capable ofresolution of images with extremely low level light sources.This is not possible yet because of manufacturing limitations.SOLIDIFICATION OF METALS

4 Body centeredStructure Pure Metals-The atoms in a metal, in the liquid phase, mdve cubicfreely, but as the temperature is lowered they lose energy and 1their motion becomes increasingly dluggish. At the freezing 4temperature, or slightly above, nuclei (small clusters of atoinsin a definite crystalline arrangement) begin t o form. Becauseof internal temperature variations some nuclei melt back to 5 Face centeredcubicthe liquid phase while in other locations in the melt new 4nuclei begin to form. As the temperature decreased, the rateof formation of nuclei exceeds that of melting and the crys- 5tals grow larger.7 Hexagonal close

As solidification proceeds, the crystal nuclei form in different packed structuredirections and the atoms tend to become disposed in a defi-nite geometrical pattern known as the space lattice. @ 7The particular basic geometric arrangement of atoms withinthe crystal depends on the particular metal. In general, metalcrystals are arranged in one of three patterns. There are thebody-centered cubic, the face-centered cubici and the hexag-onal close packed structures. This orderly structure repeatsits basic form in geometric cells aligning their parallel facetsthroughout the crystal.

Dendrites The crystals attract other atoms to their space lattice anddevelop crystalline structures called dendrites. If heat is con-tinually removed from the solid to liquid interface, the den-drites will expand and grow into the liquid metal. Thisgrowth progresses until a neighbopkg crystal of the samem4@

5form but of a different orientation obstructs the growth. Dendritic GrowthEach of the fesulting crystals is called a grain and the inter-face between the grains is called the grain boundary.If the temperature is maintained just below the freezingpoint, the rate of nucleation is low and fewer crystal growthsites develop. The resulting crystals grow larger because thereare fewer neighboring crystals to obstruct the growth. If thetemperature is lowered in such a way that no nuclei areformed at the freezing point, or below, the metal is said to beundercooled. There is a low temperature in an undercooledmetal where nucleation sites occur uniformly and rapidly Grthroughout the melt and the metal freezes with many small Grains (Crystals)sized grains.


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Chill Columnar Columnar ChillZone Zone I Zone Zone

~ b l dWallSection View of a Casting

~ d l dWall

The sketch illustrates the crystal growth sizes in a typicalmetal casting. The outer edges have small grains because thewalls of the container tended to undercool that region orimpurities in the container acted as nucleation sites. Further Nucleation-to bring togetherinto the casting, the rate of nucleation was lower and fewer into a nucleus. nuclei were present t o interfere with the growing crystals.The larger crystal grains in a casting result in a weaker overallstructure because tiny cleavage cracks will tend to progressrapidly along the facets in aligned crystal form. Conversely,multioriented crystals of many small grains teqd to impedethe advance of a cleavage crack. I t is important then, fromthe standpoint of strength, that a casting be made of manysmall grains.

Solidification Alloys-The freezing of an alloy follows the same crystalTemperatures growth sequence as a pure metal; however, as the constituentelements may have different solidification temperatures, thechange from liquid phase to solid phase occurs over a temper-ature range. Within this range both phases can exist for bothmaterials. A graphic representation of this temperature rangeis shown in Figure 1-2.Both metals in the

Metals are both

0 10 20 30 40 50 60 70 80 90 100Atomic percentage of silver

Figure 1-2 Phase Diagram of Silver and Gold


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Figure 1-2 Photomicrograph of TD Nickel6


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Temperature This figure shows the variation of the dual phase temperatureRange range with variation of composition of the alloy. It will beseen that as the percentage of silver in the gold/silver alloy isincreased toward 60%, the dual phase temperature range di-minishes. At the 60% silver point the temperature range iszero, i.e., above the temperature shown (779" ) both metalsare liquid and below 779" both are solid. This composition iscalled the eutectic composition.Detailed analysis of an alloy having the eutectic (60% silver,40% gold) composition would show a homogeneous structurewith the proportions of each element being uniform through-out the melt. In another alloy, for example 30% silver, 70%gold, the ,percentage composition would vary throughout thissolid with silver-rich particles being contained in a gold-richmatrix. This is caused by the freezing solvent (gold) rejectingsome of the liquid solute (silver). The process is called segre-gation and the result is undesirable in an alloy, from thestandpoint of maintaining homogeneous characteristics suchas corrosion resistance.FORCES INFLUENCING SOLIDIFICATIONThe forces that have an effect on the composition or shape ofa solidified metal are volume changes, surface tension, andgravity induced segregation and convection.In producing an alloy with uniform distribution of elements,it is important to insure that the temperature during themolten phase is uniform throughout. As a metal is starting tosolidify, however, quantities of hot liquid are in motion with-in the melt. The hot less-dense liquid tends to rise causing aturbulent thermal condition. Because of this, there is no uni-form temperature distribution and the alloyed metal solidi-fies with an uneven distribution of elements..An alloy is also affected by gravity-induced segregation. Theless-dense material tends to float upward in the molten phasecausing a nonuniform distribution of elements. These twofactors are presented as problems in obtaining a good, uni-formly composed alloy. In general, these problems are appar-ent in the processing of all metals but for most stqctural ordecorative use of metals it is not really necessary to achievethe ideal (perfectly uniform) distribution of elements. Largemetal structures exhibit their particular alloy characteristicsjust by the average distribution of elements. However, in verysmall structures of metal such as semiconductor crystals orthe tiny wires used in a heart pacemaker, the uniformity ofcomposition becomes very important.Surface tension is the force that holds a small drop of liquidon a flat surface in the shape of a flattened sphere. As theamount of liquid (i-e., the mass) is increased, the gravitational


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force on the liquid overrides the surface tension and the liq- Shape of a large amountuid spreads to assume a much flatter shape. The profile of the of Mercury flattened byedge of the "pool" continues to reflect the profile of the gravitational orcesoriginal drop (i.e., the effect of the surface tension is evident)but the original nearly spherical form is lost. In a weightlessenvironment the surface tension is expected to become thecontrolling force regardless of the mass of the liquid.A change in volume characteristically accompanies a changeiquid to of a small amountSolid of state from liquid to solid. Usually this change is a reduc- of Mercurytion in volume. In a few special cases the volume increases,such as freezing water to ice, a common example, and galliumwhich increases in volume as it solidifies.Liquids allowed to solidify on Earth generally have a form asshown in Figure 1-3. The hollow (or pipe) on the top of theingot results from the flow of the remaining liquid into thespaces between the already solidified dendrites. Solidificationof a liquid in a weightless environment is expected to result

, in the formation of a cavity (or cavities) inside the sphericalbody with no apparent change in outside shape. High internalstresses will result from the combination of volume changedue to solidification and the thermal stresses of cooling.Original liquid level

Section of a metalingot formed on EarthSection of a metalingot formed in aweightless environmentwithout a container

Figure 1-3 Volume Change in a Metal

THE ROLE OF CONVECTION IN COMBUSTIONConvective flow, discussed earlier as a disruptive influence inthe formation of homogeneous solids, has a major role in themuch more easily appreciated process of combustion. It isconvection that replenishes the oxygen needed to sustaincombustion. In the case of severe forest fires, the inrush ofair powered by convective flow produces local high windsthat make the situation worse. In a weightless environment,gravity-induced convection should not occur and the combus-tion process will be different. This condition will permit de-tailed study of other aspects of combustion that are usuallymasked by the convection effects. These include heat gradi-ents, flashover, and self-extinguishment.


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SKYLAB MATERIALS SCIENCE INVESTIGATIONSSixteen experiments are planned to be performed on Skylabto study the aspects of materials science briefly discussed inthe preceding paragraphs. The experiments are:M553-Sphere FormingM555-Single Crystal GrowthM556-Vapor Growth of IV-VI CompoundsM557-Immiscible Alloy CompositionsM558-Radioactive Tracer DiffusionM559-Microsegregation in GermaniumM560--Growth of Spherical Crystals

. M561-Whisker-Reinforced CompositesM562-Indium Antimonide CrystalsM563-Mixed 111-V Crystal GrowthM564-Halide EutecticsM565-Silver Grids Melted in SpaceM566-Aluminum-Copper EutecticThese thirteen experiments are described in Section 2. Thefollowing three experiments are described in Section 3:M479-Zero Gravity FlammabilityM55l-Metals MeltingM522-Exothermic Brazing

CREW ACTIVITIESA Skylab crew member will follow prescribed procedureswhile performing the materials experiments. He will preparethe work areas for each experiment, obtain the particularexperiment specimen and install it in the appropriate facility,and initiate the experiment process. He will observe and re-cord any outward reactions that the experiments produce. Hewill control the heating and cooling rates used in some exper-iments, vent or depressurize and repressurize the work cham-ber as appropriate, and provide water sprays when required.


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Finally, he will remove and store the experiment specimensand apparatus and clean the work areas in preparation for thenext experiment.DATAInformation resulting from these experiments will be derivedfrom postmission analysis of telemetered data and returnedspecimens formed.Photographic data of those activities suitably exposed willalso be available. The specific data generated by each experi-ment will be discussed in that experiment description. Gener-ally this data and the results of specimen analyses are ex-pected to be available between 90 days and a year after per-formance of the experiment.RELATED CLASSROOM DEMONSTRATIONSWater may be used to demonstrate some of the solidificationprocesses of metals.

Crystal Nucleation and crystal growth can be demonstrated withGrowth water by lowering the temperature of pure water belowits freezing point. Foreign objects of small radii shouldnot be present in the water, and it is sometimes necessaryto wax the container. At a temperature of about -4" orlower, drop a small ice crystal into the undercooled waterand it will freeze immediately. The ice crystal acted as anucleation site. .Dendrite Dendritic growth of ice crystals can be observed by low- 'vGrowth ering the temperature of a glass plate to below the freez-ing point of water (i.e., by chilling the plate in the freezersection of the refrigerator), and maintaining that temper-ature while allowing cool water vapor to condense on theplate. This produces frost patterns that are characteristicof dendritic growth. (See illustration.)

Dendrite growth of wateThe grain boundaries of a piece of metal are normally crystalsinvisible. A metallographic technique to observe a metalspscimen is to etch the grains to make them visible. Themetal specimen may be prepared by highly polishing andetching it with a dilute etchant and washing it with alco-hol and water. The specimen may then be observed usinga microscope with low angle illumination. (It may requirea second polishing and etching to produce a useful sam-ple, as illustrated.) The etching fluids are usually dilute(2-4%) alcholic solutions of acids or bases. Examples in-clude:- steel, 2% nitric acid in alcohol or 4% picric acid in

alcohol; Microscopic view of graiboundaries made visible b- gold and platinum, aqua regia; chemical etching


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- brasses and copper alloys, -2%solution of ferric chlo-ride;- tin, 2%nitric acid in alcohol;- aluminum, hydrofluoric acid.

Look closely a t a piece of galvanized steel. Note the fan-like groupings of zinc crystals covering the surface. Theseare grains of zinc crystals overlapping each other.Convection The role of convection in combustion is easily demon-

strated by placing a candle at the base of a container,such as the chimney of a kerosene lamp. The base of thischimney is closed and the top is open. Note how long thecandle continues t o burn. Now suspend a T-shaped pieceof material reaching almost down to the flame andslightly offset. The air mass begins a convective flowdown one side of the divider and up the other side.

ConvectiveFlow

Convection in Combustion


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Section 2Physical Metallurgy andCrystal Manufacture


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This section describes a series of experiments designed toinvestigate the physical, chemical, and thermal mechanismsthat control the manufacture of a variety of metallicmate ri als . By performing these investigations in theweightless environment of Skylab, information can bederived related to the current theories about the influence ofgravity on the physical and chemical processes of melting andsolidification of metals.BACKGROUND

Crystal For- The investigations discussed in the fo'llowing paragraphs dealmation with the effect of gravity on crystal formation, on the mixing

of metals in alloys, and on the value of surface tension as ashaping influence.In Section 1 he effect of uneven heat flow on the crystallinestructure of metals was discussed. Variations in crystal sizeoccur because of uneven conditions of undercooling arisingfrom heat loss to the atmosphere surrounding the melt or tothe container in which the metal solidifies. In this weightlessenvironment, small quantities of pure metals and alloyssolidified in a free floating condition out of contact withexternal heat sinks will be compared with identical melts thatsolidified while still attached t o a support.The alloy combinations used in these investigations includematerials of different melting temperatures and densities.Solidification of alloys having components with suchdifferences can result in segregation in which the centralportion of a dendritic crystal is richer in the element havingthe higher freezing point. If the lower freezing point also hasthe lower density, the segregation can also be accompaniedby stratification of the constituent elements when theprocess is performed on Earth. This phenomenon should notoccur in the weightless environment of Skylab.Use of metallic mixtures with wide density differences resultsin undesirable stratification on Earth to the extent that theproperties sought cannot be achieved. An example is thepossible use of crystal "whiskers" of very high tensile Whiskers-Elongated singlestrength to reinforce low strength metals. crystals can be used to reinforcelow strength metals.By uniformly distributing these whiskers through a lowerstrength material, a composite material of very high strengthcan be achieved. Relative densities play a significant rolein whisker reinforced materials. In these cases the densitydifferences cause the whiskers to float on the surface ofcomposite material. In a gravity-free environment, uniformdistribution should be possible.Another gravity-related phenomenon that influences metalsolidification is convection while the material is in the liquid


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phase. Convective flow of the liquid metal can occur in thewhole melt or in separate areas depending on variations inlocal temperatures. These flows can have adverse influenceson the resulting metal properties, particularly in the area ofdisrupting segregation.Depending on the required properties, segregation ofconstituent elements in the metal mixtures may or may notbe desirable. Solidification of certain metal mixtures ofeutectic composition in which th e freezing temperatures ofthe elements are the same, results in distinct segregation ofthe crystals of the components. ~e j' ec tion f one componentby the other occurs within the liquid phase just ahead of thecrystal growth and can cause parallel crystal formation inwhich lamella, or rods, develop through the solid.

Lamellar These linear or lamellar crystals can introduce desirable L amellar-para llel plates oCrystals properties such as super conduction of electricity, optical metal crystals resulting from acharacteristics, directional magnetism, etc. Local or general sing1econvective flows can prevent the formation of thesestructural features by disrupting the development of thecrystals.With the elimination of gravity-related stratification orconvective flow, other forces become influential in materialprocessing. These include diffusion and surface tension.Diffusion of one material through another occurs by theprobabilistic migration of the atoms. The paths of theindividual atoms is random but there is a general flow fromareas of high concentration to areas of low concentration.Diffusive flow is generally accelerated by heating, i.e., themotion of the atoms is more energetic. On Earth, gravity canplay an important part especially when a significant densitydifference occurs. In a weightless environment, thegravitational influence is eliminated and the diffusion can bestudied.The relative roles of gravity and surface tension in formingmetals in the liquid phase was mentioned in Section 1.Theinfluence of surface tension on molten metals will be studiedin two investigations in the Skylab environment. Ahomogeneous material in the liquid phase in free fall shouldform a sphere and since no container is required to hold it inspace, i t will retain that shape while solidifying.The experiments related to the above areas of investigation,and described in the following paragraphs, are all performedwith in th e Skylab Materials Processing Facility. Thisequipment is described in Section 4 of this volume.Except for experiments M553 and M555, the crystalmanufacturing experiments in this section will be performedin similar procedures. The metal specimens for each


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experiment are encased in cartridges (Figure 2-1) of similarconfiguration that fit in the electric furnace. There areindividual differences between the cartridges and the furnacesin the arrangement of heat flow paths. The experimentspecimen melting and freezing takes place entirely inside thecartridge.

ExperimentCartridge Hot zone Gradient zone Cool zoneom- iFigure 2-1 A Typical Experiment Cartridge Exposed to theHeating and Cooling Zones of the Electric Furnace

SPHERE FORMING EXPERIMENT (M553)SCIENTIFIC OBJECTIVESBy melting metals in a weightless environment and allowing Free floating melt maximizesthem to freeze while attached to a support or while floating undercooling.free out of contact with any structure, it would be possiblet o demonstrate that solidification may be achieved at muchlower levels of undercooling than on the Earth. I t should alsob e possible to determine the effects of melting andsolidifying in a low gravity environment on the magneticproperties of the metal, and the low gravity effects associatedwith freezing an alloy that has a wide freezing range and awide density difference between components. In addition,the role of surface tension in shaping molten metal in theabsence of gravity-induced forces will be studied.MATERIALThe materials selected for this experiment represent a widerange of metals. High purity nickel (Ni) was selected becauseit is representative of unalloyed metals having a single meltingpoint. Nickel with one percent silver (Ni-1% Ag) was chosenbecause it is representative of alloys having a narrow melting Microsegregation-the segrega-range, approximately 5" C, and a density range (Ni, 8.8 tion of one element because ofgrn/cm3 Ag, 10.45 gm/cm3) that will allow segregation differences in freezingrates.upon solidification on Earth permitting relatively simplestructural analysis for comparison with pure nickel. Silver inthis alloy will inhibit grain growth and provide a basis for thestudy of microsegregation. Nickel with 30 weight percentcopper (Ni-30% Cu) is an alloy with a fairly wide meltingrange, approximately 50C, but almost no difference indensity between the two elements. Nickel with 1 2 weightpercent tin (Ni-12% Sn) is an alloy with wide melting range,approximately 15OoC, and slight density difference betweenelements.


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PERFORMANCE

Sphere Form-ing Apparatus

Several samples of the four metals tha t are to be melted aremounted on the periphery of a wheel. An electron beam isthe heat source. (See Section 4.) The sphere formingapparatus (Figure 2-2) is placed in the work chamber and thechamber is depressurized. The wheel rotates until eachsample to be melted comes in line with the electron beam.Some melted samples are ejected t o float freely inside thechamber and solidify in a spherical shape; other samples willmelt and solidify while still attached to the wheel.

r Drive motor

'LElectron beamY~ Sphere formingspecimen wheel

0 0

Figure 2-2 Sphere Forming Apparatus

DATADuring the experiment, the time required to melt eachsample is recorded and a film recording of each melt is made.All samples are returned to Earth and the followingmeasurements will be taken:1) chemical analysis of the specimen by various methods Mass Spectrography-convertingsuch as wet chemistry, mass spectrography, vacuum molecules into ions and thenfusion, and emission spectrography; separating the ions according totheir mass charge ratio.2) standard metallographic techniques to evaluate the

microstructure, segregations, grain size and microporosityof specimens;

3) sphericity;4) surface smoothness using the scanning electronmicroscope.

Film Records In addition, the film records will .be examined and correlatedwith high-speed (200 frameslsec) motion pictures takenduring duplicate runs with similar samples and apparatus onEarth.

16


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GALLIUM ARSENIDE CRYSTAL GROWTH (M555)BACKGROUNDSingle crystals of gallium arsenide (GaAs), a commerciallyvaluable semiconductor, have been prepared by a variety oftechniques: growth from the melt, growth by vapor phasereaction, and growth from metallic solutions. In all cases, thegoal has been to prepare material of the highest possiblechemical homogeneity and crystalline perfection.Although growth from the melt can produce a relatively largeamount of material in a given time, the technique presents anumber of serious problems such as thermal convection.Crystals can be grown at temperatures lower than the meltingtemperature by either vapor phase or liquid solution growthtechniques. In vapor phase growth, temperature fluctuationsare injurious to crystal perfection, and since the system haslow thermal mass, its response to system temperatures is. rapid. Thus, precise temperature control of the growthapparatus is necessary. Growth of crystals from metallicsolutions offers a valuable method of producing high qualitymaterial; however, thermally driven convection currents haveintroduced difficulties. This problem would, of course, beeliminated in weightless conditions.In one method of controlled solidification on Earth, themolten metal is supported in a horizontal "boat" and is madet o freeze progressively from one end by slowly moving anelectric furnace along the boat. The leading edge of the boatis tapered to reduce the number of nuclei forming there. Asmall single cry~tals, sometimes provided as a ready-madestarting point, or seed, from which the crystal can grow. Theseed is oriented at the face angle of the desired crystal. Theboat sometimes has a bend in it that also aids crystalorientation. (See illustration.) Then, if no competitivenucleus interferes and if there are no thermal convections,th e entire melt will solidify into a single crystal. Boat for Single Crystal GrowthMATERIALThe material selected for this experiment is GaAs with a sili-con dopant. Three arrangements of the experiments are:1) pure GaAs crystal grown on a pure GaAs seed;2) pure GaAs crysta! grown on a silicon doped GaAs seed;3) silicon doped GaAs crystal grown on a pure GaAs seed.SCIENTIFIC OBJECTIVESThe major advantages anticipated from a reduced gravityenvironment on the growth of single crystals are:


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1) improved cry s talline perfection because of staticconvectionless melt;2) better doping uniformity because of the absence of Doping-the process of adding

temperature fluctuations; dopant to a material3) more uniform starting melts because the less dense solidmaterial will no t concentrate and "float";4) more uniform growth due to static, diffusion controlled,transport of the components of the melt.PERFORMANCE

Spherical Crys- In space the "boat" must consist of an enclosed tube. (Seetal Growth Figure 2-3.) The furnace is a heater in the Material ProcessingFacility. (See Section 4.)

YN' %

Gallium arsenidephsourceQuartzdiffusion

One millimeter -diameter holes

SeedAgalliumsolvent

Figure 2-3 Cartridge fo r Spherical Crystal Growth

Upon heating, the GaAs source material will dissolve into theliquid gallium, diffuse through the diffusion plate, anddisperse throughout the liquid. At the lower temperatureend, the GaAs will begin its crystalline growth on asuspended single crystal seed. After the crystal growth, thetemperature of the specimen must be maintained above 30"Ct o keep the gallium molten since i t expands upon freezing.The liquid phase will be maintained until the single crystal isretrieved on Earth.DATAUpon return to Earth, the growth material will be analyzedby techniques already developed for the evaluation of GaAs.


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Such techniques include chemical etching for the study ofimpurity distxibution, x-ray topographic analysis for thestudy of crystal lattice perfection, and a variety of electricalmeasurements to characterize the semiconducting propertiesof the material. These data will be used to compare thespace-grown material with material grown by similartechniques on Earth, as well as with Earth-grown materialfrom other sources.

VAPOR GROWTH OF IV-VI COMPOUNDSBACKGROUND

Semi- The numbers IV and VI refer to the main groups of elementsconductors on the periodic table of elements. The particular compoundsin this experiment are germanium telluride (GeTe) andge rm an iu m sel enide (GeSe). Mixed crystals of these. compounds are used extensively as semiconductors; however,more efficient and increased utilization of the compoundcould be realized if more perfect crystals could be produced.The problem here is that perfectly uniform crystals cannot beproduced on Earth because of thermal convection in thecrystal growing process. These crystals are grown from the Weightlessness inhibits convec-vapor phase by placing specific amounts of semiconductor tion and supports uniformity ofcompound in an enclosed quartz tube and heating until the growth.compound vaporizes. One end of the tube is allowed to cooland the compound begins to solidify there. As the vaporizedgermanium and tellurium diffuse down the tube, convectioncauses fluctuations in temperature. Turbulent flow developsin the transfer of the vapor mass down the tube resulting in acrystal growth with nonuniform distribution of elements. Inthe weightlessness of a space experiment, convection shouldbe inhibited and vapor can be expected to flow uniformlyand produce a uniform composition.SCIENTIFIC OBJECTIVEThe objective of this experiment is to determine the degreeof improvement that can be obtained in the perfection andchemical uniformity of crystals grown by chemical vaportransport under weightless conditions of space.PERFORMANCEMixed crystals of GeSe and GeTe compound semiconductorswill be grown by chemical transport through a temperaturegradient in a transport agent, germanium tetraiodide, frompolycrystalline sources of the two component materials. Thegrowth process will be carried out in sealed quartz ampulescontained in metal cartridges. (See Figure 2-4.)


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Vaporizedc0mp0un7Vapor growth crystalsCopper heat sink-, The rat e of vaporization is muchgreater in the presence of atransport agent (in this caseGe14) th an in a vacuum.Figure 2-4 Vapor Growth of IV-VI Compo unds

DATAAfter return to Earth, the samples will be evaluated forchemical composition and homogeneity, crystal perfection,trace impurities, and optical and electrical properties, incomparison with samples produced under similar processconditions on Earth. The processes used for analysis areemission spectroscopy, spark source mass spectrometry,conductivity measurements, scanning electron microscope,and x-ray topography.

IMMISCIBLE ALLOY COMPOSITIONS (M557)BACKGROUND

New Alloys Immiscible alloys are mixtures of metals that segregate onEarth when melted. The segregation is such that the metalsactually stratify; the less dense metal floats on top of thedense metal. If some combinations of these metals could bemade to mix, new alloys of superior properties may bedeveloped. For example, gold and germanium could be usedas a new superconductor material. A mixture of lead, indium,and tin has a potential use as a superior superconductor inhigh magnetic fields.SCIENTIFIC OBJECTIVEThe obiective of this experiment is to melt three immiscible Emission Spectroscopy-radia-mixtures and refreeze them to determine the effects of tion emitted in the form of dis-weightlessness on segregation. crete wave lengths called spectrallines provides analytical tool.PERFORMANCEThe experiment consists of three mixtures in three separatesections of the same experiment cartridge (Figure 2-5.) Twomixtures in the hot zone of the furnace will undergo melting--ot zone Gradient zoneFigure 2-5 Experiment Cartridge with Ampules of Immiscible Alloys


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and then isothermal solidification. The mixture in the Isothermal-indicating constantgradient temperature zone of the experiment cartridge will be temperatures-partially melted and allowed t o solidify directionally.The immiscible alloy compositions are:

amp ule A-gold-23.2% germa nium (isothelmalsolidification)amp ule B-lead-45% zinc-10% antimony (isothermalsolidification)am pu le C-lead-15% indium-f 5% tin (directionalsolidification)

Densities (gm/cm3)gold-18.88germanium- 5.49lead - 1.34

.o zinc- 6.92antimony - 6.62indium- 7.3tin - 7.28

DATAMetallurgical Metallurgical analysis will be made on the specimens onAnalysis Earth. The surfaces will be etched and viewed through a

scanning electron microscope to verify the homogeneity ofthe mixtures.

RADIOACTIVE TRACER DIFFUSION (M558)BACKGROUND

Diffusion in In a metal bar composed of two different metalsPure Metals mechanically joined together, the atoms of one metal will

diffuse i ~ t ohe other when the metals are melted; the metalwith the lower melting point will diffuse faster than theother. In a pure elementary material where there is no high orlow concentration of atoms and the energy level of all of theatoms is about th e same, diffusion still takes place. If thebar is heated, diffusion takes place at a faster rate becauseexcited atoms have a greater probability of changing places.Also, dislocations and vacancies are more numerous in heatedmetals and the atoms will tend to migrate into the holes. In aweightless condition, the extent of the diffusion should belimited to that caused by the energetic motion of the excitedatoms (Brownian motion) and that caused by the artificialgravity pressures caused by spacecraft accelerations.

Directional Solidification--theprocess of cooling a melt bydrawing the heat from just oneend of the container and allow-ing the melt to solidify towardthe warmer end.


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To measure this diffusion process, a bar of metal is used inwhich a certain portion contains a specific amount ofradioactive isotope of the same metal. As the radioactivematerial diffuses, the extent of diffusion can be measured bythe distribution of radiation levels. This is usually determinedby measuring radiation levels of each set of lathe turningsobtained by machining the chilled bar.SCIENTIFIC OBJECTIVE

Self-diffusion The objective of this experiment is s to measure self-diffusion"d Impurity and impurity diffusion effects in liquid metals in a weightlessDiffusion environment and characterize the distributing effects, if any,caused by spacecraft acceleration.MATERIALAND PERFORMANCEThree rods of zinc metal are prepared with a section of Tracer-a radioactive isotoperadioactive zinc (Zn6 ) plated to one end of each of two rods that can be traced through theand in the midsection of the third rod. The zinc rods are process.encased in a tube of tantalum and sealed in the experimentcartridges.(See Figure 2-6.) The rods will be melted in themultipurpose electric furnace, held at a constant temperaturewhile the radioactive atoms diffuse into the liquid metal, andthen frozen.

Zinc rod7 Radioactive zinc plating\ \ I6 IIt

Figure 2-6 Radioactive Tracer Diffusion ExperimentDATAUpon return to Earth, the zinc rods will be sectioned andmachined, and the concentration of the diffused radioactivezinc will be measured. Results will be analyzed to determinevalues of the liquid diffusion coefficients in the samplematerials and characterize deviations from ideal behaviorbecause of spacecraft accelerations.

MICROSEGREGATION IN GERMANIUM (M559)BACKGROUNDAs crystals solidify, there is some segregation of impurities ona very small scale. Impurities are preferentially rejected orincorporated into a freezing crystal. Utilizing even the mostcareful techniques, this segregation causes nonuniforrnity insemiconductor "doping".The central portion of a dendritic crystal is richer in theelement having the higher freezing point. The other element,


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still in the liquid phase, is forced outside the dendrite. This Microsegregation can influenceamount of segregation has little effect on large scale electrical properties of crystals.characteristics because the various concentrations of differentmaterials average out. As smaller and smaller segments of thematerial are used (as in microminiature circuitry), theconcentration of material from one "micropoint" to the nextbecomes critical and "averaging" is no longer possible. Inaddition to this problem, gravity-induced convection withinthe melt further enhances the uneven distribution ofmaterials.SCIENTIFIC OBJECTIVEThe objective of this experiment is to determine the extentof microsegregation of doping material in germanium causedby convectionless directional solidification in space.

PERFORMANCEMicrosegrega- Single-crystal rods of germanium doped with antimony (antion electron donor), gallium, and boron (electron acceptors)willbe placed in cartridges and positioned in the multipurposefurnace so that one end of each rod extends out of thefurnace hot zone. (See Figure 2-7.) When the furnace isheated, only the part of each rod that is within the hot zonewill melt, leaving a solid part to serve as a seed for regrowth Seed--a single crystal used as aof the crystal. The rods will be solidified directionally at the starting point for crystal

lowest available cooling rate to promote formation of single growth in a liquid metal.crystals.

Germanium rod insiderGi;)--i I I- - - -- - - 4\- Heat sinkHot zone

Figure 2-7 Microsegregation in Germanium

DATAThe specimens will be analyzed upon return to Earth.Concentrations of the doping impurities will be determined byelectrical measurement and etching of the samples. Theresulting concentration profiles will be analyzed to determinet h e extent of segregation of the impurities, and theeffectiveness of free fall in suppressing microsegregation willbe evaluated. Comparisons will be made with specimensobtained from similar experiments performed on Earth.


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GROWTH OF SPHERICAL CRYSTALS(M560)BACKGROUNDOn the Earth, gravitational forces necessitate the use of acontainer t o hold a liquid metal. Unfortunately, i t is difficultt o produce a metal structure with high chemical uniformityin a container, as a container material tends to alloy with themolten metal and contaminate the melt or damage thesurfaces. Also, thermal convections through the liquid metalcause varying crystal growth patterns resulting in nonuniformcompositions. In the weightless environment of Skylab, themetal structure can be produced without any of these effects.SCIENTIFIC OBJECTIVEThe objective of this experiment is to grow a doped indiumantimonide crystal of high chemical homogeneity.PERFORMANCEPrepared samples of indium antimonide (InSb) doped withselenium will be melted inside a spherical shape quartz tube(Figure 2-8.) A solid seed crystal fixed t o the inside wall ofthe tube will provide a starting point for the metal tocrystallize. Under the influence of surface tension, the liquidmetal should assume a spherical shape and attach itself to theseed crystal. Heat will be removed through the seed crystal.In this way, the crystal will grow from the inside out.

/II\1oped indium antimonide crystalHot zone melted and allowed to solidify

into a spherical shapeFigure 2-8 Cartridge for Spherical Crystal Growth

DATAThe sample sphere will be analyzed on Earth. The returnsamples will be evaluated by:1) high re so lut ion etc hin g t o determine chemicalhomogeneity (dopant concentration^)^ This will indicategrowth interface stability;2) x-ray diffraction to characterize structural perfection;3) measurements of electrical properties, e.g., carrierconcentration, mobility, and lifetime;4) sc ann in g electron microscope and ion microprobe

analysis t o determine homogeneity of samples on an evensmaller scale, and the topography and surface roughness.


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WHISKER-REINFORCED COMPOSITES (M561)

BACKGROUNDHigh Strength The bond between atoms in a metal is very strong, muchWhiskers stronger than any practical material that has been produced.

However, metals are not as strong as they could be because ofdefects that exist in the crystal. A displaced atom, a void, amisaligned crystal, and an impurity are examples of defectsthat cause stress fields and result in a weaker metal. Crystalsof practical size cannot be produced free from defects.However, the theoretical high strength can be approximatedin "whiskers." Whiskers are small crystals that are producedso that very few defects can occur. These small whiskers canbe used as reinforcing material for other metals. If these highstrength whiskers are distributed throughout a material ofrelatively low strength, the resulting alloy could approach thestrength of the whiskers. The total structure then absorbs a

. loading stress tha t would easily break the weaker element.The silicon carbide (Sic) whisker has very high strength andcan be used to mix with various metals. However, goodquality composite metals reinforced with Sic whiskers havebeen difficult to produce because the low density whiskertends to float out of the high density molten metal. Another Sintered--a process for formingproblem is that the metal does not "wet" the S ic whisker metal pieces by compacting(i.e., ideal contact with the whisker is not achieved) and voids Powderedoccur.

In this experiment Sic whiskers will be oriented lengthwise ina sintered pack of silver. The weightless environment in theSkylab is expected to improve the uniformity of distributionof the metal and the whiskers since density differences willnot be a factor. A compressive force will be externallyapplied continuously during storage, melting, andsolidification to remove voids that may occur.SCIENTIFIC OBJECTIVEThe objective of this experiment is to produce void-freesamples of silver uniformly reinforced with oriented Sicwhiskers.PERFORMANCESintered compacts of silver containing distributions of~nidirectionall~riented Si c whiskers (1 mm long by 1micron diameter) will be melted in the multipurpose electricfurnace under pressure from a piston actuated by a spring.(See Figure 2-9.)


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Graphite rod7 r Silica rod

L Sample of sintered Steel disksilver with siliconcarbide whiskers

Figure 2-9 Whisker-Reinforced Composites

DATAAfter solidification and return to Earth, the samples will beevaluated as follows:1) calculated ideal density compared with the measureddensity;2) mechanical tests conducted to determine Young'smodulus and hardness numbers;3) x-ray microanalysis performed and the internal structureof the sample checked with electron microscope to verifya void-free homogeneous mixture.

INDIUM ANTIMONIDE CRYSTALS (M562)BACKGROUNDIndium antimonide crystals (InSb) are the basic componentsof some semiconductors. In order to have the desiredelectrical properties, the crystals are doped with smallamounts of materials such as tellurium. Growth ratefluctuations due to gravity-induced convection currents andrejection of the dopant from the growing crystal interface Dopant concentration is morecause serious problems in the production of these crystals. uniform in the d~~encef con-The convection currents periodically cool and heat the vection currents.interface, thus initiating faster and slower gtowth rates. Sincethe concentration of dopant depends on the growth rate,there are periodic bands of impurities in the resultant crystal.Thus electrical properties vary with the widely disperseddopant.SCIENTIFIC OBJECTIVEThe objective of this experiment is to produce doped semi-conductor crystals of high chemical uniformity and structuralperfection, and to evaluate the influence of weightlessness inattaining these properties.PERFORMANCEHigh quality single crystals of InSb will be prepared in thelaboratory, doped with tellurium, precision machined, and


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etched t o fi t into heavy wall quartz ampules. Half of each Ion Microprobe Analysis-ancrystal (about 7.6 cm length) will be melted and regrown at a electron beam excites the x-rayrate of 1 .3 cm/hr using the unmelted half as a seed. spectra of the elements presentin a specimen. The x-rays areanalyzed by their wave lengthsDATA as the "probe" is moved alongthe specimen.Upon return to Earth, 2.5 cm of each crystal will be remeltedand regrown in the same ampule under the same thermalconditions that .it was subjected to in space. Subsequently,extensive analysis will be carried out on all three portions ofthe crystals by using the following techniques:

Analytical 1) high resolution etching techniques in conjunction withMethods interference contrast microscopy for establishing dopantmicrodistribution and morphology of the growthinterface;

2) x-ray diffraction;3) x-ray topography;4) scanning electron microscope;5) m ic roan al y ti ca l techniques-spectroscopy and ionmicroprobe analysis;6) established parameters (carrier concentfation andmobilities) as a function of temperatures down to liquidhelium or below.

MIXED 111-V CRYSTAL GROWTH (M563)BACKGROUNDThe numbers 111-V refer t o the main group of elements in the Mixture ratio control is key toperiodic table of elements. The metals in this experiment, properties.indium antimonide and gallium antimonide, are used in theproduction of semiconductors. In order to producesemiconductors with optimum conduction and bandpasscapabilities, it is necessary to mix the metal elements inspecific proportions. The problem here is that convections inthe liquid cause nonuniform crystal growth through localsegregation of the materials. Uneven mixture ratios result.SCIENTIFIC OBJECTIVE

The objective of this experiment is to determine howweightlessness effects directional solidification ofsemiconductor alloys and, if single crystals are obtained, todetermine how their semiconducting properties depend onalloy composition.PERFORMANCE~ 1 1 0 ~ ;f indium antimonide (InSb) and gallium antimonide(GaSb) in proportions of 0.1 indium to 0.9 gallium, 0.3


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indium to 0.7 gallium, and 0.5 indium to 0.5 gallium areplaced in separate silica ampules. These samples will bemelted and allowed to solidify slowly.DATAThe ingot samples will be brought back t o Earth for analysisto determine microstructure and compositional uniformityby x-ray diffraction, electron microprobe analysis, andelectrical measurements. Samples solidified under similarconditions on Earth will be used for comparison.

HALIDE EUTECTICS (M564)BACKGROUNDAs a liquid eutectic composition of two components Eutecticran alloy with a com-solidifies, the crystal formation of one component rejects the position such that all elementsother component resulting in a parallel growth of crystals freeze simultaneOusly-that can take the form of either platelets or rods extendingthroughout the solid in the direction of crystal growth.

Sodium

//olid ~h as e . .:....Direction of growth

t' 1

Liquid phase 7Figure 2-10 Rods in Lamaller Crystal GrowthThe eutectic composition of sodium chloride and sodiumfluoride solidifies into crystalline rods of sodium fluoride.The rods are transparent through their length and if a crystalof this composition could be grown without defects, i t couldbe used as fiber optics material. The problem is that in the


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formation of the crystal on Earth, thermal convection withinthe liquid phase causes discontinuous crystal growth. As aresult, the sodium fluoride rods are too short for anypractical use. In a weightless environment, the thermalconvection within the melt will not exist and a fiberlikecrystal should result.SCIENTIFIC OBJECTIVEThe objective of this experiment is to produce highlycontinuous controlled structures of halide compositions.PERFORMANCEIngots of the sodium fluoride and sodium chloride eutectics1.27 cm in diameter and about 1 0 cm long, will be grown bymelting the mixture and allowing them to cool slowly anddirectionally solidify.

Sodium fluoride, sodium chloride eutectics'specimen-ot zoneFigure 2-11 Experiment Cartridge for Halide EutecticsDATAPostflight analysis will include:1) metallographic examination and x-ray diftkaction studyto identify and characterize alloy phases;2) electron microprobe analysis to determine concentrationin the transverse and longitudinal sections;3) measurement of electrical, superconducting, and opticalproperties.

SILVER GRIDS MELTED IN SPACE (M565)BACKGROUNDThe forces of gravity on a liquid metal are much greater than Cohesive forces become domi-the forces of cohesion. Consequently, a solid metal structure nant forces in orbital environ-on Earth loses its shape when melted. In a weightless ment-condition, a liquid metal would be subject to surface tensionforces only, which would tend to draw the melt into aspherical shape.By using a specific configuration for the original material, orby applying physical constraints to the specimen, other


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shapes might be achieved. In this experiment, discs with Surface tension forces may leadvarious patterns of holes are used to determine how the to optimal strengthlweight rasurface tension forces reconfigure the patterns. The resulting tios-discs will have shapes formed by surface tension forces. Sinceunrestricted surface tension tends to minimize the surfacearea of a given configuration, the resultant shapes will beimportant considerations in the design of grids with optimumstrength-to-weight ratios.SCIENTIFIC OBJECTIVEThe objective of this experiment is to determine how poresizes and shapes change in grids when they are melted andresolidified in a zero gravity environment.PERFORMANCEDiscs of silver with small holes of different number andspacings will be mounted inside a quartz ampule and melted

. and refrozen in space.

quartz ampule

Typical silver gridsFigure 2-12 Silver Grids Melted in Space

DATAThe samples returned from space will be studied tocharacterize the morphology and geometry of theconfigurations.

ALUMINUM-COPPER EUTECTIC (M566)BACKGROUND

Lamellar The aluminum and copper eutectic composition isStructures representative of types of alloys that freeze in a lamellarcrystal pattern, i.e., forming platelets. (See Figure 2-13.)However, thermal convections within the melt occurringduring the solidification process can cause irregular plateletgrowth. The weightless environment of Skylab will eliminatethe problem of gravity-induced thermal convection and thecrystals should grow in a continuous lamellar pattern. Ifcontinuously perfect lamellar structures are formed, variousalloys with lamellar growth patterns could be grown with


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numerous practical applications such as superconductors,optical material, capacitors, semiconductors, or directionalmagnetics.SCIENTIFIC OBJECTIVEThe objective of this experiment is to determine the effectsof weightlessness on the formation of lamellar structure ineutectic alloys when directionally solidified.

Figure 2-13 Platelets in Lamaller Crystal GrowthPERFORMANCEThree rods of 67% pure aluminum-33% copper eutecticalloy in individual ampules will be partially melted and thendirectionally solidified.DATA-The returned samples will be evaluated by comparisons withsamples produced under similar conditions on the Earth.

CLASSROOM DEMONSTRATIONSDIFFUSION WITH RADIOACTIVE TRACERSRelatively safe radio isotopes such as iodine 127 may be usedto determine diffusion rates in solution.

Student Fill a tube with KI or NaI solution of known concentration.Activity Place the tube in a horizontal position. Slowly introduce a


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known quantity of radioactive iodine at one end. Periodicallyremove the cover and sample a small amount of the solutiona t in cr em en ta l distances from the end. Repeat theexperiment with vertical tubes of the solution and add theradioactive iodine t o the top of the tubes. Check fordiffusion downward.LIQUIDMETAL IN FREE FALLThe shape of metal in a weightless environment can bedemonstrated by allowing liquid lead or tin t o fall somedistance (over 3 meters) into a tank of water. Melt some leador tin and carefully pour the liquid over a heated steel screen.The molten metal will pass through the screen and drops willfall into the water. (See Figure 2-14.) The metal will freezequickly thereby retaining most of the free-fall shape.

3 meters

Container. .. " I

Figure 2-14 Demonstrationof Liquid Metal in Free Fall

Sphere forming experiment


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Wide Range of The solidified drops of metal may have other than sphericalDrop Shapes shapes because of various stresses that exist in theexperiment. The liquid metal may develop oscillationsresulting from the stretching and release of the droplet. Also,the drag forces of the fall through air will tend to flatten thedrop. Try dropping the liquid metal from varying heights up 'to several feet and note the variations in drop shape for the

different increments in drop height.CAUTION Adequate safety precautions should be appliedto avoid burns.CRYSTALS OF SODIUM BROMATEDissolve a saturated solution of sodium bromate in water andallow the liquid to cool. Saturate a string with sodiumbromate crystals and allow to dry. Suspend the string in thesolution and place the apparatus in a refrigerator. Cool thesolution to about 10 to 20" for three or four days. Crystalsof sodium bromate will attach and grow seed crystals on thestring.


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Section 3Space OperationsSupport Equipment


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The three experiments described in this section relateprimarily to processes and techniques having applications infuture manned space flight operations. In addition, theexpe r imen ts pro duce da ta t h a t wi ll enhance theunderstanding of the physical principles involved in particularprocesses.

ZERO-GRAVITY FLAMMABILITY (M479)BACKGROUND

Flame Prop- In the Earth environment and in the absence of artificallyagation In- supplied oxidizers, convection of air plays an important partfluenced by in the burning of materials. The amount of oxygen providedGravity t o a fi re d e p en d s . o n convection of air and it is

convection-induced heat flow that causes material t o bumfaster from the bottom up than from th e top down.In weightlessness, convection currents are diminished or even Flame Propagation-process ine liminated. The burning of materials in weightlessness which the flame migrates.permits the study of diffusion and other influences in theburning process.The experiment will be conducted in the work chamberdescribed in Section 4.SCIENTIFIC OBJECTIVESThe objectives of this experiment are to determine the:1) extent of surface flame propagation and flashover to

adjacent materials;2) rates of surface and bulk flame propagation;3) ability of the flame to extinguish itself;4) ability of vacuum to extinguish the flame;5) ability of water spray to extinguish the flame.MATERIALSThe materials selected for this experiment are aluminizedmylar film, nylon sheet, neoprene coated nylon fabric,polyurethane foam, bleached cellulose paper, and Teflonfabric.In six tests, the samples of the six materials will. be ignitedand then extinguished by opening the work chamber to thevacuum of space. In another six tests on th e same materials,water will be used to extinguish the fire. (See Figure 3-1.)


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Ignitor

Figure 3-1 Typical Flammability SpecimensAnother set of tests using bleached cellulose paper willinvestigate the capability of a flame to fl.ash over from onematerial to another across different distances. Two sheets ofthe material are mounted in frames with separation distancesof 0.3,0.6, and 1.27 cm.DATAMotion picture coverage of ignition and flame propagationwill serve as the primary data record. Color film coverage at24 frames per second is used for all but one test series; thattest will use infrared film. Each test will be photographed inits entirety so that combustion rates can be determined bypostflight analysis of the film.

METALS MELTING EXPERIMENT (M551)BACKGROUNDThis experiment will melt the surface of a metal duringfree-fall conditions. Solidification processes in metals areexpected to behave differently under weightless conditionsthan under conditions on Earth. In the absence of gravity,heat transport should be dominated by conduction, and masstransfer should be dominated by diffusion. On Earth, both ofthese processes are heavily influenced by gravity-inducedcirculating convection currents.An electron beam will be used as the heat source. (SeeSection 4.) Analyses of these specimens will provide new datarelative to metal flow and hardening. The migration anddiffusion of the melted and frozen metals will be studied.The data obtained will relate to the properties of weldstrengths and control of the welding process.SCIENTIFIC OBJECTIVEOne objective of this experiment is to demonstrate metaljoining and cutting techniques and define their tolerances and


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limitations in a space environment. A second objective is toanalyze the behavior and solidification of molten metal inreduced gravity.

MATERIALSThe materials for this experiment support this objective inthat a wide range of phenomena can be studied using thefollowing samples:1 ) aluminum 2219, which represents~ solid solution withcomponents of different density, has been studiedextensively, especially with respect to dendritic growth;2) stainless steel 304 represents an alloy with components ofsimilar density;3) tantalum represents a pure metal and its solidificationbehavior differs substantially from that of the other two

alloys.PERFORMANCE

Weld Test Basica lly , t h e experiment will be conducted like aconventional weld test. Discs of the sample metals will rotatein front of an electron beam heat source (Figure 3-2). Theelectron beam is powered at about 1.6 kw and focused on aspot about 1.5 mm in diameter on the sample disc. As thedisc moves, the melt left in the track will freeze rapidlybecause the rest of the disc serves as a heat sink. Each disc ismachined to produce several thicknesses of metal. At the endof one revolution of the disc the beam will heat one spotuntil a hole is burned through the metal.

2.5 rpm

Figure 3-2 Materials Melting Experiment

DATA

A l u m i n u m 2 2 1 9 i s a naluminumcopper alloy that hassuperior properties to otheraluminum alloys; it has excellentw e l d a b i l i t y a nd is us edextensively in the constructionof airborne and space vehicles.Stainless steel 304 is low carbonsteel used for food processingequipment, chemical equipment,recording wire, and structuralapplications.

The operator will record process conditions and noteobservations. Color motion pictures will be taken a t a rate of24 frameslsec during each run.


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Analytical After the specimens are returned t o Earth, each sample willMethods be ana1yzed using various techniques including visual

examination, radiography, physical testing, materials analysis,scanning electron microscopy, and x-ray diffraction.The film records will be examined and correlated withhigh-speed (240 frames/sec) motion pictures taken duringduplicate runs with similar sazinples and apparatus on Earth.

EXOTHERMIC BR AZING EXPERIMENT (M 552)BACKGROUND

Pipe joining An exothermic brazing package is a device used to repair orexperiment join a pair of metal tubes. A metal joining sleeve with brazematerial contained in internal annular grooves in the sleeve

and the heating material are all contained in the package. Theheating inaterial is ignited and when melting occurs the brazematerial flows to form a seal and structural joint between thetubes and the sleeve (Figure 3-3).

Annular rings ofCut away view of sleeve to brazing materialbe brazed to pipe

Ignitor

Braze materialbetween sleeveand pipe ---\

\\

Thermal insulator

Braze material/ in capillary gap

Figure 3-3 Exothermic Brazing Experiment

The capillary flow of the braze material and the degree ofcontact with the sleeve and tube metals depend greatly onthe surface tension of the liquid metal and on the gapcharacteristics.


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FlowVelocity The equation, V = D y16 p L, represents the flow velocity ofof Liquid liquid metal in the absence of gravityMetalwhereD = gap distancey = surface tension in the liquidp = liquid viscosityL = distance from the liquid to the capillary opening,suggesting very hi& velocities may be developed in a widegap capillary. The velocities might be such that turbulentflow takes place. (This will be of interest since turbulent flowin this application has never befo~e een studied.)Experiments show that this equipment can be used in verylow ambient pressure, wbich suggests a potential applicationfor construction and repair in future space programs.SCIENTIFIC OBJECTIVESThe objectives of this experiment are to :1) test and demonstrate this method of brazing in spacerepair;2) study surface wetting and capillary flow effects inweightless molten metals;3) study concentration gradients a+ the braze base metal

interface resulting from diffusion and convection of basemetal into the liquid during and after capillary flow, aswell as diffusional transport of copper i n b he solid basemetal (silver being substantially insoluble Q both 304Lsteel and pure nickel).

The experiment equipment consists of a sample h b e with agap cut in a portion of the center representing two k bes endto end'(Figure 3-3). Four samples of different configurationsof metal or gap dimensions are used. They are:1 ) 304L stainless steel with a 0.127-mm capillary gap;2) 304L stainless steel with a 0.5-mm capillary gap;3) pure nickel with a 0.25-mm capillary gap;4) pure nickel with a tapered gap ranging from 0.75 mm tozero.

304L stainless steel contains amaximum of 0.03%carbon.


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304L stainless steel was selected to simplify sample analysiswhile retaining a material of engineering interest. I t issuperior to other stainless steels in terms of cleanliness andweldability.&re nickel was selected since this material is readily wet Tom-a unit of pressure, 1 mm(virtually zero contact angle) by the eutectic braze alloy at of Hgany vacuum greater than tor..Braze alloy, a eutectic composition of 71.8% silver, 28%copper, and 0.2% lithium, is included in a sleeve that fits overthe sample inside the exothermic heater.Radioactive tracer is added to more readily assess braze alloyflow and dispersion patterns.PERFORMANCEThe brazing packages will be ignited in sequence and eachwill burn for 90 seconds. Gases from the brazing packageswill be vented to the work chamber and from the chamber tospace. After brazing tests, the case will be returned to Earthunopened for analysis.DATAEach sample will be analyzed and examined by radiographic,metallographic, electron microscopy, and physical testmethods.


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Section 4Experimental ProgramSupporting Facilities


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EXPERIMENTAL PROGRAM SUPPORTING FACILITIES

Access

Viewing

All of the experiments discussed in this volume areperformed in the Materials Processing Facility (M512). Thisfacility consists of an enclosed work chamber and equipmentstorage provisions. Figure 4-1 illustrates the major features ofthe facility.Control panel

Work chamber

Flammabilityspecimen holder

Vent linevalves,-

Multipurpose electric

Ekothermic" / I- Vacuumcleaner Single crystal growthbraze package connection storage containerFigure 4-1 Materials Processing Facility

WORK CHAMBERThe work chamber (Figure 4-1) is a 41.27 cm sphere with a Work chamber is an experimen-hinged cover to provide access to the chamber of installation tal laboratory supporting a widefor removal of experiment equipment. The cover has a range of experimentsviewing port with x-ray opaque glass to protect the crewfrom radiation while observing the experiment process. Thework chamber is connected t o the space environment with a10.16 cm line that allows the chamber to be depressurized byopening two vent valves.A second viewport is provided for the 16mm camera. Afloodlight located next to the camera port illuminates theinterior of the chamber. A vacuum cleaner port is providedf o r cleaning the work chamber after performance ofexperiment M479. The vacuum cleaner will also be used toretrieve the "floating" spheres formed during experimentM553.


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A chamber pressurization system is provided that allows thepressures in the work chamber and spacecraft to equalize. Awater system is provided to spray a series of flammabilitysamples inside the work chamber in the zero-gravityflammability experiment (M479).Other provisions include viewing mirrors and protectiveshields, and a heat sink for the crystal growth experiments.A tungsten absorber plate is permanently mounted in thework chamber. This plate is attached t o the chamber walldirectly opposite the electron beam gun to protect the wallfrom the beam. The electron beam is the energy source forsome of the experiments.ELECTRON BEAM GUN

Supporting In the electron beam gun electrons from a hot filament areEquipment accelerated by a high potential (20 kv) and then regulatedand focused to bombard the experiment workpiece. Thebeam produces 1.6 kw at 80 mA. A simplified diagram of thesystem is shown in Figure 4-2.

Focusing coils ------IDeflection coils

Work chamber(depressurized)

Figure 4-2 Electron Beam Gun Diagram

The filament serves as the source of the electrons which thenpass through a cathode bias cup causing them t o convergeand pass through a hole in the center of the anode. Thevelocity of the electrons is a function of the potentialbetween the cathode and anode, and the highest velocity is atthe anode. A focus coil causes the electron beam to convergeon the workpiece where the diameter of the electron beam isabout 3 mm.MULTIPURPOSE ELECTRIC FURNACEThe multipurpose electric furnace (Figure 4-3)s intended tosupplement the capabilities of the materials processing42


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facility by providing means to perform numerousexperiments on solidification, crystal growth, and otherprocesses involving phase changes in materials. The furnacesystem will be used t o perform eleven experiments involvingphase changes at elevated temperatures in systems comprisingselected combinations of solid, liquid, and vapor phases.

Figure 4-3 Cut-Away View of the Multipurpose Furnace

The multipurpose electric furnace has three specimen cavitieswhich allow three samples t o be processed at one time. Thefurnace is constructed so as to provide three differenttemperature zones along the length of each sample cavity.Each sample material will be enclosed in a cartridge which isdesigned to provide temperature distribution through use ofvarious insulating and conducting materials.

ExperimentControl Pre-programmed

A control system is provided to control the furnacetemperature. Any specified temperature within the furnace'scapability ( 0 to 1000C) can be selected by the astronautoperating the system. Timing circuits in the controller willenable the astronaut to program the l