6.9.2.3.6 The following document was updated on 05-17-89 and contains 44003 characters. STUDYING MATERIALS AND PROCESSES IN MICROGRAVITY: MATERIALS SCIENCE Materials science includes such diverse processes as converting sand to silicon crystals for use in semiconductors, producing high-strength, temperature-resistant alloys and ceramics, separating biological materials into valuable drugs and chemicals, and studying the basic phenomena that influence these processes. Materials processing is melting, molding, crystallizing, and combining or separating raw materials into useful products. The history of science and civilization goes hand in hand with advances in materials science and technology. In some cases, progress in materials science on Earth has been limited: materials will not mix to form new alloys; crystals have defects that limit their performance; biological materials cannot be separated well enough to form some ultra-pure substances needed for medicine; crystals clump together instead of forming distinctly; glasses are contaminated by processing containers. Many of these problems are related to a constant force on Earth -- gravity. The presence of gravity has been counteracted in low-gravity aircraft flights and drop tubes, which offer about 30 seconds and 4 seconds of microgravity, respectively. Although the period of microgravity is brief, these test facilities are beneficial for research in preparation for spaceflight. The pull of gravity cannot be escaped at any altitude; at a 322 kilometer (200 mile) orbit, it is still 90 percent as strong as at the EarthUs surface. However, its effects can be virtually cancel-led by remaining in "free fall," that is, by remaining in orbit around the Earth as a satellite does. Spaceflight offers extended periods of low gravity; long duration is important for most solidification experiments, especially crystal growth. It is impossible to sustain a comparable microgravity environment on Earth. NASAUs microgravity science program uses spaceflight to eliminate or counteract gravity-induced problems that hamper materials scientists on the ground: buoyancy-driven convection in liquids, contamination from vessels that contain samples, and induced stresses that cause defects in crystals. Dramatic improvements in material properties have been achieved in recent microgravity experiments as our ability to control temperature has improved. Similar improvements can be expected in the future as our understanding of the effects of mass transport increases along with our ability to control convective flows. Pioneering experiments from 1969 to 1975 aboard Apollo-era spacecraft and the Skylab space station led the way to microgravity science payloads developed for the Space Shuttle in the late 1970s. The Shuttle/Spacelab has proven useful for carrying many new automated and manually controlled facilities developed for materials science research. Automated systems are appropriate for simpler experiments that need less crew involvement but still require the return of samples and equipment to the ground for analysis. The automated Materials Experiment Assembly (MEA) combined low-cost sounding rocket techniques with the extended microgravity duration of the Shuttle. This carrier supports three or four experiment modules in the payload bay. For more sophisticated experiments requiring intense observation and crew control, facilities have been developed for the shirt-sleeve laboratory environment of the Spacelab module and for the Shuttle middeck. Spacelab offers scientists a place to do exploratory work such as attempting new processing techniques or testing basic theories. Scientists serve as crewmembers to observe and control experiments. Thinking in Terms of Microgravity: Because gravity is a dominating factor on Earth, it is difficult to think in terms of reduced gravity. Results from the early Shuttle/Spacelab missions prove that scientists are meeting this challenge as they develop techniques and attempt experiments that are affected by gravity in laboratories on the ground. The first space product is now on the market: monodisperse latex spheres, precision microspheres that can be produced in space with improved uniformity. These spheres, which were produced in an apparatus in the Shuttle middeck during five missions, have been recognized as a calibration standard for microscopy. Many of the experiments accomplished to date are not aimed at production but seek to discover more about the fundamental physics and chemistry of materials processes on Earth. In microgravity, space scientists can use techniques to improve measurement accuracy and to try to observe phenomena that are not detectable on Earth. Analyses of samples produced in microgravity allow scientists to determine how gravity affects materials processing. For example, convection and sedimentation dominate the transport of heat and matter in many systems, but in space the effects of weaker forces such as surface tension are unveiled. Clarification of these phenomena may lead to better processing techniques on Earth and result in the discovery of materials with novel and commercially interesting properties. The types of materials processed aboard the Shuttle/Spacelab include crystals and electronic materials, metal alloys and composites, glasses and ceramics, fluids and chemicals, and biological materials. Crystals and Electronic Materials: Crystals have achieved far greater value as electronic materials than they ever had as gems. Man has improved on nature's offerings but has been halted by bottlenecks that prevent some crystals from reaching their theoretical performance limits. Before crystal growth can be improved, scientists must determine what factors are responsible for crystal defects and learn how to control them. Striking results were obtained with experiments on mercury iodide, a soft crystal valued for its potential as a nuclear radiation detector because it operates at room temperature without a bulky cooling system. Controlling the growth of a large mercury iodide crystal in microgravity was demonstrated with the Spacelab 3 Vapor Crystal Growth System. For the first time, crewmembers on the Shuttle and scientists on Earth monitored a crystal as it grew in microgravity. Images were relayed to the ground via television, and the crew viewed the crystal through a microscope imaging system. This allowed the growth of the crystal to be tracked through each stage, and scientists changed parameters such as temperature to adjust the growth and reduce defects, much as they do in ground-based laboratories. A seed crystal mounted on a small, cooled finger (sting) at the base of the ampoule was a condensation point for material evaporated from a source at the top. The crystal grown in space for 100 hours was comparable to the best terrestrial crystals. The crystal quality, seen by reflecting X-rays, appeared to be better than the ground-based crystal used as a standard. Gamma ray tests showed the interior quality to be better than terrestrial mercury iodide crystals. During the Spacelab 3 mission, more basic knowledge about crystal growth in microgravity was obtained by growing triglycine sulfate (TGS) crystals in the Fluid Experiment System. Triglycine sulfate has potential as an infrared radiation detector at room temperature. This crystal has not met expected standards because, when grown to useful sizes, it develops defects which limit its performance. For this experiment, TGS crystals were grown from solution with liquid TGS fluid solidifying on a seed crystal. The crystal and fluid are transparent, which makes it possible to record images of fluid motions. The growth chamber was in the center of a precision optical system which allowed photography by three techniques: shadowgraphy; schlieren, by which variations in fluid density make flow patterns visible; and interference holography, using lasers to record density variations near the sample. The TGS crystals shed light on how defects are formed and what role convection plays in creating defects, something that is not well understood. At the beginning of growth, a portion of the seed crystal is dissolved to form a smooth growth surface. In Earth-grown crystals, there is always a visible line where the seed crystal stops and the new growth begins; this introduces defects into the crystal. In the space-grown crystals, this line was not detected. This indicates that in the absence of convection the transition is smoother between the seed and the start of new growth. A Spacelab 1 crystal growth experiment examined insoluble crystals (calcium and lead phosphates) that grow quickly to form plate-like crystals which are easily studied by X-ray techniques. Large crystals were grown, and the portions of the crystals grown in microgravity were free of defects. Defects were evident in portions of the crystals grown as the Shuttle landed, suggesting that defects are reduced in microgravity. Another Spacelab 1 experiment studied processes linked to the distribution of dopants (trace elements) that give crystals desired electrical properties. For example, the conductivity of semiconductors is dramatically changed by adding dopants. However, nonuniform distribution of these dopants can interfere with the operation of electrical devices that use crystals. For most applications, the semiconductors produced on Earth are adequate, but for some highly specialized applications more uniformly doped, defect-free crystals are needed. Earlier experiments determined that convection that varies over time caused dopant striations in crystals. The Mirror Heating Facility (Spacelab 1) modeled float-zone Earth-processing methods to determine whether the troublesome convective flows were produced by buoyancy or surface tension. Two experiments were done in an attempt to grow defect-free, single crystals of silicon. However, the space-grown crystals had the same marked dopant striations seen in Earth-grown crystals, confirming that Marangoni convection (flow driven by surface tension) may be a dominant cause of the defects on Earth and in space. In ground-based experiments after Spacelab 1, the silicon seed crystal was coated with a thin oxide layer to prevent Marangoni flow as the crystal grew. The striations were eliminated, indicating that this is a successful technique for reducing the effects of Marangoni flow. For Spacelab D1, the experiment was repeated using this technique, and striation-free crystals also were grown in space. On the MEA-A1 mission, germanium selenide crystals were formed inside heated quartz ampoules. The size of the crystal and the location of crystal formation were far different than expected. On Earth, the crystals were small and formed a crust around the ampoule walls. In space, larger crystals nucleated in the middle of the ampoule away from the walls. The crystals were almost flawless, with strikingly improved surface qualities. The experiment was repeated on the MEA-A2 mission (flown with Spacelab D1), and similar results were obtained. This indicates that the vapor-transport technique may be an excellent way to produce crystals in space. Metals, Alloys, and Composites: Scientists continue in their quest to improve metallurgical processes, to form better and novel alloys, and to test theories of metal and alloy processing. This type of processing is so complex that it is difficult to measure and model and even more difficult to control. In space, gravity-related phenomena such as convection are reduced, thus eliminating one complex mechanism for mass and heat transfer and simplifying processes for study. Perhaps the most fundamental advances made in this area on the Shuttle were in understanding how liquified metals diffuse through each other. Diffusion is the movement of atoms past each other; each material has an inherent diffusion coefficient which describes the ability of atoms to move past each other in that material. Gravity-induced convection complicates diffusion measurements on Earth. Spacelab 1 results indicate that space may be the only place where accurate measurements of the coefficients can be made. Spacelab 1 experiments showed that pure diffusion can be measured so well in space that thermomigration, also called Soret diffusion, is clearly evident. In a binary mixture in which a temperature gradient is maintained, thermomigration causes the constituents to separate according to their atomic weights. The heavier components will migrate toward the cool end of a furnace and the light components will migrate toward the hot end. For one Spacelab experiment studying thermomigration, the Gradient Heating Facility, which had hot and cold ends to force a physical process to move in a given direction, provided a temperature drop of 648 degrees Fahrenheit from one end of the sample to the other. A sample of tin containing 0.5 percent cobalt was processed. Due to convective mixing, samples processed on the ground were evenly mixed; however, those processed in flight had double the cobalt concentration at the hot end of the ampoule. The accuracy of these measurements was 300 times better than ground-based experiments had achieved. This experiment may influence research to separate isotopes of metals with greater efficiency. A similar experiment using common isotopes of tin measured its diffusion coefficient with an accuracy 10 to 40 times greater than the best ground-based experiments. Radiation analysis showed how much of the trace quantity of tin-124 had migrated into the tin-112 making up the bulk of the sample. Because isotopes are chemically identical, any movement of one into the other must be caused purely by diffusion instead of any chemical effect. Several tubes with different diameters were used to isolate variations caused by the walls. A striking result was the high accuracy, unmatched in ground tests, of data indicating that the diffusion coefficient was much smaller than indicated by ground-based experiments. Accuracy in this figure will greatly improve the ability to model metal-mixing experiments both on the ground and in space, and the improved precision of diffusion measurements at different temperatures will help scientists establish the mechanism by which diffusion takes place in liquid metals. A large number of alloys belong to an interesting class called eutectics. A eutectic material is a mixture of two materials that has a lower melting point than either material alone. In the liquid phase the two materials that form a eutectic are completely miscible, but in the solid phase they are almost completely immiscible. Therefore, as two materials that form a eutectic solidify, they go from a single liquid phase to two distinct solid phases. Because many alloys are eutectics, scientists are interested in understanding the distribution of the immiscible solid phases. If a eutectic alloy is directionally solidified, long rods or lamella (sheets of one phase sandwiched between another phase) are formed; the alloy may have desirable properties, such as added strength or higher magnetic performance in one direction. As a result of space experiments, scientists are reexamining a classical theory on the formation of eutectics. The theory assumes there is no convection in the melt when the eutectic materials are processed in space. The theory works quite well on Earth, but an earlier rocket experiment produced a eutectic with rod spacing quite different than what was predicted by the classical theory. This was puzzling, but when the experiment was repeated in ground laboratories where a magnetic field was used to damp convection, experimenters got the same results. Scientists were faced with a paradox: a theory based on no convection worked fine when convection was present, but the theory did not work when convection was absent. For the Spacelab 1 mission, the same experiment was repeated with other eutectic systems. Some of them had smaller rod spacing than predicted, others had the predicted rod spacing, and others even had larger rod spacing than predicted by the theory. Apparently, space experiments have revealed some unidentified effect that controls rod spacing in eutectic systems. More space samples will have to be processed to determine if the classical theory on convection in eutectic processing needs revision. Glasses and Ceramics: Optical engineering is being revolutionized by new glasses, crystals, and other materials that surpass conventional substances in quality. However, production of these superior materials is difficult, because some glasses have chemical mixes that are highly reactive with containers while others are extremely sensitive to contamination levels of even a few parts per billion. For example, certain fluoride glasses are of great interest for their infrared transmission properties. These glasses can be made on Earth, but trace contaminants from processing containers have prevented them from reaching their theoretical performance level. Containerless processing, in which a sample is suspended and manipulated without touching contaminating containers, is an attractive solution to these problems. Containerless processing on massive samples can only be done in microgravity where the acoustic and electromagnetic forces used for suspension and manipulation are not overwhelmed by gravity. Currently, there is only a limited amount of data on how materials might be processed in this manner, but experiments such as the Spacelab 3 Drop Dynamics Module (DDM), which demonstrated that liquid drops could be levitated and manipulated acoustically in microgravity, will help scientists develop instruments and techniques for containerless processing of glasses and other materials. (The DDM results are discussed in the Fluid and Chemical Processes section of this chapter.) For the first time, a glass sample was levitated, melted, and resolidified in space in the Single Axis Acoustic Levitator experiment carried aboard MEA-A2. This sample, a spherical glass shell containing an air bubble, was similar to fuel containers for inertially confined fusion experiments. These fusion experiments require that the glass shell have extremely smooth inner and outer surfaces and that the wall of the shell be perfectly uniform in thickness. The perfection in surface smoothness, wall thickness, sphericity, and concentricity required for large diameter glass shells that are inertially confined fusion targets is essentially impossible to maintain on Earth due to gravity-induced distortion; however, it might be possible to obtain this perfection by reprocessing the glass shell using containerless processing techniques in microgravity. When this experiment was conducted in space, the sample melted and remained suspended. However, just before it resolidified, the air bubble inside migrated to the surface and broke through the outer wall, leaving a solid glass sphere. Bubble migration in the absence of gravitational convection is of great interest to materials scientists, and they are analyzing this experiment to determine why the bubble reacted in this unexpected fashion. Two other samples were levitated and melted during the MEA-A1 and MEA-A2 missions, but when the samples were cooled, the levitation became unstable and the samples became attached to the sample confinement cage. More experiments are needed to study containerless processing of glass and other types of samples. Fluid and Chemical Processes: In microgravity, it is possible to observe fluid movement and behavior that are masked by gravity-driven flows on Earth. Fluid physics research may give scientists insight into crystal growth, glass processing, and other material processes. The goal of the Spacelab 1 Fluid Physics Module experiment was to investigate fluid processes in microgravity. Two-inch-wide disks were used to support a column of liquid with free cylindrical surfaces. Because gravity does not collapse the liquid column in space, the disks were pulled apart to create a bridge almost 3 inches long (8 centimeters). (On Earth, 1/8th inch or 0.3 centimeters is the greatest possible height for columns of this fluid.) The disks were rotated together and in opposite directions and heated unevenly so that the behavior of the fluid under forces other than gravity could be observed. One experiment used a fluid column to study Marangoni convection, which occurs when temperature gradients change the surface tension of a molten material, making the liquid surface move. By suspending tracers in the liquid bridge, scientists were able to observe fluid flows attributed to Marangoni convection in a fluid column that was almost 25 times bigger than any ever studied on Earth. Although detailed studies of Marangoni convection have been done on a small scale in terrestrial laboratories, it had never been studied in such a large sample. Scientists are analyzing films of this large fluid column to study detailed processes that occurred without the gravitational distortions that complicate measurements on Earth. The Spacelab 3 Drop Dynamics Module provided the first opportunity to answer scientific questions that had been asked for more than 300 years. These fluid physics theories could not be studied experimentally because gravity precludes levitation of liquids without introducing forces that significantly mask the phenomena being studied. In microgravity, sound waves were used to levitate and manipulate drops of water and glycerin. As the principal investigator controlled the experiment, the drops were photographed. The experiments confirmed that some of the age-old assumptions about drop behavior in relatively simple situations were correct. Other results were unexpected. The bifurcation point when a spinning drop takes a dog-bone shape in order to hold itself together came earlier than predicted under certain circumstances. In another case, a rotating dog-bone drop returned to a spherical shape and stopped rotating quickly rather than slowly, apparently from differential rotation on the inside. By analyzing the physical processes inside drops suspended in microgravity, scientists have the opportunity to experimentally test basic fluid physics theories that have applications in other areas of physics. The drop experiments also demonstrated a potentially valuable processing technique. By suspending glasses and other materials inside a processing chamber so that the material does not touch container walls, scientists may be able to process purer specimens than those produced on Earth. The value of having an expert scientist to conduct space experiments was evident as well. The principal investigator was a part of the crew, enabling him to repair the instrument when it developed a problem on orbit, make valuable real-time observations, and adjust the experiment parameters to view subtle changes in drop behavior. For another Spacelab 3 experiment, the Geophysical Fluid Flow Cell, a rotating spherical system was used to model patterns of convection and other interesting fluid motions that are found in stellar and planetary atmospheres. Fluid physicists are interested in the flow characteristics of the fluids themselves, and meteorologists, planetologists, and astrophysicists are interested in the large-scale circulation of fluids under the influence of rotation, gravity, and heating. The thermally driven motion of a fluid in a spherical experiment is similar to that in a thermally driven rotating, shallow atmosphere or in a deep ocean on a spherical planet. It is very difficult to do controlled experiments with this type of system in an Earth-based laboratory, because terrestrial gravity distorts the flow patterns in ways that do not correspond to actual planetary flows. In space, gravity is reduced and electrostatic forces can be used to mimic gravity on a scale appropriate for the model. A 16-mm movie camera photographed global flow patterns as revealed by dyes and schlieren patterns resulting from fluid density changes. More than 50,000 images were recorded in 103 hours of simulations. Some expected features such as longitudinal banana-shaped cells like those which may exist on the sun were observed. Other images are being compared to current models of atmospheric flow patterns for planets such as Jupiter and Uranus. Space is the only place where these models can be tested accurately. A Spacelab 2 experiment investigated the basic properties and behavior of a material that is not yet well understood but may be useful for new technology. Liquid helium is of interest as a coolant for infrared telescopes and detectors that operate at extremely low temperatures. Below 2.2 degrees Kelvin (-456 degrees Fahrenheit), liquid helium is transformed into superfluid helium, which moves freely through pores so small that they block normal liquid and conducts heat about 1,000 times better than copper. Because superfluid helium is an entirely different state of matter from conventional fluids, it is being studied in space to improve our fundamental understanding of the physics of matter. Many subtleties of superfluid helium behavior are unknown because gravitational effects disturb the superfluid state, where the laws of quantum mechanics predominate over the laws of everyday existence. Future space experiments are planned for which the temperature of the helium must be constant to a few millionths of a degree. Spacelab 2 experiments showed that the helium temperature does remain constant and stable. The large-scale motions of liquid helium also are important because they could disturb the attitude control systems essential for pointing telescopes of large helium-cooled observatories planned for the 1990s. A Spacelab 2 bulk fluid motion experiment measured the amplitude and decay of the sloshing motion caused by small orbiter motions. It appears the motions are so small that they will not affect the ultrasensitive telescopes and experiments. Biological Processing: Biological materials such as cells, proteins, and enzymes can be processed to create valuable medical and pharmaceutical products. Before many of these materials can be used for medical purposes, they must be separated from other substances. Convection and sedimentation on Earth make it difficult to separate these biological substances in ultra-pure forms and high concentrations. The Continuous Flow Electrophoresis System (CFES) is used to separate and purify biological cells and proteins in space. This instrument has been flown six times, and after each flight the instrument and technique have been refined for more effective processing. Investigators have been able to increase the concentration of material separated and purified during a given period. For two proteins, the throughput of desired product was 500 times greater than achieved on the ground in the same instrument. The space-produced substances are being evaluated by a pharmaceutical company. Materials and life scientists also share an interest in protein crystals. Single crystals of sufficient size and perfection are needed to analyze the molecular structure of numerous proteins and enzymes. Knowledge of the structure is a prerequisite for optimal utilization of the proteins for medical, pharmaceutical, and bioengineering applications. These crystals can be grown by the simultaneous counter-diffusion of a protein and salt solution into a buffer solution. As the proteins start to crystallize on Earth, the different densities of the crystal and the solution result in convection, which can lead to a large number of small, imperfect crystals. Thus, one of the great limitations in protein crystal research has been the inability to produce large, pure crystals for analysis. Fortunately, preliminary experiments aboard the Shuttle and Spacelab indicate that much larger and higher quality crystals can perhaps be grown in space where convection is reduced and crystals float freely in solution. During the Spacelab 1 mission, crystals of lysozyme (a basic protein) and beta-galactosidase (a key genetic ingredient) were produced of sufficient size and perfection for X-ray structural analysis. The crystals were several times larger than those produced in the same facility on the ground. The successful Spacelab 1 experiment sparked a united effort by a team of scientists who developed an apparatus that uses vapor diffusion to grow protein crystals. Several proteins have been processed in this developmental apparatus; many of the space crystals were large, and indications are that the quality is high. The crystals also formed more distinctly, rather than clumping together. In the case of one protein, a new crystal form was identified and has since been produced in ground laboratories. Based on these preliminary results, a larger facility with a more controlled environment is being developed. Gaining Experience to Shape the Future: These first-generation space experiments have proven the feasibility of a variety of materials processing techniques in space. These experiments have provided some valuable fundamental knowledge, revealing the nature of phenomena that are masked or not easily observed on Earth. A second generation of experiments with more clearly defined objectives and better instrumentation is needed to quantify results. Spacelab has proven that crewmembers acting as operators and observers will be extremely important for experimentation, because unanticipated results can only be spotted by the trained eye, and a simple adjustment may rescue or change the nature of an experiment. On the Space Station, with crewmembers to observe experiments and equipment for analyzing samples in orbit, it will not be necessary to return all specimens to Earth for characterization before running the next experiment in space. Productivity will be enhanced by the additional power and space for experiments on the Space Station. The Space Station will use sophisticated data systems to display real-time data to investigators in space and on the ground. This will make collaboration between scientists more practical. Data will be archived so that each experiment can build on results from previous studies. The Space Station will permit long-duration experiments in an environment more similar to terrestrial laboratories. A dramatic increase in experiment time over the few tens of hours performed to date will occur. Experiments in microgravity will stretch over periods comparable to those on Earth, greatly increasing the types of materials that can be processed to full term. This will be a great advantage to experiments in areas such as solution and vapor crystal growth which require 15 to 30 days of continuous growth to produce crystals of the desired size. It may be that experiments that do not need a pressurized module or frequent human intervention can be attached outside on the station or flown on free flyers. Free flyers will have a more stable microgravity environment that is not disturbed by crew motions and other Space Station activities. They will be ideal for mature manufacturing facilities where processing is routine and products only need retrieval. Teleoperated or remote vehicles may be used to retrieve and replace samples. The Shuttle/Spacelab has helped train both investigators and crewmembers for future materials processing experiments. Scientist crewmembers and investigators on the ground have learned to work together, observing and adjusting parameters to improve experiment results. The upcoming International Microgravity Laboratory (IML) missions will give scientists around the world an opportunity to coordinate research. Some experiments from previous missions, such as the Spacelab 3 crystal growth experiments, will be reflown and some new experiments will be attempted. This mission will provide valuable research opportunities to U.S. scientists and to their international partners who will work with them aboard the Space Station. Aboard the Spacelab J mission, the Japanese will do their first manned materials processing experiments in space. NASA continues to examine ways to improve Shuttle/Spacelab research. In the future it may be possible to extend missions, providing longer periods for research. This will allow a larger experiment base to be developed and contribute to the evolution of more mature hardware to take advantage of long-term stays aboard the Space Station. MATERIALS SCIENCE INVESTIGATIONS OSS-1/STS-3 % Monodisperse Latex Reactor System** J.W. Vanderhoff, Lehigh University Bethlehem, Pennsylvania STS-6 % Continuous Flow Electrophoresis System*** D. Clifford, McDonnell Douglas Aerospace Co. St. Louis, Missouri Materials Experiment Assembly P A1 (MEA-A1)/STS-7 Gradient General Purpose Rocket Furnace % Vapor Growth of Alloy-Type Semiconductor Crystals H. Wiedemeier, Rensselaer Polytechnic Institute Troy, New York Isothermal General Purpose Rocket Furnace % Liquid Phase Miscibility Gap Materials S.H. Gelles, S.H. Gelles Laboratories, Inc. Columbus, Ohio Single Axis Acoustic Levitator % Containerless Processing of Glass Melts D.E. Day, University of Missouri Rolla, Missouri Materialwissenschaftliche Autonome Experimente Unter Schwerelosigkeit (MAUS)/STS-7 % Solidification Front H. Klein, DFVLR Cologne, Germany % Stability of Metallic Dispersions G.H. Otto, DFVLR Cologne, Germany Spacelab 1/STS-9 Materials Science Double Rack -- Fluid Physics Module % Capillary Forces in a Low-Gravity Environment J.F. Padday, Kodak Research Laboratory Harrow, England % Coupled Motion of Liquid-Solid Systems in Near-Zero Gravity J.P.B. Vreeburg, National Aerospace Laboratory Amsterdam, The Netherlands % Floating Zone Stability in Zero-Gravity I. Da Riva, University of Madrid, Spain % Free Convection in Low Gravity L.G. Napolitano, University of Naples, Italy % Interfacial Instability and Capillary Hysteresis J.M. Haynes, University of Bristol, United Kingdom % Kinetics of the Spreading of Liquids in Solids J.M. Haynes, University of Bristol, United Kingdom % Oscillation of Semi-Free Liquid Spheres in Space H. Rodot, National Center for Scientific Research Paris, France Gradient Heating Facility % Lead-Telluride Crystal Growth H. Rodot, National Center for Scientific Research Paris, France % Solidification of Aluminum-Zinc Vapor Emulsion C. Potard, Center for Nuclear Studies Grenoble, France % Solidification of Eutectic Alloys J.J. Favier and J.P. Praizey Center for Nuclear Studies Grenoble, France % Thermodiffusion in Tin Alloys Y. Malm jac and J.P. Praizey Center for Nuclear Studies Grenoble, France % Unidirectional Solidification of Eutectics G. M ller, University of Erlangen, Germany Isothermal Heating Facility % Bubble-Reinforced Materials P. Gondi, University of Bologna, Italy % Dendrite Growth and Microsegregation of Binary Alloys H. Fredriksson, The Royal Institute of Technology Stockholm, Sweden % Emulsions and Dispersion Alloys H. Ahlborn, University of Hamburg, Germany % Interaction Between an Advancing Solidification Front and Suspended Particles D. Neusch tz and J. P tschke Krupp Research Center Essen, Germany % Melting and Solidification of Metallic Composites A. Deruyttere, University of Leuven, Belgium % Metallic Emulsion Aluminum-Lead P.D. Caton, Fulmer Research Institute Stoke Poges, United Kingdom % Nucleation of Eutectic Alloys Y. Malm jac, Center for Nuclear Studies Grenoble, France % Reaction Kinetics in Glass G.H. Frischat, Technical University of Clausthal, Germany % Skin Technology H. Sprenger, MAN Advanced Technology Munich, Germany % Solidification of Immiscible Alloys H. Ahlborn, University of Hamburg, Germany % Solidification of Near-Monotectic Zinc-Lead Alloys H.F. Fischmeister, Max Planck Institute Stuttgart, Germany % Unidirectional Solidification of Cast Iron T. Luyendijk, Delft University of Technology The Netherlands % Vacuum Brazing W. Sch nherr and E. Siegfried Federal Institution for Material Testing Berlin, Germany % Vacuum Brazing R. Stickler and K. Frieler University of Vienna, Austria Mirror Heating Facility % Crystallization of a Silicon Drop H. K lker, Wacker-Chemie Munich, Germany % Floating Zone Growth of Silicon R. Nitsche and E. Eyer University of Freiburg, Germany % Growth of Cadmium Telluride by the Traveling Heater Method R. Nitsche, R. Dian, and R. Sch nholz University of Freiburg, Germany % Growth of Semiconductor Crystals by the Traveling Heater Method K.W. Benz, Stuttgart University, and G. M ller, University of Erlangen, Germany Special Equipment % Adhesion of Metals in UHV Chamber G. Ghersini Information Center of Experimental Studies, Italy % Crystal Growth by Co-Precipitation in Liquid Phase A. Authier, F. Le Faucheux, and M.C. Robert University of Pierre and Marie Curie, Paris, France % Crystal Growth of Proteins W. Littke, University of Freiberg, Germany % Mercury Iodide Crystal Growth R. Cadoret, Laboratory for Crystallography and Physics Les Cezeaux, France % Organic Crystal Growth K.F. Nielsen, G. Galster, and I. Johannson Technical University of Denmark Lyngbyg, Denmark % Selfdiffusion and Interdiffusion in Liquid Metals K. Kraatz, Technical University of Berlin, Germany Spacelab 3/51-B Crystal Growth Facility % Mercury Iodide Crystal Growth* R. Cadoret and P. Brisson Laboratory for Crystallography and Physics Les Cezeaux, France Drop Dynamics Module % Dynamics of Rotating and Oscillating Free Drops T. Wang, NASA Jet Propulsion Laboratory Pasadena, California Fluid Experiment System % Solution Growth of Crystals in Zero Gravity System R. Lal, Alabama A&M University Huntsville, Alabama Geophysical Fluid Flow Cell % Geophysical Fluid Flow Cell Experiment J.E. Hart, University of Colorado Boulder, Colorado Vapor Crystal Growth System % Mercuric Iodide Growth W.F. Schnepple, EG&G, Inc., Goleta, California Spacelab 2/51-F % Properties of Superfluid Helium in Zero-Gravity P.V. Mason, NASA Jet Propulsion Laboratory Pasadena, California % Protein Crystal Growth**** C.E. Bugg, University of Alabama in Birmingham, Alabama Spacelab D1/ 61-A Materials Science Double Rack -- Cryostat % Protein Crystals* W. Littke, University of Freiburg, Germany Fluid Physics Module % Capillary Experiments* J.F. Padday, Kodak Research Laboratory Harrow, United Kingdom % Convection in Nonisothermal Binary Mixtures J.C. Legros, University of Brussels, Belgium % Floating-Zone Hydrodynamics* I. Da Riva, University of Madrid, Spain % Forced Liquid Motions* J.P.B. Vreeburg, National Aerospace Laboratory Amsterdam, The Netherlands % Marangoni Convection A.A.H. Drinkenburg, University of Groningen The Netherlands % Marangoni Flows* L.G. Napolitano, University of Naples, Italy % Separation of Fluid Phases R. Naehle, DFVLR Cologne, Germany Gradient Heating Facility % Cellular Morphology in Lead-Thallium Alloy B. Billia, University of Marseille, France % Dendritic Solidification of Aluminum-Copper Alloys D. Camel, Center for Nuclear Studies Grenoble, France % Doped Indium Antimonide and Gallium Indium Antimonide C. Potard, Center for Nuclear Studies Grenoble, France % Ge-GeI4 Chemical Growth J.C. Launay, University of Bordeaux, France % Ge-I2 Vapor Phase J.C. Launay, University of Bordeaux, France % Thermal Diffusion J. Dupuy, University of Lyon, France % Thermomigration of Cobalt in Tin J.P. Praizey, Center for Nuclear Studies Grenoble, France High Temperature Thermostat % Self- and Interdiffusion* K. Kraatz, Technical University of Berlin, Germany Isothermal Heating Facility % Homogeneity of Glasses* G.H. Frischat, Technical University of Clausthal, Germany % Liquid Skin Casting of Cast Iron* H. Sprenger, MAN Advanced Technology Munich, Germany, and I.H. Nieswagg, Delft University of Technology The Netherlands % Nucleation of Eutectic Alloys* Y. Malm jac, Center for Nuclear Studies Grenoble, France % Ostwald Ripening* H.F. Fischmeister, Max Planck Institute Stuttgart, Germany % Particle Behavior at Solidification Fronts D. Langbein, Battelle-Institute Frankfurt, Germany % Separation of Immiscible Alloys* H. Ahlborn, University of Hamburg, Germany % Skin Technology* H. Sprenger, MAN Advanced Technology Munich, Germany, and I.H. Nieswaag, Delft University of Technology The Netherlands % Solidification of Composite Materials* A. Deruyttere, University of Leuven, Belgium % Solidification of Suspensions* J. P tschke, Krupp Research Center Essen, Germany Mirror Heating Facility % Floating Zone Growth of Silicon* R. Nitsche, University of Freiburg, Germany % Growth of Cadmium Telluride by the Traveling Heater Method* R. Nitsche, University of Freiburg, Germany % Growth of Semiconductor Crystals by the Traveling Heater Method* K.W. Benz, University of Stuttgart, Germany % Melting of Silicon Sphere* H. K lker, Wacker-Chemie Munich, Germany Materials Science Experiment Double Rack for Experiment Modules and Apparatus -- Gradient Furnace with Quenching Device % Aluminum/Copper Phase Boundary Diffusion H.M. Tensi, Technical University, Munich, Germany % Solidification Dynamics S. Rex and P.R. Sahm, RWTH Aachen, Germany High-Precision Thermostat % Heat Capacity Near Critical Point J. Straub, Technical University, Munich, Germany Monoellipsoid Heating Facility % Indium Antimonide-Nickel Antimonide Eutectics G. M ller, University of Erlangen, Germany % Traveling Heater Method (PbSnTe) M. Harr, Battelle-Institute, Frankfurt, Germany % Vapor Growth of Cadmium Telluride R. Nitsche, University of Freiburg, Germany Process Chamber -- Holographic Interferometric Apparatus % Bubble Transport A. Bewersdorff, DFVLR Cologne, Germany % GETS A. Ecker and P.R. Sahm, RWTH Aachen, Germany % Phase Separation Near Critical Point H. Klein, DFVLR Cologne, Germany % Surface-Tension Studies D. Neuhaus, DFVLR Cologne, Germany Interdiffusion Salt Melt Apparatus % Interdiffusion J. Richter, RWTH Aachen, Germany Marangoni Convection Boat Apparatus % Marangoni Convection D. Schwabe, University of Giessen, Germany Materials Experiment Assembly-A2 (MEA-A2)/61-A ***** Gradient General Purpose Rocket Furnace % Semiconductor Materials R.K. Crouch, NASA Langley Research Center Hampton, Virginia % Vapor Growth of Alloy-Type Semiconductor Crystals* H. Wiedemeier, Rensselaer Polytechnic Institute Troy, New York Isothermal General Purpose Rocket Furnace % Diffusion of Liquid Zinc and Lead R.B. Pond, Marvalaud, Inc. Westminster, Maryland % Liquid Phase Miscibility Gap Materials S.H. Gelles, S.H. Gelles Laboratories, Inc. Columbus, Ohio Single Axis Acoustic Levitator % Containerless Melting of Glass* D.E. Day, University of Missouri Rolla, Missouri Materials Science Laboratory-2 (MSL-2)/61-C ***** Automated Directional Solidification Furnace % Orbital Processing of Aligned Magnetic Composites D.J. Larson, Grumman Aerospace Corporation Bethpage, New York Electromagnetic Levitation Furnace % Undercooled Solidification in Quiescent Levitated Drops M.C. Fleming, Massachusetts Institute of Technology Cambridge, Massachusetts Three-Axis Acoustic Levitator % Dynamics of Compound Drops T. Wang, NASA Jet Propulsion Laboratory Pasadena, California Physical Phenomena in Containerless Glass % Processing Model Fluids R.S. Subramanian, Clarkson University Potsdam, New York * Reflight ** 5 flights completed (STS-3, -4, -6, -7, and -11) *** 6 flights completed (STS-6, -7, -8, 41-D, 51-D, and 61-B) **** 4 flights completed (Spacelab 2, 51-D, 61-B, and 61-C) ***** MEA-A2 is sometimes referred to as MSL-1; The MSL-2 mission was the first MSL flight.