As a solid solution semiconductor having a large separation between liquidus and solidus, mercury cadmium telluride (MCT) presents a formidable challenge to crystal growers desiring an alloy of high compositional uniformity. To avoid constitutional supercooling during Bridgman crystal growth it is necessary to solidify slowly in a high temperature gradient region. The necessary translation rate of less than 1mm/hr results in a situation where fluid flow induced by gravity on earth is a significant factor in material transport. The advanced automated directional solidification furnace (AADSF) is equipped to provide the stable thermal environment with a high gradient, and the required slow translation rate needed. Ground based experiments in AADSF show clearly the dominance of flow driven transport. The first flight of AADSF in low gravity on USMP-2 provided an opportunity to test theories of fluid flow in MCT and showed several solidification regimes which are very different from those observed on earth. Residual acceleration vectors in the orbiter during the mission were measured by the orbital acceleration research experiment, and correlated well with observed compositional differences in the samples.

This paper discusses the flight experiment 'Coupled Growth in Hypermonotectics' schedules to fly aboard the life and microgravity spacelab mission during the summer of 1996. The experiment is designed to directionally solidify samples in immiscible alloy systems in an attempt to obtain an improved understanding of the physics controlling the solidification process. This paper specifically addresses some of the unique difficulties concerning ampoule design for these experiments. As an example, an ampoule material must be utilized that is not wet by the minor immiscible liquid phase. In addition, a means must be provided to accommodate thermal contraction and solidification shrinkage during processing in order to avoid free surface formation on the melt. An attempt has also been made to control thermal end effects in order to obtain a relatively constant growth rate during processing. The final design results in an ampoule assembly that contains insulating segments, dummy samples, moving pistons and a high temperature spring assembly. The details of this design and the results of ground based testing will be discussed.

Samples of ZBLAN optical fiber were heated to the pulling and crystallization temperature in microgravity aboard a sounding rocket and on the ground at 1g. This was done in order to better understand the effects of gravity on the crystallization behavior of ZBLAN fibers. Samples heated in 1g at both temperatures crystallized. Samples heated to the crystallization temperature in microgravity were contaminated with water upon re-entry. Samples heated to the pulling temperature showed no evidence of crystallization in microgravity.

The technique of x-ray projection microscopy is being used to view, in real time, the structures and dynamics of the solid-liquid interface during solidification. By employing a hard x-ray source with sub-micron dimensions, resolutions of 2 micrometers can be obtained with magnifications of over 800 X. Specimen growth conditions need to be optimized and the best imaging technologies applied to maintain x-ray image resolution, contrast and sensitivity. It turns out that no single imaging technology offers the best solution and traditional methods like radiographic film cannot be used due to specimen motion (solidification). In addition, a special furnace design is required to permit controlled growth conditions and still offer maximum resolution and image contrast.

In a microgravity environment, gravity-dependent effects such as buoyancy, convection and hydrostatic pressure are minimized, providing an ideal environment for investigating diffusion-controlled, nonwetting crystal growth processes. To evaluate the influence of microgravity on the resultant crystal quality, Synchrotron white beam x-ray topography is applied to characterize defect structures in both flight and ground-based CdZnTe single crystals. Transmission x-ray topographs recorded from one flight sample revealed regions of very low dislocation density with individual dislocations clearly resolved. Dislocations of very high density arrayed na mosaic pattern were observed in all ground-base samples grown under identical growth conditions except for the gravity conditions. This observation indicates that the flight samples have much higher structural perfection than the ground-based samples. On the other hand, studies of defect configurations in a different flight sample revealed that structural defects and distributions can be strongly influenced by rapid cooling, thermal gradients, and constrained growth. Large thermal stresses induced by rapid cooling can be multiplied by wall contact leading to the formation of extensive slip bands and small angle tilt boundaries starting at the crystal periphery and propagating into the interior of the sample. It is concluded that an optimization of post solidification cooling rate is important to minimize the occurrence of slip.

In order to stimulate the space environment for basic research into the crystal growth mechanism, Hg_0.8Cd_0.2Te crystals were grown by the vertical Bridgman- Stockbarger method in the presence of an applied axial magnetic field. The influence of convection, by magneto hydrodynamic damping, on mass transfer in the melt and segregation at the solid-liquid interface was investigated by measuring he axial and radial compositional variations in the grown samples. The reduction of convective mixing in the melt through the application of the magnetic field is found to have a large effect on radial segregation and interface morphology in the grown crystals. Direct comparisons are made with a Hg_0.8Cd_0.2Te crystal grown without field and also in the microgravity environment of space during the second United States Microgravity Payload Mission.

The dynamics of oxidation or reduction reactions in multicomponent, transition-metal-cation-bearing oxides involves the coupled diffusion of electron holes (polarons) and component cations. As a consequence, internal reactions, resulting in the nucleation/crystallization at a reaction front of higher-order oxides or of the more-noble metal component, respectively, dominate dynamic behavior. In the amorphous state, such reactions result in homogeneous nucleation of this product phase, suggesting an approach to the preparation of fine, uniform-grained ceramics directly from inviscid melts: the redox-reaction-front oxide or metal phase can act as a dispersed heterogeneity for nucleation of other, 'majority' phases. This approach, for which microgravity containerless processing is ultimately required, is illustrated with results from ferrous iron- bearing aluminosilicate melts and glasses. For example, oxidation of the melt at 1400 degrees C results in 'isothermal undercooling': the liquidus temperature and primary phase are a function of oxygen activity and thus sub-micrometer magnetite forms at the internal reaction front. The dynamics are rapid; chemical diffusion during oxidation is dominated/rate-limited by motion of the divalent, network-modifying cations. Dynamic reduction, i.e., formation of metal at an internal reduction front via rapid cation diffusion, occurs as well, a kinetical 'mirror image' of the oxidation process.

We use a Green's function technique for deep defect energy level calculations in mercury cadmium telluride, mercury zinc telluride, and mercury zinc selenide. The formation energy is calculated from the difference between the total binding energy with an impurity cluster and with a perfect cluster. These alloys are among those that have been experimentally grown in microgravity aboard the Space Shuttle. To evaluate the quality of these crystals, it is necessary to characterize them, and one important aspect of this characterization is the study of deep defects which can limit carrier lifetime. Relaxation effects are calculated with molecular dynamics. The resulting energy shift can be greater for the interstitial case than the substitutional one. Relaxation in vacancies is also considered. The charged state energy shift (as computed by a modified Haldane- Anderson model) can be twice that caused by relaxation. However, different charged states for vacancies had little effect on the formation energy. For all cases we considered the concentration of Cd or Zn in the range appropriate for a band gap of 0.1 eV. The emphasis of our calculation is on chemical trends. Only limited comparison to experiment and other calculations is possible, but what there is supports the statement that our results are at least of the right order of magnitude.

New possibilities of the x-ray diffraction method for studies of some single crystals with special physical properties are analyzed. It is demonstrated that wide range temperature diffraction data, special single crystals experiments under strong electric fields, and charge density analysis in crystals might enrich our knowledge on the nature of the crystal properties.

We present the results of study of thin film optical waveguides based on photocrosslinkable polyimide with glass transition temperature approaching 400 degrees C. The birefringence of the waveguides can possibly be reduced by eliminating the effect of gravity on the conditions of the film fabrication. We propose fabrication technique that allows us to change the orientation of the substrate and to analyze the gravity effect on the polyimide waveguide. This technique uses UV assisted film deposition from polyimide solution on a transparent substrate mounted as a removable wall of the container with the solution. The technique is also suitable for film fabrication at low gravity conditions. In order to investigate possible effects that can occur during UV assisted liquid deposition at low gravity, we studied UV exposed polyimide films made by spin coating at normal conditions. We describe the appearance of a gradient index waveguide on the top of polyimide coat exposed to UV light. The proposed mechanism of the waveguide formation includes photocrosslinking followed by UV assisted modification of the material which leads to the increase of the optical absorbance in UV region accompanied by the refractive index increase in visible region. Theoretical model based on this approach allowed us to reconstruct the refractive index profile n the waveguide. The profile is in good agreement with that obtained from the waveguide mode spectrum measured with prism coupling technique.

Crystals grown in space have been shown to be of higher quality than 'earth-grown' crystals because defect-free specimens are obtained in the absence of gravity-fueled convection. Defect-free organic crystals are of particular interest because they can exhibit high optical nonlinearities. However, as these are molecular crystals, they tend to be brittle and cannot be easily fabricated into thin films or fibers as can polymer analogs. Polymers having a controlled supramolecular structure and morphology are even more promising candidates as nonlinear optical materials (NLOM). We have previously demonstrated the rationale for orienting biopolymers, materials with known supramolecular structure, in an electric field under microgravity conditions in order to optimize the nonlinearity of the biopolymer. Now focusing on the feasibility of improving upon the NLO activity of the biopolymer system by using a metal dopant, we report on the morphological characterization of electric field aligned polymer/silver colloid composites. By analogy to the microgravity processing of metal/ceramic alloys (known as 'cermets'), the resulting 'polymet' should benefit from homogeneous orientation of the minor metal phase within the polymer phase and further contribute to the potential of polymeric NLOM.

Polydiacetylenes are a unique class of highly conjugated organic polymers that are of interest for both electronic and photonic applications. Many of these applications require high quality thin polydiacetylene films, i.e., films possessing minimal impurities and inhomogeneities, uniform thicknesses, and few defects such as light scattering centers. The growth of such films is not trivial. Photodeposition from solution is a novel process, discovered in our laboratory, which shows excellent potential for producing high quality polydiacetylene films, superior to those grown by conventional techniques. The basic method is quite simple; a diacetylene monomer solution is irradiated with UV light through quartz, glass, or other transparent substrate and a thin polydiacetylene film results. During the course of this process thermal density gradients arise due to uneven heat generation throughout the monomer solution. These gradients can then, under the influence of gravity, give rise to buoyancy-driven convection. Additionally, changes in monomer concentration may induce solutal convection. This convection affects transport of material to and from the growing polydiacetylene film, and thus affects the dynamics of the growth process, and thereby also the microstructure, morphology, and properties of the film. Evidence of this is seen when the films are viewed under a microscope; they exhibit small particles of solid polymer which form in the bulk solution, get transported by convection to the surface of the growing film, and become embedded. Also convection tends to cause the film thicknesses to be less uniform, and may even affect the molecular orientation of the films. We have been actively studying the fundamental science of diacetylene polymerization in solution and polydiacetylene film photodeposition from solution, including the kinetics, mechanism, and photo-chemistry of the process, and the nature and properties of the films obtained. Initial results of this work have just been published in J. Am. Chem. Soc. The thrust of our research is to investigate in detail, both in 1-g and in low-g, the effects of convection (and the lack thereof) on this novel and interesting reaction.

In this paper, we will take a closer look at the state of the art of polydiacetylene, and metal-free phthalocyanine films, in view of the microgravity impact on their optical properties, their nonlinear optical properties and their potential advantages for integrated optics. These materials have many attractive features with regard to their use in integrated optical circuits and optical switching. Thin films of these materials processed in microgravity environment show enhanced optical quality and better molecular alignment than those processed in unit gravity. Our studies of these materials indicate that microgravity can play a major role in integrated optics technology. Polydiacetylene films are produced by UV irradiation of monomer solution through an optical window. This novel technique of forming polydiacetylene thin films has been modified for constructing sophisticated micro-structure integrated optical patterns using a pre-programmed UV-laser beam. Wave guiding through these thin films by the prism coupler technique has been demonstrated. The third order nonlinear parameters of these films have been evaluated. Metal-free phthalocyanine films of good optical quality are processed in our laboratories by vapor deposition technique. Initial studies on these films indicate that they have excellent chemical, laser, and environmental stability. They have large nonlinear optical parameters and show intrinsic optical bistability. This bistability is essential for optical logic gates and optical switching applications. Waveguiding and device making investigations of these materials are underway.

We will present the results of study of nonlinear optical organic compounds based on dye doped polymeric micron size spherical particles. These particles are generated on the ground at artificial low gravity. Free falling drops of polymer solution or metal take on the shape close to spherical. The fabrication at real low gravity can substantially improve the sphericity of the particles and their identity. We show that the particles, being combined with different organic chromophores, can potentially increase their nonlinear optical response in practical applications. This effect is associated with the break of symmetry at the particle surface and the interaction of the resonant modes with non-symmetrical molecules at the particle surface. Constructive light interference in an array of microspheres additionally enhances nonlinear response. In our experiments we used polystyrene microspheres with diameter from 1.7 to 5.3 microns. Two- dimensional quasi-crystals were fabricated from polystyrene microspheres and characterized for their structural and nonlinear optical properties. The quasi-crystals were produced with the method based on Langmuir-Blodgett thin film technique. As possible dopants we studied a NPO dye, derivatives of DIVA, disperse dyes. Some of the create Langmuir-Blodgett films combined with spherical particles in the same technological process.

The crystallization features of thin single crystalline films of mNA and COANP compounds grown between two fused quartz plates, one of which has a recess in the middle, are described. The depth of the recessed spot was of the grown crystal thickness which range d form 1 to 10 micrometers. A possible explanation of the crystallization peculiarities of the COANP compound is given .The crystallographic and optical indicatrix orientations of the crystal s are discussed, and applied to measurement of the efficiency of the second harmonic of the Nd:YAG laser operating at 1.064 micrometers, and generated by our films. The pattern of the intensities of the second harmonic generation is discussed, and a possible explanation of the discrepancy between the experimental and theoretical data is given.

Several different approaches are presented for the separation and conversion of isolated molecules in solution to solid, single-molecule particles. With an electrospray process single molecules and few molecule cluster are isolated. Tested were an amorphous polystyrene and a crystalline poly(ethylene oxide). Particle size- and shape- distributions were characterized using scanning electron microscopy. The influence of the small particle size on physical parameters are discussed. Observations of electrosprayed polymer particles are used to suggest an extension of the general electrospray model.

A review of structural investigations of polymer cyclolinear organosiloxanes and monomer hydroxyderivatives of organosiloxanes which form thermotropic liquid crystalline phases is presented. In order to investigate the structure of these compounds x-ray diffraction of solid crystalline and liquid crystalline samples have been done as well as spectroscopic investigations and molecular modeling. Molecular modeling based on the obtained earlier results on hydroxyorganosiloxanes gave us the possibility of predicting the existence of the same phase for the hydroxycarbosilanes that were synthesized and described in present work. The molecular modeling of cyclolinear organosiloxanes gave us possibility to describe structure of their representative on atomic level.

A unified approach for direct simulations of fluid flow, heat transfer, and phase changes is discussed. The method is based on writing one set of conservation equation for all phases involved, allowing arbitrary changes in material properties and adding singular terms at phase boundary to ensure that the correct boundary conditions are incorporated. This approach allows the conservation equations to ge solved on a fixed grid in a very efficient way. By explicit tracking of the phase boundary by a lower dimensional moving grid, the method is capable of producing accurate solutions for complex phase boundaries. Examples of simulations of the solidification of pure materials, binary alloys, and drops impinging on a solid surface are shown.

Thermoelastic calculations for CdTe grown by the vertical Bridgman method are presented. Finite element calculations are verified by some experimental data. Solidification interface velocity, charge temperature and stress distributions are computed for prescribed ampoule withdrawal rates and several ampoule support systems. The support systems include various materials and seed-wafer transition zone geometries. Crystal stress in excess of the critical resolved shear stress is used as the figure of merit to judge the performance of a particular system. Emphasis is focused on the transition region between the seed and wafer. A processing strategy is proposed and desirable support system characteristics are presented.

A numerical model of heat transfer using combined conduction, radiation and convection in AADSF was used to evaluate temperature gradients in the vicinity of the crystal/melt interface for variety of hot and cold zone set point temperatures specifically for the growth of mercury cadmium telluride. Reverse usage of hot and cold zones was simulated to aid the choice of proper orientation of crystal/melt interface regarding residual acceleration vector without actual change of furnace location on board the orbiter. It appears that an additional booster heater will be extremely helpful to ensure desired temperature gradient when hot and cold zones are reversed. Further efforts are required to investigate advantages/disadvantages of symmetrical furnace design (i.e., with similar length of hot and cold zones).

The Georgia Tech SUmmer Undergraduate Packaging Research and Engineering Experience for Minorities (GT-SUPREEM) is an eight-week summer program designed to attract qualified minority students to pursue graduate degrees in packaging- related disciplines. The program is conducted under the auspices of the Georgia Tech Engineering Research Center in Low-Cost Electronic Packaging, which is sponsored by the National Science Foundation. In this program, nine junior and senior level undergraduate students are selected on a nationwide basis and paired with a faculty advisor to undertake research projects in the Packaging Research CEnter. The students are housed on campus and provided with a $DLR3,000 stipend and a travel allowance. At the conclusion of the program, the students present both oral and written project summaries. It is anticipated that this experience will motivate these students to become applicants for graduate study in ensuring years. This paper will provide an overview of the GT-SUPREEM program, including student research activities, success stories, lessons learned, and overall program outlook.

The Alliance for Nonlinear Optics is a group of seven faculty at five universities who are working together to develop and test nonlinear optical materials. Each school has its own approach to outreach. In general the group has worked with the academic departments to supplement the departmental efforts. Some of the programs are formal, such as the Visiting Scientist Program at New Mexico Highlands University. Others are informal, such as the faculty efforts to interact informally with the high schools in Puerto Rico. One effort that has been successful is Discovery Day or Science Day, a special day when high school students from around the state are invited to the university for programs in science and engineering. This program has become so popular that it will have to be offered twice this year to meet the demand. Students have been very successful in putting on a chemical magic show in area elementary schools.

An aspect of the National Science Foundation Engineering Research Center in Data Storage Systems (DSSC) program that is valued by our sponsors is the way we use our different educational programs to impact the data storage industry in a positive fashion. The most common way to teach data storage materials is in classes that are offered as part of the Carnegie Mellon curriculum. Another way the DSSC attempts to educate students is through outreach programs such as the NSF Research Experiences for Undergraduates and Young Scholars programs, both of which have been very successful and place emphasis and including women, under represented minorities and disable d students. The Center has also established cooperative outreach partnerships which serve to both educate students and benefit the industry. One example is the cooperative program we have had with the Magnetics Technology Centre at the National University of Singapore to help strengthen their research and educational efforts to benefit U.S. data storage companies with plants in Singapore. In addition, the Center has started a program that will help train outstanding students from technical institutes to increase their value as technicians to the data storage industry when they graduate.

In 1992, NASA awarded Fisk University a 5 year grant to establish a center for research and education on photonic materials are synthesized, characterized and, in some cases, developed into devices with applications in the fields of radiation detectors and nonlinear optical crystals, glasses and nanomaterials. The educational components include participation in the research by 3 types of students majoring in Physics, Chemistry and Biology: 1) Fisk undergraduates participating during the academic year. 2) Fisk graduates performing their Maser Thesis research. 3) Fisk and other HBCU's and Minority Institutions' undergraduates attending a 10 week summer workshop with a very rigorous program of study, research and progress reporting. Funds are available for supporting participating students. Prerequisite, schedules of activities, evaluation procedures and typical examples of the outcome are presented.

The Department of Physics at Hampton University generates over 4.5 M dollars of external research funding annually and operates three research centers, the Nuclear High Energy Physics Research Center, the Research Center for Optical Physics, and the Center for Fusion Training and Research. An integral component of these centers is an active outreach and recruitment program led by the Associate Director for Outreach. This program includes summer internships and research mentorships, both at Hampton University and at national laboratories such as CEBAF and NASA Langley. Faculty presentations ar local area elementary schools, middle schools and high schools are also under the auspices of this program.

We have measured the rate of diffusion of aqueous CuSO₄ into pure water across a free liquid interface both on the ground and in 'microgravity' aboard the STS-43 mission of the Space Shuttle. Because both experiments were carried out under isothermal conditions with the CuSO₄ solution on the bottom and the pure water on the top, there was no obvious source of buoyancy. Moreover, the expected decrease in the diffusion coefficient due to hydrostatic pressure diffusion of CuSO₄ was two orders of magnitude less than the experimental error, which was 3-4 percent. Thus, within this error, our experiments show that there is not effect of gravity on diffusion in the case of a gravitationally stabilized, isothermal liquid. This is in contrast to the results obtained by others using melts under non-isothermal conditions where effects as large as 10 percent have been reported.

In a joint experiment between the Northrop-Grumman Science and Technology Center and the University of Alabama in Huntsville, Consortium for Materials Development in Space, single crystals of mercurous chloride were grown in the Space Experiment Facility (SEF) transparent furnace that was flown on Spacehab 4 in May 1996. Mercurous chloride is an acousto-optical material with an unusually low acoustic velocity and high acousto-optical figure of merit. Single crystals of this material can be readily grown in normal gravity by closed-tube physical vapor transport, but the crystals generally contain structural inhomogeneities which degrade the optical performance. The nature and cause of these defects are not completely understood, but their degree appears to correlate with the Rayleigh number that characterizes the convective transport during their growth; hence, it is suspected that uncontrolled convection may play a role in the defect structure. The objective of the flight experiment was to reduce the convective flows by several orders of magnitude to see if the structural inhomogeneities can be reduced or eliminated. This paper will describe the physical and thermal properties of the SEF furnace, the ampule design and loading procedure, and the ground testing, and will also present the preliminary flight results.

Highly segregated macrostructures tend to develop during processing hypermonotectic alloys because of the density difference existing between the two liquid phases. The approximate 4-6 seconds of low-gravity provided by Marshall Space FLight Center's 105 meter drop tube was utilized to minimize density-driven separation and promote uniform microstructures in hypermonotectic Ag-Ni and Ag-Mn alloys. For the Ag-Ni alloys a numerical model was developed to track heat flow and solidification of the bi-metal drop configuration. Results, potential applications, and future work are presented.

An experiment to study the effects of spacecraft accelerations on solute diffusion and thermo-solutal convection is presented. The experiment focuses on two phenomena of interest to crystal growers and fluid dynamists, namely, the transport of concentration that approaches purely diffusion limited conditions in low gravity, and the effect of a temperature gradient on the developed solute profile. Ground experiments and modeling studies are discussed and a space experiment concept that can be used to test the results is presented. Optical interferometry is used to delineate the subtle effects of onboard accelerations on solute diffusion and a shadowgraph technique is utilized to discern fluid motion. The proposed experiment is a follow-up of the thermal diffusion demonstration experiment that flew as the science payload of an active vibration isolation system called STABLE on STS-73 in October 1995.

DAN, 4-(N,N-dimethylamino)-3-acetamidonitrobenzene is an organic nonlinear optical material with particularly high polarizability of the molecule. In order to provide a sound base for the optimization of (flight) crystal growth experiments, we have performed vapor pressure measurements with DAN, and studied the growth morphology at various temperatures. Vapor pressure data were obtained between 50 and 140 degrees C, employing a specially designed, non- contaminating, and computer-controlled experimental set-up. Thermal decomposition of DAN was found to set in around 90 degrees C. Crystal growth morphologies were monitored by optical microscopy at various temperatures. Smoothly faceted growth, indicating adequate surface mobility of adatoms, was obtained at temperatures above 115 degrees C. As a consequence, for crystal growth at this high temperature, continuous removal of decomposition products is required to sustain practical growth rates.

A beam deflection apparatus with a high resolution has been developed which allows monitoring of temperature and concentration gradients in the region around a TGS (triglycine sulphate) crystal growing from an aqueous solution. The developed optical setup consists of two measuring arms that allow inspection of the test region along two perpendicular directions. With a lateral position sensing device the deflection of a mildly focused laser beam traversing the medium to be tested have been measured along one inspection axis, while a 2D analysis of the test region is performed in the orthogonal direction by means of a properly focused light blade and a CCD camera. Experimental verification of the technique has been performed utilizing TGS crystal growth by means of the 'cooled sting' method. The experiment takes place in a double-wall glass cell, the temperature of the TGS crystal can be adjusted independently from the solution temperature. Systematic measurements have been performed which allow to characterize concentration gradients and thermal convection in the vicinity of the crystal. Analysis of experimental results shows the high sensitivity of this method. This technique is well suited as a diagnostic tool for monitoring and controlling crystal growth experiments in microgravity.

The German Space Agency (DLT) commissioned Dornier GmbH to construct the Tiegelfreies Electromagnetisches Prozessieren unter Schwerelosigkeit (TEMPUS) facility for conducting containerless experiments on metallic samples in low earth orbit. TEMPUS, utilizing electromagnetic positioning and heating, was flown on the IML-2 Spacelab mission in July 1994 and is scheduled to fly again on the MSL-1 mission in March of 1997. TEMPUS requires non contact temperature measurement. In particular, nucleation and heat capacity measurements have special requirements for accurate temperature measurement. For these measurements, the facility has optical pyrometer capabilities at the specific wavelength of 633nm as well as the integrated wavelength ranges of 1000 to 2500 nm and 3000 to 4000 nm. The instrument and calibration procedures are described herein. The uncertainty in the temperature measurement on TEMPUS has been quantified, and the implications on the accuracy of nucleation and heat capacity measurements is discussed.

The constitutive behavior of uncemented granular materials such as strength, stiffness, and localization of deformations are to a large extent derived from interparticle friction transmitted between solid particles and particle groups. Interparticle forces are highly dependent on gravitational body forces. At very low effective confining pressures, the true nature of the Mohr envelope, which defines the Mohr-Coulomb failure criterion for soils, as well as the relative contribution of each of non-frictional components to soil's shear strength cannot be evaluated in terrestrial laboratories. Because of the impossibility of eliminating gravitational body forces on earth, the weight of soil grains develops interparticle compressive stresses which mask true soil constitutive behavior even in the smallest samples of models. Therefore the microgravity environment induced by near-earth orbits of spacecraft provides unique experimental opportunities for testing theories related to the mechanical behavior of terrestrial granular materials. Such materials may include cohesionless soils, industrial powders, crushed coal, etc. This paper will describe the microgravity experiment, 'Mechanics of Granular Materials (MGM)', scheduled to be flown on Space Shuttle-MIR missions. The paper will describe the experiment's hardware, instrumentation, specimen preparation procedures, testing procedures in flight, as well as a brief summary of the post-mission analysis. It is expected that the experimental results will significantly improve the understanding of the behavior of granular materials under very low effective stress levels.

The influence of thermal cycles (heating up to 453 K, cooling to 123 K) on the change of the elementary compositionof surface layers of 12Kh18H10T steel and VT-1-0 alloy was studied on the samples of these materials in the LAS-2000 chamber (Riber, France). Decomposition of the higher oxides of iron, nickel, formation of lower oxides were found, as well as migration of O, C, Cl, N along the grain boundaries and formation of their chemical compounds which influence the materials destruction.

Containerless processing provides a high purity environment for the study of high-temperature, very reactive materials. It is an important method which provides access to the metastable state of an undercooled melt. In the absence of container walls, the nucleation rate is greatly reduced and undercooling up to (Tm-Tn)/Tm approximately 0.2 can be obtained, where Tm and Tn are the melting and nucleation temperatures, respectively. Electromagnetic levitation represents a method particularly well-suited for the study of metallic melts. The TEMPUS facility is a research instrument designed to perform electromagnetic levitation studies in reduced gravity. It provides temperatures up to 2600 degrees C, levitation of several grams of material and access to the undercooled state for an extended period of time (up to hours).

The Advanced Automated Directional Solidification Furnace (AADSF) is a five zone tubular furnace designed for Bridgman-Stockbarger, other techniques of crystal growth involving multiple temperature zones such as vapor transport experiments and other materials science experiments. The five zones are primarily designed to produce uniform hot and cold temperature regions separated by an adiabatic region constructed of a heat extraction plate and an insert to reduce radiation from the hot to the cold zone. The hot and cold zone temperatures are designed to reach 1600 degrees C and 1100 degrees C respectively. AADSF operates on a multi- purpose experiment support structure within the cargo bay of the Space Shuttle on the United States Microgravity Payload (USMP) missions. Two successful flights, both employing the directional solidification or Bridgman-Stockbarger technique for crystal growth have been made, and crystals of HgCdTe and PbSnTe grown in microgravity have been produced on USMP- 2 and USMP-3 respectively. The addition of a sample exchange mechanism will enable three different samples to be processed on future flights including the USMP-4 mission.

This paper presents an overview of the STABLE microgravity isolation system developed and successfully flight-tested in October 1995. A description of the hardware design and operational principles is given. Samples of measured flight data are presented, including an evaluation of attenuation performance provided by the actively controlled electromagnetic isolation system. Preliminary analyses show that the acceleration environment aboard STABLE's isolated platform was attenuated by a factor of more than 25 between 0.1 and 100 Hz. STABLE was developed under a cooperative agreement between National Aeronautic and Space Administration, Marshall Space Flight Center, and McDonnell Douglas Aerospace. The flight hardware was designed, fabricated, integrated, tested, and delivered for launch during a five month period.

The capabilities of the Space Station glovebox facility is described. Tentatively scheduled to be launched in 1999, this facility called the Microgravity Sciences Glovebox will provide a robust and sophisticated platform for doing microgravity experiments on the Space Station. It will provide an environment not only for testing and evaluating experiment concepts, but also serve as a platform for doing fairly comprehensive science investigations. Its design has evolved substantially from the middeck glovebox, now flown on Space Shuttle missions, not only in increased experiment volume but also in significant capability enhancements. The system concept, functionality and architecture are discussed along with technical information that will benefit potential science investigators.

The Space Shuttle Furnace Facility (SSFF) is the modular, multi-user scientific instrumentation for conducting materials research in the reduced gravity environment of the International Space Station. The facility is divided into the Core System and two Instrument Racks. The core system provides the common electrical and mechanical support equipment required to operate experiment modules (EMs). The EMs are investigator unique furnaces or apparatus designed to accomplish specific science investigations. Investigations are peer selected every two years from proposals submitted in response to National Aeronautics and Space Administration Research Announcements. The SSFF Core systems are designed to accommodate an envelope of eight types of experiment modules. The first two modules to be developed for the first instrument rack include a high temperature gradient furnace with quench, and a low temperature gradient furnace. A new EM is planned to be developed every two years.

The Universal Multizone Crystallizator (UMC) is a special apparatus for crystal growth under terrestrial and microgravity conditions. The use of twenty-five zones allows the UMC to be used for several normal freezing growth techniques. THe thermal profile is electronically translated along the stationary sample by systematically reducing the power to the control zones. Elimination of mechanical translation devices increases the systems reliability while simultaneously reducing the size and weight. THis paper addresses the UMC furnace design, sample cartridge and typical thermal profiles and corresponding power requirements necessary for the dynamic gradient freeze crystal growth technique. Results from physical vapor transport and traveling heater method crystal growth experiments are also discussed.

The concept, design and analysis of a unique, thermal diffusion demonstration experiment (Chuck) is described. Chuck flew as the science payload of an active vibration isolation system called STABLE on STS-73 in October 1995. The experiment was designed to contribute to materials science studies, besides other disciplines, by providing quantitative data (through optical interferometry) on heat transfer in a fluid subjected to varying levels of vibration in a low-gravity environment. It employed very simple geometry, in a well understood circumstance, to allow materials science investigators to verify analytical and numerical models currently utilized for design and theoretical studies in a wide range of experiments. Its design, build, testing and integration was achieved in a record five months duration using essentially off the shelf components and minimal costs.

During preparation for research of processes crystal growth in conditions of space flight are spent investigation main regularity of processes crystal growth CdTe. In result is determined influence of such parameters of process crystal growth, as a way preparations of a material, way seeding and shape of the container, distribution of temperature in the field of a melt and crystal, speed crystal growth. As criterion for assessment of their influence are adopted the geometrical sizes of monocrystals and their structural perfection. Under our assumptions this problem is connected with the structure of liquid, which can be various depending on stoichiometic composition and mode of cooling before crystallization. For stabilization of a structure proposed two-temperature annealing of a polycrystalline load in vapor of Cd. Chosen experimentally conditions of crystal growth has let to increase reproducibility results. Its influence we consider from the point of view of formation of an optimum structure in associated melt, capable to supply optimum conditions crystal growth.

Problem of crystal growth process simulation for the cadmium-mercury-tellurium alloy from tellurium solution by the travelling heater method under microgravity conditions is considered. The main attention is drown to the formulation of boundary conditions at the interfaces and calculation of the growth rate. Limitation of the local thermodynamic equilibrium approximation and uncertainty in determination of growth parameters in this case is shown. Non-equilibrium model of HgCdTe crystal growth from solution is considered. It includes one matching parameter, the kinetic factor, which should be determined from experiment. Comparison of the calculation results obtained by the equilibrium and by the non-equilibrium rom experiment. Comparison of the calculation results obtained by the equilibrium and by the non-equilibrium model shows, that the kinetic factor does not influence the crystal growth rate since a certain value. Results of the calculation of HgCdTe crystal growth process at the seed from cadmium telluride are given as well.

An electrostatic levitation furnace (ELF) is under development for the Japanese Experiment Module in the International Space Station, which will be operational around 2000. This paper describes the features and development status of the furnace, and some expected experiments which utilize the ELF's containerless processing environment.