An overview of the current NASA microgravity materials science flight research program is given. The focus of these experiments is on crystal growth, solidification fundamentals, and thermophysical property measurements of materials.

Zeolite crystals are one of the Chemical Process Industry's most valuable catalytic and adsorbent materials. Large, essentially defect-free zeolite crystals could be used to better understand zeolite catalysis mechanisms, and could help in designing better zeolite adsorption systems. In addition, if zeolites could be made large enough, they could be used to make zeolite membranes; these could be used as reactors/separators, resulting in highly improved efficiency. Space provides a unique environment to grow large zeolites by allowing them to continue to grow suspended in their nutrient field. In order to better utilize this microgravity environment, it is necessary to control the nucleation event. Triethanolamine (TEA) can be used to control the time release of aluminum in a zeolite A solution. In a 1 g environment, the use of TEA resulted in a 25 - 50X increase in average and maximum crystal size. It is proposed that if fluid motion can be controlled and the rate of nutrient transport increased, substantially larger zeolite crystals can be formed in microgravity, using such nucleation control agents.

The drawing of glass fibers from preform rods is restricted, by gravity-induced sagging of the molten glass, to a narrow range of viscosity/pulling speed combinations. A scaling analysis of the forces acting on the elongating melt indicates that the absence of gravity would extend this range and permit the drawing of low viscosity melts to form glass-clad single crystal fibers and crystallite-free fibers of glasses such as ZBLAN. Therefore, fiber drawing in microgravity could yield cost-effective products such as ultra-low-loss infrared fibers. Fiber drawing experiments are ideally suited for Shuttle/Spacelab missions, because of their short duration, moderate power demands, and insensitivity to g-jitter, and can even be advantageously performed in lunar gravity. To facilitate such experiments, a prototype spaceflight apparatus has been developed, under NASA sponsorship, that occupies less than 0.16 m3 of volume and weighs less than 27 kg.

A Get Away Special (GAS) experiment payload to investigate microgravity effects on solidification phenomena of selected experimental samples has been manifested for flight on STS-42. The first flight of the furnace assembly will (1) investigate the p-n junction characteristics for advancing semiconductor device applications, (2) study the effects of gravity-driven convection on the growth of HgCd crystals, (3) compare the textures of the sample which crystallizes in microgravity with those found in chrondrite meteorites, and (4) modify glass optical characteristics through divalent oxygen exchange. The space flight experiment consists of many small furnaces. While the experiment payload is in the low gravity environment of orbital flight, the payload controller will sequentially activate the furnaces to heat samples to their melt state and then allow cooling to resolidifaction in a controlled fashion. The materials processed in the microgravity environment of space will be compared to the same materials processed on earth in a one-gravity environment. This paper discusses the design of all subassemblies (furnace, electronics, and power systems) in the experiment. A complete description of the experimental materials also is presented.

There are many organizations in the United States contributing to commercial aspects of crystal growth in space. These include five of NASA's Centers for the Commercial Development of Space, many private companies, and government laboratories. Projects range from growth of large bulk crystals to preparation of thin epitaxial films and small crystals. In most cases the prospect for manufacturing in space remains doubtful because of the high cost and long lead time required for work in space, although these problems are being attacked by NASA's Office of Commercial Programs. Thus at present the commercial reasons for research on crystal growth in space are to evaluate the potential for manufacturing in space, to develop the technology that would be required for this manufacturing, to gain information about the influence of gravity on crystal growth, and to prepare high quality benchmark crystals and devices that can be used as targets for earth-based programs.

The objective of some experiments performed in space is to study the effect of minimized convection on various processes. The Shuttle orbiter can provide long periods of microgravity for performing experiments. However, residual gravitational accelerations still remain. Accelerometers have been placed in the Spacelab to measure these accelerations. The Accelerometers are capable of measuring inputs as small as 10-6 gs. However, these levels are typically masked by the background `noise' accelerations due to crew activity and mechanical vibrations generated by the experiment facilities. In May 1985, Spacelab 3 flew on the Shuttle orbiter. The fluid experiment system (FES), a multiuser facility, was on board with the Triglycine Sulfate (TGS) crystal growth experiment. The FES is a holographic system that is capable of taking single and double exposure holograms. A series of holograms is recorded during the experiment run. The experiment is analyzed on the ground using the series of holograms taken during the run. The main purpose of the TGS experiment was to examine diffusion limited crystal growth by minimizing convection in the microgravity environment of the Spacelab. The seed crystal was attached to a platform. However, in one of the test cells, tiny crystals were found floating free in the growth solution during the experiment. Since the free crystals were in a viscous fluid, the `noise' accelerations of the Shuttle were damped out. This made it possible to measure the constant gravitational acceleration by tracking the positions of these crystals throughout the experiment. This paper presents the velocities and hence accelerations obtained by measuring the position of the free crystals from the holograms. An improved experiment is planned on IML-1 in the FES using polystyrene spheres as markers to aid in characterizing the residual accelerations present in the Spacelab.

The growth of InP by metalorganic chemical vapor deposition (MOCVD) in a horizontal reactor is being modeled with a commercially available computational fluid dynamics modeling code. The mathematical treatment of the MOCVD process has four primary areas of concern: (1) transport phenomena, (2) chemistry, (3) boundary conditions, and (4) numerical solution methods. The transport processes involved in CVD are described by conservation of total mass, momentum, energy, and atomic species. Momentum conservation is described by a generalized form of the Navier-Stokes equation for a Newtonian fluid and laminar flow. The effect of Soret diffusion on the transport of particular chemical species and on the predicted deposition rate is examined. Both gas-phase and surface chemical reactions are employed in the model. Boundary conditions are specified at the inlet and walls of the reactor for temperature, fluid flow, and chemical species. The coupled set of equations described above is solved by a finite difference method over a nonuniform rectilinear grid in both two and three dimensions. The results of the 2-D computational model is presented for gravity levels of zero- and one-g. The predicted growth rates at one-g are compared to measured growth rates on fused silica substrates.

Buoyancy driven flow in the crystal melt is one of the leading causes of segregation. Natural convection arises from the presence of thermal and/or solutal gradients in the melt and it is not possible to completely eliminate the convection even in the low gravity environment of space. This paper reports the results of computational modeling research that is being done in preparation for space-based experiments. The commercial finite element code FIDAP was used to simulate the steady convection of a gallium-doped germanium alloy in a Bridgman- Stockbarger furnace. In particular, the study examines the convection-suppressing benefits of inserting cylindrical baffles in the molten region to act as viscous dampers. These thin baffles are assumed to be inert and noncontaminating. The results from this study show the manner in which the streamlines, velocities, and temperature fields at various gravity levels are affected by the presence of baffles. The effects of changing both the number and position of the baffles are examined and the advantages and disadvantages of using baffles are considered.

Research in high temperature crystal growth and alloy solidification is usually limited to operation in opaque furnaces to limit the heat losses and radiative cooling effects on the sample charge. Due to this limitation, it is difficult to observe the nature of the solid-liquid interface of the material being investigated. The interface region is the area where all compositional or microstructural characteristics of the material are defined. An understanding of the solidification event and the effects of processing parameters such as the G/R ratio or thermal gradient to growth rate ratio, on the interface morphology and morphological stability are of long standing interest. Those interested in processing materials in space or in the microgravity environment are primarily concerned with the disruptive effects of gravity induced convective flows and Marangoni-induced fluid flow in the diffusion field at the solid- liquid interface during directional solidification. If fluid flow fields near the interface can be eliminated, growth of the solid is diffusion controlled. Diffusion controlled growth represents the optimum condition for compositional homogeneity and has only been achieved in capillary tubes in earth-bound experiments. The majority of the body of research performed in real time characterization of the directional solidification process has dealt with low-temperature `model' systems using transparent substances such as succinonitrile, ice, and ammonium chloride. Research in the area of interface morphology in metals and alloys is in most cases limited to metallographic examination of the `frozen-in' microstructure using rapid quenching. There has also been considerable interest in determining the correlation between furnace/ampoule velocity and interface velocity during directional solidification and directional casting. X-ray systems, ultrasonic techniques, and radioscopy have been used to provide real- time interface shape-process parameter correlation, however these techniques have limitations in terms of resolution, bulk, and calibration accuracy. The concept of a visibly transparent directional solidification furnace offers answers to many of the problems thus described, but introduces many other problems in furnace design and control methods. Laboratory transparent furnaces are available from several vendors in the United States and a two zone furnace for chemical vapor transport studies has been developed by Boeing for flight on board the Space Transportation System. Evolution of laboratory systems into flight qualifiable hardware will require a better understanding of transparent furnace design requirements. This paper describes the design and progress of a transparent furnace technology development project currently underway at Teledyne Brown Engineering.

The production of synthetic zeolites represents a large ($500 - $600 million per year) commercial market. However, this market is somewhat limited by the size of crystals (4 - 10 (mu) ) normally produced on Earth. The production of large (> 100 (mu) ) crystals in significant quantities could offer a variety of new applications in the petroleum, medical, bioseparations, and waste management industries. Microgravity processing is one way to obtain these large crystals. To this end, the Battelle Advanced Materials Center for the Commercial Development of Space (CCDS) is funding the development of the Zeolite Crystal Growth (ZCG) Facility, an orbiter middeck payload currently manifested on the USML-1 Spacelab mission to be launched in June 1992. ZCG team members include Battelle, Worcester Polytechnic Institute (WPI), Teledyne Brown Engineering (TBE), and Intek, Inc. This paper describes the design and development aspects of the ZCG Facility. A brief description of the ZCG Facility, its unique operating environment inside the Shuttle Orbiter, and some of the engineering design decisions that were affected by this environment are discussed.

Some of the key work on the growth of second- and third-order nonlinear optical (NLO) organic thin film by vapor deposition is reviewed. The experimental methods used to grow thin films of p-chlorophenylurea, diacetylenes, and phthalocyanines and the characteristics of the resulting films are also reported. Moreover, shortfalls in the growth of films from the vapor and two suggestions that may advance this field of study are presented.

The first International Microgravity Laboratory (IML-1), scheduled for spaceflight in early 1992 includes a crystal-growth-from-solution experiment which is equipped with an array of optical diagnostics instrumentation which includes transmission and reflection holography, tomography, schlieren, and particle image displacement velocimetry. During the course of preparation for this spaceflight experiment we have performed both experimentation and analysis for each of these diagnostics. In this paper we describe the work performed in the development of holographic particle image displacement velocimetry for microgravity application which will be employed primarily to observe and quantify minute convective currents in the Spacelab environment and also to measure the value of g. Additionally, the experiment offers a unique opportunity to examine physical phenomena which are normally negligible and not observable. A preliminary analysis of the motion of particles in fluid was performed and supporting experiments were carried out. The results of the analysis and the experiments are reported.

High resolution in-situ observation methods were developed for the investigation of crystal growth mechanisms from solution phases. Crystal surfaces were observed by phase sensitive microscopies and the concentration gradient and the surface concentration of a solution were measured by interferometries. In order to investigate the morphological instability of a crystal based on a surface kinetics model, in-situ observations of crystal growth in microgravity were planned. The first model was flown in September 1991. These observation methods would further be developed by employing newly developed real time phase shift interferometry, which is more than 100 times sensitive than the other interferometries. This would be very suitable also for the investigation of transient phenomena on crystal growth in a drop tower.

While the growth of bulk crystals and thin layers from vapor is a method with increasing importance and great potential, the theoretical understanding of this technique is quite limited. In particular, the influence of impurities and natural convection on the transport mechanism is not well understood. Density gradients in the vapor phase can be measured by the deflection of a laser beam traversing the growth cell perpendicular to the main direction of material transport. The suitability of this method has been demonstrated in a laboratory setup using iodine as reference material. Optical gradients dn/dz < 10 exp -6/cm can be detected when the region of transport has a depth of 1 cm. The results of the first experiments are in the range predicted by theory. However, to obtain more reliable and precise data, the thermomechanical properties of the total setup have to be improved. Since the beam deflection technique can be realized in a small volume and does not need exhaustive diagnostics instrumentation or data processing, it can easily be adapted to a spaceflight experiment.

The effect of mixing in liquid upon the dissolution and growth rates on the faceted surface during solution growth process in GaP has been studied by means of the in situ observation setup, which was composed of an infrared microscope with an interferometer. The measured dissolution rates agree remarkably well with the boundary layer model, in which it is assumed that solute concentration in the liquid ahead of the boundary layer is homogenized by convection and the surface concentration is not equal to the equilibrium value. The estimated thickness of the boundary layer suggests the existence of the convective flow in the liquid, and this effect is certified with unidirectional solidification in succinonitrile-acetone, which is a transparent alloy system, by means of the in situ observation technique with a common-path microscope interferometer.

The meaningful exploration of the potential of reduced gravity environment for the advancement of crystal growth is complex. It is to a significant extent contingent on the conduct of reproducible experiments in a quantifiable environment. However, most of all it depends on our ability to extract from grown matrices quantitative analytical information on a scale commensurate with that of gravitation related segregation effects and defect structures. A new optical approach, based on NIR microscopy supported by computational image analysis and contrast enhancement, has recently been developed and applied to the characterization of elemental and compound semiconductors. This approach permitted, for the first time, a quantitative microsegregation analysis of GaAs and InP; using NIR dark field illumination in transmission mode makes it now possible to detect submicron precipitates in semi-insulating GaAs. The developed techniques, providing for rapid, quantitative, nondestructive analysis, have been shown to be fully compatible with telescience operation.

The holographic interferometer in two directions of observation (HOLIDDO) instrument is dedicated to the characterization of transparent media which evolve with time in a microgravity environment. It is a multiuser facility, the heart of which is an exchangeable experimental cell adapted to the investigator's requirements. Optical characterization is made either by direct viewing or by interferometric holography imaging in two perpendicular directions which permits reconstruction of a 3-D object. The optical bench allows a depth of field of 30 mm with a resolution better than 50 micrometers . An Fe-LiNbO3 crystal has been selected for storing holograms with a large lifetime, which is necessary for a real time survey. The laboratory model, which is functionally representative of the future flight unit, is now available for testing space experiments.

Irregularities in three crystals grown in space and four terrestrial crystals have been compared by high resolution monochromatic synchrotron x-radiation diffraction imaging. For two of the materials, mercuric iodide and lead tin telluride, features consistent with the presence of additional phases in terrestrial samples have been suppressed in the comparable crystals grown in microgravity. Comparison of the images of highly purified terrestrial mercuric iodide with those of lower purity space and terrestrial material suggests specific detector performance models. These models ascribe the improved performance of detectors made from space-grown mercuric iodide to reduction in a widely dispersed impurity phase rather than to extreme macroscopic lattice regularity. While the general grain structure of lead tin telluride is not strongly affected by growth in microgravity, the subgrain uniformity of the space crystal is substantially higher than that of the comparable terrestrial crystal. The greater uniformity is associated with suppression of the second phase that appears to be characteristic of the terrestrial crystal examined.

An effort to characterize the fluid dynamics of nonisothermal, chemically reactive flows of gaseous mixtures inside fused silica chemical vapor deposition (CVD) reactor vessels is underway at the NASA Langley Research Center. This effort is in support of microgravity investigations of fluid dynamics and multiphase flows. A quantitative understanding of the basic fluid dynamics associated with CVD is necessary to achieve improvements in layer thickness and compositional uniformity, in abruptness of alloy interfaces, and in growth efficiency. To perform this research, a three-component laser velocimetry (LV) system has been adapted specifically for quantitative determination of the mixed convective flows found in chambers used for crystal growth and film formation by CVD. A discussion of the advantages and disadvantages of this instrument compared to flow visualization and particle image velocimetry (PIV) techniques is presented. A fundamental limitation on the application of all particle-based velocimetry techniques in nonisothermal systems is addressed which involves a measurement bias due to the presence of thermal gradients. This bias arises from thermophoretic effects which cause seed particle trajectories to deviate from gas streamlines. Data from a horizontal research CVD reactor are presented which indicate that current models for the effects of this thermophoretic force are not adequate to predict the thermophoretic bias in arbitrary flow configurations. Thermal effects on the flow field inside the research reactor were investigated by comparing data obtained from the reactor both at room temperature and heated to growth temperature by radio frequency (rf) induction. Heating of the susceptor was found to increase the gas velocities parallel to the face of a slanted susceptor by up to a factor of five and to result in as much as a factor of eight increase in velocity components directed toward the hot surface.

The problem of the separation of crystals from their feeding solutions and their conservation at the end of the crystallization under microgravity is investigated. The goal to be reached is to propose an efficient and simple system. This method has to be applicable for an automatic separation on board a spacecraft, without using a centrifuge. The injection of an immiscible and inert liquid into the cell is proposed to solve the problem. The results of numerical modeling, earth simulation tests and experiments under short durations of weightlessness (using aircraft parabolic flights) are described.

A computer controlled scanning ultramicroscope has been built to assist in the characterization of transparent crystals. The device measures the scattering of a focused He-Ne laser beam by crystalline defects. As an XYZ translation table moves the crystal under the ultramicroscope, the scattered light is measured by a photodetector whose output is digitized and recorded. From this data, contour maps or 3-D perspective plots of the scattering regions of the crystal can be generated to assist in finding patterns of defects which might be correlated with perturbations in the growth process. The verified resolution of the present instrument is about 1 micrometers , which is limited by the minimum step of the stepper-motor driven translation stages, optical diffraction effects, and the sensitivity of the detector at the laser light frequency. The instrument was used to build a database of defects patterns in commercial laboratory grown triglycine sulphate (TGS) crystals, and to map defects in a TGS crystal grown from aqueous solution during the flight of Spacelab 3. This crystal shows indications of a reduction both in the generation of defects at the seed-new growth interface and in their propagation into the new crystal.

Using Cauchy's equation and previously available data, the refractive index versus wavelength relationship for triglycine sulphate aqueous solution has been determined. The variation of the index as a function of the temperature and of the concentration is then obtained using the Murphy-Alpert and the Lorentz-Lorenz relationships respectively. These refractive properties should be useful in relevant crystal growth experiments using two-color holographic and other interferometric diagnostic techniques.

Mercurous chloride crystals hold promise for many commercial applications. This material, produced using physical vapor transport (PVT) growth methods, has unique optoelectronic properties making it suitable in many acousto-optic applications. Research is being undertaken within the NASA Center for Commercial Development of Crystal Growth in Space, to determine the potential of using microgravity to grow crystals, thereby producing reduced defect density and, thus, fewer scattering centers and improved acousto-optic behavior. A major indicator of this potential is the velocity field behavior which exists within an ampoule during growth. Circulatory behavior would be indicative of natural-convective-induced flows and, hence, of strong potential for microgravity-affected crystal quality. Laser-Doppler velocimetry methods are being developed to examine the flow of mercurous chloride vapor in situ. Measurements have been made of the velocity profile during PVT growth of mercurous chloride at temperatures of near 300 degree(s)C. The results to date are indicative of a natural circulation pattern but have been found to be strongly dependent on the geometric characteristics of the heating system. This paper describes the measurement system which has the capability of measuring velocities as low as 10-5 m/s. A calibration system developed and used to determine the accuracy of the LDV system at these low velocities also is described. Finally, the paper presents the results obtained to date in mercurous chloride crystal growth in cylindrical ampoules at 300 degree(s)C.

A computer simulation of a two-color holographic interferometric (TCHI) optical system was performed using a physical (wave) optics model. This model accurately simulates propagation through time-varying, 2-D or 3-D concentration and temperature fields as a wave phenomenon. The model calculates wavefront deformations that can be used to generate fringe patterns. This simulation modeled a proposed TriGlycine sulphate TGS flight experiment by propagating through the simplified onion-like refractive index distribution of the growing crystal and calculating the recorded wavefront deformation. The phase of this wavefront was used to generate sample interferograms that map index of refraction variation. Two such fringe patterns, generated at different wavelengths, were used to extract the original temperature and concentration field characteristics within the growth chamber. This proves feasibility for this TCHI crystal growth diagnostic technique. This simulation provides feedback to the experimental design process.

The Surface Tension Driven Convection Experiment (STDCE) is a space transportation system flight experiment to study both transient and steady thermocapillary fluid flows aboard the USML-1 Spacelab mission planned for June 1992. One of the components of data collected during the experiment is a video record of the flow field. This qualitative data is then quantified using an all-electronic, two-dimensional particle image velocimetry (PIV) technique called particle displacement tracking (PDT) which uses a simple space domain particle tracking algorithm. Results using the ground-based STDCE hardware, with a radiant flux heating mode, and the PDT system are compared to numerical solutions obtained by solving the axisymmetric Navier Stokes equations with a deformable free surface. The PDT technique is successful in producing a velocity vector field and corresponding stream function from the raw video data which satisfactorily represents the physical flow. A numerical program is used to compute the velocity vector field and corresponding stream function under identical conditions. Both the PDT system and numerical results were compared to a streak photograph, used as a benchmark, with good correlation.

The normal characterization of a Bridgman crystal growth procedure is to note the ingot preparation, ampoule size and material, the ampoule translation rate, and the furnace zone temperatures. Even though these are important parameters which must be recorded and controlled they may not represent a sufficient set to produce repeatable growth results. One of the primary growth variables, the actual growth rate, is often ignored. Even though it is well recognized that the actual growth rate is not equal to the ampoule translation rate the difference is usually assumed small and the stochastic nature of the difference has not been previously reported. These variations between pull rate and growth rate are especially acute in unseeded growth subjected to deep supercooling. This paper discusses both elemental (Ge) and alloy (PbSnTe) crystal growth that is monitored, via radiography, to reveal both the interface position and shape in real time. Both seeded and unseeded growth are examined. The actual growth rate is shown to be a strong function of the degree of supercooling. Actual growth rates that exceed the pull rate by a factor of greater than two have been observed and the interface shape has been observed to change from concave to flat to convex during the growth.

Two optical methods were recently developed for in situ monitoring of the growth process of mercuric iodide crystals. The first method uses resonance fluorescence spectroscopy (RFS) for the determination of iodine vapor present in the growth ampule, which is an important parameter in determining the stoichiometry, and therefore the quality of the crystals. The second method, reflectance spectroscopy thermometry (RST) measures the crystal face temperature with a present accuracy of +/- 1.5 degree(s)C.

By incorporating advanced technology in fiberoptics, diode lasers, and holographic optical elements with knowledge gained from previous Spacelab work, we have produced a design of a versatile, miniaturized, stand alone, crystal solution growth chamber. Diagnostics instrumentation include the following: (1) crystal growth rate monitor, (2) growth/dissolution monitor with feedback, (3) solution diagnostics, (4) multiple wavelength holography, (5) single wavelength or color Schlieren with video recording. Availability of such a chamber will allow for much greater access to microgravity than is provided by presently available crystal growth research cells.

Many kinds of crystals can be grown by processes in which liquid reactant solutions diffuse into pure solvent and react chemically, as follows, to form single crystals, which are relatively insoluble: A (soluble) + B (soluble) + ... = C (insoluble) + D (soluble) + We call these solute diffusion processes or diffusion processes. Three examples are (1) CaCO3 grown from aqueous solutions of CaC12 and NH4HCO3; (2) PbS, from aqueous solutions of PbCl2 and CH3CSNIH2; and (3) tetrathiofulvalenetetracyanoquinonedimethane (TTF-TCNQ), from solutions of TTF and TCNQ in acetonitrile. We chose these examples to study in experiments performed on the NASA Long Duration Exposure Facility (LDEF). All three have been grown by ground-based solute diffusion processes.

A quantitative real-time image processing system has been developed which, by software control, can be reconfigured for a multiplicity of tasks critical to the processing and characterization of semiconductor materials. In thermal imager mode, two-dimensional temperature distributions of semiconductor melt surfaces (900 degree(s)C - 1600 degree(s)C) can be obtained with temperature resolution better than +/- 0.5 degree(s)C and spatial resolution of better than 0.5 mm. This capability has been applied to the analysis of melt surface thermal field distributions. Temporal and spatial image processing techniques, combined with multitasking computational and data acquisition capabilities have been used to establish this approach to thermal imaging as a multimode sensor for systems control during crystal growth. A second configuration of the image processing engine in conjunction with bright and dark field transmission optics is used to determine, post growth, the microdistribution of free-charge carriers and submicron-sized crystalline defects in elemental and compound semiconductors. These techniques are nonintrusive. The infrared absorption characteristics of wafers are determined with a spatial resolution of less than 10 micrometers and, after calibration, are converted into charge carrier density. These experimental configurations for sensing, control, and characterization are readily adaptable for remote telescience operation.

L-Arginine Phosphate (LAP) is a new nonlinear optical material with higher efficiency for harmonic generation compared to KDP. Crystals of LAP were grown in the laboratory from supersaturated solutions by temperature lowering technique. Investigations revealed the presence of large dislocation densities inside the crystals which are observed to produce refractive index changes causing damage at high laser powers. This is a result of the convection during crystal growth from supersaturated solutions. It is proposed to grow these crystals in a diffusion controlled growth condition under microgravity environment and compare the crystals grown in space with those grown on ground. Physical properties of the solutions needed for modelling of crystal growth are also presented.