Papers by Keyword: Microgravity

Abstract: The first results are presented of ESA MAXUS 8 sounding rocket benchmark experiment on γ-TiAl (Nb,B) intermetallics solidification, that was a part of the IMPRESS EU FP6 project. Having the aim to investigate the columnar and equiaxed primary microstructures formation at diffusion controlled melt growth, an experiment was designed applying the power-down directional solidification technique with fixing quench in automatic spaceborne furnace module TEM03-5M. Two related alloys were tested: one inoculated with boron grain refiner Ti-44Al-7.5Nb-2.7B (at.%); and the other Ti-45.5Al-8Nb (at.%) without grain refinement. The series of terrestrial reference processes has been performed accordingly in counter-gravity solidification direction. The numerical studies of heat-mass transfer, melt hydrodynamics and temporal solidification dynamics of these alloys have been implemented under the earth-and zero-gravity approximations using the GIGAN software package (IPPE). The comparison is performed of numerical model findings with the real microstructure and composition of samples, whose analyses were carried out by backscattered scanning electron microscopy (SEM) and X-ray microprobe (EDX) techniques. The convection-induced peritectic macrosegregation effect appearance and development in ground-based reference ingots is analytically observed and numerically studied. The achieved microstructure formation in space benchmarks is discussed.

Abstract: In this work special attention is paid on the direct visualization of the diffusion process of oil droplets in supercritical carbon dioxide as well as a better characterization of the process by quantitative evaluation of the diffusion coefficients obtained with a shearing interferometer. Experiments are also to be carried out under microgravity in to improve the experiment condition where the influence of gravity-driven convection that usually dominates the transport process is minimized.

Abstract: t is believed that a microgravity environment may maintain ideal depletion zones of protein (PDZ) and impurity (IDZ) around growing crystals and may contribute to growing high-quality crystals. This can lead to an X-ray diffraction data collection of higher resolution with lower mosaicity, because of the better internal order and fewer defects in the crystals when compared to ground-grown crystals. The extent of these depletion zones are dependent on a competition between the diffusion of the molecules in the solution (indexed by the diffusion coefficient, D) and the adsorption of those into the growing crystal (indexed by the kinetic constant, β). If we use the D/β value as an index of the extent of PDZ and IDZ, a lower D/β value is ideal for maintaining PDZ and IDZ. Using experimental results, we could easily obtain the D/β value. When we combined the D/β value with the quality of protein crystals obtained in microgravity experiments provided by Japanese Space Agency (JAXA), we found that the effects of microgravity contributed to obtaining superior crystals especially if the D/β value was less than 3 mm. The numerical analysis of the PDZ and IDZ shows that the radius of the crystal (R) is also related to the PDZ and the IDZ. If the Rβ/D value is large, both the PDZ and the IDZ provide a filtration effect, but if the Rβ/D value is small, only the IDZ does.

Abstract: Growing high quality crystals is a bottleneck in the multi-stepped process of three-dimensional structural analyses of protein. It is known that a microgravity environment may maintain ideal depletion zones of protein and impurity around a growing crystal and the filtering effect of these depletion zones may contribute to obtaining high-resolution X-ray diffracting crystals with superior internal order. The effects of these depletion zones around growing crystals are thought to be the main mechanisms for the improvement of crystal quality in microgravity. A competition between the diffusion of protein molecules in the solution (indexed by the diffusion coefficient, D) and the adsorption of those into the growing crystal (indexed by the kinetic coeffcient, β) decides the extent of depletion zones. Lower D values and higher β values indicate that these effects are more obvious in numerical analyses. Therefore we use the D/β value as an index for these effects. The most effective method of lowering the D/β value is using viscous precipitant reagents, such as a high molecular weight polyethylene glycol (PEG) to decrease the D value and using highly homogenous protein samples to increase the β value. In this report, we briefly introduce simple yet practical methods of estimating D and β values followed by a numerical analysis to understand the filtration effects, and the results of crystallization experiments in microgravity when controlling the diffusive field around the growing crystals using the D/β value as an index.

Abstract: As a preliminary experiment for the growth of InGaSb alloy crystals under microgravity at International Space Station (ISS), bulk crystal was grown under terrestrial condition using the same gradient heating furnace (GHF). Czochralski grown GaSb <111>B single crystal was used as a seed and feed crystals for the growth of InGaSb bulk crystals. During the growth, heat pulses were intentionally introduced periodically to create the growth striations. From the striations, the growth rate of the grown crystal was estimated. The results show that the growth rate was gradually increased from the beginning of the growth and became stable. On the other hand the In composition of the grown crystal decreased along the growth direction. From the In composition, the temperature gradient in the solution was estimated and it was almost the same of that fixed during the growth.

Abstract: Self-propagating High-temperature Synthesis (SHS) technology is characterized with high-temperature generation, spontaneous reaction propagation and rapid synthesis. Our research and development on simultaneous synthesis and sintering has progressed by applying mass force effects to SHS technologies; metal-ceramic composite pipe formation with centrifugal force on thermite reactions (“Centrifugal-thermite Process”) and fine ceramic composite synthesis under micro-gravity environments (MGE) formed with a free-fall, parabolic flight and sounding rocket. The process has successfully attained to produce more than 3 m long composite-layered pipes with significant feature for the production in its reaction propagation under centrifugal effect as well as the centrifugal force and reaction heat. In the latter, the TiB2-Al composite synthesis under a free fall MGE, for example, has made clear that the lack of mass migration and the improvement of wetting between TiB2 and Al under the MGE affect the formation of a fine and dense cermet-like structure in the products. An advanced approach on the mass-forced SHS technologies performed is introduced by designing product densities and SHS reaction system.

Abstract: Containerless solidification of Bi32.5In51Sn16.5 eutectic alloy under microgravity conditions was investigated by using a 3 m length drop tube. The Bi-In-Sn system is an important material for lead-free solder and fuse element for electrical protection. It has a low eutectic melting temperature of 60°C, which is suitable for experiments in restricted environments like the International Space Station (ISS), where the security requirements are very strict. Droplets, with diameters in the range of 200 to 400 m, solidified under microgravity, were obtained consistently with irregular ternary eutectic structure, whereas, previous results under normal gravity presented both regular lamellar and irregular structures.

Abstract: In this paper, mass measurement devices (MMDs) developing by the authors for use in the International Space Station (ISS) are reviewed. First, Space Balance, which is a small mass measurement device (SMMD), is reviewed. In Space Balance, the momentum conservation between two objects, the subject mass and the reference mass, are compared. Then Space Scale, which is a body mass measurement device (BMMD), is reviewed. In Space Scale, a human subject is pulled using rubber string. Force is measured using a force transducer and acceleration is measured using optical interferometer. Both Space Balance and Space Scale have shown high accuracies in the ground experiments.

Abstract: The problem of numerical modeling of directional solidification of TiAl refractory intermetallics aboard the MAXUS 8 sounding rocket is considered. The research is of relevance to the FP6 Integrated project IMPRESS (Intermetallic Materials Processing in Relation to Earth and Space Solidification). Attention is paid to columnar-to-equiaxed microstructure transition (CET) phenomenon and mushy zone evolution in Ti-45.9Al-8Nb (at %) alloy being processed in TEM 01-3M high-temperature (up to 17000C) furnace. In this three-zone resistive furnace the “bent” temperature profile is applied with two strongly different axial thermal gradients, presumably allowing the achieving of CET conditions along the sample of 160 mm length. Temperature profile evolution is defined by power-down furnace operation. 2D-numerical study of heat transfer and realtime-scale solidification dynamics of TiAl-Nb under zero gravity approximation is performed. The approaches used for solution of Navier-Stokes equations and phase transition (Stefan) problem are briefly described. The solidification time is shown to be satisfying the 12-minute microgravity limit aboard a MAXUS. The position and the time at which CET may be triggered are predicted and confirmed in line with the Hunt diagram. The comparison is performed of model predictions with the real microstructure of TiAl-Nb reference sample solidified on-ground in TEM 01-3M facility.

Abstract: In the frame of an international cooperation a 4 year long project was executed to determine thermal conductivity in metallic melts. During the project, the University of Miskolc designed and developed unique apparatus which was capable to perform measurements under microgravity conditions. The experiments were carried out at the Drop Tower „Bremen” where the conditions of reduced gravity could be provided for 4.7 s and a gravity level of 10-5g was achieved. The registered temperature distribution data of the examined melts always show a clear difference between the experiments measured in the normal and in the low gravity environment. During the evaluation of the datasets it was proven, that the well known canonical evaluations could not be used with high reliability for all the measurements, for all the materials and for all the geometry used. Besides of the understanding of the underlying physics and evaluating the measured data, the Crank-Nicolson method and error function analysis were used at the beginning, some numerical analyses were also initiated to simulate the system in FEM (Marc). The results showed acceptable results, but also pointed out a need for further study, so a detailed numerical analysis on a specialized FVM (Fluent) system was started. The code used for the numerical simulation (Fluent) was able to handle the heat conductivity, the liquid flow, the complex material parameters changes and the used geometries as well. With this technique, from the data of the drop experiments, the pure - free from the effect of the liquid flow - thermal conductivity could be separated. The results show that after these simulations, using different conditions (temperature, gravity level, etc.) for one material the same thermal conductivity value could be determined, within acceptable tolerance.