A laser light scattering equipment with a large-capacity photon counting memory was developed. The equipment was designed for high speed data acquisition for experiments conducted in shorttime microgravity facilities, such as the Kamisunagawa and Toki dropshafts. The photon counter had 1 M channels, which could provide 10 second data accumulation with a sampling time of 10 µs. Short-time correlogram was obtained for latex particles in a water and the time resolution of particle size analysis was investigated. It was found that a duration of 10 seconds was not short for observing the processes with this system when the sufficient scattering intensity was given.
Supercooled p-cresol melt was investigated using polarized light scattering method under low-gravity. Relaxation of metastable liquid was induced by applying pressure change within the range of 1- 160 bar. Convective flow was observed after changing pressure, showing inhomogeneous density change in the sample. Remarkable oscillation of scattering intensity was observed under gravity, whereas low-gravity experiments showed single peak after changing pressure. These results indicates convective flow affects the processes of pressure relaxation in supercooled melts. In applying Landau's phenomenological theory of phase change, macroscopic flow was related to the molecular ordering. Correlation length of ordered clusters under low-gravity was estimated to be 2.3 times larger than that of clusters under gravity. Thus convective shear flow diminished the size of clusters against the ordering tendency due to non-equilibrium conditions. Both forces are considered to induce the observed oscillatory relaxation under gravity.
Dynamic light scattering experiments were conducted to understand the phenomena of liquid phase separation. The alloy of succinonitrile-ethanol, which is in monotectic composition_, was cooled from mono-phase temperature to two-phase region . The scattering intensity increased drastically near the critical temperature . The self-correlation function of the scattering intensity shows two peaks in the particle size distribution, one is less than 50 nm and the other is from 150 nm to 200 nm. The former is from residual impurities, and the latter is attributed to the concentration fluctuation near the critical temperature. It was concluded that the dynamic light scattering experiments has a high potential in phase separation phenomena studies, particularly in a microgravity environment .
Solidification mechanisms of hypo-eutectic, eutectic, and hyper-eutectic alloys under the microgravity conditions and formation mechanisms of gravitational segregation on earth are considered. Experiments are performed by using the Sounding Rocket TR-1A 4. Six samples of Sn-Pb eutectic alloys containing 35, 38.1 and 39 mass%Pb are used. Two series of experiments are performed; Samples which are melted before launching are solidified under the microgravity conditions and others are melted and solidified under the microgravity conditions. Each sample occurs undercooling before the eutectic solidification. Granular crystals of primary Pb disperse homogeneously throughout the samples under the microgravity conditions. No gravitational segregation of samples appear under the microgravity conditions. Dendrite arms are detached by release of the latent heat during recalescence of undercooling and solidification.
In order to obtain the -true- diffusion coefficient of liquid Pbc1-x)SnxTe, a microgravity experiment was conducted using the Japanese sounding rocket, TR-1A 4. The diffusion couple (Pbo.sTe- Pb0_7Sn0_3Te) of a 2 mm diameter column was melted and kept at 1277 K followed by quenching with injecting helium gas. The diffusion during heating and cooling periods was taken into account in an analytical solution of Fick's second law with the assumption of D = AT 2 (A is constant). The diffusion coefficient at 1277 K was obtained as 7.9 X 1-0 9 m2/s for the present, which is larger than a calculated value from the diffusion coefficient of 1227 K obtained by TEXUS rocket experiment with the assumption of D = AT 2 (A is constant). The results of detailed analysis are to be presented in the near future.
A space experiment was carried out to investigate Marangoni convection in a liquid bridge. The three-dimensional velocity profile of Marangoni convection in a large liquid bridge between two coaxial disks was measured under microgravity using sounding rocket TR-IA#4. A large scale liquid bridge of 50 mm in diameter was formed successfully and sustained stably. In the first stage of the temperature difference of 11 K, flow field was axi-
symmetric . In the final period, temperature difference was increased up to 50 K. The Marangoni convection was enhanced and a non-axisymmetric flow profile was observed. The flow was measured with the use of four CCD cameras. The positions of tracer particles were determined and three-dimensional flow field was obtained.
Marangoni convection in molten silicon was studied from the viewpoint of a heat and mass transfer for a low Prandtl number liquid. Using the NASDA rocket TR-IA #4, the temperature oscillation in molten silicon having a column shape was precisely measured in microgravity conditions. Fourier-transformation analysis showed oscillation with a particular frequency of 0.1 Hz while the column was forming and non-periodic oscillation after it had formed . The appearance of a nonperiodic-oscillatory flow mode would be supported by a high Marangoni number, such as 30,000 calculated from a recently reported temperature coefficient of surface tension for molten silicon.
Growth rate of a dislocation-free Ba (NO 3) 2 crystal was measured in microgravity by real-time phase-shift interferometry (RPSI) which could resolve the steps with one nm high in 1/30 s. Due to the temperature decrease by 6 degree to grow the crystal, the thermal distortion of the glass window, on which the seed crystal was glued, was found to be 20 times larger than the growth of the seed crystal. This difficulty was overcome by measuring the distortion rate of the glass window by analyzing the phase-shift interference fringes precisely to be subtracted from the apparent growth rate of the crystal face. This successful analysis lead a clear difference of growth mechanism at low supersaturation: homogeneous 2D-nucleation in microgravity whereas heterogeneous 2D-nucleation in normal gravity. This difference would also lead to the difference in the perfection of crystals in microgravity.
Fluidic devices for space experiments require an effective degasser to remove gas from gas-liquid two-phase flow. A method of using magnetic buoyancy force to remove bubbles from liquid has been studied. Magnetic buoyancy force (1 cm3) is shown by F= (1/2) (xc-xd grad H2. Xe, XL are the magnetic susceptibilities of gas and liquid (1 cm3) , respectively. Since XL - Xc and most liquid are diamagnetic, magnetic buoyancy force is considered to work toward a stronger magnetic field. In the experiment using a compact permanent magnet, N2 bubbles in pure water were found to move toward a stronger magnetic field in normal gravity. The present study suggests the possibility of an effective degasser in fluidic devices for space experiments.
Operations of Sp ace Station MIR was started in 1986 by former Soviet Union, and many foreign countries have been utilizing this permanent space station , now operated by Russian Federation, for their space experiment. JGC Corporation has conducted Escargot Breeding and Protein Crystallization space experiments. Outline of MIR and procedures for utilization of it are presented in this