A thermal diffusion field around a growing ice dendrite was observed under 4.5 s microgravity (μg) conditions using a drop shaft at Microgravity Laboratory of Japan (MGLAB). A single ice crystal was grown in 99.9% D2O water. The thermal diffusion field was observed as the bend of interference fringes. The interference fringes were analyzed by the Windowed Fourier Transform (WFT) method, a newly developed method for analysis. It was clearly shown that the thermal diffusion field continuously develops around the ice crystal growing in the supercooled water. This result provides direct evidence that the latent heat released at the growing interface diffuses in the environment around the crystal.
The solidification morphology in the solidification of ternary alloy, succinonitrile-ethanol-acetone, is observed in-situ.Peculiar morphology to ternary alloy solidification is found near the monotectic composition of the alloy. Dimensions of the morphology is about one order of magnitude smaller than those of ordinary dendrites in the same solidification conditions (the growth rate and temperature gradient). In the microgravity condition the dimensions become larger than those solidified on the ground.
This paper carried out both experimental and theoretical researches on the formation mechanism of the globular microstructure formed during semi-solid processing of a binary alloy, with focus on the strong convection effect induced by the forced stirring during the processing. Direct observation of the crystal growth of a transparent model alloy, succinonitrile-5 at%water, during semi-solid processing with a self-made experimental device indicates that strong melt convection induced by forced stirring during semi-solid processing will change the crystal growth morphology from dendritical to spherical shape. This morphology change does not originate from dendrite arm fragmentation, instead from the increase of the interfacial morphological stability. The convection effect on the interfacial morphological stability was mainly referred to that strong convection will influence the solute transfer. The convection effect on the solute transfer was accounted for through added a convective loss of solute term in the solute transfer equation. The equation was numerically resolved, and the result indicates that, when the convective loss of solute induced by the tangential flow in front of a spherical crystal is taken consideration in the solute transfer equation, the concentration gradient at the solid/liquid interface decrease. And this leads to an increase in the interfacial morphological stability. The theoretical and experimental results of convection effect on the interfacial morphological stability indicates the same tendency, but the theoretical value is remarkably smaller than the experimental value. The future improvement of theoretical modeling should consider at least two factors: (a) more accurate description of convection effect on the solute transfer, (b) multi-particle effect on the decrease of the melt undercooling.
We have developed a new crystal growth method named the traveling liquidus-zone (TLZ) method and
found that the TLZ method is promising for growing compositionally homogeneous alloy crystals such as
In₁₋ₓGaₓAs. Our one- dimensional TLZ growth model predicts precisely the sample translation rate
for growing homogeneous In₁₋ₓGaₓAs crys- tals. In addition to the homogeneous crystal growth mode,
supersaturation mode and supercooling mode exist in the TLZ method and these modes were examined
experimentally and single crystals were found to be grown more easily when the supercooling
controlled the growth process. Estimation of critical degree of supersaturation for avoiding poly-
crystallinity is expected for further development of the TLZ method.
Recent investigations about the morphological instability, which occurs on the ice disk grown in supercooled bulk water, are reviewed on the basis of various ground experiments. It is well known that ice crystals grow as the circular disks at their initial growth stages and their growth trajectories are categorized into two types depending on the growth kinetics of basal planes. Despite of the trajectory types, the morphological instability on ice disk occurs at the edge plane immediately after its thickness reaches a critical value. A theoretical model based on the anisotropic kinetic effect is developed to explain the ice disk growth trajectories and the occurrence of morphological instability. The experimental results of ice free growth under the short-term microgravity condition are also summarized and finally the future perspective for the space experiment is briefly described.
In situ observations were carried out in faceted transparent organic materials grown unidirectionally by multiwavelength interferometry, which enabled us to measure the distribution of temperature and solute concentration distributions in the liquid in the vicinity of the solid/liquid interface simultaneously. The aim of the experiments was to reveal a mechanism of a faceted cellular array growth taking account of an influence of latent heat of fusion of the material upon a temperature distribution in the melt. Some experimental results were briefly summarized in the present report.
The recovery capsule of the USERS Spacecraft called Recovery Vehicle (REV) was splashed down at the open sea east of the Ogasawara Islands and successfully recovered on May 30, 2003 after approximately 8.5 months of on-orbit operation under good microgravity condition. This success established the innovative space experiment infrastructure, and opened the door for the communities which require better micro-gravity environment with less constraints and cost. The USERS spacecraft consist of the Service Module (SEM) and the Re-entry Module (REM) in which includes the REV. It was launched from the Tanegashima Space Center on September 10, 2002, and performed the Super-conductive Bulk Material Processing Experiment (SMAP). This paper will first descx'ibe the project outline and clarifies the requirements for the ideal unmanned space experiment infrastructure with consideration of the advantages of the unmanned space system. The on-orbit experiment operation of the SMAP will be introduced for the clarification of the image of this infrastructure utilization. The conditions and interfaces for the potential users such as onboard environments, interfaces with bus system, normal experiment operation sequence, etc. will be also explained using the SMAP as an example. USERS Project has been promoted by the Ministry of Economy, Trade and Industry (METI) and the New Energy and Industrial Technology Development Organization (NEDO) , and developed by the Institute for Unmanned Space Experiment Free Flyer (USEF) , to establish an unmanned on-orbit experiment infrastructure.
Recent advanced topics on crystal growth have been discussed for the last one year in the three symposiums sponsored by JSF and former NASDA. All these topics are not directly related to the present space experiments, but we have confident that these topics will surely be investigated also in space in a near future. The topics cover self-assemblage of nanomaterials, chilarity of molecules and the control of microstructure of crystals.