Mikito Mamiya

Thermal Expansions of Pure and Al-doped CsLiB6O10 Crystals for Nonlinear Optical Applications

Changes in X-ray powder diffraction patterns of pure and Al-doped CsLiB6O10 (CLBO) crystals for nonlinear optics upon heating are observed between room temperature and 500°C. The crystals undergo linear elongation by about 2×10-5 deg-1 along the a-axis, and contraction by about -2×10-5 deg-5 is observed along the c-axis. Such extraordinary behavior on heating is a reflection of the structure of CLBO which costists mainly of a combination of hexagonal B3O4 rings, and a marked difference in linkage of the rings appears between the a- and c-axes. No significant changes in the thermal expansion coefficients are observed on Al-doping, though considerable expansions along the a- and c-axis are observed.

Diamagnetic Anisotropy Detected by a Magnetic Oscillation in Drop Tube without Suspending Crystals with Fiber

A method designed to detect magnetic anisotropy Δχ with high sensitivity is improved considerably using microgravity. Oscillation of a magnetically stable axis of a crystal with respect to a magnetic field is observed in the improved method. A fiber that suspends the sample in a horizontal field in conventional methods is omitted using microgravity produced in a drop capsule; in previous methods, the restoration force of the fiber was the standard for measuring Δχ. Oscillations of ordinary diamagnetic materials such as apophyllite, calcite, KH2PO4, gypsum, Rochelle salt and urea were achieved at a field intensity of 1.30 T. Biotite and graphite oscillated at 0.0126 T; a small magnetic torque of 4 ×10-10 Nm was detected for the two materials.

Magnetic ejection of diamagnetic sub-millimeter grains observed by a chamber-type μG generator orientated to identify material of a single particle

A principle to identify the material of a single particle without destroying the sample is examined by an experiment in microgravity (μG). Such an identification is important as a first stage of analyzing various grains of primitive materials. The identification was based on diamagnetic susceptibility χDIA obtained from translation of the grain induced by a magnetic field. When a grain is released in an area of a monotonously decreasing field under μG conditions, it will be ejected in the direction of the field reduction; here, the area is occupied with diffused gas medium. The material identification of a primitive grain is possible by comparing the measured χDIA with published values; an intrinsic χDIA value is assigned to a material according to a molecular orbital model. We report here that the ejection is realized for sub-mm-sized crystals of various organic and inorganic materials. By developing a short drop shaft (μG duration ~0.5 s), the proposed material identification can be easily performed in an ordinary chamber. Using conventional methods, χDIA cannot be detected for a small sample of diameter below the level of a millimetre. The achieved result is a step to realize the identification of micron-sized grains that compose primitive materials.

Thermal Conductivity Measurement of Molten Indium Antimonide Using Hot-Disk Method in Short-Duration Microgravity

The thermal conductivity of molten indium antimonide (InSb) was measured using the hot-disk method in short-duration microgravity. The hot-disk sensor was made of molybdenum foil (thickness, 20 µm; radius of sensor region, 3.05 mm) cut in a conducting pattern and placed between two aluminum nitride (AlN) plates (plate thickness, 0.05 mm). Because AlN had not chemically reacted with molten InSb, the molybdenum foil in the hot-disk sensor was completely protected against the molten InSb. The thermal conductivity of molten InSb was measured during short-duration microgravity using a 10 m drop tower to confirm the thermal convection effect during the measurement. The thermal conductivity of molten InSb measured in microgravity was 17.3 W·m-1·K-1 at 824 K and increased with temperature. The thermal conductivities measured in normal gravity were found to be higher than those measured in microgravity. The thermal conductivity of molten InSb at melting point (798 K), i.e., 16.5 W·m-1·K-1, was obtained by the extrapolation of the thermal conductivity of the molten InSb against temperature.

Effect of magnetic field on metallurgical structure of magnetostrictive alloys solidified unidirectionally in microgravity

TbFe2 alloy solidification experiments were conducted in a static magnetic field in microgravity using a 10 m drop tower. When TbFe2 melt was solidified in a magnetic field from 0 to 0.12T in microgravity, a [111] crystallographic alignment dominated with an increased magnetic field, but the planar macrostructure was random. The magnetostrictive constant of TbFe2 solidified in magnetic field of 0.12T in microgravity was 2000 ppm at the external 1. 6T magnetic field. When TbFe2 melt was solidified unidirectionally in a 0. 1 T magnetic field in microgravity, a [111] crystallographic alignment dominated, and the planar structure grew and oriented along the solidification direction. The magnetostrictive constant of TbFe2 solidified unidirectionally in a 0. 1 T magnetic field in microgravity was 4500 ppm at the external 1. 6T static magnetic field. For all solidification in normal gravity, the maximum magnetostrictive constant remained at 2000 ppm at the external 1. 6T static magnetic field. TbFe2 crystals grew predominantly along the same direction as the magnetic field, and the planar structure oriented along the solidification direction in microgravity.

Synthesis of high-performance magnetostrictive Tb0.3Dy0.7Fe2 by unidirectional solidification in microgravity.

Giant magnetostrictive materials, Tb0.297Dy0.679Fe2, were synthesized by unidirectional solidification of a mixture of Tb0.99Fe2 and Dy0.97Fe2 alloys in microgravity with magnetic field of 0–0.12 T. Tb0.297Dy0.679Fe2 is a mixed crystal of TbFe2 and DyFe2. Tb0.297Dy0.679Fe2 synthesized in microgravity with no magnetic field had sheet dendrites structure with 300 (cooling direction) × 200 × 30 μm (thickness) and Fe‐rich layer between the sheet dendrites, and they exhibited a tendency for crystalline orientation of <110> and <111> with the cooling direction. The magnetostriction with the cooling direction was 9000 ppm at an external magnetic field of 120 mT. In contrast, Tb0.297Dy0.679Fe2 synthesized by unidirectional solidification in normal gravity with no magnetic field had a dendrite structure with a 30‐μm diameter × 250‐μm length growing in the cooling direction and no preferred orientation. The magnetostriction along the cooling direction was 2000 ppm at an external magnetic field of 120 mT. Analysis of the solidification in microgravity with magnetic field revealed that the dendrites oriented along the cooling direction and that the tendency for crystalline orientation of <110> and <111> with the cooling direction increased with magnetic field. Examination of the solidification in normal gravity with magnetic field indicated that Tb0.297Dy0.679Fe2 consisted of sheet dendrites without orientation and revealed no preferred orientation. The magnetostriction along the cooling direction increased with increases in the magnetic field. The effects of microgravity and magnetic field on the structure and crystalline orientation were considered.

Development of Hot-Disk Sensor for Molten Metal, and the Thermal Conductivity Measurement of Molten Bismuth and Tin using Hot-Disk Method

The thermal conductivities of molten bismuth and tin were measured using the hot-disk method. A hot-disk sensor was made of molybdenum foil (thickness, 20 µm; radius of sensor region, 3.05 mm) cut in a conducting pattern and placed between two aluminum nitride plates (plate thickness, 0.05 mm). Aluminum nitride did not corrode because of its contact with a molten metal and thus the molybdenum foil was protected from the molten metal. The thermal conductivities of molten bismuth and tin were measured during a short-duration of microgravity using a 10 m drop tower, to confirm the thermal convection effect during the measurement. The thermal conductivities measured in normal gravity were found to be approximately equal to those measured during the microgravity (during microgravity, thermal convection is suppressed), up to 977 K. Moreover, at 1083 K, normal gravity results were found to be higher than microgravity results.

Development of a unidirectional cooling technique for synthesizing compound semiconductors in 10 m drop tower

The solidification process and structures of CdTe solidified in microgravity were studied using the unidirectional cooling apparatus in a 10 m drop tower. Since the drop tower provides 1.4 seconds of microgravity, the unidirectional cooling apparatus cools samples rapidly by cooling gas. The system adopts a Pt heater, which accurately heats samples to a maximum of 1300°C. The sample is placed in an ampoule under vacuum conditions. A flat wall in the ampoule divides the inner sealed sample from the outer open side. A nozzle blowing cooling gas is directed on to the outer wall, and cools the sample until solidification. The cooling properties were measured during CdTe solidification in microgravity. The result shows that solidification occurred between 0.9 and 1.3 seconds after release, so solidification is completed in microgravity. Optical microscope (OM) observation of the sample solidified in microgravity revealed that it produces CdTe and Te phases with segregation patterns, and the structures are ordered along the cooling direction, whereas no order is observed in the structures of the terrestrial sample solidified under 1 g.

Solidification of GaSb on a ceramic substrate in short-duration microgravity

We cooled GaSb melt rapidly in short-duration microgravity using a 10 m drop tower. When silica glass was used as the substrate, the bottom of the melt solidified into a thin plate of single crystal in microgravity and the rest of the melt solidified based on the single crystal in terrestrial conditions. Thus, a large grain (grain size 1.5 mm) occupied almost the entire area of the sample. In contrast, when silicon carbide was used as the substrate, the bottom of the melt that solidified in microgravity was polycrystal (grain size 0.1 mm). These results indicated that nucleation rate in microgravity was suppressed by the silica glass substrate. The reduced rate of nucleation could be attributed to both the smoothness of the silica glass surface and the lack of convection flow due to microgravity.

Visualization study of bubble generation and collapse in He II under microgravity condition

A visualization experiment to investigate the heat transfer mechanism of He II boiling under microgravity was carried out using the drop-tower which can realize free fall experiments for about 1.3 seconds. The transient behaviors of vapor bubbles around a thin heater wire were optically visualized using a high speed video camera. Time variations of the size of vapor bubble were analyzed. The vapor generation and growth rate were investigated. A vapor bubble collapses slowly when heat current was stopped after generation of a vapor bubble made by a pulsated heat input. In this study, the behavior of bubble shrinking and the growth of vapor column around wire were also compared.