Takashi Tsurue

Thermal conductivity measurement of liquid materials by a hot-disk method in short-duration microgravity environments

The thermal conductivities of silicone oils with various viscosities and mercury were measured by a hot-disk method in short-duration microgravity environments. The thermal conductivities of silicone oil with low viscosity were affected by the thermal convection on the ground, but the thermal convection was suppressed in microgravity. The thermal conductivities of highly viscous samples were not influenced by thermal convection. The thermal conductivity of mercury measured in microgravity was about 3% lower than that measured on the ground around room temperature. The thermal conductivity measurement conditions on the ground and in microgravity for which there was no influence from thermal convection could be estimated by using the Rayleigh number.

Thermal Conductivity Measurement of Molten Silicon by a Hot-Disk Method in Short-Duration Microgravity Environments

The thermal conductivity of molten silicon was measured by a hot-disk method in short-duration microgravity environments. The hot-disk sensor was made of molybdenum foil cut in a conducting pattern and covered with an aluminum nitride plate. Aluminum nitride has good resistivity against corrosion from silicon melt and the molybdenum foil was protected from the molten silicon. The thermal conductivity of molten silicon measured on the ground was estimated to be 45.6 Wm-1K-1 at the melting point (1687 K). The thermal conductivity of molten silicon measured in microgravity was about 5% lower than that measured on the ground.

Synthesis of Si–Ge Alloy by Rapid Cooling in Short-Duration Microgravity

We solidified Si–Ge alloys by rapid cooling in short-duration microgravity. When the Si–Ge melt was solidified by contact with the copper chill block (cooling rate; 100 K/s), the samples solidified in microgravity and on the ground had large grains (about 0.2 mm diameter), and were segregated. When we splat-solidified Si–Ge melt on the copper chill block by using argon gas pressure (4×105 Pa), the solidified sample contained less Ge than the starting material because of the heterogeneity of the Ge component in the melt. When we splat-solidified the Si–Ge melt in microgravity, we obtained a layer with a fine structure (less than 1 µm diameter) on the side contacting the copper chill block because of the high cooling rate (>5000 K/s). A 100-µm-thick layer with fine structure was obtained by doping with P; this layer was much thicker than that in the nondoped sample. The thermal conductivity of the sample splat-solidified in microgravity was lower than that of the arc-melted sample.

Wetting of molten indium under short-time microgravity

The wetting of molten indium on quartz glass was investigated under short-time microgravity. The shape of molten indium under normal gravity was ellipsoidal and the shape under microgravity was spherical. The contact angles under microgravity were smaller than those under normal gravity and were constant during the microgravity condition. The contact angles under normal gravity and under microgravity decreased with increasing temperature. The contact angles decreased and the difference of contact area between normal gravity and microgravity increased with the amount of indium per droplet. Work of adhesion between molten indium and quartz glass was evaluated using the contact area and the potential energy of the droplet in the change from normal gravity to microgravity.