Takeshi Okutani

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 silicon-based polymer films by UV laser ablation deposition of poly(methylphenylsilane)

Abstract The deposition of silicon-based polymer film by UV laser ablation of poly(methylphenylsilane) (PMPS) was studied. Deposited films were formed by UV laser ablation deposition of PMPS. The molecular weights of the deposited films were smaller than that of the original polymer. The films exhibited a broad molecular weight distribution ranging from a few hundred to ca. 20 000. The molecular weight distribution of the film depended on the laser fluence and the laser wavelength. The ablation process caused the SiSi bonds in the PMPS to be converted into SiC bonds, at the same time the deposited films contained the same side chain bonds as PMPS. In addition, the deposited films displayed a SiH and an inorganic-like network SiC bond, which was not contained in the original PMPS. The ablation at 351 nm suppressed the formation of both the SiH and the inorganic-like network SiC bond.

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.

Light emission properties of poly(diphenylsilylenemethylene) and poly(diphenylsiloxane) by UV laser irradiation

Abstract Unique light emission phenomena of poly(diphenylsilylenemethylene) (PDPhSM) and poly(diphenylsiloxane) (PDPhSO) by UV laser irradiation were observed. When PDPhSM films were irradiated with an excimer laser (KrF, 248 nm), light emission, whose spectra were broad ranging from 300–500 nm and exhibiting a large peak at 340 nm, was observed. Blue-green light emission was observed for several seconds, after the laser light was turned off. Furthermore, the emission spectra were found to change with a number of laser shots irradiated. The emission peak at 340 nm decreased rapidly, while the emission in the range from 400–600 nm increased gradually as the sample was repeatedly irradiated with the laser. A similar characteristic light emission was also observed with PDPhSO films.

Development of stable supports consisting of SiCSi composite for high temperature combustion catalysts

Abstract SiC-Si composite, that is stable in oxidizing atmosphere at 1300°C and has thermal shock resistance, was prepared from a powder mixture of porous β-SiC, which was prepared from rice hulls, and Si metal. To use an SiC-Si composite as a structural support for a high temperature combustion catalyst, the foaming SiC-Si composite form with continuous bubbles was prepared from foaming SiC form and the mixture of the porous β-SiC and Si metal. The foaming SiC form was prepared from the foaming polyurethane form and a β-SiC fine particles. The β-SiC fine particles having an average diameter of 0.3 μm was coated on the foaming polyurethane form. The polyurethane part of the form was burned out and the coating β-SiC was sintered to form the foaming SiC form. The SiC form was coated on the porous SiC and Si metal powder mixtures and was heated at 1500°C in argon to prepare the foaming SiC-Si composite. The foaming composite was stable in an oxidizing atmosphere at 1300°C and was highly resistance to thermal shock. The compression stress of the foaming SiC-Si composite form (175 kg/cm2was about twice that of the a-axis of honeycomb-shaped cordierite (> 85 kg/cm2).

Effect of target modification on deposition rates of hexaphenyldisilane by laser ablation

Abstract The effects of target modification on film deposition rates of hexaphenyldisilane (HPDS) due to ablation by a 248-nm KrF excimer laser at different fluences and repetition rates were studied. When the repetition rate was less than 20 Hz and the laser fluence was below 100 mJ/cm2, some interlocked cones were generated on the surface of the HPDS targets, which caused the laser ablative process to grind to a halt after a given number of laser pulses. However, when the repetition rates exceeded 20 Hz, it was possible to prevent the cones from being interlocked, so that the laser ablative process or film deposition process could continue, even though a similar laser fluence was used. The doping of other Si-based organic materials into HPDS affected the critical laser fluences and repetition rates below which the interlocked cones were generated. Finally, a general physical model of the target modification for laser ablation of Si-based organic materials was suggested based on the laser processing parameters.

Electronic absorption spectra of radical ions of alkyl silicon network polymers

Abstract Absorption spectra of radical ions of silicon network polymers formed by γ -irradiation have been measured in rigid matrices at 77 K. Both the radical anion and cation showed very broad absorption bands in visible and near-infrared wavelength regions. The radical anion spectrum was sensitive to photoillumination and changed the band shape by selective photobleaching. Thermal annealing of the radical cation caused a blue shift of the absorption spectrum. The broad band shape and the selective band bleaching indicated the coexistence of various cyclic structures in the network polysilane radical ion spectra.

Synthesis of silicon-based polymer films by excimer laser-induced photo-reaction of phenylsilane and methylphenylsilane

The synthesis of silicon-based polymer films was studied by excimer laser (248 nm)-induced photo-reaction of phenylsilane and methyl-phenylsilane at reduced pressure. IR and UV–VIS results showed that the films were composed of Si–C network structures with phenyl rings. Copyright