Papers by Author: Masaki Narisawa

Abstract: Melt spinnable silicone resin with a low carbon content was spun to fiber form with an averaged diameter of 16.8 m. When the resin fiber was cured by SiCl4 vapor and pyrolyzed at 1273K in inert atmosphere, Si-O-C fiber with smooth surface was obtained. The measured tensile strength was relatively low. The fiber, however, showed oxidation resistance during high temperature exposure under an air flow. When the fiber was cured by TiCl4 with an increased vapor pressure at 313K, 40% mass gain was observed after the curing. SiO2-TiO2 fiber was obtained by pyrolysis in an air flow, while SiOC-TiO2 fiber was obtained by pyrolysis in an inert atmosphere. Structure of TiO2 and the resulting fiber surface morphology strongly depended on the temperature and the atmosphere during the pyrolysis.

Abstract: Silicon carbide (SiC) based fibers with continuous pore structures were synthesized by the precursor method using a polycarbosilane (PCS) and polymethylhydrosiloxane (PMHS) polymer blends. The pore formation process can be explained by hydrogen gas dissolution in the polymer melt and desaturation process of the dissolved gas during the fiber spinning. We investigated the effect of PMHS additives with different chemical and physical natures on the obtained pore structures, because PMHS decomposition process played a role of hydrogen gas source. The individual polymer melts were characterized by viscosity measurement, gas chromatograph analysis and thermogravimetric (TG) analysis in order to obtain details of pore structure control.

Abstract: Polymethylsilsesquioxane (PMSQ) fiber was exposed to metal chloride vapors in a controlled atmosphere or electron beam irradiation in air to promote the curing process. The cured fibers were pyrolyzed at 1273K to compare the efficiency of individual curing method. The cured fibers were investigated by FT-IR, an optical microscope and TG analysis. In the case of successful curing, averaged diameter and tensile strength were analyzed on the obtained Si-O-C fibers.

Abstract: Silicon carbide base ceramic tubes were synthesized from blend polymers of polycarbosilane (PCS) and methylhydrogen silicon oil (H-oil) by polymer precursor method. This precursor method consisted of melt spinning, thermal oxidation curing and pyrolysis processes. Pore structure observed at cross sections of obtained tubes depended on H-oil content, melt-spinning temperature and oxidation curing conditions. At 578K for melt-spinning, however, a considerable amount of H-oil was decomposed during the spinning process. The resulting H-oil contents were usually lower than the starting H-oil contents. In the case of the 578K melt spinning, however, unique single pore structures were often observed in the tubes by adjusting the curing conditions. At 40% of the H-oil content, large pores with thin walls were observed at the cross-section, while such structures were difficult to be controlled. By reducing the melt-spinning temperature to 543K, the starting H-oil contents could be maintained during the spinning process. The cross sections of the tubes often showed multi pores in this case.

Abstract: TiO2/SiC was prepared by oxidizing the TiC-SiC precursor obtained by carbothermic reduction process of TiO2-SiO2 binary oxide. An XRD analysis indicated the formation of the mixture of anatase and rutile phases of TiO2 crystalline after the oxidation of TiC-SiC sample. TiO2/SiC photocatalyst exhibited a higher photocatalytic reactivity than TiO2-SiO2 binary oxide prepared by the conventional sol-gel method. These results indicate the advantages of SiC nano powders as catalyst support of the TiO2 photocatalysts, and TiO2/SiC photocatalyst is effective for the degradation of organic compounds diluted in water.