Si-Ti-C-O系繊維の高温熱分解に及ぼす表面酸化被覆層の効果

Abstract

The pyrolysis of Si-Ti-C-O amorphous fibers (Tyranno fiber) coated with oxide layers of various thicknesses was investigated in an argon stream at 1673 K. Oxide layers were formed on the surface of the fiber in an oxygen stream at 1673 K. The thicknesses of the oxide layers were 0.12, 0.21, 0.42 and 0.65 μm. The fibers with the oxide layers of various thicknesses were heated rapidly and kept in an argon stream at 1673 K. During this heat treatment, the mass change of the coated fibers was measured continuously with a thermobalance. The heat-treated fibers were examined with X-ray diffraction, AES, SEM and TEM observation.The fiber with oxide layer of 0.12 μm thickness pyrolyzed completely, and the growth and coarsening of the β-SiC crystal were observed. The pyrolysis of the fibers with oxide layers 0.21, 0.42 and 0.56 μm in thickness was inhibited significantly. The degree of crystallization to β-SiC in the inner area of the fiber increased as the thickness of the oxide layer increased. The oxide layer of the fiber was removed by chemical etching treatment, and it was prepared in order to measure its tensile strengh. The tensile strength of the fiber was inversely proportional to the size of β-SiC crystallite. The tensile strength of the fiber with the oxide layer of 0.21 μm thickness was 58% as large as that of the original fiber.If the Tyranno fiber is coated with an oxide layer of more than 0.21 μm thickness, the high-temperature strength of the fiber can be improved fairly.