Effect of oxidation condition on thermal stability of Si-C-O fiber coated with SiO2 film

To improve the high-temperature stability, Si-C-O fibers (Nicalon) were oxidized at temperatures of 1073-1773 K under an oxygen partial pressures of 2.53 x 10(4)-1.01 x 10(5) Pa and then were exposed to 1773 K in argon, X-ray diffraction, resistivity measurement and tensile test were conducted for both the oxidized and the exposed fibers. Pit an early stage of oxidation, the characteristics of oxidized fibers abruptly changed, This was because an incomplete SiO2 coating caused pyrolysis of the fibers. High levels of tensile strength was retained in the as-oxidized state at elevated oxidation temperatures and under high oxygen partial pressure. The strength of the oxidized fiber could be controlled by the imperfections of the SiO2 film. After exposure in argon, the highest strength was retained in the fiber oxidized at 1373 K under an oxygen partial pressure of 2.53 x 10(4) Pa, that is, in the fiber having SiO2-film thickness of 0.2 mu m.