化学量論的炭化ケイ素系繊維 (Hi-Nicalon-S) の酸化速度と機械的特性

抄録

The oxidation behavior of stoichiometric SiC fiber (Hi-Nicalon-S) was investigated and compared with those of Nicalon and Hi-Nicalon fibers. Hi-Nicalon-S fiber was oxidized in Ar-O₂ gas mixtures with 25-100% O₂ at 1273-1773K. The oxidation rates were measured with thermobalance experiments. The thickening in SiO₂ film produced a large decrease in the strength of the as-oxidized fiber. The SiO₂ film-removed fiber (unoxidized core) retained high strength independent of the SiO₂ film thickness. The oxidation rate obeyed the diffusion-controlled contracting-disc formula. The rate constant was proportional to the oxygen partial pressure of Ar-O₂ gas mixture. The activation energy was 79kJ/mol. The oxidation rate was considered to be controlled by the diffusion of oxygen molecule through the micropores in SiO₂ film. Compared to Nicalon and Hi-Nicalon, Hi-Nicalon-S is resistant to oxidation and has good strength in the oxidized state.