EFFECT OF OXYGEN PARTIAL-PRESSURE ON OXIDATION RATE OF SI-C-O FIBER

The oxidation mechanism of Si-C-O fiber (Nicalon) has been investigate d by considering the effect of partial pressure and temperature on the oxidation rate. The kinetic data of Nicalon were described by the two -dimensional disc-contracting formula. The rate constants were proport ional to the partial pressure of O-2. In earliest stage of oxidation, the rate equation for reaction control was applicable and the activati on energy was estimated to be 45 kJ/mol. The initial oxidation of Nica lon is considered to be determined by both the gas-phase diffusion and chemical reaction. When the fiber was completely coated with SiO2 fil m, the oxidation rate obeyed the equation for diffusion control and th e activation energy was 102 kJ/mol. It is considered that the rate-det ermining step is the diffusion of oxygen molecules through the pores o f SiO2 film.