Variation of the Oxidation Rate of Silicon Carbide with Water‐Vapor Pressure

Abstract

Chemically vapor deposited silicon carbide (CVD SiC) was oxidized at temperatures of 1000°‐1400°C in H 2 O/O 2 gas mixtures with compositions of 10‐90 vol% water vapor at a total pressure of 1 atm. Additional experiments were conducted in H 2 O/argon mixtures at a temperature of 1100°C. Experiments were designed to minimize impurity and volatility effects, so that only intrinsic water‐vapor effects were observed. The oxidation kinetics increased as the water‐vapor content increased. The parabolic oxidation rates in the range of 10‐90 vol% water vapor (the balance being oxygen) were approximately one order of magnitude higher than the rates that were observed in dry oxygen for temperatures of 1200°‐1400°C. The power‐law dependence of the parabolic oxidation rate on the partial pressure of water vapor at all temperatures of the study indicated that the molecular species was not the sole rate‐limiting oxidant. The determination of an activation energy for diffusion was complicated by variations in the oxidation mechanism and oxide‐scale morphology with the partial pressure of water vapor and the temperature.