Active-to-Passive Transition in the Oxidation of Silicon Carbide and Silicon Nitride in Air

The active-to-passive transition in the oxidation of SiC and Si₃N₄ was determined in a flowing air environment as a function of temperature and total pressure. The experimentally observed transition temperatures ranged from a low of 1347°C to a high of 1543°C for partial pressures of oxygen of 2.5 and 123.2 Pa, respectively. The SiC and Si₃N₄ samples had approximately the same transition point for a given pressure. In general, the higher the flow rate, the higher the transition temperature for a given pressure. The transitions for SiC measured in this study agree with previous data for the transition of SiC measured in pure oxygen at reduced pressures and in oxygen inert gas mixtures.