High‐Temperature Oxidation of Chemically Vapor‐Deposited Silicon Nitride in a Carbon Monoxide‐Carbon Dioxide Atmosphere

Oxidation behavior of chemically vapor‐deposited silicon nitride (CVD‐Si₃N₄) in CO─CO₂ atmospheres between 1823 and 1923 K was investigated using a thermogravimetric technique. Mass loss of Si₃N₄ (active oxidation) was observed in a region of P_CO2/P_CO < 1, while mass gain (passive oxidation) was observed at around P_CO2P_CO= 10. In the active oxidation region below P_CO2P_CO= 10 ^–4, carbon particles were formed on the Si³N⁴ surface as an oxidation product, and the mass‐loss rates were independent of P_CO2/P_CO In the active oxidation region above P_CO2/P_CO= 10^–4 the mass‐loss rates decreased with increasing P_CO2/Pco. The critical P_CO2/P_CO value from the active to passive oxidation was 2 orders of magnitude larger than the calculated value predicted from the Wagner model.