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 oxidat ion) was observed in a region of P-CO2/P-CO < 1, while mass gain (pass ive oxidation) was observed at around P-CO2/P-CO 10. In the active oxi dation region below P-CO2/P-CO 10(-4), carbon particles were formed on the Si3N4 surface as an oxidation product, and the mass-loss rates we re independent of P-CO2/P-CO. In the active oxidation region above P-C O2/P-CO 10(-4), the mass-loss rates decreased with increasing P-CO2/P- CO. 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.