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The active to passive transition in the oxidation of sintered 0~-SiC has been determined by a thermodynamic approach and then experimentally under flowing air at high temperatures (1673-1973 K) and low pressures (oxygen partial pressure from 200-2100 Pa). Then, the physico-chemical behaviour of samples was compared for two different environments such as air-plasma atmosphere generated by microwaves, and a molecular atmosphere. The thermodynamic calculation does not predict any variation of the oxidation transition when changing the chemical state of oxygen (Q2 or O) but experimentally the domain characterized by the formation of a passive layer of silica is extended to lower pressure under atomic oxygen (for the same temperature range) than in the case of molecular oxygen.

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