Abstract
The oxidation resistance at 1400°C of silicon nitride alloys hot‐pressed with magnesia was investigated as a function of the phase content of the alloys. The extent of oxidation, the products of oxidation, their stratification, and the continuity of the oxide scale are all dependent on the initial composition. Also, the compositions of the alloys themselves change during oxidation. The findings can be interpreted on the basis of compositional paths in the equivalence phase diagram. Reasons for the outward diffusion of Mg and impurities are given and the effect of the secondary phase on oxidation kinetics is discussed.

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