Oxidation of silicon nitride sintered with ceria and alumina

Abstract

Sinter-hipped silicon nitride with additions of ceria and alumina has been subjected to oxidation for up to 72 h at various temperatures. Within the experimental temperature range (1250–1425°C), a parabolic weight gain was observed with an activation energy of 350 kJ mol⁻¹ for the process. On oxidation there formed an oxide scale whose morphology depended on temperature and cooling rate, and a subscale, at the interface between the substrate and the oxide scale, consisting of β3-Si₃MN₄ grains, a Ce-rich silicate glass, and Si₂N₂0. The morphology and phase content of the oxide products were characterised by X-ray diffractometry and electron microscopy. Detailed analyses by SEM showed that the oxide scales were not homogeneous, but exhibited several layers with important microstructural and compositional variations through their thickness.

MST/1107