The firing behavior of α-Si3N4 powder corroded under hydrothermal conditions was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM analysis suggest that the hydorothermal treatment enhances the α-β phase transition in α-Si3N4 and the formation of Si2ON2 phase from α-Si3N4 during firing at high temperature. In paticular, TEM analysis indicate that the grown β-Si3N4 grains contain an α-Si3N4 core under the α-β phase transition in α-Si3N4.
