Factors influencing structural evolution in the oxide of hot-pressed Si3N4-Y2O3-SiO2 materials

X-ray diffraction, SEM, EDS and WDS studies were performed on the structure and morphology of the oxide scale developed on hot-pressed compositions of the Si3N4-Si2N2O-Y2Si2O7 sub-system subjected to short-term ( 30 h) oxidation in air at 1273-1673K. Viscosity of the oxide glassy phase, ionic mobility and oversaturation degree of the atomic species involved were the most important parameters in the control of structural evolution of the oxide. Clear links appear to exist between compositional parameters of the grain-boundary phase of the hot-pressed materials and the evolution of the crystal phases in the oxide scale. The Mi/Y ratio (Mi, total amount of metal impurities) in the grain-boundary phase plays a major role in the transport properties of the oxide glassy phase. 11pp 6fig 4tab