Concentration gradient of solute ions within α-SiAlON grains

The morphology and composition of α-SiAlON grains have been studied in a material prepared from α-Si3N4, AlN, Al2O3 and Yb2O3 powders. TEM analysis has shown that some α-SiAlON grains contain an α-Si3N4 core, indicating that α-SiAlON grains are nucleated from α-Si3N4 seed crystals. The initial precipitation on α-Si3N4 showed a higher content of Al and Yb than the subsequent precipitation, indicating that the concentration of Al and Yb in the liquid increases temporarily at the initial stage of α-SiAlON formation and decreases later.