Room Temperature Strength of β-sialon Fabricated Using α-Si₃N₄ Powder and an Aluminumhydroxide Solution

Abstract

β-sialon, with z=0.5, was fabricated by hot-pressing of a spray dried mixture of α-Si₃N₄ powder and aluminumdydroxide aqueous solution prepared by hydrolysis and peptization of aluminum-iso-propoxide. Flexural strength, phase composition and microstructure of the sintered bodies have been investigated. Phases identzfied by XRD in the sintered body were β-sialon and O'Sialon. Hydrolization of Si₃N₄ during mixing with aluminumhydroxide solution gave an increaseing amount of O'sialon compared with a sample prepared without water i.e., aluminum-iso-propoxide dissolved in C₆H₁₄ solution. The microstructure study showed that β-sialon consisted of 0.5-2μm equiaxed grains and a small amount of 2-5μm plate-like grains which was assumed to be O'sialon. The room temperature flexural strength (3-point bending) was 119kg/mm². This value was slightly lower than that of β-sialon obtained/from aluminum-iso-propoxide solution. However it was remarkably higher than that of β-sialon obtained from Al₂O₃ powder mainly due to a finer and more homogeneous microstructure. The degradatiom of the strength as compared with β-sialon from aluminum-iso-propoxide solution has been explained by the existence of plate like grains which occurred due to a higher amount of oxgen from the hydrolysis of Si₃N₄.