The effect of precursor composition and sintering additives on the formation of β-sialon from Al, Si and Al 2O 3 powders

Abstract

A study was performed to investigate the effect of increasing the Al or Al 2O 3 precursor content, above the stoichiometric amount, on the formation of β-sialon by pressureless sintering of Al, Si and Al 2O 3 powders in flowing nitrogen gas. The effect of adding Y 2O 3 or Fe to the precursor mixture, on the β-sialon formation, was also studied. The phase morphology and yield produced by the various compositions were examined using X-ray diffraction (XRD). Additional Al 2O 3 decreases the β-sialon phase yield and results in a greater amount of Al 2O 3 in the final sintered material. Additional Al improved the conversion to β-sialon up to a maximum of 4 wt% Al beyond which the β-sialon:15R sialon ratio in the sintered material decreases. 1 wt% Y 2O 3 was determined to be the optimum sintering additive content, as yttrium aluminium garnet (YAG) was found to be present in materials formed from higher Y 2O 3 containing precursors. The presence of Fe in the precursor powder retards the formation of β-sialon by preferentially forming Fe silicides at low temperatures, thus depleting the reaction system of elemental Si, favouring the formation of 15R sialon.