AbstractSilicon aluminium oxynitride (β′sialon) powders have been prepared by reacting kaolin–carbon mixtures at 1400–1500°C in flowing nitrogen. The kaolin/carbon ratio in the starting mixtures must be accurately controlled to obtain single phaseβ′powders. The overall reaction rate increased with increasing nitrogen flowrate. However, if the nitrogen flowrate was too high, the amount of 15Rand AlN phases in the reaction products increased. A change of carbon source in the starting mixtures affected the phase composition as well as the morphology of the product powders. It was found that the evaporation of SiO is a most important factor in the reaction, strongly affecting the phase composition of the reaction products.MST/1346b