Abstract: The effect of alumina contents on the z value in Sialon phase at the synthesis of ZrN-Sialon composites by carbothermal reduction-nitriding of zircon and industrial alumina under various temperatures was investigated by XRD and SEM.The results showed that the products at both 1 500 and 1 550 ℃ are mainly granular ZrN and prismatic β-Sialon.When the alumina content is stoichiometric or exceeding 5%，Sialon phase exists in the type of Si₃Al₃O₃N₅（β-Sialon，z =3），and when exceeding 10% or 20%，it is in the type of Si₂Al₄O₄N₄（β-Sialon，z =4）.The products at 1 600 ℃ are ZrN and Sialon，and Sialon phase transforms to 15R-SiAl₄O₂N₄ which has plate-like morphology.Increasing alumina content can promote the transformation of Sialon phase.The proper alumina content is stoichiometric or exceeding 5% and the optimizing synthesizing temperature is 1 550 ℃.

Key words: Zircon, Carbothermal reduction-nitriding, ZrN-Sialon composites, Alumina contents, z value in Sialon phase