Carbothermal Preparation of β-SiAlON Powder at Elevated Nitrogen Pressures

Abstract

β-SiAlON powders have been prepared by carbothermal nitridation of kaolin or SiO 2 plus Al 2O 3 mixtures at 1450-1800°C and elevated nitrogen pressures (1-50 bar). Powders with widely variable particle size and morphology were obtained depending on temperature, pressure, gas-flow rate, and raw-material type. An elevated nitrogen pressure effectively reduced SiO loss and suppressed SiC formation. Pure β-SiAlON powder of composition Si 2·8Al 3·2O 3·2N 4·8 and with a fine particle size (∼1 μm) was produced at 1650°C, 50 bar N 2 and a high gas-flow rate for 2 h. The nitridation rate was hampered by an increase of the CO concentration in the system.