Preparation of Both Reactive α-Si<sub>3</sub>N<sub>4</sub> and SiC Mixed Powder in Flame-Isolation Nitridation Shuttle Kiln

Abstract

α-Si3N4possesses excellent sintering activity, which is used to prepare high performance Si3N4-based ceramics and composite refractory. Si3N4powder is always synthesized by nitriding silicon in controlled-atmosphere furnace whose furnace volume is very small(effective volume: 1840×1420×1660mm), the extreme reaction heat is difficult to diffuse, which leads to high reaction temperature and conversion of α-Si3N4to β-Si3N4, thus α-Si3N4is difficult to be obtained in controlled-atmosphere furnace. While flame-isolation nitridation shuttle kiln has much larger furnace volume to conduct reaction heat (effective volume: 11500×4190×1684mm), so it owns homogeneous temperature field and stable low-temperature environment which benefits the preparation of α-Si3N4. Thermodynamic analysis of Si-N system is shown that Si3N4can be formed by two formats: direct nitridation of Si(s) and indirect nitridation of SiO(g); to ensure completely nitridation, the particle size of silicon powder should be less than 88μm. With reclaimed powder from polysilicon cutting slurry as starting materials, both reactive α-Si3N4and SiC mixed powder were successfully prepared in flame-isolation nitridation shuttle kiln. Because of the gas-gas reaction between SiO(g) and N2(g), α-Si3N4is fiber-like and in favor of processing high quality Si3N4-based materials.