SYNTHESIS AND CHARACTERIZATION OF SILICON-NITRIDE WHISKERS

Silicon nitride whiskers were synthesized by the carbothermal reduction of silica under nitrogen gas flow. The formation of silicon nitride whiskers occurs through a gas-phase reaction, 3SiO(g)+3CO(g)+2N2(g)=Si3N4(β)+3CO2(g), and the VS mechanism. The generation of SiO gas was enhanced by the application of a halide bath. Various nitrogen flow rates resulted in different whisker yields and morphologies. A suitable gas composition range of N2, SiO and O2 is necessary to make silicon nitride stable and grow in a whisker form. The oxygen partial pressure of the gas phase was measured by an oxygen sensor and the gas phase was analysed for CO/CO2 by gas chromatography. Silicon nitride was first formed as a granule, typically a polycrystalline, and then grown as a single crystal whisker from the {1 0 0} plane of the granule along the 〈 210 〉 direction. The whiskers were identified as β′-sialon with Z value ranging from 0.8 to 1.1, determined by lattice parameter measurements. © 1990 Chapman and Hall Ltd.