Synthesis and characterization of silicon nitride whiskers

Abstract

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)+2N 2 (g)=Si 3 N 4 ( β )+3CO 2 (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 N 2 , SiO and O 2 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/CO 2 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.