Synthesis and thermal stability of SiC-Si 3N 4 composite ultrafine particles by laser-induced gas-phase reaction

Abstract

SiC-Si 3N 4 composite ultrafine particles (UFPs) with various compositions were prepared by laser-induced gas-phase reaction. These particles were heat-treated in Ar or Ar + N 2 atmosphere at a temperature range from 300 K to 1773 K. Structural changes such as crystalline phase, particle shape, particle size distribution and composition after heat treatment were investigated by X-ray diffraction, transmission electron microscopy, specific surface area analysis and chemical analysis. SiC-Si 3N 4 composite UFPs have the composite SiC, metallic Si and Si 3N 4 phases depending on the nitrogen and carbon contents. They are thermally stable up to 1573 K in Ar without significant changes in crystalline phase and microstructures, but the nitrogen containing SiC phase decomposes into SiC, Si and Si 3N 4 phases accompanied by a remarkable increase in particle size above 1773 K. However, a small amount of nitrogen in the atmosphere could suppress the phase transformation and particle size growth.