Characterization of ultrafine SiCSi3N4 composite powder after heat-treatment in Ar + N2

Ultrafine SiCSi3N4 composite powder synthesized by laser-induced gas-phase reaction was heat-treated at a temperature range of 295–1773 K in a mixture gas flow of Ar + N2. The changes in crystalline structure, shape, particle size, crystalline size, chemical composition, specific surface area and defect state were investigated by X-ray diffraction (XRD), transition electron microscope, chemical analysis, specific surface area analysis and electron spin resonance. No significant changes in the structure are observed after the heat treatment below 1673 K in Ar + N2, similar to the result of the heat-treatment in Ar. At or above 1673 K, the characteristic changes occur, but these depend on the heating atmosphere. The precipitation of metallic silicon, which is observed in the heat-treatment in At, is suppressed by introducing only 5% N2 to the atmosphere. The composite powder with a desired composition of SiC and Si3N4 can be obtained by adjustment of the nitrogen partial pressure.