Synthesis and characterization of silicon nitride powders produced in a d.c. thermal plasma reactor

Abstract

Ultra-fine silicon nitride powder was synthesized from the SiCl₄-NH₃-H₂-Ar system using a d.c. plasma torch reactor (production rate 150–400 g h⁻¹). The powder produced is pure white, fluffy and amorphous. The particles are spheroidal in shape with a mean diameter between 30–60 nm forming aggregates of 0.1–0.4 μm depending on the operational conditions. Chemical analysis on the crude powder handled at ambient atmosphere revealed: N(−NH₄Cl):37–39%, O:3–5% and Cl:2–3%. The amorphous powder can be crystallized around 1500 °C under nitrogen to give an α-phase content in excess of 90%. Infrared spectra can be used to semi-quantitatively determine the NH₄Cl content of the crude powder. That proportion is between 2.5 and 4%. The influence of some process parameters e.g. (N/Si and H₂/N molar ratios, internal pressure) on powder properties was also investigated. The N/Si molar ratio was found to be the most important parameter for the powder composition whereas the internal pressure plays a major role on the powder morphology.