Preparation of SiC ultrafine particles from SiH2Cl2 and C2H4 gas mixtures by a CO2 laser

Abstract

Preparation of SiC ultrafine particles from SiH2Cl2-C2H4 mixtures by a CO2 laser was investigated. The powders with specific surface area in the 8–150 m2 g−1 range were obtained by irradiating SiH2Cl2-C2H4 gas mixtures with a CO2 laser at atmospheric pressure. X-ray diffraction of the products showed that silicon, SiC and free carbon were produced and the composition of the powders depended on the C2H4/SiH2Cl2 ratio. The reaction flame temperature changed from less than 1273 K to more than 3073 K with the laser power density and C2H4/SiH2Cl2 ratio. When SiH2Cl2 was irradiated with the CO2 laser, the reaction temperature was less than 1273 K and silicon particles were formed. When the SiH2Cl2-C2H4 mixture was irradiated with a CO2 laser, the reaction temperature was low ( 0.3). SiC was formed at both high and low reaction flame temperatures. It was considered that the rapid increase in the reaction flame temperature was caused by the initiation of exothermic reactions and the increase in laser absorption which was caused mainly by carbon particle formation. Hysteresis was observed between the reaction flame temperature and the power density of the laser beam. It was found that SiH2Cl2 underwent a disproportionation reaction on irradiation with the CO2 laser, and silicon and SiC particles were formed through the various products of the disproportionation reaction. In particular, at low reaction flame temperature, the reactive species, such as SiH4 and SiH3Cl, produced by the disproportionation of SiH2Cl2 were considered to play an important role in the formation of silicon and SiC particles.