Microwave plasma synthesis of nano-sized silicon carbide at atmospheric pressure

Abstract

The favourable physical and mechanical properties of silicon carbide (SiC) nanopowders allow application across many areas, including high-power, high-frequency electronics and high-temperature technologies. Many different synthesis methods for the creation of SiC nanoparticles have been studied, including carbothermic reduction, pulsed laser deposition, sol-gel processes, microwave heating and various plasma techniques. Among the different synthesis methods reported in the literature, very few experiments investigate the microwave-induced plasma synthesis of SiC nanoparticles. The few reported studies show promising results with regard to particle size and production rate. In this work, the synthesis of SiC nanoparticles from methyltrichlorosilane (MTS) is reported using a microwave-induced plasma, operating at atmospheric pressure. The investigation was done experimentally using a 1 500 W power supply, a microwave generator operating at 2.45 GHz, a stub tuner, a waveguide and a sliding short. Quartz tubes were used, in which the plasma was generated and maintained. Hydrogen served as an added reductant for the conversion reaction, and argon served as the MTS carrier gas. The parameters studied were the H2:MTS molar ratio and the total enthalpy, in the ranges 0 to 10 and 70 to 220 MJ/kg respectively. X-ray diffraction studies confirmed the presence of β-SiC and optical emission spectrometry showed the majority of peaks to be that of elementary silicon, carbon and argon, indicative of MTS decomposition in the plasma. Scanning electron microscopy shows average individual particle sizes ranging between 50 and 135 nm, whereas transmission electron microscopy shows average individual particle sizes ranging from 15 to 140 nm. Larger agglomerates are also present, ranging in sizes from 460 to 1 800 nm. Through response surface methodology (RSM), it was shown that the optimum conditions for the production of nanoparticles lie within the range of enthalpy > 180 MJ/kg and H2:MTS ratio of > 5.