INDUCTION PLASMA SYNTHESIS OF ULTRAFINE SIC POWDERS FROM SILICON AND CH4

Ultrafine SIC powders have been synthesized from elemental silicon and methane using induction plasma technology. The powder products were c haracterized by X-ray diffraction, thermogravimetric analysis, scannin g and transmission electron microscopy, electron probe microanalysis, infrared spectroscopy, and surface area measurement. The powders colle cted from various sections of the reactor system showed different feat ures reflecting different compositions and powder morphologies. The pu rest SIC powder was collected in the metallic filter. It was composed of both alpha- and beta-phase of SiC with small levels of free silicon and carbon. The reaction route used is based on the evaporation of th e injected pure silicon starting powder, followed by carburization of the silicon vapour using methane. The silicon evaporation rate was fou nd to depend strongly on the particle size of the silicon powder. Usin g silicon powder with a mean particle diameter of 100 mu m, at a plasm a power level of P=43.2 kW, the conversion of silicon to SiC and the o verall SiC content in the product powder was 44.2% and 50.8 wt%, respe ctively. The injection probe position was Z=9.3 cm, the silicon feed r ate was 4 g min(-1), and the C/Si molar ratio was 0.7. Using silicon p articles with a mean diameter of 45 mu m, the conversion and overall c ontent of SiC increased to 70.4% and 73.9 wt%, respectively, under the same plasma operating conditions and powder feed rates. By appropriat e selection of experimental conditions, ultrafine SIC powder of high q uality was achieved.