Formation of silicon carbide particles behind shock waves

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Abstract
The formation of silicon carbide powder in a 3% SiH4-3% CH4-Ar mixture was studied in a shock tube. The experiments were conducted at the temperature of 800–3650 K, pressures of 0.46–4.16 atm, and reaction times of 1–2 ms. The progress of reaction was monitored by the attenuation of a He-Ne (633 nm) laser beam. Powders collected at the end wall of the tube were identified to be β-SiC and at high temperatures contained particles having sizes up to 0.5 μm. The large particles had the form of thin single-crystal platelets with hexagonal and truncated triangular shapes. The transmitted laser light intensity as a function of reaction time exhibited a pronounced minimum at incident shock temperatures above 1700 K. A reaction model is proposed that explains the experimental observations. It is postulated that SiC particles are nucleated homogeneously, along with Si particles. The latter are etched by the products of methane pyrolysis and the chemical species formed by the etching add to the growth of SiC particles.