A facile approach to microwave heating synthesis of silicon carbide from unmixed silicon powders

Abstract

Microwave heating is often used to fabricate silicon carbide (SiC) from mixtures of silicon and carbon powders. Mixing these reactant powders has been considered important because the carbonization of silicon has long been regarded as a solid-state reaction occurring via atomic diffusion among powders. Here, we present a facile alternative approach to microwave-heating synthesis of SiC from silicon powder which was simply embedded in graphite powder without mixing with the graphite powder. 10-min microwave heating in air turned the silicon powder into a consolidated chunk of almost fully carbonized β-SiC. This result suggests that carbon atoms experienced a millimeter-order mass transfer from graphite to silicon within 10 min. Atomic diffusion alone can hardly explain such a large transfer of carbon atoms within such a short period. The rapid reaction displayed by the long-distance mass transfer of carbon can be explained instead by gas-solid carbonization between carbon monoxide (CO) and solid silicon, since the atmosphere in which the reaction occurred comprised a vast majority of CO gas, according to the Boudouard equilibrium.