The chemistry of the carbothermal synthesis of β-SiC : reaction mechanism, reaction rate and grain growth

Evidence is given that in the present case the reaction mechanism of ß-SiC formation from silica and carbon is a direct solid-state reaction in which silica migrates over the silicon carbide surface to the carbon. A high value (440 kJ/mol) of activation energy is obtained for this reaction. This high value indicates that the reaction rate is determined by the diffusion of C atoms in carbon. As soon as the silica layers surrounding the silicon carbide particles have disappeared grain growth of ß-SiC occurs. The mechanism for grain growth of ß-SiC seems to be surface diffusion of Si and C atoms in SiC. The measured value of the activation energy for grain growth of ß-SiC is 450 kJ/mol. Grain growth of a-SiC results in platelets.