Abstract
The mechanism of the carbothermic reduction of SiO2 containing Al2O3 has been investigated. The reduction rate has been measured by means of thermogravimetry under an argon atmosphere at temperatures from 1773 K to 1973 K.
The addition of small amounts of Al2O3 to SiO2 increases the reduction rate of SiO2 and the yield of SiC. The formation of SiC is retarded by the excess addition of Al2O3. In particular, most of SiO2 is evaporated as SiO at the low temperature.
At the early stage of the reaction, the reduction rate is controlled by the chemical process on the surface of the graphite particles at the lower content of Al2O3 and by that on the surface of the SiO2-Al2O3 particles at the higher content of Al2O3, respectively. At the low temperature, the rate-determining step is the chemical reaction on the SiO2-Al2O3 particles independently of Al2O3 content. The rate is strongly dependent on the phase present in SiO2-Al2O3.
At the late stage of the reaction, the reduction rate is determined by the gaseous diffusion through the porous layer of Al2O3 left on the SiO2-Al2O3 particles.
