1988 Volume 52 Issue 10 Pages 945-953
The mechanism of reduction of silica-graphite mixtures has been investigated at temperatures between 1673 and 2073 K under argon atmosphere. The rate of reduction has been determined by thermogravimetry and chemical analysis. The reduction products are both SiC and SiO. The production ratio of SiC increases significantly with increasing temperature and C/SiO2 mixture ratio.
In the early stage of the reduction, the rate equation for interfacial reaction control is applicable to the reduction of SiO2 with graphite. The apparent activation energy is 361 kJ/mol. The rate determining step is considered to be the chemical process at the surface of graphite particles.
When the reaction proceeds and the continuous layer of SiC is formed around the graphite particles, the rate of reduction shows a parabolic rate equation. The activation energy is 426 kJ/mol. The reduction of SiO2 is controled by the diffusion of carbon in SiC.
At temperatures below 1773 K, the reduction rate cannot be represented by the above rate equations.
