Kinetics of Carbothermal Reduction of Quartz Under Vacuum

The kinetics of reduction of 0.2 mol of –70?mesh quartz particles by 0.2 mol of graphite were determined in a batch reactor between 0.25 and 10 −0 torr. The effects of temperature, CO partial pressure, SiO 2 phase transformation, and alkali and alkaline‐earth oxide additives on the rate of reaction were studied. Increasing CO overpressure retarded carbothermal reduction. At 1400−C, addition of 5 wt% alkali oxide inhibited the reaction, whereas the same amount of alkaline‐earth oxide decreased the induction time; CaO was the best promoter. The initial reaction rate obeyed the cubic power law of nucleation growth at weight losses <15%, with an apparent activation energy of 77 kcal/mol. At higher weight losses, the Austin‐Rickett equation with an exponent near 2 was more applicable. The results are consistent with a model based on a transitory phase intermediate.