Quartz-Cristobalite Transformation and Its Effect on Reactions in Si Production: Initial Studies

In Si and FeSi production, the main Si source is SiO₂, in the form of quartz. Reactions with SiO₂ generate SiO-gas that further reacts with SiC to Si. During heating, quartz will transform to other SiO₂ modifications with cristobalite as the stable high temperature phase. Transformation to cristobalite has been investigated and shown to be a slow process where the rate varies between the investigated quartz types.The effect of quartz versus cristobalite as SiO₂ source has been studied for reaction (1) 2SiO₂ + SiC = 3SiO + CO, by heating of pellets with SiO₂ + SiC in Ar-gas. The reaction was faster with cristobalite than with quartz. Initial experiments indicates that this is the case only in Ar and not in CO-atmosphere The higher specific surface area of cristobalite is believed to contribute to the higher rate. The industrial consequences of the observed difference between quartz types are discussed.