A study of the effect of quartz-to-cristobalite transformation on SiC generation in metallurgical-grade silicon production

Abstract

Abstract Silicon carbide (SiC) is an essential intermediate product formed during the smelting process of metallurgical-grade silicon (MG-Si), and its production efficiency is a key factor in determining the overall efficiency of MG-Si production. In this study, we investigated the effect of quartz-to-cristobalite transformation on SiC generation in industrial silicon production and elucidated the differences in the reaction characteristics of quartz and cristobalite when they interacted with carbonaceous reductants. The experimental results indicated that the rate of direct carbothermal reduction of cristobalite was 1.45 times that of quartz. Moreover, the indirectly formed SiC layer in the cristobalite/C diffusion couple exhibited a thickness of 920.87 µm, which was 1.55 times that in the quartz/C diffusion couple. Both the reaction thermodynamic calculations and crystal transformation theory analysis revealed that the changes in the chemical energy and crystal structure of SiO2 during the phase transformation process reduced the stability of cristobalite compared with quartz at high temperatures. Consequently, cristobalite reacted more easily with C at high temperatures to form SiC and SiO. The results of the study are highly significant for improving the reaction mechanism in the smelting process of MG-Si and enhancing the production efficiency of MG-Si.