Fei Li, Hantao Wang, Zedong Han
Industrial silicon (Si) production is based on the high-temperature reduction reaction between quartz and carbon, but the difference in the Si-to-carbon ratio (Si/C) in the furnace significantly affects the reaction behavior and yield, and its mechanism of action needs to be studied in depth. In this study, carbon and Si composite agglomerates were prepared from typical industrial Si feedstocks, and the high-temperature reaction properties of the agglomerates were systematically investigated in the range of 1625–1675 °C for three different Si to carbon molar ratios (mol(SiO2): mol(C) = 1:3, 1:1, and 3:1). The weight loss (η) and reaction rate (dη/dt) of the agglomerates were monitored in real time by ultra-high-temperature thermogravimetric analysis (TGA); the product phase compositions and microstructures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy spectroscopy (EDS), and the difference between the actual and theoretical reaction processes was investigated by introducing the reaction matching (ΔW). The results show that the reaction paths and product morphology under different Si/C ratios are significantly different: at a Si/C ratio of 1:3, the agglomerates mainly generate granular β-SiC, and the reaction process is close to the theoretical value; at a Si/C ratio of 1:1, there are obvious SiO and CO gas-phase products escaping, which results in a lower degree of the actual reaction; and at a Si/C ratio of 3:1, due to the insufficient carbon source, the SiC generation and consumption are difficult to balance, and the reaction activity increases with the temperature. The reaction activity shows a complex phase change with increasing temperature. This study elucidates the mechanism of quartz carbothermal reduction reaction under different Si/C ratios, which provides a theoretical basis for the optimization of industrial Si production dosage and the stable control of furnace condition.