Formation of Impurity Inclusions in Silicon when Smelting in Ore-Thermal Furnaces

Abstract

Silicon production by carbon reduction of silica-containing raw materials is performed in ore-thermal furnaces. The process proceeds at high temperatures (above 2,000°C). Consumers place high demands on the chemical purity of the silicon smelted, but the finished product contains a negligible amount of impurities. We have analyzed the causes for the impurity inclusions in silicon forming in smelting based on the data on the behavior of various elements penetrating the process with quartzite and reducing agent ashes. The chemical composition of furnace slag and silicon samples from the Silicon JSC of RUSAL (Russia) has been analyzed using various techniques, i.e. metallographic, X-ray fluorescence, X-ray diffraction, and X-ray spectral microanalysis. It has been established that the main source of non-metallic inclusions in silicon are furnace slag particles enmeshed in the melt when it is released from the tap. Due to the high degree of iron passing into the melt when smelting, the main metal inclusions are metal aluminum solutions based on iron, silicon, and other elements: FeSi2Al0,3, FeSi1,5Al0,3, and FeSi2Ti. The main way to improve the smelted silicon quality is to select feed with a minimum amount of impurities and conduct the process at optimal temperatures in the quartzite melting zone.