Cavity Formation in Silicon Furnaces

The production of high silicon alloys plays an important role in the Norwegian economy. In recent years, excavations of various submerged arc furnaces have helped shed light on the internal workings of the production process. It is postulated that one of the key features of Si/FeSi furnaces is the presence of a cavity around the electrodes, resulting from the condensation of SiO(g). Industrial excavations revealed that a cavity is formed in certain furnaces but not all. The focus of this article is to shed more light on the mechanism behind the formation of the cavity using small scale laboratory equipment. Brown and white condensates of SiO has been identified in the experiments and are believed to be the main reason behind cavity formation since they glue the charge together and prevent any further downward movement of the charge. An induction furnace was used to simulate the production of various FeSi alloys under different parameters, including temperature, type of carbon reductants, amount of iron in the system and the effect of a SiO source on cavity formation. It was found that the cavity is formed faster in the case where iron was found in larger amounts and temperature played only a minor effect. The addition of SiO source, as in a Si+SiO2 layer, at the beginning of the experiments had the predict effect of facilitating cavity formation in the case of FeSi75 and 96. On the other hand, for FeSi52, this layer hindered the formation of the cavity and the exact reason behind this behaviour is remains unidentified. Lastly, a mechanism for cavity formation is proposed based on the observations from the experiments.