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Synthesis of silicon nanowires from carbothermic reduction of silica fume in RF thermal plasma



Silica fume, which is a by-product of metallurgical-grade silicon production, is a low cost material with high SiO2 concentration and small particle size (<1 µm). These properties make it a good candidate for radio-frequency (RF) thermal plasma processing. In this article, the use of silica fume as a reactant is promoted for the RF thermal plasma synthesis of high-charge capacity, high cyclability anode materials for lithium-ion batteries. In order to obtain these materials, the carboreduction of silica fume is followed by an in-flight growth of silicon nanowires in the plasma reactor. The impact of the addition of catalysts and the use of different plasma gases on the yield and the properties of the product has been investigated by X-ray diffractometry (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), and transmission electron microscopy (TEM). It is found that the addition of metal catalysts has a significant effect on the synthesis. It not only promoted the formation of silicon nanowires, but also improved the yield of the reaction upwards of 300%. An insight on the mechanisms leading to the silicon nanowires formation is also discussed in the results section.