Electrochemical Behavior of Si(IV) and the Preparation of WSi₂ Alloys in Molten CaO–SiO₂–CaF₂

Silicon has been applied in many fields, such as high-purity semiconductors, high-temperature resistant materials, optical fiber connection materials, organosilicon compounds, and alloys. In this work, silicon was extracted from the Bayan Obo tailing by high-temperature electrolysis. The reduction process of Si(IV) and the effect of CaF₂ content on the reduction process were studied in the SiO₂–CaO–CaF₂ melt. The Si(IV) ions in the SiO₂–CaO system with 10 wt pct CaF₂ were reduced by a one-step four-electrons transfer process. In the SiO₂–CaO melt with 15, 20, and 30 wt pct CaF₂, the reduction process of Si(IV) was a two-step two-electrons transfer process: Si(IV) + 2e → Si(II) and Si(II) + 2e → Si(0). The reduction process of Si(IV) to Si(II) was reversible and was controlled by diffusion. The diffusion coefficient was 1.52 × 10⁻⁸ cm² s⁻¹. Si and WSi₂ were prepared under a current density of − 0.55 A cm⁻² at 1738 K. It was found that the WSi₂ alloys were formed because of the alloying of Si(IV) and W.