Pinpoint and bulk electrochemical reduction of insulating silicon dioxide to silicon

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Abstract
Silicon dioxide (SiO2) is conventionally reduced to silicon by carbothermal reduction, in which the oxygen is removed by a heterogeneous–homogeneous reaction sequence at approximately 1,700 °C. Here we report pinpoint and bulk electrochemical methods for removing oxygen from solid SiO2 in a molten CaCl2 electrolyte at 850 °C. This approach involves a 'contacting electrode', in which a metal wire supplies electrons to a selected region of the insulating SiO2. Bulk reduction of SiO2 is possible by increasing the number of contacting points. The same method was also demonstrated with molten LiCl-KCl-CaCl2 at 500 °C. The novelty and relative simplicity of this method might lead to new processes in silicon semiconductor technology, as well as in high-purity silicon production. The methodology may be applicable to electrochemical processing of a wide variety of insulating materials, provided that the electrolyte dissolves the appropriate constituent ion(s) of the material.