Direct Electrolytic Reduction of Amorphous SiO₂ Powder Refined from Diatomaceous Earth

Abstract

Amorphous SiO₂ powder refined from diatomaceous earth (DE-SiO₂) was pressed into pellets, and the electrolytic reduction of them has been investigated in molten CaCl₂ at 1123 K. The DE-SiO₂ pellets were successfully reduced to Si by electrolysis at 1.00 and 1.20 V vs. Ca²⁺/Ca. Observations with a scanning electron microscope revealed that the reduced Si has the rod-like nanostructure, and that the reduction rate for the DE-SiO₂ pellet is higher at more negative electrode potential. Furthermore, the reduction rate for the DE-SiO₂ pellet is higher than that for the fumed-SiO₂ pellet. The high reduction rate of the DE-SiO₂ pellet and the evolution of rod-like nanostructure are probably derived from its peculiar porous structure. DE-SiO₂ will be one of the most promising Si sources in the industrial-scale electrolytic reduction in both aspects of the reduction rate and the abundance of the resources.