A New Electrolytic Production Process of Silicon Using Liquid Zn Alloy Cathode in Molten Salt

Abstract

Electrolytic production process for solar-grade Si utilizing liquid Si–Zn alloy cathode in molten CaCl₂ has been proposed. Toward the establishment of the process, the behavior of liquid Zn metal was investigated in molten CaCl₂ at 1123 K. The evaporation of Zn metal was largely suppressed by an immersion into molten salt, which enables the use of Zn electrode in spite of the high vapor pressure of Zn. The cyclic voltammetry suggested the reduction of SiO₂ at 1.45 V vs. Ca²⁺/Ca on a Zn cathode. After the potentiostatic electrolysis at 0.9 V, Si particles with diameters of 2–30 µm were precipitated in the solidified Zn matrix by the slow cooling process of the produced liquid Si–Zn alloy. The alloying rate between solid Si and liquid Zn was measured as 4.56 μm s⁻¹, and it linearly decreased with the Si content in liquid Zn phase.