Si production by direct electrolytic reduction of solid SiO2 in molten CaCl2

Abstract

Morphological and crystallographic investigations were conducted on the Si produced by direct electrolytic reduction of solid SiO2 in molten CaCl2 at 1123 K. From the results of SEM, it was proved that the produced Si had columnar shape. FE-SEM observation showed that the Si column had basically a hexagonal prismatic and stacking structure. The results of TEM and ED revealed that the Si column was a single crystal having {111} twin planes perpendicular to the major axis of the column. It is explained that amorphous Si is firstly formed by electrochemical reduction and then thermally transformed to crystalline Si. Purity of the Si was proved by EDX to be more than 99.9%. Current efficiency for the reduction of SiO2 to Si was calculated as 74% at 0.70 V.