Charge transport properties of cryolite–silica melts

Electrodeposition of silicon from a cryolite based electrolyte at a relatively low temperature is a promising approach to generate high purity silicon. In order to obtain fundamental data pertaining to electrowinning of silicon from cryolite–SiO2 melts, charge transport properties of the melt such as conductivity and electronic and ionic transference numbers were measured. Each property was determined for a range of temperatures and SiO2 contents. It was found that addition of silica to cryolite generally decreases the transport rate of charge carriers. The temperature on the other hand had a positive effect on the electronic and ionic conductivities. The variations arise from the structural changes in the melt, particularly formation of complex ions involving Na, Si, and Al.