Structural correlations and chemistry of the Na3AlF6 − SiO2 melt as an electrolyte for the solar grade silicon (SOG − Si) electrowinning

Abstract

Molten system Na 3 AlF 6 −SiO 2 was examined by high temperature NMR. Further characterizations of the samples prepared by Rapid Solidification Processing (RSP) technique and by spontaneous solidification were performed by X-ray diffraction and solid state NMR. The high solubility of SiO 2 in molten cryolite and the immiscibility phenomenon were observed. Using thermogravimetric analysis, weight losses were detected, which could be attributed to the formation of the volatile products. The results of the present study are the evidence that SiO 2 reacts with molten Na 3 AlF 6 under the formation of the volatile SiF 4 , non−volatile NaF, and alumino−silicate AlSi 3 O 8 species. NMR spectroscopy coupled with diffraction−based methods was proved as a promising approach to obtain information about the structure and chemistry of this rather complex system.

Fluorine in Complex Alumino-Boro-Silicate Glasses: Insight into Chemical Environment and Structure

“…25 Sodium alumino-fluoride flux processes have been suggested as a means of electrowinning silicon from silica. 26 Silicate and phosphate glasses are the main matrices for immobilization of many nuclear wastes, 27,28 some of which include fluoride. 29,30 Recently, there has been increased interest in high-fluorine-containing glasses and glass ceramics, to accommodate radioactive wastes from fluoride-based molten salt reactors.…”

“…Phosphate- and fluoride-containing glasses are also important for medical applications, such as bioglasses for dental applications. − Fluoride-containing oxide melts high in calcium and silicon are common slags in metallurgy, , and related compositions are used as mold fluxes for continuous casting . Sodium alumino-fluoride flux processes have been suggested as a means of electrowinning silicon from silica …”