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

Molten system Na3AlF6 - SiO2 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 SiO2 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 SiO2 reacts with molten Na3AlF6 under the formation of the volatile SiF4, non - volatile NaF, and alumino-silicate AlSi3O8- 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. (C) 2021 Published by Elsevier B.V.

Automated summary

The molten system Na3AlF6 - SiO2 was studied using high temperature NMR, revealing the high solubility of SiO2 and immiscibility phenomenon in the cryolite. Weight losses detected in thermogravimetric analysis were attributed to the formation of volatile products. The study demonstrated that SiO2 reacts with molten Na3AlF6 to form volatile SiF4, non-volatile NaF, and alumino-silicate species AlSi3O8-, highlighting the potential of NMR spectroscopy coupled with diffraction-based methods in analyzing complex chemical systems.