Mechanistic Study on Aluminothermic Reduction of SiO2 by Molten AlCl3 Salts

Abstract

In order to obtain pure Si, it is necessary to undergo a strong reduction reaction to remove oxygen from SiO2. There are many kinds of previous studies to reduce SiO2, but lots of energy was consumed. The use of molten AlCl3 and Al metal enables a reduction reaction that separates pure silicon even below the melting temperature of Al metal (250℃). After the molten AlCl3 produced activated Al from Al metal, activated Al-centered complex structures (e.g. Al3Cl7-) were formed. They adsorbed on SiO2, leading to intense reduction reactions and producing AlOCl as a by-product. AlCl3 was separated from adsorbed [Al3Cl7]- complex, and adsorbed separately on SiO2. Density Functional Theory (DFT) calculation was employed to investigate the total reduction mechanism, which was composed of three stages: adsorption on SiO2, two times transfer of Cl, and oxygen removal. The activation energy of the oxygen removal reaction was found to be 86.12 kcal/mol and determined as the rate-determining step. Overall mechanism was similarly observed through the reactive molecular dynamics simulation, suggesting the possibility of the low temperature reduction of SiO2 with the help of molten AlCl3