Formation of Si grains from a NaSi melt prepared by reaction of SiO2 and Na

•A mixture of Na2SiO3 and NaSi was prepared by reaction of SiO2 and Na at 650 °C.•Single crystals of NaSi were obtained by cooling of the Na2SiO3 and NaSi mixture.•Coarse Si grains were crystallized by Na evaporation from the mixture at 830 °C.•The yield of the Si grains was 85% of the ideal amount expected from the reaction.

A mixture of Na2SiO3 and NaSi was found to be formed by reaction of SiO2 and Na at 650 °C as follows: 5Na+3SiO2→2Na2SiO3+NaSi. Single crystals of NaSi were grown by cooling the mixture of Na2SiO3 and NaSi with an excess amount of Na from 850 °C, and polycrystalline Si was obtained by vaporization of Na from the crystals. Coarse grains of Si were also crystallized by Na evaporation after the formation of Na2SiO3 and Si-dissolved liquid Na at 830 °C. The Si grains were collected by washing the product with water. The yield of the Si grains was 85% of the ideal amount expected from the reaction.