Controlled preparation of silicon and magnesium silicide on silica glass substrate through magnesiothermic reduction

• Published in: International journal of ceramic engineering & science 2020-03, Vol.2 (2), p.66-75
• Main Authors: Henmi, Takashi, Shiono, Takeshi, Matsubara, Keisuke, Kiyomura, Tsutomu, Kurata, Hiroki, Wakasugi, Takashi, Okada, Arifumi, Kadono, Kohei
• Format: Article
• Language: English
• Subjects: Acids; carbothermic reduction; Crystal structure; Crystallinity; Glass substrates; Heat; Intermetallic compounds; magnesiothermic reduction; Magnesium; magnesium silicide; Microscopy; Morphology; Oxidation; Reaction time; Reduction; Silica glass; Silicides; silicon; Silicon dioxide; Silicon substrates; Temperature; Thickness; transmission electron microscopy
• ISSN: 2578-3270; 2578-3270
• DOI: 10.1002/ces2.10039

Magnesiothermic reduction has received attention as a method to produce silicon retaining the morphology of the silicon dioxides that serve as the starting materials of the reduction. We performed the reduction of silica glass substrates with magnesium deposited on them under various conditions, including changing the reaction temperature from 500 to 700°C, changing the reaction time from 15 to 420 minutes, and changing the thickness of the deposited magnesium film from 6.6 to 12.1 μm. Crystalline products and their amounts were investigated using X‐ray diffraction. In these reactions, the silica glass substrates were reduced to silicon and/or magnesium silicide depending on the conditions. Under the conditions where the reaction temperature is higher, the reaction time is longer, and the thickness of the magnesium is thinner, silicon was generated more predominantly than magnesium silicide, and vice versa. Under the intermediate conditions, both crystalline silicon and magnesium silicide were generated. Furthermore, it was revealed that the magnesium silicide was rapidly generated within 15 minutes at temperatures higher than 600°C. Then, as the reaction continued, the amount of magnesium silicide gradually decreased, and that of silicon increased. From these results, a two‐step reaction model was proposed: At first, silicon dioxide is reduced to magnesium silicide with the complete consumption of the deposited magnesium; and subsequently, the magnesium silicide reacts with unreacted silicon dioxide and silicon in the intermediate oxidation states to produce silicon. Based on this model, silicon and magnesium silicide were selectively prepared under well‐controlled conditions. We carried out the magnesiothermic reduction in which silica glass substrates are reduced by magnesium deposited on the substrates at various conditions. To explain the experimental results, we proposed a two‐step reaction model. Based on this model, we carried out practically the magnesiothermic reduction in a two‐step scheme and succeeded to produce magnesium silicide and silicon selectively.