Separation of boron from silicon by steam-added electron beam melting

• Published in: Separation and purification technology 2019-05, Vol.215, p.242-248
• Main Authors: Shi, Shuang, Guo, Xiaoliang, An, Guangye, Jiang, Dachuan, Qin, Shiqiang, Meng, Jianxiong, Li, Pengting, Tan, Yi, Noor ul Huda Khan Asghar, H.M.
• Format: Article
• Language: English
• Subjects: Boron removal; Electron beam melting; Oxygen self-circulating path; Photovoltaic; Solar-grade silicon
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2018.12.080

•Boron can be separated from silicon in the form of BO by incorporating water vapor above melt surface.•The vapor of BO reacts with electrons to form monatomic boron and O2− so that boron is removed.•O2− migrates in the direction of silicon melt under the effect of electric field, and dissolves again in the melt.•Oxygen self-circulating path is established so that boron can be removed continuously. Removal of boron from silicon is a tough task by traditional directional solidification and vacuum refining techniques, due to its large and inappropriate segregation coefficient and low saturated vapor pressure. At high temperature boron react with oxygen to form volatile boron oxides which can be evaporated. So, the removal procedure of boron from silicon melt is investigated by incorporating a small amount of water vapor above the melted surface. The results show that boron is oxidized to mainly form BO and evaporated with 28% removal efficiency by average. It is considered that oxygen atoms experience a series of physical and chemical processes, such as a chemical reaction in the bulk of the melt, evaporation from the melt surface, transportation across the gas phase and ionization due the electron beam, which is conducive to the continuous removal of boron.