Silicon Production from SiO Gas via Gas-Phase Reactions

The production of silicon with hydrogen is very challenging, although it is possible to get partway there, as SiO gas can form from SiO₂ and H₂. For some applications, metallurgical grade silicon is only an intermediary to gas-phase silicon species and “not needed” from a value-chain point of view. This work explores the possibility of going directly from SiO gas to useful Si-based gases with gas-phase chemistry. In particular, it looks into reactions between SiO gas and Cl₂ gas to form SiCl₄, which can be turned into raw materials for polysilicon production in the Siemens process. If successfully implemented, this would make CO₂-free polysilicon production possible. The work is theoretical in nature and is based on thermodynamical calculations using FactSage. Assessing the process steps in isolation, calculations show that both SiO formation from H₂ and SiO₂ and the formation of SiCl₄ from SiO are thermodynamically favourable. Combining the two steps in a process is likely to be challenging however, since if H₂/H₂O from the first step is present during the second, this will interfere with the chlorination of SiO, representing a serious bottleneck. Unless SiO can somehow be separated from H₂/H₂O at very high temperatures, success seems to be dependent on rapid quenching while suppressing back-reactions.