After reaction, MgO, Mg2Si and unreacted Mg is removed by
hydrochloric acid, yielding silicon product. In these reactions, magnesium
(b.p.5650uC) functions as a reducing agent. Previously, the Mg and SiO2 reactants were placed at separate locations, and Mg
vapor diffuses to react with SiO2
34. Upon testing, this configuration
limited the yield and scalability, because the Si product near the Mg
source was further converted to Mg2Si (reaction (3)), while the SiO2
far from Mg source was not reduced. Instead, we conduct the reaction
with Mg and SiO2 powder premixed together to increase the
scalability and yield. Both reactions (1) and (2) takes place in this
configuration, because Mg powder is in direct contact with SiO2, and
the Mg has high enough vapor pressure at elevated temperature (e.g.
1 Pa at 428uC)