Mechanism of Boron Removal Using Calcium Silicate Slag Containing CaCl2 Under O2 Atmosphere

The removal of boron from silicon is a crucial step for silicon purification by the metallurgical route. The mechanism of boron removal was investigated by a combined method of using calcium silicate slag containing CaCl2 and O-2 gas blowing. It is proved both experimentally and theoretically that the combined refining method is favorable for boron removal from silicon and shows a significantly enhanced boron removal. Thermodynamic calculations show that in addition to borate, a gaseous BOCl species is generated during the processing by the combined refining technique. Ab initio molecular dynamics simulations of BOCl gaseous species formation show that the Si-B bond breaks and a new Si-O-B structure is formed when the oxygen is introduced into the Si-B lattice plane. The existence of chloride further leads to the breaking of the Si-O bond and ultimately generates the O-B-Cl structure that escapes from the Si lattice plane in the form of free boride BOCl.