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 O2 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.