Boron Removal from Metallurgical-grade Silicon by Slag Refining with Yttria-Silica System

A new slag system, Y2O3-SiO2-CaF2 system, was adopted in purification of Si for photovoltaic application. The partition ratio of boron (L-B) between slag and silicon was studied under different mass ratio of slag to silicon and varying basicity at 1873K. Scanning electron scope and electron probe micro analysis were used to detect the distribution of impurity elements in silicon after slag refining. The experimental results show that the mass ratio of slag to silicon did not affect the trend of slag basicity with L-B, and high mass ratio of slag to silicon would decrease LB. Silicon was surrounded by amorphous slag. Impurity elements are concentrated in slag. Yttrium oxide's role in slag and kinetic analysis of boron removal are also discussed.