Boron removal from UMG-Si by hybrid melting utilizing steam plasma torch and EMCM

The specific purification process was developed to remove impurity element boron from UMG-Si (Upgraded Metallurgical Grade Silicon) by the steam plasma and EMCM (Electro Magnetic Continuous Melting). Some plasma reactive gases lead to volatilization of boron on the surface of liquid silicon because of the lower evaporation pressure than that of silicon. Boron is removed as volatile compounds such as B_xH_zO_y , B(OH)_x, B_xO_y. The experiment was carried out in various surrounding gas conditions of plasma. Injecting gas (hydrogen and steam) with argon which is carrier gas of steam plasma torch was best for the refinement. The removal ratio of boron impurity was increased with increasing the flow ratio of steam. The final Boron concentration was decreased to 0.17 ppmw from 2.9 ppmw of initial content.