Purification of chromium by hydrogen plasma-arc zone melting

Purification of chromium by hydrogen plasma-arc melting (H-PAM) and hydrogen plasma-arc zone melting (H-PZM) has been examined. Especially, reduction of non-metallic impurities, such as oxygen, nitrogen, carbon and sulfur, that have harmful influences on the mechanical properties of chromium, has been investigated. Two kinds of chromium, about 99% (2N-Cr) and 99.99% (4N-Cr) in purity, were used as the starting materials. Remarkable deoxidation, slight denitrogenization and decarburization of chromium were observed in H-PAM, while no reduction of sulfur was observed. Activated hydrogen atoms dissociated in high temperature plasma-arc probably take part in the refining reactions, e.g. deoxidation represented by O_ + 2H = H2O. In addition, it was found that oxygen, nitrogen, carbon and even sulfur concentrations were further reduced at the head side of chromium rods by segregation during H-PZM. Thus, H-PZM with both the segregation effect and the refining effect by H was available to decrease the non-metallic impurities of chromium.