Residual hydrogen reduction and refining effect during two-step hydrogen-argon plasma arc melting of cerium

Abstract

Herein, the two-step hydrogen-argon plasma arc melting technology (HPAM-APAM) namely hydrogen plasma arc melting (HPAM) followed by argon plasma arc melting (APAM), was put forward to successfully realize the application of HPAM on cerium refining. The residual hydrogen content was significantly decreased to 79 ppm with the increase of APAM time to 40 min. The contents of volatile impurities Li and Mg were greatly reduced to less than 0.1 ppm. Paradoxically, the contents of Ti and W with low vapor pressures could be reduced to 2 ppm, whereas the impurities Fe and Si with high vapor pressures were hardly removed. The analysis indicated that the reduction of W and Ti was ascribed to the formation of volatile WO3 and TiO, while the negligible reduction of Fe and Si was attributed to the strong interaction strength with cerium based on “alloy phase formation theory”. A new kinetic refining mechanism by the activated H during HPAM process was proposed. This work helps to extend HPAM to refine hydrogen absorbing metals and provides new insights into the removal mechanism of metallic impurities.