Investigating Impurities Removal Behavior from Terbium by the Combined Plasma Melting and Directional Solidification

The combined argon plasma melting and directional solidification method (denoted as APDS) was innovatively proposed to enhance the purification efficiency of Tb metal in this work. Theoretical computation and experimental analysis were used to explore the removal behavior of the three impurity groups during APDS, which included high volatility impurities of Ca, Mg, Mn and Cr, medium volatility impurity of Ti, and low volatility impurities of Al and Ni. The evaporation removal ratio of Ca and Mg after APDS process exceeds 99.9%, indicating that Ca and Mg are mainly removed by vacuum volatilization. Mn, Cr, Ti, Ni, and Al had evaporative removal ratios of 49%, 37%, 1.3%, 7%, and 14%, respectively. And the contents of these impurities increases with the increase of solidification fraction. It was shown that Mn and Cr were removed by the combined action of volatilization and directional solidification, and Ti, Ni and Al were primarily removed by the directional solidification. By using the innovative combination approach, the impurities in Tb were removed simultaneously and effectively.