Impurity removal in Zr and Hf metals by Ar-H2 plasma arc melting

Removal of metallic impurities from commercially pure Zr and Hf metals by Ar-H2 plasma arc melting has been examined. The adding H2 gas to the Ar plasma led to an enhancement of a great removal of A1, Cr, Mn, Fe, Ni, and Cu impurities which could not be much removed by only Ar plasma arc melting. As a result, most impurities in the Zr and the Hf metals by Ar-H2 plasma arc melting were removed down to a few mass ppm levels. It was found that impurities with higher vapor pressure than those of the Zr and the Hf metals were easily eliminated by Ar-H2 plasma arc melting. The dominant reason for the removal of the metallic impurities from the Zr and the Hf metals by the H2 addition is as follows: (a) elimination of the oxide layer on the molten surface of the metal by hydrogen atoms, (b) increase in the temperature of the molten metal due to the higher thermal conductivity of the hydrogen plasma arc melting, and (c) transfer enhancement of impurity vapors from the gaseous and molten surface boundary by hydrogen atoms