Solid State Deoxidation of Some Rare Earth Metals and Reduction of Their Interstitial Impurity Concentrations by Electron Beam Melting

Abstract

One of the problems with which we meet when we use the commercially available rare earth metals is the presence of interstitial impurity elements, particularly oxygen. Its amount often exceeds a thousand mass ppm. According to the thermodynamical values for the rare earth-oxygen system, some of the rare earth metals should be deoxidized by electron beam melting and by solid state deoxidation treatment using such a low oxygen atmosphere as is offered by the equilibrium in the Ca(l)–CaO(s) system. These were experimentally examined for La, Nd, Pr, Gd, Tb and Dy metals by the use of respectively an electron beam furnace with water-cooled copper hearth and a muffle furnace with the sealed iron container including calcium chips and a calcia crucible. Most significant decrease of oxygen content by electron beam melting, 1600 mass ppm→780 mass ppm, was found for La metal, and that by calcium treatment, 1890 mass ppm→370 mass ppm, was found for Pr metal.