Electron-Beam Float Zone and Vacuum Purification of Vanadium

Abstract

Electron-beam float zone melting vanadium three passes at 3.9 in./h in 4×10−10 Torr vacuum resulted in resistance ratios of about 700 and a total impurity content of 50 wt ppm. The zoning reduced both carbon and oxygen content. However, while carbon removal was always accompanied by a lowering of the oxygen content, the reverse was not true. The removal of oxygen was probably accomplished by the formation and volatilization of VO. The mechanism for carbon removal was not clearly resolved. Nitrogen was not appreciably affected by electron-beam float zone melting. All metallic impurities, with the exception of Ta and W and possibly Si, were effectively volatilized. No evidence was found for zone refining action on any impurity. Vacuum outgassing further reduced the carbon and oxygen level. However, the oxygen removal was far more effective than the carbon. The nitrogen content increased, particularly on the specimens that lost about 40% in weight due to vanadium evaporation. However, the effect of vacuum outgassing was less on the highest purity as-zoned specimens. The same purification mechanisms apparently operated.