PURIFICATION OF ZIRCONIUM BY ELECTRON-BEA M FLOATING-ZONE MELTING

Removal of metallic and non-metallic impurities from zirconium with no minal purity of 99.8% has been investigated by the electron beam float ing zone melting (EBFZM) in a high vacuum. Metallic impurities such as iron and chromium, being more volatile than zirconium, volatilized pr eferentially and their contents were reducible to below a few mass ppm after three zone passes at the zoning speed of 2 mm/min. Although no decrease of hafnium, with a slightly lower vapor pressure than zirconi um, by volatilization was observed, the redistribution of hafnium, cau sed by segregation effect, has been found. Deoxidation of zirconium by evaporation of zirconium suboxide like ZrO was scarcely noticed, but it was found that the oxygen content was reduced to below one-half of the initial content in near the final end of the zone melted portion, due to the segregation effect. Segregation of carbon towards the final end was also found, although decarburization by the CO gas evolution was not observed. The effective distribution coefficients for oxygen a nd carbon at the zoning speed of 2 mm/min were estimated to be 1.5 sim ilar to 2 and 0.7 similar to 0.8, respectively.