Preparation of ultra-high purity cylindrical Mo ingot by electron beam drip melting

A cylindrical Mo ingot with ultra-high purity was obtained by electron beam (EB) drip melting process using a Mo rod. The Mo rod as a bar feeder was prepared from Mo powder by vacuum sintering and swaging processing. Most of impurities excluding W in the Mo ingot were removed down to below ppm level by three-times EB drip melting, where the purity of the Mo ingot except W was improved from the initial Mo powder purity of 3N (99.95%) to 5Nup (99.9998%). Furthermore, the gaseous impurities C, N and O in the Mo ingot were removed to a level below 5 ppm from the initial level of around 460 ppm by repetitive EB drip melting.