Preparation of ultrahigh purity cylindrical tantalum ingot by electron beam drip melting without sintering process

Abstract

A two-step process was used to obtain an ultrahigh purity cylindrical tantalum ingot from tantalum powder. Generally, powders cannot be used as raw materials in processes employing electron beam (EB) drip melting. We designed a process that could indeed use powders. The first step reduced the impurities in tantalum by the repeated EB melting of tantalum buttons fabricated from tantalum powder. An ultrahigh purity tantalum ingot was then fabricated by repeated EB drip melting of the refined tantalum buttons. A cylindrical ingot (Ø80×100 mm) with purity of 99·9998 was obtained. The purity of the raw tantalum powder was 99·9944, while those of tantalum buttons remelted twice and four times were 99·9989 and 99·9994 respectively. The concentration of gas impurities such as C, N and O was reduced to <10 ppm from an initial level of 3340 ppm.