Columbium metal by the aluminothermic reduction of Cb₂O₅

Summary

A practical process has been developed for the preparation of high-purity, ductile columbium metal. The process consists of reducing Cb₂O₅ with aluminum powder in a “bomb”-type reduction. The massive columbium contains approximately 2 wt % Al and 0.8 wt % O₂. These impurities, along with nitrogen and iron, can be satisfactorily removed in subsequent treatments by volatilization. Much of the impurities in the as-reduced columbium can be removed by heating in vacuum to 2000°C for 8 hr, leaving a sponge. These impurities may also be largely removed by heating for a shorter time at 2200°C; however, some loss of the columbium is encountered. Heating to 1800°C for 8 hr was found to be less efficient for impurity removal.

The purified columbium sponge prepared by heating to 2000 or 2200°C can be converted to massive, ductile metal by non-consumable arc melting. Further purification can be achieved by electron beam melting of the sponge.

The direct vacuum arc melting of the as-reduced material was found to be only partially effective for impurity removal. A duplex melting scheme in which the vacuum arc-cast ingot was remelted in an electron beam furnace yielded high-purity ductile columbium. Electron beam melting of the as-reduced columbium metal offers possibilities in a furnace designed to eliminate interference from the moderate amounts of aluminum and other volatiles present.