- <Original Papers>Production of Pure Niobium by Combination of Carbon Reduction Smelting and Electron Beam Melting
The interest in high-purity niobium has risen from the need for materials in the high temperature, superconductivity and atomic energy fields recently. In this work, the combination method, i.e. carbon reduction smelting of niobium oxide at about 2900K in Ar plasma arc and refining of the reduced-niobium with electron beam melting, was carried out to prepare high-purity massive niobium metal. The results obtained are summerized as follows : (1) Each pellet of mixture with a ratio of graphite to niobium pentoxide, C/Nb_2O_5,was selected 4.8,4.9,5.0 and 5.1,was pre-reduced prior to the reduction smelting. In Ar plasma arc heating, reduction proceeded rapidly with melting down of each pellet and the elimination of carbon and oxygen as CO-degassing proceeded slowly in the Nb-C-O molten state. Niobium of above 99% purity was obtained by a 12 min treatment. (2) Carbon and oxygen content in the reduced-niobium was dependent on the C/Nb_2O_5 ratio and in the relation between carbon and oxygen it was found that (%C)×(%O) was almost constant. It is, therefore, able to adjust carbon/oxygen ratio in the reduced-niobium by changing C/Nb_2O_5 ratio for next refining process. (3) At electron beam melting, remarkable deoxidation was found by evaporation of NbO and/or NbO_2,but decarburization as CO-degassing was possible only when excess oxygen was present in the reduced-niobium. (4) Ductile high-purity niobium, the carbon and oxygen content were 20ppm, 70ppm respectively, with a hardness of 50 HMV was produced by electron beam melting of the reduced-niobium at C/Nb_2O_5=4.9. (5) Evaporation loss of niobium besides niobium suboxide during electron beam melting decreased the recovery of niobium. (6) Metal impurities, such as Fe, Al, Si, which are more volatile than niobium were removed effectively to the levels of a few ppm with electron beam melting.
Electron Beam Melting
- 東北大學選鑛製錬研究所彙報 = Bulletin of the Research Institute of Mineral Dressing and Metallurgy, Tohoku University
東北大學選鑛製錬研究所彙報 = Bulletin of the Research Institute of Mineral Dressing and Metallurgy, Tohoku University 41 (2), 141-154, 1986-03-25