Refinement of niobium Nb2O5 through solvent extraction followed by carbo-thermic reduction

Full text: Niobium (Nb) is an essential ingredient towards realizing technical Nb3Sn superconductors through 'Internal Tin' route. Hi purity and high homogeneous Nb (known as Hi Ho Nb) is absolutely essential for high current carrying high field technical Nb3Sn superconductors. The basic raw material Nb2O5 contains impurities of intestinal and substitutional in nature. The substitutional impurities such as Ta, Mn, Fe etc are removed by careful solvent extraction where as the interstitial impurities are removed by aluminothermic reduction or carbothermic reduction. The seed refined materials is then subjected to repeated electron zone refining to obtain superconductor grade niobium. Furthermore, presence of substitutional impurities prevents effective metal refinement through pyrometallurgical technique like electron beam melting, vacuum arc melting. As a part of XI plan activities, an effort has been launched towards obtaining high homogeneity Niobium (Nb) from the NFC (Nuclear Fuel Complex) produced Nb2O5 through a series of refining processes in collaboration with Institute of Minerals and Material Technology. For testing the technical feasibility, all experiments were done in laboratory scale involving not more than 100g Nb2O5. As a part of objective, Ta was required to be removed below 400 ppm by solvent extraction. Carbothermic reduction studies of Nb2O5 using arc plasma method was carried out using graphite as the carbonaceous reductant. The study establishes that it is feasible to prepare a product of 97.47% purity Nb with 85.83% recovery of metal content from the oxide. The plasma smelted Nb reported in this investigation followed by decarburization would serve as a feed stock for electron beam melting to produce high purity superconductor grade (>99.97%) Nb