Purification of Vanadium by External Gettering
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THE pronounced effects of the interstitial impurities carbon, oxygen and nitrogen on many properties of vanadium metal have led to the development of a number of purification methods. Electrolytic refining of crude vanadium from a calcium reduction of V205 has been reported by Sullivan.l The crude vanadium from an aluminum reduction of V205 has been purified by electron beam melting as reported by Carlson, Schmidt and Krupp. 2 Zone refining has been applied to vanadium by Reed) Electrotransport purification of vanadium has been reported by Schmidt and Warner 4 and has produced metal with the largest resistance ratio to d a t e ) All of these purification methods either do not reduce the interstitial impurity concentration to low levels or produce relatively small amounts of purified metal at a substantial expenditure of time and equipment. The use of titanium alloying additions to modify and reduce the effect of O, N and C in vanadium has been reported by Keith. 6 In this technique, it is necessary to have an excess of titanium over that which precipitates as TiC, TiN or TiO and thus the properties of the metal are modified by this alloying with titanium. Also, the titanium concentration is rather low which results in a higher concentration of C, O and N remaining in solid solution in equilibrium with the titanium-interstitial compound phase. A similar application of titanium alloying to remove the effects of interstitial impurities in high purity iron has been reported by Solomon, McMahon and Leslie. 7 The strong interaction between these interstitial solutes and a more active metal can also result in an external gettering action. Brentnall and Metcalfe 7 studied the softening of niobium alloys hardened by a dispersion of ZrC that occurred when these alloys were in contact at high temperature with brazing alloys rich in titanium. They showed that this softenD. T. PETERSON is Professor and Senior Metallurgist, and H. H. BAKER is Senior Research Technician, Ames Laboratory, Iowa State University, Ames, IA 50011, and B. A. LOOMIS is with Argonne National Laboratory, Argonne, IL 60439. Manuscript submitted May 2, 1980. METALLURGICAL TRANSACTIONS A
ing was due to partitioning of the carbon to the titanium alloy and consequent loss of the ZrC precipitates. Another example is the elegant procedure for the purification of iron by zirconium via a hydrogen gas intermediary reported by Stein and Low. 9 A logical simplification of that procedure in which the getter metal was placed in intimate contact with the outside of the metal to be purified seemed worthy of investigation. The rapid diffusion of interstitial solutes compared to substitutional solutes would be utilized to remove the interstitials before the getter metal had time to penetrate inward excessively. The outer layer of getter alloy and interstitial compound could then be machined or dissolved from the purified core. The kinetics of this purification reaction can be estimated from the diffusion coefficients for the interstitial solute impurities and the dimensio
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