Article ID



Calcium Deoxidation of Niobium and Titanium in Ca-saturated CaCl2 Molten Salt


R. O. Suzuki, M. Aizawa and K. Ono


J. Alloys and Compounds, Vol.288, pp.173-182 (1999)


Niobium was deoxidized under Ca(liquid)-CaO(solid) equilibrium at 1273K to a level below the lower limit of quantitative chemical analysis, 50 mass ppm oxygen. Because Ca does not react with Nb, it is easy to remove the excess Ca and the byproduct CaO, and no reaction layer remains such as for Ti external gettering. Due to direct contact with Ca liquid, however, Nb was contaminated by carbon and nitrogen. When Ca was supplied as vapor into a CaO-saturated CaCl2 melt, Ca could saturate in the CaCl2 melt, and the impurity carbon and nitrogen in Nb was minimized. The oxygen concentration in Ti was the same as that under Ca-CaO equilibrium, and that in Nb was below 50 ppm. By Ca-halide flux deoxidation using the Ca-saturated but CaO-unsaturated CaCl2 melt, the residual resistivity ratio, RRR, of Nb exceeded that of the starting commercial Nb wire by 500. The oxygen content in Nb was estimated to be smaller than a single ppm. The activity of CaO in the salt was also evaluated at 1273K using the equilibrium oxygen concentration in Ti.