A study on the carbothermic reduction of Nb-Oxide and the refining by Ar/Ar-H2 plasma and Hydrogen solubility of Nb metal

The Ar/Ar-H2 plasma method was applied to reduce and refine high purity Nb metal. In addition, the reaction between molten Nb metal and hydrogen were also analyzed in the Ar-(20 %)H2 plasma. The metallic Nb of 99.5wt% was obtained at the ratio of C/Nb2O5 = 5.00 in the Ar plasma reduction and the O2 loss from the thermal decomposition of niobium oxides did not take place. In the Ar-(20 %)H2 plasma the metallic Nb of 99.8wt% was produced at the ratio of C/Nb2O5 = 4.80. It was observed that a major reaction of the deoxidation was the reaction with H, H2, and a deoxidation by the evaporation of NbOx did not occur but a mass loss of Nb did by a 'splash' effect. The deoxidation reaction rate obeyed the 1st order reaction kinetics and the reaction rate constant(k') of deoxidation was 7.8 x 10-7(m/sec). The solubility of hydrogen in Nb metal was 60ppm and it was larger than the solubility of molecular state hydrogen by 40ppm in the Ar-(20 %)H2 plasma method. A saturation was within 60sec and a hydrogen content was reduced below 10ppm by a Ar plasma re-treatment. (Author)