Examination of niobium electrochemistry from the reduction of Nb3Cl8 in molten LiCl-KCl eutectic

Solubility and electrochemical properties of Nb3Cl8 in LICl-KCl eutectic me lt were examined. It was found that the maximum solubility of Nb3Cl8 is not higher than 0.8 wt% within the 400-500 degrees C temperature range. At a t ungsten electrode, Nb3Cl8 is reduced to metallic niobium through two consec utive electrochemical steps: a first reversible step involving one electron charge transfer and a second rather irreversible step implying two electro ns number exchange and yielding to metallic niobium. This last step is pert urbed by the formation of niobium subhalide insoluble compounds(cluster). T he diffusion coefficients of the Nb(III) and Nb(II) species were found equa l to 2.6 x 10(-6) and 3 x 10(-6) cm(2) s(-1), respectively. According to th ese values, it was concluded that diffusive species are complexes rather th an simple ones. (C) 1999 Elsevier Science Ltd. All rights reserved.