Niobium subhalides

One of the advantages of pure chloride media is their low cost which makes them economically attractive. Unfortunately, in these media, the chemistry of refractory metal ions is very complicated, due to their high degree of oxidation (5 for Ta and Nb, 4 for Hf, 6 for W...) In some cases, each subhalide can intervene in the overall process for example, Boiko et al have observed on a chronopotentiogram of a solution of niobium ions in molten NaCl-KCl (Fig.l) five steps of reduction of Nb to Nb [8] subsequent to the successive formation of subhalides on the electrode where the coating occurs, chemical reactions such as disproportionation, adsorption or precipitation reactions may occur during the reduction process and act to the formation of powdery coatings. 

---