Studies of the electrochemistry of niobium (V) in sodium chloroaluminate and fluorochloroaluminate melts

Studies pertaining to the contamination of some molten salts by oxide impurities were conducted. Tantalum(V) was used as a Raman spectroscopic probe ion to determine the level of oxide contamination of FLiNaK; it was determined that, of the several methods examined, slow recrystallization was by far the best method for removal of oxide from the melt. Carbonyl chloride and carbon tetrachloride were found to be effective agents for removing oxide from sodium chloroaluminate. Of these two reagents, carbon tetrachloride showed greater advantages in its ability to react with oxide at lower temperatures and shorter times.

The electrochemistry of Nb(V) in sodium chloroaluminate rates at 178°C was examined, and it was determined that previously published studies were conducted in solutions of high oxide content. The reduction of NbCl₅ in COCI₂- and CCl₄-treated melts was found to proceed via essentially four steps at short times and low concentrations. At higher concentrations and long times, the reduction sequence was complicated by the appearance of an additional process which was due the reduction of the product of a chemical reaction which followed the initial reduction step.

The effect of temperature on the electrochemistry of Nb(V) in sodium chloroaluminate and fluorochloroaluminates was examined; temperature had a marked effect on the reduction of Nb(V) in these melts, but no great differences were observed between melts with and those without fluoride.

Attempts to electrolytically produce niobium metal from Nb(V) in chloroaluminates and fluorochloroaluminates were made. While varying several parameters (such as temperature, fluoride content, and applied current density), deposition of the metal was achieved in only a few cases. The best deposit was obtained using a tungsten cathode at 550°C from a chloroaluminate melt in the absence of fluoride.