Electrochemistry of niobium and tantalum, 8

The reaction between niobium and niobium pentachloride in gas phase was studied to clarify the reaction mechanism and to obtain fundamental data for fused salt electrolysis of niobium, using niobium subchlorides as a carrier salt in molten alkali halides. Niobium subchlorides were prepared from the reaction of Niobium metal with NbCl5 by a chemical transport reaction at 200 - 8000C. The composition of the products formed was analyzed by chemical analysis and x-ray diffraction. The products obtained from the disproportionation reaction at 200 - 4000C were NbCl5, NbCl4, and NbCl3, corresponding to the reaction: 2NbCl4 reversible NbCl3 + NbCl5. The products at 400 - 7000C were NbCl sub(3+x) and predominately Nb3Cl8. At 8000C, the patterns of cluster of Nb6Cl14 were observed by x-ray diffraction. The x-ray diffraction data and several gas spectra of niobium chlorides are shown. Thermochemical calculations were performed for some disproportionation reactions of niobium chlorides. (author)