ELECTROCHEMISTRY OF NIOBIUM, TANTALUM AND TITANIUM IN LOW-TEMPERATURE CARBAMIDE-HALIDE MELTS

摘要

The electroohemical behaviour of melts containing carbamide {urea; CO(NH_2)_2} at inert electrodes and the anodic dissolution of niobium, tantalum and titanium in carbamide-ammonium and alkali halide melts, as well as the structure of the complex ions formed, have been studied by electrochemical and spectroscopic methods. In carbamide-containing melts, all metals are passivated. In carbamide-chloride melts, a metal dissolution depassivator is a product of anodic oxidation of carbamide and [NH_4]Cl. Due to the different degrees of metal passivation, the electrochemical dissolution mechanisms of the metals are different, and their electroactivities decrease in the order Ti > Nb > Ta. In carbamide-[NH_4]F melt, fluoride ions have a depassivating effect on the dissolution of metals.