ON THE ELECTROCRYSTALLIZATION OF REFRACTORY METALS IN A MELT OF NaCl-KCl-NaF-MeCl_x

摘要

Reduction of group IV and V transition elements by metallothermic processes is discontinuous, energy intensive and yields in a poor metal quality. Electrowinning in a molten bath of NaCl-KCl-NaF-MeCl_x seems to be an attractive alternative. Main difficulties in electrowinning of refractory metals are their different stable valencies and the high corrosivity of the reactants. Therefore many papers deal with the understanding of the stable valencies and the reaction mechanisms in the melt to optimize electrolyte composition. Only few authors describe the electrocrystallization behavior of refractory metals under different working conditions. Morphology of the deposit is another important factor for industrial cell plants. Deposits should be dense and compact with a small specific surface to avoid salt entrainment and oxidation of the metal. By electrorefining and electrowinning titanium and niobium the influence of temperature, current density, metal and fluorine content in the melt has been investigated. Results show that the addition of fluorine changes morphology and the fraction of metal powder on the cathode increases. With a rising metal content in the bath the grain size rises also to a certain extent. Current density and temperature were found to have only a small influence on the morphology of the deposit within the investigated range.