Journal of Applied Electrochemistry, Vol.25, No.7, 671-676, 1995
Role of Free F- Anions in the Electrorefining of Titanium in Molten Alkali-Halide Mixtures
The influence of the F/Cl atomic ratio on the morphology of titanium metal, deposited by electrorefining in various alkali halide solvent mixtures and K2TiF6 solute, was investigated. A continuous transition from powdery deposits in chloride mixtures (F/Cl = 0), through dendritic deposits in chloride-fluoride mixtures (0 < C/Cl < infinity), to coherent and adherent deposits in fluoride mixtures (F/Cl = infinity), was evidenced. This dependence was explained in terms of the increase of the thermodynamic stability of TiF63- anion (and the consequent decrease of the activity of Ti3+, i.e. electrocrystallization centres available in the melt), with increase of the parameter F/Cl. This is supported by the observed increase in the decomposition potential, E(d), and the shift of the Ti3+ discharge potential, E(p), toward more negative values, in the same sequence. The influence of the F/Cl atomic ratio on current efficiency, eta, on the grain size distribution and on the chemical purity of electrodeposited titanium metallic powder, was also discussed.