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A selective review of the anodic and cathodic processes associated with electroextraction, electrorefining and plating of refractory metals (Ti, Zr, Nb and Ta) from molten salt-based electrolytes is presented with regard to the results obtained during the last two decades. Special attention is paid to the mechanism of cathodic reduction and its rate-limiting steps, as well as to the parallel chemical reactions of disproportionation and complexing. The anodic processes in corrosion and electrodissolution of Ti, Zr, Nb and Ta in molten electrolytes are also discussed. As a conclusion, a few contradictory subject-related questions are outlined and some new trends of investigation are suggested.

Anodic oxidation has proven to be a promising route for the growth of self-ordering oxide nanotubes on Ti, the best results being obtained in ethylene glycol (EG)-based electrolytes with the addition of fluoride and small amounts of water. In the present paper, emphasis is put on the investigation of barrier film growth and dissolution on Ti in EG electrolytes with the addition of H2O (0.3–2.4 M) and NH4F (0.015–0.17 M) using electrochemical and surface analytical techniques. Steady-state current–potential curves and electrochemical impedance spectra as depending on potential (−0.1/5.0 V vs. AgCl/Ag), water and fluoride content have been registered. In addition, the chemical composition of the surface of the oxides obtained at 0.1 and 1.0 V has been estimated by X-ray photoelectron spectroscopy (XPS). XPS analysis revealed the presence of a non-stoichiometric oxide containing mainly Ti4+ and a certain amount of Ti3+, with a certain degree of hydroxylation. Estimates of the total thickness of the oxide from the XPS data using a dual layer model are also presented. A kinetic model of the process is advanced to quantitatively interpret the electrochemical and surface analytical results.