Anodic behavior of titanium in the presence of titanium(III) chloride in molten lithium chloride-potassium chloride eutectic melts

It is shown that the open circuit potential of a titanium electrode in TiCl3 solutions of molten lithium chloride-potassium chloride melts behaves according to the Ti(III)/Ti(II) redox electrode potential of the reaction: Ti + 2TiCl3 ⇄ 3TiCl2. A dependence of 75 mV per a logarithmic concentration ratio of (CTi(III))2 to (CTi(II))3 was obtained. The initial dissolution rate of titanium in TiCl3 showed a first order process with respect to the TiCl3 concentration with a specific rate constant of 5.05 × 10-3 min-1. The rate determination was extended from 723 to 803 K and the activation energy was calculated to be 88.68 kJ mol-1. The actual titanium dissolution rate in TiCl3 was measured and used to verify the validity of the results obtained by the electrochemical techniques (linear polarization and Tafel methods). A correlation was developed that relates the corrosion current obtained from the Tafel methods, Icorr(Tafel), to that obtained from the actual metal dissolution, Icorr(w.d.). Tafel slopes for Ti dissolution were 90 mV decade-1 which gives an anodic transfer coefficient, $\beta$, of 1.55 while the cathodic Tafel slope is 100 mV decade-1 giving a cathodic transfer coefficient, a, of 0.5. A dissolution mechanism compatible with the experimental facts is proposed. © 1991.