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

Abstract

It is shown that the open circuit potential of a titanium electrode in TiCl 3 solutions of molten lithium chloride-potassium chloride melts behaves according to the Ti(III)/Ti(II) redox electrode potential of the reaction: Ti + 2 TiCl 3 ⇄ 3 TiCl 2. A dependence of 75 mV per a logarithmic concentration ratio of ( C Ti(III)) 2 to ( C Ti(II)) 3 was obtained. The initial dissolution rate of titanium in TiCl 3 showed a first order process with respect to the TiCl 3 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 TiCl 3 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, I corr(Tafel), to that obtained from the actual metal dissolution, I corr(w.d.). Tafel slopes for Ti dissolution were 90 mV decade −1 which gives an anodic transfer coefficient, β, 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.