Anodic dissolution of titanium in chloride-containing ethylene glycol solution

Anodic dissolution behavior of titanium in chloride-containing ethylene glycol was examined using a rotating disk electrode. A potential-independent dissolution current flowed depending on the rotation speed, species and concentration of chloride salts. In solutions with lower concentrations of chloride, a potential-independent current was controlled not only by the mass transfer process but also by the charge transfer, and the kinetic-controlling current depends on solution conductivity. In concentrated chloride solutions, the current was controlled only by mass transfer process and decreased with increase in chloride concentration. A smaller current also flowed in a solution with a high concentration of titanium species. These results indicated that the diffusion-controlling species are titanium species, not chloride ions. Electrochemical impedance spectroscopy revealed that a titanium chloride salt layer, which maintains titanium species at a high concentration, accumulates a low charge (similar to 0.1 mu F cm(-2)) and becomes thicker with increase in applied potential, is formed between the titanium substrate and diffusion layer during the mass transfer-controlling dissolution. (C) 2009 Elsevier Ltd. All rights reserved.