Electrochemical dissolution of magnetite electroplated coatings on titanium

As a part of understanding of iron and steel passivity, the dissolution rate of magnetite has been studied in anaerobic borate buffer at 25 degrees C between -0.5 and -0.75 V/SHE. The dissolution rates have been estimated from weight loss measurements. Linear weight losses in time have been obtained corresponding to constant dissolution rates. Nevertheless the rates depended on potential according to a Butler-Volmer law. Another Butler-Volmer law has been obtained for the steady-state cathodic current density flowing through the magnetite layer and ending by the proton reduction step. For both, the quantitative Butler-Volmer parameters have been estimated from the experiments. The cathodic feature of the electrochemical dissolution rate for magnetite was confirmed but the electron balance analysis has shown that this dissolution did not involved electrons as mentioned in the literature. One possible mechanism is proposed in which the kinetics of the proton reduction step tunes the outer voltage drop at the magnetite-solution interface and this voltage drop steers the kinetics of the dissolution rate. (C) 2017 Elsevier Ltd. All rights reserved.