Oxide converters represent an interesting alternative for the protection of steel surfaces that have some degree of rust. Although the mechanism of these converters is not clear, it is assumed that they react with iron oxides and generate new compounds that may have a passivation effect on the steel surface. This last point is not well established, and several authors have even spoken of an accelerating effect of these compounds. We present here a study of the electrochemical behaviour of iron oxides immersed in the rust converter. The modulus of the impedance increases significantly after a certain time of immersion, suggesting that the electronic conductivity and, consequently, the rate of the cathodic reaction tend to decrease. (C) 2009 Elsevier Ltd. All rights reserved.