Influence of Incorporated Copper on the Formation, Solid State Structure and Electrochemical Properties of γ-FeOOH

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It is well known, that the rate of the atmospheric corrosion of iron is slowed down considerably, if the metal is alloyed by small amounts of Cu. This effect is specifically pronounced during those times, when the metal surface is covered by thin electrolyte layers. As then the oxygen reduction is rate determining for the corrosion rate, the kinetics of the oxygen reduction is slowed down on Cu-containing steels with respect to pure iron. On pure iron oxygen is reduced within the oxide scale at electron conducting oxide crystals. Such oxides contain high amounts of Fe2+ states and result from an electrochemical reduction of γ-FeOOH. Therefore it is quite likely, that on Cu-containing steel the solid state properties of the oxide scale are changed such, that the electronic conductivity decreases. – In this study model electrodes of Cu-doped γ-FeOOH are investigated. The morphology of the scale is analysed by SEM, the chemical state of Cu and Fe by XPS and the structure of the scale using FT-IR spectroscopy. The results clearly show, that the morphology of the Cu-doped oxide is changed significantly and XPS data suggest, that the reducibility of the doped oxide is much less than the one of undoped γ-FeOOH.