| Abstract: | The influence of copper on corrosion and passivation of iron-chromium alloys Part II: Surface analytical examinations The formation and the breakdown of potentiostatically in 1N H2SO4 generated passive layers of Fe/Cr alloys (7 resp. 11% Cr) and those with 1% Cu has been studied by XPS analysis and angular dependent XPS. After 1 h passivation the layer thicknes reaches 1 to 4 nm. In accordance with the current densities of layer formation the thickness is increased by copper and decreased by higher Cr contents. The mean thickness of the residual layers measured immediately after selfactivation shows the same tendencies. Passive layers have higher Cr- but lower Fe-contents than the alloys, especially in the presence of copper. Copper is only detectable in the metallic state. It causes raising amounts of γ-Fe2O3, leading to the assumption, that copper accelerates passivation via oxidation, of Fe-II-cations in the-oxide lattice by means of the initially existing Cu-II-ions. Concentration depth profiles show that the Cr-enrichment is localised at the oxide/electrolyte interface. Copper is somewhat enriched near the layer/alloy interface, resulting from the initial alloy dissolution. Self activation leads to strong enrichment of copper, raising from the lower to the upper part of layer. The ambivalent effect of copper in regard of improving passivation but accelerating self activation of FeCr-alloys in H2SO4 is discussed. |
