Protective effect in sulfuric acid media of alumina and ceria oxide layers electrodeposited on stainless steel

Abstract

The influence of thin layers of Al 2O 3 and Ce 2O 3–CeO 2, electrodeposited on stainless steel OC4004, on the corrosion behaviour of the systems Al 2O 3/SS, Ce 2O 3–CeO 2/SS and Al 2O 3–Ce 2O 3–CeO 2/SS has been studied in sulfuric acid medium. A pronounced stabilizing effect on the passive state of steel and enhancement of its corrosion resistance has been established both for the samples as deposited and for the thermally treated Ce 2O 3–CeO 2/SS systems. In comparison to them the layers of Al 2O 3 have a substantial impact on the corrosion resistance of the Al 2O 3/SS system only in the cases when the system is not subjected to thermal treatment. The consecutive deposition of Al 2O 3 and Ce 2O 3–CeO 2 films on SS gives as a result an outstanding corrosion-protective effect, whereupon the corrosion potential of the system Al 2O 3/Ce 2O 3–CeO 2/SS is shifted in positive direction with ∼ 0.3 V for the samples as deposited and with ∼ 1 V—for the thermally treated samples. The so established favourable effect has been explained by the increased concentration of chromium oxides in the surface passive film, caused by the presence of cerium oxides, as well as by their action as cathode, effective with respect to the reduction corrosion reaction, shifting strongly the potential (at which this reaction is occurring) in positive direction.