Corrosion behaviour of oxide film formed on carbon steel in high temperature alkaline water in the presence of zinc and magnesium ions

ABSTRACT Magnetite films on carbon steel are known to reduce corrosion in high temperature aqueous medium. The magnetite films were modified in-situ by introducing Zn and Mg in autoclave by hydrothermal process at 250°C. The film developed in the presence of Zn were thinner with particle size 150 nm after 240 h exposure compared to that developed in the presence of Mg with particle size 223 nm. The depth distribution of Zn and Mg monitored by Rutherford backscattering spectrometry showed that Mg was present more at the top surface, whereas Zn were almost uniform across the depth of the film. Contact angle measurements and electrochemical studies of coated specimens showed an increased corrosion resistance in presence of Zn and Mg in comparison to known passive magnetite layer formed in their absence. It was shown that Zn is a better candidate for corrosion resistance of carbon steel in high temperature aqueous medium.