INFLUENCE OF FE2+ ION ON THE CORROSION OF CARBON-STEEL

The corrosion behaviour of steel containing various carbon contents in 0.05 M solutions of monocarboxylic acid (acetic acid), dicarboxylic acid (oxalic acid) and tricarboxylic acid (citric acid) in the absence or presence of Fe2+ ions at pH 2.8 was studied by determining the corrosion potential E(corr) and the corrosion rates by the polarization technique. The extent to which corrosion is promoted depends on the carbon content, the concentration of Fe2+ ion and the dissociation constant K-a of the corresponding acids. The order of the corrosion rates was oxalic < acetic < citric acid. This sequence is in good agreement with the dissociation constants K-a of the corresponding acids. It was found that the corrosion rates depend upon the dissociation constant K-a of the acids. Therefore it is estimated that the difference in the corrosion rates of steel in acetic, oxalic and citric acid can be attributed to the difference in the Delta H and Delta S values for the dissociation of each acid.