INFLUENCE OF FE2-STEEL( ION ON THE CORROSION OF CARBON)

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