Abstract
The inhibitive effect of Sn2+ ions on the corrosion of five carbon steels and pure iron in solutions of oxalic, tartaric, malic, and citric acids was studied by the polarisation technique. In oxalic acid the corrosion of pure iron and 0·1 and 0·5% carbon steels was inhibited at all Sn2+ ion concentrations, while that of 0·25, 0·65, and 0·75% carbon steel was inhibited only in 10−3 M Sn2+ solutions. Inhibition was found to be predominantly anodic occurring by adsorption of SnL2 complex anions and following the Langmuir isotherm. The anomalously high inhibition efficiency with the 0·5% carbon steel was attributed to its having a higher ratio of anodic/cathodic areas. In tartaric, malic, and citric acids, corrosion of pure iron and the investigated steels was inhibited at all Sn2+ ion concentrations and the carbon content did not affect inhibition efficiency appreciably. Inhibition was of mixed type and occurred by adsorption of SnL complex molecules together with underpotential deposition of Sn adatoms. Adsorption of the inhibitor was found to follow the Temkin isotherm.
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