Corrosion behaviour in organic acid solutions—I. Tin electrode

The corrosion behaviour of tin in oxalic, citric and tartaric acids in the pH range 2–6 and at concentrations 10−1–10−5 M was investigated. The results indicate that increasing the concentration of the organic acid and the pH of the medium up to 4 shifts the corrosion potential to a more negative value and increases the rate of corrosion. At pH values 5 and 6, a shift in the corrosion potential in a noble direction is accompanied by a decrease in the corrosion rate. A linear relationship is observed between the steady state potential (E) and the logarithmic concentration of the organic acid (log C) for the three acids studied: E = a − b log C. It was concluded here that the corrosion mechanism in the pH range 2–4 is anodically controlled by the complexing of Sn2+ ions with organic acid anions and that the order of decreasing aggressiveness is oxalic > citric > tartaric acids. Corrosion was inhibited at pH values 5 and 6 and this was attributed to film formation on the surface of tin which may result from the hydrolysis of tin complex species.