NICOLE BERTHELIN, J. M. CHRISTEN, J. PAGETTY

Preliminary results are presented on the evaluation of the potentiokinetic polarization technique for studies of localized corrosion behaviour of lacquered tinplate samples. Evaluation was performed with a 5 μm thick layer of an epoxyphenolic lacquer on tinplate and in 1% model solutions of citric, oxalic, lactic and acetic acids (2.3–2.8 pH range) and in 1% model solutions of the sodium salts of the same acids (6.4–8.0 pH range) by means of scannings of the potential first anodically and then, in the reverse direction, at a rate of 50 mV/min.

The shape of the current‐potential curves obtained, dependent on the anion type and pH of the solution, suggests the development of passive regions with localized penetration of the organic coating by the conducting phase. We interpret these results as a lacquer breakdown process that involves transport of anions at sites of low resistance electrolytic paths in the organic coating with their specific effect on the dissolution of tin from below the organic coating. These results correlate with the visible localized corrosion behaviour of the lacquered samples from direct corrosion experiments.