Abstract
It is shown that hydrogen permeation through the steel base plays a very important part in the galvanic corrosion of plain tinplate. New accurate conditions for. the electrochemical study of the hydrogen permeation flux have been designed. The specific influence of tin–iron alloy and free tin layers has been studied, showing a screening effect typical of type K plate alloy layer. No hydrogen diffusion has been detected through α 0·10 mm thick pure tin foil.
The ‘coupling shift’ exhibited by a steel electrode upon uncoupling from tin, is correlated with an increase in the hydrogen flux towards its steady state value, the maximum coupling shift value corresponding to the minimum hydrogen diffusion rate. Phenomena occurring at the steel electrode upon adding Sn2+ ions or upon coupling to tin, are of the same kind: adsorption of a cationic (i.e., positively charged) stannous complex. All factors favouring an increase in the coverage by an adsorbed complex would enhance the corrosion inhibition.
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