On the Mechanism of breakdown of passivity of iron for instationary conditions

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  • HSH.‐H. Strehblow
    H.‐H. Strehblow
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Abstract
The formation of Fe2+‐ions is studied in 0.5 M H2SO4 and 1 M HClO4 during changes of the potential of passivated iron specimen with the rotating‐ring‐disk technique. An Fe2+‐pulse is found during the decrease of the electrode potential serving as an indicator for the short exposure of small areas of bare metal to the electrolyte. In the presence of aggressive anions the repassivation of these defects is prevented leading to the formation of pits. The increase of the pit nucleation after potential changes coincides qualitatively with the occurrence of the Fe2+ transients. The adsorption mechanism may be excluded for these conditions because it postulates the action of aggressive anions for the very beginning of the breakdown process.
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