The Effect of Chelating Agents on the Transient Behavior of Passivated Iron under Cathodic Potential Pulsing

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Abstract
The passive layer was formed potentiostatically on iron in basic solution containing various chelating agents: o‐phenanthroline, malonic acid, 8‐hydroxyquinoline. 0.15N borate‐0.15N boric acid solution was also used for comparison. A cathodic potential pulse was applied to the passivated iron in the same solution, and cathodic reduction was then carried out galvanostatically in basic solution without chelating agents. The cathodic pulse reduced adsorbed oxygen on passive iron, and the coverage by adsorbed oxygen decreased depending upon the properties of the chelating agents. o‐Phenanthroline did not influence the coverage of adsorbed oxygen since it diffused away in the form of the ferrous‐o‐phenanthroline from the metal surface. The coverage by adsorbed oxygen in the solution containing malonic acid and 8‐hydroxyquinoline was low, and the cause was attributed to the replacement of adsorbed oxygen by oxalic acid or metallic chelate. The thicker passive layer was produced in the borate‐boric acid solution, and the adsorbed oxygen was replaced by the ring polymer which exists predominantly in the mixed solution and acts as a corrosion inhibitor.

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