Peculiar effect of chloride ions on the anodic dissolution of iron in solutions of various acidity

Anodic behavior of iron in chloride solutions is studied in the pH range fr om 0 to 6 and at the concentration of chloride ions from 0.2 to 3 mol/l. El ectrochemical measurements were supplemented with the raster electron micro scopy studies of electrode surfaces. The observed independence of the limit ing dissolution current of pH is explained by a hypothesis that water does not participate in the anodic process at sufficiently large anodic overpote ntials. Depending on the concentration of chloride ions, the continuity of the logi(a)-pH dependence is first interrupted and then restored; the react ion order in hydroxide ions changes from a positive value to zero. This is probably caused by the "dynamic passivation" of iron with the adsorbed oxyg en atoms and their competitive replacement by chloride ions.