Comparative study of the passivity and the breakdown of passivity of polycrystalline iron in different alkaline solutions

Abstract

The passivity and passivity breakdown of polycrystalline iron is investigated through electrochemical methods complemented with ellipsometry, by employing plain 0.04 M NaOH and saturated Ca(OH)₂ solutions with the addition of chloride salt of concentrations up to 1 M. The comparative results indicate that the initial reactions of Fe(OH)₂ formation at the inner part of the passive layer level (Fe₃O₄) are only slightly influenced by either the cation or the presence of Cl− ion in solution, in contrast to their large influence at the outer part of the passive layer (hydrous FeOOH species) where Fe²⁺/Fe³⁺ redox reactions take place. At high positive potential the breakdown of passivity is also influenced by both Cl− ion and cation present in solution.