Protection of passivated iron from corrosion in 0.1 M KClO₄ with and without Cl^- by coverage with a two-dimensional polymer film of carboxylate ion self-assembled monolayer

A film of two-dimensional polymer was prepared on an iron electrode passivated in a borate buffer solution at pH 8.49, derivatized with 16-hydroxyhexadecanoate ion HO (CH₂)₁₅ CO₂^- and then modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. The protective ability of the polymer film adsorbed on passivated iron was examined by polarization measurement in oxygenated 0.1 M KClO₄ solutions with and without 1 × 10^-4 and 1 × 10^-3 M of Cl^-. The values of the open-circuit potential, E_oc were monitored with the immersion time, t in these solutions. The E_oc value of the passivated electrode in 0.1 M KClO₄ was maintained high, more than -0.2 V/SCE in the initial region of t up to 10 h, indicating the presence of a passive film on the electrode. Thereafter, E_oc decreased to -0.4 V/SCE abruptly, exhibiting breakdown of the passive film. The value of the passivated electrode covered with the polymer film remained almost constant around -0.04 V/SCE during immersion for 45 h. The protective efficiency, P (%) of the polymer film on passivated iron was extremely high, more than 99.9% unless the passive film was broken down, indicating complete protection of iron against corrosion. The times for breakdown on the passivated electrode and polymer-coated one diminished with an increase in the concentration of Cl^-. The polymer-coated surface was analyzed by electron-probe microanalysis after immersion in 0.1 M KClO₄ for 24 h.