Prevention of passive film breakdown and corrosion of iron in 0.1 M KClO₄ with and without Cl^- by covering with an ultrathin two-dimensional polymer coating and healing treatment in 0.1 M NaNO₃

A two-dimensional polymer coating, the self-assembled monolayer of 16-hydroxy hexadecanoate ion HO(CH₂)₁₅CO₂^- modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃ was prepared on the passivated iron electrode and further, the passive film was healed by additional treatment in 0.1 M NaNO₃. This electrode was immersed in oxygenated 0.1 M KClO₄ solutions with and without 1 × 10^-4 to 1 × 10^-2 M of Cl^-. Protection of passive film against breakdown by covering the electrode with the polymer coating was examined by monitoring the open-circuit potential during immersion in the solutions for many hours to determine the time for passive film breakdown, t_bd. Repeated polarization measurements were carried out during immersion in these solutions for obtaining the protective efficiency, P. The t_bd value of the passivated, polymer-coated and healed electrode in 0.1 M KClO₄ solutions with and without Cl^- increased with a decrease in the concentration of Cl^-. No breakdown occurred on the electrode during immersion in 0.1 M KClO₄ solutions with and without 1 × 10^-4 of Cl^- for 360 h. The P values were extremely high, more than 99.9% before t_bd, indicating complete protection of iron from corrosion. The effect of healing treatment in 0.1 M NaNO₃ on passive film breakdown was investigated by electron-probe microanalysis.