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

Abstract A two-dimensional polymer coating, the self-assembled monolayer of 16-hydroxy hexadecanoate ion HO(CH2)15 CO 2 - 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, tbd. Repeated polarization measurements were carried out during immersion in these solutions for obtaining the protective efficiency, P. The tbd 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 tbd, 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.