Prevention of passive film breakdown and corrosion of iron in 0.1 M KClO 4 with and without Cl − by covering with an ultrathin two-dimensional polymer coating and healing treatment in 0.1 M NaNO 3

Abstract

A two-dimensional polymer coating, the self-assembled monolayer of 16-hydroxy hexadecanoate ion HO(CH 2) 15 CO 2 - modified with 1,2-bis(triethoxysilyl)ethane (C 2H 5O) 3Si(CH 2) 2Si(OC 2H 5) 3 and octadecyltriethoxysilane C 18H 37Si(OC 2H 5) 3 was prepared on the passivated iron electrode and further, the passive film was healed by additional treatment in 0.1 M NaNO 3. This electrode was immersed in oxygenated 0.1 M KClO 4 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 KClO 4 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 KClO 4 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 NaNO 3 on passive film breakdown was investigated by electron-probe microanalysis.