Protection of iron against corrosion in various solutions by coverage of passivated iron with a two-dimensional polymer coating prepared by using octyltriethoxysilane and healing treatment in 0.1 M NaNO₃

In order to shorten the time required for preparation of an ultrathin polymer coating on a passivated Fe electrode, a self-assembled monolayer of 16-hydroxyhexadecanoate ion HO(CH2)15CO2 - adsorbed on the electrode was modified with 1,2-bis(triethoxysilyl)ethane (C2H5O)3S(i CH2)2S(i OC2H5)3 and octyltriethoxysilane C8H17Si- (OC2H5)3. Further, the passivated and polymer-coated electrode was healed by treatment in 0.1 M NaNO3. The time for passive film breakdown, tbd and the protective efficiency, P( %) were determined by monitoring the open-circuit potential and repeated polarization measurements during immersion in 0.1 M KClO4, 0.1 M NaNO3, 0.1 M Na2SO4 and 0.1 M NaCl for many hours. The tbd values were 57.4, 240, 19.2 and 9.0 h, respectively. Breakdown of the passive film was markedly suppressed by coverage with the polymer coating and healing treatment. The P values of the electrode in these solutions were extremely high, more than 99.9% before tbd, indicating that complete protection of substrate Fe against corrosion was accomplished by covering the electrode with the healed passive film and polymer coating unless the passive film was broken down.