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 NaNO_3

摘要

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 l,2-bis(triethoxysilyl) ethane (C2H5O)3Si(CH2)2Si(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, t_(bd) 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 t_(bd) 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 t_(bd), 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.