Protection of passivated iron from corrosion in 0.1 M KClO4 with and without Cl by coverage with a two-dimensional polymer film of carboxylate ion self-assembled monolayer

A film of two-dimensional polymer was prepared on an iron electrode passivated in a borate buffer solution at pH 8.49, derivatized with 16-hydroxyhexadecanoate ion and then modified with 1,2-bis(triethoxysilyl)ethane (C2H5O)3Si(CH2)2Si(OC2H5)3 and octadecyltriethoxysilane C18H37Si(OC2H5)3. The protective ability of the polymer film adsorbed on passivated iron was examined by polarization measurement in oxygenated 0.1 M KClO4 solutions with and without 1 X 10-4 and 1 X 10-3 M of Cl-. The values of the open-circuit potential, Eoc were monitored with the immersion time, t in these solutions. The Eoc value of the passivated electrode in 0.1 M KClO4 was maintained high, more than -0.2 V/SCE in the initial region of t up to 10 h, indicating the presence of a passive film on the electrode. Thereafter, Eoc decreased to -0.4 V/SCE abruptly, exhibiting breakdown of the passive film. The value of the passivated electrode covered with the polymer film remained almost constant around -0.04 V/SCE during immersion for 45 h. The protective efficiency, P (%) of the polymer film on passivated iron was extremely high, more than 99.9% unless the passive film was broken down, indicating complete protection of iron against corrosion. The times for breakdown on the passivated electrode and polymer-coated one diminished with an increase in the concentration of Cl-. The polymer-coated surface was analyzed by electron-probe microanalysis after immersion in 0.1 M KClO4 for 24 h.