Preparation of Protective Films Containing Molybdate for Self-Healing of a Scratched Iron Surface

Nonchromate, self-healing films protective against corrosion of Fe were assessed by polymerization of 1,2-bis(triethoxysilyl)ethane ([C₂H₅O]₃Si[CH₂]₂-Si(OC₂H₅]₃; BTESE) containing ammonium heptamolybdate ([NH₄]₆Mo₇O₂₄4H₂O), which was combined tightly with ferric ion (Fe³⁺) on the surface of an Fe electrode passivated in aerated 0.1 M sodium molybdate (Na₂MoO₄). After the electrode surface was scratched crosswise with a knife-edge, the electrode was immersed in an aerated 0.1 M sodium chloride (NaCl) solution at 30°C for > 4 h, and then polarization curves were measured in the solution potentiodynamically. The anodic process of Fe corrosion was suppressed markedly by passivation of the scratched surface with molybdate ion $(MoO42−)$ oozing from the film and O₂ diffusing through the scratch. The surface covered with the film was characterized by x-ray photoelectron spectroscopy, Fourier transform infrared reflection spectroscopy, and electron probe microanalysis.