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](3)Si[CH2](2)-Si[OC2H5](3); BTESE) containing ammonium heptamolybdate ([NH4](6)Mo(7)O(24)4H(2)O), 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 30degreesC 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 O-2 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.