An Attempt to Prepare Nonchromate, Self-Healing Protective Films Containing Molybdate on Iron

Preparation of a nonchromate, self-healing protective film on an Fe surface was attempted. A protective film of 1,2-bis(triethoxysilyl)ethane ([C₂H₅O]₃ Si[CH₂]₂ Si[OC₂H₅]₃) polymer containing a fine powder of ammonium heptamolybdate tetrahydrate ([NH₄]₆Mo₇O₂₄·4H₂O) was prepared on a surface of Fe electrode passivated in aerated 0.1-M sodium molybdate (Na₂MoO₄). The protective ability of this film was examined on the covered electrode in an aerated 0.1-M sodium chloride (NaCl) solution at 30°C by polarization measurement. The protection efficiency (P) of the film was significantly high, 99.0%. After the electrode coated with the film was scratched with a knife edge, the self-healing ability of the film was estimated on the electrode in the NaCl solution by polarization measurement. The P value of the film on the scratched electrode was still high, 98.8%. The anodic process of Fe corrosion markedly was suppressed by the formation of a passive film at the scratched surface with molybdate ion $(MoO42−)$ incorporated in the polymer film, resulting in a self-healing activity of the film.