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](6)Mo7O24 . 4H(2)O) was pre pared 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 degrees 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.