Chronoamperometric studies during the polymerization of aniline from an oxalic acid solution

Potential step measurements in an aniline–oxalic acid medium shows passivation of steel occurred prior to polyaniline deposition. The steel first dissolved as Fe2+ followed by the formation of a FeC2O4 complex on the surface of the steel. A decrease in potential from 0 to −0.5 V results in a smaller anodic current density and requires more time to form the oxalate complex. Potential steps more negative than −0.6 V do not completely passivate the steel surface. X-ray photoelectron spectroscopy measurements of the passive layer suggested that it is a mixture of Fe2+ and Fe3+ oxalate layers. Atomic force microscopy imaging shows the oxalate layer is composed of large polygonal crystals whereas the polyaniline coating exhibits very small rounded-mound structures.