Corrosion protection of iron/steel by emeraldine base polyaniline: an X-ray photoelectron spectroscopy study

The emeraldine base form of polyaniline has been used as a corrosion protecting undercoat on steel and iron samples. Using X-ray photoelectron spectroscopy, the anti-corrosion performance of various application methods of the emeraldine base layer was studied, as well as the mechanism for corrosion protection. Emeraldine base polyaniline undercoats were found to offer corrosion protection for both the cold rolled steel and iron samples. The degree of protection did vary depending on the thickness of the iron oxide layer at the polymer/metal interface as well as on the thickness of the top oxide layer. The best results were achieved when both the top and interfacial oxide layers were removed prior to the polymer deposition. The mechanism for corrosion protection was found to be anodic, i.e., the polyaniline film withdraws charge from the metal, passivating its surfaces against corrosion. For all samples studied, iron as well as cold rolled steel, the iron oxide structure consisted of a thin (~15 A) layer of Fe2O3 followed by a thicker layer of Fe3O4 at the pure steel (iron) interface. Large values (up to ~1.5 cm) of throwing power were obtained for emeraldine base protected cold rolled steel.