SYNTHESES OF POLYMERIZED FILMS ON MILD STEELS BY ELECTROOXIDATION AND ELECTROREDUCTION AND THEIR CORROSION-RESISTANCE

Polymer films, based on aniline-, phenol-, normal vinyl- and heterocyclic/vinyl-type monomers, were synthesized on mild steel by various electropolymerizations (EPs), and their corrosion resistance and structure were investigated because a new coating system with corrosion resistance for mild steel has been obtained. The relationship between synthetic method, structure, and function (corrosion resistance) for coated mild steel is discussed. In electro-oxidation polymerization (EOP) incomplete, porous, and thin films were formed on steel surfaces, while in electroreduction polymerization (ERP), complete, more compact, and thicker films were formed on steel surfaces in comparison with EOP films. The most corrosion-preventive film under this experimental condition was a poly(2-vinylpyridine) film with an inhibition efficiency (eta) of corrosion of about 80-90%. The most effective EP method was a constant potential electrolysis using a two-electrode cell with an eta value of more than 90%. Since the organic layer formed during EP was ionic and the EP of 2-vinylpyridine (monomer) was promoted, the thick poly(2-vinylpyridine) film was formed on the steel surf ace. The results of structural analysis suggest that, (i) poly(2-vinylpyridine) film, (C7H7N)n, was formed on the steel surface by EP, (ii) the coated steel was composed of polymer and steel layers, and oxidation products were not present in the interface, and (iii) the solvents in the film were evaporated and the thermal-polymerization of poly(2-vinylpyridine) continued with curing.