Polypyrrole and polyaniline top coats on nickel coated mild steel

Electrochemical synthesis of very adherent polypyrrole (PPy) and polyaniline (PANi) films were achieved on 1 μm thick nickel (Ni) coated mild steel (MS) samples. Electrodeposition of Ni layer on MS was carried out galvanostatically, in an appropriate bath solution and cyclic voltammetry technique was used for synthesis of the polymer top coats, in monomer containing oxalic acid solutions. The corrosion performances of nickel coated samples with and without polymer top coats were investigated in 3.5% NaCl solution, by using electrochemical impedance spectroscopy (EIS) and anodic polarization curves. It was found that electrodeposited 1 μm thick Ni layer had quite porous structure, therefore, it could exhibit restricted barrier property and its protection efficiency diminished with time. It was shown that the presence of a polymer top coat could improve the barrier property significantly and lead to much better protection against the corrosion of underlying MS. PPy film was found to be more effective as top coat on Ni coated MS, with respect to PANi film. © 2004 Elsevier B.V. All rights reserved.