Poly(ortho-ethoxyaniline) in corrosion protection of stainless steel

Corrosion protection of stainless steel (13% Cr) coated with poly(ortho-ethoxyaniline) (POEA) has been investigated. The layers of POEA were synthesised from sulphuric and phosphoric acid solutions by means of cyclic voltammetry. The protecting properties of the layers in supporting electrolytes were investigated by monitoring the open circuit potential (Eoc) vs. time, and by electrochemical impedance spectroscopy (EIS). It was found that polymer layers provide corrosion protection, i.e. they help to stabilise the potential of the metal in the passive potential region. The protective properties of POEA layers have shown to be superior to polyaniline (PANI) layers, which is explained by a denser morphology of POEA. The behaviour of POEA obtained on stainless steel, examined by EIS, is different from the one obtained for POEA on Pt electrode. The registered resistance in the case of POEA on stainless steel represents the charge transfer resistance at polymer/solution interface, i.e. the polymer resistance. These measurements show that a part of the layer is reduced, i.e. that there is an interaction between polymer layer and stainless steel. EIS measurements prove the influence of monomer on stainless steel oxide formation and suggest that polymer is partly incorporated into the oxide film.