Corrosion protection using polyaniline coating formulations

Growing environmental concerns regarding the use of heavy metals in coating formulations has led to a new coating strategy employing inherently conducting polymers (ICP) as a key component. ICPs (such as polyaniline, polypyrrole and polythiophene) are electrically conductive owing to a system of conjugated double bonds. Observations of metal passivation complement this conductive nature and offer a viable alternative to traditional corrosion protection (1-8). A key potential advantage that the ICP coating technology offers is toleration of pin holes and minor scratches. The basis for this argument is that, since the ICP coating is conductive, the entire coating acts to passivate any areas of exposed metal. This paper describes a model for polyaniline (PANI) corrosion protection and presents data which clearly demonstrate significant corrosion protection in a salt fog environment. ESCA and electrochemica data are presented which show that an Fe-PANI complex is formed in the process of coating steel with PANI. The Fe-PANI complex is shown to catalytically reduce oxygen. Preliminary electrochemical impedance results are also presented which show an additional time constant at 20 kHz, which appears to correlate with the effectiveness of PANI toward corrosion protection.