Electrochemical Analysis of a Polypyrrole/Al Flake Composite Pigment for Corrosion Inhibition

For many years, hexavalent chromates have been the gold standard for corrosion inhibition on structures made out of aluminum or its alloys.  The use of hexavalent chromates has been especially widespread on aluminum 2024, used in the construction of aircraft, due to its susceptibility to localized corrosion.  Due to its inherent toxicity however, hexavalent chromates are being taken out of use.  Therefore there is a need for an environmentally friendly alternative for hexavalent chromates.  Conducting polymers such as polypyrrole are a group of materials that have shown some promise as corrosion inhibitors.  There are many problems associated with the application of polypyrrole.  These problems are due to the insolubility of polypyrrole in common solvents, which make processing difficult, as well as poor adhesion and mechanical properties.  The technique applied by this group in order to circumvent these issues has been to coat polypyrrole onto an aluminum flake pigment via an aqueous chemical oxidation reaction that could be easily scaled up by industry.  By incorporating this composite pigment into an epoxy binder, both the processing and mechanical limitations of polypyrrole can be overcome.  In this study, electrochemical techniques such as a combined SVET/coupling current measurement, coupling current measurements, electrochemical AFM, and a scanning ion probe were used to further reveal the mechanism by which these pigments inhibit corrosion.