Polymeric Complexes of Polyaniline as Anticorrosion Coatings

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the green state to the blue state in two weeks to one month time. The polymer is shown to protect the metal surface via cyclic, impedance and salt spray testing prior to this color change. We feel confident though, with the right chemical modifications, it is quite feasible to develop a conductive polymer coating that will remain conductive at higher pHs and still offer suitable wetting, adhesion and corrosion protection. When testing in salt environments with a pH below 4.0, our double strand coating offers excellent protection as presented in this paper. It is well known in the aircraft industry that the Environmental Protection Agency (EPA) has set guidelines for the eventual elimination of chromate conversion coatings for corrosion protection of aluminum alloys 16. The implications of these guidelines are serious and far reaching. The push is on for the development of a suitable replacement for chromate conversion coatings. Experience with the testing of Alodine 600 and 1200 chromate conversion coatings under cyclic polarization, impedance spectroscopy and ASTM B- 117 salt spray tests shows that this is a difficult goal. The chromates are the best and to date nothing seems to be able to perform better or at least as equally as well and have the same ease in applying the coating to the metal's surface. We believe conductive polymer coatings have the potential to perform as well as the chromates with further development work and offer an easy application method to the metal surface. Over the last three years a large amount of data has been collected about the science of applying the double strand conductive polymer complex as a coating to different aluminum alloys samples and testing under cyclic polarization, electrochemical impedance spectroscopy, ASTM B117 salt spray exposure, XPS and Auger surface analysis, SEM image analysis and X-ray diffraction analysis. Compelling information has led use to be able to get a firmer understanding of the mechanism of the corrosion protection for conductive polymers. EXPERIMENT The electrical conducting polymer was synthesized by a previously reported template-guided polymerization method to obtain a polymeric molecular complex that contains polyaniline and its polymeric dopant poly(acrylic acid) 1. The dried product was further processed by esterification with methanol to allow conversion of about half of the carboxylic functional groups to methyl ester functional groups. The resulting molecular complex of polyaniline and poly(methylacrylate-coacrylic acid) is soluble in an organic solvent, such as ethyl acetate. This green colored solution is used as an electroactive coating on metals. Two types of high-strength aluminum alloys, AA7075-T6 and AA2024-T3, were tested. Test coupons (5 cm x 5 cm square) were first polished with 600 grit silicon carbide paper, then cleaned with a degreaser and de-ionized water. The polyaniline coating solution was casted on the coupon. A uniform film of the conductive polymer id formed after the solvent was evaporated under room temperature. The