Applications of the scanning vibrating electrode technique to the study of corrosion protection by conducting polymers

Due to environmental and human health concerns associated with chromate-containing coatings, the need to find replacements is essential. One promising strategy to achieve this goal is to use electroactive-conducting polymers as corrosion inhibition coatings.;Two forms of solvent-soluble polypyrrole coatings (poly(3-octyl pyrrole) and poly(3-octyldecyl pyrrole)) on metals were studied by SVET. On cold-rolled steel, oxidation currents occurred within a defect, and reduction currents were distributed uniformly across the conducting polymer surface. The corrosion delay time was significantly longer than that of a chromated-epoxy coating. On Al 2024-T3, after a significant delay from the time of initial immersion, oxidation current occurred at the polymer surface, and reduction current was distributed within the defect area. The oxidation process appears to involve removal of metal from copper-rich regions of the alloy surface beneath the poly(3-octyl pyrrole) (POP) coating. It is suggested that the polymer provided thermodynamic assistance to the oxidation process through metal ion complexation; alternatively, metal ions may be transported through the coating to the electrolyte. Results of SVET studies on a POP-coated Al/Cu model alloy are also presented. The SVET results of POP primer with a topcoat (polyurethane or epoxy) on Al 2024-T3 showed that no significant oxidation occurred in the defect during the period of immersion, indicating that the conducting polymer/topcoat provided excellent corrosion protection and could potentially be used to replace chromated coatings. The current density distribution on poly(3-octyldecyl pyrrole)-coated Al 2024-T3 was similar to that on POP-coated Al 2024-T3.;The SVET and EIS results of two electrodeposited polypyrroles (one doped with Tiron (Ppy-Tiron) and one doped with p-toluene sulfonate (Ppy-PTS))-coated Al 2024-T3 showed that the Ppy-Tiron coatings provided better corrosion protection than the Ppy-PTS-coated Al 2024-T3. The results are attributed to the stronger adhesion of the Ppy-Tiron with the Al substrate, and the higher conductivity and less overoxidation of the Ppy-Tiron polymer than that of Ppy-PTS.;Two forms of polyaniline (emeraldine base (EB) and a fully doped sulfonated water soluble polyaniline (NSPAN))-coated Al 2024-T3 were also studied by SVET, with the results indicating the two polyanilines have the ability to delay the onset of corrosion within a defect.