Corrosion protection of aluminum alloy (AA2219-T6) using sulfonic acid-doped conducting polymer coatings

Abstract

In this paper, the corrosion protection behaviour of epoxy blended sulfonate-doped polyaniline and polypyrrole coatings deposited on aluminum alloy AA2219-T6 substrates was studied by exposure to artificial seawater. Sulfonate doped-PANi and -PPy were successfully synthesized by oxidative polymerization. The synthesized particles were investigated using SEM, TEM, FTIR, TGA and DRS, whilst their coating performance was studied using a combination of EIS, potentiodynamic polarization, X-ray diffraction and FT-IR spectroscopy. An appropriate quantity of organic fillers, namely p-toluene sulphonic acid (p-TSA), camphor sulphonic acid (CSA) and sulfosalicylic acid (SSA), were mixed with the corresponding conductive polymers (CPs). Acid-doped polyaniline (PANi) and polypyrrole (PPy) were blended in epoxy matrices and coatings were applied on AA2219-T6 to assess the passivation of the metal surface towards corrosion. The optimal concentration of 1 wt% dopant resulted in low levels of corrosion impact on exposure to seawater for 14 days. The improved anticorrosion performance of the composite coatings compared to neat epoxy as revealed through EIS and Tafel tests was attributed to the redox ability of PANi and PPy. Sulphonate-doped CP composite coatings further reduced the penetration of aggressive ions from the electrolyte. 1 wt% of p-TSA-PANi/epoxy coating provided the best corrosion protection and the proposed healing function due to the passivation of PANi along with the chelation of doped H ions with iron ions. Hence, we propose a plausible model to describe the anti-corrosion mechanism of doped-PANi and examine the role of doped anions in the corrosion process.