Corrosion protection of epoxy coatings containing 2-hydroxyphosphonocarboxylic acid doped polyaniline nanofibers

The corrosion of metals always has been a severe problem and therefore the development of anti-corrosion coatings has become a spontaneous pressing issue of the moment. In this paper, the anticorrosive properties of 2-hydroxyphosphonocarboxylic acid doped polyaniline (HPA-PANI)/epoxy composite coatings on low carbon steel were investigated. Firstly, HPA-PANI was successfully synthesized by oxidative polymerization. The characterization results exhibit that the average diameter of HPA-PANI nanofibers is approximate 50 nm. According to the polarization curve and the EIS test, the performance of the composite coating was greatly improved compared to the pure epoxy coating. The composite coatings slowed down the penetration of electrolytes and aggressive ions, and improved the corrosion resistance. These were attributed to the redox ability of PANI. After immersion in 3.5 wt% NaCl solution for 30 days, the corrosion layers of the coatings were characterized by SEM-EDS and XPS. We found that 1.0 we% of HPA-PANI/epoxy coating had the best protection performance and self-healing function due to the passivation of PANI and the chelation of dedoped HPA ions with iron ions. Therefore, we propose a plausible model to describe the anti-corrosion mechanism of HPA-PANI, and analyze the role of doped ions (HPA) in the corrosion process.