Effect of Chloride-Doped Polyaniline Content on the Adhesion, Barrier Property and Corrosion Behaviour of Zinc Phosphate Epoxy Primer in 3 wt% NaCl Solution

In the present work, HCl doped polyaniline (Pani-Cl) was chemically synthesized. Chemical structure of Pani-Cl powder was confirmed using UV-visible, infrared spectroscopy and electrical conductivity measurements. Synthesized Pani was added to commercial zinc phosphate primer paint (ZP) to enhance its anticorrosion properties. The anticorrosion performance of coatings containing 0.1- 0.4 wt% polyaniline on carbon steel was evaluated in 3.0 wt% NaCl solution by open circuit potential (OCP), polarization curves and electrochemical impedance spectroscopy (EIS) measurements. The experimental results showed that the coating with 0.2 wt% of Pani-Cl (ZP-Pani0.2) provides higher anticorrosion properties and offers better barrier characteristics in the paint film, as compared with original primer. After a period of 600 hours, carbon steel coated with ZP-Pani0.2 showed good resistance against corrosion (low corrosion rate and high resistance). Besides, the OCP value was higher than that of ZP-coated steel due to the barrier effects of Pani-Cl. However, the use of more than 0.2 wt% Pani-Cl additives reduced the coating's protection efficiency. Paints adhesion was evaluated by cross cut test. It was found that paints containing 0.3 and 0.4 wt% of polyaniline present lower adhesion, as compared with the reference paint.