Preparation and corrosion protection of three different acids doped polyaniline/epoxy resin composite coatings on carbon steel

In this investigation, the corrosion resistances of hydrochloric acid (HCl), p-toluenesulfonic acid (TSA) and dodecylbenzene sulfonic acid (DBSA) doped polyaniline (PANI)/epoxy resin (EP) composite coatings on carbon steel were studied. Firstly, HCl, TSA and DBSA doped PANIs were obtained using chemical oxidative polymerization, respectively. The structures of PANIs were characterized by optical analytical facilities, and the electrochemical reversibility and stability were investigated by cyclic voltammetry. Subsequently, the as-prepared PANIs as fillers were added into epoxy resin by solution blending and PANI/EP composite (PEC) materials with two-component were coated on the surface of carbon steel. The corrosion resistance of EP and PEC coated carbon steels in 3.5 % NaCl solution was evaluated by electrochemical corrosion measurements, the obtained corrosion parameters reveal that the introduction of PANI fillers with redox ability could enhance the corrosion resistance of epoxy resin. PEC-DBSA coating is more protective than PEC-TSA and PEC-HCl coatings with corrosion rate of 0.04 mm/year and protection efficiency of 97.65 %. After immersing the scratched PEC coatings in 3.5 % NaCl solution for 90 days, it was found from the SEM characterization that the carbon steel surface beneath PEC-DBSA coating has a uniform, dense and continuous passivation film. The excellent corrosion protection of PEC-DBSA coating was ascribed to the formation of a layer thickened passivation film on carbon steel surface by the highly conductive PANI-DBSA through the reversible-stable redox reaction, and the barrier effect increased by the compatibility of small particles size PANI-DBSA with epoxy resin. Therefore, a conclusion was depicted that organic acid doped PANIs possessed higher electrical conductivity and redox activity, which is suitable to be used as corrosion inhibitor of epoxy resin coatings.