Corrosion Resistance of Epoxy Phosphate/Waterborne Epoxy Coatings on Steel

The preparation of an inhibitor used for waterborne epoxy coating and its corrosion resistance were investigated in this research.Waterborne epoxy phosphate was synthesized by the reaction of bisphenol A epoxy resin and phosphoric acid and then neutralization using N,N-dimethyl ethanolamine.Three different coatings(E44,0.2% P-E44and0.5% P-E44)were obtained by adding epoxy phosphate into the two-component waterborne epoxy resin.The protective performance of epoxy phosphate/waterborne epoxy coatings based on Q235 steel immersed in 3.5% NaCl solution was investigated by polarization curves and electrochemical impedance spectroscopy(EIS).The results show that the corrosion current density of the 0.2% P-E44/Q235 carbon steel system(0.431μA/cm2)is lower than that of the E44/Q235 carbon steel system(0.928μA/cm2)and 0.5% P-E44/Q235 carbon steel system(0.553μA/cm2)after 24 hours.During the immersion of 24 hours,the coating capacitances Qcof the three coatings gradually increase,and the coating resistances Rcand charge transfer resistances Rctgradually decrease.Epoxy phosphates can significantly improve the corrosion resistance of waterborne epoxy coatings on Q235 steel.The epoxy phosphate content of 0.2% achieves high corrosion protection performance.