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 investiga- ted 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-E44 and 0.5% 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 (0.431muA/cm~2) is lower than that of the E44/Q235 carbon steel system (0.928 muA/cm~2)and 0.5% P-E44/Q235 carbon steel system (0.553 muA/cm~2) after 24 hours.During the immersion of 24 hours,the coating capacitances Q_c of the three coatings gradually increase,and the coating resistances R_c and charge transfer resistances R_(ct) gradually 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