Study on corrosive electrochemical behaviors of zinc-rich and graphite-filled epoxy coatings in 3.5 wt% NaCl solution

Environment behaviors and degradation mechanisms of two organic epoxy coatings coated on carbon steel sheets in 3.5 wt% NaCl neutral solution were studied by electrochemical impedance measurements and atomic force microscopy (AFM). The results showed that the coating resistance (R(p)) of the graphite-filled epoxy coating tested, which presents the film barrier performance, is higher than those of 6101 epoxy resin for initial seawater immersion, but the coating resistance of the zinc-rich epoxy coating was lower than that of 6101 epoxy resin. After salt spray tests, zinc-rich epoxy coating coated on the metal still has good anti-corrosion performances due to the existence of protection effects called electrochemical and chemical protection. Those behaviors and degradation mechanisms of two coatings can be explained by a series of measured electrochemical impedance spectroscopy measurements, and two equivalent circuit models were proposed to explain the degradation processes of the two organic coatings.