Mixed simultaneous barrier and passivation mechanisms by Cloisite 30B and cerium conversion coating to reinforce the epoxy coating’s adhesion and anti-corrosion properties

Abstract

Increasing the corrosion resistance and adhesion of the organic coatings is always a desire in industrial properties. Thus, in this research, the corrosion resistance properties of epoxy/nanoclay nanocomposites were investigated for their application in organic coatings on metal surfaces. The results demonstrated that the sample containing 1.5 wt% of nanoclay exhibited the highest impedance modulus (1.22 ×108 ohm.cm2) after 4 weeks of immersion in a 3.5 wt% NaCl electrolyte environment. Subsequently, a cerium conversion coating was applied to the surface of st-37 steel under optimal conditions. Electrochemical tests revealed that the corrosion resistance of the surface improved with the application of the cerium conversion coating, resulting in an increase in charge transfer resistance from 1041 to 1742 ohm.cm2. Moreover, the polarization test showed a decrease in current density from 24.9 to 5.4 μA/cm2. Pull-off, salt spray, and electrochemical impedance tests demonstrated that the cerium conversion coating enhanced the adhesion and corrosion resistance of the organic coating system. The epoxy/nanoclay nanocomposite, in its optimal state, was applied to the steel surface modified by the cerium-based conversion coating, confirming the improvement of the optimal coating system. Quantitative results indicated that after 7 weeks of immersion in a corrosive electrolyte, the impedance modulus of the epoxy coating containing 1.5 wt% nanoclay combined with the cerium conversion coating was equal to 1.51 × 1010 ohm.cm2.