The effect of mixture of mercaptobenzimidazole and zinc phosphate on the corrosion protection of epoxy/polyamide coating

• 2-mercaptobenzimidazole improved protective performance of epoxy with zinc phosphate.
• Protective function of pigmented coating was affected by organic inhibitor content.
• Corrosion resistance of bare mild steel in NaCl solution was improved by the mixture.
• Solution phase study confirmed deposition of protective layer in the case of mixture.
• Contribution of the pigment and inhibitor to the layer was studied by SEM/EDX.

The protective performance of solvent-borne epoxy/polyamide coatings formulated with zinc phosphate anticorrosion pigment was improved through the addition of 2-mercaptobenzimidazole as an organic corrosion inhibitor. In addition to determining the optimum percentage of mercaptobenzimidazole, the electrochemical impedance spectroscopy data could show the influence of inhibitor concentration on the epoxy behavior within 35 days of immersion in 3.5 wt% NaCl solution. The improved corrosion protection and adhesion strength in the presence of the pigment and inhibitor were connected to the deposition of a protective layer at the coating/substrate interface which might limit active zones for electrochemical reactions. The precipitation was confirmed using electrochemical impedance spectroscopy, polarization curves and SEM/EDX surface analysis.