Adhesion and Cathodic Delamination Properties of Epoxy Coating Reinforced by Magnetite/Hydroxyapatite on Carbon Steel Substrate

In this study, magnetite/hydroxyapatite nanoparticles were incorporated at a concentration of 5 wt.% to enhance both the adhesion strength and cathodic delamination resistance of an epoxy coating applied to a carbon steel substrate. Magnetite/hydroxyapatite (FoHAP) was prepared with varying Fe3O4 to hydroxyapatite weight ratios, ranging from 10 to 50 wt.%. The adhesion test was quantitatively assessed using the pull-off method following the ASTM D4541 standard and qualitative evaluations were conducted using the cross-cut method following the ASTM D3359 standard. The results demonstrated that the coating reinforced with magnetite/hydroxyapatite nanoparticles exhibited a superior adherence compared to both the unpigmented epoxy and the coating with hydroxyapatite alone. Furthermore, assessments of the cathodic delamination process and the electrochemical impedance spectroscopy revealed that the optimized Fe3O4/HAP ratio of 10 wt.% correlated with a reduced area of delamination, indicating the reinforcement in cathodic delamination protection and also the adhesion properties of the nanoparticle-enhanced coating.