Synergistic effects of GO–Zn–PA fillers on the interfacial barrier properties of composite epoxy coatings: A comprehensive study

A novel composite waterborne coating, GO–PA–Zn/WEC, was successfully prepared by functionalizing graphene oxide (GO) nanosheets with divalent zinc ion Zn(II) and phytic acid (PA) as fillers through the hydrothermal method. FTIR, XRD, SEM-EDS, TEM, TGA, and XPS were employed to demonstrate the successful grafting and/or adsorption of Zn(II) and PA inhibitors on GO surface. Electrochemical impedance spectroscopy (EIS) tests proved that the low-frequency impedance value (|<i>Z</i>|_{0.01 Hz}) of the steel with GO–Zn–PA/WEC coating (1.13 × 10⁶ Ω·cm²) was 5 times as high as that of WEC coatings (2.17 × 10⁵ Ω·cm²). Furthermore, the |<i>Z</i>|_{0.01 Hz} (2.01 × 10⁵ Ω·cm²) even exhibited a magnitude approximately 20-fold of the conventional WEC coating (0.99 × 10⁴ Ω·cm²) after 14 days of immersion, demonstrating superior durability performance. Corrosion products beneath the coatings after 14 days of immersion were also analyzed by SEM, EDS, and XPS. Results reveal that the anticorrosion mechanism basing on synergistic effects of GO–Zn–PA fillers is as follows: (1) physical barrier effect of GO for the intrusion of corrosive species; (2) the protective layer formed by PA and Zn(II) in the defect area at the anode and cathode sites by producing sediment of Fe₍₃−<i>x</i>_)/2H_<i>x</i>PO₄⁽³−<i>x</i>⁾ and Zn(OH)₂, respectively; (3) crosslinking structure of PA–Fe(II)–Zn(II) via chelation. This study provides a simple route for the design and manufacture of highly anticorrosive composite coatings.