Effect of zinc anodes on the behaviour of antifouling coatings applied on copper alloys

This study investigates antifouling coatings for the corrosion protection of bronze propellers in pleasure boats, cathodically protected by sacrificial anodes. Currently, no standards exist to evaluate their resistance to cathodic delamination. This work develops a specific testing procedure using electrochemical methods to assess cathodic delamination in coated bronze panels. Samples with various antifouling formulations were characterized for cathodic disbonding resistance and barrier properties, with coating morphology analysed via SEM. Accelerated cathodic disbonding tests in artificial seawater at −2 V vs Ag/AgCl were evaluated through Potentiodynamic and Potentiostatic Polarization and Electrochemical Impedance Spectroscopy (EIS).

Results showed that increasing pigment volume concentration (PVC) in the primer enhanced delamination resistance by limiting aggressive species transport. Adding a silane adhesion promoter further reduced delaminated areas and improved adhesion, though slightly reducing barrier properties due to increased water uptake. Replacing a graphite-containing topcoat with a titanium dioxide-based (white) one significantly improved both barrier properties and cathodic disbonding resistance. EIS confirmed that titanium dioxide coatings exhibited higher impedance than graphite-rich ones, due to the absence of conductive regions in the white topcoat.