The influence of magnetic field on the electrochemical behaviors of coating for EMI shielding in marine environment

Electrochemical impedance spectroscopy (EIS) is applied to research the protection performance of single and double system of Ni/acrylic polyurethane electromagnetic shielding coating which influenced by external magnetic field in 3.5wt% NaCl solution. The stereo microscope and SEM are adopted to represent the surface of Ni/Acrylic polyurethane electromagnetic shielding coating and cross-section morphology characteristics after soaking. The results suggest that magnetic field slows down the performance of the solution diffusion in single Ni-based coating, which delays the decrease of the low frequency impedance |Z|_{0.01 Hz} with the increase of immersion time. It shows that the magnetic field makes Ni particles rearrange inside the coating and reducing the inner coating defects. As for the double-layer system of Ni/Acrylic polyurethane electromagnetic shielding coating, EIS results show that the applied magnetic field makes the low frequency impedance |Z|_{0.01 Hz} fall faster, however, the magnetic field direction has no obvious effect on the low frequency impedance|Z|_{0.01 Hz}. Analysis shows that magnetic field optimize the distribution of Ni in coating and improves the corrosion resistance of electromagnetic shielding coating. But for the failure process of topcoat (Acrylic polyurethane), the magnetic field plays a main role in accelerating the diffusion of electrolyte. In summary, the magnetic field accelerates the corrosion process of double coating system.