Performance of zinc-rich coatings evaluated using AFM-based electrical properties imaging

The paper presents the results of investigation of polyvinyl zinc-rich coating exposed to 97% relative humidity atmosphere for 40 days. Condition of the coating and evolution of its protective properties were determined with the novel AFM-based approach capable of providing surface profiles, local dc current maps as well as local impedance spectra. The proposed technique allowed insight into the local changes of coating topography and electrical properties accompanying a transition from purely electrochemical to barrier mechanism of protection. The AFM-based approach made it possible to assess what fraction of the coating surface was covered with non-conductive zinc corrosion products at given stage of exposure and what the advance of transition between particular protection mechanisms was. The results provided additional, complimentary information as compared to the global averaging techniques such as classical electrochemical impedance spectroscopy and electrochemical potential measurements.