Electrochemical impedance spectroscopy investigation of the corrosion at metallic substrates covered by organic coatings

The corrosion protection characteristics of an epoxy-polyamide coating were investigated by electrochemical impedance spectroscopy in immersion tests performed in a 3.0% NaCl solution. Carbon steel and galvanized steel substr ates were employed. A porous film was produced on the metallic substrates, which allows for electrochemically reactive areas to be developed inside th e ports. An effective corrosion-resistant system was produced in the case o f the galvanized steel substrates, due to the precipitation of zinc-contain ing corrosion products that contribute to the sealing of the coating. Conve rsely, no effective protection was round For carbon steel specimens, since in this case the local accumulation of the corrosion products causes swelli ng of the coating.