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 substrates were employed. A porous film was produced on the metallic substrates, which allows for electrochemically reactive areas to be developed inside the pores. An effective corrosion-resistant system was produced in the case of the galvanized steel substrates, due to the precipitation of zinc-containing corrosion products that contribute to the sealing of the coating. Conversely, no effective protection was found for carbon steel specimens, since in this case the local accumulation of the corrosion products causes swelling of the coating.

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