Application of Impedance Spectroscopy to Study the Atmospheric Corrosion of Galvanized Steel Coated With Epoxy Paint

Many investigators have studied the atmospheric corrosion of polymer-coated metal by electrochemical impedance spectroscopy using an extraneous electrolyte. It is now possible to eliminate this electrolyte and obtain impedance spectra in situ using a monitor. This monitor is made by depositing a 400 nm thick gold layer to cover 10% of the surface of a painted metal. This monitor was used to study the influence of SO sub 2 and Cl exp - on the atmospheric corrosion of galvanized steel coated with an epoxy-polyamide coating. SO sub 2 concentrations in the ppb range were used in a specially designed atmospheric chamber. An indoor version of the so-called scab test was used to study the influence of Cl exp - ions. Impedance spectra obtained using this monitor provided an insight into the processes occurring at the coating /substrate interface. The monitor is an efficient tool for studying the atmospheric corrosion of polymer-coated metals.