Corrosion monitoring of galvanised coatings through electrochemical impedance spectroscopy

In this work, corrosion of industrial galvanised coatings is monitored through potentiodynamic and electrochemical impedance spectroscopy (EIS) methods and supported by real-time immersion tests. For such purpose, the corrosion behaviour is studied in different media (NaCl, NaOH and rain water), at different concentrations and varying immersion times. The results show that EIS allows to establish the interfacial reactions and the dissolution mechanisms occurring in three corrosive media, hence to foresee the protection conferred by these coatings. The impedance diagrams of the coated steel do not provide information on the slowest reactions, which only occur in natural rain water. Finally, each Zn/medium interface is characterised by a specific equivalent circuit giving a similar impedance response.