Evaluation of corrosion protection by polymer coatings using electrochemical impedance spectroscopy and noise analysis

Abstract

The degradation of different polymer coating systems on steel exposed to natural (NS) and artificial (AS) seawater has been monitored using electrochemical impedance spectroscopy (EIS) and electrochemical noise analysis (ENA). The aim of this project is to determine the impact of microorganisms on the degradation of the protective properties of polymer coatings on steel during exposure to NS. The marine test sites were Port Hueneme, California and Key West, Florida. A new approach has been developed to obtain electrochemical impedance spectra and noise data via modem from the laboratory using equipment placed at the remote test sites. Potential and current noise data were determined simultaneously. The experimental approach is described and representative data from exposure to NS and AS are presented for coating systems with different combinations of primers and topcoats. Electrochemical noise data have been analyzed in the time and frequency domains. Noise data presented as spectral noise plots have been compared to impedance spectra in Bode plots. The noise resistance R n was found to be independent of frequency and equal to the polarization resistance R p only for frequency-independent spectral noise plots. The limitations of ENA resulting from the limited available bandwidth compared to EIS have been discussed.