Embedded electrode electrochemical noise monitoring of the corrosion beneath organic coatings induced by ac–dc–ac conditions

The degradation of urethane topcoat/epoxy primer systems used for military aircraft and industrial applications were monitored using the electrochemical noise method and measured with embedded electrodes. The degradation was induced by the ac–dc–ac method. The trend in the noise resistance parameter was consistent with the trend in the low frequency impedance modulus obtained from electrochemical impedance spectroscopy experiments. The localization index was not informative about the corrosion mechanism. However, the two shot noise parameters, average charge of event and event frequency, were able to characterize the corrosion process beneath the coating. There was a change from uniform corrosion to localized corrosion on the metal substrate associated with the aircraft coating as indicated by the decrease in frequency event as this coating failed. There was an increase in the charge per corrosion event of the substrate of the industrial coating indicating that the uniform corrosion occurring became more severe as the coating failed.