Electrochemical noise analysis (ENA) for active and passive systems in chloride media

Electrochemical noise data (ECN) have been collected for several active systems (mild steel/NaCl, brass/NaCl, Al 6061/NaCl and Al 2024/NaCl) and a passive system (SS 316L/Ringer's solution). The ECN data have been analyzed in the time and frequency domains. Parameters such as the noise resistance R n and the skewness and kurtosis of potential and current fluctuations have been determined from the analysis in the time domain. It has been concluded that the localization index (LI) is not related to a particular corrosion mechanism. Comparisons of spectral noise impedance spectra obtained from power spectral density (PSD) plots with traditional impedance spectra have been made. Good agreement has been observed for all systems after trend removal. Comparisons have also been made between R n and the polarization resistance R p obtained from analysis of the impedance spectra. It has been observed that R n generally is a function of the bandwidth Al of the ECNM. For the passive system SS316L/Ringer's solution R n was much smaller than R p . The relationship between potential and current fluctuations has been evaluated. For the two Al alloys random fluctuations occurred, while for mild steel a systematic trend of potential versus current was observed. After trend removal only random fluctuations remained for this system. It is possible to make corrections of the experimental values of standard deviations of the potential (σV) and current (σI) fluctuations as well as R n assuming linear drift of the potential and current fluctuations.