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

Electrochemical noise data (ECN) have been collected for several active sys tems (mild steel/NaCl, brass/NaCl, Al 6061/NaCl and Al 2024/NaCl) and a pas sive 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 po wer spectral density (PSD) plots with traditional impedance spectra have be en made. Good agreement has been observed for all systems after trend remov al. Comparisons have also been made between R-n and the polarization resist ance R-p obtained from analysis of the impedance spectra. It has been obser ved that R-n generally is a function of the bandwidth Deltaf of the ECNNI. 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 ev aluated. For the two Al alloys random fluctuations occurred, while for mild steel a systematic trend of potential versus current was observed. After t rend removal only random fluctuations remained for this system. It is possi ble to make corrections of the experimental values of standard deviations o f the potential (sigmaV) and current (sigmaI) fluctuations as well as R-n a ssuming linear drift of the potential and current fluctuations. (C) 2001 El sevier Science Ltd. All rights reserved.