Electrochemical noise analysis (ENA) for active and passive systems in chloride media
By Murray, J.N; Stephenson, L.D & Kumar, A
Published in Electrochimica Acta
2001
Abstract
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 Rn 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 Rn and the polarization resistance Rp obtained from analysis of the impedance spectra. It has been observed that Rn generally is a function of the bandwidth Δf of the ECNM. For the passive system SS316L/Ringer's solution Rn was much smaller than Rp. 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 Rn assuming linear drift of the potential and current fluctuations.