00418 ELECTROCHEMICAL NOISE ANALYSIS (ENA) FOR ACTIVE AND PASSIVE SYSTEMS

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Product Number: 51300-00418-SG

ISBN: 00418 2000 CP

Author: F. Mansfeld, Z. Sun, E. Speckert and C. H. Hsu

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Electrochemical noise data (ECN) have been collected for three active systems (mild steel/NaCl, A1 6061/NaCI and A1 2024/NACl) and a passive system (Ti-6A1-4V/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, but reflects the degree of similarity of the corrosion kinetics of the two electrodes used for the electrochemical noise measurement (ECNM). Comparisons of noise impedance spectra with traditional impedance spectra have been made. Good agreement has been observed for the passive system, but not for the active systems. 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 delta f of the ECNM. For the passive system Rn was much smaller than Rp. The relationship between potential and current fluctuations has been evaluated for all four systems. For the two Al alloys random fluctuations occurred, while for mild steel a systematic trend of potential vs. current was observed. For the Ti alloy noise from the measurement system seemed to dominate the ECN data. Keywords: steel, aluminum alloys, titanium alloy, electrochemical noise, electrochemical impedance.