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This paper describes a study of electrochemical measurements that included the analysis of potential noise fluctuations recorded during the free corrosion of a strain-hardened aluminum alloy exposed to an aerated saline solution. The analysis of spontaneous electrochemical noise (EN) generated during these experiments was made by various analysis techniques specifically designed to reveal the stochastic and fractal nature of signals and shapes. The paper demonstrates how rescaled range analysis and stochastic process detector techniques can serve to highlight features present in the frequency domain of transformed data records. It is also shown that the corrosion cell made with aluminum exposed to an aqueous aerated saline solution is an excellent source of noise, which can be easily varied by changing the pH of the solution to force depassivation phenomena. The analysis of spontaneous EN by complementary methods is demonstrated to be a practical approach for the identification of the physical phenomena causing the EN. It is also demonstrated that monitoring the electrochemical impedance spectroscopy behavior in parallel to EN can be valuable because it helps to establish some fundamental correlations in real time and define the sensitivity of each technique under similar conditions. In the present study, the drastic changes recorded by EN measurements when the solution pH was slightly reduced are indicative of the tremendous sensitivity of EN monitoring to changes in the corroding environment.
electrochemical noise, stochastic, chaos, depassivation, aluminum corrosion, analysis methods
Professor, Royal Military College, Kingston, Ontario