A crevice corrosion study by electrochemical noise analysis

The use of the Electrochemical Noise Analysis (ENA) for the evaluation of c revice corrosion is illustrated in the case of AISI430 stainless steel in 3 % sodium chloride. A crevice former was used in order to induce a crevice c orrosion attack. Current and potential noise signals were simultaneously re corded allowing the determination of the noise resistance (R-n). ENA was able to detect the four stages mechanism of crevice corrosion. The comparison of R-n with the Polarization Resistance (R-p) determined by Elec trochemical Impedance Spectroscopy gave good agreement in particular during the initiation and propagation of the attack. The evaluation of the noise data in the frequency domain gave interesting r esults in particular in the evaluation of the roll-off slopes in the Power Spectrum Density (PSD) plot that are correlated to the corrosive status. Fi nally a new analysis for noise data is shown. The application of spectral r atio discriminant function to noise data in the frequency domain, permits t o deduce the best sampling frequency and sampling duration for ENA acquisit ion, able to discriminate between two different situations.