Spectral analysis of electrochemical noise with different transient shapes

The noise spectra under different transient shapes were calculated and the relationship between the spectral parameters (roll-off slope and roll-off frequency) in the frequency domain and the transient variables in the time domain were analyzed. The influence of corrosion types on noise spectra was considered. It is shown that a 'white' noise always appears in the low-frequency range of the noise spectrum and the roll-off slope of the spectrum in the high-frequency range depends on the transient shape, not the corrosion type. During pitting, the roll-off frequency of the noise spectrum is directly related to the time constant of the exponential function contained in the noise transient in the time domain and reflects the repassivation or growth rate of the metastable pits. For the triangular- and delta-shaped transients generally generated during passivity or general corrosion, the roll-off frequency is related to the time interval of the current transient during the current rise or drop stage. Although spectral analyses can extract useful information from the noise transients, the spectra cannot display the difference of any two transients that are symmetrical in shape in the time domain. (C) 2000 Elsevier Science Ltd. All rights reserved.