The Frequency Dependence of the Noise Resistance for Polymer‐Coated Metals

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Abstract
Electrochemical noise and impedance data for polymer‐coated steel exposed to seawater have been analyzed in the time and frequency domains. Good agreement between spectral noise plots and impedance spectra was observed provided that accurate collection of current noise data was not affected by instrument limitations. The frequency range in which valid spectral noise plots for polymer‐coated steel can be obtained is quite limited compared to impedance plots. The noise resistance equals the polarization resistance only if both the potential and current power spectral density plots have the same slope resulting in frequency independent spectral noise plots. This means that the impedance spectra have to display a dc limit in the frequency region in which noise data are collected, i.e., the sampling frequency f s for collection of noise data must be less than the breakpoint frequency f b related to the dc limit of the impedance spectrum. In general, it has to be concluded that for protective coatings for which impedance spectra are capacitive between 1 Hz and 1 mHz, the frequency region in which meaningful noise data can be collected, is a function of the measurement bandwidth. Therefore interpretation of in terms of a single coating property is not possible.

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