Correlation between electrochemical impedance and noise measurements of waterborne coatings

A modified equivalent electric circuit is proposed to establish correspondence between impedance and noise measurements in waterborne coatings in saline media (NaCl). The polarization resistance (Rp) given by the impedance modulus when frequency approaches to zero can not directly be compared with noise measurements since this latter accounts only for the pore resistance of the paint of low barrier protective coatings while Rp parameter represents the sum of all the resistances at the system. The results have shown that the pore resistance data can be attributed to noise resistance when (i) the coating exhibit porosity presenting diffusion mechanism as rate-determining step, and (ii) when the sampling frequency of recorded data gives a Nyquist frequency of 1 Hz.