Potentiostatic Pulse Testing for Assessment of Early Coating Failure

Potentiostatic Pulse Testing (PPT) was investigated as a technique to assess the early stage of organic coating failure. Current transients collected from dummy cells and real coated samples were fitted to an exponential decay function to evaluate the values of equivalent circuit parameters. PPT only provided values for only some of the circuit elements, whereas Electrochemical Impedance Spectroscopy (EIS) revealed most values of the assumed circuit elements. However, it was difficult to know a priori whether to use a one- or two-time-constants model for EIS data obtained from the real coated panels. Fast Fourier Transform (FFT) analysis was used to compare the data generated in the two different domains. The impedance spectra from the Fourier transforms was over only a part of the frequency range accessible by the EIS, but the spectra from the two methods exhibited reasonably good agreement.