An electrochemical impedance spectroscopy technique based on an equivalent circuit used for the evaluation of metallic substratum/organic coating/electrolyte systems as well as the importance of each parameter and the way to calculate it is analysed. It is emphasised that the classical semi circumference in the complex plot, which describes the response of a parallel RC circuit, is not real axis centred. This fact makes it necessary to consider the organic film and electrochemical double layer capacitance as pseudo‐capacitances which depend on a fractional power of the frequency. Starting from mathematical relationships over the total impedance algorithms based on the least squares methods are proposed to fit experimental data requiring less processing time than iterative techniques. The methodology is described analysing the charge transfer resistance, ionic resistance and dielectric capacitance variation at increasing immersion times for naval steel/chlorinated rubber (with different PVC)/artificial sea water systems. Parameters thus obtained correlate well with the naval steel/organic coating deterioration with time, also determined by using corrosion potential measurements and visual assessment.
Ambrosi, V. and Di Sarli, A. (1993), "Development of a mathematical treatment for electrochemical impedance data obtained from coated metals: Part 1", Anti-Corrosion Methods and Materials, Vol. 40 No. 9, pp. 4-9. https://doi.org/10.1108/eb007329Download as .RIS
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