Modelling of the thin organic film/carbon steel interface

Abstract

The electrochemical impedance spectroscopy (EIS) has been used for the modelling of the alkyd organic film/carbon steel interface in 3% NaCl solution. Both the dielectric properties of the organic film and the corrosion processes of the metallic substrate were investigated with this method. Analysis of the impedance spectra (Nyquist and Bode plots) and the interpretation with the fitting software developed by Boukamp, established the presence of two time constants in the first 250 immersion hours. One time constant concerning the organic layer describes the electrical and barrier properties of film. The second time constant concerning the substrate represents the corrosion reactions at the film/metal interface. For long immersion periods, after the formation of the conductive pathways in the film and the development of the diffusion processes, are necessary another two time constants concerning these phenomenons. The error magnitude between the measured and calculated data with these electric equivalent circuits is satisfactory. The physical properties obtained from the principal elements of the equivalent electric circuits are in concordance with those obtained from others testing methods.