The charge transfer reaction in Nyquist diagrams of painted steel

When applying the AC impedance technique to metal-paint systems, it is of interest to identify the corrosion reaction of the metallic substrate in the arcs appearing on the complex plane of the Nyquist diagrams. This article shows how difficult it sometimes is to obtain direct information on this reaction on the basis of the diagrams obtained. The use of peelable films has been demonstrated to be very useful for this research. With these films it is possible to separate the effect of the metallic substrate from that of the film in the impedance diagrams, first measuring with the film adhered to the metallic surface and then with the same film detached from the substrate.