Analogue circuit of the inductive polarization resistance

The electrochemical techniques used to measure metallic corrosion rely on making a direct electrical contact to the working electrode. The inductive or non-contacting method is based in the application of an external electrical signal that does not need to make physical contact to the metal to polarize it. In previous papers, its feasibility has been justified for inducing such external polarization and furthermore, to use it to obtain the polarization resistance. It has also found that the inductive Rp (called Rpi) agrees with the gravimetric losses in certain electrolyte/metal systems. In the present paper the best analogue circuit modelling the phenomenon is justified. The signal, when externally applied, first induces a resistive response and later polarizes the metal and charges the double layer. This is verified experimentally and modelled by using dummy circuits and a finite element model. In order to correctly reproduce the process, an interfacial element with the properties of the double layer has been introduced in the FE model. Without this interfacial element the response is purely resistive. The circuit found to best fit the experiments considers a resistance in series with an element having another electrolyte resistance element in parallel to a Randles circuit. This means that the applied current runs first through the entire electrolyte and the bar and then the metal polarizes having in parallel an electrolyte resistive component.