The processing of experimental data with the harmonic method

A method for evaluating Ic, Ba and Bc, and based on the expansion of i (ΔE) in a Fourier series of cosωt is proposed and the main mathematical developments are expounded. Some considerations on the accuracy of processing theoretical and experimental data are given and procedures to obtain faithful results are suggested. The validity and accuracy of the method was assessed by processing theoretical polarization curves for values of V0 ranging from 4 to 32 mV and performing numerical integration using the Simpson method. Results for Ic=3 mAcm−2, Ba=40 mV and Bc=80 mV show that using a suitable approximation of h (t), g (t) and f (t) it is possible to compute very accurately the value of Ic, the values of Ba and Bc reproducing faithfully the true ones only when V0<24 mV. The goodness of the method in processing experimental data was checked by examining the behaviour of various systems with corrosion rates ranging from 0.060 to 26.405 mAcm−2 and comparing the values of Ic, Ba and Bc with those obtained for the same cases with the NOLI method. All polarization curves were usually best-fitted over the ΔE [−50,50] mV interval with a polynomial of the fourth degree. The results were very promising, being the values of Ic, Ba and Bc rather close to those provided by the NOLI method, and indicated that the present approach is a valid tool to process polarization curves relating to a wide class of electrochemical systems. At last, it was proved that the dependence of Ic, Ba and Bc on V0 is negligible when the linear approximation works properly.