The processing of experimental data with the harmonic method

Abstract

A method for evaluating I c, B a and B c, and based on the expansion of i (Δ E) in a Fourier series of cos ωt 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 V 0 ranging from 4 to 32 mV and performing numerical integration using the Simpson method. Results for I c=3 mAcm −2, B a=40 mV and B c=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 I c, the values of B a and B c reproducing faithfully the true ones only when V 0<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 I c, B a and B c with those obtained for the same cases with the NOLI method. All polarization curves were usually best-fitted over the Δ E [−50,50] mV interval with a polynomial of the fourth degree. The results were very promising, being the values of I c, B a and B c 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 I c, B a and B c on V 0 is negligible when the linear approximation works properly.