THE DETERMINATION OF THE ELECTROCHEMICAL PARAMETERS AND SOLUTION RESISTANCE VALUES BY A NON-LINEAR METHOD

Abstract

The mathematical developments of a numerical method proposed to process experimental polarization curves, which exhibit the characteristic Tafel behaviour, in order to compute the values of B a , B c , i c o r and R s are discussed in detail and the basic relationships for its correct application are given. Examination of some simulated polarization curves, described by values of R s ranging from 0.01 to 100 and values of i c o r equal to or less than 30 mAcm - 2 , showed that this method works properly and reproduces faithfully the actual values of the four parameters, independently of their initial values. Experimental applications concern the behaviour of iron in 1 N H 2 SO 4 solutions containing KCl at various concentrations and 25°C. The experimental polarization curves were of the current-transient type and the values of the solution resistance were determined by performing sinusoidal current measurements at a frequency of 10 4 Hz. The method was successful to provide the correct order of magnitude of R s for various systems, whereas the values of B a , B c and i c o r were in good agreement with those obtained using the NOLI method. However, for four cases R s took negative values, but the values of B a and B c did not differ significantly from the expected ones. Even if negative values of R s are unacceptable, from a mathematical point of view in these four cases the method worked properly, the three numerical sequences always attaining convergence. Such results seem clearly to indicate that the accuracy and reproducibility of experimental data play a very important role to process successfully polarization curves. At last, Rs must keep the same value throughout the performance of a polarization curve of the current-transient type.