A CONTRIBUTION TO THE UNDERSTANDING OF THE LINEAR-POLARIZATION METHOD

A concise survey of the historical developments and experimental implications of the polarization resistance method is exposed. Some theoretical consideration on the validity of the results. obtained using an approximate function around the free corrosion potential, are given. The theory concerns the representation of the constant corrosion current density I(c) = I(c)(eta) by a series expansion. The validity of the mathematical developments is verified by examining the behaviour of the function i = 0.1 [exp (eta/15) - exp (-eta/30)] mA cm-2. The application of the inversion method of a numerical series is successful and the use of a third-degree polynomial provides a satisfactory evaluation of I(c). The best-fitting of the polarization curves with a fourth-degree polynomial has been examined to illustrate the choice criterion of a suitable approximate function of the form factor F(eta). Examination of the two calibration charts relating to the behaviour of ARMCO iron in 0.5 m and 1 N sulphuric acid solutions. containing some primary aliphatic amines or KCl at different concentrations, at 25-degrees-C. shows that the existence of an empirical relationship of linear type between corrosion current density and polarization resistance is justified.