Corrosion rate monitoring of metallic materials using the linear response

Basic concepts concerning the validity, reliability and fields of application of the polarization resistance technique are discussed. The influence of the ohmic drop on the evaluation of the corrosion rate is also considered and a dimensionless quantity is introduced in order to use properly the apparent polarization resistance. The linear polarization technique has been applied to the study of the behaviour of Armco iron in some H 2SO 4 and HCl solutions at various temperatures using the POLAN program which analyses the polarization curve with the NOLI method for computing the values of I c, α and β. Without examining the shape of the polarization curve in the vicinity of ΔE = 0, the value of R p was computed by means of the best-fitting of experimental data over the ΔE interval [−10, 10] mV with the monomial i = R p −1 ΔE. This procedure produces an approximately accurate value of i′(0). The results are compared with those obtained through the use of the exponential form over the same ΔE interval. From this comparison the conclusion is reached that, if the choice of the amplitude of the ΔE interval is proper, the two schemes practically provide the same value of the corrosion rate. In many practical applications, the use of the linear response could be preferred on account of its simplicity.