Analysis of experimental data with the Mansfeld method

Abstract An assessment of the reliability and accuracy of the improved Mansfeld method was made by processing experimental polarization curves for iron in HCl and H 2 SO 4 solutions, having different compositions, at temperatures ranging from 25 to 75°C. Polarization curves were of the current–transient type, each current pulse lasting 0.1 s and being applied when the free corrosion potential reverted very close to its initial value. Experimental values of the electrode potential were corrected to account for the contribution of the ohmic drop and experimental polarization curves were generally fitted over the Δ E interval ±50 mV with a polynomial of the fourth degree. For all the examined cases, the values of ln i (Δ E ) u 0 \sinh( u 0 Δ E \2) were computed over a ±45 mV interval at steps of 3 mV. For each case, the root of G ( u 0 ) was determined using the Newton method, the first derivative G ′( u 0 ) being evaluated numerically. The results were very satisfactory and showed that the improved approach is able to provide reliable values of B a , B c , I c and R p , as shown by comparison with values obtained with the NOLI and INTER1 methods. The difference among the three determinations of these quantities was negligible from a practical point of view. For all cases the values of R p , computed with the Mansfeld method, were practically coincident with those of i ′(0) −1 , confirming the fact that the three techniques are self-consistent.