Influence of normal and radial contributions of local current density on local electrochemical impedance spectroscopy.

A new tri-electrode probe is presented and applied to local electrochemical impedance spectroscopy (LEIS) measurements. As opposed to two-probe systems, the three-probe one allows measurement not only of normal, but also of radial contributions of local current densities to the local impedance values. The results concerning the cases of the blocking electrode and the electrode with faradaic reaction are discussed from the theoretical point of view for a disk electrode. Numerical simulations and experimental results are compared for the case of the ferri/ferrocyanide electrode reaction at the Pt working electrode disk. At the centre of the disk, the impedance taking into account both normal and radial contributions was in good agreement with the local impedance measured in terms of only the normal contribution. At the periphery of the electrode, the impedance taking into account both normal and radial contributions differed significantly from the local impedance measured in terms of only the normal contribution. The radial impedance results at the periphery of the electrode are in good agreement with the usual explanation that the associated larger current density is attributed to the geometry of the electrode, which exhibits a greater accessibility at the electrode edge

Modeling coating flaws with non-linear polarization curves for long pipelines

Document type: Part of book or chapter of boo

Numerical simulations for cathodic protection of pipelines

Abstract: Mathematical models may be used for design or evaluation of cathodic protection (CP) systems. This chapter provides a historical perspective and a mathematical framework for the development of such models. The mathematical description accounts for calculation of both on- and off-potentials at arbitrarily located surfaces, thus making this approach attractive for simulation of external corrosion direct assessment (ECDA) methods. The approach also allows simulation of independent CP systems. Application of the model is presented for three cases: (a) enhancing interpretation of ECDA results in terms of the condition of the buried pipe; (b) simulating the detrimental influences of competing rectifier settings for crossing pipes protected by independent CP systems (e.g., rectifier wars); and (c) simulating the influence of coatings and coating holidays on the CP of above-ground tank bottoms. Document type: Part of book or chapter of boo