7 - The Use of a.c. Techniques in the Study of Corrosion and Passivity

Abstract

This chapter describes the application of electrode impedance analysis to kinetic studies of corrosion, passivation, and the passivity process. One of the most classical and easy methods for studying the electrode kinetics is the plotting of the steady-state current-potential polarization curve. This curve shows the overall reaction rate, according to Faraday's laws, with respect to potential. For a very simple electrode process—for example, a single electron transfer reaction—the steady-state polarization curve allows the electrode kinetics to be analyzed thoroughly. However, electrochemical systems are much too intricate to be investigated by this method alone. To acquire further experimental information about electrode kinetics, various nonsteady-state methods are introduced. In these methods, time plays the role of an additional parameter to the current and the potential. Among nonsteady-state techniques such as chronovoltammetry, chronoamperommetry, and cyclic voltammetry, impedance methods are characterized by the use of a perturbing electrical signal whose amplitude is vanishingly small, that is, the interfacial electrical characteristics are linearized.