Corrosion Rates from Impedance Measurements: An Introduction

Abstract

The majority of published papers dealing with electrochemical impedance measurements adopt a mathematical approach; this has tended to make the subject somewhat esoteric. Here the subject is dealt with in terms of basic impedance concepts and how these may be used to interpret data in relation to a simple equivalent circuit. This is then extended to cover equivalent circuits containing elements exhibiting diffusion controlled behaviour. A range of experimental techniques which may be used to obtain impedance measurements, together with a new corrosion monitor based on the ‘tangential impedance’ technique, are explained. Graphical methods of data interpretation are given that avoid excessive numerical manipulation and which also allow the charge transfer resistance to. be extracted from systems exhibiting mixed diffusion–charge transfer control.