Recording and Analysis of AC Impedance Data for Corrosion Studies * I. Background and Methods of Analysis

Abstract

A brief review is given of the application of AC impedance measurements to electrochemical proc­ esses. Only very few applications for corrosion processes have been reported. The background and various methods of analysis of AC impedance data are discussed. The parameters which char­ acterize the corrosion behavior can be determined from plots of the frequency dependence of the impedance in the complex plane which result in semicircles for very simple cases. These parameters can also be determined from straight line plots of the real part Z' vs wZ or Z..k», where Z.. is the imaginary part of the impedance and the frequency f is expressed asw = 2rl. Additional methods of analysis include evaluation of the frequency dependenceof the series resistance R. and seriescapacitance C.' the absolute value of the impedance IZI and the phase angleo. Experimental results obtained with a system for automatic recording and analysis of impedance data are given for a dummy cell which represents a corroding electrode.