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

A brief review is given of the application of AC impedance measurements to electrochemical processes. 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 characterize 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 ωZ″ or Z″/ω, where Z″ is the imaginary part of the impedance and the frequency f is expressed as ω = 2πf. Additional methods of analysis include evaluation of the frequency dependence of the series resistance R_s and series capacitance C_s, the absolute value of the impedance |Z| and the phase angle δ. 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.