The computer has made the collection and interpretation of data easier. The advent of computer controlled instrumentation made it possible to easily acquire electrochemical impedance data; unfortunately the complex nature of the data made it difficult to interpret. One classical approach to interpretation is to hypothesize an equivalent circuit to model the electrochemical system. Since the equations and algorithms of electrical circuits are well defined, a computer program can do an excellent job of modeling these equivalent circuits. We will discuss how the use of a commercially available impedance modeling program can be used in the interpretation of real impedance data.
Cinnamaldehyde is known to act as an inhibitor to steel corrosion in hydrochloric acid. The mechanism for protection is assumed to be twofold. The chemisorption of trans-cinnamaldehyde (TCA) is usually proposed as the major contributor to inhibition. A secondary, but significant, contribution is caused by the polymerization of the TCA to form a film. Growcock and Lopp [ 1 ] have studied the nature of these two mechanisms. They showed through corrosion rate studies, organic analysis, NMR, FT-IR and GC/MS the nature and function of the organic film formed by TCA.
We have studied the film formation of TCA on 1018 steel in HCL solutions using electrochemical impedance spectroscopy. Experiments were run to try to distinguish the difference between the two major inhibition mechanisms. The impedance spectrum of an adsorbed TCA diffusion barrier should differ from the spectrum of either a polymer film or a combination polymer film and diffusion barrier. The Equivalent Circuit modeling program of Boukamp  was used to assist in interpretation.