Random and systematic error as a function of sample area in electrochemical impedance spectroscopy data

The goal of this study was the evaluation of random and systematic error sources in electrochemicalimpedance spectroscopy (EIS) measurements that originate from the EIS equipment and measurementprotocol in contrast to errors related to the coating/metal system. By using well-defined, homoge-neous, and defect-free polyvinylfluoride (Tedlar) release films, highly reproducible EIS spectra couldbe obtained. Thus, it was thus possible to study data variability originating from the EIS measurementprocedure while keeping the film/metal system constant. Parameters gained from EIS spectra such asfilm resistivity, dielectric constant and exponent n of the non-ideal capacitance were evaluated as a func-tion of sample area and compared to reference material properties. For larger sample sizes the valuesobtained by EIS experiments correlated well with the reference values, validating the EIS technique forthe determination of absolute values for electrical properties of coatings. However, to obtain an accuratevalue for film resistivity and relative dielectric constant, a sample area of at least 11.4 cm2was necessaryto avoid the introduction of measurement artifacts. The implications of the findings for corrosion testingwith small sample areas (e.g., as used in high-throughput corrosion testing) are discussed.