The correlation between substrate mass loss and electrochemical impedance spectroscopy data for a polymer-coated metal

Research has been carried out to evaluate the correlation between substrate mass loss and data generated by electrochemical impedance spectroscopy (EIS). Experiments were carried out as a function of exposure time for both polymer-coated and bare samples. Mass loss was determined in situ and in real time with a vibrating sample magnetometer (VSM). In all cases, the sample was held potentiostatically at the open circuit potential (OCP) while EIS data were collected. Mass loss data calculated from electrochemical impedance (EI) spectra were then compared to equivalent data generated on the VSM. Although previous research has investigated the correlation for bare samples [W. J. Lorenz and F. Mansfeld, Corros. Sci., 21, 647 (1981)] establishing this relationship for a coated substrate is more convoluted. The difficulty results from errors associated with solution uptake within the polymer, and corrosion product entrapment. Such errors obviate the use of traditional gravimetric techniques and, until now, the relationship between substrate mass loss and EIS has not unequivocally been established for polymer-coated samples. Although the current research indicates that EIS can accurately define the mass loss for a bare sample, the correlation for coated samples has, generally, not been as good.