ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY OF COATED ALUMINUM BEVERAGE CONTAINERS .1. DETERMINATION OF AN OPTIMAL PARAMETER FOR LARGE-SAMPLE EVALUATION

Future environmental regulations will limit the volatile organic content of many coatings, including those used on the infernal walls of aluminum (Al) cans. Thus, the coating industry is interested in rapid development and testing of new coatings. Commercial coating evaluation requires testing of a large number of samples and statistical analysis of data to determine the performance of the population. The present study focused on determining a performance parameter that could be obtained quickly from impedance spectra. An equivalent circuit model (ECM) was developed by examining uncoated Al and coated Al containing intentional defects in chloride (Cl-) solution. Three parameters of the model - coating capacitance (C-c) pore resistance (R(pore)), and low-frequency impedance (determined from data at similar to 0.05 Hz) - were examined for three thicknesses of the same coating. They were evaluated in terms of correlation to visual performance and facility of acquisition. Results indicate the low-frequency impedance was the optimal parameter because it correlated with visual performance and could be obtained readily from the data. A future study will use this parameter to determine the coating performance of a population using statistical methods.