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 conte nt of many coatings, including those used on the infernal walls of alu minum (Al) cans. Thus, the coating industry is interested in rapid dev elopment and testing of new coatings. Commercial coating evaluation re quires testing of a large number of samples and statistical analysis o f data to determine the performance of the population. The present stu dy focused on determining a performance parameter that could be obtain ed quickly from impedance spectra. An equivalent circuit model (ECM) w as developed by examining uncoated Al and coated Al containing intenti onal defects in chloride (Cl-) solution. Three parameters of the model - coating capacitance (C-c) pore resistance (R(pore)), and low-freque ncy impedance (determined from data at similar to 0.05 Hz) - were exam ined for three thicknesses of the same coating. They were evaluated in terms of correlation to visual performance and facility of acquisitio n. Results indicate the low-frequency impedance was the optimal parame ter because it correlated with visual performance and could be obtaine d readily from the data. A future study will use this parameter to det ermine the coating performance of a population using statistical metho ds.