ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY OF ELECTROCOATED ALUMINUM FOOD CANS

Electrochemical impedance spectroscopy (EIS) was used to evaluate in situ the corrosion performance of aluminium food cans coated with two different proprietary coatings, packed with eight different food products and stored for two years. The food products were acidified onions, chicken noodle soup, green beans, pet food, pasta and sauce, sauerkraut, three bean salad, and tomato sauce. Triplicate cans of each variable were measured, giving a total of 48 cans with one impedance spectrum per can. The question was how to reduce each of these EIS spectra to a single numerical value in order to compare the performance of the coatings with the various food products. In this paper, three methods were used to reduce the EIS data to numerical performance indicators: (1) low frequency impedance; (2) break-point frequency; and (3) percent ideal behavior. All three indicators reflected the extent of corrosion and/or coating degradation and were in good agreement with blister ratings obtained by visual examination.