requires the examination of large numbers of cans to ensure that a statistically significant result is obtained.
Electrochemical measurements have been used toThe use of ac impedance measurements in the study of investigate the corrosion resistance of food cans coated metals has increased greatly in recent years.2 produced from a steel-polymer laminate material, Electrochemical impedance spectroscopy (EIS) instrumen-Ferrolite, over periods of up to 30 days. The aim of tation allows the impedance of the metal/coating/electrolyte this work was to develop a predictive corrosion test interface to be measured over a wide frequency range. procedure, whereby short term results could be Under favourable conditions, a clear resolution of the used to predict long term container performance.parameters associated with the coating, the corrosion Electrochemical impedance spectroscopy (EIS) and reaction, and any diffusional processes occurring near the dc linear polarisation techniques were used to study surface may be achieved.2 It was the aim of the work the effect of increasing polymer laminate film described here to determine the suitability of the EIS thickness, and to compare Ferrolite performance technique as a predictive corrosion test method for food with that of a conventional vinyl organosol lacquer.cans, in which short term EIS results are used to predict Testing was carried out using a sealed in electrode long term container performance. In so doing, an attempt system, where electrodes were fitted to commercial has been made to correlate short term electrochemical can ends before filling. This electrode system was measurements with long term iron pickup data established found to perform well over a 30 day period, and the through shelf life storage trials. Used in conjunction with results indicate that Ferrolite cans possessed a an experimental database the EIS technique could become significantly greater resistance to corrosion than a powerful tool, the principal benefit being to minimise the conventionally lacquered cans. Predictably, as the time between the initial development of a novel coating Ferrolite film thickness increased, coating and and its commercial implementation. polarisation resistance values also increased. UnderTraditionally, steel cans have been manufactured from a pack test conditions, coating and polarisation tinplate material, but more recently an electrochromium resistance parameters initially decreased rapidly, coated steel (ECCS) or tin free steel (TFS) substrate has which is consistent with hydration and ion been developed.3-5 In order to provide an additional degree migration processes occurring within the film. After of corrosion protection, organic lacquers are applied to the 30-40 days, the rate of change in resistance internal surface of ECCS cans. A further development in decreased and was consistent with longer term can technology has seen the emergence of polymer laminate degenerative effects such as corrosion. Coating coatings applied to the ECCS substrate.6 Considerable resista...
