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1992
Conference Paper
Titel
Assessing protective layers on metal packaging material by electrochemical impedance spectroscopy -EIS-
Titel Supplements
Paper no. 25
Abstract
In electrochemistry the alternating current (AC) methods enlarge the possibilities of electrochemical analysis especially in the case of barrier layers such as coatings on metal surfaces. However, the frequency dependent resistance (impedance) expressed by amplitude and phase angle (Phi) is a very complex parameter referring to a combination of different resistance elements. Therefore the interpretation of EIS-spectra must be aided by using equivalent circuit models fitting the experimental results. At ILV, an equivalent circuit model has been developed, which enables excellent phase sensitive simulation (PSS) of impedance spectra to obtain full information about the coating properties. The model is consistent throughout time-dependent degradationsof coatings and is used preferrentially to assess protective properties by short time testing. Due to the high sensitivity of impedance measurements the individual sample performance, depending on coating porosity or failures, renders more di fficult the evaluation of general coating characteristics. Short time testing of a sufficient number of parallel samples will give more valid results. A rapid test procedure including intermediate cathodic treatment by direct current (DC) has been introduced. This AC/DC/AC method can be applied also as 2-pole-measurement directly on coated metal surfaces.
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