10158 New Interpretation of Corrosion Behavior of Coated Metals by Combination of Impedance and Scanning Kelvin Probe Measurements

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Product Number: 51300-10158-SG

ISBN: 10158 2010 SG

Author: Ralf Feser, Kathrin Schnier and Svenja Haarmann

Publication Date: 2010

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The corrosion behaviour of organic coatings is often investigated by salt spray test or other industrial tests which combine a salt exposition with constant or alternating climate conditions. To interpret the corrosion behaviour more completely; impedance measurements and Scanning Kelvin Probe measurements were performed. Normally, the results of both electrochemical techniques are interpreted by themselves. Usually the impedance measurements give information about the interphase at the metal polymer coating interface in case of an unscratched organic coating (polymer coating may be is better). Depending on the coating system various resistances and capacities can be determined. Therefore, electrochemical impedance method gives information about the stability of the interface in undisturbed conditions.

With Scanning Kelvin Probe measurements, the potential difference between delaminated and intact surface areas could be determined. This value is a measure of the destruction of the binding between metal and coating. A combination of the results coming out from both techniques gives a new possibility to characterize the quality of coatings and to predict their behaviour in industrial applications. In principal a delamination current will be calculated from the information of charge transfer resistance and potential difference. This approach is demonstrated on two different systems. One system was a model coating system consisting sandwich electrode, the other system was a cathodic dip coating with various pre-treatments. The impedance and Scanning Kelvin Probe measurements will be shown and the results will be used to calculate the delamination current.

Keywords: Organic coating, delamination, electrochemical impedance, Scanning Kelvin Probe