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