Organic coatings Kelvin probe

Again, the Kelvin probe can be used to monitor the local corrosion potential of a partly coated metal surfece in a humid atmosphere. If, for example, the presence of the organic molecule changes the kinetics of the metal dissolution reaction, then this is reflected in a change of the corrosion potential an acceleration of the metal dissolution will shift the corrosion potential cathodically, a retardation will shift the corrosion potential anodically. As an example. Figure 22 shows a map of the corrosion potential of an iron surface that is partly coated by one monolayer of octadecylsilanol as measured with the Kelvin probe in a humid atmosphere [87]. The corrosion potential changes locally by several 100 mV due to the presence or absence of the film and it has been proved that the anodic potentials correspond to the areas that are coated by the polymer [53]. The potential plot of Figure 22 is therefore a representation of the inhibition of the anodic metal dissolution in a humid atmosphere. 

Other than for electrodes immersed in bulk electrolyte, on electrodes covered by ultrathin layers the electrode potential may differ significantly across the electrode surface. Hence, localised measurements are of interest, being performed by scanning the tip across the sample. This was first applied for organic coated metals where the coating was electrochemically delaminating, driven by corrosion [12-14, 29], Even on the submicron scale the Kelvin probe technique can be applied for such studies, and then based on a modified atomic force microscope, see [34, 35]. Recent developments are the combination of Kelvin probe and SECM [36] and the use of Kelvin probe for hydrogen detection [37]. 

G. Williams, H. N. McMuiray, and D. A. Worsley, Cerium(III) inhibition of corrosion-driven organic coating delamination studied using a scanning Kelvin probe technique , J. Electrochem. Soc., 149, B154 (2002). 

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