Application of EIS and SKP methods for the study of the zinc/polymer interface

Electrochemical impedance spectroscopy (EIS) and Scanning Kelvin probe (SKP) were applied to study the zinc/polymer interface. The coating capacitance and the drop of potential across the zinc/epoxy interface are investigated as a function of water penetration and hydrolysis of adhesion bonds. Water penetrates to the interface, decreasing thus the potential drop and increasing the capacitance. Further removal of water leads to the restoration of bonds accompanied by a decrease in capacitance and the return to the initial potential distribution across the interface. Commercial high-performance coil coatings applied to galvanized steel were studied in order to correlate the interface stability and the tendency to blistering. EIS and SKP measurements allowed the evaluation of the electrochemical conditions at the interface. Local adhesion failures caused non-uniformity in the potential profile measured by SKP. Monitoring of changes in impedance at low frequency related to the interface during temperature cycling may be useful for the evaluation of the tendency to blistering.