Electrochemical Impedance Spectroscopy (EIS)
Electrochemical Impedance Spectroscopy (EIS) is an experimental method for evaluating the protectiveness of organic coatings.
It is particularly useful for coating characterization as it can simultaneously measure degradation of a coating caused by exposure to an electrolyte and the change in corrosion rate of the substrate caused by coating perforation. During the test, an AC voltage of varying frequency is applied to the sample, which allows collection of information about the electrochemical reactions. The capacitance of the coating will change during the experiment as a result of water swelling or absorption. Typically, a three-electrode arrangement with a working electrode, a reference electrode and a counter-electrode is used to perform EIS in aqueous solutions.
The higher the impedance of a coating, the lower is its permeability to corrosives, and hence the more protective the coating.