Electrochemical impedance spectroscopy (EIS) is a modern technique to investigate various non-conductive coatings on conductive materials such as metals.
For the impedance spectrum the coated component is excited (modulated) with a sinusoidal current. The resulting voltage is measured with amplitude and phase over a large frequency range.
The impedance is calculated from the modulation current and the resulting modulation voltage.
If pores are present in the top layer, both the resistance of the solution in the pores and the capacitance of the electrochemical double layer can be measured. Two semicircles can then be seen in the Nyquist diagram.
The covering layer can be determined in terms of thickness and porosity.
With electrochemical impedance spectroscopy (EIS) it is possible to investigate protective properties of coatings not only qualitatively but also quantitatively.
Among other things
- the barrier effect
- the water absorption
- the delamination
can be investigated.