Characterization of the water uptake and electrolyte uptake of organic coatings and the consequences by means of electrochemical impedance spectroscopy and UV–vis spectroscopy

• We measure the electrolyte uptake of coatings.
• We develop a description of EIS spectra (phase model) without simulation with an equivalent circuit.
• We show that the electrolyte uptake initiates the corrosion not the water uptake.
• We describe a new kind of swelling that solidifies a coating to improve the barrier properties.

A new method to the investigation of the electrolyte uptake in a coating is presented. By means of UV–vis spectroscopy without nitrogen atmosphere in the region of 189 nm the concentration change of the overlaying electrolyte over a coating could be defined. In combination with the analysis of the water/electrolyte uptake by means of the electrochemical impedance spectroscopy (EIS) the resulting electrolyte uptake could be defined on a qualitative level. Furthermore a simple analysis of EIS spectra by a graphical interpretation of the Nyquist spectra has been developed. With the EIS spectra analysis in the same timeline as the water/electrolyte uptake a model for the processes inside a coating during corrosive stress has been obtained. It shows that the fast water uptake is followed by a slow ion uptake and this causes the initiation of a corrosion process at the interface.