Electrochemical impedance spectroscopy or EIS is a technique to measure the general barrier properties of coatings. More specifically water and ion permeability of coatings can be determined as a function of time. This information is particularly valuable in quality control, comparison of performance of different coatings and follow up of coatings in situ. The main advantage of the technique is the limited amount of time needed for a measurement: within 24 hours a fingerprint of the coating is taken (duration is dependent on coating type and thickness).
Since EIS does not rely on visual aspects, differences in coating performance can already be established prior to visual signs of degradation. Corrosion processes taking place underneath the coating can be measured as well by means of EIS.
EIS measurements can be combined with an accelerated degradation test in the lab to better understand the degradation of the coating and to reduce test times.
Water and ion permeability of coatings
Based on a series of EIS measurements and fitting of the data in a model water and ion permeability of a coating can be determined within a short time (typically 24 hours). These measurements are very useful in the frame of coating selections and during development of new coatings.
Detecting defects (non-destructive)
Besides visual control and the destructive holiday spark test defects can also be detected by means of EIS measurements that are performed in situ.