Electrochemical Impedance Spectroscopy (EIS) is a well-established quantitative method for the accelerated evaluation of the anti-corrosion performance of protective coatings. Within short testing times, EIS measurements provide reliable data, allowing for the prediction of the long-term performance of the coatings. The result of EIS is the impedance of the electrochemical system as a function of frequency.
EIS is a versatile testing procedure, and can be performed under different conditions of stress, depending on the performance of the tested coatings.
A measuring cell is placed on the coated panel (working electrode), filled with a 3,5% NaCl solution. A graphite electrode is used as counter electrode, and a standard Ag/AgCl cell as reference electrode. Measurements are carried out over a broad frequency range from 100 kHz to 10 mHz, using a 50 mV amplitude sinusoidal voltage.
Impedance spectroscopy data is modelled as an equivalent circuit:
From the equivalent circuit modelling, three significant parameters are obtained: coating resistance, water uptake and corrosion rate.
VLCI has 5-year experience operating EIS for various industries and applications. We use two different potentiostats:
We perform different types of EIS measurements: