Corrosion Testing via Electrochemical Impedance Spectroscopy (EIS)

How it works

EIS Principle

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.

Experimental Setup

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.

Data Interpretation

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.

Our Expertise

VLCI has 5-year experience operating EIS for various industries and applications. We use two different potentiostats:

• one for precision laboratory testing, equipped with a multiplexer that increases our testing capacities eightfold.
• and another portable one equipped with magnetic probes for non-destructive on-site measurements.

We perform different types of EIS measurements:

• Standard EIS (ISO 16773) measures barrier performance and water uptake during immersion, and gives relevant results within three weeks. It can be extended for even longer-term testing.
• Accelerated EIS (ISO 17463) applies electrical stress to promote delamination and speed up corrosion processes. This approach is very useful for barrier performance comparison in only 24 hours.
• Linear Polarization Resistance (LPR) is another quick electrochemical method for measuring corrosion resistance. In LPR experiments, the potential is swept in a small range around the open-circuit potential, and the resulting current of the system is measured.

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