Why Use Electrochemical Techniques for Corrosion Measurement?
- Corrosion is an electrochemical process.
- A broad range of electrochemical techniques have been developed specifically for corrosion measurement.
- Electrochemical techniques are fast.
- Electrochemical techniques are sensitive.
- Nevertheless, there are some Corrosion Engineers who don’t use electrochemical techniques…probably because they don’t understand them.
Electrochemical Techniques and Corrosion
- Corrosion is the chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties. (ASTM G 15: Standard Terminology Related to Corrosion.)
- Corrosion is caused by a redox reaction.
- Fundamentally, corrosion is an electrochemical process, so using electrochemical techniques is obvious.
Electrochemical Techniques are Fast!
- Corrosion is an inherently slow process. A typical corrosion rate is 10 milli-inches per year (mpy) or 0.254 millimeters per year (mmpy).
- The “best” corrosion tests are weight loss measurements after exposure. However, they are very slow (days, weeks, or months).
- Electrochemical instruments polarize the sample to accelerate the corrosion process and make the measurement in minutes or hours. The electrochemical corrosion rate is “instantaneous”.
Electrochemical Techniques Are Sensitive!
- Electrochemical techniques can measure very low corrosion rates.
- A sample with a low corrosion rate will exhibit a low current during the electrochemical experiment. Corrosion scientists may use “corrosion rate” and “current” interchangeably.
- The best measure of a specific potentiostat’s ability to measure low corrosion rates is the lowest current range.
Gamry Instruments for Corrosion Measurement