What Does Free Corrosion Potential Mean?
Free corrosion potential is the absence of a net electrical current that flows to and from a metal's surface. The corroding metal has a potential that is expressed as Ecorr.
The free corrosion potential is measured through the voltage difference between the immersed metal and the appropriate reference electrode in a given environment.
Corrosionpedia Explains Free Corrosion Potential
Free corrosion potential is an important variable and is useful when monitoring corrosion in some complex field situations.
A small laboratory experiment can be set up where two electrodes are connected to an electrolyte. The electrodes are then connected to a voltmeter. The voltmeter measures small voltages across the electrodes without drawing much current. We can use the experiment to measure the corrosion potential of a given piece of metal using a laboratory cell.
The electrode used as the reference should be contained in the lugging capillary. This ensures that the reference electrode is not contaminated by the environment. It also prevents the corrosive agents from leaking into the environment.
After taking measurements, the magnitude and sign of the voltage is recorded and then reported as the corrosion potential. The sign of the voltage is very important. For example, a voltmeter reading of -0.45 V indicates that the metal used, in reference to the electrode, is negative. If the metal was connected to the low point with our reference electrode connected to the high point, then the reading would change to +0.45 V.
The reference electrode is usually connected to the low point, which is referred to as the instrumental ground, in order to avoid any reporting confusion.
The table below shows some common materials and their corrosion potentials in a saltwater environment.