Is there a NO corrosion application for a linear polarization resistance? Any example?
And what is the technical justification for using +/- 10 mV as a signal of disturbance in linear polarization resistance? Is there a book that justifies this? Thank you in advance.
Dear Dr. Luis Santiago ,
linear polarization resistance (LPR) is a quick, nondestructive testing technique commonly used in material corrosion studies to gain corrosion rate data. For this method the material is polarized, typically on the order of ±10mV, relative to its Open Circuit (OC) potential—the potential measured when no [net] current is flowing. As the potential of the material (working electrode) is changed, a current will be induced to flow between the working and counter electrodes, and the material’s resistance to polarization can be found by taking the slope of the potential versus current curve. This resistance can then be used to find the corrosion rate of the material using the Stern-Geary equation.
For more details, i suggest you to have a look at the sourcee, Gamry notes, available at:
https://www.gamry.com/application-notes/corrosion-coatings/corrosion-techniques-polarization-resistance/
and
https://www.gamry.com/application-notes/corrosion-coatings/basics-of-electrochemical-corrosion-measurements/
Best regards, Pierluigi Traverso
It is a common believe that if you ploarize the working electrode up to 20 or 25 mV with respect to its OCP, the type of polarization would be a linear polarization in whivh there is a linear relationship between the current and potential but it doesn't mean that no corrosion would occure because when you pass the OCP in anodic direction the corrosion would occur and you can find the corrosion current by calculating the slope of E vs I to get the polarization resistance and then using Stern-Geary equation. To find out the corrosion rate you can use the calculated current density in Faraday law.
So, it means that no corrosion is not an accurate expression for LPR technique and as soon as the potential of the working electrode pass the open circuit potential in the anodic direction, the corrosion would start to happen.
I hope this is helping
Dear Luis,
Linear polarisation resistance (LPR) methods can be used to characterise a material medium pair by scanning the current–potential (i–E) domain. The method consists of applying to the metal very small voltage variations (typically less than 30 mV) above and below its corrosion potential. Measurements can be used to detect deviations from steady-state conditions in which little or no corrosion is occurring to cases where rapid corrosion is taking place. The corrosion rates measured using LPR when localized corrosion is taking place is generally not accurate. In these situations, LPR can be used as a diagnostic indicating tool.
LPR measurements can also be adversely influenced by electrochemically active species. Linear polarization resistance (LPR) is a quick, nondestructive testing technique commonly used in material corrosion studies to gain corrosion rate data. For this method the material is polarized, typically on the order of ±10mV, relative to its Open Circuit (OC) potential—the potential measured when no current is flowing. As the potential of the material (working electrode) is changed, a current will be induced to flow between the working and counter electrodes, and the material’s resistance to polarization can be found by taking the slope of the potential versus current curve.
Ashish
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