linear polarization resistance

Linear Polarization Resistance:

The theoretical basis of the LPR technique was founded in a publication dating back to 1957. In the LPR technique, a potential (typically of the order of 10-20 mV) is applied to a freely corroding sensor element and the resulting ("linear") current response is measured. This small potential perturbation is usually applied step-wise, starting below the free corrosion potential and terminating above the free corrosion potential. The polarization resistance is the ratio of the applied potential and the resulting current response. This "resistance" is inversely related to the uniform corrosion rate.

In order to calculate a corrosion rate with the LPR technique, several fundamental assumptions must be made. These include:

Corrosion damage in the uniform (general) mode.

A particular, relatively simple, kinetic model (known as activation control) for both the anodic and cathodic reactions.

A single anodic and a single cathodic reaction.

Known values of the Tafel constants.

A negligible solution resistance (hence the technique is most suited to solutions of relatively high conductivity).

A stable free corrosion potential.

The reported "accuracy" of LPR measurements should give due consideration to the above assumptions.

References/Literature:

M. Stern and A.L. Geary: "Electrochemical Polarization", Journal of the Electrochemical Society, Vol. 104, No.1, January 1957, p.56.

Links:
An outline is available on the site of KH Design and Development
www.khdesign.co.uk