# Polarization Resistance

on . Posted in Cathodic Protection

Polarization resistance, abbreviated as $$P_r$$, is a term commonly used in the field of electrochemistry, particularly in the study of corrosion.  It is a measure of the resistance to electrochemical reactions occurring at the surface of a metal immersed in a corrosive environment.  The concept is often employed in techniques like electrochemical impedance spectroscopy (EIS) to assess and monitor corrosion processes.  When a metal is exposed to a corrosive environment, electrochemical reactions take place at its surface, leading to corrosion.  These reactions involve the transfer of electrons between the metal and the surrounding environment.  The polarization resistance quantifies the resistance encountered by these electrochemical reactions.

The corrosion process typically involves anodic and cathodic reactions.  The anodic reaction involves the dissolution of metal, and the cathodic reaction involves reduction processes.  The polarization resistance is related to the overpotential, which is the deviation of the electrode potential from its equilibrium value during these electrochemical reactions.  A higher polarization resistance indicates a lower corrosion rate.  Monitoring polarization resistance over time can provide valuable information about the corrosion behavior of a material and the effectiveness of corrosion protection measures.

In practical applications, techniques like EIS involve applying small amplitude alternating current signals to the metal surface and measuring the resulting impedance.  The polarization resistance can then be extracted from the impedance data, providing insights into the corrosion kinetics and the effectiveness of corrosion inhibitors or coatings.

### Polarization Resistance Formula

$$R_p = ( \Delta E \;/\; \Delta i ) _{\Delta E \to 0}$$
Symbol English Metric
$$R_p$$ = polarization resistance $$yrs$$ $$yrs$$
$$\Delta E$$ = polarization from corrosion potential $$V$$ $$kg-m^2 \;/\; s^3-A$$
$$\Delta I$$ = polarization current $$I$$ $$C \;/\; s$$