What is Linear Polarization Resistance (LPR) and what does it measure?

• A. LPR measures the slope of the polarization curve near the corrosion potential to estimate corrosion rate via polarization resistance
• B. LPR measures ambient humidity
• C. LPR measures coating thickness
• D. LPR measures diffusion rate of ions only

Answer: (A)

Linear Polarization Resistance measures the small, linear portion of the electrochemical response right around the corrosion potential. By applying a tiny shift in potential and recording the resulting current, you get a straight-line region whose slope is the polarization resistance ( Rp = ΔE/ΔI ). This slope tells you how resistant the metal is to charge transfer during corrosion. The corrosion rate is then estimated from Rp using the Stern-Geary relation, i_corr ≈ B / Rp, where B depends on the anodic and cathodic Tafel slopes for the specific metal and environment. So, LPR provides a quick, in-situ estimate of corrosion rate from the polarization resistance, not measurements of humidity, coating thickness, or ion diffusion rates.