Corrosion parameters using 2nd Stern calculation

Abstract

A voltammetric curve i = f(Vg) having a zero current potential can be processed according to the 2^nd Stern method. The second Stern method gives the zero current potential and the polarisation resistance as results.
The Rp polarisation resistance is an important parameter to evaluate the anti-corroding strength of a corrosion inhibitor or to study a corrosion process at a metal surface. The polarisation resistance of a sample can be followed and recorded in real time (using the General corrosion (Rp) method) then checked by running the second stern method from the voltammetric curves obtained. The second stern calculation is an ideal tool to check the polarisation resistance values.

This voltammetric curve was obtained from a Pot. Linear V method carried out on a Inox 10/18 [AISI430] (demonstration curve: Polarisation curve Inox18 10_025.CRV).

Curve in blue: experimental curve.
Curve in red: parabola found.

The second Stern calculation give the zero current potential (E (i=0)) as the point of the parabola intercepting the abscissa (potential) axis, and Rp as the slope of the tangent found.
E (i = 0)) can be assimilated to the corrosion potential and Rp to the polarisation resistance of the electrochemical system. The correlation coefficient displayed (Coef.: 1.000) indicates the quality level of the parabolic regression. This coefficient is comprised between 0 and 1. Closer to 1 this coefficient is, better is the regression.

The 2^nd Stern calculation method is an ideal tool to determine the polarisation resistance of an electrochemical system. The Rp polarisation resistance can also be determined by using the 1^st Stern (Tafel) method (see Examine your experiment: Corrosion parameters using Tafel calculation).