I believe its 10th such paper which just briefly mentioned how they used anodic current density at cathodic protection potential extracted from the polarization curves, to estimate the corrosion rate using Faraday's law.
I am not sure which formula they have used to calculate the corrosion rate. I am assuming something where you plug in the value of anodic current density and you get the corrosion rate. There are various formulae i came across just not sure how to use it.
Here is the snippet of the topic.
Calculating the corrosion rate from a polarization curve when cathodic protection is applied involves several steps. Here’s a simplified explanation:
Identify the Tafel Regions: Locate the anodic and cathodic Tafel regions on the polarization curve. These are the linear portions of the curve at higher and lower potentials, respectively.
Determine the Tafel Slopes: From the Tafel regions, determine the slopes of the anodic and cathodic branches. These slopes are necessary for calculating the corrosion current density.
Extrapolate to Find ( E_{corr} ): Extrapolate the Tafel lines to intersect at the corrosion potential (( E_{corr} )). This is the potential where the anodic and cathodic currents are equal.
Calculate Corrosion Current Density (( i_{corr} )): The intersection point gives you the corrosion current density (( i_{corr} )), which is the rate of metal dissolution.
Apply the Stern-Geary Equation: Use the Stern-Geary equation to relate the Tafel slopes, ( E_{corr} ), and ( i_{corr} ) to the corrosion rate (( CR )):
CR=n⋅F⋅A⋅ρB⋅icorr
Where:
( B ) is the Stern-Geary constant.
( n ) is the number of electrons transferred.
( F ) is Faraday’s constant.
( A ) is the area of the metal surface.
( \rho ) is the density of the metal.
Adjust for Cathodic Protection: When cathodic protection is applied, the potential shifts in the negative direction. You’ll need to adjust the ( E_{corr} ) accordingly and recalculate the ( i_{corr} ) at this new potential.
Consider Polarization Effects: Cathodic protection often involves polarization, which can change the effective corrosion rate. The degree of polarization can be estimated by the difference between the free corrosion potential and the protected potential.
Use the Correct Reference Electrode: Ensure that the potential measurements are referenced to the correct electrode, such as a saturated copper/copper sulfate reference electrode (Cu/CuSO4).
Account for IR Drop: Voltage drops other than those across the structure-to-electrolyte boundary must be considered for valid interpretation of the voltage measurement.
By following these steps and using the information from the polarization curve, you can estimate the corrosion rate under cathodic protection. For precise calculations and considerations specific to your system, consulting corrosion engineering literature or a professional in the field is recommended123.
The Stern-Geary constant, often denoted as ( B ), is a proportionality constant used in the calculation of corrosion rates from polarization resistance measurements. It relates the polarization resistance (( R_p )) to the corrosion current density (( i_{corr} )) through the Stern-Geary equation:
B=icorr2.303(ba+bc)
Where:
( b_a ) is the anodic Tafel slope,
( b_c ) is the cathodic Tafel slope.
The value of ( B ) can be determined empirically from separate weight loss measurements or calculated from the anodic and cathodic Tafel slopes obtained from a Tafel plot. The Tafel slopes themselves can be evaluated experimentally using real polarization plots12.
The Stern-Geary constant is crucial because it allows for the conversion of polarization resistance measurements into corrosion rates, which are more meaningful for assessing the integrity and lifetime of metallic structures. It’s a key parameter in corrosion science and engineering, particularly when evaluating the effectiveness of cathodic protection systems2.