Current Distribution on a Cathode Covered by a Thin Film Electrolyte in Crevice Corrosion - An Analytical Model

Abstract

Analytical solutions were developed to model the current distribution on an electrode covered by a thin electrolyte layer where the current is fed from the edge. Separate models were developed for the Tafel and the linear kinetics regimes. The model provides the current density profiles and the total current capacity of the cathode in crevice corrosion. Results are shown to be in good agreement with numerical simulations. Conditions for the saturation of the cathodic current as well the trends in the variation of the cathode capacity as a function of electrode length are identified.

Crevice Corrosion Damage Evolution in High Temperature Brines

“…Recently, an analytical solution has been developed [15]. The analytical solution can be more robust and less tedious than numeric methods.…”

“…Particulate effects can be easily included. Figure 15 [15] presents an overview of the analytical approach for current distribution and cathode capacity in thin electrolyte layers. The treatment analyzes a cathode decoupled from the anode with the crevice mouth held at a constant potential corresponding to the repassivation potential for the metal/environment of interest.…”

“…This effective region accounts for 90% of the total ECS Transactions, 11 (27) 39-53 (2008) cathodic current capacity. Figure 16 [15] presents results for the Tafel kinetics regime. The current density is greatest at the mouth of the crevice and decreases with distance along the surface of the metal.…”

“…Numerical models for current distribution and cathode current capacity have been applied successfully for conditions in thin electrolyte layers: electrode kinetics, solution conductivity, length [14], crevice gap, pH, mass transfer effects [9], semi-analytical modeling approach for total cathodic current [13], and modified electrode and solution properties to include particulate effects [5]. Recently, an analytical solution has been developed [15]. The analytical solution can be more robust and less tedious than numeric methods.…”

“…The Wagner number is defined as the ratio of activation resistance to the ohmic resistance. A schematic diagram of the resistances and their effect on current distribution is shown in figure 17 [15]. For Wagner number much greater than one, activation resistance dominates, and a more uniform current distribution results.…”