Analysis of kinetic and ohmic polarization effects in passivation processes under potentiodynamic control
✍ Scribed by Simon L. Marshall
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 676 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0013-4686
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✦ Synopsis
Abstra~-A theoretical model for a surface reaction involving the deposition of a nonconducting porous layer is described. The model includes explicitly the ohmic and kinetic contributions to the total reaistante of the reaction, and a current-balance condition is applied to determine in a self-consistent manner the corresponding contributions to the total overpotential. The relative importance of the kinetic and ohmic effects is expressed by the value of the Wagner number, Wo, which is equal to the ratio of polarixation resistance to ohmic resistance, and includes the combined effect of 6lm thickness, electrolyte conductivity and reaction exchange current density. It is shown that the linear polarization law is a good approximation if Wa < 0.1, and that the theory reduces to the Layer-Pore Resistance model when Wa = 0. Analytical expressions are given for the current-potential curves in the liiit of linear polarization, and for the relation between peak currents and potential scan rates for linear and nonlinear polarization models. The use of these expressions in the analysis of experimental results is demonstrated, and the behaviour predicted by the theory in the linear and nonlinear polarization regimes is compared.