Passivity of Metals: Potential-Step Transients for Passive Current Density and Barrier Layer Thickness in the Point Defect Model

TL;DR

This paper applies a corrected point defect model to analyze the transient behavior of passive current density and barrier layer thickness in metals, clarifying the model's parameters and its experimental implications.

Contribution

It introduces a corrected variant of the point defect model and demonstrates its application to potential-step transients, improving understanding of passive film behavior.

Findings

Functional forms match previous models but parameter compositions differ significantly.

The corrected model explains the experimental success of the earlier flawed model.

The theory aids in analyzing transients from potential switching in passive metals.

Abstract

In an earlier pre-print we developed a variant of the point defect model that corrected a flaw in one of the defect reactions and to be specific reaction 3 of the original point defect model was replaced by reaction 3prime of the variant. Here we apply the corrected model to find the time evolution of the passive current density and the barrier layer thickness. Though the functional forms agree with the forms reported earlier by Macdonald and co-workers, the composition of the parameters differ significantly. This explains the experimental success of the flawed model. This semblance is also manifested in the diagnostics for the current transient involving the time-derivative of the current density. The present theory will be useful for the correct analysis of transients which result from switching the potential in the anodic or cathodic direction from an initial steady state.