Modeling of electrochemical oxide film growth-a PDM refinement

The Point Defect Model (PDM) is known for over 40 years and has brought deeper insight to the understanding of passivity. During the last decades it has seen several changes and refinements, and it has been widely used to analyze growth kinetics of different alloys. Nevertheless, the model has been based on still unconfirmed assumptions, as constant and potential independent electric field strength. To overcome this limitation, we introduce a Refined PDM (R-PDM) in which we replace those assumptions by using additional equations for charge distribution including new physically valid boundary conditions based on considering finite dimensions for the defects by introduction of two defect layer at the film boundaries and by calculating the potential drop at the surface of the film towards the solution over the compact double layer. The calculations by the R-PDM show that the original PDM assumptions are only valid for very specific parameter combinations of oxide film growth and vacancies transport and cannot generally be taken for granted. We believe our findings of electric field and potential drop dependency on the external potential to pave the way for a more realistic description of passive layer formation.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

The Point Defect Model (PDM) has been used to understand passivity for over 40 years. However, the model is based on unconfirmed assumptions. To address this limitation, a Refined PDM (R-PDM) is proposed, which includes additional equations and boundary conditions to account for finite dimensions of defects. The calculations using R-PDM show that the original assumptions of PDM are only valid for specific parameter combinations and cannot be generally assumed. These findings contribute to a more realistic description of passive layer formation.