A nonlinear phase-field model of corrosion with charging kinetics of electric double layer

Abstract

A nonlinear phase-field model is developed to simulate corrosion damage. The motion of the electrode−electrolyte interface follows the usual kinetic rate theory for chemical reactions based on the Butler−Volmer equation. The model links the surface polarization variation associated with the charging kinetics of an electric double layer (EDL) to the mesoscale transport. The effects of the EDL are integrated as a boundary condition on the solution potential equation. The boundary condition controls the magnitude of the solution potential at the electrode−electrolyte interface. The ion concentration field outside the EDL is obtained by solving the electro−diffusion equation and Ohm’s law for the solution potential. The model is validated against the classic benchmark pencil electrode test. The framework developed reproduces experimental measurements of both pit kinetics and transient current density response. The model enables more accurate information on corrosion damage, current density, and environmental response in terms of the distribution of electric potential and charged species. The sensitivity analysis for different properties of the EDL is performed to investigate their role in the electrochemical response of the system. Simulation results show that the properties of the EDL significantly influence the transport of ionic species in the electrolyte.