Phase-Field Modeling of pH-Dependent Corrosion Reactions at an Iron/Aqueous Solution Interface

Tuesday, 3 October 2017
Prince George's Exhibit Hall D/E (Gaylord National Resort and Convention Center)
C. Tsuyuki, A. Yamanaka (Tokyo University of Agriculture and Technology), and Y. Ogimoto (Fuji Electric Co., Ltd.)
There has been a growing demand for corrosion prediction. To describe the time-space evolution of a metal/aqueous solution interface, a phase-field (PF) method is promising because of its suitability for simulating moving interfaces. Yet, only a few attempts are reported concerning the PF simulation of corrosion reactions. Here we propose a PF modeling of pH-dependent general corrosion of iron in an aqueous solution. Our PF model consists of three governing equations: First one is the Allen-Cahn equation derived from the Butler-Volmer electrochemical reaction kinetics, in which the activity of OH- ions is taken into account in order to express the pH-dependent motion of an iron/solution interface as proposed by Bockris [J. O’ M Bockris et al., Electrochimica Acta 4, 325-361 (1961)]. Second is the Cahn-Hilliard equation that describes the diffusion of ions in the solution. And the last one is the Poisson equation to calculate the distribution of an electrostatic potential. As for the simulation parameters, the diffusion coefficients of ions, the corrosion potential, and the corrosion current density to estimate the mobility of the interface, are given by Corrosion Analyzer software (OLI Systems Inc.). Using the proposed PF model, we can successfully reproduce the pH-dependent general corrosion of pure iron in an HCl solution. Simulation results demonstrate that the PF model is available to predict the iron dissolution and the evolutions of Fe2+, H+, and OH- ions concentrations in the solution.