Numerical Analysis Model of Galvanic Corrosion with Ion Movement and Reactions

Numerical analysis models for galvanic corrosion has been developed in recent years, but most of the ordinary models only can calculate current density and potential distribution in an electrolyte solution. In order to make clear corrosion mechanism, more information such as pH, ion and corrosion product distributions are necessary. However, it is difficult to compute these phenomena by mathematical model because various kinds of ions and complex reactions exist in corrosion progress. Calculating ion movement with satisfying charge conservation is especially difficult. We have developed a new numerical analysis model for galvanic corrosion that can calculate ions movement and reactions. In this model, ion density distribution is corrected by solving Poisson's equation to satisfy charge conservation. Equilibrium reactions are computed after calculating ion transportation. Galvanic corrosion of a model Zn/steel couple in a NaCl solution was calculated with this model. The difference of ion and corrosion product distribution in 50 ppm and 50000 ppm NaCl solutions was discussed. Corrosion product distribution obtained by this numerical analysis model was well agreed with OH− distribution on a galvanic corrosion specimen measured by FT-IR method qualitatively.