Phase Field Modeling of Interface Motion Due to Transport-Limited Electrochemical Reactions
Friday, October 7, 2005, 3:30 PM
Room 833 SWM
Adam C. Powell, IV Thomas B. King Assistant Professor of Materials Engineering, MIT
A new Cahn-Hilliard phase field model of transport-limited electrochemistry describes phase boundary motion due to oxidation and reduction reactions at metal-electrolyte interfaces. A case study for the binary model is carried out in the Fe-FeO system (unsupported electrolyte) in two and three dimensions. When there is no convection, a high electric field and low surface tension cause the cathode interface to be unstable, leading to growth of dendrites, which can eventually short-circuit the cell. Stability behavior of the model is in good agreement with linear stability theory for small amplitude sinusoidal perturbations in electrodeposition. When the electrodes and electrolyte are low-viscosity fluids, flow provides an additional mechanism for stabilizing the interface, and a new semi-analytical stability criterion is developed to describe this phenomenon. This binary model is extended to a ternary system and a representative case is carried out using a simplified Ti-Mg-Cl system. Two-dimensional ternary simulations show qualitatively correct behavior of interfaces and electrical potential due to electronically mediated reactions between magnesium and titanium chloride.