Curvature Effects in Alloy Dissolution

An elemental metal can dissolve at kink sites at low everpotentials producing no new interfacial rea. When an ideal solid solution alloy undergoes selective dissolution, this situation is not possible owing to atomic-scale disorder. Dissolu-tion of the less noble constituent can proceed only by injection of regions of negative curvature into the solid surface, which increases the interfacia [ area. We present a thermodynamic analysis which accounts for these capillary effects in alloy dissolution. The phenomenon f the critical potential for macroscopic selective dissolution is analyzed in terms of a kinetic roughening transition. This transition results from a competition between curvature-dependent dissolution and surface diffusion. An expression for the critical potential as a function of alloy composition is developed. The dealloying threshold corresponds to a critical composition on the line of critical potentials defining the roughening transition. Today there are a number of issues related to electro-chemistry and corrosion in alloy systems that are poorly understood. Since alloy dissolution is an irreversible pro-cess, standard thermodynamic formal isms that assume mi-croscopic reversibility appropriate for elemental metals do not apply over composit ion ranges of interest in alloy sys-