CURVATURE EFFECTS IN ALLOY DISSOLUTION

An elemental metal can dissolve at kink sites at low everpotentials pr oducing no new interfacial area. When an ideal solid solution alloy un dergoes selective dissolution, this situation is not possible owing to atomic-scale disorder. Dissolution of the less noble constituent can proceed only by injection of regions of negative curvature into the so lid surface, which increases the interfacial area. We present a thermo dynamic analysis which accounts for these capillary effects in alloy d issolution. The phenomenon of the critical potential for macroscopic s elective dissolution is analyzed in terms of a kinetic roughening tran sition. This transition results from a competition between curvature-d ependent dissolution and surface diffusion. An expression for the crit ical potential as a function of alloy composition is developed. The de alloying threshold corresponds to a critical composition on the line o f critical potentials defining the roughening transition.