Interplay of surface diffusion and surface tension in the evolution of solid/liquid interfaces. Dealloying of beta-brass in aqueous sodium chloride

The dealloying of beta-brass in 0.5 M aqueous NaCl was studied by electroch emical techniques at different temperatures in the range 278 K less than or equal to T less than or equal to 318 K, complemented with in situ scanning tunneling microscopy (STM) imaging. In the potential region where the elec trodissolution of zinc and the formation of vacancies and copper islands ta ke place, two different roughness regimes were distinguished. When dealloyi ng involves only a few monolayers (ML) the process approaches a quasiunifor m alloy electrodissolution, whereas after electrodissolution of more than 2 0 ML, void formation takes place. In both regimes the interface evolution w as analyzed by applying the dynamic scaling method to in situ STM imaging d ata. The first roughness regime exhibits a stable interface consisting of c opper-rich islands that coarsen with time according to a surface diffusion controlled process. The second roughness regime exhibits an unstable interf ace due to a curvature dependent corrosion rate enhancing zinc electrodisso lution at cavities. The overall interface evolution is well-described by a differential stochastic equation containing an electrodissolution term and surface rearrangement terms related to surface diffusion and negative surfa ce tension effect.