Evolution of nanoporosity in dealloying

Dealloying is a common corrosion process during which an alloy is 'parted' by the selective dissolution of the most electrochemically active of its el ements. This process results in the formation of a nanoporous sponge compos ed almost entirely of the more noble alloy constituents(1). Although consid erable attention has been devoted to the morphological aspects of the deall oying process, its underlying physical mechanism has remained unclear(2). H ere we propose a continuum model that is fully consistent with experiments and theoretical simulations of alloy dissolution, and demonstrate that nano porosity in metals is due to an intrinsic dynamical pattern formation proce ss. That is, pores form because the more noble atoms are chemically driven to aggregate into two-dimensional clusters by a phase separation process (s pinodal decomposition) at the solid-electrolyte interface, and the surface area continuously increases owing to etching. Together, these processes evo lve porosity with a characteristic length scale predicted by our continuum model. We expect that chemically tailored nanoporous gold made by dealloyin g Ag-Au should be suitable for sensor applications, particularly in a bioma terials context.