Bulk diffusion regulated nanopore formation during vapor phase dealloying of a Zn-Cu alloy

Dealloying is a robust method for fabricating 3D bicontinuous porous materials with open porosity and large specific surface areas. The formation of nanopores usually results from two kinetically competing processes at dealloying fronts: desertion of sacrificed elements and self-assembly of lingered elements by diffusion. Since surface and interface diffusivities are usually much higher than bulk, dealloying is typically fulfilled by the fast processes while the slow bulk alloy diffusion in precursor alloys is not commonly involved into the formation of open porosity during a dealloying process. Here we report that open pore formation in a Cu₁₂Zn₈₈ alloy is regulated by the bulk alloy diffusion during high-temperature vapor phase dealloying. The growth of dealloyed porous microstructure is facilitated by the formation of an up-front γ-Cu₃₄Zn₆₆ intermediate phase and, thereby, the dealloying kinetics is mediated by the evolution of the solid intermediate phase through bulk diffusion. The two-step dealloying process may pave a new way to tailor porous microstructure by designing and controlling intermediate phase formation.