Refinement of Nanoporous Copper by Dealloying MgCuY Amorphous Alloys in Sulfuric Acids Containing Polyvinylpyrrolidone

Nanoporous Cu was fabricated by dealloying Mg65Cu25Y10 amorphous alloy in a mixed solution of poly-vinylpyrrolidone (PVP) and sulfuric acid. A significant change was observed in the pore and ligament size when dealloying in the mixed solution rather than in a 0.1 M H2SO4 solution free of PVP: in the mixed solution containing 10 g/L PVP the mean sizes of pores and ligaments were 10 nm and 14 nm, whereas they were 66 nm and 84 nm in the PVP-free solution. With increasing concentration of PVP in the dealloying solutions, the size of nanopores and ligaments decreased in the following manner: the decrease was small in the PVP concentration range of 0 to 0.1 g/L (Type I), and large in the 0.1 to 10 g/L range (Type II). A decrease in the surface diffusivity of more than three orders of magnitude was noted with the addition of 10 g/L PVP. This can be explained by the restrictions on free diffusion of Cu adatoms due to the adsorption of PVP macromolecules which force Cu adatoms to diffuse in a relatively narrower range, and thus smaller Cu ligaments and nanopores formed. The introduction of organic macromolecule into dealloying solution helps refine nanoporous structures.