Influence of Alloy Composition and Dealloying Solution on the Formation and Microstructure of Monolithic Nanoporous Silver through Chemical Dealloying of Al-Ag Alloys

We present a facile and effective route to fabricate monolithic nanoporous silver (NPS) ribbons through chemical dealloying of melt-spun Al-Ag alloys comprising alpha-Al(Ag) and Ag2Al under free corrosion conditions. The microstructure of the NPS ribbons was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX). The experimental results show that alloy composition and dealloying solution have a significant influence on the dealloying process and the formation of NPS. The Al-Ag alloys with 15-40 atom % Ag can be fully dealloyed in the 5 wt % HCl solution, but a minor amount of undealloyed Ag2Al can be detected in the as-dealloyed ribbons from the Al-45 and 50 Ag alloys. The existence of alpha-Al(Ag) can supply penetration paths for the solution and promote the dealloying of Ag2Al in the two-phase Al-Ag alloys. Moreover, the synergetic dealloying of alpha-Al(Ag) and Ag2Al in the two-phase Al-Ag alloys and fast surface diffusion of Ag result in the formation of NPS with a homogeneous porous structure. The Al-Ag alloys with 15-50 atom % Ag cannot be fully dealloyed in the 20 wt % NaOH solution, leading to the formation of NPS/Ag2Al composites. In addition, the Al-60 Ag alloy containing a single Ag2Al phase does not react with the 5 wt % HCl or 20 wt % NaOH solution even at high temperatures (90 +/- 5 degrees C).