Fabrication of nanoporous silver and microstructural change during dealloying of melt-spun Al-20 at.%Ag in hydrochloric acid

摘要

Ag nanoporous structure has been fabricated by dealloying of Al-20 at.%Ag in 2 M HCl at room temperature. We describe the changes of phase constitution and microstructural morphology during the dealloying. The bi-phase structure of α-Al and γ-Ag_2Al was obtained using melt-spinning, and considerable amount of γ-Ag_2Al was suppressed. According to the phase quantitative analysis, 5.6 % γ-Ag_2Al was precipitated at the grain boundary and inside the grain. At the early stage of dealloying process, the deep channel occurred at the interface of α-Al and γ-Ag_2Al due to concentration gradient of Ag; and then, α-Al was preferentially dealloyed with comparison to γ-Ag 2Al and formed 3-dimensional nanoporous structure which showed the open-pore/ligament bi-continuous structure. After 720 min, γ-Ag 2Al was dealloyed and formed 2-dimensional pored-wall structure. At the end of dealloying reaction, the initial grain/intermetallic wall structure was maintained. The Ag nanoporous structure was gradually coarsened with the increase of dealloying time, from 25 ± 5 nm at 20 min to 113 ± 22 nm at 720 min. The calculated coefficient of surface diffusion of Ag was 2.34 × 10~(-17) m~2/s. The surface diffusivity of Ag obtained in this study showed two orders of magnitude higher than the Au dealloyed from Au-Ag precursor at the similar temperature.