Microstructure evolution of silver-rich clusters during nanoporous gold dealloying
The existence of silver-rich clusters in nanoporous gold (NPG) made by dealloying has been reported . Even though these clusters play a critical role for the surprising catalytic activity of NPG, their formation and evolution during dealloying and coarsening of NPG remains to be studied in detail. Atomistic kinetic Monte Carlo (KMC) simulation studies have evolved as an approach towards understanding the atomic scale mechanisms of dealloying  and of the microstructure evolution in the resulting nanoporous metal . Here, using KMC, we study silver-rich clusters in dealloyed NPG. Emphasis is on following the evolution over extended time scales. During our simulations, the silver fraction is reduced from 75% in master alloy to <2% of dealloyed sample, and the ligament size increases from initially 2 to 5 nm. The evolution of the net residual silver content shows two stages, primary and secondary dealloying, with quite different dealloying rate. During the primary dealloying stage, both the silver cluster size and ligament size do not change. In contrast, during the secondary dealloying stage, the ligaments grows to more than 2.5 times of their initial size but the mean silver cluster size stays invariant. This implies that experiments exploring the cluster size may access the signature of the microstructure at the very early stages of dealloying. The stages have so far remained elusive to the experimentalist. Our finding that the initial silver cluster size varies with the dealloying potential suggests such studies also as a signature of the local dealloying conditions at the corrosion front.