Mechanisms of nanostructure formation by dealloying

• Applicant: Professor Dr.-Ing. Jörg Weißmüller
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Computer-Aided Design of Materials and Simulation of Materials Behaviour from Atomic to Microscopic Scale
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 510071612

Dealloying consists in the almost complete dissolution of only one component from a binary solid solution or an intermetallic compound, generating porosity at the scale of few nanometers from a homogeneous parent phase. Due to the outstanding definition, uniformity and reproducibility of their nanoscale microstructure, nanoporous metals produced in this way, and prototypically nanoporous gold, have become model systems for understanding size- and interface effects on the mechanical as well as functional behavior of nanoscale systems. At the state of the art, dealloying can be realistically modeled by atomistic numerical simulation. In other words, the key elementary processes at the atomic scale have been identified. However, open questions remain: what characteristic length scale is formed, what percentage of the sacrificial component remains in the structure, and how do these parameters depend on the experimental control parameters, in particular the composition of the initial phase and the driving force for dissolution? Answering these questions would enable further refinement of the process and thus the fabrication of homogeneous monolithic bodies of nanomaterials with structure sizes potentially < 5nm. Such materials could then be produced not only as pure components, but also as solid solutions. This would further expand the already highly interesting spectrum of mechanical properties and functional properties of nanoporous metals. The project aims at developing an empirical database, an understanding of the underlying mechanisms, and a materials law with predictive character. The work program in the project is based on an initial hypothesis for the interactions that determine the microstructural evolution. The hypothesis considers the dissolution of the less noble component, the passivation by enrichment of the more noble component at the surface, and the redistribution by curvature-driven diffusion. Closely matched experiments and atomistic simulations will be used to test the hypothesis and develop it further based on the observations. The experiment investigates the electrochemical dealloying of Ag-Au-Pt with different starting compositions, focusing on starting alloys diluted in the noble component, and alloyed with Pt to suppress coarsening by surface diffusion. Microstructural evolution during dealloying is monitored ex situ as well as in situ with small-angle X-ray scattering. Kinetic Monte Carlo simulations mimic the experiment under matched conditions. In addition, simple model scenarios - not accessible to the experiment - are investigated and the results compared with the expectations based on the initial hypothesis.

• DFG Programme: Research Grants