Mechanisms of nanostructure formation by dealloying

脱合金化是指从二元固溶体或金属间化合物中几乎完全溶解一种组分，在均匀的母相中产生几纳米尺度的孔隙。由于其纳米级微观结构的出色定义，均匀性和可重复性，以这种方式生产的纳米多孔金属和原型纳米多孔金已成为理解纳米尺度系统的机械和功能行为的尺寸和界面效应的模型系统。在目前的技术水平上，可以通过原子数值模拟真实地模拟脱合金过程。换句话说，原子尺度上的关键基本过程已经被确定。然而，仍然存在一些悬而未决的问题：形成了什么样的特征长度尺度，在结构中保留了多少百分比的牺牲成分，以及这些参数如何依赖于实验控制参数，特别是初始相的组成和溶解驱动力？回答这些问题将有助于进一步改进该工艺，从而制造出结构尺寸可能小于5nm的纳米材料的均匀整体体。这样，这些材料不仅可以作为纯组分生产，而且可以作为固溶体生产。这将进一步扩展纳米多孔金属的机械性能和功能特性的高度有趣的光谱。该项目旨在建立一个经验数据库，了解潜在的机制，以及具有预测性的材料规律。项目中的工作计划是基于决定微观结构演变的相互作用的初始假设。该假设考虑了低贵金属成分的溶解，高贵金属成分在表面富集的钝化，以及曲率驱动扩散的再分布。密切匹配的实验和原子模拟将被用来检验这一假设，并在观察的基础上进一步发展它。实验研究了不同起始成分的Ag-Au-Pt的电化学脱合金，重点研究了起始合金中贵金属成分的稀释，以及与Pt合金的表面扩散抑制粗化。用小角x射线散射法监测了非原位和原位脱合金过程中的显微组织演变。动力学蒙特卡罗模拟模拟了匹配条件下的实验。此外，还研究了实验无法获得的简单模型情景，并将结果与基于初始假设的期望进行了比较。

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.