Mechanisms of nanostructure formation by dealloying

去合金化包括从二元固溶体或金属间化合物中仅一种组分几乎完全溶解，从均匀的母相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，以及原型纳米多孔金，已成为模型系统，用于理解尺寸和界面对纳米级系统的机械和功能行为的影响。在现有技术中，脱合金可以通过原子数值模拟来真实地建模。换句话说，在原子尺度上的关键基本过程已经确定。然而，开放的问题仍然存在：什么特征长度尺度形成，什么百分比的牺牲组件仍然在结构中，以及这些参数如何取决于实验控制参数，特别是初始相的组成和溶解的驱动力？解决这些问题将能够进一步改进该工艺，从而制造结构尺寸可能小于5 nm的纳米材料的均匀单块体。这样的材料不仅可以作为纯组分生产，而且可以作为固溶体生产。这将进一步扩大已经非常有趣的纳米多孔金属的机械性能和功能特性的范围。该项目旨在开发一个经验数据库，了解潜在的机制，以及具有预测性质的材料法。该项目的工作计划是基于一个初步假设的相互作用，决定微观结构的演变。该假设认为，溶解的不太贵的组件，钝化富集的更贵的组件在表面上，和再分配曲率驱动的扩散。紧密匹配的实验和原子模拟将被用来测试假设，并根据观察结果进一步发展它。 实验研究了具有不同起始成分的Ag-Au-Pt的电化学去合金化，重点是在贵组分中稀释的起始合金，并且与Pt合金化以抑制通过表面扩散的粗化。在脱合金过程中的微观结构的演变监测非原位以及原位与小角X射线散射。动力学蒙特卡罗模拟在匹配条件下模拟实验。此外，简单的模型场景-无法访问的实验-进行了调查，并与基于初始假设的预期结果进行了比较。

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.