Gold gains many useful properties when it is formed into a nanoporous structure, but it also becomes macroscopically brittle due to flow localization and may therefore be unreliable for many applications. The goal of this work was to establish processing/structure/property relationships of nanoporous gold, discover controllable structure features, and understand the role of structure on flow localization. The nanoporous gold structure, consisting of a 3D network of nanoscale gold ligaments, was quantified with an automatic software developed for this work called AQUAMI, which uses computer vision techniques to make statistically reliable numbers of repeatable and unbiased measurements per image. AQUAMI increased the efficiency and accuracy of characterization in this work, allowed for the conduction of more experiments, and provided better confidence in morphology and size distribution of the complex NPG microstructural features. Nanoporous gold was synthesized while varying numerous processing factors such as dealloying time, annealing time, and mechanical agitation. Through the expanded scope of synthesis experiments and detailed analysis, it was discovered that the curvature of the ligaments and the distribution width of ligament diameters could be controlled through processing. In situ tensile experiments in SEM and TEM revealed that large ligaments arrested crack propagation while curved ligaments increase ductility by straightening in the tensile direction and forming geometrically required defects, which inhibit dislocation activity. Through synthesis and microstructure characterization, two new controllable structure features were discovered experimentally. In situ mechanical testing revealed the role these structures play on the deformation behavior and flow localization of nanoporous gold. / Doctor of Philosophy / Nanoporous gold contains a network of connected pores running through and between at network of solid gold ligaments or struts. It somewhat resembles the structure of coral. The nanoscale pores and ligaments give the material many useful properties. However, this structure also makes the material very fragile and unreliable in many potential application environments. The goal of this research is to investigate how the structure makes the material so fragile and look for ways the material might be made less fragile while still preserving its useful properties. The material properties are controlled through the material’s structure, which in turn is controlled by processing. To control the structure of nanoporous gold, the structure first had to be characterized. A software called AQUAMI was developed, which uses computer vision, to automatically calculate many features of the structure by looking at an image of it. This software was much faster and more accurate than making hundreds of hand measurements on each image. To find new ways to control the structure through processing, nanoporous gold was synthesized in many different conditions and then the structure was analyzed to determine the effect of each synthesis condition. It was discovered that a single specimen could be given a larger variety of ligament thicknesses by making it with a weaker acid or a smaller variety by heating the structure after forming it. Stirring during synthesis resulted in a structure with curvier ligaments. Mechanical tests were performed in electron microscopes to see how these features affected deformation. Large ligaments slowed crack propagation suggesting that a larger variety of ligament diameters could increase strength by having more large ligaments. Curved ligaments deformed more without breaking by straightening during deformation. Through this work, new ways of controlling the nanoporous gold structure were found and mechanical tests suggest that controlling these features may increase the material’s strength making it reliable in more environments
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/100733 |
| Date | 06 May 2019 |
| Creators | Stuckner, Joshua Andrew |
| Contributors | Materials Science and Engineering, Murayama, Mitsuhiro, Corcoran, Sean G., Reynolds, William T. Jr., Mirzaeifar, Reza |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, video/mpeg, video/mpeg, video/mpeg, video/mpeg, video/mpeg, application/x-zip-compressed, video/mpeg |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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