Vacuum thermal dealloying of magnesium-based alloys for fabrication of nanoporous refractory metals
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Research Letter
Vacuum thermal dealloying of magnesium-based alloys for fabrication of nanoporous refractory metals Maria Kosmidou , Michael J. Detisch, Tyler L. Maxwell, and T. John Balk, Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506, USA Address all correspondence to T. John Balk at [email protected] (Received 27 November 2018; accepted 17 January 2019)
Abstract A specialized dealloying technique called thermal dealloying was developed over 10 years ago for certain biomedical materials. This method is not widely used for synthesizing nanoporous metals. However, it offers advantages over conventional dealloying processes for fabrication of nanoporous structures, and is highly suitable for refractory metals that may be susceptible to oxidation during chemical/electrochemical dealloying and liquid metal dealloying. In this study, nanoporous structures were successfully fabricated from magnesium-based precursor alloys via sublimation of magnesium at elevated temperature under vacuum conditions. Different refractory metal diffusion rates affect the resulting density and amount of retained magnesium in each nanoporous material.
Nanoporous metals have seen significant interest in recent years as high surface area metallic structures that may hold interest for applications such as sensing,[1, 2] catalysis,[3–5] biomedical applications,[6, 7] and battery materials.[8] This interest is due to the unique structure of nanoporous metals as well as the ease of production through various dealloying processes. The typical nanoporous metal structure provides a high surfacearea-to-volume ratio, including high-curvature ligaments, and a metallic surface with a large amount of porosity.[9] Generally speaking, dealloying is a selective dissolution process wherein a sacrificial component is removed from a precursor alloy, allowing the other metallic component(s) to surface diffuse and form a bicontinuous, interconnected porous structure. Multiple dealloying techniques have been investigated and developed in recent years. Electrochemical dealloying[10–12] employs a chemical etchant, sometimes in conjunction with an electric bias, to selectively remove the sacrificial element from the precursor alloy system. Liquid metal dealloying[13–15] uses a molten metal/alloy bath to induce the dissolution process and remove the sacrificial alloy component. These techniques have extended the range of metallic systems that can be successfully dealloyed, to incorporate a wider range of materials that includes noble metals, transition metals with some degree of oxidation resistance, and certain refractory metals.[16] There are limitations to these techniques, however. Electrochemical dealloying is limited to systems with a sufficiently large gap in electrode potentials between the two alloying elements.[17] This typically restricts the application of the method to noble metals and similarly corrosion resistant metals. Liquid metal dealloying exploits differences in the
melting points of an alloy’s constitu
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