FIELD

The present invention generally relates to metal foams, and more particularly, to processes for tailoring the macroscopic shape, metallic composition, mechanical properties, and pore structure of nanoporous metal foams prepared through combustion synthesis via direct write three-dimensional (3D) printing of metal energetic ligand precursor inks made with water and/or one or more organic thickening agents.

BACKGROUND

Nanoporous metal foams (NMFs) are a class of advanced porous architectures that combine metallic compositions with macroporosity, mesoporosity, and sub-micron microporosity typical of sol-gel-derived pore networks. NMFs thus present a nexus of chemistry, nanostructure, and macrostructure. See image100ofFIG. 1. The elemental composition can be variable and allows for applications in structural materials, hydrogen storage, heat transfer, catalysts, etc. The fine structure dictates catalytic activity, surface area/kinetics, etc. The macrostructure allows for the engineering, design, and control of flow paths and pressure drop. Development of processes for controlling porosity over nano-length, micro-length, and macro-length scales and strategies for controlling monolithicity will be important for maximizing the potential of NMFs for technological applications. Chemical reactions200for producing [Fe(BTA)3][NH4]3and Cu(BTA)(NH3)2are shown inFIG. 2.

However, while a handful of metals, such as gold, can be readily rendered into nanoporous foams through dealloying techniques, the porosity and morphology of such foams is limited in scope, and this dealloying does not extend well to most transition and main-group metals. Combustion synthesis to produce metal foams using metal bistetrazoleamine (mBTA) complexes, for example, is a straightforward process for preparing aerogel-like densities and open-celled pore networks of a wide variety of metals. However, one primary disadvantage of the combustion synthesis approach to date has been the difficulty in producing the foam material in relevant form factors, thus limiting applications where macroscopic forms and shape control are desired. Accordingly, an improved process for producing metal foams may be beneficial.

SUMMARY

Certain embodiments of the present invention may provide solutions to the problems and needs in the art that have not yet been fully identified, appreciated, or solved by conventional metal foam synthesis techniques. For example, some embodiments of the present invention pertain to processes for tailoring the macroscopic shape, metallic composition, mechanical properties, and pore structure of nanoporous metal foams prepared through combustion synthesis via direct write 3D printing of metal energetic ligand precursor inks made with water and/or an organic thickening agent.

In an embodiment, a method for producing nanoporous metal foam includes direct write 3D printing a metal energetic ligand precursor ink by extruding the metal energetic ligand precursor ink into a printed structure and allowing the printed structure to dry, producing the nanoporous metal foam. The printed structure exhibits porosity at a macro structural scale.

In another embodiment, an additive manufacturing process for producing hierarchically structured nanoporous metal foam includes extruding a slurry including one or more metal energetic ligand precursors into a structure with a prescribed pattern and density. The process also includes heating the structure in an inert atmosphere such that the one or more metal energetic ligand precursors of the structure undergo self-sustaining combustion synthesis that transforms the one or more energetic metal ligand precursors into a foaming gas, leaving behind a zero-valence state metal. The process further includes heat treating the structure to strengthen the structure and produce a post-processed structure. In some embodiments, only the post-processing is performed at a temperature higher than room temperature.

In yet another embodiment, a process includes 3D printing a metal energetic ligand precursor ink by extruding the metal energetic ligand precursor ink into a structure and allowing the printed structure to dry, producing a nanoporous metal foam. The metal energetic ligand precursor ink is a slurry that includes one or more metal energetic ligands, as well as water, at least one binder, or both. The one or more metal energetic ligand precursors include mBTA, metal cyanimide, metal dicyanamide, metal 5-aminotetrozole, or any combination thereof. The process also includes heating the structure in an inert atmosphere such that the one or more metal energetic ligand precursors of the structure undergo self-sustaining combustion synthesis. The process further includes heat treating the structure to strengthen the structure and produce a post-processed structure. The metal energetic ligand precursor ink comprises a slurry of the one or more metal energetic ligand precursors, water, and at least one binder, or the metal energetic ligand precursor ink comprises a slurry of the one or more metal energetic ligand precursors and at least one binder.

