Barochemistry to Multifunctional High Energy Density Solid: Extended Phases of N 2 , CO, and N 2 +CO at High Pressures
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Barochemistry to Multifunctional High Energy Density Solid: Extended Phases of N2, CO, and N2+CO at High Pressures Choong-Shik Yoo Department of Chemistry and Institute for Shock Physics and, Washington State University, Pullman, WA 99164, U.S.A. ABSTRACT Many simple diatomic and triatomic molecules such as N2 and CO2 have the potential to form extended “polymeric” solids under extreme conditions, which can store a large sum of chemical energy in its three-dimensional network structures made of strong covalent bonds. Diatomic nitrogen is particularly of interest because of the uniquely large energy difference between that of the single bond (160 kJ/mol) and that of the triple bond (954 kJ/mol). As such, the transformation of a singly bonded polymeric nitrogen back to triply-bonded diatomic nitrogen molecules can release nearly 5 times the energy of TNT without any negative environmental impact. In this paper, we will describe our recent research efforts to synthesize novel extended phases of isoelectronic systems of N2 and CO, as well as those of N2+CO mixtures to lower the transition pressures and enhance the stability of recovered products at ambient condition. INTRODUCTION Despite great advances in research over many decades, today’s energetic materials are in low density, of low material strength, and are highly sensitive to shock. They burn incompletely, degrade, and age. These characteristics arise from low-dimensional open molecular structures with voids, grain boundaries, and defects. Overcoming these limitations is one of the grand challenges of our time. It will require development of structurally advanced energetic materials such as diamond-like extended solids in monolithic three-dimensional (3D) network structures in high density (~3 g/cc) and high-energy (~10 eV/nm) states without chemical heterogeneities or structural defects (Figure 1).
Figure 1. Structures of energetic materials: HMX with a large (~90%) empty space, a composite explosive with large grain boundaries, and high energy density (>10 eV/nm) CO2-V in quartz-like 3D network structure without grain boundaries.
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Conventional energetic materials consist largely of molecular solids with strong intramolecular covalent bonds and weak intermolecular van der Waals bonds. The large disparity between the inter- and intra-molecular distances (e.g., dinter/dintra~ 2.5-3.0) results in the relatively low densities (< 2.0 g/cc) and open structures (nearly 90% empty) of energetic molecular solids. Most energetic materials crystallize into structures of relatively low symmetry that are prone to structural distortions and high chemical sensitivities. The energetic processes of energetic materials can be described in terms of oxidationreduction reactions within each molecule but also across the molecular interfaces. They ar
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