Anisotropic Impact Sensitivity and Shock Induced Plasticity of TKX-50 (Dihydroxylammonium 5,5'-bis(tetrazole)-1,1'-diolate) Single Crystals: From Large-Scale Molecular Dynamics Simulations
Q An and T Cheng and WA Goddard and SV Zybin, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 2196-2207 (2015).
Dihydroxylammonium 5,5'-bis(tetrazole)-1,1'-diolate (TKX-50) is a newly synthesized energetic material with high energy storage, low impact sensitivity, and low toxicity. These features make it a viable candidate to replace such commonly used energetic materials as RDX and CL-20 in the next generation of explosives. Sensitivity determines the engineering application of energetic materials (EMs) and has been widely studied for various EMs. To understand the origin of the anisotropic sensitivity and properties of this new synthesized EM, we report a flexible classical force field for TKX-50 developed to reproduce the molecular properties (geometry, vibrational frequencies and torsion barriers) and the crystal properties (cell parameters and lattice energy). We then used this force field in molecular dynamics (MD) simulations to predict such thermodynamic and mechanical properties as isothermal compressibility, thermal expansion, elastic moduli, and heat capacity. Furthermore, we carried out large scale (similar to a half million atoms) MD simulations to investigate the mechanical response to shocks in the 100, 010 and 001 directions. The predicted Hugoniot elastic limits (HELs) are 6.1 GPa for 100, 14.2 GPa for 010 and 9.1 GPa for 001 shocks. Thus, single crystal TKX-50 shows anisotropic impact sensitivity with 010 as the most sensitive direction and 100 as least sensitive. The plastic deformations in shock compression along the 100 direction primary arise from the (001)/210 and (010)/001 slip systems of. For the 010 shock, the primary slip systems are (100)/021 and (001)/210. However, no obvious slip system was observed for 001 shock.
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