Anisotropic hydrogen bond structures and orientation dependence of shock sensitivity in crystalline 1,3,5-tri-amino-2,4,6-tri-nitrobenzene (TATB).

The orientation dependence of shock sensitivity in high explosive crystals was explored in this study. As a widely used wood explosive, 1,3,5-tri-amino-2,4,6-tri-nitrobenzene (TATB) is insensitive to thermal ignition and mechanical impact. Its typical anisotropic crystal structure suggests anisotropic shock sensitivity. Shockwaves were applied to an incised TATB crystal along three orthogonal directions using the multiscale shock technique (MSST) combined with the ReaxFF method to study the origin of anisotropic shock sensitivity. The physical and chemical responses of the TATB crystal during shock were investigated. The results show that the temperature, stress, volume compressibility, and decomposition rate of TATB are strongly dependent on the shockwave direction. In other words, the sensitivity of TATB to mechanical shock is strongly dependent on the crystal orientation. TATB is relatively sensitive along the directions parallel to the (001) crystal plane (X and Y directions) and is highly insensitive along the [001] direction (Z direction). We calculated the energy of intermolecular hydrogen bonds and the elastic constants of the TATB crystal using ab initio simulations, which also show anisotropy. We found that the unique structure of intermolecular hydrogen bonds and the difference in temperature rise induced by orientation-related compressibility are primarily responsible for the anisotropic shock wave sensitivity.

Comparison study of carbon clusters formation during thermal decomposition of 1,3,5-triamino-2,4,6-trinitrobenzene and benzotrifuroxan: a ReaxFF based sequential molecular dynamics simulation.

Carbon rich clusters are usually found after the detonation of explosives, which greatly hinder their further decomposition into small molecules. A comparison study of thermal decomposition and clusters formation between 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and benzotrifuroxan (BTF) crystals was conducted to uncover the mechanisms behind their distinct differences in sensitivity and reaction violence, which has not been investigated in detail. The simulations of heating at 3500 K, then expansion and cooling were conducted through reactive molecular dynamics using the ReaxFF-lg force field. As a result, the initial low decay rate indicates that TATB is more stable than BTF under high temperatures, while once ignited it decays faster than BTF. Nevertheless, BTF decomposes more completely with a higher potential energy release, a greater amount of final products, and higher reaction frequencies, and shows higher reaction violence than TATB. More and heavier clusters occur in TATB crystals compared with those in BTF. Large clusters form during the heating process and then partly dissociate during expansion and cooling. A faster cooling rate facilitates larger clusters formation. Graphitic geometries as well as carbon rings and carbon chains are common in the stable clusters. Besides, further simulations show that a lower heating temperature facilitates larger clusters formation both in TATB and BTF. Our results are expected to deepen the insight into the mechanisms of carbon clusters formation and the different performances of TATB and BTF.

Self-assembly of single-wall carbon nanotubes during the cooling process of hot carbon gas.

In this work, self-assembly mechanism of single-wall carbon nanotube (SWCNT) during the annealing process of hot gaseous carbon is presented using reactive force field (ReaxFF)-based reactive molecular simulations. A series of simulations were performed on the evolution of reactive carbon gas. The simulation results show that the reactive carbon gas can be assembled into regular SWCNT without a catalyst. Five distinct stages of SWCNT self-assembly are proposed. For some initial configurations, the CNT was found to spin at an ultra-high rate after the nucleation. Graphical abstract Self-assembly process of single-wall carbon nanotube from the annealing of hot gaseous carbon.