ReaxFF molecular dynamics simulations of shock induced reaction initiation in TNT

Thermodynamic pathways and reaction initiation mechanisms of shocked TNT (2, 4, 6-trinitrotoluene, formula C ₆ H ₂ (NO ₂ ) ₃ CH ₃ ) with shock velocities in the range of 6 -10 km·s ^-1 using the first-principles-based ReaxFF reactive force field molecular dynamics and the multiscale shock technique (MSST) are reported in this paper. The decomposition reactions occur at a shock velocity of 7 km·s ^-1 or higher. The shock initiation pressure, 25.1 GPa, is obtained from Rankine-Hugoniot relation. According to the link between macroscopic shock initiation and microscopic chemical reaction events, the formation of TNT-dimer and decomposition to C ₇ H ₅ O ₅ N ₃ are the dominant initial route for shock induced reaction initiation. At shock speeds equal to or higher than 8km·s ^-1 , TNT-dimer is formed and subsequently decomposed to C ₇ H ₅ O ₅ N ₃ , NO ₂ and NO. The quantity of NO ₂ molecules reaches maximum when TNT molecules decompose completely. Furthermore, when NO ₂ molecules are consumed fully, the volume of reaction system begins to expand. TNT molecules are dimerized at each shock condition, and the quantity of dimers is the largest at a shock initiation velocity of 7 km·s ^-1 . Finally, the formation and evolution of carbon-containing clusters in shocked TNT are analyzed.