ReaxFF molecular dynamics simulations of shock induced reaction initiation in TNT

Abstract

Thermodynamic pathways and reaction initiation mechanisms of shocked TNT (2, 4, 6-trinitrotoluene, formula C6H2(NO2)3CH3) 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 C7H5O5N3 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 C7H5O5N3, NO2 and NO. The quantity of NO2 molecules reaches maximum when TNT molecules decompose completely. Furthermore, when NO2 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.