Initial thermal decomposition of TNT/C₁₀H₈ cocrystal: reactive molecular dynamics simulations

The discussion of shock initiation and detonation with ReaxFF reactive force field has centered nearly around conventional energetic materials. The comprehensive molecular dynamics of thermal decomposition of condensed phase TNT/C₁₀H₈ cocrystal with the ReaxFF/lg potential function are studied, which adds a long range correction term to the total energy expression of original ReaxFF. The thermal decomposition of TNT single crystal is performed similarly to determine the main effect of C₁₀H₈ on the overall thermal characteristics of cocrystal. Furthermore, the activation energies associated with endothermic and exothermic stages of cocrystal thermal decomposition are found to be 35.7 kcal/mol and 56.1 kcal/mol, respectively. Its activation energy at primary endothermic stage is compatible with that of TNT single crystal, but the activation energy at secondary exothermic stage is higher than the value calculated for TNT. In addition, the heat output calculated during the exothermic step of TNT/C₁₀H₈ cocrystal is less than that of TNT at the same temperature. The decay rate of reactants by curve fitting shows that C₁₀H₈ inhibits the decomposition of TNT in cocrystal. NO₂, NO and HONO are major primary decomposition products by the way of identification analysis. The distribution of NO₂ /TNT_-NO2, NO/TNT_-NO, HONO/TNT_-HONO shows that the decomposition proceeds via bimolecular reaction. Main final products of cocrystal are N₂, H₂O, CO₂, and CO, and the initial decomposition routes of C₁₀H₈ is C-H bond dissociation as a result of C-C bond dissociation energy of C₁₀H₈ in cocrystal is higher than C-H bond, and this process may promote the formation of H₂O.