Ranking the Drop-Weight Impact Sensitivity of Common Explosives Using Arrhenius Chemical Rates Computed from Quantum Molecular Dynamics Simulations.

Drop-weight impact tests are used routinely to characterize the handling safety of explosives. Numerous studies have sought to connect various physical and chemical properties of the energetic molecules and materials to their measured impact sensitivities. Wenograd in the early 1960s demonstrated that there is a strong dependency of the drop-heights on the critical temperatures required for explosives to undergo prompt reactions. Reactive quantum molecular dynamics simulations with the 31 density functional tight binding model have been used to compute the delay time before the thermal explosion of the secondary explosives erythritol tetranitrate (ETN), pentaerythritol tetranitrate (PETN), cyclotrimethylene trinitramine (RDX), cyclotetramethylene tetranitramine (HMX), trinitrotolune (TNT), and 3,3'-diamino-4,4'-azoxyfurazan (DAAF) as a function of the initial temperature and pressure. The delay time to explosion data are consistent with Arrhenius chemical kinetics, which is expected for thermally activated processes in materials and in accord with experimental measurements. The critical temperatures required for the materials to undergo prompt explosions display the same dependence on drop height as was observed by Wenograd. Hence, quantum-based reactive molecular dynamics simulations are potentially a tool for ranking the drop-weight impact sensitivity and handling safety of explosives.