Energetic Materials Frontiers (Dec 2020)
Reactive molecular dynamics insight into the influence of volume filling degree on the thermal explosion of energetic materials and its origin
Abstract
The volume filling degree (VFD) is a universal property of materials whose influence is often overlooked in the assessment of their property and performance. The present work exemplifies its significance by evaluating its influence on the thermal explosion of a typical 1,3,5-trinitro-1,3,5-triazinane (RDX) energetic material (EM) and the related underlying mechanism, with experimental measurements of the critical temperature for an explosion delay of 5 s (T5s), and reactive molecular dynamics (MD) simulations. Three samples with different VFDs are accounted for in the T5s measurements, whereas seven RDX-containing models are established for our MD simulations, considering two kinds of surfaces, four VFDs of 1, 0.5, 0.1, and 0.05, and three heating styles. The experimental measurements show that a higher VFD leads to a lower T5s, or readier thermal decay. The origin of the VFD influence on T5s is that a smaller VFD favors dissociation reactions such as the NO2 partition, and disfavors the combination ones such as NO2 consumption in rapid complete decay to obtain final stable products and enhance heat release. Particularly, the reduced VFD increases the energy required to complete decay, lowers the decay rate and heat release, and results in reduced temperature, pressure elevation and explosion power, in agreement with the experimental observation that a higher VFD causes a lower T5s. Moreover, the origin of the VFD influence is principally from the pressure effect. Therefore, the VFD is crucial in the thermal decomposition of EMs because various VFDs can cause a significant difference in power. Moreover, the difference in the surface effect on the thermal decay of RDX between the (021) and (210) faces is clearly discriminated under adiabatic heating, because more activated molecules are found around the (021) face owing to the higher internal energy. In summary, the influence of VFD is significant when dealing with issues related to the surfaces of EMs.
