The solid phase thermal decomposition and nanocrystal effect of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) via ReaxFF large-scale molecular dynamics simulation.

The solid phase thermal decomposition and nanocrystal effect are extremely important to understand the ignition, combustion, reaction growth and buildup to detonation under shock wave action. To explore the basic mechanism at the atomic level and understand the interaction among nanocrystal lattices, molecules, and intermediates during the solid phase decomposition, ReaxFF large-scale molecular dynamics simulation at 1000-3000 K was demonstrated on the solid phase of nanocrystalline RDX with a size in the range of 5-12 nm. Based on the analysis of the RDX decay and chemical species, we found that the whole decomposition process can be divided into the solid-affected stage and the following less-condensed phase stage. From the results of NO2 diffusion and high frequency reaction statistics for the nanocrystal effect on the RDX decay, intermediate diffusion was found to be strongly associated with the chemical pathway. In addition, it was found for the first time that the thermal decomposition of RDX originates from the inside of the nanocrystal instead of its surface. Furthermore, a promising uniform energy distribution mechanism transfer by vibration inside the nanocrystalline RDX was demonstrated. The detailed information derived from this study can aid in the thorough understanding of the size effect on the chemical kinetics of nanoexplosives, especially for thermal decomposition and reaction growth.