Unraveling the Temporal Evolution and Kinetics Characteristics of Crucial Products in β-HMX Thermal Decomposition via ReaxFF-MD Simulations

Abstract

The temporal evolution of crucial products and their kinetics features are important for understanding the reaction behaviors of high explosives pyrolysis. We perform the large-scale and long-duration reactive force field molecular dynamics simulations to unravel the intricate reaction characteristics of β-HMX thermal decomposition across 1250-2500 K. The temperature-dependent reaction pathways and kinetics features of gaseous products, intermediates, and carbon clusters are systematically investigated. The results demonstrate that the initial reaction mechanism shifts from N-O cleavage to N-NO2 homolysis at elevated temperatures, which increases the energy barrier for N2 formation from 9.02 to 27.93 kcal·mol-1, attributed to the depletion of original N-N coordination precursor. H2O is consumed at high temperatures, corresponding to the enhanced CO2 and H2 production through water-gas shift-like reactions. Intermediate nitrogen oxides (NO2, NO3, NO) exhibit rapid formation-consumption cycles, while their hydrogenated derivatives (NO2H, NO3H, NOH) display higher stability with the higher dissociate energy barriers. Carbon clusters evolve from nitrogen-rich C3N3 heterocycles below 1750 K to C/O-dominated quasi-planar structures above 2000 K. These insights into intermediates dynamics, competing reaction pathways, and carbon cluster evolution will establish a theoretical foundation for developing combustion product equations of state, advancing the performance prediction of high explosives.