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 kinetic features is important for understanding the reaction behaviors of high-explosive 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 kinetic 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 the 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, and NO) exhibit rapid formation–consumption cycles, while their hydrogenated derivatives (NO₂H, NO₃H, and NOH) display higher stability with higher dissociation 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 intermediate 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.