Thermal Decomposition Mechanism of Nitroglycerin by ReaxFF Reactive Molecular Dynamics Simulations

The decomposition processes of nitroglycerin (NG) at various temperatures (2500, 2750, 3000, 3250 and 3500 K) are simulated by the reactive molecular dynamics simulations with ReaxFF-lg. The initial decomposition pathway of NG, the evolution of the main products and the reaction kinetic parameters for the different stages are analyzed. The results show that the main initial decomposition mechanisms of NG are O-NO₂ bond dissociation and the hydrogen capture reaction of NO₂. The main products of NG thermal decomposition are NO₂, NO, HNO, CO₂, N₂, and H₂O, while CO₂, N_2, and H₂O are the final products. As the temperature increases, the processes of O-NO₂ bond dissociation and the hydrogen capture reaction of NO₂ accelerate, resulting in accelerated decomposition of NG. The reaction kinetic parameters are calculated for three different reaction stages. The activation energy and the pre-exponential factor obtained in the initial decomposition stage are 69.58 kcal mol⁻¹ and 32.53 s⁻¹. The activation energy and the pre-exponential factor obtained in the intermediate decomposition stage are 111.78 kcal mol⁻¹ and 29.12 s⁻¹. At 3250 K, the rate constants of N₂ and CO₂ reach maximum while the rate constant of H₂O increases continuously with increasing temperature. Accordingly, the mechanism of initial thermal decomposition of NG under the high temperatures is proposed detailedly.