Molecular dynamics study of the effect of H₂O on the thermal decomposition of α phase CL-20

The response of the mechanisms of the α polymorph of CL-20 (α-CL-20) to high temperature is important for understanding the phenomenon of shock initiation, shock ignition, and detonation. The thermal decomposition of α-CL-20 hydrate and pure α-CL-20 were studied by ReaxFF reactive molecular dynamics simulations to obtain the time evolution of water molecules and the effect of H₂O on the mechanisms of CL-20 at high temperatures. It was determined that the initial decomposition mechanisms of CL-20 are not dependent on the presence of water, but the secondary reaction pathways are. At low temperatures (T<1500 K), there is no relationship between the H₂O, hydrate CL-20, and pure CL-20 systems, as the mechanism is only the dissociation of the N-NO₂ bond to form the NO₂ radical. At high temperatures (1500 K≤T≤2500 K), water molecules act as a reactant or form catalytic systems with NO₂ radical to form OH radical, leading to the formation of O₂, H₂O₂, and other products. Water molecules accelerate the secondary stage reaction of hydrate systems, leading to increased secondary reaction rates and number of NO₂ radicals in the CL-20 hydrate compared with the pure CL-20 system. At very high temperatures (T>2500 K), the dissociation of water molecules competes with the initial thermal decomposition pathway of CL-20, leading to a larger rate constant for the pure CL-20 than for the hydrate CL-20.