Investigating the decomposition mechanism of CL-20/MTNI cocrystal explosive under high temperature and high pressure using ReaxFF/lg molecular dynamics simulations

Abstract

The CL-20/MTNI cocrystal, as a novel energetic material (EMs), possesses the advantages of high energy content and low sensitivity, making it a promising substitute for traditional EMs. However, the thermal decomposition mechanism of this cocrystal has not been thoroughly investigated. Therefore, we utilized the ReaxFF/lg force field to study the thermal decomposition of CL-20/MTNI cocrystal at different temperatures (2500, 2750, 3000, 3250, and 3500 K) and pressures (3000 K/0.5 GPa, 3000 K/1.0 GPa, and 3000 K/1.5 GPa). The evolution of species, initial decomposition mechanisms, and changes in the number of final products were analyzed. The results indicate that hexanitrohexaazoisowuzane (CL-20) completely decomposes within 55 ps, while 1-methyl-2,4,5-trinitroimidazole (MTNI) decomposes completely within 110 ps, suggesting that CL-20 has lower thermal stability compared to MTNI. The high-temperature decomposition of CL-20/MTNI cocrystal exhibits three main possible reaction pathways. Firstly, the denitration of CL-20 occurs, followed by the denitration of MTNI, and finally, the nitro group isomerization of MTNI. This indicates that the nitro groups in CL-20 have lower thermal stability compared to those in MTNI within the CL-20/MTNI cocrystal. Analysis of the five final products reveals that the quantities of NO2 and NO are higher than other species, attributed to the higher nitrogen and oxygen content in the CL-20/MTNI cocrystal structure. As the temperature increases, the decomposition and conversion of NO2 are accelerated, leading to a sharp decrease in the quantity of NO2 and an increase in the content of NO. However, when the pressure increases, both the quantities of NO2 and NO exhibit a trend of initially increasing and then decreasing, with a noticeable increase in the quantity of N2. This indicates that high pressure accelerates the thermal decomposition of NO2 and NO.