The thermal decomposition process of Composition B by ReaxFF/lg force field

Composition B is a melt-cast explosive consisting of mixtures of TNT and RDX. It has many excellent properties, but there are still multiple safety problems when it is used. Therefore, it is of importance to understand the thermal decomposition mechanism of Composition B. In this paper, during the establishment of the supercell model, the mass ratio of TNT to RDX is about 2:3, which accords with the actual proportion of formula of Composition B. Afterward, the thermal decomposition reaction of Composition B is conducted at various temperatures (2000 K, 2500 K, 3000 K, 3500 K, and 4000 K) by using molecular dynamics simulation of ReaxFF/lg. In terms of potential energy (PE) evolution, primary reaction, intermediate product, final product, and clusters, the thermal decomposition mechanism of Composition B is made an analysis. The activation energy of Composition B is 141.8 kJ/mol by fitting the kinetic parameters of the reaction. During the decomposition process of Composition B, the decay rate of RDX is faster than that of TNT, and the decay rates of TNT and RDX is accelerated significantly with the increasing temperature. The higher the temperature, the shorter the time difference between the two to fully decompose. It can be revealed from the result that the initial reaction path of Composition B decomposition is N-NO₂ of RDX cleavage to form NO₂, followed by the reaction of TNT with NO₂ and other molecules. The initial decomposition reaction path of Composition B is the similar at different temperatures. The main products are small molecules (NO₂, NO, N₂O, H₂O, CO₂, N₂, H₂, HNO₂, and HNO). Temperature can make a great difference for the structure of clusters. Large clusters in the system will break down into smaller molecules at high temperature.