The thermal decomposition mechanism and kinetic study of TNBP based on molecular dynamics

2,8-Bis (2,4,6-trinitrophenyl)-5,11-dioxo-2,4,6,8,10,12-hexacyclo[7.3.0.03,7]dodecane-1(12),3,6,9-tetraene (TNBP) is a new thermally stable explosive renowned for its exceptional detonation performance and thermal stability, making it highly valuable for applications in supersonic weapons, aerospace engineering, and ultra-deep well perforation. This study utilizes reactive molecular dynamics simulations to elucidate the thermal decomposition mechanism and kinetics of TNBP. Under both non-isothermal and isothermal conditions, the initial decomposition stages involve key reactions such as intermolecular oxygen transfer, dimerization, and NO dissociation. The primary decomposition products include small molecules like NO₂, NO, N₂, H₂O, CO₂, H₂, HNO₂, and HNO, alongside a range of clustered molecular species. Structural analysis indicates that TNBP's highly stable cyclic framework restricts cluster growth at lower temperatures. As the temperature rises, the rapid dissociation of H and N atoms from these clusters promotes a structural transition toward chain-like configurations. Furthermore, unlike RDX, TNBP pyrolysis generates a significant quantity of clusters, which effectively suppress the migration of atoms and retard heat transfer-this is identified as a crucial factor contributing to its superior thermal stability. Finally, kinetic parameters, including the activation energy (E_a) and pre-exponential factor (lnA), were determined for different stages of the pyrolysis process through reaction kinetics modeling. This work provides fundamental insights into TNBP's behavior under extreme high-temperature conditions, offering a theoretical basis for the design and synthesis of novel heat-resistant energetic materials.

Molecular dynamics simulations of the thermal decomposition behavior of TNBP were conducted using the Large-scale Atomic/Molecular Parallel Simulator (LAMMPS) in conjunction with the ReaxFF/lg reaction force field. First, a 2 × 2 × 1 supercell model was constructed based on X-ray diffraction crystal data. To obtain a reasonable initial equilibrium configuration, the system underwent 5 ps of geometric optimization under NPT conditions (300 K, 1 atm) with a time step of 0.1 fs and a temperature damping coefficient of 10 fs. The applicability of the ReaxFF/lg force field in describing the TNBP system was verified by comparing crystal parameters with the interatomic radial distribution function. To investigate the impact of elevated temperatures on TNBP thermal decomposition, two heating simulation protocols were employed: First, the system was heated from 300 to 2700 K at a rate of 12 K·ps^-1 under NVT conditions. Second, isothermal kinetic simulations of 200 ps were conducted at four temperatures: 2500 K, 2750 K, 3000 K, and 3250 K. During simulations, molecular species information and thermodynamic data were output every 10 fs, with bond-level evolution and atomic trajectories recorded synchronously.