Effects of Nanoparticle Size on the Thermal Decomposition Mechanisms of 3,5-Diamino-6-hydroxy-2-oxide-4-nitropyrimidone through ReaxFF Large-Scale Molecular Dynamics Simulations.

ReaxFF-lg molecular dynamics method was employed to simulate the decomposition processes of IHEM-1 nanoparticles at high temperatures. The findings indicate that the initial decomposition paths of the nanoparticles with different sizes at varying temperatures are similar, where the bimolecular polymerization reaction occurred first. Particle size has little effect on the initial decomposition pathway, whereas there are differences in the numbers of the species during the decomposition and their evolution trends. The formation of the hydroxyl radicals is the dominant decomposition mechanism with the highest reaction frequency. The degradation rate of the IHEM-1 molecules gradually increases with the increasing temperature. The IHEM-1 nanoparticles with smaller sizes exhibit greater decomposition rate constants. The activation energies for the decomposition are lower than the reported experimental values of bulk explosives, which suggests a higher sensitivity.

Effects of oxidizing molecules on the thermal decomposition of TTDO by ab initio molecular dynamics simulations.

Oxidizing molecules play a very important role in improving the comprehensive properties of energetic materials. Recently, a series of energetic cocrystals containing 2,4,6-triamino-1,3,5-triazine-1,3-dioxide (TTDO) and oxidizing molecule have been successfully prepared. Therefore, ab initio molecular dynamics were used to simulate the thermal decomposition process of TTDO, TTDO:H2O2, TTDO:HNO3, and TTDO:HClO4 crystals at 3000 K to study the role of oxidizing molecules during the thermal decomposition of TTDO. The initial decomposition paths of the TTDO crystal include N-H bond breaking, C-N bond breaking, and intramolecular and intermolecular H transfers. The formation mechanisms of H2O, N2, and CO2 in the four crystals are completely different. The key formation mechanism of H2O is the combination of O with OH, that of N2 is the formation of the -N-N- structure, and that of CO2 is to form the intermediate CO-R with carbonyl structure that form the fragment with the -O-C-O- structure. All the oxidizers H2O2, HNO3, and HClO4 involve in the formation of H2O, N2, and CO2. The formation mechanisms of urea during the decomposition process of the four crystals are completely different, but the key step is to produce the structure of -N-CO-N-. An analysis of Nx shows that H2O2, HNO3 and HClO4 affect not only the types of Nx, but also its formation mechanisms. Among them, HNO3 has the greatest influence on Nx.