Molecular Dynamics Simulation Study On The Mechanism Of Low Heat Resistance Of Energetic Compounds

Heat resistance is a basic and important characteristic of energetic materials,which has always attached much attention in the development and application of energetic materials.Compared with the clear evolution mechanism of energetic compounds with high heat resistance,we are still unclear about the evolution mechanism of energetic compounds with low heat resistance,especially the chemical reaction mechanism under extreme conditions is complicated.It is a great challenge to study the coupling process of chemical reaction and physical change in experiments.Therefore,it is significance to carry out theoretical research on the mechanism of low heat resistance of energetic compounds.In this paper,the thermal stability and reaction mechanism of three kinds of low heat resistant compounds,such as nitrobionic explosives,CL-20 solvates and hydroxylamine energetic ion salts,were studied by molecular dynamics simulation(MD)and density functional theory(DFT).The specific content is as follows:(1)The Reax FF-lg reactive force field was used to simulate five nitroform explosives,TNMA,BTNEDA,BTNNA,BTNF and TNETB,at a programmed temperature of 300-2700K and four constant temperatures of 1500 K,1800 K,2000 K and 2500 K,compared with PETN and TATB.The molecular dynamics simulation(MD)results show that nitroform explosives and PETN further decompose with the rapid dissociation of NO₂ during the heating process to form a series of small molecular fragments to the final product.However,the initial decomposition of heat-resistant explosives TATB is mainly intermolecular reaction and cluster.Therefore,the rapid fragmentation eventually leads to the low heat resistance of nitroform energetic compounds.(2)The diffusion behavior and decomposition mechanism of energetic solvates CL-20/H₂O₂ and?-CL-20 under thermal stimulation were studied by molecular dynamics simulation(MD).The simulation shows that the solvent molecules will diffuse out of the unit cell during the low-temperature heating process,among which H₂O in?-CL-20 diffuses the fastest,and H₂O₂ in monoclinic CL-20/H₂O₂ has better anti-migration ability;The simulation also shows that the existence of solvent molecules can maintain the stability of cocrystals at low temperatures,and this effect disappears at high temperatures.Secondly,the presence of the solvent obtained by density functional theory(DFT)can increase the lattice energy of the crystal.(3)The ab initio molecular dynamics simulation(AIMD)was used to study the decomposition mechanism and evolution process of hydroxylamine ionic salts NH₃OH-DNABF and NH₃OH-DNBTO at a programmed temperature of 300-3500 K.The simulation results show that the initial decomposition of the two energetic ionic salts is the leaving process of the hydrogen atom on the hydroxylamine cation.The path of NO₂produced by NH₃OH-DNABF decomposition is N-NO₂ bond breaking,while the NH₃OH-DNBTO is the result of the combination of free radicals rather than C-NO₂ bond breaking.Density functional theory(DFT)also showed that hydrogen transfer inhibited the dissociation of NO₂.In summary,through the comprehensive molecular dynamics simulation(MD)study of three low heat resistance of energetic compounds,these simulation results are hoped to provide ideas and suggestions for the design,synthesis and development of heat-resistant explosives in the future.