Molecular Dynamics Simulation Of High Heat Resistance Mechanism Of Energetic Compounds

Heat-resistant energy materials are used in special high temperature environment,so the thermal performance of the materials is put forward higher requirements,and the safety problem in the process of use has been highly valued.In the process of thermal decomposition of heat-resistant energetic materials,the reaction is complicated and the experimental conditions are high.The simulation method can effectively avoid these problems and analyze the specific chemical reactions in the decomposition process.In this paper,the molecular dynamics of PYX,HNS,TATB,PETN,TKX-55 and DIO were studied by means of reactive molecular dynamics simulation,and the thermal decomposition mechanism of each substance was explored.The influence of initial decomposition reaction and cluster on the thermal decomposition process was analyzed,and the root cause of the high heat resistance of energetic materials was found.The main research contents are as follows:（1）The utilization rate of elemental CHON energetic materials is the highest,so it deserves great attention.Thermal decomposition kinetics of PYX,HNS and TATB was simulated by the Reax FF-lg field.It is found that there is a process of heat accumulation in the early stage of thermal decomposition of heat-resistant energetic materials,and the heat release is relatively low.Compared with heat sensitive materials,the initial decomposition reaction of heat-resistant energetic materials is dimer formation and hydrogen or oxygen transfer,rather than nitro dissociation.PYX,HNS and TATB generated a large number of clusters in the thermal decomposition process,which hindered the release of heat and the formation of small molecular products in the decomposition process,which was the main reason for the heat resistance of energetic materials.As the initial reaction,dimerization provides support for the growth of larger clusters.The molecular volume of TATB is smaller than that of PYX and HNS,and the strong activity of TATB after heating leads to the smooth growth of its clusters and large monomer clusters.As a heat-sensitive material,the dynamic simulation of PETN was compared with the other three heat-resistant substances,and the effect was very obvious.（2）TKX-55 is a kind of energetic eutectic with solvent component（DIO）and energetic component（BTNPBO）in its single crystal cell,which is relatively rare in the existing energetic materials.The thermal decomposition kinetics of TKX-55 was calculated and simulated by the Reax FF-lg force field,and programmed heating and thermostatic heating（2000,2500,3000,3500 K）were carried out at 300 to 3500 K.The results show that the initial decomposition reaction of BTNPBO is dimerization,ring-opening reaction of intermediate 1,3,4-oxadiazole,and nitro dissociation of intermediate on 1,3,5-trinitrophenyl group.In the ring-opening reaction,the bond breaking modes are C-O,C-N and N-N,and the three bonds break simultaneously and generate stable small molecule N₂ under the temperature programmed.The large conjugate structure of BTNPBO makes it more stable and has higher thermal stability.Therefore,TKX-55 has good heat resistance,and the weight of clusters generated by its decomposition process accounts for about 30-50%of the total weight of the system.（3）The effect of BTNPBO on the thermal decomposition of DIO was studied.Molecular dynamics simulation of pure DIO was performed by the Reax FF-lg field.It was found that the presence of BTNPBO affected the decomposition process of DIO,which was manifested by the increase of heat transfer at low temperature and the initial decomposition path in the direction of lower energy barrier,which accelerated the decomposition rate of DIO.The initial decomposition reaction of pure DIO system was the ring-opening reaction of DIO.The active molecules generated by the initial decomposition of BTNPBO in TKX-55 were adsorbed by DIO,which changed the decomposition path of DIO and inhibited the reaction rate of BTNPBO.The weak hydrogen bond interaction between BTNPBO and DIO increases the stability of TKX-55,and hydrogen transfer reaction occurs between the two.