Theory Study On The Decomposition Mechanism Of FOX-7 And CL-20 And Their Composites

The basic scientific research of energetic materials,especially the physical and chemical properties,detonation mechanism and so on,have been paid much attention by researchers.It is found that the energetic materials can not exist alone in the real pyrolysis environment,and they are not only affected by the initial cleavage products such as charged particles,free radicals,but also the interaction among molecules,the influence of polymer molecules in Polymer Bonded Explosives.In this paper,the density functional theory was applied to study the influence on the energetic material molecular cracking mechanism affected by three factors--the interactions between initial pyrolysis products and products with no crack,the interaction among the molecules in same material and molecular interactions in the PBX system.?1?To investigate the effects of charged particles?H3O+,OH-,NO₂+ and NO+?on the dissociation channel of 1,1-diamino-2,2-dinitroethylene?FOX-7?,the complexes of H3O+,OH-,NO₂+ and NO+ respectively with FOX-7 were optimized using B3 LYP,B3PW91 and PBE0 functional theory of density functional theory in 6-31++G?d,p?basis sets.The composite mode was analyzed based on bonding styles and electrostatic potential.At the same level,the activation energies of the different dissociation channels of the complexes were calculated,and the nature of change in activation energies was analyzed based on the changes of the electronic structure parameters such as bond length,bond order and bonding styles.Results show that at B3LYP/6-31++G?d,p?level,OH-makes the dissociation energies of the two configurations of C—NH₂ bond decreased by 260.6 kJ·mol^-1 and 74.3 kJ·mol^-1,respectively.H3O+,NO₂+ and NO+ make the dissociation energies of C—NO₂ bond decreased by 44²60 kJ·mol^-1.The charged particles make the dissociation energy of C—C bond of the most complexes increased,but effect on the activation energy of nitro isomerism sightly.?2?To study the effect of radicals that generated in the reaction process on FOX-7 dissociation channels,geometries and electronic structures of the complexes which consisted of radicals and FOX-7 were calculated.The PW6B95-D3 functional were used in conjunction with basis set def2-TZVP and auxiliary basis sets def2-TZVP/J in ORCA program for these calculations.The value of the Laplacian were calculated by using the quantum theory of Atomsin-Molecules to analyze intermolecular interaction.The activation energies of the different dissociation channels of each complexes were calculated and the origin of changes in the activation energies were analyzed on the basis of changes in parameter of electronic structures.The energy barrier of the subsequent dissociation was reduced due to exist of free radical.Thus,the generation of free radical was similar to those of electronic particle,which could catalyze the cracking reaction of FOX-7.?3?FOX-7 clusters were studied by density functional theory to simulate the existence of FOX-7 molecule in crystal.The intermolecular interaction of FOX-7 and its effect on decomposition mechanism of FOX-7 were described.The results show that the most important intermolecular interaction in FOX-7 clusters is O--H/H--O,the intermolecular interactions arise from the sharing electrons intermolecular which exist in some intermolecular space formed by electron transfer.When using PW6B95-D3 theory,the intermolecular interaction makes the activation energy of C—NO₂ bond cleavage decrease generally.The activation energy of cluster II nitro isomer channels was decreased by 210.9 kJ ·mol^-1,and the activation energy of nitro channel of cluster IV was increased by 39.4 kJ · mol^-1.?4?The model of CL-20 based polymer bonded explosive were constructed according to four kinds of density functional theory,such as PBE-D3,?B97XD,M062X-D3 and B3PW91-D3,and the interaction between polymer binder and CL-20 molecule and its influence on cracking were studied.The EBCP of the critical point of the interaction site between the CL-20 molecule and the polymer monomer molecule is higher than zero,and the weak interaction between the CL-20 molecule and the polymer monomer molecule in the PBX model.The strongest interaction exists between CL-20 and EVA,CL-20 has 0.01229 electron transfer to EVA,hydrogen bond and Van der Waals effect of a large area of two molecules,the binding sites at the bond critical point charge density of the 0.00812 a.u.average,and the energy of interaction was-81.6 kJ · mol^-1 in the condition of M062X-D3 functional interaction.The activation energy of CL-20 was increased by three kinds of polymers,and the activation energy of CL-20 was increased mostly by F2314,and the activation energy of?N—NO₂?2 channel was increased by 12.9 kJ·mol^-1 in the M062X-D3 theory.