Study On Thermal Decomposition Mechanism Of Diazole Nitrogen-rich Energetic Compounds

The nitrogen-rich energetic compounds of diazoles not only have excellent burst performance,but also usually have low sensitivity and good thermal stability,which have received wide attention from scholars at home and abroad.In this paper,the thermal decomposition mechanism of 3,4-Bis（3-nitrofurazan-4-yl）furoxan（DNTF）,2,4-dinitroimidazole（2,4-DNI）,1-methyl-2,4,5-trinitroimidazole（MTNI）and CL-20/MDNI cocrystal at high temperature was investigated using quantum chemical and molecular dynamics methods.The initial decomposition paths of diazole materials were obtained.The intrinsic reason for their good thermal stability was found.In addition,the mechanisms of temperature effects on the thermal decomposition paths,decomposition products and clusters were also revealed.The main studies are as follows:（1）In order to understand the thermal decomposition characteristics of 3,4-Bis（3-nitrofurazan-4-yl）furoxan（DNTF）,the thermal decomposition reaction of DNTF at 300 K-4000K temperature programmed and constant temperature of 2000 K,2500 K,3000 K,3500 K and 4000 K was simulated by quantum chemistry and ab initio computational molecular dynamics method.The thermal decomposition mechanism of DNTF at different temperatures was analyzed from the aspects of product evolution,cluster,potential energy curve and reaction path.The analysis of products,show that the initial small molecular products are NO,NO₂,CO,CO₂ and N₂,and the final small molecular products are CO₂ and N₂.In the early stage,the ring-opening reaction of furoxan in DNTF structure is the main trigger reaction,and the C-C bond is broken at the initial stage of reaction.The carbon chain structure produced by decomposition forms various cluster structures in the form of C-N bond.In addition,it was found that temperature significantly affects the decomposition rate of DNTF,but does not change its initial decomposition path.（2）The thermal decomposition mechanism of 2,4-DNI and MTNI imidazole energetic compounds at constant high temperature was investigated by Reax FF/lg molecular dynamics method.The reasons for the good thermal stability of 2,4-DNI and MTN were explained by the analysis of the initial decomposition pathways.The dimerization reaction of MTNI firstly occurs at different high temperatures,then the C-NO₂ bond and O-NO bond break to form NO₂and NO respectively,and finally the imidazole ring opens.Hydrogen transfer and dimerization reactions can effectively delay the energy release of energetic materials.Therefore,2,4-DNI and MTNI displayed better thermal stability.In addition,the hydrogen atom in 2,4-DNI molecule is more active than in methyl group of MTNI molecule,and the active hydrogen atoms tend to cause thermal decomposition reactions to occur.2,4-DNI and MTNI produced a large number of clusters during thermal decomposition.These clusters prevent the compound from continuing to decompose into gaseous small molecules,thus retarding the release of energy.The reaction kinetic parameters of 2,4-DNI with MTNI,including the chemical reaction rate constant,activation energy and pre-exponential factor,were obtained by fitting the potential energy change curve of the system during thermal decomposition by Arrhenius equation.（3）The thermal decomposition mechanism of CL-20/MDNI cocrystal was evaluated by Reax FF/lg molecular dynamics method.The interaction mechanism between CL-20 and MDNI during thermal decomposition was revealed through the initial decomposition path.The breaking of N-NO₂ bond in CL-20 molecule is the trigger reaction of thermal decomposition of CL-20/MDNI cocrystal.Part of the nitro groups falling off from CL-20 molecules will combine with MDNI molecules,which hinders the further thermal decomposition of MDNI.This is an important reason why the sensitivity of CL-20/MDNI cocrystal is lower than that of CL-20.The MDNI molecule first undergoes a dimerization reaction at high temperature,which is similar to the initial decomposition path of 2,4-DNI and MTNI.The dimer will then decompose into C₄H₄O₅N₄ and C₄H₄O₃N₄,completing the intermolecular oxygen transfer.The end products of the thermal decomposition of CL-20/MDNI cocrystal are N₂,CO₂,H₂O and H₂.In a certain temperature range,increasing the temperature can significantly promote the decomposition rate and degree of CL-20/MDNI cocrystal.