Study On Decomposition Mechanism Of NTO Based Mixed Explosives

As a typical high energy density material（HEDM）,NTO plays an important role in plastic bonded explosives and melt-cast explosives,but the potential thermal decomposition mechanism of NTO based mixed explosives is rarely explored.Thermal decomposition is a basic process of any energetic material exposed to external stimuli,so it is very important to master and analyze the thermal decomposition mechanism of NTO based mixed explosives.Based on the reactive molecular dynamics,the thermal decomposition of six systems,including NTO/HTPB,NTO/Poly-NIMMO,NTO/HMX,NTO/TNT,NTO/HMX/Poly-NIMMO and NTO/HMX/HTPB,at different temperatures was studied,and the initial reaction paths of different systems and the effects of other components on the thermal decomposition of NTO were revealed.In addition,the thermal decomposition simulation of some systems is supplemented by quantum chemistry and first-principles methods,and the reliability of decomposition paths is verified from the perspective of molecular structure and energy.Especially,considering the strong acidity of NTO,the interactions between NTO and binder Poly-NIMMO,high-energy component HMX were fully analyzed.The specific contents and results of this paper are as follows:（1）The thermal decomposition of NTO/Poly-NIMMO and NTO/HTPB PBXs systems was studied at constant temperature.In the NTO/HTPB system,reaction analysis and molecular snapshot prove that the N atom in CHON obtained by decomposition of NTO is N4,not N1.A large number of-OH produced by HTPB react with NTO and its decomposition products,and the calculated activation energies in the initial decomposition stage and intermediate decomposition stage are smaller than that in the pure NTO system,including the change trend of the final product H₂O,which proves that HTPB will accelerate the decomposition of NTO.Similarly,the initial reaction path proves that the-OH and-NO₂ generated by the decomposition of Poly-NIMMO will promote the thermal decomposition of NTO,which changes the final product of the thermal decomposition of NTO,and the change of bond number also verifies the above analysis.The analysis of clusters shows that the maximum number of clusters increases with the increase of temperature in a certain temperature range,but too high temperature has an inhibitory effect on the maximum number of clusters.In addition,the intermolecular interaction between NTO and Poly-NIMMO proves that the active H atoms of NTO will form strong hydrogen bonds with O atoms and N atoms of Poly-NIMMO,which will reduce the acidity of NTO/Poly-NIMMO system.（2）The thermal decomposition process of NTO/HMX based PBXs system and NTO/TNT melt-cast explosive system at five temperatures was analyzed.In this chapter,the layered model has been applied to the mixed explosive system for the first time,which is a new conception of the mixed explosive model,and the innovation of the model makes the simulation process more reasonable.Although the systems of them are different,the results show that-NO₂ of HMX and TNT can quickly capture H atoms of NTO,and then accelerate the thermal decomposition of NTO,which is similar to the experimental results.The difference is that in NTO/HMX system,the maximum number of clusters still follows the law of"first rising and then falling",but in NTO/TNT system,after 3000 K,the maximum number of clusters will not change significantly,and the clusters in NTO/TNT system will be more difficult to decompose.The analysis of IGMH and AIM shows that there will be hydrogen bonds between NTO and HMX,which will reduce the influence of NTO acidity and improve the application space of NTO in mixed explosives.（3）Based on the analysis of different two-component systems,the potential mechanism of thermal decomposition of NTO/HMX/Poly-NIMMO and NTO/HMX/HTPB three-component systems at different temperatures was revealed.The activation energies of the initial decomposition stage and the intermediate decomposition stage of the Poly-NIMMO mixed system are 46.942 k J·mol^-1 and 65.959 k J·mol^-1,respectively,and those of the HTPB mixed system are 48.508 k J·mol^-1 and 60.717 k J·mol^-1,both of which are smaller than those of the corresponding NTO/HMX system,which indicates that the NTO decomposition energy barrier is further reduced.Compared with the two-component system,the decomposition rate of NTO in the three-component system is further accelerated.In NTO/HMX/HTPB,the number of hydrogen transfer reactions is greatly reduced,while in NTO/HMX/Poly-NIMMO,the number of decomposition reactions of HNO₂ is greatly increased.Thanks to-NO₂ of HMX and Poly-NIMMO,and-OH of Poly-NIMMO and HTPB,the reaction rate of NTO in different decomposition stages of the two systems increased.It is worth mentioning that the number of clean-energy H₂ and NH₃ molecules in the final product has increased,which will provide a new idea for the reuse of waste explosives.