Theoretical Study On The Structure And Thermal Properties Of HMX Based Crystals

Safety mechanism is a crucial but very complicated topic in the field of energetic materials.This mechanism depends on the multilevel structures of energetic materials,their external stimulation styles,and environmental conditions.For example,at the molecular level,sensitivity is believed to be governed by molecular stability.At the crystal level,however,the molecular stacking mode and crystal shape,size,and defects can affect this sensitivity.At the device level,sensitivity is further influenced by shape,size,surface,and interfacial structures.Therefore,it is important to study the influence of the explosives sructures on the sensitivity.In this work,we selected an illustrative example of polymorphic HMX with prominent comprehensive performance as our objective.By using the method of quantum chemistry and crystal structure analyses,we studied the interaction of three single crystal of HMX(?-??-and ?-HMX)and co-crystal based on HMX to provide details and laws of intermolecular interactions of co-crystal explosives at the atomic and molecular level.Moreover,by using DFTB method simulation,we studied the chemical reaction of three single crystal of HMX under the condition of high temperature.The main results are as follows:Firstly,we took a systemic analyses on the crystal packing of 3 single crystal of HMX(?-??-and ?-HMX)and 11 HMX cocrystal explosive.As a result,we found that relationship between the crystal packing and impact sensitivity of these crystals.The packing model of?-HMX with the most impact insensitive in its polymorph is wavelike stacking.These are regular cavity in the packing model of ?-HMX which is high sensitivity,which may be one of the reasons of forming hot.The molecule structures of conformers observed in HMX co-crystals could influence packing structures and insensitive of crystals.These co-crystals which in consisted of HMX and cycle conjugated molecule without electron-absorbing branch are low insensitive.Secondly,we study the thermal effect and forms effect on the thermal decomposition of the mechanism of the primary thermal decay steps of condensed state HMX.As a result,theN—NO2 partition dominate the initial decay steps in ?-HMX,which are kinetic controlled;the C—N partition dominate the initial decay steps in ?-HMX,which are energetics controlled.At low temperature,the rate of decomposition of three HMX pure forms is ?-HMX > ?-HMX >?-HMX;At high temperature,the rate of decomposition of three HMX pure forms is?-HMX > ?-HMX > ?-HMX.In the case of programmed heating from,the decomposition rate of ?-HMX is most slow,and potential energy released is least.There are some initial decay mechanism which caused by secondary reaction in ?-HMX,and find that the formation of secondary reaction are related with C—H partition,formation and transfer of free H.Summarily,we study crystal packing of three pure HMX forms and eleven HMX co-crystals,the structure and ESP of coformer molecules,the decomposition of polymorphs of HMX at different thermal models.All these findings are expected to enrich the knowledge of both energetic materials and co-crystals,and enhance the rationalization of crystal design.