| The brisant nitramine explosives(RDX,HMX and CL-20)have relatively high detonation heats,detonation velocities and detonation pressures.They can be extensively used in composite explosives and solid propellants so that the weapons will be benefitted.However,the raw nitramine explosives are sensitive during development,procuction,storage,transportation and application,which seriously threatens the safety of the ammunitions and the lives.Thus,the reduction in sensitivity had become a research focus in order to insure the safety.This thesis was based on the method of co-crystallization to low the sensitivity.Those main works were as follows.Molecular simulation was used to do the dynamic simulations of nitramine explosives,prediction of molecular structure of co-crystals and prediction of morphology of co-crystals.CL-20/RDX and CL-20/AP co-crystals were prepared by evaporation method,and were characterized by different methods.Based on the nano-crystallization technology,to combine co-crystallization and nano-crystallization,freeze drying method was used to prepare nano-sized CL-20/NQ and HMX/NQ co-crystals.The specific research contents are as follows:Firstly,a series of theoretical simulations of CL-20/TNT co-crystal were carried out.The electrostatic potential calculation of CL-20 and TNT was carried out by the Dmol3 module of molecular dynamics calculation software Materials Studio.Based on the results of electrostatic potential calculation,Forcite module was used to build CL-20/TNT co-crystal model.Using this co-crystal model,the supercell was constructed to do the molecular dynamics simulation,and a series of properties of the co-crystal were compared with CL-20.It is found that the properties of CL-20/TNT co-crystal were better than that of CL-20 from the cohesive energy density,the bond length and the mechanical properties simulations.The Polymorph Predictor module was used to simulate to obtain a series of CL-20/TNT co-crystal molecular structures,and the most likely co-crystal molecular structure was screened.The results indicated that the most likely molecular structure of CL-20/TNT co-crystal was in the orthorhombic space group PBCA,which was consistent with the actual single crystal of CL-20/TNT co-crystal.Three methods of the Morphology module(BFDH,Growth Morphology and Equilibrium Morphology)were used to predict the morphology of CL-20/TNT co-crystal theoretically.The results showed that the prediction by Equilibrium Morphology was the most accurate,which proved that Morphology was a useful method to predict the morphology of co-crystal.It can be used as a new theoretical guidance for the preparation of co-crystal.Secondly,a series of theoretical simulations of CL-20/DNT co-crystal were carried out.The electrostatic potential calculation of CL-20 and DNT was carried out by the Dmol3 module of molecular dynamics calculation software Materials Studio.Based on the results of electrostatic potential calculation,Forcite module was used to build CL-20/DNT co-crystal model.Using this co-crystal model,the supercell was constructed to do the molecular dynamics simulation,and a series of properties of the co-crystal were compared with CL-20.It is found that the properties of CL-20/DNT co-crystal were better than that of CL-20 from the cohesive energy density,the bond length and the mechanical properties simulations.The Polymorph Predictor module was used to simulate to obtain a series of CL-20/DNT co-crystal molecular structures,and the most likely two co-crystal molecular structures were screened.The results indicated that the most likely molecular structure of CL-20/DNT co-crystal was in the triclinic space group P-1,which was consistent with the actual single crystal of CL-20/DNT co-crystal.At the same time,almost the same simulation structure with the single was found,which showed the correctness of the simulation.Three methods of the Morphology module(BFDH,Growth Morphology and Equilibrium Morphology)were used to predict the morphology of CL-20/DNT co-crystal theoretically.The results showed that the prediction by Equilibrium Morphology was the most accurate,but still has some difference with the reality.Morphology was a useful method which can be used as a new theoretical guidance for the preparation of co-crystal.Thirdly,a series of theoretical simulations of CL-20/RDX co-crystal were carried out.The electrostatic potential calculation of CL-20 and RDX was carried out by the Dmol3 module of molecular dynamics calculation software Materials Studio.Based on the results of electrostatic potential calculation,Forcite module was used to build CL-20/RDX co-crystal model.Using this co-crystal model,the supercell was constructed to do the molecular dynamics simulation,and a series of properties of the co-crystal were compared with CL-20.It is found that the properties of CL-20/RDX co-crystal were better than that of CL-20 from the cohesive energy density,the bond length and the mechanical properties simulations.The Polymorph Predictor module was used to simulate to obtain a series of CL-20/RDX co-crystal molecular structures,and the most likely three co-crystal molecular structures were screened.The results indicated that the most likely molecular structure of CL-20/RDX co-crystal was in the triclinic space group P-1.CL-20/RDX co-crystal was prepared using solvent evaporation method with acetonitrile as solvent by the feed molar ratio1:1.Then the as-prepared co-crystal was characterized by SEM,PXRD,infrared spectroscopy,Raman spectroscopy,which pro,ved the formation of the co-crystal explosive;DSC was employed to characterize the thermal properties of the co-crystal,showing that the decomposition behaviors of the co-crystal were different from the two kinds of raw materials.The mechanical sensitivity of the co-crystal explosive was tested.The results showed that the CL-20/RDX co-crystal had obvious lower mechanical sensitivity compared with the raw material CL-20,even at the same level with RDX.It is proved that the co-crystallization is an effective method to reduce the sensitivity of nitramine explosives.Fourthly,a series of theoretical simulations of CL-20/AP co-crystal were carried out.The electrostatic potential calculation of CL-20 and AP was carried out by the Dmol3 module of molecular dynamics calculation software Materials Studio.Based on the results of electrostatic potential calculation,Forcite module was used to build CL-20/AP co-crystal model.Using this co-crystal model,the supercell was constructed to do the molecular dynamics simulation,and a series of properties of the co-crystal were compared with CL-20.It is found that the properties of CL-20/AP co-crystal were better than that of CL-20 from the cohesive energy density,the bond length and the mechanical properties simulations.The Polymorph Predictor module was used to simulate to obtain a series of CL-20/AP co-crystal molecular structures,and the most likely three co-crystal molecular structures were screened.The results indicated that the most likely molecular structure of CL-20/AP co-crystal was in the monoclinic space group P21/c.CL-20/AP co-crystal was prepared using solvent evaporation method with methanol as solvent by the feed molar ratio 1:1.Then the as-prepared co-crystal was characterized by SEM,PXRD,infrared spectroscopy,Raman spectroscopy,which proved the for mation of the co-crystal explosive;TG/DTG/DSC was employed to characterize the thermal properties of the co-crystal,showing that the decomposition behaviors of the co-crystal were different from the two kinds of raw materials.The hygroscopicity of the co-crystal explosive was tested.The results showed that the CL-20/AP co-crystal had obvious lower hygroscopicity compared with the raw material AP.It is proved that the co-crystallization is an effective method to reduce the hygroscopicity of AP.Fifthly,the electrostatic potential calculation of CL-20 and NQ was carried out by the Dmol3 module of molecular dynamics calculation software Materials Studio.Based on the results of electrostatic potential calculation,Forcite module was used to build CL-20/NQ co-crystal model and the hydrogen bonds between CL-20 and NQ molecule was simulated.The results indicated that CL-20 and NQ can form co-crystal under certain conditions.Nano-sized CL-20/NQ co-crystal was prepared using freeze drying method by the feed molar ratio 1:1.Then the as-prepared nano co-crystal was characterized by SEM,PXRD,infrared spectroscopy,Raman spectroscopy,which proved the formation of the nano co-crystal explosive;DSC was employed to characterize the thermal properties of the co-crystal,showing that the decomposition behaviors of the co-crystal were different from the two kinds of raw materials.The mechanical sensitivity of the co-crystal explosive was tested.The results showed that the CL-20/NQ co-crystal had obvious lower mechanical sensitivity compared with the raw material CL-20.It is proved that the co-crystallization and nano-crystallization was combined in one material,which is an effective way to reduce the sensitivity of nitramine explosives.Finally,the electrostatic potential calculation of HMX and NQ was carried out by the Dmol3 module of molecular dynamics calculation software Materials Studio.Based on the results of electrostatic potential calculation,Forcite module was used to build HMX/NQ co-crystal model and the hydrogen bonds between HMX and NQ molecule was simulated.The results indicated that HMX and NQ can form co-crystal under certain conditions.Nano-sized HMX/NQ co-crystal was prepared using freeze drying method by the feed molar ratio 1:1.Then the as-prepared nano co-crystal was characterized by SEM,PXRD,infrared spectroscopy,Raman spectroscopy,which proved the formation of the nano co-crystal explosive;DSC was employed to characterize the thermal properties of the co-crystal,showing that the decomposition behaviors of the co-crystal were different from the two kinds of raw materials.The mechanical sensitivity of the co-crystal explosive was tested.The results showed that the HMX/NQ co-crystal had obvious lower mechanical sensitivity compared with the raw material HMX.It is proved that the co-crystallization and nano-crystallization was combined in one material,which is an effective way to reduce the sensitivity of nitramine explosives. |
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