Synthesis and Properties of Insensitive and High Energy Azole-based Energetic Salts

Author:Zhang Man

Supervisor:zhou zhi ming


Degree Year:2016





Insensitivity and high-energy explosives are the eternal theme for researchers.Therefore,considering the overall performance,the development of energy and thermal stability compatable to HMX,sensitivity compatable to TATB to satisfy the new needs of our weapons and equipment has been expected.Highly heat-resistant heterocyclic energetic compounds with high nitrogen content are attracting more and more attentions due to their low hydrocarbon content,low characteristic signal,low pressure on the environment and high enthalpy of formation.Compared with the molecular analogues,the energetic salts have the characteristics of low vapor pressure,low sensitivity and good thermal stability,which have become an important research trend in the field of energetic materials.Energetic salts have excellent tunability,through the careful design of different anions and cationic components to improve its properties,which gradually becoming an important branch of energetic materials in recent years.A novel N-bridged structure of N-(3,5-dinitro-1H-pyrazol-4-yl)-1H-tetrazol-5-amine,and its selected nitrogen-rich energetic salts are designed and synthesized.All compounds are fully characterized by 1H and 13C NMR spectroscopy,IR spectroscopy,and elemental analysis.Salts 2.4,2.12,and 2.13 are also characterized by 15N NMR.Of these,salts2.9·H2O and 2.13 are further confirmed by single-crystal X-ray diffraction.The densities of these compounds ranged from 1.67 to 1.86 g cm-3.All energetic salts exhibit excellent thermal stabilities with decomposition temperatures ranging from 216 to 299°C and all are insensitive to impact.Decomposition of these thermally stable compounds(salts 2.5,2.6,and 2.7)occur at 299,296,and 290°C,respectively.Theoretical performance calculations(Gaussian 03 and EXPLO5 v6.01)provide detonation pressures and velocities for the energetic salts in the ranges 25.9-37.4 GPa and 8264-9364 m s-1,respectively;six of the energetic compounds have detonation velocities>9000 m s-1.Notably,the unique overall performance of salt 2.7 thus forms exceeds those of commonly used explosives such as HMX,and competes with that of CL-20.Thus,due to its impact insensitivity(IS>40 J,fairly high detonation velocity(v D=9364 m s-1),exceptional thermal stability(Td=290°C),salt 2.7 is a prospective candidate for a new class of insensitive,highly energetic compound explosives.(E)-1,2-bis(3,5-dinitro-1H-pyrazol-4-yl)diazene(H2NPA)and its seven kinds of energetic salts were synthesized via straightforward diazotization of4-amino-3,5-dinitropyrazole.The explosive contains four nitro groups,has an azo-bridged framework,and was fully characterized by 1H and 13C NMR spectroscopy,IR spectroscopy,and elemental analysis.The-N=N-bond increases the enthalpy and the nitrogen content,which contributes to the improvement of the decomposition temperature.Crystal structures of K2NPA(three-dimensional metal-organic framework,3D MOF),and salt 3.4 are determined by single-crystal X-ray diffraction and 15N NMR,and their properties(density,thermal stability,and sensitivity towards impact and friction)are investigated.And the overall morphology of K2NPA was obtained by scanning electron microscope.All the salts exhibit thermal stabilities with decomposition temperatures ranging from 156 to 315°C.All the compounds are decomposed directly.Among these,the decomposition temperatures of salts 3.2,3.4,and 3.8 were higher than that of RDX(230°C)by 27,74 and 14°C,respectively.Salt 3.4 has a higher thermal stability(Td=304°C)than HMX(Td=287°C)and is near to TATB(Td=324°C).Therefore,salts 3.2 and 3.4 can be classified as highly heat-resistant energetic compounds(Td>250°C).These results demonstrate that the-N=N-bond bridged heterocycles facilitates the thermal stability compared to their starting material LLM-116(Td=178°C).The density of H2NPA and its energetic salts are rang in1.70-2.15 g cm-3.The densities of salts and 3.2 and 3.7 are close to RDX(d=1.82 g cm-3).The metal salt K2NPA has the highest density(d=2.15 g cm-3).And the heats of formation are between 45.7–1040.1 kJ mol-1.The impact sensitivities of H2NPA and salts 3.4,3.5,3.7(IS=40 J),indicating that they belong to insensitive energy compounds.The detonation properties are evaluated by the EXPLO5 v6.01 program using the measured density and calculated heat of formation.The detonation pressures and detonation velocities are range in 26.0-36.6 GPa,and 8224-9083 m s-1,respectively.The detonation performance of salt3.3(vD=9038 m s-1,Pcj=35.5 GPa)is superior to RDX detonation performance(vD=8748 m s-1,Pcj=34.8 GPa).The guanidinium salt 3.4 is also found to exhibit a high thermal stability(Td=304°C)that is superior to that of HMX,insensitivity to impact(IS>40 J)and friction(FS>360 N)as comparable to those of TATB,and a high detonation performance(vD=8391 m s-1).The obtained metal-organic explosive combines exceptional thermal stability(Td=315.0°C)with a high density(d=2.15 g cm-3)and possesses ideal calculated detonation velocity(vD=8275 m s-1)and pressure(Pcj=31.1 GPa)values.Moreover,its suitable impact sensitivity of 1.5 J and friction sensitivity of 60 N make K2NPA an outstanding,highly heat-resistant,green primary explosive.Twelve salts of 3-nitro-1,2,4-triazol-5-one(NTO)(ammonium,hydrazinium,guanidinium,aminoguanidinium,diaminoguanidinium,triaminoguanidinium,N-carbamoylguanidinium,semicarbazidium,1,5-diamino-1,2,4-tetrazolium,3,4,5-triamino-1,2,4-triazolium,3,6,7-triamino-7H-[1,2,4]triazolo[5,1-c][1,2,4]triazol-2-ium,and4,4′,5,5′-tetraamino-3,3′-bi-1,2,4-triazolium)were synthesized.The new salts were fully characterized by 1H and 13C NMR spectroscopy,infrared spectroscopy,and elemental analysis.The crystal structures of salts 4.10 and 4.11 were determined by single-crystal X-ray diffraction.All energetic salts except salt 6 exhibit excellent thermal stabilities with decomposition temperatures ranging from 203 to 270°C.The densities of salts ranged from1.65 to 1.88 g cm-1 as measured by a gas pycnometer.Theoretical performance calculations(Gaussian 03 and EXPLO5 v6.01)yielded detonation pressures and detonation velocities for the energetic salts,ranging from 24.4 to 38.1 GPa and 8136 to 9575 m s-1,respectively.In particular,salt 4.2 has an outstanding detonation performance(Pcj=38.1 GPa,vD=9575m s-1)with a satisfactory acidity compared to that of NTO(pKa=5.63 versus pKa=2.37).Furthermore,the particles of salt 4.2 form two-dimensional blades of submicron size,as determined by scanning electron microscopy analysis.Meanwhile,salt 4.2 was compatible with TNAZ,TATB,TKX-50,Al,NH4ClO4,CL-20,TNT,and F2603 fluororubber,as determined by differential scanning calorimetry or vacuum stability tests.Considering the performance and stability,salt 4.2 is expected to become a kind of insensitive high energy energetic material.In this paper,a new type of explosive precursors and their energetic salts are designed on the platform of bridged azazole bicyclic molecules,aiming at the inherent contradiction of the energy and sensitivity of explosives.The asymmetric energetic materials with-NH-bridged dinitropyrazole ring and tetrazole ring have the advantages of high density,high enthalpy of formation and high detonation.The decomposition temperature of hydroxylamine salt is 290°C,higher detonation velocity(vD=9364 m s-1)than HMX,impact sensitivity(IS>40 J)which is a prospective candidate for a new class of insensitive,highly energetic compound explosives.The symmetric azo energetic materials with-N=N-bridged dinitropyrazole rings were synthesized as ion salt precursors.Its metal potassium salt with 3D MOF structure has high heat resistance(Td=315℃),high density(d=2.15g cm-3),and the detonation velocity(vD=8246 m s-1)much higher than Pd(N3)2,which has a higher application prospect in the direction of green detonator.Meanwhile,the decomposition temperature of biguanide salt is as high as 304℃,which has potential application value in heat-resistant explosive.Among the 12 salts of NTO,the hydrazine salt has excellent performance,the decomposition temperature is over 200℃and the detonation velocity is up to 9575 m s-1.The compatibility test of hydrazine salt has highlighted the potential value of NTO in practical application.At the same time,NTO has been produced in large scale in China,and the raw material of hydrazine salt has been solved,which is expected to be mass produced.