Investigation On The Interaction Of Main Component Of Composition B With Modifier And Synthesis Of Energetic Compounds With Low Melting-Point

TNT based melt-cast explosives usually behave poor mechanical performance and safety problems.Nowadays,developing advanced weapons and munitions is urgent for modifying and enhancing the toughness and elasticity of melt-cast explosives.In this work,the characteristic parameters of toughness and elasticity for characterizing typical brittle-material were firstly presented based on melt-cast explosives,and the corresponding test-methods were established.Then,the nature of brittleness in TNT based melt-cast explosives were investigated through analyzing micro-mechanical properties of TNT and RDX single-crystals,together with observing the crystalline behaviors of TNT.The approaches for enhancing toughness and elasticity were also proposed.In the studies of modifiers selection,ten types of modifiers were designed and prepared based on the theoretical investigations on the interfacial-interaction between modifiers and TNT molecules by molecular dynamics(MD)simulations.Influences on the toughness and elasticity by different conditions and factors were considered,such as the types,content and blending technics of modifiers.Investigation of the intermolecular interaction between explosives is one of the significant means on solving the physical and chemical issues in the energetic components.This work combines theoretical studies and experiments,and investigates the intermolecular-interaction between TNT or RDX and modifiers by employing molecular dynamics(MD)and quantum chemical methods,which further aims to providing the selection principle of modifiers for reinforcing melt-cast explosives.Subsequently,the selective modifiers were using for modification experiments,in which the interfacial interaction and mechanical properties of unmodified and modified samples were studied,with configuration evolvement,mechanism and behavior between different modifiers and energetic materials.Via a series of studies,the cognition from configurations and properties between modifiers and TNT based melt-cast explosives was strengthened,then the mechanism between various polymers,energetic-polymers,nano-material etc.and melt-cast explosives was disclosured,which provide the fundation for the applications of toughening and reinforcing melt-cast explosives.These investigations include:(1)Melt-cast explosive belongs to the composite highly filled with energetic crystals,deep insight into the mechanical behavior of energetic crystals in the melt-cast explosives,helps to understand the fundamental mechanical performances.In this work,Harshfeld surface,2D fingerprint plots and nanoindentation experiments were combined and carried out to study the micromechanical properties and brittleness for the first time.We find that there is no strong hydrogen-bond(HB)interactions in the TNT crystal and its brittleness can attribute to the weak van der Waals(vdW).Subsequently,the solution to reinforce the melt-cast explosives were presented as follows:one is to synthesize the modifiers having the analogous framework with TNT through the molecular design;another one is to select the proper modifier for toughneing and reinforcing composition B via the theoretical and experimental analysis.(2)Fifteen kinds of modifiers were designed by analyzing the characteristics of Comp B,and molecular dynamics simulation of modifiers with RDX and TNT were investigated.Through the cohesive energy density(CED)and solubility parameter(SP)analysis,the compatibility and solubility of melt-cast explosives with modifiers were studied.Based on the elastic constants,the influences of modifiers on the Comp B were summerized.The method for selecting the toughening and reinforcing modifiers was proposed:the tensile modulus(T)was used for determining the reinforcement,the ratio of bulk modulus(B)and shear modulus(S),the cauchy pressure(C12-C44)were applied for determining the toughness.Selection of proper modifiers for toughening and reinforcing melt-cast explosives via detailed theoretical analysis,which provided the principles for experiments.(3)According to the selection of modifiers in the computational investigations,the modification experiments of Comp B(the ratio of TNT and RDX is 35:65)were used for validation.The influences of different modifiers and their amounts on the microscopy and mechanical performances were investigated,as well as the reinforcing and toughening mechanisms.The Brazilian Test comfirmed that the tensile modulus of composition B modified with 123 resin promoted from 4.86 GPa to 10.46 GPa,and the relative strength increased from 0.82 MPa to 2.68 MPa;its compressive modulus was enhanced from 6.85 GPa to 12.73 GPa,and the relative strength increased from 25.56 MPa to 42.10 MPa.The methods included scanning electronic microscopy analysis via fractured surfaces in modified Comp B,tensile and compressive mechanical characterizations etc.Through the modification experiments,the trends for mechanical properties were found to be basically consistent with the theoretical predictions.(4)Two kinds of modifiers having trinitrotoluene frameworks similar with TNT were investigated,which were energetic polymers and mononitrotoluene energetic plasticizers,and their mechanical properties with composition B were studied by computational methods.Meanwhile,the Brazilian Test was employed for characterizing the mechanical properties of the modified composition B with energetic plasticizers,and the tensile modulus was improved from 4.86 GPa to 6.14 GPa.Subsequently,scanning electronic microscopy(SEM),powder X-ray diffraction patterns combining with quantum chemisty(QC)and molecular dynamics(MD)simulations were used for comfirming the intermolecular interaction between o-NT,p-NT and TNT.It is evident that the interaction energy of RDX and TNT is only-1.586 kJ/mol,and that of TNT and o-NT,p-NT are-131.557 kJ/mol and-95.640 kJ/mol,respectively.That of RDX with o-NT,p-NT are-48.487 kJ/mol and-4.620 kJ/mol,respectively.These results indicate that the interaction between energetic plasticizer and TNT is higher than one with RDX,and they are far stronger than the weak interaction of TNT and RDX.This strong interaction can attribute to the hydrogen-bond(HB)and ?-? interactions.(5)In the investigation of modified TNT with inorganic oxide nanoparticle,we studied two nanoparticles(silica and zinc oxide)modified TNT and their intermolecularinteractions through experimental and theoretical methods.UV-vis spectrum and powder X-ray diffraction patterns(PXRD)comfirmed that strong interactions existed between nano zinc-oxide,silica and TNT molecules,which could improve the physical properties of TNT.Comparison of their intermolecular interactions illustrates that inorganic oxide nanoparticle could be taken for toughening and reinforcing modifiers for TNT based molten explosives.(6)Twenty novel energetic salts with fused rings and C-C bonded structures were synthesized.Base on the study of relationship between cation/anion and melting-point,the molecular design of anion is helpful for altering the melting-point.N,N'-dinitro-N,N'-bis(3-dinitromethyl-furazanate-4-yl)methylenediamine were synthesized.Meanwhile,based on the motivation of energetic plasticizer FEFO,new energetic compound 5,6-di(2-fluoro-2,2,-dinitroethoxy)furazano[3,4-b]pyrazine was synthesized,which was also a insensitive and highly energetic compound.Single crystal X-ray diffraction was employed for characterizing their crystal structures.They were fully characterized by multinuclear NMR spectroscopy,infrared spectrum and elemental analyses.Their thermal properties,detonation performance and sensitivities were investigated.