Abstract:Herein， we develop a new method to prepare the ammonium dinitramide/pyrazine-1， 4-dioxide （ADN/PDO） cocrystal， which is highly efficient and environmental-friendly due to utilizing the reaction crystallization with pure water as the solvent， and also comprehensively characterized its performance. The morphology and structure of the cocrystal were characterized by optical microscopy （OP）， powder X-ray diffraction （PXRD）， and single crystal X-ray diffraction （SXRD）， respectively. In detail， the ADN/PDO cocrystal was prismatic and formed by the combination of ADN and PDO molecules at a molar ratio of 2∶1. Moreover， the ADN/PDO cocrystal belongs to the monoclinic crystal system with a space group of P2₁/c， owning a theoretical density of 1.779 g·cm^-3 at room temperature. Furthermore， through the differential scanning calorimetric （DSC） measurement， it turned out that the melting point of the prepared ADN/PDO cocrystal is 113.3 ℃， which is 21.3 ℃ higher than that of ADN， and the decomposition temperature is slightly higher than that of ADN， demonstrating good thermal stability of the prepared ADN/PDO cocrystal. Then， the hygroscopicity of the prepared cocrystal， measured by the weight increment method， is significantly low at only 2.6%， while that of ADN is at 45%. In addition， calculated by the NASA CEA， the theoretical specific impulse of the cocrystal reaches 277.9 s while that of ADN is 197.5 s， demonstrating the high energy performance of the cocrystal. In conclusion， the reported method based on the reaction crystallization successfully enables the efficient production of a high-energy， low-hygroscopic ADN/PDO cocrystal， thereby facilitating the further assessment of its application performance.

Abstract:In order to study the potential mechanism of unexpected ignition of confined charge in the process of penetrating multi-layer target， by integrating the designs of multi-layer nested strikers and bidirectional limited structure， a nonlinear amplification experimental method of confined charges under continuous multiple impacts loading was established. The effectiveness of the experimental method， and the intrinsic mechanism of nonlinear response amplification were analyzed. The influence of nonlinear response of charges under multiple impacts loading on ignition behaviors was studied. The results show that the experimental method can implement multiple impacts loading with sub-millisecond pulse width， and 100 MPa-scale peak stress value. When the characterized frequency of loading is close to the intrinsic frequency of confined charges， structural nonlinear response amplification emerges， and the stress amplitude increases gradually. For the same striker velocity and mass， while varying frequency of loading， the PBX-3 charges could be ignited if structural nonlinear response is amplified and could not be ignited if structural nonlinear response is not amplified. It is found that the structural nonlinear response amplification effect is an important factor leading to charge ignition.

Abstract:Two new explosives， C₈H₂₄N₄（ClO₄）₄ and C₈H₂₄N₄（NO₃）₄∙2H₂O， were prepared from 1，4，7，10-tetranitrocyclododecane by salt formation with nitric acid and perchloric acid respectively， which are expected to be used as emergency reserve materials of weapons in emergency wartime. The structures， thermal properties， and detonation performances of the target products were studied through single crystal X-ray diffraction， infrared spectroscopy， elemental analysis， differential thermal analysis， thermogravimetric analysis， and EXPLO 5.0 program. Results indicate that C₈H₂₄N₄（ClO₄）₄ crystallizes in the orthogonal crystal system， Pcc2 space group with a crystal density 1.968 g∙cm^-3. The crystal of C₈H₂₄N₄（NO₃）₄∙2H₂O is a dihydrate with a crystal density of 1.642 g∙cm^-3， which belongs to the monoclinic crystal system P2₁/n space group. The thermal decomposition peak temperatures of C₈H₂₄N₄（NO₃）₄∙2H₂O and C₈H₂₄N₄（ClO₄）₄ are 293.2 ℃ and 284.1 ℃， and activation energies are 131.76 kJ·mol^-1 and 195.18 kJ·mol^-1， respectively. Compounds C₈H₂₄N₄（NO₃）₄∙2H₂O and C₈H₂₄N₄（ClO₄）₄ exhibit excellent detonation properties， showing very promising performance values （C₈H₂₄N₄（NO₃）₄∙2H₂O， V=8058 m∙s^-1， p=24.0 GPa； C₈H₂₄N₄（ClO₄）₄， V=8680 m∙s^-1， p=36.2 GPa）. Moreover， the impact sensitivities of C₈H₂₄N₄（NO₃）₄∙2H₂O and C₈H₂₄N₄（ClO₄）₄ are 36 J and 33 J， respectively， and their friction sensitivities are higher than 360 N.

Abstract:The planetary motion of impeller in the vertical mixer can effectively promote the dispersed circulation and homogeneous distribution of different material components， which has been employed in the preparation procedure of solid propellant slurry. However， the mixer involves complex interfaces and motions that it is difficult to study the mixing mechanism and rheological property of slurries by traditional methods. Based on the smoothed particle hydrodynamics （SPH）， the continuum was discretized into the conserved particles with physical quantities for simulating the interaction between the propellant slurry and blades under laminar flow. A meshless method for the mixing process of propellant slurries in non-Newtonian fluid state was developed by combining the Herschel-Bulkley （HB） constitutive model. The numerical simulations were compared with the experiments to verify the accuracy of the proposed model. The correlations of the blade motion parameters and power consumption were explored. The effects of geometric configurations and rotation modes on the mixing uniformity of slurries and the torque loads of impellers were analyzed. Research findings indicate that the simulation and literature experiment results have a good agreement that the average relative error between them is around 4.98% in the non-Newtonian fluid with shear rate index n=0.47. The mixing uniformity index of planetary impellers increased by 8.9% and 7.3% respectively than those of central and eccentric impellers after stirring for 2.65 s. The maximum amplification in torque can reach 38.4% within the revolution radius range of 0.11D_w-0.23D_w at Reynolds number Re=1.

Abstract:The octahedral cyclotrimethylenetrinitramine crystal （O-RDX） with an average particle size of 9.35 μm was prepared through the solvent-antisolvent method in the dimethylsulfoxide （DMSO） -ethylene glycol （EG） system using 1-ethyl-3-methylethimidazole acetate （EmimOAc） as an additive. The effects of crystallization parameters such as solvent system， solution concentration， crystallization temperature， additive and stirring speed on the growth behavior of RDX（cyclotrimethylenetrinitramine） crystals were systematically studied. It was observed that the main factor influencing the growth of RDX crystals was the supersaturation. With the gradual decrease of supersaturation， RDX crystals experienced the changes of rough growth， 2D growth and spiral growth， and the morphology of RDX crystals gradually evolved from dendritic to octahedral crystals. The results of analytical tests revealed that O-RDX crystals were in the α-form which was consistent with the raw RDX， showing high crystal density with few crystal internal defects and an increase of 5 ℃ in decomposition temperature. Moreover， compared to the raw RDX， the impact sensitivity and the friction sensitivity of O-RDX decreased by 60% and 50%， respectively. To further explore the formation mechanism of O-RDX， adhesion energy model and the molecular dynamics method were applied to simulate the crystal morphology of RDX in the presence of EmimOAc. The simulated results demonstrated that there were six main crystal faces of RDX： （1 1 1）， （2 0 0）， （1 0 2）， （0 2 0）， （2 1 0）， and （0 2 1）. The formation of the double-cone octahedral morphology originated from the uniform growth rates of the main crystal faces of RDX under the action of EmimOAc. The theoretical simulations generally agreed well with the experimental phenomena.

Abstract:In recent years， molecular perovskite energetic materials have emerged as a kind of new-concept energetic materials， offering a new approach to design practicable single explosives for different applications by rational assembling diverse ionic components. Ammonium chlorate （NH₄ClO₃） is commonly used as an oxidizer benefiting from its high oxidizing ability， but its high hygroscopicity greatly limits its application. By mixing sodium chlorate， aqueous ammonia， and triethylenediamine （dabco）， then acidizing the aqueous solution， we have obtained a new molecular perovskite energetic material， （H₂dabco）（NH₄）（ClO₃）₃（DAC-4）. X-ray single-crystal diffraction analysis revealed that DAC-4 possesses an ABX₃-type perovskite structure belonging to the cubic space group Pmm with a crystallographic density of 1.86 g·cm^-3. DAC-4 exhibits exceptional theoretical detonation performances， with detonation heat， velocity， and pressure of 4.91 kJ·g^-1， 8.43 km·s^-1， and 32.6 GPa， respectively. DTA showed that DAC-4 has a decomposition peak temperature of 106 ℃， higher than that of ammonium chlorate （75 ℃）. Moisture absorption experiments demonstrate that DAC-4 remains nearly non-hygroscopic after being stored for near 2 month at relative humidity below 86%， the weight of DAC-4 only increases by 0.18%， much lower than that of ammonium chlorate （30%）.

Abstract:To study the transfer characteristics of explosion energy released by the charge confined to tubes of different materials with lateral annular slits， explosion experiments were conducted involving charges with or without confinement to tubes of four materials. The high speed schlieren photographic system and shock wave overpressure monitoring system were employed to capture the propagation process of shock wave and obtain the distribution law of overpressure respectively， so that the explosion energy transfer law for the charges confined to tubes with lateral annular slits and the influence of tube material on its energy transfer characteristics were analyzed. The results showed that after the explosion of the charge confined to tubes with lateral annular slit， both the detonation product and shock waves firstly propagated outward towards the direction with slit， but the propagation towards the opposite direction is relatively delayed. Compared with the symmetric distribution of overpressure generated by a conventional cylindrical charge， the lateral annular slits in tubes could increase the overpressure in the direction with slit， but decrease that in the opposite direction. The asymmetric distribution of overpressure proved that the charge confined to tubes with lateral annular slits induced Munroe Effect in the slit direction. The hierarchy of Munroe Effect caused by lateral annular slits presented by materials： stainless steel （SS） > polyvinyl chloride （PVC） > fiber reinforced plastic （FRP） > plexiglass （PMMA）.

Abstract:To study the characteristics of after-effect parameters of shaped charge jet penetrating finite thickness steel target， the experiments on small shaped charge jet formation and penetration on finite thickness plate with after-effect target were carried out. The numerical simulation on the process of shaped charge jet penetrating finite thickness target plate was carried out by ANSYS/LS-DYNA finite software. The influence of target plate thickness， standoff and after-effect material density on the after-effect parameters of shaped charge jet penetration was analyzed， including the residual jet tip diameter d， tip velocity v and after-effect initiation ability v²d. The results show that with the increase of target thickness， the after-effect initiation ability v²d shows a linear attenuation trend， and around 16% of the initial initiation parameter is lost for every 20 mm increase in thickness. In the range of standoff that the jet keeps continuous， with the increase of standoff， the after-effect initiation ability v²d first increases and then decreases， and its stagnation point appears at the standoff of 8 times the shaped charge diameter. In the range of common explosive density， with the increase of after-effect material density ρ， the attenuation rate of after-effect initiation ability v²d first decreases and then increases. At the same time， there is a stagnation point in the v²d-ρ curve. The peak value of v²d is distributed between ρ=1.6-1.8 g·cm^-3， and the stagnation point position moves to the right with the increase of penetration time.

Abstract:In order to investigate the thermal erosion characteristics and variation law of triple base propellant， various kinds of gun propellants with different components content were prepared. The erosion characteristics were determined through simulated test in a semi-closed bomb. The analysis reveals the impact of energy component and plasticizer content on gun propellant explosion temperature， and the impact of explosion temperature on erosion characteristics. The results indicate that changes in the explosion temperature of gun propellant， attributed to variations in cyclotrimetheylenetrinitramine （RDX）， nitroguanidine （NQ） and dioctyl phthalate （DOP） content， significantly affect erosion characteristics. An increase of 1% in RDX content results in an increase in explosion temperature by 0.59% and an increase in erosion rate by 1.23%. Compared with the absence of RDX， the erosion rate of 2% RDX-containing propellant increase 23.38%. Notably， an increase of 1% in NQ content reduces the explosion temperature by 0.23% and the erosion rate by 0.56%. An increase of 1% in DOP content reduces the explosion temperature by 2.99% and the erosion rate by 7.01%. For the triple base propellants within the range of explosion temperature from 2600-3100 K， an exponential relationship between the rate of erosion mass and explosion temperature is established， and characteristic coefficients of RDX， NQ， DOP system is given respectively， which is 0.106， 0.101， 0.163.

Abstract:In order to explore the application prospect of a novel azido plasticizer 1，5-diazide-3-oxapentane （AZDEGDN） in gun propellant formulation， a semi-solvent method was adopted to prepare double- and triple-base gun propellants using AZDEGDN as the plasticizer， and the morphology， density as well as static combustion performance at different temperatures of AZDEGDN-containing propellants were studied. Results show that the AZDEGDN-containing double-base propellant （ADG-2） and triple-base propellant （ADG-3） without obvious defects in appearance can be prepared by semi-solvent extrusion process. SEM test shows that solid additives hexogen （RDX） and nitroguanidine （NGu） are uniformly distributed within ADG-3 propellant. The density of ADG-2 is 1.44 g·cm^-3 and ADG-3 is 1.52 g·cm^-3， both close to their theoretical density， indicating that the internal structures of AZDEGDN-containing propellants are relatively dense. The closed vessel tests demonstrate that the static combustion performances of both ADG-2 and ADG-3 propellants at room temperature （20 ℃） are stable. The burning rates increase evenly with the increase of pressure， without obvious turning phenomenon in burning rate-pressure curves （u-p curves）. The maximum combustion pressure of ADG-2 and ADG-3 propellants is 237.71 MPa and 263.80 MPa， and the burning rate pressure index is 0.9098 and 0.9754， respectively. The addition of RDX and NGu results in an increase of 15.5% and 10.9% in the burning rate pressure index of AZDEGDN-containing propellants in the low pressure range （50-100 MPa） and medium pressure range （100-150 MPa） respectively， while the burning rate pressure index in the high pressure range decreases by 4.2%. At high temperature （50 ℃） and low temperature （-40 ℃）， ADG-3 propellant can still keep stable combustion. The maximum combustion pressure changes from 263.80 MPa at room temperature to 265.92 MPa and 261.13 MPa， respectively. Besides， the combustion time changes from 14.70 ms to 13.52 ms and 16.40 ms respectively， and the burning rate pressure index changes from 0.9754 to 0.9464 and 0.9938 respectively. It is concluded that AZDEGDN-containing gun propellant is simple and mature in preparation method， dense and defect-free in structure， and also stable in static combustion performance， which is expected to become a kind of novel low-ablation gun propellant.

Abstract:In order to describe the characteristics of the crystal morphologies of hexogen （RDX）， octogen （HMX）， and hexanitrostilbene （HNS）， the unified kinetic three-dimensional partitioning method was used to simulate the real-time growth morphologies of these three energetic material crystals. The influence of crystal growth conditions on crystal morphology and the topology of crystal face were studied. The research results show that the predicted crystal shape of RDX is rhombus-like， with the main crystal faces being （0 1 0）， （1 0 0）， and （1 1 0）. The crystal morphology of HMX exhibits a columnar shape， with the main crystal faces including （0 1 1）， （0 1 0）， and （1 1 -1）. The crystal morphology of HNS has a flake-like shape， with the （1 0 0） face having the largest exposed area. The predicted crystal morphologies of energetic materials are consistent with experimental results. When RDX， HMX， and HNS crystals exhibit 2D nucleation and growth modes， a higher driving force （Δμ=418.59 kJ·mol^-1） causes the molecular layers of the crystal to continuously stack， resulting in layered growth. When the temperature is low， growth units first attach to the crystal faces in the platform area， gradually forming "island-like" agglomerations， followed by epitaxial growth. When the crystal face is sufficiently large， multiple "island-like" structures of different sizes may appear， gradually merging over time. At lower driving force （Δμ=27.21 kJ·mol^-1）， HNS crystals exhibit spiral dislocation growth， where the （1 0 0） crystal face triggers lamellar growth through a spiral axis， resulting in "terraced" crystal face. Adsorption ability analysis reveals that the kink sites and step surfaces of the helix have strong adsorption ability， while the sites on the face have weak adsorption ability.

Abstract:Traditional methods are difficult for the purification of TATB due to its poor solubility. Green deep eutectic solvent （CS-1） displays good solubility toward TATB， so CS-1 was used as the solvent with water as back extractant to develop a new purification method for TATB in this study. The difference between this method and other methods were investigated for the purification of TATB. Purification conditions including the amount of back extractant， washing times and drying methods were comprehensively optimized to improve the purity of TATB. Finally， a new method has been established for highly efficient separation and green purification of TATB. Through this method， high-purity TATB was obtained with the purity of （99.7±0.2）% and good recovery of 92.5%. Further， spectroscopic monitoring was combined with theoretical simulation to study the kinetics of the purification of TATB， and then a purification mechanism has been proposed， which is based on the dissociation of TATB’s complexes through the competition of hydrogen bonding between CS-1 and water.

Abstract:A novel nonmetallic salt， 3，5，7-triamino［1，2，4］triazolo［4，3-a］［1，3，5］triazine pentazolate （4）， was synthesized through a metathesis reaction by employing AgN₅ as precusor with 3，5，7-triamino［1，2，4］triazolo［4，3-a］［1，3，5］triazine hydrochloride. The structural characterization were carried out by X-ray single crystal diffraction， infrared spectroscopy （IR）， elemental analysis （EA）， nuclear magnetic resonance （NMR）， and thermal decomposition behavior were determined by thermogravimetric analysis （TG） and differential scanning calorimetry （DSC）. The enthalpy of formation of compound 4 was calculated using atomization method， the detonation performance was predicted using EXPLO5， and sensitivity was tested using BAM testing method. The results show that compound 4 exhibits a monoclinic crystal structure with a crystal density of 1.644 g·cm^-3 and belongs to the P2₁/n space group. This compound has a nitrogen content of 77%， a thermal decomposition temperature of 113.8 ℃， and an enthalpy of formation of 491.5 kJ·mol^-1. Furthermore， its detonation velocity was calculated at 7913 m·s^-1， detonation pressure at 19.6 GPa； The impact sensitivities measured were >40 J， and friction sensitivity >360 N.

Abstract:Polycyclic energetic compounds with high nitrogen content have attracted much attention owing to their distinctive advantages in constructing novel energetic molecules with low mechanical sensitivity， good thermal stability and high density. The construction of polycyclic skeletons involves the incorporation of tetrazole into fused heterocycle， serving as high-energy organic fuel and hydrogen bond donors. Three self-assembled non-hydrated energetic compounds， namely 7-amino-6-（2H-tetrazol-5-yl）-pyrazolo［1，5-a］pyrimidine （1）， 7-diamino-6-（2H-tetrazol-5-yl）-［1，2，4］triazolo［1，5-a］pyrimidine perchlorate （2）， and 2，7-diamino-6-（2H-tetrazol-5-yl）-［1，2，4］triazolo［1，5-a］pyrimidine perchlorate （3）， were synthesized through noncovalent self-assembly of polycyclic skeleton with the oxidizing structural unit HClO₄ rich in hydrogen bond acceptors. The structural characterization employed nuclear magnetic resonance （NMR） spectroscopy and single crystal X-ray diffraction， while thermal behaviors and mechanical sensitivities were determined by differential scanning calorimetry-thermogravimetry and BAM methods. Detonation performances were predicted utilizing the Gaussian 09 program and EXPLO5 V6.05.02. The results show that three compounds exhibit high crystal densities （ρ： 1.75-1.86 g·cm^-3）， good thermal stabilities （decomposition temperature （onset）： 184-260 ℃）， and good detonation performances （detonation velocity： 7343-7570 m·s^-1； detonation pressure： 21.1-22.8 GPa）， surpassing those of traditional explosives trinitrotoluene （TNT）. Both compound 1 （impact sensitivity （IS） > 40 J， friction sensitivity （FS）=216 N） and compound 3 （IS=25 J， FS=240 N） exhibit low mechanical sensitivity.

Abstract:In order to solve the inhomogeneous component distributions and low combustion efficiency in the preparation process of nano-thermite， the core-shell structured nAl@Cu（BTC）/Fe（BTC） was prepared via a layer by layer assembly technique. The structure， morphology， thermal reaction performance （thermite-reaction temperature） and combustion performance （combustion time， ignition delay time， and combustion temperature， etc.） of nAl@Cu（BTC）/Fe（BTC） were studied. The results show that the thickness and morphology of the coating layer can be regulated during the layer by layer assembly process. As the thickness of the coating layer increases， the nano-thermite gradually changes from rough and loose to smooth and dense. The nano-thermite with alternating 12 layers of Cu（BTC）/Fe（BTC） possesses a severe burning effect with a fast flame propagation rate that reaches the maximum flame within 0.710 seconds. Besides， this sample also achieves a moderate ignition delay time （0.509 s）， the shortest combustion time （2.036 s）， and the highest combustion temperature （1425 ℃）. Meanwhile， its decomposition peak temperature of aluminum oxidation reaction can be reduced to 552.5 ℃ and 735.0 ℃ due to the synergistic effect of Cu（BTC） and Fe（BTC）.

Abstract:1，3，5，5-Tetranitro-hexahydropyrimidine （DNNC） and 1，4，6，6-tetranitro-1，4-diazepane （TNDA） were synthesized from the reaction of 2，2-dinitropropane-1，3-diol with tert-butylamine and ethylenediamine， respectively. Their structures were characterized by nuclear magnetic resonance （NMR）， fourier infrared spectroscopy（FT-IR）， and single crystal X-ray diffraction. Meanwhile， their thermal behaviors and mechanical sensitivities were determined by differential scanning calorimetry-thermogravimetry（DSC-TG） and the BAM methods. Furthermore， isodesmic reactions and EXPLO5 were used to predict detonation parameters. The crystal structures indicate that the cyclohexane skeleton in DNNC and the cycloheptane skeleton in TNDA are both chair conformations. Both of them have extensive intermolecular and intramolecular non-classical hydrogen bonds. The results of DSC-TG show that the phase transition temperatures of DNNC and TNDA are 155.0 ℃ and 154.5 ℃， respectively. Furthermore， their peak decomposition temperatures are 215.3 ℃ and 205.9 ℃. In addition， DNNC and TNDA possess good mechanical sensitivity. Their impact sensitivities are 25 J and 17.5 J， and friction sensitivities are 144 N and 240 N. Besides， their theoretical detonation velocities are 8772 m·s^-1 and 7828 m·s^-1， and detonation pressures are 34.8 GPa and 25.0 GPa.

Abstract:In order to investigate the combustion characteristics of Al powders in NOx， the reaction mechanism of Al with three nitrogen oxides （NO₂， NO and N₂O） was studied by means of density functional theory ωB97X. Firstly， the geometries of reactants， intermediates， transition states and products were optimized with all parameters. The authenticity of intermediates and transition states was confirmed by frequency analysis. The transition states were further determined by intrinsic reaction coordinates （IRC） calculation， and then the detailed reaction paths and mechanisms were obtained. High precision single-point energy of each structure was obtained by using the double hybrid functional PWPB95 combined with DFT-D3 correction and def2-TZVPP basis set. The rate constants of the related reactions were calculated by using the variational interpolation transition state theory， and the Arrhenius expressions for each reaction are obtained. The results show that the reaction process of Al with NO and NO₂ is that Al and O atoms join together to form the intermediate of the complex， and then break the N─O bond through the ternary ring transition state to form the product. When Al reacts with N₂O， Al reacts with N atoms to form a complex and then the elimination reaction takes place through the ring transition states. The activation energies of the reaction of Al with NO₂， NO and N₂O are 4.3 kJ·mol^-1，249 kJ·mol^-1 and 13.4 kJ·mol^-1， respectively. From 2400 K to 4100 K， the reaction rate of Al with NO₂ and N₂O is higher than 106 m³·mol^-1·s^-1， which indicates that the reaction is easy to take place and the reaction rate is very fast， and the reaction rate of Al with NO is about 1/10000 of that of Al with NO₂ and N₂O.

Abstract:To study the effects of extrusion system nozzle runner structural parameters （cone angle， outlet diameter， and molding section length） on the fluid flow of energy-containing material extrusion process in the direct-in-writing-forming （DIW） technology， an extrusion model of high-viscosity energy-containing materials based on the Polyflow Extrusion module was established， and was verified by extrusion experiments under the working conditions of direct-write 3D printing. The study analyzed the effects of cone angle range （90°-130°）， outlet diameter （0.75-2 mm）， and molding section length （5-20 mm） on the extrusion process of high-viscosity energy-containing materials through the established model. The results show that the Polyflow Extrusion module can accurately simulate the flow behavior of composite energy-containing materials. When the cone angle is 100°， and the nozzle outlet diameter is between 1.5 mm and 1.75 mm， the extrusion process is relatively stable with small extrusion expansion. Additionally， as the length of the molding section grows， the required inlet pressure increases while the outlet expansion effect decreases.

Abstract:To improve the thermal safety and synthetic efficiency during the synthesis process of 3-Nitro-1，2，4-triazol-5-one （NTO） by conventional methods， a continuous flow reaction system was designed and prepared based on the solid contents and kinetics at different reaction stages of nitration. The continuous flow synthesis of NTO was realized by combining microfluidic reaction technology with tubular reaction technology， using 2，4-dihydro-1，2，4-triazol-5-one （TO） and 85% nitric acid as the main raw materials. The reaction conditions and continuous flow system were optimized. NTO with a purity of 99.53% and a yield of 81.4% was achieved at a reaction temperature of 45 ℃， a nitration residence time of 9 min， a molar ratio of n（TO）∶n（HNO₃） equals 1∶6. The chemical structure of NTO synthesized by the continuous flow method was characterized by ¹H and ¹³C NMR， element analysis （EA）， infrared spectroscopy （FT-IR）. In addition， the crystal form， particle morphology， thermal stability and mechanical sensitivity were characterized by the powder X-ray diffraction （XRD）， thermal analyzer （DSC-TG）， optical microscope and BAM technology. The results show that NTO grows into stable β-form. At the heating rate of 10 ℃·min^-1， the thermal decomposition peak temperature is 276.23 ℃ and the mass loss rate during thermal decomposition is 85.12%. The impact sensitivity is over 40 J， and the friction sensitivity is over 360 N. Compared with NTO synthesized by the flask method， the thermal decomposition peak temperature is increased by 2.95 ℃， and the mass loss rate is elevated by 4.44%. The mechanical sensitivities is similar， the crystal morphology is regular and the particle size distribution range is narrowed. The continuous flow synthesis time is 90% shorter than that of the flask process， with 3.4% higher of the yiel， and the preparation efficiency and safety are improved.

Abstract:To better evaluate the thermal safety risk of continuous flow reactions， a study was conducted using a tubular reactor as an example. By constructing a reaction system model based on heat balance and material balance， the actual heat transfer and thermal safety risk of continuous flow reaction systems were investigated. To address the adiabatic temperature rise reaction phenomenon at the inlet end of a channel reactor， a method based on the critical reaction half-life was proposed as a criterion for thermal safety assessment. Two major reaction conditions with high thermal safety risk were identified： when the total heat release of the target reaction is greater than 800 J·g^-1， and the reaction half-life of the reaction at the reaction temperature is less than the critical reaction half-life； when the total heat release of the decomposition reaction is greater than 800 J·g^-1， and the reaction half-life of the target reaction at the reaction temperature is less than the critical reaction half-life， while the reaction half-life of the decomposition reaction at 100% MTSR（maximum temperature that the process reaction can reach） is also less than the critical reaction half-life.Furthermore，the accuracy and practicality were verified through the nitration reaction of chlorobenzene，and the results show that an explosively decomposition reaction could occur in the channel reactor under these conditions，thus confirming the high-risk thermal safety conditions of continuous flow reactions determined by this evaluation method.

Abstract:In order to study the damage evolution and mechanical properties of solid propellants， uniaxial tensile and stress relaxation tests were performed on NEPE propellant. The resulting stress-strain curves and relaxation master modulus curves were obtained. A nonlinear viscoelastic constitutive model considering microscopic damage was developed under finite deformation. This model enables multiscale analysis of the mechanical response of propellants by incorporating the evolution of microvoids with various factors， including temperature， strain rate， confining pressure， and cyclic stress softening. The model was then implemented into ABAQUS with the parameters determined based on experimental data. Subsequently， the model was employed to predict the mechanical response of NEPE propellant under different loading conditions. The results demonstrate that the model accurately predicts the uniaxial tensile response of propellants under wide temperature ranges （223-333 K） and loading rates （1-200 mm·min^-1）. Moreover， the model exhibits reasonable predictability in cyclic loading， confining pressure tests， and biaxial tensile tests， thereby validating its effectiveness under complex stress conditions. Notably， the model necessitates only a small set of model parameters and can be easily programmed into commercial software， providing theoretical guidance for the multiscale analysis of the structural integrity of solid rocket motors.

Abstract:As a composite material composed of fillers and matrix， the damage of hydroxylated polybutadiene （HTPB） propellant mainly involves particle breakage， matrix fracture， and debonding of the bonding interface layer. To further explore its structural damage and mechanical performance evolution under external loading， a combination of micro CT， high-speed CCD camera， and all atom molecular dynamics simulation was used to analyze the multi-scale damage of the propellant under in-situ loading. The results indicate that the typical damage process of the propellant begins with the failure of the bonding interface layer， extends to the growth of debonding pores， evolves through the merging of pores， accelerates the collection of local large deformations， and terminates at the fracture of the matrix. Meanwhile， the interface binding energy and stress concentration degree cause the large ammonium perchlorate （AP） particles to debond first， and the porosity and strain exhibit an exponential function relationship. Furthermore， the traction separation curve of the micro interface layer conforms to an exponential cohesive force model， where the initiation and expansion of micro voids disrupt their cohesion， while the molecular spacing affects the evolution of stress.

Abstract:The relationship between crystal defects and hotspots formation of explosives under dynamic loading is a hot research topic in energetic materials. Understanding the mechanism of hotspots formation and its role in the ignition and sensitivity of high explosives are of great importance due to the needs of safety assessment of explosives and developing insensitive munitions. In this work， the ReaxFF reactive force field and molecular dynamics method were applied to investigate the dynamic responses of single crystal cyclotetramethylene tetranitramine （HMX） explosive with cylindrical voids under shock loading. Moreover， the effect of void size and double voids were studied. It is found that the shock induced collapse of voids includes three stages， namely， the plastic deformation on the upstream of the void， the movement of upstream atoms towards the centerline and the downstream of the void forming flowing atoms， and the collision of flowing atoms on the downstream. The main mechanism of hotspots formation is the collision of flowing atoms on the downstream that transforms kinetic energy into thermal energy leading to rapid temperature rise. The high temperature of hotspots initiates local chemical reactions， and the breaking of N─NO₂ bond in HMX molecule with NO₂ formation is the principal initial reaction mechanism. The void collapse process and hotspots formation mechanism of cylindrical void is similar to spherical void， while the convergence effect is weaker and the velocity of formed flowing atoms is lower for cylindrical void， resulting in significantly low hotspot temperature and weak chemical reactions. Besides， the collapse of cylindrical void forms shear bands around， which was not observed for spherical void. With the increase of void size， the velocity of flowing atoms goes up， the shear bands are wider， and the hotspot temperature is higher and hotspot area is larger， leading to more violent chemical reactions. For the sample with two voids that are aligned along the shock direction with a distance of void radius， the collapse of voids is similar to single void. The shock pressure reduces when the shock wave propagates through the upstream void due to the reflected rarefaction wave. Therefore， the velocity of the flowing atoms formed during the collapse of the downstream void is smaller， and the temperature of the second hotspot is lower. The current findings are beneficial to comprehend the effects of crystal defects on hotspots formation and subsequent ignition of explosives and can provide physical mechanism and laws cognition to construct macro-theoretical models.

Abstract:Isomerism is common in energetic compounds. Isomers may have differences in energy and safety performance. Investigating the mechanisms in these differences contributes to a deeper understanding of the structure-performance relationship of energetic compounds. The thermal decomposition mechanisms of three isomeric energetic compounds， 2，6-diamino-3，5-dinitro-1-oxide pyrimidine （LLM-105）， 3，5-diamino-4，6-dinitro-1-oxide diazine， and 1，4-dinitrofurazan ［3，4-b］ pyrazine （DNFP）， were studied using the self-consistent-charge density-functional tight-binding method （SCC-DFTB） under program heating and isothermal heating conditions. The results show that there is a strong hydrogen bond network in the LLM-105 crystal， enabling a molecular hydrogen transfer reaction accounting for 68.75% in the early stage of decomposition， which plays an important role in its high thermal stability； The skeleton structure of 3，5-diamino-4，6-dinitro-1-oxide diazine was prone to ring-opening through N─N bond cleavage under heating， resulting in lower thermal stability compared to LLM-105； The bond dissociation energy of DNFP for nitro group cleavage is 172.3 kJ·mol^-1， which is significantly lower than the other two isomers. Additionally， its fused-ring skeleton was also susceptible to ring-opening through C─C and N─O bond cleavage， resulting in the lowest thermal stability. In summary， the bond dissociation energy of the weakest bond in the molecule， the stability of the ring skeleton structure， and the hydrogen bond network of the crystal are important structural factors that determine the thermal stability of energetic compounds.