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Abstract:In order to compare the densities, heats of formation, detonation velocities, and detonation pressures of the energetic pentazolate salts at the same level, density functional theory (DFT) method was used to study the sixteen N₅ˉ based nonmetallic energetic salts synthesized in the past two years. According to the Born-Haber energy cycle, the calculated heats of formation of the pentazolate salts are between 95.2 kJ·mol^-1 and 1362.0 kJ·mol^-1 at the MP2/6-311++G(d,p) level. The average heat of formation of the salts formed by the triazole-containing cation and N₅ˉ is the highest among the five types of N₅ˉ salts. The densities(at 298.15 K) of these pentazolate salts range from 1.395 g·cm^-3 to 1.650 g·cm^-3, which are much lower than the theoretical densities of all-nitrogen compounds. The detonation velocities and detonation pressures calculated by the Kamlet-Jacobs formula agree well with the calculation results from EXPLO5. Most of the N₅ˉ-containing ionic salts have detonation velocities between 6500 m·s^-1 and 8000 m·s^-1 and detonation pressures between 15 GPa and 26 GPa, which are lower than RDX. The theoretical detonation performance of biguanidinium, hydroxylammonium, and hydrazinium pentazolates are outstanding. Their detonation velocities (8622-9032 m·s^-1) are equal or slightly higher than that of RDX, and their detonation pressures (29.5-32.3 GPa) are lower than that of RDX. Thus, their predicted performance are not revolutionary. They do not exhibit the distinct advantages of all-nitrogen anion derivatives, and are far from the expectation of their ultra-high energy.

Abstract:In order to study the flow field structure of HTPB propellant during the pouring process, the ameliorated Hurschel-Bulkley viscosity model, which can characterize the viscosity change of the solid propellant slurry during solidification, was used to simulate and analyze the pouring process of the slurry flooring. The theoretical results were compared with the experimental data, which show that the slurry will confluence after passing through the holes of the tube sheet. The slurry after confluence will accumulate in the engine shell under the action of gravity, while the surface of the slurry will be irregular concave and convex. However, under the action of gravity, the slurry will gradually be leveled and fill the holes without forming holes. A part of the strip separated by the tube sheet converges and flows downward along the groove between the wings, while the other part flows downward directly. During the flow process, the phenomenon of the tensile fracture occurs. The total pouring time is 104 min, the total mass of pouring slurry is 160.3 kg, and the average mass flow rate is 5.4 g·(hole·min)^-1. The error between the simulation value and the measured value is 8.65%, 2.06% and 5.93% respectively.

Abstract:To investigate the distribution characteristics of propellant grains during ignition and flame-spreading of modular charge, a visualized modular charge experiment platform was designed. The test of Φ130 mm×100 mm single-modular charge ignition, rupture of the cartridge, and the movement of the propellant grains was conducted, and recorded by high speed camera system. A three-dimensional unsteady-state gas-solid two-phase flow model of the modular charge cartridge rupture and particle movement was established based on the gas phase-solid particle coupling method. Under different initial loading conditions of the cartridge, the distribution characteristics of propellant grains during the modular charge ignition and instantaneous process of flame spreading were analyzed. The simulation results indicate that, in the four simulated conditions that the distance between the initial loading position of modular cartridge and the primer is 40, 80, 120 mm and 150 mm, during the modular charging ignition and flame-spreading, the grains are finally distributed in the cartridge and the chamber on the right side of the modular cartridge. And they appear as a combination form horizontal and slope from primer side to pressure control diaphragm side. When the distance between the initial loading position of the modular charge and the primer is increased from 40 mm to 150 mm, the axial length of the horizontal stack is reduced from 269.5 mm to 200.4 mm, and the slope angle of the sloped stack is reduced from 25.03° to 21.31°. As the initial loading position of the module moves to the right, the axial length of the horizontal stack of grains becomes short, the stack thickness increases, and the slope angle of the sloping stack decreases.The numerical simulation results are basically consistent with the the sloping accumulation of the propellant grains observed experimentally, which verifies the rationality of the model.

Abstract:The diffusion coefficients and mechanisms of NG(nitroglycerin), BTTN(1,2,4-butanetriol trinitrate) and TMETN(trimethylolethane trinitrate) in PEG/N-100(polyethylene glycol/curing agent) were studied by molecular simulations. The order of diffusion coefficients is NG > BTTN > TMETN. By comparing the three systems, the weakest diffusion of TMETN was attributed to the following two aspects: firstly, the strongest binding force between TMETN and PEG/N-100 as well as the weakest self aggregation ability of PEG/N-100 in the system; secondly, the largest size of TMETN among the three plasicizer systems. The effects of temperature and plasticization ratio on the diffusion properties of TMETN were investigated. With the increasing temperature, the diffusion coefficient of TMETN increased slowly at first and then sharply, which was consistent with the law of accelerated aging at high temperature; the position of hydrogen bond moved backward and the peak value decreased owing to the high temperature, suggesting the weakened interaction between plasticizer and binder; meanwhile, the fractional free volume of system increased. With the increase of plasticization ratio (2.5, 2.8, 3), the diffusion coefficient of TMETN decreased. Mesoscopic studies showed that the improvement of compatibility was one of the reasons.

Abstract:Cracks in polymer bonded explosives (PBXs) may occur during manufacturing, transportation and storage stages. The surface crack of explosives has an important influence on their mechanical properties and detonation performance. Quantitative detection of the depth of the surface crack is of great significance to the process of surface crack removal. The numerical simulation of surface crack depth estimation was investigated by using Rayleigh surface waves which propagate along the cylindrical and spherical surfaces of PBXs. The propagation patterns of surface waves were studied on these two types of surfaces. The reflection and transmission of surface waves at different frequencies in PBXs with crack of varied depth were simulated through the finite element method (FEM).The FEM results indicate that the depth of crack in curved surfaces can be deduced according to the amplitude variations of reflected and transmitted waves.

Abstract:In order to improve the dispersion uniformity and catalytic efficiency of burning rate catalysts in solid propellant grain, NC/GAP composite spherical powders containing burning rate catalysts Fe₂O₃, CuO, CNTs and Cu₂Cr₂O₅ were prepared by internal dissolution method and their related physicochemical properties were tested and analyzed. The results show that the NC/GAP composite spherical powders containing the above burning rate catalyst have been successfully prepared by the internal dissolution process, the spherification degree is high, the dispersibility is goodand the particle size of spherical powders iscontrollable. The burning rate catalysts are compounded into NC/GAP composite spherical powders by physical blending, which haveno effect on the molecular structure of NC and GAP. In addition, the introduction of burning rate catalysts accelerates the thermal decomposition of NC/GAP spherical powders. The initial thermal decomposition temperatures of composite spherical powders containing Fe₂O₃, CuO, CNTs and Cu₂Cr₂O₅ were 10.15, 15.38, 15.42 ℃ and 13.97 ℃ earlier than that of pure NC/GAP spherical powders, respectively. It indicated that CuO and CNTs had obvious catalytic effect.

Abstract:To satisfy the application of new type of metal alloy fuels in propellants and explosives, the spherical Al-Si alloy fuels with Si mass fraction of 12% and 20% were prepared by high-speed centrifugal atomization with absent-oxygen atmosphere. SEM, XRD, metallographic analysis were taken to study the structures and the constitutions of the alloys. Oxygen bomb calorimeter and TG-DSC were used to investigate the heat of combustion and thermal oxidation characteristics of the fuels. The morphologies and components of Al-20Si thermal oxidation products were tested in situ at 550, 620 , 1000 ℃ and 1200 ℃. Results show that the Al-Si particles are typical spherical, and core-shell structures. The shell is mainly formed from primary silicon and its particle size increases with an increased in the particle size of the alloy fuel. The cores is a three-dimensional structure of reticulated Si skeleton. The heat of combustion of Al-12Si is 29.285 kJ∙g^-1, and the mass of thermal oxidation reaction to 1200 ℃ is 51.17%. The heat of combustion of Al-20Si is 29.039 kJ∙g^-1, and the mass of thermal oxidation reaction to 1200 ℃ is 43.33%.

Abstract:To prepare spray-drying precursor nano-Al suspension with good dispersion stability, nano-Al suspension was prepared by mechanical stirring and ultrasonic dispersion, and the dispersion stability of nano-Al in RDX solution was investigated. Based on the measurement of ultraviolet spectrophotometer, the effects of dispersion rate, dispersion time, ultrosonic time, temperature and nano-Al particle size were systematically studied. The microphology structure of spray-drying samples were analyzed by scanning electron microscopy. The results showed that the aluminum powders with particle size of 50-100 nm, the best dispersion stability was achieved at the following conditions: stirring rate of 400 r·min^-1, dispersion time of 30 min, ultrasonic time of 3-10 min, suspension concentration of 1%, temperature of 25 ℃.

Abstract:To establish the relationship between the microscopic chemical reaction mechanism and the macroscopic explosion pressure in the initial stage of methane explosion, the coupling relationship between content changes of key free radicals or molecules (such as CO₂, C₂, CHO•, OH•, C₃) and explosion pressure was investigated experimentally. The flame emission spectrum explosion pressure were obtained by a 20-Litre standard spherical explosion container and a grating spectrometer. Studies show that large amounts of CO₂ are produced during the pressure rising period, while the formation of C₂ and CHO• are primarily in the explosion induction period and they are consumed rapidly when explosion pressure rises. The content of OH• is at a high level throughout the methane explosion. The rapid increase of CO₂ accompanies with pressure rising, which reveals a positive correlation. On the contrary, the consumption of C₂ and CHO• accelerates when explosion pressure rises, revealing that they are correlated negatively. Formation reduction of C₂ and CHO• and their corresponding contents during the explosion induction period, suppression on OH• production during the whole methane explosion and decrease or inhibition in CO₂ formation can slow down or inhibit the explosion process and effectively reduce the methane explosion pressure. The result shows that it is possible to inhibit explosion and reduce the pressure efficiently through the manipulation of decreasing the production of C₂ and CHO• in the induction period, reducing the content of OH• throughout methane explosion and suppressing the formation of CO₂.

Abstract:Aiming at the disposal of waste liquid-solid Fuel Air Explosive(FAE) composed of isopropyl nitrate and magnesium powder, a physical separation method was proposed to separate magnesium powder from isopropyl nitrate and to recycle metal magnesium powder, and then the isopropyl nitrate was converted into non-explosive isopropanol by chemical hydrolysis and was recycled. The impact sensitivity and friction sensitivity of liquid-solid FAE were tested, and the separation effects of liquid-solid FAE by various methods, i.e., gravity filtration, decompression filtration, pressure filtration, centrifugal filtration, were studied. The results show that the liquid-solid FAE has a strong ability to bear the impact of collision and friction during the separation, and the separation of liquid-olid FAE by centrifugal filtration has advantages of fast speed and high safety. The scale-up process for hydrolysis of isopropyl nitrate were studied and the hydrolysis conditions of isopropyl nitrate were determined: V(isopropyl nitrate)∶V(water)=1∶3, n(isopropyl nitrate)∶n(NaOH)=1∶1.1, reaction temperature at 150 ℃, reaction time of 30 min. On this basis, the process flow, unit devices, structure and technical parameters of the mobile equipment for treating the liquid-solid FAE were proposed, and the treatment equipment was developed accordingly. The test results of the equipment are shown as follows: after centrifugal filtration process of 2.6 kg liquid-solid FAE for 3 min, the content of isopropyl nitrate in magnesium powder is 0.69%, which indicates the liquid-solid separation effect is perfect; after hydrolysis process of 15 kg isopropyl nitrate for 30 minutes, the conversion rate of isopropyl nitrate reaches 99.4%, which indicates the hydrolysis of isopropyl nitrate completes thoroughly.

Abstract:Nano explosives have attracted wide attention due to their unique performance advantage, but the lack of understanding of this type of biological toxicity will limit their industrial application. In order to determine the toxicity effect of nanometer hexanitrophosphonium(HNS), triaminotrinitrobenzene(TATB), and 2,6-diamino-3,5-dinitropyrazine-1-oxide(LLM-105) on RAW264.7 macrophages. The RAW 264.7 cells were treated with different concentrations of nanoparticles for 24 h. CCK-8 assays were applied for testing macrophage cytotoxicity in vitro, which were based on mitochondrial activity evaluation. In order to determine the mechanism of cell death, lactate dehydrogenase (LDH) in supernatant, superoxide dismutase (SOD) and malondialdehyde (MDA) intra-cellular fluid were determined. The morphologic change of RAW 264.7 was also observed. The results showed that all three types of nano-explosives could significantly reduce the activity of RAW264.7 cells and showed a dose-dependent relationship. Their half inhibitory concentrations (IC₅₀) on RAW264.7 cells were 49.3，211.3 μg·mL^-1， and 6.6 μg·mL^-1，respectively. The RAW264.7 cells exhibited various morphological changes such as shrinkage and roundness. The LDH activity in the supernatant also showed an upward trend. In addition, TATB and LLM-105 decreased the activity of SOD, the content of MDA increased with concentration of LLM-105. The results clearly indicated that nano-matter HNS, TATB, and LLM-105 have toxic effects on RAW264.7 cells, destroying the integrity of the cell membrane and triggering oxidative stress are important elements of cytotoxicity.

Abstract:In recent years, the theoretical evaluation method of thermal safety based on thermal decomposition kinetics has attracted extensive attention, and has gradually developed into an important supplement to traditional experimental methods. In this paper, the research progress of thermal safety evaluation based on thermal decomposition kinetics is reviewed. Three methods for obtaining kinetic parameters are introduced, namely, simple linear fitting method, isoconversional method and model-based simulation method. The applicable conditions of these methods are discussed. The modeling process and characteristics of the model-based simulation method are analyzed. On this basis, combined with several important thermal safety indicators, the practical application of thermal safety evaluation of energetic materials and other dangerous substances based on thermal decomposition kinetics is introduced. At the end, some controversial issues are discussed, such as the method selection when solving the thermal decomposition parameters (isoconversional method or model-based simulation method); and the implementation of the experimental scheme for energetic materials with molten decomposition characteristics. It is proposed that more attention should be paid to the compatibility of sample status, experimental techniques, and evaluation goals.

Abstract:Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50), as a new energetic ionic salt, is currently attracting considerable attention. The latest progress of the researches on TKX-50 is reviewed in this article, covering molecular synthesis route, crystal structure and phase transition, thermomechanical response characteristic, detonation performance, safety, compatibility and toxicity. TKX-50 possesses an applicable potential due to its advantages of ready synthesis, high energy, low mechanical sensitivity and low toxicity. However, in contrast to the conventional CHNO energetic materials, because of the different composition and inter-particle interaction of TKX-50, it possesses different thermo-mechanical properties and related origins. It is noted that the unsatisfactory thermal stability and compatibility may be an important fact constraining its application; and the thermo-mechanical response mechanism and energy release mechanism of energetic ionic salts like TKX-50 are different from those of traditional energetic materials composed of neutral CHNO molecules. All these require further insights.

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