Abstract:To address the low energy release efficiency of aluminum powder as a metallic fuel， aluminum-based composite fuels containing 3%-6% polyvinylidene fluoride （PVDF） were prepared using mechanical alloying. The powders were characterized using scanning electron microscopy （SEM） and X-ray diffraction （XRD） to analyze their microstructures and phase compositions. The active aluminum content was measured by gas volumetric analysis， and the combustion calorific values were determined using oxygen bomb calorimetry. Thermal oxidation properties were evaluated through thermogravimetric-differential scanning calorimetry （TG-DSC） and a custom-built rapid heating oxidation setup. SEM and XRD results revealed that the composite aluminum powder modified with 4% PVDF dispersion prevented the formation of a continuous Al₂O₃ shell during heating. TG-DSC analysis showed a 76.7% oxidation weight gain at 1300 ℃ for the composite powder， representing a 35.8% improvement over pure aluminum powder （40.9%）. Rapid oxidation tests at 1100 ℃ demonstrated a 64.6% weight gain after 120 s for the composite powder， which is 41.2% higher than the 23.4% weight gain of pure aluminum. These findings highlight the critical role of PVDF dispersion modification in enhancing the oxidation activity and efficiency of aluminum powder.

Abstract:To elucidate the effect of polyvinylidene fluoride （PVDF） content on the combustion performances of aluminum-based solid propellants， Al@PVDF composite powders with coating contents ranging from 2% to 14% were prepared via the solvent and non-solvent method. The thermal reactivity of Al@PVDF composite powders and the energy release and combustion performances of the corresponding solid propellants were analyzed using thermogravimetric-differential scanning calorimetry， constant volume combustion tests， and simultaneous ignition experiments. Results indicate that the PVDF coating significantly enhances the thermal reactivity of aluminum. At the 6% PVDF coating content， the aluminum powder achieves the maximum thermal weight gain and exothermic enthalpy value of 78.96% and 16.14 kJ·g^-1， respectively. As the PVDF content increases， the energy release of solid propellants exhibits a trend of initial increase， following by a decrease， subsequent re-increase， and final decline， and reaching the maximum heat release of 6026 J·g^-1 and pressurization of 4.45 MPa at 10% coating content. The ignition delay time of aluminum-oxygen reaction decreases from 53 ms to 12 ms. The pressure exponent of burning rate underwent a three-stage evolution， declining from 0.43 to 0.36， and further to 0.26. Analysis of condensed combustion products （CCPs） reveals a stage-dependent mechanism of PVDF content on combustion performances： the low coating content （2%-4%） inhibits molten aluminum agglomeration via pyrolysis products； the medium content （6%-8%） accelerates particle fragmentation and ignition but induces secondary agglomeration； the high content （10%-14%） generates excessive pyrolysis products that promote secondary fragmentation of agglomerates in gas-phase region.

Abstract:To explore the application of in-situ Raman spectroscopy for monitoring the curing reaction of energetic materials by using toluene diisocyanate （TDI） as curing agent， both in-situ infrared （IR） and Raman spectroscopy were employed to study the spectral changes before and after the curing reaction of 3，3-bis（azidomethyl）oxetane-tetrahydrofuran co-polyether （PBT）-TDI system. The Raman bands suitable for quantitative monitoring of the curing process were analyzed， and the results were evaluated. The vibrational modes of the Raman bands of reactants and products were identified using density functional theory （DFT） method. The correlation between the curing reaction results obtained from IR and Raman spectroscopy was also discussed. Results show that the peak of 1534 cm^-1 in Raman spectroscopy of the PBT-TDI system exhibits a low signal-to-noise ratio， making it unsuitable for quantitative analysis. The reaction degree calculated from the peak of 1743 cm^-1 in Raman spectroscopy is significantly higher than that derived from the peak of 2269 cm^-1 in IR spectroscopy. The peak of 1505 cm^-1 in Raman spectroscopy is associated with the stretching vibration of the isocyanate （NCO） group. The differences in the degree of reaction is due to the number of individual NCO groups in the TDI molecules participating in the reaction. The two methods show complementary roles in monitoring the curing process.

Abstract:A novel cage-like energetic compound， 4，4，8，8-tetranitro-2，6-dioxaadamantane， was synthesized via four steps involving oxidative cyclization， oxidation， oximation and gem-dinitration by using 9-oxabicyclo［3.3.1］nona-2，6-diene as raw material. Its structure was characterized by nuclear magnetic resonance（NMR）， Fourier transform infrared spectroscopy （FT‐IR） and elemental analysis （EA）， and single crystal X-ray diffraction （SC-XRD）was adopted to further confirm its crystal structure. The thermal stability was investigated by differential scanning calorimetry‐thermogravimetry（DSC‐TG）analysis， and detonation parameters were predicted by EXPLO5. Results show that 4，4，8，8-tetranitro-2，6-dioxaadamantane has a crystal density of 1.75 g·cm^-3 and belongs to monoclinic system， space groups P2₁/c. Its thermal decomposition temperature is 190.6 ℃， theoretical detonation velocity is 7705 m·s^-1， and detonation pressure is 25.75 GPa.

Abstract:Boron powder is often used as a combustible agent in energetic materials due to its high calorific value， volume calorific value and clean combustion products. However， the surface oxide layer of boron powder makes it difficult to ignite and brings low combustion efficiency. In order to improve the ignition and combustion performances， boron powder was wetly milled in hot acetonitrile to remove the surface oxide layer for obtaining pre-treated boron powder with high activity， according to the good solubility of boron oxide in acetonitrile solvent. Acetonitrile and n-hexane were used as a dual control agent， and then the pretreated boron powder and highly active aluminum were performed a secondary ball milling to finally prepare the boron-aluminum composite powder with surface-activated boron. The morphological characteristics， thermogravimetric， ignition and combustion characteristics of boron and composite powder were studied. The results showed that the content of surface boron oxide of boron powder was reduced after pretreatment with acetonitrile， pretreatment boron powder was easier to react with oxygen when heated in air， and the percentage of mass increase was 25.6% more than that of untreated boron powder. After pretreatment with hot acetonitrile， the surface boron oxide content decreased， the active boron content increased， and the ignition and combustion performances were significantly improved. The mass of composite powder with boron-aluminum mass ratio of 60/40 increased by 93% when heated in air， the ignition temperature was 738.1 ℃ at low heating rate， and the particle combustion time was 11.2 ms.

Abstract:To effectively mitigate the combined impulsive and fragmentary loads exerted by near-field explosion， a multi-layer composite protective structure has been developed， incorporating an anti-penetration layer， a coordinated support layer， and a cushioning energy-absorption layer. A finite element analysis model was established and validated through near-field explosion experiment. Utilizing the outcomes of finite element simulations， a response surface approximation model for the composite protective structure was constructed. With the areal density and overall thickness of the composite protective structure as the optimization targets， a multi-objective optimization of the thickness distribution was conducted under the individual and combined effects of fragments and shock waves using the Non-dominated Sorting Genetic Algorithm II （NSGA-II）. And the Pareto optimal solution set was obtained. The findings demonstrate that， in comparison to the initial design， the areal density of the optimized composite protective structure subjected to the individual action of fragments can be decreased by up to 19.2%， with a maximum thickness reduction of 10.0%. Under the individual action of shock waves， the areal density can be reduced by up to 34.9%， and the thickness by up to 27.5%. Under the combined action of shock waves and fragments， the areal density can be reduced by up to 19.2%， and the thickness by up to 10.0%. For application scenarios where the thickness is constrained to no more than 40 mm， the optimized composite protective structure exhibits an approximately 17.5% reduction in areal density and a 9.1% reduction in total thickness compared to the initial design. It was noted that the Pareto optimal solution sets obtained from the individual fragment action and the combined action are nearly identical， indicating that the composite protective structure significantly diminishes the influence of shock waves on the subsequent fragment impact， thereby effectively mitigating the combined effects of shock waves and fragments.

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Abstract:The process parameters have a direct impact on the 3D printing quality of solid propellant grains. To more reasonably adjust the 3D printing process parameters and improve printing quality， based on the single-layer stacking process， a numerical simulation method was employed to conduct an orthogonal experimental study on three influencing factors： extrusion speed， printing height， and printing temperature. The degree of influence of each factor was calculated through variance and range analysis. The grey relational analysis method was adopted for comparison， and the optimal combination of process parameters was selected after comprehensively considering the printing accuracy of special points. A method for calculating the printing line spacing based on single-line cross-sectional data was proposed for the first time， and simulation and experimental verification were conducted. The results indicated that the extrusion speed had the greatest impact on printing quality. When the extrusion speed was set to 12 mm·s^-1， the nozzle height was 1.2 mm， and the printing temperature was 55 ℃， the printed part exhibited optimal quality. After parameter adjustment， the tensile strength of the specimen increased from 0.21 MPa to 0.43 MPa， and the density rose from 1.43×103 kg·m^-3 to 1.65×103 kg·m^-3. Single-layer printing simulations and experiments demonstrated a significant improvement in molding quality after parameter adjustment.

Abstract:In order to investigate the reaction characteristics of oxidizer-fuel composite materials with different particle sizes in constant-volume combustion， laser ignition and detonation environment of high energy explosive hexanitrohexaazaisowurtzitane （CL-20）， three particle sizes of perfluoropolyether-functionalized micro/nano aluminum （nAl_150@xPEPE， μAl_1@xPEPE and μAl_5@xPEPE， where x=2.5%， 5.0%， 7.5%） was constructed by particle suspension method， and CL-20 based aluminized explosive was prepared by kneading granulation method. The pressure-time curve， laser-induced ignition process， energy release rate and efficiency of samples in CL-20 were studied by means of closed constant-volume explosive device， laser ignition， detonation velocity and detonation heat test equipment， respectively. The results showed that with the increase of PFPE mass fraction， the peak pressure and pressurization rate of nAl_150@xPEPE samples and μAl_1@xPEPE samples increased gradually， while the peak pressure of μAl_1@7.5%PEPE sample reached 4138.4 kPa and its pressurization rate reached 0.216 MPa·ms^-1. However， when the PFPE mass fraction exceeded 5.0%， the pressurization rate seemed to slow down. At the same time， with the increase of PFPE mass fraction， the burning rate of PFPE-functionalized micro/nano aluminum in CL-20 increased gradually. When x=7.5%， the burning rate of all the three samples with different particle sizes in CL-20 increased by 2.1 cm·s^-1， 1.8 cm·s^-1 and 2.3 cm·s^-1， respectively. In addition， four kinds of fuel-rich CL-20 based aluminized explosives were designed. Among them， the measured detonation velocity of JWL-3 explosive （62% CL-20/32% μAl_1@5.0%PEPE/6% binder） was 8125 m·s^-1， the measured detonation heat was 8049.8 kJ·kg^-1， and the energy release efficiency reached 86.10% （measured by detonation heat）.

Abstract:Using a dynamic laser monitoring technique， the solubility of 3-nitro-l，2，4-triazole-5-one （NTO） was investigated in two different binary systems， namely hydroxylamine nitrate （HAN）-water and boric acid （HB）-water ranging from 278.15 K to 318.15 K. The solubility in each system was found to be positively correlated with temperature. Furthermore， solubility data were analyzed using four equations： the modified Apelblat equation， Van’t Hoff equation， λh equation and CNIBS/R-K equations， and they provided satisfactory results for both two systems. The average root-mean-square deviation （10⁵RMSD） values for these models were less than 13.93. Calculations utilizing the Van’t Hoff equation and Gibbs equations facilitated the derivation of apparent thermodynamic properties of NTO dissolution in the two systems， including values for Gibbs free energy， enthalpy and entropy. The %ζ_H is larger than %ζ_TS， and all the %ζ_H data are ≥ 58.63%， indicating that the enthalpy make a greater contribution than entropy to the ΔG_soln^o.