3D printing technology enhances the combustion characteristics of hybrid rocket fuels by enabling complex geometries. However, improvements in regression rates and energy properties of monotonous 3D printed fuels have...3D printing technology enhances the combustion characteristics of hybrid rocket fuels by enabling complex geometries. However, improvements in regression rates and energy properties of monotonous 3D printed fuels have been limited. This study explores the impact of poly(vinylidene fluoride) and polydopamine-coated aluminum particles on the thermal and combustion properties of 3D printed hybrid rocket fuels. Physical self-assembly and anti-solvent methods were employed for constructing composite μAl particles. Characterization using SEM, XRD, XPS, FTIR, and μCT revealed a core-shell structure and homogeneous elemental distribution. Thermal analysis showed that PVDF coatings significantly increased the heat of combustion for aluminum particles, with maximum enhancement observed in μAl@PDA@PVDF(denoted as μAl@PF) at 6.20 k J/g. Subsequently, 3D printed fuels with varying pure and composite μAl particle contents were prepared using 3D printing. Combustion tests indicated higher regression rates for Al@PF/Resin composites compared to pure resin, positively correlating with particle content. The fluorocarbon-alumina reaction during the combustion stage intensified Al particle combustion, reducing residue size. A comprehensive model based on experiments provides insights into the combustion process of PDA and PVDF-coated droplets. This study advances the design of 3D-printed hybrid rocket fuels, offering strategies to improve regression rates and energy release, crucial for enhancing solid fuel performance for hybrid propulsion.展开更多
The weak interface interaction and solid-solid phase transition have long been a conundrum for 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane(HMX)-based polymer-bonded explosives(PBX).A two-step strategy that involves...The weak interface interaction and solid-solid phase transition have long been a conundrum for 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane(HMX)-based polymer-bonded explosives(PBX).A two-step strategy that involves the pretreatment of HMX to endow—OH groups on the surface via polyalcohol bonding agent modification and in situ coating with nitrate ester-containing polymer,was proposed to address the problem.Two types of energetic polyether—glycidyl azide polymer(GAP)and nitrate modified GAP(GNP)were grafted onto HMX crystal based on isocyanate addition reaction bridged through neutral polymeric bonding agent(NPBA)layer.The morphology and structure of the HMX-based composites were characterized in detail and the core-shell structure was validated.The grafted polymers obviously enhanced the adhesion force between HMX crystals and fluoropolymer(F2314)binder.Due to the interfacial reinforcement among the components,the two HMX-based composites exhibited a remarkable increment of phase transition peak temperature by 10.2°C and 19.6°C with no more than 1.5%shell content,respectively.Furthermore,the impact and friction sensitivity of the composites decreased significantly as a result of the barrier produced by the grafted polymers.These findings will enhance the future prospects for the interface design of energetic composites aiming to solve the weak interface and safety concerns.展开更多
Energetic Semiconductor bridge(ESCB)based on reactive multilayered films(RMFs)has a promising application in the miniature and intelligence of initiator and pyrotechnics device.Understanding the ignition enhancement m...Energetic Semiconductor bridge(ESCB)based on reactive multilayered films(RMFs)has a promising application in the miniature and intelligence of initiator and pyrotechnics device.Understanding the ignition enhancement mechanism of RMFs on semiconductor bridge(SCB)during the ignition process is crucial for the engineering and practical application of advanced initiator and pyrotechnics devices.In this study,a one-dimensional(1D)gas-solid two-phase flow ignition model was established to study the ignition process of ESCB to charge particles based on the reactivity of Al/MoO_(3) RMFs.In order to fully consider the coupled exothermic between the RMFs and the SCB plasma during the ignition process,the heat release of chemical reaction in RMFs was used as an internal heat source in this model.It is found that the exothermal reaction in RMFs improved the ignition performance of SCB.In the process of plasma rapid condensation with heat release,the product of RMFs enhanced the heat transfer process between the gas phase and the solid charge particle,which accelerated the expansion of hot plasma,and heated the solid charge particle as well as gas phase region with low temperature.In addition,it made up for pressure loss in the gas phase.During the plasma dissipation process,the exothermal chemical reaction in RMFs acted as the main heating source to heat the charge particle,making the surface temperature of the charge particle,gas pressure,and gas temperature rise continuously.This result may yield significant advantages in providing a universal ignition model for miniaturized ignition devices.展开更多
The study of transient heat conduction in multilayered slabs is widely used in various engineering fields. In this paper, the transient heat conduction in multilayered slabs with general boundary conditions and arbitr...The study of transient heat conduction in multilayered slabs is widely used in various engineering fields. In this paper, the transient heat conduction in multilayered slabs with general boundary conditions and arbitrary heat generations is analysed. The boundary conditions are general and include various combinations of Dirichlet, Neumann or Robin boundary conditions at either surface. Moreover, arbitrary heat generations in the slabs are taken into account. The solutions are derived by basic methods, including the superposition method, separation variable method and orthogonal expansion method. The simplified double-layered analytical solution is validated by a numerical method and applied to predicting the temporal and spatial distribution of the temperature inside a landfill. It indicates the ability of the proposed analytical solutions for solving the wide range of applied transient heat conduction problems.展开更多
The effect of introducing attenuation on Lamb wave dispersion curves is studied in this paper. Attenuation is introduced to a three-layered composite plate by an adhesive bond layer with viscous behavior. No changes a...The effect of introducing attenuation on Lamb wave dispersion curves is studied in this paper. Attenuation is introduced to a three-layered composite plate by an adhesive bond layer with viscous behavior. No changes are required to the transfer matrix formulation for the propagation of elastic waves. By introduction of a complex wavenumber, the model can be used to the propagation of attenuative Lamb waves. Numerical examples for a three-layered aluminium-epoxy-aluminium plate show that attenuation values of each mode in plates are related not only to attenuation, but also to the thickness of the bonded layer, which is in agreement with practical situations.展开更多
The core-shell 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-Trinitrotoluene(CL-20/TNT)composite was prepared by spray-drying method in which sensitive high energy explosive(CL-20)was coated with in...The core-shell 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-Trinitrotoluene(CL-20/TNT)composite was prepared by spray-drying method in which sensitive high energy explosive(CL-20)was coated with insensitive explosive(TNT).The structure and properties of different formulations of CL-20/TNT composite and CL-20/TNT mixture were characterized by scanning electron microscopy(SEM),Transmission electron microscopy(TEM),Laser particle size analyzer,X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),differential scanning calorimetry(DSC),impact sensitivity test and detonation performance.The results of SEM,TEM,XPS and XRD show that e-CL-20 particles are coated by TNT.When the ratio of CL-20/TNT is 75/25,core-shell structure is well formed,and thickness of the shell is about 20e30 nm.And the analysis of heat and impact show that with the increase of TNT content,the TNT coating on the core-shell composite material can not only catalyze the thermal decomposition of core material(CL-20),but also greatly reduce the impact sensitivity.Compared with the CL-20/TNT mixture(75/25)at the same ratio,the characteristic drop height of core-shell CL-20/TNT composite(75/25)increased by 47.6%and the TNT coating can accelerate the nuclear decomposition in the CL-20/TNT composites.Therefore,the preparation of the core-shell composites can be regarded as a unique means,by which the composites are characterized by controllable decomposition rate,high energy and excellent mechanical sensitivity and could be applied to propellants and other fields.展开更多
A facile and economical approach was developed for the large-scale production of powdered core-shell structured PTFE/Al (CS-PA) energetic materials through ultrasonic-assisted mixing. The low-cost micrometer-sized PTF...A facile and economical approach was developed for the large-scale production of powdered core-shell structured PTFE/Al (CS-PA) energetic materials through ultrasonic-assisted mixing. The low-cost micrometer-sized PTFE and Al particles were used as starting materials. Under high-power ultrasonic waves, the PTFE powder was dispersed into nano-to sub-micrometer-sized particles and then encapsulated the Al microparticles to form the core-shell structure. The heat of combustion, burning rate, and pressurization rate of the powdered CS-PA were measured. The thermal-initiated reaction behavior was further evaluated using thermogravimetry-differential scanning calorimetry. Subsequently, the bulk CS-PA with a uniform microstructure was obtained via cold isostatic pressing of the powdered CS-PA followed by vacuum sintering. For the bulk CS-PA, the quasi-static compression behavior was characterized, and the impact-initiated reaction processes were conducted using the Split Hopkinson Pressure Bar (SHPB) and evaluated by a high-speed camera. Compared to physically mixed PTFE/Al materials, the powdered and bulk CS-PA demonstrated enhanced thermal- and impact-initiated reaction characteristics respectively, proving the effectiveness of our approach for constructing core-shell structures.展开更多
Inspired by the phenomenon of superhydrophobic plants and animals in nature,1,3,5,7-tetranitro-1,3,5,7-tetrazocane(HMX)@copper stearate(CS)core-shell composites with similar properties was prepared.A rough shell layer...Inspired by the phenomenon of superhydrophobic plants and animals in nature,1,3,5,7-tetranitro-1,3,5,7-tetrazocane(HMX)@copper stearate(CS)core-shell composites with similar properties was prepared.A rough shell layer on the surface of the HMX was observed by scanning electron microscopy(SEM),and a series of in-depth characterization confirmed the successful generation of CS and the coreshell structure of the samples.Differential scanning calorimeter(DSC)proves that the crystal transition temperature(204℃)and high temperature decomposition exothermal temperature(284℃)of HMX@CS is almost unchanged compared with pure HMX,which means HMX and CS have good compatibility.Then,the H50 of the samples also increased continuously(16.6 cm→33.7 cm)when the CS shell content increased from 1%to 5%,indicating that the CS shell has a certain buffering performance,and CS will absorb some heat and melt under the stimulation of impact due to its low melting point,which improved impact sensitivity of HMX effectively further.Moreover,HMX@CS has excellent hydrophobic and oleophilic performance,shows excellent wettability with lipid binder,and samples with appropriate CS shell content can continue to combustion stably after covering water.This waterproof and low sensitivity coating provides a new way for the development of multifunctional energetic materials.展开更多
Copper azide(CA), as a primary explosive with high energy density, has not been practically used so far because of its high electrostatic sensitivity. The Cu2O@HKUST-1 core-shell structure hybrid material was synthesi...Copper azide(CA), as a primary explosive with high energy density, has not been practically used so far because of its high electrostatic sensitivity. The Cu2O@HKUST-1 core-shell structure hybrid material was synthesized by the “bottle around ship” methodology in this research by regulating the dissolution rate of Cu2O and the generation rate of metal-organic framework(MOF) materials. Cu2O@HKUST-1 was carbonized to form a Cu O@porous carbon(CuO@PC) composite material. CuO@PC was synthesized into a copper azide(CA) @PC composite energetic material through a gas-solid phase in-situ azidation reaction.CA is encapsulated in PC framework, which acts as a nanoscale Faraday cage, and its excellent electrical conductivity prevents electrostatic charges from accumulating on the energetic material’s surface. The CA@PC composite energetic material has a CA content of 89.6%, and its electrostatic safety is nearly 30times that of pure CA(1.47 mJ compared to 0.05 mJ). CA@PC delivers an outstanding balance of safety and energy density compared to similar materials.展开更多
Ce O2@Si O2 core-shell nanoparticles were prepared by microemulsion method, and metalloporphyrins were immobilized on the Ce O2@Si O2 core-shell nanoparticles surface via amide bond. The supported metalloporphyrin cat...Ce O2@Si O2 core-shell nanoparticles were prepared by microemulsion method, and metalloporphyrins were immobilized on the Ce O2@Si O2 core-shell nanoparticles surface via amide bond. The supported metalloporphyrin catalysts were characterized by N2 adsorption-desorption isotherm(BET), scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), ultraviolet and visible spectroscopy(UV-Vis), and Fourier transform infrared spectroscopy(FT-IR). The results show that the morphology of Ce O2@Si O2 nanoparticles is core-shell microspheres with about 30 nm in diameter, and metalloporphyrins are immobilized on the Ce O2@Si O2 core-shell nanoparticles via amide bond. Especially, the core-shell structure contains multi Ce O2 core and thin Si O2 shell, which may benefit the synergistic effect between the Ce O2 core and the porphyrin anchored on the very thin Si O2 shell. As a result, this supported metalloporphyrin catalysts present comparably high catalytic activity and stability for oxidation of ethylbenzene with molecular oxygen, namely, ethylbenzene conversion remains around 12% with identical selectivity of about 80% for acetophenone even after six-times reuse of the catalyst.展开更多
A nanocomposite of manganese dioxide coated manganese hexacyanoferrate was synthesized by a facile co-precipitation method and tested as active electrode material for an electrochemical supercapacitor. A way called &q...A nanocomposite of manganese dioxide coated manganese hexacyanoferrate was synthesized by a facile co-precipitation method and tested as active electrode material for an electrochemical supercapacitor. A way called "Deep electro-oxidation" was used to generate manganese dioxide coated layer for stabilizing the electrode material. The structure and ingredient of the resulting MnHCF/MnO2 composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray Photoelectron Spectroscopy. Electrochemical testing showed a capacitance of 225.6 F/g at a sweep rate of 5 mV/s within a voltage range of 1.3 V, and high energy density of 37.2 Wh/kg at a current density of 0.5 A/g in galvanostatic charge/discharge cycling. It is suggested that the two different components, manganese hexacyanoferrate core and manganese dioxide shell, lead to an integrated electrochemical behavior, and an enhanced capacitor. The electrochemical testing and corresponding XPS analysis also demonstrated that the manganese coordinated by cyanide groups via nitrogen atoms in MnHCF did not get involved in the charge storage process during potential cycles.展开更多
Global navigation satellite system-reflection(GNSS-R)sea surface altimetry based on satellite constellation platforms has become a new research direction and inevitable trend,which can meet the altimetric precision at...Global navigation satellite system-reflection(GNSS-R)sea surface altimetry based on satellite constellation platforms has become a new research direction and inevitable trend,which can meet the altimetric precision at the global scale required for underwater navigation.At present,there are still research gaps for GNSS-R altimetry under this mode,and its altimetric capability cannot be specifically assessed.Therefore,GNSS-R satellite constellations that meet the global altimetry needs to be designed.Meanwhile,the matching precision prediction model needs to be established to quantitatively predict the GNSS-R constellation altimetric capability.Firstly,the GNSS-R constellations altimetric precision under different configuration parameters is calculated,and the mechanism of the influence of orbital altitude,orbital inclination,number of satellites and simulation period on the precision is analyzed,and a new multilayer feedforward neural network weighted joint prediction model is established.Secondly,the fit of the prediction model is verified and the performance capability of the model is tested by calculating the R2 value of the model as 0.9972 and the root mean square error(RMSE)as 0.0022,which indicates that the prediction capability of the model is excellent.Finally,using the novel multilayer feedforward neural network weighted joint prediction model,and considering the research results and realistic costs,it is proposed that when the constellation is set to an orbital altitude of 500 km,orbital inclination of 75and the number of satellites is 6,the altimetry precision can reach 0.0732 m within one year simulation period,which can meet the requirements of underwater navigation precision,and thus can provide a reference basis for subsequent research on spaceborne GNSS-R sea surface altimetry.展开更多
Al/Ni reactive multilayer foil(RMF)possesses excellent comprehensive properties as a promising substitute for traditional Cu bridge.A theoretical resistivity model of Al/Ni RMF was developed to guide the optimization ...Al/Ni reactive multilayer foil(RMF)possesses excellent comprehensive properties as a promising substitute for traditional Cu bridge.A theoretical resistivity model of Al/Ni RMF was developed to guide the optimization of EFIs.Al/Ni RMF with different bilayer thicknesses and bridge dimensions were prepared by MEMS technology and electrical explosion tests were carried out.According to physical and chemical reactions in bridge,the electrical explosion process was divided into 5 stages:heating of condensed bridge,vaporization and diffusion of Al layers,intermetallic combination reaction,intrinsic explosion,ionization of metal gases,which are obviously shown in measured voltage curve.Effects of interface and grain boundary scattering on the resistivity of film metal were considered.Focusing on variations of substance and state,the resistivity was developed as a function of temperature at each stage.Electrical explosion curves were calculated by this model at different bilayer thicknesses,bridge dimensions and capacitor voltages,which showed an excellent agreement with experimental ones.展开更多
遥感图像目标检测在军事侦察、智慧农业等领域意义重大,特别是小目标检测一直获得持续关注。然而,遥感图像中的小目标面临特征信息不足、检测难度大等问题,成为困扰遥感检测应用发展的最大障碍。为此,提出YOLO-HF(you only look once-hy...遥感图像目标检测在军事侦察、智慧农业等领域意义重大,特别是小目标检测一直获得持续关注。然而,遥感图像中的小目标面临特征信息不足、检测难度大等问题,成为困扰遥感检测应用发展的最大障碍。为此,提出YOLO-HF(you only look once-hybrid feature)算法,该算法在传统YOLOv7模型的网络中,引入通道注意力和自注意力的混合注意力机制提取目标深层特征,并将浅层特征和深层特征进行融合,增加局部特征的丰富性;为进一步加强对全局信息的关注,在提取特征后为小尺度目标添加全局注意力机制,实现全局特征表达能力的提升;为避免传统损失函数对小目标位置偏差敏感,导致检测效果不佳,选择使用一种新的度量方式,将其嵌入边界框损失函数的计算中,从而加快损失函数的收敛,实现小目标检测精度的提升。实验结果表明:与传统YOLOv7算法相比,所提算法在RSOD和NWPU VHR-10数据集上均表现出优越性,特别地,在RSOD数据集上均值平均精度提升了2.90%,在NWPU VHR-10数据集上均值平均精度实现了3.61%的提升。展开更多
基金funded by the National Natural Science Foundation of China(Grant No.06101213)the National Natural Science Foundation of China(Grant No.22105160).
文摘3D printing technology enhances the combustion characteristics of hybrid rocket fuels by enabling complex geometries. However, improvements in regression rates and energy properties of monotonous 3D printed fuels have been limited. This study explores the impact of poly(vinylidene fluoride) and polydopamine-coated aluminum particles on the thermal and combustion properties of 3D printed hybrid rocket fuels. Physical self-assembly and anti-solvent methods were employed for constructing composite μAl particles. Characterization using SEM, XRD, XPS, FTIR, and μCT revealed a core-shell structure and homogeneous elemental distribution. Thermal analysis showed that PVDF coatings significantly increased the heat of combustion for aluminum particles, with maximum enhancement observed in μAl@PDA@PVDF(denoted as μAl@PF) at 6.20 k J/g. Subsequently, 3D printed fuels with varying pure and composite μAl particle contents were prepared using 3D printing. Combustion tests indicated higher regression rates for Al@PF/Resin composites compared to pure resin, positively correlating with particle content. The fluorocarbon-alumina reaction during the combustion stage intensified Al particle combustion, reducing residue size. A comprehensive model based on experiments provides insights into the combustion process of PDA and PVDF-coated droplets. This study advances the design of 3D-printed hybrid rocket fuels, offering strategies to improve regression rates and energy release, crucial for enhancing solid fuel performance for hybrid propulsion.
基金the support for this work by National Natural Science Foundation of China(Grant Nos.22175139 and 22105156)。
文摘The weak interface interaction and solid-solid phase transition have long been a conundrum for 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane(HMX)-based polymer-bonded explosives(PBX).A two-step strategy that involves the pretreatment of HMX to endow—OH groups on the surface via polyalcohol bonding agent modification and in situ coating with nitrate ester-containing polymer,was proposed to address the problem.Two types of energetic polyether—glycidyl azide polymer(GAP)and nitrate modified GAP(GNP)were grafted onto HMX crystal based on isocyanate addition reaction bridged through neutral polymeric bonding agent(NPBA)layer.The morphology and structure of the HMX-based composites were characterized in detail and the core-shell structure was validated.The grafted polymers obviously enhanced the adhesion force between HMX crystals and fluoropolymer(F2314)binder.Due to the interfacial reinforcement among the components,the two HMX-based composites exhibited a remarkable increment of phase transition peak temperature by 10.2°C and 19.6°C with no more than 1.5%shell content,respectively.Furthermore,the impact and friction sensitivity of the composites decreased significantly as a result of the barrier produced by the grafted polymers.These findings will enhance the future prospects for the interface design of energetic composites aiming to solve the weak interface and safety concerns.
基金supported by the National Natural Science Foundation of China(Grant Nos.22275092,52102107 and 52372084)the Fundamental Research Funds for the Central Universities(Grant No.30923010920)。
文摘Energetic Semiconductor bridge(ESCB)based on reactive multilayered films(RMFs)has a promising application in the miniature and intelligence of initiator and pyrotechnics device.Understanding the ignition enhancement mechanism of RMFs on semiconductor bridge(SCB)during the ignition process is crucial for the engineering and practical application of advanced initiator and pyrotechnics devices.In this study,a one-dimensional(1D)gas-solid two-phase flow ignition model was established to study the ignition process of ESCB to charge particles based on the reactivity of Al/MoO_(3) RMFs.In order to fully consider the coupled exothermic between the RMFs and the SCB plasma during the ignition process,the heat release of chemical reaction in RMFs was used as an internal heat source in this model.It is found that the exothermal reaction in RMFs improved the ignition performance of SCB.In the process of plasma rapid condensation with heat release,the product of RMFs enhanced the heat transfer process between the gas phase and the solid charge particle,which accelerated the expansion of hot plasma,and heated the solid charge particle as well as gas phase region with low temperature.In addition,it made up for pressure loss in the gas phase.During the plasma dissipation process,the exothermal chemical reaction in RMFs acted as the main heating source to heat the charge particle,making the surface temperature of the charge particle,gas pressure,and gas temperature rise continuously.This result may yield significant advantages in providing a universal ignition model for miniaturized ignition devices.
基金Projects(41530637,41877222,41702290)supported by the National Natural Science Foundation of China
文摘The study of transient heat conduction in multilayered slabs is widely used in various engineering fields. In this paper, the transient heat conduction in multilayered slabs with general boundary conditions and arbitrary heat generations is analysed. The boundary conditions are general and include various combinations of Dirichlet, Neumann or Robin boundary conditions at either surface. Moreover, arbitrary heat generations in the slabs are taken into account. The solutions are derived by basic methods, including the superposition method, separation variable method and orthogonal expansion method. The simplified double-layered analytical solution is validated by a numerical method and applied to predicting the temporal and spatial distribution of the temperature inside a landfill. It indicates the ability of the proposed analytical solutions for solving the wide range of applied transient heat conduction problems.
文摘The effect of introducing attenuation on Lamb wave dispersion curves is studied in this paper. Attenuation is introduced to a three-layered composite plate by an adhesive bond layer with viscous behavior. No changes are required to the transfer matrix formulation for the propagation of elastic waves. By introduction of a complex wavenumber, the model can be used to the propagation of attenuative Lamb waves. Numerical examples for a three-layered aluminium-epoxy-aluminium plate show that attenuation values of each mode in plates are related not only to attenuation, but also to the thickness of the bonded layer, which is in agreement with practical situations.
文摘The core-shell 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-Trinitrotoluene(CL-20/TNT)composite was prepared by spray-drying method in which sensitive high energy explosive(CL-20)was coated with insensitive explosive(TNT).The structure and properties of different formulations of CL-20/TNT composite and CL-20/TNT mixture were characterized by scanning electron microscopy(SEM),Transmission electron microscopy(TEM),Laser particle size analyzer,X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),differential scanning calorimetry(DSC),impact sensitivity test and detonation performance.The results of SEM,TEM,XPS and XRD show that e-CL-20 particles are coated by TNT.When the ratio of CL-20/TNT is 75/25,core-shell structure is well formed,and thickness of the shell is about 20e30 nm.And the analysis of heat and impact show that with the increase of TNT content,the TNT coating on the core-shell composite material can not only catalyze the thermal decomposition of core material(CL-20),but also greatly reduce the impact sensitivity.Compared with the CL-20/TNT mixture(75/25)at the same ratio,the characteristic drop height of core-shell CL-20/TNT composite(75/25)increased by 47.6%and the TNT coating can accelerate the nuclear decomposition in the CL-20/TNT composites.Therefore,the preparation of the core-shell composites can be regarded as a unique means,by which the composites are characterized by controllable decomposition rate,high energy and excellent mechanical sensitivity and could be applied to propellants and other fields.
基金This work was supported by the National Natural Science Foundation of China(No.51571033,11804022)the Science and Technology on Transient Impact Laboratory Foundation(No.6142606183208).
文摘A facile and economical approach was developed for the large-scale production of powdered core-shell structured PTFE/Al (CS-PA) energetic materials through ultrasonic-assisted mixing. The low-cost micrometer-sized PTFE and Al particles were used as starting materials. Under high-power ultrasonic waves, the PTFE powder was dispersed into nano-to sub-micrometer-sized particles and then encapsulated the Al microparticles to form the core-shell structure. The heat of combustion, burning rate, and pressurization rate of the powdered CS-PA were measured. The thermal-initiated reaction behavior was further evaluated using thermogravimetry-differential scanning calorimetry. Subsequently, the bulk CS-PA with a uniform microstructure was obtained via cold isostatic pressing of the powdered CS-PA followed by vacuum sintering. For the bulk CS-PA, the quasi-static compression behavior was characterized, and the impact-initiated reaction processes were conducted using the Split Hopkinson Pressure Bar (SHPB) and evaluated by a high-speed camera. Compared to physically mixed PTFE/Al materials, the powdered and bulk CS-PA demonstrated enhanced thermal- and impact-initiated reaction characteristics respectively, proving the effectiveness of our approach for constructing core-shell structures.
基金financially supported by the National Natural Science Foundation of China (Grant NO.11702268)Sichuan provincial key S&T Special Projects (Grant NO.19DZX0106)
文摘Inspired by the phenomenon of superhydrophobic plants and animals in nature,1,3,5,7-tetranitro-1,3,5,7-tetrazocane(HMX)@copper stearate(CS)core-shell composites with similar properties was prepared.A rough shell layer on the surface of the HMX was observed by scanning electron microscopy(SEM),and a series of in-depth characterization confirmed the successful generation of CS and the coreshell structure of the samples.Differential scanning calorimeter(DSC)proves that the crystal transition temperature(204℃)and high temperature decomposition exothermal temperature(284℃)of HMX@CS is almost unchanged compared with pure HMX,which means HMX and CS have good compatibility.Then,the H50 of the samples also increased continuously(16.6 cm→33.7 cm)when the CS shell content increased from 1%to 5%,indicating that the CS shell has a certain buffering performance,and CS will absorb some heat and melt under the stimulation of impact due to its low melting point,which improved impact sensitivity of HMX effectively further.Moreover,HMX@CS has excellent hydrophobic and oleophilic performance,shows excellent wettability with lipid binder,and samples with appropriate CS shell content can continue to combustion stably after covering water.This waterproof and low sensitivity coating provides a new way for the development of multifunctional energetic materials.
基金the financial support by Postgraduate Research & Practice Innovation Program from Jiangsu Science and Technology Department under Grant number KYCX19_0320。
文摘Copper azide(CA), as a primary explosive with high energy density, has not been practically used so far because of its high electrostatic sensitivity. The Cu2O@HKUST-1 core-shell structure hybrid material was synthesized by the “bottle around ship” methodology in this research by regulating the dissolution rate of Cu2O and the generation rate of metal-organic framework(MOF) materials. Cu2O@HKUST-1 was carbonized to form a Cu O@porous carbon(CuO@PC) composite material. CuO@PC was synthesized into a copper azide(CA) @PC composite energetic material through a gas-solid phase in-situ azidation reaction.CA is encapsulated in PC framework, which acts as a nanoscale Faraday cage, and its excellent electrical conductivity prevents electrostatic charges from accumulating on the energetic material’s surface. The CA@PC composite energetic material has a CA content of 89.6%, and its electrostatic safety is nearly 30times that of pure CA(1.47 mJ compared to 0.05 mJ). CA@PC delivers an outstanding balance of safety and energy density compared to similar materials.
基金Projects(J21103045,J1210040,J1103312) supported by the National Natural Science Foundation of ChinaProject supported by the Fundamental Research Funds for the Central Universities of China
文摘Ce O2@Si O2 core-shell nanoparticles were prepared by microemulsion method, and metalloporphyrins were immobilized on the Ce O2@Si O2 core-shell nanoparticles surface via amide bond. The supported metalloporphyrin catalysts were characterized by N2 adsorption-desorption isotherm(BET), scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), ultraviolet and visible spectroscopy(UV-Vis), and Fourier transform infrared spectroscopy(FT-IR). The results show that the morphology of Ce O2@Si O2 nanoparticles is core-shell microspheres with about 30 nm in diameter, and metalloporphyrins are immobilized on the Ce O2@Si O2 core-shell nanoparticles via amide bond. Especially, the core-shell structure contains multi Ce O2 core and thin Si O2 shell, which may benefit the synergistic effect between the Ce O2 core and the porphyrin anchored on the very thin Si O2 shell. As a result, this supported metalloporphyrin catalysts present comparably high catalytic activity and stability for oxidation of ethylbenzene with molecular oxygen, namely, ethylbenzene conversion remains around 12% with identical selectivity of about 80% for acetophenone even after six-times reuse of the catalyst.
文摘A nanocomposite of manganese dioxide coated manganese hexacyanoferrate was synthesized by a facile co-precipitation method and tested as active electrode material for an electrochemical supercapacitor. A way called "Deep electro-oxidation" was used to generate manganese dioxide coated layer for stabilizing the electrode material. The structure and ingredient of the resulting MnHCF/MnO2 composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray Photoelectron Spectroscopy. Electrochemical testing showed a capacitance of 225.6 F/g at a sweep rate of 5 mV/s within a voltage range of 1.3 V, and high energy density of 37.2 Wh/kg at a current density of 0.5 A/g in galvanostatic charge/discharge cycling. It is suggested that the two different components, manganese hexacyanoferrate core and manganese dioxide shell, lead to an integrated electrochemical behavior, and an enhanced capacitor. The electrochemical testing and corresponding XPS analysis also demonstrated that the manganese coordinated by cyanide groups via nitrogen atoms in MnHCF did not get involved in the charge storage process during potential cycles.
基金the National Natural Science Foundation of China under Grant(42274119)the Liaoning Revitalization Talents Program under Grant(XLYC2002082)+1 种基金National Key Research and Development Plan Key Special Projects of Science and Technology Military Civil Integration(2022YFF1400500)the Key Project of Science and Technology Commission of the Central Military Commission.
文摘Global navigation satellite system-reflection(GNSS-R)sea surface altimetry based on satellite constellation platforms has become a new research direction and inevitable trend,which can meet the altimetric precision at the global scale required for underwater navigation.At present,there are still research gaps for GNSS-R altimetry under this mode,and its altimetric capability cannot be specifically assessed.Therefore,GNSS-R satellite constellations that meet the global altimetry needs to be designed.Meanwhile,the matching precision prediction model needs to be established to quantitatively predict the GNSS-R constellation altimetric capability.Firstly,the GNSS-R constellations altimetric precision under different configuration parameters is calculated,and the mechanism of the influence of orbital altitude,orbital inclination,number of satellites and simulation period on the precision is analyzed,and a new multilayer feedforward neural network weighted joint prediction model is established.Secondly,the fit of the prediction model is verified and the performance capability of the model is tested by calculating the R2 value of the model as 0.9972 and the root mean square error(RMSE)as 0.0022,which indicates that the prediction capability of the model is excellent.Finally,using the novel multilayer feedforward neural network weighted joint prediction model,and considering the research results and realistic costs,it is proposed that when the constellation is set to an orbital altitude of 500 km,orbital inclination of 75and the number of satellites is 6,the altimetry precision can reach 0.0732 m within one year simulation period,which can meet the requirements of underwater navigation precision,and thus can provide a reference basis for subsequent research on spaceborne GNSS-R sea surface altimetry.
基金National Natural Science Foundation of China(Grant No.11872013)for supporting this project.
文摘Al/Ni reactive multilayer foil(RMF)possesses excellent comprehensive properties as a promising substitute for traditional Cu bridge.A theoretical resistivity model of Al/Ni RMF was developed to guide the optimization of EFIs.Al/Ni RMF with different bilayer thicknesses and bridge dimensions were prepared by MEMS technology and electrical explosion tests were carried out.According to physical and chemical reactions in bridge,the electrical explosion process was divided into 5 stages:heating of condensed bridge,vaporization and diffusion of Al layers,intermetallic combination reaction,intrinsic explosion,ionization of metal gases,which are obviously shown in measured voltage curve.Effects of interface and grain boundary scattering on the resistivity of film metal were considered.Focusing on variations of substance and state,the resistivity was developed as a function of temperature at each stage.Electrical explosion curves were calculated by this model at different bilayer thicknesses,bridge dimensions and capacitor voltages,which showed an excellent agreement with experimental ones.
