Fabrication and characterization of mussel-inspired layer-by-layer assembled CL-20-based energetic films via micro-jet printing

Three-dimensional (3D) micro-jet printing is a droplet deposition technique based on liquid-phase materials. To improve the deposition density and performance of energetic films with micro/nanoscale on an energetic chip, polydopamine (PDA) was utilized as a linker bridge to induce the in-situ self-assembly of CL-20-based energetic film via 3D micro-jet printing. The self-assembly was extensively characterized by confocal laser scanning microscopy (CLSM), SEM, power-XRD, XPS, and DSC. The performance of the self-assembled film was verified by the mechanical properties and detonation properties, and a possible self-assembly mechanism in the layer-by-layer micro-jet printing process was proposed. The results indicated PDA-induced self-assembly enhanced the physical entanglement between the binders and energetic crystal, reduced the porosity from 15.87% to 11.28%, and improved the elastic modulus and the detonation performance of the CL-20-based energetic film. This work proposes a novel and promising energetic film design and fabrication strategy to enhance the interaction between the energetic composite layers in the micro-jet printing process.     

Nitro-tetrazole based high performing explosives: Recent overview of synthesis and energetic properties

Heterocyclic skeleton (Azoles) and different energetic groups containing high performing explosives are highly emerged in recent years to meet the challenging requirements of energetic materials in both military and civilian applications with improved performance. For this purpose tetrazole (Azole) is identified as an attractive heterocyclic backbone with energetic functional groups nitro (-NO₂), nitrato (-ONO₂), nitrimino (-NNO₂), and nitramino (–NH–NO₂) to replace the traditionally used high performing explosives. The tetrazole based compounds having these energetic functional groups demonstrated advanced energetic performance (detonation velocity and pressure), densities, and heat of formation (HOF) and became a potential replacement of traditional energetic compounds such as RDX. This review presents a summary of the recently reported nitro-tetrazole energetic compounds containing poly-nitro, di/mono-nitro, nitrato/nitramino/nitrimino, bridged/bis/di tetrazole and nitro functional groups, describing their preparation methods, advance energetic properties, and further applications as high-performing explosives, especially those reported in the last decade. This review aims to provide a fresh concept for designing nitro-tetrazole based high performing explosives together with major challenges and perspectives.     

Insensitive energetic microspheres DAAF/RDX fabricated by facile molecular self-assembly

Insensitive energetic materials are promising in the defense weapons field. However, energetic materials still suffer from great challenges and the concern about their safety limits their utilization. In this work, insensitive energetic explosive 3,3′-diamino-4,4′-azoxyfurazan/hexahydro-1,3,5-trinitro-1,3,5-triazine (DAAF/RDX) microspheres were fabricated by self-assembly method. Rod-like DAAF/RDX was prepared by mechanical ball milling for comparison. DAAF/RDX composites with different mass ratios (90:10, 80:20, and 70:30) were obtained. The morphologies and structures of as-obtained DAAF/RDX composites were characterized by scanning electron microscopy (SEM), powder x-ray diffraction (PXRD) and fourier transform infrared spectroscopy (FT-IR). The results showed that DAAF/RDX microspheres exhibited regular shaped microspheres with sizes from 0.5 to 1.2 μm. There was no crystal transition during the modification process. The thermal properties of as-obtained materials were then evaluated by differential scanning calorimetry (DSC) and materials studio software. DAAF/RDX microspheres showed an advanced decomposition peak temperature compared with rod-like DAAF/RDX. The binding energy and peak temperature values at zero β_i (T_P0) of DAAF/RDX (90:10) increased by 36.77 kJ/mol, 1.6 °C, and 58.11 kJ/mol, 12.3 °C compared to DAAF/RDX (80:20) and DAAF/RDX (70:30), indicating the better thermal stability of DAAF/RDX (90:10). The characteristic drop height (H₅₀) of DAAF/RDX (higher than 100 cm) composites was higher than that of raw RDX (25 cm), suggesting significant improvements in mechanical safety. The preparation of DAAF/RDX microspheres is promising for the desensitization of RDX and useful for the formation of other materials and future wide applications.     

Dielectric constant predictions for energetic materials using quantum calculations

The dielectric constant (DC) is one of the key properties for detection of threat materials such as Improvised Explosive Devices (IEDs). In the present paper, the density functional theory (DFT) as well as ab-initio approaches are used to explore effective methods to predict dielectric constants of a series of 12 energetic materials (EMs) for which experimental data needed to experimentally determine the dielectric constant (refractive indices) are available. These include military grades energetic materials, nitro and peroxide compounds, and the widely used nitroglycerin. Ab-initio and DFT calculations are conducted. In order to calculate dielectric constant values of materials, potential DFT functional combined with basis sets are considered for testing. Accuracy of the calculations are compared to experimental data listed in the scientific literature, and time required for calculations are both evaluated and discussed. The best functional/basis set combinations among those tested are CAM-B3LYP and AUG-cc-pVDZm, which provide great results, with accuracy deviations below 5% when calculated results are compared to experimental data.     

Thermal and combustion behavior of Al-MnO2 nanothermite with poly(vinylidene fluoride -co- hexafluoropropylene) energetic binder

Fluoropolymers get increasing attention in energetic materials application due to the high fluorine content. To explore the effect of poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) on Al/MnO2 nanothermite, the samples with different contents are prepared and characterized by SEM, TG-DSC, XRD, and their ignition and combustion behavior are tested and recorded. The results show that P(VDF-HFP) as an energetic binder can combine the nanothermite components together, even exist in the gaps. The integrity of energetic materials has been improved. Thermal analysis shows that the addition of P(VDF-HFP) greatly changes the thermal reaction processes, and the exothermic peaks appear early, but the utilization of fuel and oxidizer is not efficient from the XRD results. Furthermore, the appropriate addition of P(VDF-HFP) can directly reduce the ignition energy threshold and increase the combustion time, which is necessary for the potential ignition charge application. The possible reasons for above phenomena are discussed and analyzed. This research provides a reference for improvement of thermite-based ignition charge formulation.     

Thermodynamics and performance of Al/CuO nanothermite with different storage time

The storage stability of energetic materials is important for its application. Here, the storage stability of Al/CuO nanothermite, which was prepared by electrospray method and stored with different storage time, was systematically researched. The activation energy of Al/CuO nanothermite was calculated by differential scanning calorimetry (DSC). The ignition temperature and the curve pressure history of Al/CuO nanothermite was measured using ignition temperature measuring device and constant-volume pressurization tests, respectively. Further, the thermites were characterized by X-ray Diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and Transmission electron microscopy (TEM). The results show that the morphology of the thermites did not change significantly. The activation energy was decreased from 254.1 kJ/mol to 181.8 kJ/mol after storage for 13 months. When stored for 0, 7 and 13 months, the peak pressures of Al/CuO nanothermite were 685.8 kPa, 626.3 kPa and 625.5 kPa, respectively. In addition to the ignition temperature, it was 775 ℃, 739 ℃ and 754 ℃, respectively. This result indicated that the ignition and combustion properties of Al/CuO nano-thermite are obviously reduced when stored for a long time, at room temperature.     

Research progress on advanced rail materials for electromagnetic railgun technology

Electromagnetic railgun attracts more and more attention due to its advantage in speed,cost,and obscurity.It is found that the rail should withstand huge mechanical and thermal shocks during the launching operation.The forms of rail failure are accompanied by gouge,grooving,transition,and arc ablation,etc.The service life of the rail has become a bottleneck restricting the development of elec-tromagnetic railgun technology.A series of researches are carried out to solve rail failure,including analysing the failure mechanism and using various advanced rail materials.This paper provides a comprehensive review of rail materials,including material composition,preparation,microstructure,and properties.We begin from a short background of the requirement of the rail material.Then a detailed investigation of rail materials is described,and the performances of those materials are introduced.Finally,further development prospect of rail material is discussed.     

Coating processes towards selective laser sintering of energetic material composites

This research aims to contribute to the safe methodology for additive manufacturing (AM) of energetic materials. Coating formulation processes were investigated and evaluated to find a suitable method that may enable selective laser sintering (SLS) as the safe method for fabrication of high explosive (HE) compositions. For safety and convenience reasons, the concept demonstration was conducted using inert explosive simulants with properties quasi-similar to the real HE. Coating processes for simulant RDX-based microparticles by means of PCL and 3,4,5-trimethoxybenzaldehyde (as TNT simulant) are reported. These processes were evaluated for uniformity of coating the HE inert simulant particles with binder materials to facilitate the SLS as the adequate binding and fabrication method. Suspension system and single emulsion methods gave required particle near spherical morphology, size and uniform coating. The suspension process appears to be suitable for the SLS of HE mocks and potential formulation methods for active HE composites. The density is estimated to be comparable with the current HE compositions and plastic bonded explosives (PBXs) such as C4 and PE4, produced from traditional methods. The formulation method developed and understanding of the science behind the processes paves the way toward safe SLS of the active HE compositions and may open avenues for further research and development of munitions of the future.     

Formulation development and characterization of cellulose acetate nitrate based propellants for improved insensitive munitions properties

Cellulose acetate nitrate (CAN) was used as an insensitive energetic binder to improve the insensitive munitions (IM) properties of gun propellants to replace the M1 propellant used in 105 mm artillery charges. CAN contains the energetic nitro groups found in nitrocellulose (NC), but also acetyl functionalities, which lowered the polymer's sensitivity to heat and shock, and therefore improved its IM properties relative to NC. The formulation, development and small-scale characterization testing of several CAN-based propellants were done. The formulations, using insensitive energetic solid fillers and high-nitrogen modifiers in place of nitramine were completed. The small scale characterization testing, such as closed bomb testing, small scale sensitivity, thermal stability, and chemical compatibility were done. The mechanical response of the propellants under high-rate uni-axial compression at, hot, cold, and ambient temperatures were also completed. Critical diameter testing, hot fragment conductive ignition (HFCI) tests were done to evaluate the propellants' responses to thermal and shock stimuli. Utilizing the propellant chemical composition, theoretical predictions of erosivity were completed. All the small scale test results were utilized to down-select the promising CAN based formulations for large scale demonstration testing such as the ballistic performance and fragment impact testing in the 105 mm M67 artillery charge configurations. The test results completed in the small and large scale testing are discussed.     

Preparation and property of CL-20/BAMO-THF energetic nanocomposites

A sol-gel freezing-drying method was utilized to prepare energetic nanocomposites based on 2, 4, 6, 8, 10, 12-hexanitro-2, 4, 6, 8, 10, 12-hexaazaisowurtzitane (CL-20) with 3, 3-Bis (azidomethyl) oxetane-tetrahydrofuran copolymer (BAMO-THF) as energetic gel matrix. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman, Fourier-transform infrared spectroscopy (FT-IR) and differential thermal analyser (DTA) were utilized to characterize the structure and property of the resultant energetic nanocomposites. Compared with raw CL-20, the average particle sizes of CL-20 in CL-20/BAMO-THF energetic nanocomposites were decreased to nano scale and the morphologies of CL-20 were also changed from prismatic to spherical. FT-IR detection revealed that CL-20 particles were recrystallized in BAMO-THF gel matrix during the freezing-drying process. The thermal decomposition behaviors of the energetic nanocomposites were investigated as well. The thermolysis process of CL-20/BAMO-THF nanocomposites was enhanced and the activation energy was lower compared with that of raw CL-20, indicating that CL-20/BAMO-THF nanocomposites showed high thermolysis activity. The impact sensitivity tests indicated that CL-20/BAMO-THF energetic nanocomposites presented low sensitivity performance.     

直接挤出成型用环氧树脂的流变性及其可打印性

直接挤出成型制造适用于任何含或不含添加剂的膏状或凝胶状复合材料,对复合材料制造技术具有深远意义。通过探讨热固性环氧树脂的流变学行为与挤出成型特性,得出热固性环氧树脂在直接挤出成型制造应用中的通用性流变学参数。通过向复合材料中加入增稠剂,对其流变学行为进行设计。结果表明:在高剪切速率(50 s~(-1))和低剪切速率(0.01 s~(-1))下,添加30%纳米黏土的环氧树脂的流变学行为较适合挤出式3D打印工艺。利用龙门式气动挤出式3D打印机,对复合材料的打印成型质量进行试验分析和验证。结合试验结果探讨了喷头高度对复合材料成型质量的影响,并且提出适用于喷头高度临界值的计算方法。探讨了挤出率、剪切速率等因素对成型质量的作用规律。针对多层打印问题,提出包含补偿系数的多层打印的临界喷头高度的计算方法。以上研究对促进基于复合材料的挤出式3D打印具有积极意义。     

Structure design and property adjustment of new cage rich-nitrogen pentazolyltetraazacubanes as potential high energy density compounds

In this study, based on two attractive energetic compounds pentazole (PZ) and tetraazacubane (TAC), a new family of high energy and high nitrogen compounds pentazolyltetraazacubanes were designed. Then, a different number of NH₂ or NO₂ groups were introduced into the system to further adjust the property. The structures, properties, and the structure-property relationship of designed molecules were investigated theoretically. The results showed that all nine designed compounds have extremely high heat of formation (HOF, 1226-2734 kJ/mol), good density (1.73–1.88 g/cm³), high detonation velocity (8.30–9.35 km/s), high detonation pressure (29.8–39.7 GPa) and acceptable sensitivity (ΔV: 41-87 ų). These properties could be effectively positive adjusted by replacing one or two PZ rings by NH₂ or/and NO₂ groups, especially for the energy and sensitivity performance, which were increased and decreased obviously, respectively. As a result, two designed pentazolyltetraazacubanes were predicted to have higher energy and lower sensitivity than the famous high energy compound in use 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane, while two others have better combination property than 1,3,5-Trinitro-1,3,5-triazacyclohexane. In all, four new pentazolyltetraazacubanes with good combination performance were successfully designed by combining PZ with TAC, and the further property adjustment strategy of introducing a suitable amount of NH₂/NO₂ groups into the system. This work may help develop new cage energetic compounds.     

The effect of sintering and cooling process on geometry distortion and mechanical properties transition of PTFE/Al reactive materials

In this research, the effect of the sintering and cooling process on geometry distortion and mechanical properties of PTFE/Al reactive material is investigated. Six particularly selected sintering temperatures, three different cooling modes (annealing cooling, normalizing cooling and rapid cooling), three different initial cooling temperatures, as well as six different final cooling temperatures were designed to compare the effects of sintering temperature, cooling rate, initial cooling temperature and final cooling temperature on the properties of reactive materials. Geometry distortion was quantitatively analyzed by a statistic on the dimensional changes of the specimens and microscopic morphology. A mechanical response properties transition from brittle to ductile was found and analyzed. By combining the thermodynamic properties of PTFE and unsteady heat conduction theory, mechanisms of cooling induced morphology change, temperature induced distortion and strength decrease were obtained. The results showed that the cooling rate has the most significant effect on the morphology transformation, while initial cooling temperature has more significant effect on the dimensional distortion than final cooling temperature. As to the mechanical properties transition from brittle to plastic, a more prominent effect of initial cooling temperature than cooling rate and final temperature was revealed.     

Preparation of ammonium nitrate-based solid composite propellants supplemented with polyurethane/nitrocellulose blends binder and their thermal decomposition behavior

To improve the performance of solid composite propellants (SCPs) supplemented with ammonium nitrate (AN) as an oxidizer, the incorporation of energetic ingredients such as explosives, energetic binders or catalysts is a common effective approach. For this purpose, polyurethane (PU), a typical inert binder, was mixed with nitrocellulose (NC) as an energetic polymer. Numerous composite solid propellant compositions based on AN and NC-modified polyurethane binder with different NC ratios were prepared. The prepared formulations were characterized using Fourier transform infrared spectroscopy (FTIR), RAMAN spectroscopy, X-ray diffraction (XRD), electron densimetry, thermogravimetric (TG) analysis, and differential scanning calorimetry (DSC). A kinetic study was then performed using the iterative Kissinger-Akahira-Sunose (It-KAS), Flynn-Wall-Ozawa (It-FWO), and non-linear Vyazovkin integral with compensation effect (VYA/CE) methods. The theoretical performances, such as theoretical specific impulse, adiabatic flame temperature, and ideal exhaust gaseous species, were also determined using the NASA Lewis Code, Chemical Equilibrium with Application (CEA). Spectroscopic examinations revealed the existence of NC and full polymerization of PU in the prepared propellants. According to density tests, the density of the propellant increases as the nitrocellulose component increases. According to the thermal analysis and kinetics study, the increase in NC content catalyzed the thermal decomposition of the AN-based composite solid propellants. Based on the theoretical study, increasing the amount of NC in the propellant increased the specific impulse and, as a result, the overall performance.     

多层粘弹阻尼复合结构阻尼性能的研究

制备了多层粘弹阻尼复合结构,并研究了其阻尼性能.实验结果表明,多层粘弹弱约束阻尼复合结构的阻尼性能优于多层粘弹自由阻尼复合结构的阻尼性能.     

Novel aluminum-based fuel: Facile preparation to improve thermal reactions

To improve the thermal properties of aluminum (Al) in the energetic system, a coated structure with ammonium perchlorate (AP) was prepared by a facile approach. And N, N-Dimethylformamide (DMF) was chosen as an ideal solvent based on heterogeneous nucleation theory and molecular dynamics simulation. This coated structure could enlarge the contact area and improve the reaction environment to enhance the thermal properties. The addition of AP could accelerate oxidation temperature of Al with around 17.5 °C. And the heat release of 85@15 composition rises to 26.13 kJ/g and the reaction degree is 97.6% with higher peak pressure (254.6 kPa) and rise rate (1.397 MPa/s). An ideal ratio with 15 wt% AP was probed primarily. The high energy laser-induced shockwave experiment was utilized to simulate the reaction behavior in hot field. And the larger activated mixture of coated powder could release more energy to promote the growth of shockwave with higher speed up to 518.7 ± 55.9 m/s. In conclusion, 85@15 composition is expected to be applied in energetic system as a novel metal fuel.     

Size dependent free vibration analysis of functionally graded piezoelectric micro/nano shell based on modified couple stress theory with considering thickness stretching effect

Higher-order shear and normal deformation theory is used in this paper to account thickness stretching effect for free vibration analysis of the cylindrical micro/nano shell subjected to an applied voltage and uniform temperature rising. Size dependency is included in governing equations based on the modified couple stress theory. Hamilton's principle is used to derive governing equations of the cylindrical micro/nano shell. Solution procedure is developed using Navier technique for simply-supported boundary conditions. The numerical results are presented to investigate the effect of significant parameters such as some dimensionless geometric parameters, material properties, applied voltages and temperature rising on the free vibration responses.     

Effect of microstructure on short pulse duration shock initiation of TATB and initial response mechanism

Micro-TATB particles with different sizes and 3D nanoporous TATB architectures with different specific surface areas were prepared through recrystallization to study short pulse duration shock initiation properties by electric gun technology. For micro-TATB, the initiation threshold significantly decreases with TATB average size ranging from 79.7 μm to 0.5 μm. For 3D nanoporous TATB architecture, the initiation threshold decreases and then increases with specific surface areas increased from 9.6 m²/g to 36.2 m²/g. The lowest initiation thresholds are obtained for the micro-TATB with average sizes of 1.3 μm and 0.5 μm, and 3D nanoporous TATB architecture with specific surface area of 22.4 m²/g. The shock initiation thresholds of micro-TATB and 3D nanoporous TATB architectures show significantly decreases with the porosity increased. The decomposition reaction and thermal conductivity properties were further investigated to understand the initial response mechanism. High porosity provides more collapse sites to generate high temperature for formation of hot spots. The low thermal conductivity and decomposition temperature could enhance the formation and ignition of the hot spots, and initial decomposition reaction of TATB. The effect of the decomposition temperature is higher than that of the thermal conductivity on the shock initiation properties. The enhanced decomposition reaction could promote energy release and transfer process from the ignition to the combustion. This work offers a new insight to understand the effects of microstructure on the shock initiation properties and the initial response mechanism of TATB.     

军用装备镁合金表面微弧氧化层SEM微观形貌及耐蚀性分析

利用微弧氧化技术的恒电流方式,在含有Na：SiO,和KF等电解质的溶液中制备了AZ91D镁合金微弧氧化层,通过扫描电镜观察分析及Cu加速盐雾腐蚀试验,研究了电解液中Na：SiO,和KF质量浓度对微弧氧化层结构及耐蚀性的影响。结果表明：在相同反应条件下,微弧氧化层厚度和表面粗糙度随Na：SiO,和KF质量浓度的增加而增加,微弧氧化层的耐蚀性取决于其表面粗糙度和厚度,粗糙度小、具有一定厚度的致密微弧氧化层耐蚀性好。