Voids and Density Distributions in 2,4,6,8,10,12‐Hexanitro‐2,4,6,8,10,12‐Hexaazaisowurtzitane (CL‐20) Prepared Under Various Conditions

The density distributions of six samples of CL‐20 were measured using the density gradient technique. This technique was used to determine which preparation procedure produced the highest average CL‐20 density. Assuming crystals with fewer flaws result in reduced sensitivity to shock initiation, higher average crystal density (closest to the theoretical maximum density) would imply the least number of voids or inclusions. Based on hot‐spot theory, better crystals, i.e., smaller number of flaws will reduce the shock sensitivity and perhaps other impact initiation mechanisms as well. Six samples from different synthesis and crystallization procedures gave average densities from 2.042 to 2.0230 g/cm³ as measured by density gradient. Assuming the voids have no density, the crystals were between 99.90 to 98.98% of the theoretical maximum density (TMD for ε‐CL‐20 is 2.044 g/cm³). An attempt was made to account for the density difference by identifying voids in the crystals using polarized light microscopy. This method also gave some insight into the different morphologies produced by different crystallization techniques. In 3 cases voids on the order of several micrometers could be resolved in large CL‐20 crystals.     

Thermal and Sensitivity Study of Dihydroxyl Ammonium 5,5′‐Bistetrazole‐1,1′‐diolate (TKX‐50)‐based Melt Cast Explosive Formulations

Dihydroxyl ammonium 5,5′‐bistetrazole‐1,1′‐diolate (TKX‐50) is a promising energetic material with predicted performance similar to RDX as well as to CL‐20. In the present study, TKX‐50 was evaluated as a possible replacement for RDX in TNT‐based, aluminized as well as non‐aluminized melt cast formulations. Thermal analysis reveals the compatibility of TKX‐50 with benchmark explosives like RDX and TNT in explosive formulations. This paper describes the thermal and sensitivity study of TKX‐50 with RDX and TNT‐based melt cast explosives. The result indicated that TKX‐50 can be effectively used as a RDX replacement in melt cast explosive formulations. TKX‐50/TNT‐based aluminized composition shows more thermal stability than RDX/TNT based composition, which clearly indicated the usefulness of TKX‐50 in melt cast explosive formulations.     

Review on Melt Cast Explosives

A systematic overview of melt cast explosives is given. The research on melt cast explosives over several decades can be divided into three broad areas: (i) aromatic compounds with C CH₃, N CH₃, OCH₃ C NO₂, N NO₂ and ONO₂ groups, (ii) improved synthesis of compounds, which are currently used in formulations or which have shown promise for such use and (iii) the preparation of melt cast formulations with various compositions. Exudation, high volume change from liquid to solid, super cooling, irreversible growth, fragility and unpredictable sensitivity are the disadvantages of existing melt cast formulations.     

Partial Reparametrization of the BKW Equation of State for DNAN‐Based Melt‐Cast Explosives

DNAN‐based melt‐cast explosives are a type of new, insensitive munitions (IM) explosives. Quickly determining munitions’ explosive properties is extremely important during the formulation design stage. The aim of this study was to partially reparameterize BKW‐EOS (only β and κ were reparameterized on the basis of the parameters (α , β , κ , and θ ) of classical BKW‐RDX set and BKW‐TNT set) to more accurately predict the properties of DNAN‐based melt‐cast explosives. A new set of parameters β and κ was obtained (β =0.19, κ =9.81) according to measured detonation velocity and detonation pressure for ideal DNAN‐based melt‐cast formulations (DNAN/RDX and DNAN/HMX). For non‐ideal DNAN‐based melt‐cast formulations (DNAN/RDX/Al and DNAN/HMX/Al), aluminum oxidation degree was first determined according to the measured detonation heat; then, another new set of parameters β and κ was obtained in the same way as the ideal formulations (β =0.24, κ =8.5). The predicted detonation properties with BKW reparametrization for DNAN‐based melt‐cast explosives agreed with the measured data.     

Ageing of Australian DNAN Based Melt‐Cast Insensitive Explosives

2,4‐Dinitroanisole (DNAN) is a new melt‐cast matrix ingredient that replaces traditional TNT in TNT‐based melt‐cast explosives. Aside from sensitiveness improvements, the use of DNAN allows for the continued operation of existing melt‐cast facilities (for example the Australian Munitions plants located at Mulwala and Benalla) without the need for major plant modifications. Researchers at Defence Science and Technology Group (DST Group) have developed several DNAN based formulations that have been extensively characterized. In an effort to better understand the ageing properties of these formulations, an accelerated ageing program was undertaken. Testing was conducted under two different ageing conditions; the first test condition was conducted at a constant 60 °C with ambient humidity and the second test condition was the A2 diurnal cycle (representative of hot dry climates). Analysis of the formulation density, sensitiveness, mechanical and thermal properties was made at three‐month intervals for a period of 12 months and results compared with conventional explosives similarly aged. For all DNAN‐based formulations there was negligible change in impact, friction, electrostatic discharge, and thermal testing over time. These results highlight the ability of the ARX formulations to diurnal temperature cycling and to hold favorable sensitiveness properties to various stimuli.     

Investigation of CL‐20 and RDX Nanocomposites

Nanocrystalline explosives offer a number of advantages in comparison to conventional energetics including reduced sensitivity and improved mechanical properties. In this study, formulations consisting of 90 % hexanitro‐hexaazaisowurtzitane (CL‐20) or cyclotrimethylene trinitramine (RDX) and 10 % polyvinyl alcohol (PVOH) were prepared with mean crystal sizes ranging from 200 nm to 2 μm. The process to create these materials used a combination of aqueous mechanical crystal size reduction and spray drying. The basic physical characteristics of these formulations were determined using a variety of techniques, including scanning electron microscopy, X‐ray diffraction, and Raman spectroscopy. Compressive stress‐strain tests on pressed pellets revealed that the mechanical properties of the compositions improved with decreasing crystal size, consistent with Hall‐Petch mechanics. In the most extreme case (involving CL‐20/PVOH formulations), crystal size reduction from 2 μm to 300 nm improved compressive strength and Young’s modulus by 126 % and 61 %, respectively. These results serve to highlight the relevance of structure‐property relationships in explosive compositions, and particularly elucidate the substantial benefits of reducing the high explosive crystal size to nanoscale dimensions.     

Preparation and Performances of Castable HTPB/CL‐20 Booster Explosives

HTPB/CL‐20 castable booster explosives were prepared successfully by a cast‐cured process. Scanning electron microscope (SEM) and the charge density test were employed to characterize the molding effect of HTPB/CL‐20 explosives. The propagation reliability, detonation velocity, mechanical sensitivity, thermal decomposition characteristics and thermal stability of the HTPB/CL‐20 explosives were also measured and analyzed. The results show that, when CL‐20 content is less than 91 wt.‐%, the charges with better molding effect were obtained easily. The critical diameter of HTPB/CL‐20 explosives is less than 1 mm, which exhibits good propagation reliability. When the density of HTPB/CL‐20 charge with 91 wt.‐% CL‐20 is 1.73 g cm⁻³, its detonation velocity can reach 8273 m s⁻¹. Moreover, this kind of explosives has low mechanical sensitivity and good thermal stability.     

Reduced Sensitivity RDX Obtained From Bachmann RDX

In recent years much interest has been generated in a quality of reduced sensitivity RDX (RS‐RDX), like I‐RDX^® which, when incorporated in cast cure and even pressable plastic bonded explosives (PBX compositions), can confer reduced shock sensitivity as measured through gap test. At crystal level, lot of work has been done to try to determine which property or properties may explain the behaviour of the corresponding cast PBX composition. But up to now, and despite an international inter‐laboratory comparison (Round Robin) of seven lots of RDX from five different manufacturers conducted from 2003 to 2005, even if some techniques lead to interesting results, there is no dedicated specification to apply to RS‐RDX. This quality (I‐RDX^®) has proved to retain its low sensitivity even after ageing, which does not seem to be the case for standard RDX produced by the Bachmann process (when re‐crystallized under I‐RDX conditions in order to obtain RS‐RDX). It has been shown that the higher sensitivity of RDX produced by the Bachmann process, or the evolution of sensitivity after ageing of RS‐RDX produced from Bachmann RDX may be linked to the presence of octogen (HMX) during the crystallization process. In order to check such hypothesis, low HMX content RDX produced by the Bachmann process has been prepared and evaluated in cast PBX composition (PBX N 109). Results of the characterization of such quality of RDX and its evaluation in cast PBX composition as well as ageing behaviour are presented and discussed; there are indications that removal of HMX from Bachmann RDX may lead to RS‐RDX, which retains its RS character even after ageing.     

Evaluation of the Energy Fluence in the Small Scale Gap Test

The Small Scale Gap Test is a relatively simple experimental tool to obtain a measure of the shock sensitivity of explosives. An evaluation of this test is carried out with use of a computer simulation. The simulated pressures in the water gap compare to experimental data and justify the obtained energy fluence in the shock wave versus distance in the water gap. The initiating shock pulse can be represented by an equivalent planar shock with an effective diameter of only 15 mm and a pulse duration of ≈1 µs. For the type of explosives that show some non‐ideal behavior and that have a relatively large critical diameter, the initiation pressure might provide an inadequate value for the shock sensitivity. It is recommended that besides using a critical shock pressure criterion also a critical energy fluence criterion is applied to rank the shock sensitivity of explosives.     

老化对TNT基熔铸炸药性能的影响

为了研究老化对炸药性能的影响,对自然贮存的3种熔铸炸药TNT／RDX、TNT／RDX／Al和 TNT／HMX／Al进行了加速老化试验。通过扫描电镜、真空安定性试验研究了老化前后3种炸药的微观形貌和安全性能,并测试了老化前后3种炸药的感度和爆速。结果表明,老化后炸药颜色变深,体积膨胀,质量变轻。样品的放气量小于2 mL／g ,热感度变化也较小。机械感度的变化与炸药组分和老化方式有关。TNT／RDX的爆速随着贮存时间的增加而降低,与整体加速老化情况一致,TNT／RDX／Al和 TNT／HMX／Al的爆热随贮存时间的增加变化趋势相反,说明两者老化机理可能不同。     

Shock-sensitive cyclotrimethylenetrinitramine (RDX)

A form of RDX with a shock sensitivity comparable with that of PETN has been produced by sublimation. However, the material is as insensitive to heat, impact, friction and static discharge as are the normal forms of RDX, and it has a similar storage life. The shock sensitivity tests were performed with these explosives either cast in TNT or bonded in silicone rubber.     

A Low‐Sensitivity Composition Based on FOX‐7

1,1‐Diamino‐2,2‐dinitroethene (DADNE, FOX‐7) is considered to be an explosive combining comparatively high performance and low sensitivity. In the present study, FOX‐7 has been evaluated as a possible replacement of RDX in TNT‐based melt‐cast compositions. A composition containing FOX‐7, TNT, Al and wax, and a method of preparing it were proposed. Its sensitivity to impact, friction, shock wave, jet impact, fast heating, and its thermal stability were tested. Some detonation parameters like the detonation pressure, velocity and heat were measured. Moreover, the Gurney velocity, the so‐called effective exponent of the expansion isentrope and the JWL equation of state of the detonation products were determined from the results of a cylinder test. The detonation characteristics were compared with that obtained for cast TNT.     

PBX炸药细观结构冲击点火的二维数值模拟

为了研究冲击加载下非均质炸药的点火机理,对PBX炸药细观结构在冲击加载下的响应过程进行了二维数值模拟.首先对炸药颗粒的压制过程进行数值模拟,获得PBX炸药的细观结构模型.然后对炸药冲击点火进行数值模拟计算,考虑了热力耦合作用和炸药自热反应,分析了炸药颗粒尺寸、密度和黏结剂对炸药冲击点火的影响.结果表明,冲击作用下PBX...     

Investigation of HMX‐Based Nanocomposites

Advanced munition systems require explosives which are more insensitive, powerful, and reactive. For this reason, nano‐crystalline explosives present an attractive alternative to conventional energetics. In this study, formulations consisting of 95 % octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) and 5 % polyvinyl alcohol (PVOH) were prepared with mean crystal sizes ranging from 300 nm to 2 μm. The process to create these materials used a combination of mechanical particle size reduction and spray drying, which has the advantages of direct control of crystal size and morphology as well as the elimination of ripening of crystals (which occurs during slurry coating of nanomaterials). The basic physical characteristics of these formulations were determined using a variety of techniques, including scanning electron microscopy and X‐ray diffraction. Compressive stress‐strain tests on pressed pellets revealed that the mechanical properties of the compositions improved with decreasing crystal size, consistent with Hall‐Petch mechanics. The 300 nm HMX/PVOH composition demonstrated a 99 % and 129 % greater strength and stiffness, respectively, than the composition with 2 μm HMX. The formulations were subjected to the Small Scale Gap Test, revealing a significant reduction in shock sensitivity with decreasing crystal size. The formulation containing 300 nm HMX registered a shock initiation pressure 1.6 GPa above that of the formulation with 2 μm HMX, a 44 % improvement in sensitivity. These results serve to highlight the relevance of structure‐property relationships in explosive compositions, and particularly elucidate the substantial benefits of reducing the high explosive crystal size to nano‐scale dimensions.     

干燥技术在制备纳米粉体中的应用

由于纳米粒子的表面效应,用湿法制备出的纳米粉体的前躯体在干燥过程中极易形成团聚,已经不能采用传统的干燥方法。根据粉体干燥的理论,阐述了纳米粉体干燥过程的团聚机理,综述了微波干燥法、超临界干燥法、冷冻干燥法、共沸蒸馏法、喷雾干燥法等在制备纳米粉体中的应用,并指出了各种方法的优缺点。     

Facile and green preparation of thermal and ph sensitive hydrogel microspheres based on spray drying and the diels–alder reaction

Thermal and pH dual‐sensitive hydrogel microspheres were fabricated using spray drying. During the spray drying, chemical crosslinks were formed in situ via the Diels–Alder reaction without the involvement of any catalysts or organic solvents. The structures and morphologies of the products were characterized by Fourier Transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), Raman spectroscopy, scanning electron microscopy (SEM), X‐ray diffraction (XRD), and thermogravimetric analysis (TGA). A general weighing method was applied to study the swelling behavior of the microspheres at different temperatures and pHs. Using urea as a model molecule, the ability of the microspheres to control the release of urea was explored by spectrophotometry and calculated from the calibration curve obtained from the reaction of urea and diaminobenzaldehyde. The as‐prepared microspheres show a reversible and reproducible volume change with varying pH or temperature, and their swelling ratios increase with increasing temperature or pH. Furthermore, the urea release rates can be tuned by changing the pH or the temperature. Since spray drying can easily produce microspheres on a large scale, the strategy demonstrated here has the potential for applications in the green preparation of hydrogel microspheres. POLYM. ENG. SCI., 59:1999–2007, 2019. © 2019 Society of Plastics Engineers     

Some New High Energy Materials and their Formulations for Specialized Applications

Energetic materials form an integral part of most weapon systems and a large number of new high‐energy materials: thermally stable explosives, high‐performance explosives, melt‐castable explosives, insensitive high explosives and energetic binders have been reported in the literature in recent years. Some explosive formulations based on these new energetic materials are also vaguely reported. This paper examines these materials and their formulations from the point of view of stability, reliability, safety and specific applications.     

Optical properties of blown and cast polyethylene films: Surface versus bulk structural considerations

In this article we report on some surprising, and we believe new, findings regarding the factors affecting the optical properties (haze) of polyethylene blown and cast films. A comprehensive investigation of blown and cast films made from conventional Ziegler‐Natta catalyzed linear low density polyethylene (LLDPE) as well as metallocene‐catalyzed LLDPE (mLLDPE) resins was conducted. The large majority of the contribution to the total haze in the blown and cast films was observed to come from the surface roughness of the films, with the bulk (internal) contribution being relatively minor. Using a variety of analysis and characterization methods, including atomic force microscopy, small angle light scattering, and wide angle X‐ray scattering, we determined that the surface roughness in these films was a result of the development of distinct spherulitic‐like superstructures formed during the blown or cast film processing. Furthermore, these superstructures were observed only in the mLLDPE blown films, and not in the LLDPE blown films processed at similar conditions. Analysis of the rheological and molecular characteristics of these various mLLDPE and LLDPE resins revealed that the mLLDPE resins exhibited considerably lower molecular weight, narrower molecular weight distribution, lower zero shear viscosity, and lower melt elasticity compared with the LLDPE resins of similar melt index. These observations support our general finding and primary conclusion from this work that in polyethylene blown and cast films made using typical processing conditions, the optical haze properties are adversely affected because of enhanced surface roughness caused by the formation of spherulitic‐like superstructures in polymer melts that possess fast relaxing and low melt elasticity rheological characteristics. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2845–2864, 2000     

Pulverisierung hochviskoser Flüssigkeiten

Different processes for pulverizing malt extract are compared in view of quality and hygroscopicity. Three different processes with and without carriers are verified and it is demonstrated that processes without carriers (spray‐drying) yield very hygroscopic powders. Processes with carriers, i.e., flour, using fluidised bed agglomeration are proved to be reasonable.     

Altering Reactivity of Aluminum with Selective Inclusion of Polytetrafluoroethylene through Mechanical Activation

Micrometer‐sized aluminum is widely used in energetics; however, performance of propellants, explosives, and pyrotechnics could be significantly improved if its ignition barriers could be disrupted. We report morphological, thermal, and chemical characterization of fuel rich aluminum‐polytetrafluoroethylene (70–30 wt‐%) reactive particles formed by high and low energy milling. Average particle sizes range from 15–78 μm; however, specific surface areas range from approx. 2–7 m² g⁻¹ due to milling induced voids and cleaved surfaces. Scanning electron microscopy and energy dispersive spectroscopy reveal uniform distribution of PTFE, providing nanoscale mixing within particles. The combustion enthalpy was found to be 20.2 kJ g⁻¹, though a slight decrease (0.8 kJ g⁻¹) results from extended high energy milling due to α‐AlF₃ formation. For high energy mechanically activated particles, differential scanning calorimetry in argon shows a strong, exothermic pre‐ignition reaction that onsets near 440 °C and a second, more dominant exotherm that onsets around 510 °C. Scans in O₂‐Ar indicate that, unlike physical mixtures, more complete reaction occurs at higher heating rates and the reaction onset is drastically reduced (approx. 440 °C). Simple flame tests reveal that these altered Al‐polytetrafluoroethylene particles light readily unlike micrometer‐sized aluminum. Safety testing also shows these particles have high electrostatic discharge (89.9–108 mJ), impact (>213 cm), and friction (>360 N) ignition thresholds. These particles may be useful for reactive liners, thermobaric explosives, and pyrolants. In particular, the altered reactivity, large particle size and relatively low specific surface area of these fuel rich particles make them an interesting replacement for aluminum in solid propellants.