Characterization of Aluminum Nanopowder Compositions

The thermal behaviour of two different Al nanopowders and a micron‐sized Al powder was studied using DSC, simultaneous TG‐DTA, and accelerating rate calorimetry (ARC). The results show that the reactivity of Al powder increases as the particle size decreases. The thermal stability of the smaller Al nanopowder (Als) in water and in a humid atmosphere was determined using ARC and TG‐DTA, respectively. Atomic Absorption Spectrometry (AAS), X‐Ray Photoelectron Spectrometry (XPS) and Auger Electron Spectrometry (AES) were used to characterize the surface chemistry of Alex. The outgassing behaviour for mixtures of RDX and the various Al powders was investigated using TG‐DTA‐FTIR‐MS. Evolution of NO₂ and N₂O from a chemical interaction between Al nanopowders and RDX was observed. The effect of Als and Alex on the thermal stability of TNT, RDX, Comp B, and AP was determined using ARC. Addition of Als significantly lowered the onset temperature for TNT and RDX decomposition. Electrostatic discharge (ESD) sensitivities of Al nanopowders and their mixtures with TNT, Comp B, RDX and AP were determined. The results show that the AP/Als mixture is very sensitive to ESD. Standard dust explosibility tests demonstrated that Alex is highly explosible.     

5‐Amino‐3,4‐dinitropyrazole as a Promising Energetic Material

The nitrogen‐rich energetic compound 5‐amino‐3,4‐dinitropyrazole (5‐ADP) was investigated using complementary experimental techniques. X‐ray diffraction indicates the strong intermolecular hydrogen bonding in 5‐ADP crystals. Compound exhibits low impact sensitivity (23 J) and insensitivity to friction. The activation energy of thermolysis determined to be 230±5 kJ mol⁻¹ from DSC measurements. Accelerating rate calorimetry indicates the lower thermal stability (173 °C) of 5‐ADP than that of RDX, which is probably the main concern about using this compound. 5‐ADP also exhibits good compatibility with common energetic materials (viz. TNT, RDX, ammonium perchlorate), including an active binder. The burning rate of 5‐ADP monopropellant is higher than that of benchmark HMX, while the pressure exponent 0.51±0.04 is surprisingly low. Addition of ammonium perchlorate does not affect the pressure exponent of 5‐ADP, while the burning rate increases. The 5‐amino‐3,4‐dinitropyrazole exhibits a notable combination of combustion performance, low sensitivity, and good compatibility, which renders it as a promising energetic material.     

Influence of Particle Size and Mixing Technology on Combustion of HMX/Al Compositions

In this work, two widely used components of high‐energy condensed systems – HMX and aluminium – were studied. Morphology, thermal behaviour, chemical purity and combustion parameters of HMX as a monopropellant and Al/HMX as a binary system were investigated using particles of different sizes. It was shown that in spite of the differences in composition and particle size, combustion velocities are almost identical for micrometer‐sized HMX (m‐HMX) and ultrafine HMX (u‐HMX) monopropellants under pressure from 2 to 10 MPa. Replacement of the micrometer‐sized aluminium with ultrafine one in the system with m‐HMX leads to a burning rate increase by a factor of 2.5 and the combustion completeness raise by a factor of 4. Two mixing techniques to prepare binary Al/HMX compositions were applied: conventional and ‘wet’ technique with ultrasonic processing in liquid. Applying wet mixing results in a burning rate increase of 18% compared to the conventional mixing for systems with ultrafine metal. The influence of the component's particle size and the composition microstructure on the burning rate of energetic systems is discussed and analysed.     

Continuous Crystallization of Submicrometer Energetic Compounds

This study introduces the conception of an apparatus to crystallize continuously nanosized explosive or more generally nanosized organic materials. These materials can be elaborated in pure state or in form of mixtures of energetic and inert materials. The installation can produce nano‐RDX or nano‐PETN from 1 to 10 g h⁻¹ using a reactor containing one ultrasonic piezoelectric transducer. The present study describes the different parameters which influence the crystallization process. It presents first results of the parametric study of the influence of these parameters. The most important parameters which were already identified are the frequency of the ultrasonic piezoelectric transducer, the nature of the solvent, the liquid level in the reactor, the temperatures in the system, and the passing time of the aerosol droplets in the oven.     

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.     

Theoretical and experimental determination of tensile properties of nanosized and micron‐sized CaCO3/PA66 composites

The objective of this research was to investigate the probability of reinforcing Polyamide66 (PA66) with both micron‐sized and nanosized calcium carbonate (CaCO₃) particles. For this purpose, micron‐sized and nanosized CaCO₃ particles were used as fillers to prepare microcomposites (conventional composites) and nanocomposites via a polymer solution method. The microcomposites and nanocomposites were found to have higher modulus and lower strength than neat PA66. Also, nanocomposites had higher modulus and strength than microcomposites. Theoretical prediction of elastic modulus was carried out using Rule of mixtures, Guth, Nicolais–Narkis, Hashin–Shtrikman, and Halpin–Tsai equations. Calculated results show that these equations cannot predict the results accurately for the work carried out. However, these models can be used with confidence for the prediction of elastic modulus as experimental data are higher than the calculated values. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

纳米含能材料研究进展

综述了纳米含能材料组分和复合物的制备方法和性质,指出国内外研究的含能材料纳米级组分包括纳米铝粉、纳米硼粉和纳米级单质炸药。纳米复合物主要包括单质炸药（氧化剂）纳米晶分布于连续基质所形成的纳米复合物、介稳态分子间复合物和碳纳米管与含能材料组分的纳米复合物。纳米级铝粉和硼粉的制造技术是电爆法和等离子体法;纳米级单质炸药的制备方法是各种基于超临界流体的处理技术;Sol—Gel法是制备含能纳米复合物的主要方法。     

Energetic Materials: Crystallization,Characterization and Insensitive Plastic Bonded Explosives

The product quality of energetic materials is predominantly determined by the crystallization process applied to produce these materials. It has been demonstrated in the past that the higher the product quality of the solid energetic ingredients, the less sensitive a plastic bonded explosive containing these energetic materials becomes. The application of submicron or nanometric energetic materials is generally considered to further decrease the sensitiveness of explosives. In order to assess the product quality of energetic materials, a range of analytical techniques is available. Recent attempts within the Reduced‐sensitivity RDX Round Robin (R4) have provided the EM community a better insight into these analytical techniques and in some cases a correlation between product quality and shock initiation of plastic bonded explosives containing (RS‐)RDX was identified, which would provide a possibility to discriminate between conventional and reduced sensitivity grades.     

On the Reliability of Sensitivity Test Methods for Submicrometer‐Sized RDX and HMX Particles

Submicrometer‐sized RDX and HMX crystals were produced by electrospray crystallization and submicrometer‐sized RDX crystals were produced by plasma‐assisted crystallization. Impact and friction sensitivity tests and ballistic impact chamber tests were performed to determine the product sensitivity. Rather than reflecting the quality of the particles, we found the sensitivity tests to be unreliable for submicrometer particles. The used impact test was not accurate enough, while in the friction and ballistic impact chamber tests the submicrometer‐sized crystals were distributed among the grooves of the porcelain plate or among the grains of the sandpaper used in these tests. These observations stress the need for revisiting the current standards used for determining the hazardous properties like friction and impact sensitivity of energetic materials in the case, where the sample consists of submicrometer‐sized crystals. Recommendations were suggested to develop new test methods that only use the interactions between the particles and therefore allow the application of sensitivity tests for submicrometer/nano‐sized energetic materials.     

New High‐Nitrogen Materials Based on Nitroguanyl‐Tetrazines: Explosive Properties,Thermal Decomposition and Combustion Studies

This paper describes the explosive sensitivity and performance properties of two novel high‐nitrogen materials, 3,6‐bis‐nitroguanyl‐1,2,4,5‐tetrazine ( 1 , (NQ₂Tz)) and its corresponding bis‐triaminoguanidinium salt ( 2 , (TAG)₂(NQ)₂Tz)). These materials exhibit very low pressure dependence in burning rate. Flash pyrolysis/FTIR spectroscopy was performed, and insight into this interesting burning behavior was obtained. Our studies indicate that 1 and 2 exhibit highly promising energetic materials properties.     

Formation and Characterization of Nano‐sized RDX Particles Produced Using the RESS‐AS Process

It has been shown that nano‐sized particles of secondary explosives are less sensitive to impact and can alter the energetic performance of a propellant or explosive. In this work the Rapid Expansion of a Supercritical Solution into an Aqueous Solution (RESS‐AS) process was used to produce nano‐sized RDX (cyclo‐1,3,5‐trimethylene‐2,4,6‐trinitramine) particles. When a saturated supercritical carbon dioxide/RDX solution was expanded into neat water, RDX particles produced from the RESS‐AS process agglomerated quickly and coarsened through Ostwald ripening. However, if the pH level of the suspension was changed to 7, particles were metastably dispersed with a diameter of 30 nm. When the supercritical solution was expanded into air under the same pre‐expansion conditions using the similar RESS process, RDX particles were agglomerated and had an average size of approximately 100 nm. Another advantage of using a liquid receiving solution is the possibility for coating energetic particles with a thin layer of polymer. Dispersed particles were formed by coating the RDX particles with the water soluble polymers polyvinylpyrrolidone (PVP) or polyethylenimine (PEI) in the RESS‐AS process. Both PVP and PEI were used because they have an affinity to the RDX surface. Small and well‐dispersed particles were created for both cases with both PVP and PEI‐coated RDX particles shown to be stable for a year afterward. Several benefits are expected from these small polymer coated RDX particles such as decreased sensitivity, controlled reactivity, and enhanced compatibility with other binders for fabrication of bulk‐sized propellants and/or explosives.     

Laser‐induced Deflagration for the Characterization of Energetic Materials

Standard propellant and detonation tests typically performed to characterize the performance of energetic materials require large quantities of material (at least tens of grams) and can be expensive and time‐consuming. This work introduces a method for characterizing the deflagration of energetic materials in a laboratory setting, using only 15–20 mg of energetic material. Temperature, energy release and emission signatures were measured and analyzed for the laser‐induced deflagration of 8 different conventional military explosives. Graphite nanoparticles and micron‐sized aluminum powder were added to the explosive compositions to investigate their effect on the emission signatures. A high‐speed color camera recorded the deflagration events and was utilized as a full‐color pyrometer to calculate the average temperatures and image hotspots; the temperatures maps were compared to those measured by conventional two‐color pyrometry. The laboratory‐scale method presented here can be applied to novel energetic materials under development that may be available only in limited quantities to evaluate their potential as propellants or reduced emission signature explosives prior to scale‐up.     

Research on the Combustion Properties of Propellants with Low Content of Nano Metal Powders

A comparison of various experimental results for combustionrelated properties evaluation, including burning rates, deflagration heat, flame structures and thermal decomposition properties, of AP/RDX/Al/HTPB composite propellants containing nano metal powders is presented. The thermal behavior of n‐Al (nano grain size aluminum) and g‐Al (general grain size aluminum i.e., 10 μm) heated in air was also investigated by thermogravimetry. The burning rates results indicate that the usage of bimodal aluminum distribution with the ratio around 4 : 1 of n‐Al to g‐Al or the addition of 2% nano nickel powders (n‐Ni) will improve the burning behavior of the propellant, while the usage of grading aluminum powders with the ratio 1 : 1 of n‐Al to g‐Al will impair the combustion of the propellant. Results show that n‐Al and n‐Ni both have a lower heating capacity, lower ignition threshold and shorter combustion time than g‐Al. In addition n‐Al is inclined to burn in single particle form. And the thermal analysis results show that n‐Ni can catalyze the thermal decomposition of AP in the propellant. The results also confirm the high reactivity of n‐Al, which will lead to a lower reaction temperature and rather higher degree of reaction ratio as compared with g‐Al in air. All these factors will influence the combustion of propellants.     

Confocal Scanning Laser Microscopic Study of the RDX Defect Structure in Deformed Polymer‐Bonded Explosives

The influence of an explosion‐driven deformation on the defect structure in RDX crystals embedded in a polymer‐bonded explosive was investigated by means of confocal scanning laser microscopy. The images were compared to the defect structure in the as‐received RDX grades, embedded in an epoxy resin. In this way it is possible to qualitatively analyze the changes in defect structure of the RDX crystals that were induced by the explosion‐driven deformation. For the first time, these data therefore provide experimental confirmation of how shock waves mechanically interact with energetic crystals – a topic that, up to now, was only explored by means of simulations.     

Development of Polyurethane‐Based Solid Propellants Using Nanocomposite Materials

Mechanically‐activated nanocomposites (MANCs) of nano‐aluminum (nAl)/X (X=Cu, Ni, Zn, Mg, and graphite) were used as replacements for reference nAl powder and as catalytic ingredients in polyurethane (PU) propellants. The effects of their use on combustion heat, burning rate, and thermal decomposition were investigated. It was found that MANCs have catalytic effects and the modified propellants have enhanced the released heat, burning rate, and thermal decomposition properties. MANCs‐based propellants have improved the processing and the mechanical properties with acceptable safety aspects. They can be used for catalytic applications in solid propellants to improve their energetic, burning rate, and thermal decomposition characteristics.     

A New Energetic Salt Semicarbazide 5‐Dinitromethyltetrazolate: A Promising Explosive Alternative

The design and synthesis of new environmentally friendly energetic materials with excellent performance and reliable safety have received considerable attention. A new energetic salt of semicarbazide 5‐dinitromethyltetrazolate (SCZ ⋅ DNMZ) was synthesized by using semicarbazide and 5‐dinitromethyltetrazolate (DNMZ) as raw materials, and fully characterized by using elemental analysis, FT‐IR spectroscopy, ¹H, ¹³C, and ¹⁵N nmR and mass spectrometry. The monocrystal of the salt was obtained and the structure was determined by X‐ray single‐crystal diffractometer. Results show that it belongs to monoclinic space group P 2₁/c with a high density of 1.867 g cm⁻³. The thermal decomposition behavior was tested by DSC and TG‐DTG technologies; the non‐isothermal kinetic parameters for the salt were calculated. The enthalpy of formation for the salt is directly dependent on the combustion heats data with a result of 341.5 kJ mol⁻¹, which is about three times higher than that of RDX. The detonation pressure (P ) and detonation velocitiy (D ) of the salt were determined as 8931 m s⁻¹ and 36.2 GPa, which are also higher than that of RDX. The impact sensitivity was tested with a result of 10.8 J. We can draw a safe conclusion that the salt has provided a promising future by using as a kind of explosive alternative. The discovery also contributes significantly to the expansion and application of the N‐heterocyclic compounds applied as energetic materials.     

Polystyrene nanocomposite materials: Preparation,morphology, and mechanical,electrical, and thermal properties

In this study, we prepared polystyrene (PS) resin nanocomposites with antistatic properties by melt‐blending PS with nanoscale zinc oxide (ZnO). The effects of nanoscale ZnO on the electrical and physical characteristics of the PS nanocomposites were investigated. Two kinds of nanoscale powders, spherical zinc oxide (s‐ZnO) and zinc oxide whisker (w‐ZnO), were selected. The coupling agents vinyltriethoxysilane (VTES) and phenyltriethoxysilane (PTES) were used to improve the compatibility between the nanopowders and PS resin. The addition of s‐ZnO and w‐ZnO improved the antistatic characteristics of the materials. The surface resistivities of the s‐ZnO and w‐ZnO nanocomposites were significantly reduced by modification with VTES and PTES. The addition of ZnO nanopowder increased the flexural modulus and reduced the flexural strength. The silane coupling agents improved the flexural properties of the nanocomposites. The glass‐transition temperatures and thermal degradation temperatures of the ZnO/PS nanocomposites increased with ZnO content. Treatment with silane increased the glass‐transition temperatures and thermal degradation temperatures of the composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2266–2273, 2005     

Laboratory‐Scale Method for Estimating Explosive Performance from Laser‐Induced Shock Waves

A new laboratory‐scale method for predicting explosive performance (e.g., detonation velocity and pressure) based on milligram quantities of material is demonstrated. This technique is based on schlieren imaging of the shock wave generated in air by the formation of a laser‐induced plasma on the surface of an energetic material residue. The shock wave from each laser ablation event is tracked for more than 100 μs using a high‐speed camera. A suite of conventional energetic materials including DNAN, TNT, HNS, TATB, NTO, PETN, RDX, HMX, and CL‐20 was used to develop calibration curves relating the characteristic shock velocity for each energetic material to several detonation parameters. A strong linear correlation between the laser‐induced shock velocity and the measured performance from full‐scale detonation testing has been observed. The Laser‐induced Air Shock from Energetic Materials (LASEM) method was validated using nitrocellulose, FOX‐7, nano‐RDX, three military formulations, and three novel high‐nitrogen explosives currently under development. This method is a potential screening tool for the development of new energetic materials and formulations prior to larger‐scale detonative testing. The main advantages are the small quantity of material required (a few milligrams or less per laser shot), the ease with which hundreds of measurements per day can be obtained, and the ability to estimate explosive performance without detonating the material (reducing cost and safety requirements).     

The Mechanical Properties of Minimally Processed RDX

We report for the first time the mechanical properties of RDX crystals in a conventionally processed, sub‐millimeter form that have had no additional mechanical processing. Nanoindentation of RDX powders was used to measure the elastic modulus (19.1±1.9 GPa), hardness (0.741±0.098 GPa), and yield point (onset of plastic deformation) on the as‐grown faces of seven different RDX crystals, selected to provide random orientations. Properties within each crystal showed narrow distributions, while the range of properties across all crystals is indicative of testing a variety of orientations. The elastic modulus and hardness are within the range of other published reports on bulk and mechanically polished RDX. The distribution in yield point behavior, with the onset of plasticity occurring between 0.1 and 0.7 GPa, indicates that powders of RDX likely contain a significant number of dislocation sources in the as‐processed condition, suggesting that deformation sources are prevalent in the energetic component of plastic bonded explosives prior to incorporating into pressed forms.