Secondary Explosives Research Articles

Evaluation of SSRT‐Test by Classical Gravimetric Analysis and Optical Topographic Measurement: A Comparative Study

AbstractTo establish a database of performance values in the small‐scale shock reactivity test (SSRT), common secondary explosives based on organic nitrates (e. g. PETN) and nitramines (e. g. RDX and HMX) as well as aromatic (e. g. TNT), heteroaromatic (e. g. TKX‐50 and MAD−X1) and open chain systems (e. g. FOX‐7) were investigated. The evaluation of the test results was carried out by two different methods. On the one hand, manually by weighing out the resulting dents with sand, and on the other hand, optically with the aid of a profilometer. The two analysis methods were compared and evaluated with respect to their absolute results and absolute as well as relative standard deviations.

An Alliance of Polynitrogen Heterocycles: Novel Energetic Tetrazinedioxide-Hydroxytetrazole-Based Materials.

Energetic materials constitute one of the most important subtypes of functional materials used for various applications. A promising approach for the construction of novel thermally stable high-energy materials is based on an assembly of polynitrogen biheterocyclic scaffolds. Herein, we report on the design and synthesis of a new series of high-nitrogen energetic salts comprising the C-C linked 6-aminotetrazinedioxide and hydroxytetrazole frameworks. Synthesized materials were thoroughly characterized by IR and multinuclear NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction and differential scanning calorimetry. As a result of a vast amount of the formed intra- and intermolecular hydrogen bonds, prepared ammonium and amino-1,2,4-triazolium salts are thermally stable and have good densities of 1.75–1.78 g·cm−3. All synthesized compounds show high detonation performance, reaching that of benchmark RDX. At the same time, as compared to RDX, investigated salts are less friction sensitive due to the formed net of hydrogen bonds. Overall, reported functional materials represent a novel perspective subclass of secondary explosives and unveil further opportunities for an assembly of biheterocyclic next-generation energetic materials.

Core‐Shell Hetero‐Framework derived Copper Azide Composites as Excellent Laser‐Ignitable Primary Explosives

AbstractLaser initiation has attracted increasing interest owing to its extraordinary safety and high reliability. However, traditional metal complex‐based laser‐ignitable primary explosives are limited by high input laser energy and low detonation ability. In this study, an efficient laser‐ignitable primary explosive‐based copper azide is prepared by constructing core‐shell hetero‐framework Cu‐MOF@COF as the precursor. The pyrolysis of Cu‐MOF@COF hybrid material affords copper azide (CA) nanoparticle confined in a porous carbon shell, referred to CA@C Shell. The evenly coated porous carbon shell functions as light‐to‐heat conversion layer efficiently promoting the laser initiation process of inside CA. Consequently, CA@C Shell can be initiated at lower laser energy thresholds (0.80 mJ at 1064 nm). This value is significantly lower than typical laser ignitable metal complex tetraamine‐cis‐bis(5‐nitro‐2H‐tetrazolato‐N2)cobalt(III)perchlorate (726 mJ at 808 nm). Moreover, the CA@C Shell successfully detonates the secondary explosives CL‐20 by laser energy when it is assembled in a micro‐detonator system. This study offers a unique method for constructing high performance laser‐ignitable primary explosives for micro‐detonator applications.

A new nitrate-based energetic molecular perovskite as a modern edition of black powder

In recent years, energetic molecular perovskites, which serve as an energetic material design platform, have shown potential for designing primary and secondary explosives. To explore their potential in gunpowder and pyrotechnics, this study constructed a new nitrate-bridged molecular perovskite, (H2dabco)[K(NO3)3] (DAN-2, H2dabco2+ ​= ​1,4-diazabicyclo-[2.2.2.]octane-1,4-diium), based on potassium nitrate—a major component of black powder. The single-crystal structure analysis indicated that DAN-2 possesses a cubic perovskite structure in the space group Pm3¯m. Theoretical calculations revealed that DAN-2 has an energy level slightly higher than TNT and much higher than black powder. Adding DAN-2 into a typical propellant formulation can increase the impetus while significantly lowering the flame temperature. Moreover, DAN-2 has a lower sensitivity (IS ​= ​29 ​J, FS > 360 ​N) than TNT (IS ​= ​15 ​J, FS ​= ​360 ​N). It is worth mentioning that DAN-2 can avoid the environmental concern of sulfide-induced acid rain since it does not bear any sulfur. Therefore, DAN-2 can be considered a new single explosive and a modern edition of black powder obtained via mixing oxidative KNO3 and a reductive organic fuel at the molecular scale. Furthermore, it displays promising potential in the field of gunpowder and pyrotechnics.

Tracking Thermal Decomposition Chemistry in Secondary Solid Explosives with X-ray Diffraction

We present an approach for measuring thermal decomposition kinetics in crystalline solids using X-ray diffraction to track the loss of crystallinity that accompanies condensed phase decomposition chemistry. We apply this method to systems for which extracting thermodynamic parameters has been historically difficult: organic molecular crystals that thermally decompose below their melting points, such as solid explosives. To demonstrate this method, we measured the rate of solid, thermal decomposition versus temperature in three different secondary solid explosives and the sugar fructose. In all cases, we observed an acceleration in the thermal decomposition rate with increasing temperature, which forms a vertical asymptote, a phenomenon known as melt acceleration. We show that observing the vertical asymptote in the thermal decomposition rate allows for identifying the thermodynamic melting point, which is not trivial to determine when melting and thermal decomposition happen simultaneously. We expect this method to be useful for studying thermal decomposition and for extracting thermodynamic data for secondary solid explosives, data that are needed for modeling and understanding faster phenomena, such as detonation. We also expect this method to be relevant to other organic molecular crystals in which thermal decomposition and melting overlap, such as sugars or pharmaceuticals.

Searching for high performance asymmetrically substituted teterazine energetic materials based on 3-hydrazino-6-(1H-1,2,3,4-tetrazol-5-ylimino)-s-tetrazine

Tetrazine compounds are promising candidates of high performance energetic materials (EMs). For the purpose of exploring high performance asymmetrically substituted teterazine explosives, 3-hydrazino-6-(1H-1,2,3,4-tetrazol-5-ylimino)-s-tetrazine was selected as the precursor and a series of teterazine EMs were prepared based on three synthetic strategies. All the obtained compounds were fully characterized and the crystal structures of seven compounds were further confirmed by single crystal X-ray diffraction. The thermal dynamics and thermal safety parameters, the detonation properties and impact sensitivities were also obtained. The results revealed that compounds 15–17 show excellent energetic properties (detonation velocities > 9000 m·s−1, detonation pressures > 30 GPa) and have impact sensitivities (8–12 J) that comparable or lower than RDX. Compounds 9–13 are insensitive to impact and have detonation velocities range from 8452 to 8775 m·s−1. These compounds can be good candidates of high performance secondary explosives or insensitive EMs.

Elastic and phonon-mode anomalies with temperature in the energetic material C6H6N4O8

Temperature-dependent Brillouin and Raman spectroscopic investigations are carried out on energetic material 4,10-Dinitro-2,6,8,12-tetraoxa-4,10-diazatetracyclo $[{5.5.0.0}^{5,9}{.0}^{3,11}]$ -dodecane (TEX; ${\mathrm{C}}_{6}{\mathrm{H}}_{6}{\mathrm{N}}_{4}{\mathrm{O}}_{8}$) from \ensuremath{-}196 to 180 \ifmmode^\circ\else\textdegree\fi{}C, close to its sublimation point, to study its elastic and phonon mode behaviors. Ambient values of experimental shear ($G$) and bulk ($K$) moduli of TEX are obtained as $G=5.6\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and $K=17.7\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. We have computed the elastic tensor and obtained the averaged bulk and shear moduli to compare with the experimentally obtained polycrystalline values. The known lower sensitivity of TEX compared with similar caged secondary explosives as CL-20, Royal Demolition eXplosive, and \ensuremath{\beta}-High Melting eXplosive is reckoned as due to its inherently high bulk modulus. We report direct experimental evidence of rapid reduction in elastic constant of TEX from 20 to 80 \ifmmode^\circ\else\textdegree\fi{}C, much before its melting point. Though there are no phase transitions in this temperature span, all Raman bands exhibit softening behavior around this temperature. We observe two distinct anomalies. Some bending modes such as bending of CNC $(356\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1})$, in-plane bending of NNO $(552\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1})$, bending of NCO $(610\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1})$, in-plane bending of NNO (635 $\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$), and in-plane bending of ONO and OCO (712 $\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$) exhibit slight hardening before and after the elastic anomaly. However, the asymmetric stretching modes at 1574 $\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ (asymmetric stretch of NO) and 1590 $\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ (asymmetric stretch of ${\mathrm{NO}}_{2}$) exhibit hardening below 20 \ifmmode^\circ\else\textdegree\fi{}C but soften after 80 \ifmmode^\circ\else\textdegree\fi{}C. This hardening switching over to softening above the anomaly indicates a release of stiffness manifesting from a conformational change to exo-endo and aiding the increasing compressibility. Emergence of new diffraction peaks $\ensuremath{\sim}50{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ and even observed at 150 \ifmmode^\circ\else\textdegree\fi{}C, which is well above the elastic anomaly, suggests that the material at high temperature may be isostructural to that at low temperature. In this paper, we establish that the high bulk modulus value of TEX contributes to its lower sensitivity; however, we also clearly demonstrate reduction in elastic modulus accompanied by anomalous behavior of Raman modes. This decrease in elastic modulus leading to increased compressibility may result in increased sensitivity of the explosive material just above room temperature.

Hydrogen peroxide – A promising oxidizer for rocket propulsion and its application in solid rocket propellants

This paper discusses the potential use of hydrogen peroxide as oxidizer for solid rocket propulsion. While hydrogen peroxide is a liquid in normal conditions, it may be used in solid rocket motor grains. Use of hydrogen peroxide of HTP class (High Test Peroxide) is proposed. It has been known for many decades but its utilization has been historically limited to liquid propellants. Until recently is application even in liquid state in rocket propulsion for space and defence has been limited due to storability and safety issues. With the availability of new grades of HTP with higher purity and concentrations, enhanced performance, safety and storability are possible. This results in HTP being considered for a wide range of rocket propulsion systems: as oxidizer in bipropellant and hybrid propulsion systems, as well a monopropellant. To ensure proper analysis of the potential of using HTP in next-generation solid rocket propellants, this paper reviews existing rocket propulsion applications of HTP. Modern use requires high performance and common current composite propellant compositions utilize ammonium perchlorate (AP) as oxidizer, what has several disadvantages, which are discussed. Alternative oxidizing compounds include ammonium dinitiramide (ADN), ammonium nitrate (AN), hydrazinium nitroformate (HNF), hexanitrohexaazaisowurtzitane (HNIW) and several other secondary explosives. Key properties of solid propellant oxidizers are listed and discussed. The need for further alternatives, despite numerous recent advances in solid rocket oxidizer technology is justified. The global push forward high performance green propulsion is one of the main motivations behind considering HTP for solid rocket propulsion. Theoretical performance of solid rocket motors using solid grains containing a high mass fraction of HTP is presented. This includes performance considering several fuels and additives and different oxidizer loadings. Up to date concepts of using hydrogen peroxide in solid propellants are reviewed. Solid cryogenic propellants using hydrogen peroxide are mentioned, but focus is given to solid propellants which could ensure flexible operations, thus use in state-of-the-art solid rocket motors. Challenges of HTP application as an oxidizer for solid propulsion are listed. This includes a discussion concerning its reactivity, thus limited compatibility with organic materials. Recommendations for further experimental work are proposed. Potential technology applications are listed with explanations why these particular niches may benefit from utilization of the new solid propellant technology.

Polynitro-Functionalized Azopyrazole with High Performance and Low Sensitivity as Novel Energetic Materials.

The development of energetic materials is still facing a huge challenge because the relationship between energy and sensitivity is usually contradictory: high energy is always accompanied with low sensitivity. Here, a high-energy, low-sensitivity energetic polynitro-functionalized azopyrazole (TNAP) and its energetic salts have been synthesized. The structural characterization of these compounds was analyzed by elemental analysis, 1H and 13C NMR spectroscopies, and infrared spectroscopy. The single-crystal structure of compounds K2TNAP, TNAP, 5, and 6 was obtained by X-ray diffraction, and K2TNAP is a novel energetic metal-organic framework. The calculated detonation properties of TNAP (9040 m s-1 and 36.0 GPa) are superior to that of RDX (8796 m s-1 and 33.6 GPa). In addition, TNAP also has lower mechanical sensitivity (IS > 40 J, FS = 244 N) and higher decomposition temperature (Td = 221 °C) than RDX (IS = 7.4 J, FS = 120 N, and Td = 204 °C). These experimental results suggest that TNAP may become a new candidate for secondary explosives.

Computational assessment of nitrogen-enriched, stable and insensitive tris(1,2,4,5-tetrazin-3-yl)amine building block for energetic applications

In this work, we report an approach for designing a series of energetic compounds derived from nitrogen-rich tris(1,2,4,5-tetrazin-3-yl)amine backbone. Based on available synthetic method, nitrogen content (70.8%), heat of formation (1371 ​kJ·mol-1), density (1.67 ​g·cm-3), detonation parameters (7.75 ​km·s-1, 24.30 ​GPa), and experimentally reported high decomposition temperature (231 ​°C), less sensitivity to accidental impact (42 ​J) and friction (360 ​N) data, tris(1,2,4,5-tetrazin-3-yl)amine found to be an efficient building block for designing energetic materials. The explosophoric functional groups –NO2, –NH2, –ONO2, –NHNO2, and N3 were introduced in the tris(1,2,4,5-tetrazin-3-yl)amine framework to further improve energetic properties. All tris(1,2,4,5-tetrazin-3-yl)amine derivatives have a much higher heat of formation than TNT (2,4,6-trinitrotoluene) and RDX (1,3,5-trinitro-1,3,5-triazinane). Crucially, higher detonation velocities (>9.10 ​km·s-1) and detonation pressures (>35.20 ​GPa) were calculated for –NO2, –ONO2, and –NHNO2 substituted compounds compared to RDX. Considering the experimental and computed stability of tris(1,2,4,5-tetrazin-3-yl)amine towards high temperatures and mechanical stimuli, the entire designed molecules are expected to be less sensitive and stable for energetic applications. These advantages make tris(1,2,4,5-tetrazin-3-yl)amine an effective building block. There is no denying that the insertion of energetic functional groups will undoubtedly benefit the development of secondary explosives and propellants.

Tetrazole‐Based Energetic Metal‐Organic Frameworks: Impacts of Metals and Ligands on Explosive Properties

AbstractNew energetic materials are required to compensate for the shortcomings of the current ones. Especially secondary explosives are the ones with low‐sensitivity, while maintaining energetic performance similar to those of primary ones, and particularly useful when safety must be ensured. Herein, we report two energetic metal‐organic frameworks (eMOFs), eMOF‐1, [Mn5(mtz)6.1(atz)2.9(NO3)] (mtz=5‐methyltetrazole, atz=5‐aminotetrazole) and eMOF‐2, [Cu(mtz)2], both of which have unique detonation and sensitivity properties. In particular, eMOF‐1, firstly reported here, shows better energetic performance when compared with the previously reported material, Cd‐based mtz MOF, an isostructural series. In addition, eMOF‐2 synthesized in water shows a great detonation performance, whereas isotopological Zn‐based mtz MOF did not show a meaningful performance as an explosive. Therefore, such reticular approach, i. e. replacing metal ions or ligands in isostructural frameworks, can be quite effective for the development of a new breed of energetic materials.

Polymer-bonded secondary explosives

In this paper, a review of the available literature on physical and explosive properties of explosive compositions containing a secondary explosive and a polymer binder (PBX) is presented. The review focused on an analysis of the properties of compositions containing mostly synthetic polymers. The review showed that, at the moment, the most commonly used composition is a hexogen-based explosive bonded with a chemically cross-linked hydroxylterminated polybutadiene. The use of energetic polymers in PBX compositions was observed only in the experimental systems tested on a laboratory scale. The most popular methods of forming compositions include pressing a previously phlegmatized explosive or chemical cross-linking of the composition in the projectile shell. Compositions which can be formed and reloaded using injection machines are known, but due to many limitations, the method is not widely used.

Review of modern military insensitive high explosives

In the last twenty years, high energetic materials have changed significantly. Several factors have influenced the development of these materials, which include new operational requirements such as insensitive ammunition (IM), as well as factors in the availability of new materials and new production techniques, safety assessment, and modeling. All this enables more efficient use of materials and a more detailed understanding of the processes involved in the application of new technologies. This work presents new insensitive secondary high explosives such as TATB, FOX-7, GUDN, NTO, and others that are in different stages of development. A review of these explosives is given and their stability, reliability, and specific application are described. Energy materials are known to be chemical compounds or mixtures that contain significant amounts of energy and it has been shown that successful design of new energetic materials with customized performance properties and increased stability is possible. The properties of new insensitive energetic materials must be further researched and improved before they can be used in new or existing systems. Insensitive ammunition testing is a vital component of many national IM programs. The international community has established requirements for testing the insensitivity of materials and developed six unique tests based on testing the response of the material to the effects of heat, impact, or shock.

Selective Synthesis and Characterization of the Highly Energetic Materials 1-Hydroxy-5H-tetrazole (CHN4 O), its Anion 1-Oxido-5H-tetrazolate (CN4 O- ) and Bis(1-hydroxytetrazol-5-yl)triazene.

For the first time, an adequate selective synthesis, circumventing the formation of 2‐hydroxy‐5H‐tetrazole, of 1‐hydroxy‐5H‐tetrazole (HTO), as well as the synthesis of bis(1‐hydroxytetrazol‐5‐yl)triazene (H3T) are reported. Several salts thereof were synthesized and characterized which resulted in the formation of new primary and secondary explosives containing the 1‐oxidotetrazolate unit. Molecular structures are characterized by single‐crystal X‐ray diffraction, 1H and 13C NMR, IR, and elemental analysis. Calculation of the detonation performance using the explo5 code confirmed the energetic properties of 1‐hydroxy‐5H‐tetrazole. The detonation properties can be adjusted to the requirements for those of a secondary explosive by forming the hydroxylammonium (6) or hydrazinium (7) salts, or to meet the requirements of a primary explosive by forming the silver salt 4, which shows a fast DDT on contact with a flame. The sensitivities of all compounds towards external stimuli such as impact, friction, and electrostatic discharge were measured.

Safe preparation of CuN3 for improved ignition performance of Ni-Cr bridge wire electric initiating explosive devices

The electric initiating explosive devices (EIEDs) are playing an increasingly important role in both military and civilian applications. With respect to good electrical conductivity and flexural strength, carbon paper can be endowed with primary explosive so that it serves as an independent module just like an ignition component in the EIEDs to satisfy the modular integration of EIEDs. But a traditional primary explosive cannot meet the need of sustainably developed devices. New energetic films need to be designed for EIEDs. The heat release and activation energy of the CA-CP film are 1402 J·g−1 and 104 kJ·mol−1, respectively. The electrostatic sensitivity of the CA film, whose E50 reaches up to 4.81 mJ, has been well improved due to its interweaved fibers. Moreover, the cuprous azide film could be successfully ignited under water after a hydrophobicity treatment. Herein, the CA-loaded carbon paper has been successfully integrated with the Ni-Cr bridge EIEDs for a greatly improved ignition performance, which will subsequently lead to a vast enhancement in the ability of EIEDs to ignite the secondary explosives or devices.

A Short Review of Nitric Esters and Their Role in Energetic Materials.

A review of energetic materials based on the nitric ester functionality is presented. Examined are materials that are classified as primary explosives, pressable secondary explosives, melt-castable secondary explosives, and rocket- and gun-propellant materials. Disclosed are the molecular structures, physical properties, performances, and sensitivities of the most important legacy nitric esters, as well as the relevant new materials developed within the past several years. Where necessary, discussions of the synthetic protocols to synthesize these materials are also presented.

Pressure-Induced In Situ Construction of P-CO/HNIW Explosive Composites with Excellent Laser Initiation and Detonation Performance

Laser initiation is a popular research topic in the energetic community. Particularly, the direct ignition of secondary explosives by laser ignitors is considered to be an advanced strategy for enhancing safety and promoting the miniaturization of weapons. Here, to improve the laser sensitivity of secondary explosives, P-CO synthesized under high pressure was employed as a coating for HNIW owing to its laser sensitivity and excellent energetic properties. In this operation, HNIW underwent an obvious isostructural phase transition from the ε-phase to the γ'-phase in the pressure range of 1.0-4.8 GPa. Subsequently, sub-nanoscale HNIW-based composites were formed when CO in situ polymerized to P-CO on the surfaces of HNIW at 5.1 GPa. This HNIW-based composite could be ignited at a much lower laser power (0.49-0.65 W) compared with pure HNIW (2.75-2.98 W) when excited by an Nd:YAG laser with a wavelength of 1064 nm. Additionally, the DFT calculations demonstrated that the arrangement density between HNIW and P-CO was significantly enhanced as the pressure increased. Thus, the introduction of advanced materials into explosive formulations through high-pressure technology is a novel and feasible strategy for developing multipurpose energetic materials.

Facile synthesis of 4-amino-3,5-dinitropyrazolated energetic derivatives via 4-bromopyrazole and their performances

The development of practical synthetic strategies towards novel energetic materials fulfilling various civilian and military purposes is a desirable but challenging task. 4-Amino-3,5-dinitropyrazole, an insensitive energetic material, has great potential as an effective building block for the construction of promising primary and secondary explosives. Herein, a facile strategy for the synthesis of 4-amino-3,5-dinitropyrazolate-based energetic derivatives is achieved using 4-bromopyrazole as starting material. The resulted energetic compounds 1–9 were well characterized through IR spectroscopy, multinuclear NMR spectroscopy, and differential scanning calorimetry. The results show that the extension of the three-dimensional caged packing structure related to the hydrogen bonding interactions and self-assembling of potassium ions with 3,5-dinitro-4-aminopyrazolate ligands, could reinforce its thermal stability with a decomposition temperature of 307.0 °C. Thermal stability, sensitivities, as well as detonation performances were studied by the experimental tests and calculated methods. Overall, this work offers a significant improvement and can lead to the broad practical use of 4-amino-3,5-dinitropyrazole as a building block for promising energetic materials.

Crystal Structure and Properties of an Energetic Perchlorate Complex Compound with Copper and Cytosine

AbstractA coordination compound from copper(II) perchlorate with cytosine was synthesized. The molecule contains copper(II) cation, four cytosine ligands, and two perchlorate anions. The single crystals of the compound were grown from the methanol solution. The crystal structure was determined by single‐crystal X‐ray diffraction. The compound crystallizes in the orthorhombic system (Pbcn space group) with crystal parameters: a=19.454(2) Å, b=10.185(2) Å, c=13.604(1) Å, V=2695.83(5) Å3, Z=4, and F(000)=1508 as a solvate with one methanol molecule in the asymmetric unit. It was characterized with elemental analysis, differential scanning calorimetry (temperature of decomposition – 270.1 °C), differential thermal analysis, infrared spectroscopy. Small‐scale safety testing was done to determine the impact and friction sensitivity. The title compound has sensitivity typical to secondary explosives (7.5 J, 230 N). Measured density and enthalpy of formation were used to calculate detonation parameters. With detonation velocity and pressure of 6132 m/s and 14.6 GPa, respectively, it has the moderate performance.

Professor Dr. Thomas M. Klapötke

Professor Dr. Thomas M. Klapötke