Low Mechanical Sensitivity Research Articles

Preparation and characterization of superfine spherical TKX‐50 with a hollow structure by spray drying

AbstractMicro/nano energetic materials with regular morphologies exhibit high energy release efficiency, superior charge performance, and low mechanical sensitivity. Exploring dihydroxylammonium 5,5′‐bistetrazole‐1,1′‐diolate (TKX‐50) with spherical microstructures and excellent comprehensive properties is of great significance for potential applications. In this work, a kind of superfine spherical TKX‐50 was fabricated by spray drying method. The as‐prepared TKX‐50 had a narrow particle size distribution with d50=3.14 μm, high sphericity of 0.944 with hollow structure and bulk density of 1.851 g/cm3. And its formation mechanism was proposed. The results of XRD and FT‐IR demonstrated that spray drying would not change the crystal structure of TKX‐50. TG‐DSC results showed that the initial decomposition and the peak temperature of superfine spherical TKX‐50 was about 10 °C lower than raw TKX‐50, and the apparent activation energy was 4.584 kJ ⋅ mol−1 lower than raw TKX‐50, due to the dramatic change in morphology. TG‐DSC‐FTIR‐MS provided a new understanding of decomposition process of TKX‐50, and the results illustrated that the main gas products were N2, H2O, N2O, NH3, NO, NH2, CO2, and HCN. Superfine spherical TKX‐50 underwent similar decomposition path as raw TKX‐50 but stood out in its larger occupation of the first decomposition which meant a more complete decomposition and its faster rate of the whole decomposition process. More importantly, the impact sensitivity (H50) increased from 50.1 cm to 70.8 cm, and the friction sensitivity (P) decreased from 24 % to 0 %, showing improved safety performance.

Combination of Energetic Tetrazole and Triazole: Promising Materials with Exceptional Stability and Low Mechanical Sensitivity as Propellants and Gas Generators.

An innovative synthesis of 5-((1H-tetrazol-5-yl)methyl)-4H-1,2,4-triazole-3,4-diamine (TMT) based on triazole and tetrazole frameworks bearing double amino groups was reported. It is worth mentioning that TMT is insensitive to impact and friction (IS > 40 J, FS > 360 N), thus enabling it to have an exceptional thermal decomposition behavior that is superior to RDX and TNT. Meanwhile, it also has relatively high energetic performance (Dv = 8.417 km/s). A series of energy-containing salts TMT-1-8 were also investigated for their potential applications. Except for TMT-4 and TMT-7, the remaining nitrogen-rich salts have initial decomposition temperatures above 200 °C. Furthermore, the salts with positive heat generation all have extraordinary gas production, especially for TMT-1 (Vo = 840.5 dm3/kg), TMT-2 (Vo = 803.9 dm3/kg), and TMT-7 (Vo = 844.3 dm3/kg). The low mechanical sensitivities of the TMT series were discovered, and a majority of them have impact sensitivities exceeding 40 J with friction sensitivities exceeding 360 N which are superior to TNT (IS = 15 J, FS = 353 N). The intermolecular and intramolecular interactions of the crystals TMT-1-3 were explored by Hirshfeld surfaces, 2D fingerprint plots, noncovalent interaction (NCI) analysis, and electrostatic potential surface analysis to understand the physicochemical property changes in relation to the structure. Consequently, this novel tri/tetrazole and polyamine system as a promising material provides the impetus for the development of gas generators and propellants.

Process and performance of DAAF microspheres prepared by continuous integration from synthesis to spherical coating based on microfluidic system

In order to improve the energy output consistency of 3, 3′-diamino-4, 4′-azoxyfurazan (DAAF) in the new insensitive booster and the safety and efficiency in the preparation process, a continuous preparation system of DAAF from synthesis to spherical coating was designed and established in this paper, which combined ultrasonic micromixing reaction with microdroplet globular template. In the rapid micromixing stage, the microfluidic mixing technology with ultrasonic was used to synergistically strengthen the uniform and rapid mass transfer mixing reaction between raw materials to ensure the uniformity of DAAF particle nucleation-growth, and to prepare high-quality DAAF crystals with uniform structure and morphology and concentrated particle size distribution. In the microdroplet globular template stage, the microfluidic droplet technology was used to form a droplet globular template with uniform size under the shear action of the continuous phase of the dispersed phase solution containing DAAF particles and binder. The size of the droplet template was controlled by adjusting the flow rate ratio between the continuous phase and the dispersed phase. In the droplet globular template, with the diffusion of the solvent in the dispersed phase droplets, the binder precipitates to coat the DAAF into a ball, forming a DAAF microsphere with high sphericity, narrow particle size distribution and good monodispersity. The problem of discontinuity and DAAF particle suspension in the process was solved, and the coating theory under this process was studied. DAAF was coated with different binder formulations of fluororubber (F2604), nitrocellulose (NC) and NC/glycidyl azide polymer (GAP), and the process verification and evaluation of the system were carried out. The balling effects of large, medium and small droplet templates under different binder formulations were studied. The scanning electron microscope (SEM) results show that the three droplet templates under the three binder formulations exhibit good balling effect and narrow particle size distribution. The DAAF microspheres were characterized by powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermo-gravimetric (TG) and sensitivity analyzer. The results showed that the crystal structure of DAAF did not change during the process, and the prepared DAAF microspheres had lower decomposition temperature and lower mechanical sensitivity than raw DAAF. The results of detonation parameters show that the coating of DAAF by using the above three binder formulations will not greatly reduce the energy output of DAAF, and has comparable detonation performance to raw DAAF. This study proves an efficient and safe continuous system from synthesis to spherical coating modification of explosives, which provides a new way for the continuous, safe and efficient preparation of spherical explosives.

High Performance Thermoplastic Energetic Composites Using Fluorinated Energetic Polyurethanes as Binder

AbstractThe performance of energetic composite materials is largely dependent on the energy level and combustion process. The fluorine‐containing energetic polyurethanes as binder can facilitate the combustion of metallic fuels and enhance the energy level of the energetic composites. In the current report, two kinds of thermoplastic energetic composites are prepared, based on novel fluorine‐containing energetic polyurethanes as binder and also with aluminum nanoparticles (AlNPs) and ammonium perchlorate (AP). Compared with the energetic composites with fluorine‐free energetic polyurethane binder, despite the very low fluorine content, the fluorine‐containing energetic composites not only showed higher density, lower mechanical sensitivity, much higher mechanical toughness, but also a significantly improved combustion efficiency and combustion rate of the AlNPs.

Pushing the limits of the heat of detonation via the construction of polynitro bipyrazole.

The trinitromethyl group is a highly oxidized group that is found as an active functionality in many high-energy-density materials. The most frequently used previous synthetic method for the introduction of the trinitromethyl group is the nitration of heterocyclic compounds containing an acetonyl/ethyl acetate/chloroxime group. Now a novel strategy for constructing a trinitromethyl group (5) via nitration of an ethylene bridged compound, dipyrazolo[1,5-a:5',1'-c]pyrazine (2), is reported. In addition, the other two nitrated products (3 and 4) were obtained under different nitrating conditions. Compound 5 has excellent detonation performance (Dv = 9047 m s-1, P = 35.6 GPa), and a low mechanical sensitivity (IS = 10 J, FS = 216 N), with an especially attractive heat of detonation of 6921 kJ kg-1, which significantly exceeds that of the state-of-the-art explosive CL-20 (Q: 6162 kJ kg-1).

Combining the advantages of 1,3,4-oxadiazole and tetrazole enables achieving high-energy insensitive materials.

Combining the advantages of energetic heterocycles to achieve high-energy insensitive explosives is a significant challenge. Herein, based on high-energy tetrazole rings and highly stable 1,3,4-oxadiazole rings, a series of novel nitrogen rich energetic compounds 5-9 were successfully constructed. The related compounds were fully characterized by EA, FT-IR, NMR, DSC, and MS, and compounds 6-9 were further confirmed by X-ray single crystal diffraction. Among them, the energetic ion salts 6-8 show high thermal stability (Tdec > 250 °C) and low mechanical sensitivity (IS > 40 J, FS > 360 N), as well as good energy properties (7552-8050 m s-1, 19.4-23.3 GPa). In particular, the azo compound 9 exhibits competent comprehensive performances (Tdec = 226.2 °C, D = 8502 m s-1, P = 28.9 GPa, IS = 32 J, FS = 320 N). These results suggest that the strategy of integrating tetrazole and 1,3,4-oxadiazole and employing an azo structure as a bridging unit are effective approaches to construct high-energy insensitive materials.

Preparation of quasi-core/shell structured composite energetic materials to improve combustion performance.

Composite explosives with fast reaction rate, high energy release efficiency, and remarkable combustion performance can be obtained by the interaction between homogeneous energetic materials and heterogeneous energetic materials and have broad application prospects. However, ordinary physical mixtures can easily cause separation between the components in the preparation process, which is not conducive to reflecting the advantages of composite materials. In this study, high-energy composite structured explosives with RDX modified by polydopamine as the core and PTFE/Al as the shell were prepared using a simple ultrasonic method. The study of morphology, thermal decomposition, heat release, and combustion performance demonstrated that the quasi-core/shell structured samples have higher exothermic energy, faster combustion rate, more stable combustion characteristics, and lower mechanical sensitivity than the physical mixture.

Optimization of performance and sensitivity: preparation of two Ag(I)-based ECPs by using isomeric ligands.

For energetic compounds, their structure determines their performance, and even minor variations in their structure can have a significant impact on their performance. The application scenarios for energetic materials are diverse, and their performance requirements vary as well. To investigate the influence of different substituent positions on the performance of primary explosives, we prepared two Ag(I)-based complexes, [Ag(2-IZCA)ClO4]n (ECPs-1) and [Ag(4-IZCA)ClO4]n (ECPs-2), using structurally isomeric ligands, 1H-imidazole-2-carbohydrazide (2-IZCA) and 1H-imidazole-4-carbohydrazide (4-IZCA). The structures were confirmed using infrared, elemental analysis, and single-crystal X-ray diffraction. Experimental results demonstrate that both ECPs exhibit good thermal stability. However, compared to ECPs-1, ECPs-2 exhibits a lower thermal initial decomposition temperature (Td = 210 °C), lower mechanical sensitivity (IS = 27 J, FS = 84 N), and more concentrated energy output. Although theoretical predictions suggest similar detonation velocities and pressures for both compounds, actual detonation performance tests indicate that ECPs-2 has stronger explosive power and initiating capability, with potential for use as a laser initiator (E = 126 mJ). The simple preparation method and inexpensive starting materials enrich the research on primary explosives.

Boosting Laser-Ignited Combustion Performance of Energetic Materials with Low Sensitivity: Integration of Triazene-Bridged Triazole with Oxygen-Rich Moieties via Noncovalent Self-Assembly

It has long been a driving force in the development of energetic materials to hunt for novel high-energy density materials (HEDMs) with high energy and good stability. Recently, the noncovalent self-assembly strategy of energetic anions and cations to generate HEDMs is an effective strategy for introducing an oxidizer and fuel separately into the energy system. In this study, bis(1,2,4-triazolyl)triazene containing triazene (−N═N═NH−) and oxidant molecules (i.e., HNO3 and HClO4) were selected as high-energy ions to develop new high energy materials by using noncovalent self-assembly. The experimental results showed that three exemplary compounds possess excellent detonation pressure and detonation velocity (PC–J: 22.8–29.3 GPa and D: 7425–8135 m s–1), which are comparable to the classical explosive trinitrotoluene (TNT) (PC–J: 19.5 GPa and D: 6881 m s–1) as well as 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) (PC–J: 34.9 GPa and D: 8795 m s–1). Moreover, 1 and 3 exhibit low mechanical sensitivities (IS: 40 J and IS: 70 J). Thus, 1 and 3 have great potential as insensitive energetic materials. Especially, these energetic assemblies have excellent laser-ignited combustion properties and can be used as candidates for low sensitivity propellants.

Constructing a framework with 1,3,4-oxadiazole and pyrazole for new high energy insensitive salts

A novel neutral tricyclic energetic compound 5,5’ -(4-nitro-1H-pyrazole-3,5-diyl) bis (1,3,4-oxadiazol -2-amine) and a series of corresponding energetic ionic salts 7–9 were synthesized. Differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), elemental analysis, and infrared spectroscopy (IR) were used to analyze the newly synthesized compounds. Single-crystal X-ray diffraction was also used to validate the precise structure of ammonium salt 7. These energetic salts exhibit positive heat of formation (401.17 ​kJ·mol−1 to 690.66 ​kJ·mol−1), moderate detonation performance (8517 ​m·s−1 to 8803 ​m·s−1) and low mechanical sensitivity (IS ​> ​40 ​J; FS ​> ​360 ​N). It is worth noting that, in comparison to previously reported energetic salts containing nitramino 1,3,4-oxadiazole with poor thermal stability, the beginning decomposition temperatures of hydroxylamine salt 9 is greater than 180 ​°C. The newly synthesized hydroxylamine salt 9 has promise to be used as new high energy insensitive material based on the aforementioned characteristics.

Anaesthetic efficacy of intraoral topical lidocaine and prilocaine in nanostrusctured lipid nanocarriers: a randomized clinical trial

This randomized placebo-controlled crossover trial evaluated if nanostructured lipid nanocarriers (NLC) could improve the topical anaesthetic efficacy of lidocaine and prilocaine (L+P) incorporated in a xanthan-hydrogel applied in the oral cavity. There were no differences among topical formulations regarding the primary endpoints of pain intensity during needle insertion or local anaesthetic injection. Nonetheless, exploratory analyses indicate that individuals with low mechanical pain sensitivity were more susceptible to placebo effects which could also interfere with the anaesthetic effects of the topical formulations. Thus, mechanical pain sensitivity can be an interesting approach to increase assay sensitivity in clinical trials of topical anaesthesia.

The skeleton of 5,7-fused bicyclic imidazole-diazepine for heat-resistant energetic materials

In light of the low yields and complex reaction routes of some well-known 5,5-fused and 5,6-fused bicyclic compounds, a series of 5,7-fused bicyclic imidazole-diazepine compounds were developed with high yields by only two efficient steps. Significantly, the seven-membered heterocyclic ring has a stable energetic skeleton with multiple modifiable sites. However, the 5,7-fused bicyclic energetic compounds were rarely reported in the area of energetic materials. Three neutral compounds 1, 2 and 4 were synthesized in this work. To improve the detonation performances of the 5,7-fused neutral compounds, corresponding perchlorate 1a and 2a were further developed. The physicochemical and energetic performances of all newly developed compounds were experimentally determined. All newly prepared energetic compounds exhibit high decomposition temperatures (Td: 243.8–336 °C) and low mechanical sensitivities (IS: >15 J, FS: >280 N). Among them, the velocities performances of 1a (Dv = 7651 m/s) and 4 (Dv = 7600 m/s) are comparable to that of typical heat-resistant energetic material HNS (Dv = 7612 m/s). Meanwhile, the high decomposition temperature and low mechanical sensitivities (Td = 336 °C; IS = 32 J; FS > 353 N) of 4 are superior to that of HNS (Td = 318 °C; IS = 5 J; FS = 250 N). Hence, the 5,7-fused bicyclic compounds with high thermostability, low sensitivities and adjustable detonation performance have a clear tendency to open up a new space for the development of heat-resistant energetic materials.

Bis(3-(trinitromethyl)-1H-1,2,4-triazol-5-yl)methanone: A mildly acidic high-performing energetic material

High performance, acceptable thermostability, and low mechanical sensitivity are high-demand properties in the design of competitive materials. Nitrogen-rich compounds are an alternative source of green molecules. Two simple, efficient synthetic routes to a novel material, bis (3-(trinitromethyl) − 1H-1,2,4-triazol-5-yl) methanone, 5, by using inexpensive starting compounds are described. Compound 5 has interesting chemical reactivity with water in the presence of organic solvents to form a gem diol of bis (3-(trinitromethyl) − 1H-1,2,4-triazol-5-yl) methanediol, 5a. All new molecules are well characterized by advanced spectroscopic techniques. The structures of 5·Et2O, 5a·3H2O, and salt 6 are confirmed by single-crystal X-ray analysis. The densities of the solid powder compound 5, and the crystals of 5a·3H2O were measured by a gas pycnometer. The theoretical densities and Explo5 calculations of solvent-free molecules, 5 and 5a, suggest that expanding the functionality of carbonyl-bridged compounds may be an alternative way to achieve high-performing materials.

Simple reaction to prepare a heat-resistant and insensitive explosive (2-nitro-[1,2,4]triazolo[1,5-a][1,3,5]triazine-5,7-diamine) and its derivatives

• An energetic molecule (NTTD) was obtained by one-step reaction with high yield. • NTTD can act as a heat-resistant and insensitive explosive. • The reaction has many advantages, which are conducive to large-scale preparation. • The derivatives of NTTD were synthesized through simple derivatization reactions. Low cost, high yield, good safety, and simple synthesis process are the problems that must be solved in the engineering preparation of energetic compounds, even beyond the pursuit of high energy level to some extent. In this work, a novel 5,6-fused energetic molecule 2-nitro-[1,2,4]triazolo[1,5- a ][1,3,5] triazine-5,7-diamine (NTTD) was designed and easily obtained. By the introduction of oxidants (HNO 3 and HClO 4 ) and high-energy groups (–NHNO 2 ), the derivatives of NTTD were prepared, some of which exhibited good comprehensive properties. Importantly, NTTD features excellent thermostability and low mechanical sensitivities. The whole preparation process has advantages of simple operation, short time, cheap and simple reagents, good repeatability, and high yield, which are conducive to large-scale preparation, indicating that NTTD can be a potential candidate of heat-resistant and insensitive explosives.

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.

Synthesis, characterization, and crystal structure of 2-oxo-5-nitro-3-(5-nitroimino-1,3,4-oxadiazole-2-yl)-pyrazine

A novel and green energetic compound, 2-oxo-5-nitro-3-(5-nitroimino-1,3,4-oxadiazole-2-yl)-pyrazine, was designed and prepared in this study. It was identified and characterized using X-ray single-crystal diffraction, IR spectroscopy, NMR spectroscopy, mass spectrometry, differential scanning calorimetry, and elemental analysis. The newly developed compound is an insensitive booster explosive with a high detonation velocity (D ​= ​8516 ​m ​s−1), highs detonation pressure (P ​= ​31.85 ​GPa), low mechanical sensitivities (impact sensitivity: 32 ​J, friction sensitivity: > 360 ​N), and excellent thermal stability (decomposition temperature: 270 ​°C). This compound and further studies will greatly boost the application of green energetic materials with improved performance.

Nitrogen-rich ion salts of 1-hydroxytetrazole-5-hydrazide: a new series of energetic compounds that combine good stability and high energy performance.

High-efficiency explosives that combine high stability and excellent energy performance are one of the key directions of energetic materials research. In this study, a novel monocyclic hydroxytetrazole derivative (3) with high stability was prepared, and a series of insensitive energetic ionic salts were derived from it. Benefiting from their outstanding performance in terms of density, 3D hydrogen bonding and π-electron interactions, these salts are excellent in both detonation performance (D = 8709 to 9314 m s-1 and P = 29.9 to 35.6 GPa) and thermal stability (Td = 193.0-232.2 °C). The hydrazine salt (2) exhibits high detonation properties (D = 9314 m s-1 and P = 35.6 GPa), due to its high density (ρ = 1.71 g cm-3) and high heat of formation (ΔfH = 563.2 kJ mol-1 = 3.19 kJ g-1). In addition, the high thermal stability (Td = 232.0 °C) and low mechanical sensitivity (IS = 30 J and FS = 360 N) of 2 are also unmatched by HMX and TKX-50. These improved properties demonstrate the great promise of 2 as an insensitive high-energy explosive.

A series of N-trinitromethyl-substituted polynitro-pyrazoles: high-energy-density materials with positive oxygen balances.

An N-trinitromethyl strategy was employed for the synthesis of polynitro-pyrazole based high-energy-density compounds with great potential as energetic materials. The new compounds were characterized by 1H and 13C NMR, IR spectroscopy, elemental analysis, differential scanning calorimetry, and single-crystal X-ray diffraction. Compound 10 exhibits high energetic properties, has a positive oxygen balance (OB) of +2.1%, and an excellent specific impulse (272.4 s), making it a potential high-energy dense oxidizer to replace AP in solid rocket propellants. The nitration of 7 with HNO3/H2SO4 yielded the green primary explosive 12, which showed higher density, higher performance, better oxygen balance and lower sensitivities to those of currently used diazodinitrophenol. Compound 13 is a nitrogen and oxygen rich secondary explosive with a high OB (+5.0%), comparable energy (D = 9030 m s-1; P = 35.6 GPa; η = 1.03) to HMX, and much lower mechanical sensitivity (IS = 12 J, FS = 240 N).

A Zn(II) coordination polymer assembled by triazole derivative: Crystal structures and energetic behavior

It is a challenge to increase the oxygen content with maintaining the mechanical sensitivity of the energetic materials. In this work, the 1D solvent-free energetic coordination polymer [Zn3(μ3-OH)2(att)4]n1 (Hatt = 4-amino-1,2,4-triazole-5-thiol) was obtained in alkaline solution through a simple hydrothermal reaction. The X-ray crystallographic analysis indicates that there are two hydroxyl ions embedded in the three Zn(II) atoms through strong coordination bonds, which can provide a strategy for improving the oxygen content of energetic compounds. In addition, the energetic polymer 1 possesses high enthalpy of formation (2012.700 kJ·mol−1), low mechanical sensitivity (IS > 40 J, FS > 360 N) and relatively high decomposition temperature (235 °C). These results demonstrate that compound 1 has the potential application in insensitive energetic material.

Preparation and Performance Characterization of High‐Quality HNIW

AbstractIn this study, high‐quality HNIW was prepared by solvent‐antisolvent recrystallization method and mechanical ball‐milling method. The particle morphology, particle size, crystal form, and thermal stability of HNIW samples were characterized by SEM, DSC, and XRD. The purity of HNIW samples was characterized by the HPLC. The HGZ‐1 impact sensitivity meter and WM‐1 friction sensitivity meter were used to evaluate the impact sensitivity and friction sensitivity respectively. The detonation voltage of the samples was tested by the EFI system. Compared with the micron‐level HNIW obtained by four times of recrystallizations, the particle size grading mechanical ball milling method of grinding balls minimizes the particle size of the HNIW. The prepared nano‐level HNIW has an average particle size of about 200 nm and has the advantages of narrow distribution, low mechanical sensitivity, and good detonation performance. Therefore, the solvent‐antisolvent recrystallization method and mechanical ball‐milling method can be used to obtain nano‐HNIW with a narrow particle size distribution, high purity, and good performance.