Low Mechanical Sensitivity Research Articles

A heat-resistant and insensitive energetic material based on the pyrazolo-triazine framework

One of the major challenges in the field of energetic materials is to develop explosive molecules with high detonation performances and low mechanical sensitivity. In this work, a heat-resistant and insensitive energetic compound 4-amino-7-nitro-5H-pyrazolo [4,3-d][1,2,3]triazine-2-oxide (3) was designed and prepared. It was identified and characterized using X-ray single-crystal diffraction, IR spectroscopy, NMR spectroscopy, mass spectrometry, thermogravimetry, differential scanning calorimetry (TG-DSC), and elemental analysis. This novel energetic compound exhibits good detonation performances (Dv ​= ​8731 ​m ​s−1, P ​= ​31.20 ​GPa), low mechanical sensitivities (IS ​> ​20 ​J, FS ​> ​360 ​N), and excellent thermal stability (Td ​= ​291 ​°C), suggesting that compound 3 may serve as a potential high-energy and insensitive material.

Combination of 1,2,3-triazole and 1,2,4-triazole frameworks for new high-energy and low-sensitivity compounds

In this study, a series of energetic compounds based on C–C linked 1,2,3-triazole and 1,2,4-triazole were synthesized and characterized, i.e., 5-(5-nitro-2H-1,2,3-triazole-4-yl)-4H-1,2,4-triazole-3,4-diamine (compound 1), N-(3-amino-5-(5-nitro-2H-1,2,3-triazole-4-yl)-4H-1,2,4-triazole-4-yl) nitramide (compound 4), and their energetic salts (compounds 2, 3, 5, and 6). The structures of compounds 1, 2, and 4 were determined by X-ray diffraction. All the new compounds feature acceptable thermal stability (Tdec ​= ​185–266 ​°C), with thermal decomposition temperature higher than that of RDX (Tdec ​= ​204 ​°C) except for compound 6 (Tdec ​= ​185 ​°C). Moreover, the detonation velocities of compounds 5 and 6 are 9200 ​m·s−1 and 9024 ​m·s−1, respectively, which are higher than that of RDX (D ​= ​8795 ​m·s−1). Furthermore, the new compounds show low mechanical sensitivity (IS ​= ​20 ​J, FS ​= ​240 ​N) compared to RDX (IS ​= ​7.4 ​J, FS ​= ​120 ​N). These results will help to accelerate the development of new high-energy density materials.

Exploring Application of 1,2,4‐Triazole Energetic Salts: Gas Generating Agent, Propellant and Explosive Compositions

AbstractHigh‐nitrogen energetic salts as the functional materials could be applied to formulate second explosives, gas‐generating agents, and propellants due to their large gas and energy release after combustion. Herein, a series of the insensitive and highly gas productive 1,2,4‐triazole derivatives including 4,5,5′‐triamine‐3,3′‐bi‐1,2,4‐triazole (1) and 4,5′‐dinitramino‐5‐amine‐3,3′‐bi‐1,2,4‐triazole (4) as well as corresponding salts were synthesized and characterized. The crystal structures of 4,5,5′‐triamine‐3,3′‐bi‐1,2,4‐triazole (1), nitrate salt (2), 4,5′‐dinitramino‐5‐amine‐3,3′‐bi‐1,2,4‐triazole (4) and triaminoguanidine salt (9) were determined by X‐ray diffraction. For explosives candidates, energetic salts of ammonium (5), hydrazinium (6), hydroxylammonium (7), and triaminoguanidine (9) not only display the outstanding detonation performance (D, 8657–9120 m s−1, P, 27.78–33.39 GPa), but also show low mechanical sensitivities (IS≥20 J, FS≥216 N). Furthermore, the constant‐volume combustion experiment results reveal that 5, 6, 7, and 9 show excellent gas productivity (Pmax≥12.8 MPa) and pressure‐up rate (dP/dtmax≥164 GPa s−1). These compounds could be the efficient components of gas‐generating agents and propellants based on the calculated combustion parameters from EXPLO 5 software.

Professor Dr. Thomas M. Klapötke

Professor Dr. Thomas M. Klapötke

Syntheses and Characterization of two cyclo‐pentazolate salts

AbstractTwo energetic salts of cyclo‐N5−, O‐methylisoure pentazolate (1) and guanidinoacetic acid pentazolate (2), were synthesized by metathesis reaction. All the energetic cyclo‐N5− salts were characterized by single‐crystal XRD, IR spectroscopy, 1H and 13C multinuclear NMR spectroscopy, thermal analysis (DSC) and elemental analysis. They exhibit good thermal stability with decomposition temperatures of more than 100 °C and they are in excellent agreement with those reported non‐metallic salts. Salt 1 also exhibits strong π‐π interactions. The standard enthalpies of formation and detonation performances of these salts were calculated using Gaussian 09 and EXPLO5 v6.01 programs. The detonation velocities of compound 1 and 2 are both about 7400 m s−1 and these two salts exhibit low mechanical sensitivity (IS>23 J, FS>220 N). Therefore, in this work, the synthesis of the new pentazolate salts enriches the cyclo‐pentazolate salts system, which is conducive to the exploration of more heat‐resistant and higher detonation velocities pentazolate salts.

Structure‐Property Relationships of ETNC and Its Salts Compared with PETNC and Its Salts

AbstractTwo energetic compounds, erythritol tetranitrocarbamate (ETNC) and pentaerythritol tetranitrocarbamate (PETNC), and their salts, were synthesized in three steps, characterized and compared. All synthesized compounds were characterized by IR, DSC and multinuclear NMR spectroscopy. Four compounds were further investigated by single crystal X‐ray diffraction. All nonmetal salts show extremely low mechanical sensitivity (IS≥30 J; FS≥360 N). The heats of formation were calculated using Gaussian 09, and the detonation performances were calculated using EXPLO 5. Although these nonmetal salts are lower than the neutral compounds ETNC (D: 7960 m s−1, P: 27.4 GPa) and PETNC (D: 7629 m s−1, P: 24.3 GPa), they possess high detonation performances that are better than TNT. Erythritol‐based and corresponding pentaerythritol‐based energetic materials were compared in terms of their thermostability, detonation velocity and detonation pressure. They were also compared in their respective series. ETNC and PETNC and their salts have short preparation steps and are easy to isolate in high yields, and thus have promising potential applications as explosives.

3,5-difluoro-2,4,6-trinitroanisole: promising melt-cast insensitive explosives instead of TNT

ABSTRACT Finding new melt-cast explosives with desired properties to replace 2,4,6-trinitrotoluene (TNT) has been intensely-pursued in recent decades. However, the contradiction among high energy, low mechanical sensitivity and low-melting makes the innovation of insensitive high-energy-density melt-cast explosives an enormous challenge, so the melt-cast explosives of comprehensive properties better than TNT has not been found. Here, we show a new way to design melt-cast insensitive energetic compound by the introduction of C-F into nitroaromatics. This as-synthesized energetic compound exhibits excellent performance with a high-measured density of 1.81 g cm−3, high thermal decomposition temperature (>300°C), high detonation velocity of 8.54 km s−1, appropriate melting point (82°C) and low viscosity(6200 mpa·S), and extremely low mechanical sensitivities (impact sensitivity, >60 J, and friction sensitivity, >360 N), superior to those of current melt-cast explosives, such as TNT and 2,4-dinitroanisole (DNAN).

N-N=N-N]-linked fused triazoles with π-π stacking and hydrogen bonds: Towards thermally stable, Insensitive, and highly energetic materials

It is the main task and challenge to reach a fine balance between high energy density and good molecular stability in energetic material research. In this study, two series of energetic compounds, 3-amino-7,7′-azo-[1,2,4] triazolo[4,3–b][1,2,4]triazole and 3,6-diamino-7,7′-azo-[1,2,4]triazolo[4,3–b][1,2,4] triazole featuring the N4 [N-N=N-N] linkage and fused triazoles, are presented. Their structures were determined by single crystal X-ray diffraction, elemental analysis, NMR, and IR spectroscopy. Their properties were studied in terms of density, thermal stability, detonation performance, and mechanical sensitivity. The N4 [N-N=N-N] linkages accord these compounds with high heat of formation, thus increasing the detonation performance. All fused triazoles exhibit planar structures, which result in low mechanical sensitivity. Through careful investigation of crystal data, strong π-π stacking and extensive hydrogen-bonding interactions were observed between molecules, which gives positive impact on mechanical sensitivity and thermal stability. The properties between different cations (or ions) were carefully studied. Quantum chemistry calculations were performed to investigate the potential relationship between structures and properties. Among them, compound 5 possesses high thermal stability (Td: 275 °C), good detonation performance (D: 8677 m s−1; P: 36.1 GPa), and excellent insensitivity (IS: 40 J; FS: 360 N), which makes it a balanced and promising energetic material.

Highly Thermostable Insensitive Energetic Polynitrophenyl-Substituted Furazan (Furoxan)-Annelated Azepines

High thermal stability and low mechanical sensitivity are two major goals in development of energetic compounds. Six highly stable insensitive polynitrophenyl substituted furazan (furoxan) annelate...

Construction of an Unusual Two-Dimensional Layered Structure for Fused-Ring Energetic Materials with High Energy and Good Stability

Abstract The creation of high-performance energetic materials with good mechanical sensitivities has been a great challenge over the past decades, since such materials have huge amounts of energy and are thus essentially unstable. Here, we report on a promising fused-ring energetic material with an unusual two-dimensional (2D) structure, 4-nitro-7-azido-pyrazol-[3,4-d]-1,2,3-triazine-2-oxide (NAPTO), whose unique 2D structure has been confirmed by single-crystal X-ray diffraction. Experimental studies show that this novel energetic compound has remarkably high energy (detonation velocity D = 9.12 km·s−1; detonation pressure P = 35.1 GPa), excellent sensitivities toward external stimuli (impact sensitivity IS = 18 J; friction sensitivity FS = 325 N; electrostatic discharge sensitivity EDS = 0.32 J) and a high thermal decomposition temperature (203.2 °C), thus possessing the dual advantages of high energy and low mechanical sensitivities. To our knowledge, NAPTO is the first fused-ring energetic material with 2D layered crystal stacking. The stabilization mechanism toward external stimuli were investigated using molecular simulations, and the theoretical calculation results demonstrate that the ultraflat 2D layered structure can buffer external mechanical stimuli more effectively than other structures by converting the mechanical energy acting on the material into layer sliding and compression. Our study reveals the great promise of the fused-ring 2D layered structure for creating advanced energetic materials.

Combined kinetic analysis of overlapping multistep thermal decomposition of 5-nitro-2,4,6-triaminopyrimidine -1,3-di-N-oxide (ICM-102)

In this work, we studied the thermal decomposition of a promising novel energetic compounds, 5-nitro-2,4,6-triaminopyrimidine -1,3-di-N-oxide (ICM-102), in an inert atmosphere. This energetic compound with a high measured density, high thermal decomposition temperature, high detonation velocity, and extremely low mechanical sensitivities has the widely application prospect in military and civilian fields. Therefore, a reliable description of the thermal decomposition kinetics is important to prevent or control the decomposition in such applications. While previous kinetic studies published on this system use simplified methods that avoid the fact that the entire process cannot be described by a single kinetic doublet. Here, we have studied the decomposition process by first separating the overall reaction into its two constituent steps which were subsequently analysed independently. The deconvolution was carried out using Fraser-Suzuki function that is capable of fitting an asymmetric peak fitting function. The resulting kinetic models and parameters proved to be able to reconstruct the original experimental curves but are also capable of producing accurate predictions of curves recorded at heating schedule different from those employed to record the experimental data used in the kinetic analysis. Finally, we have simulated three types of major decomposition reactions of ICM-102: the hydrogen transfer reactions and the C-NO2 homolysis theoretically. The direct C-NO2 homolysis prevails with the activation barrier at 188.8 kJ mol−1. The hydrogen transfer intramolecular or intermolecular with the activation barriers at 187.3 and 190.9 kJ mol−1, respectively. The reduced activation barriers than experimental results are due to that the simulation is carried out in monomolecular or bimolecular reaction systems.

Polymerization Effects on the Decomposition of a Pyrazolo-Triazine at high Temperatures and Pressures.

4‐amino‐3‐aminopyrazole‐8‐trinitropyrazolo‐[5, 1‐c] [1, 2, 4]triazine (PTX, C5H2N8O6) has good detonation performance, thermal stability and low mechanical sensitivity, which endow it with good development prospects in insensitive ammunition applications. To study the effects of polymerization on the decomposition of PTX, the reaction processes of PTX at different conditions were simulated by quantum chemistry and molecular dynamics methods. In this paper, the effects of polymerization on the decomposition of PTX were studied in terms of species information, reaction path of PTX, bond formation and bond cleavage, evolution of small molecules and clusters, and kinetic parameters at different stages. The results show that under the high‐temperature and high‐pressure conditions, the initial reaction path of unimolecular PTX in the thermal decomposition is mainly the cleavage of C−NO2 bonds. At the same time, there are many polymerization reactions in thermal decomposition process, which may greatly affect the reaction rate and path. The higher the degree of polymerization, the larger equilibrium value of potential energy, the less energy release of thermal decomposition. Compared with the activation energy of other explosives, the activation energy of PTX is higher than that of β‐HMX and lower than that of TNT.

A novel energetic composite with a special sandwich microstructure: RDX/expanded graphite intercalation composite

In this paper, the RDX/expanded graphite (EG) intercalation composites were prepared by solvent/anti-solvent process to recrystallize RDX crystals into the holes, gaps and grooves of EG with controllable embedding ratio (maximum 87.0 wt%) and crystal size. RDX in the composites was in the most stableα-phase, which was benefit for its further application in the military industry. The stability and sensitivity of RDX were improved with higher melting and thermolysis temperature, activation enthalpy (ΔH ≠), critical temperature of thermal explosion (T b) and lower mechanical sensitivity. The advanced half-coated parallel multi-sandwiches microstructure of RDX/EG intercalation composites possessed two effects: (i) high heat conduction and (ii) hot spots isolation of the carbon microstructure, which were the key to higher performance.

5,6-Fused bicyclic tetrazolo-pyridazine energetic materials.

This study presents the synthesis of 5,6-fused bicyclic conjugated energetic compounds through a combined strategy of anchoring the catenated nitrogen-atom chain and introducing vicinal C-amino and C-nitro groups into a tetrazolo-pyridazine ring. Their crystal structures were confirmed by single crystal X-ray diffraction. Both compounds display good thermal stability, high energetic properties and low sensitivities as energetic materials.

Coplanar Fused Heterocycle‐Based Energetic Materials

AbstractThe fused nitrogen‐rich heterocycles, particularly planar structures, possess many advantages over conventional single‐ring energetic compounds. The planar π‐π stacked structures result in enhanced safety. Meanwhile, their conjugated systems give rise to good energetic properties. This review focused on the syntheses, properties, and potential applications of energetic materials based on the coplanar fused nitrogen‐rich heterocycles. Most of these compounds exhibit excellent detonation characteristics along with low mechanical sensitivity which makes them very promising candidates for highly energetic materials for civilian or military applications.

Hydrogen Bonding in CHON-Containing Energetic Crystals: A Review

Hydrogen bonding (HB) universally exists in CHON-containing energetic materials (EMs) and significantly influences their structures, properties, and performances. As time proceeds, some new types of EMs such as energetic cocrystals (ECCs) and energetic ionic salts (EISs) are thriving currently and richening insight into the HB of EMs, and these are reviewed in this article as well. The intramolecular HB mostly exists in stable molecules while seldom in less stable molecules; weak and abundant HBs dominate intermolecular interactions and consolidate crystal packing. For ECCs with neutral heterogeneous molecules, intermolecular HBs serve as one of the strategies for crystal design. In comparison, the HBs in EISs are greatly strengthened as their polarity significantly increases with ionization. A strong intramolecular HB usually enhances molecular stability with large π-bonds and packing coefficients and facilitates reversible H transfer, which is advantageous for low mechanical sensitivity. The intermolecular HB-aided π–π stacking that favors low mechanical sensitivity is observed in all three kinds of EMs, including traditional EMs with neutral homogeneous molecules, ECCs with neutral heterogeneous molecules, and EISs. However, a strong intermolecular HB in an EM causes a ready intermolecular H transfer, thereby worsening thermal stability. Thus, the influence of HBs on the stability of EMs can go both ways, and there should be a balance when new HB-containing EMs are designed.

Nitrogen‐rich Salts based on 3‐Dinitromethyl‐[1,2,4]triazine: Synthesis, Characterization, and Performance

1,1‐Diamino‐2,2‐dinitroethylene (FOX‐7), one of the most well‐known energetic materials, has attracted broad attention around the world. To extend the chemistry of FOX‐7, we present here a series of energetic salts based on 3‐dinitromethyl‐[1,2,4]triazine, which is prepared from FOX‐7. All these salts were fully characterized using 1H NMR, 13C NMR, IR, and elemental analysis. In addition, the potassium salt (2), ammonium salt (5), and guanidinium salt (7) were further confirmed by single‐crystal X‐ray diffraction. Extensive hydrogen bonds were observed in these salts. The salts exhibit moderate densities varying from 1.63 to 1.76 g·cm–3. All the compounds possess good thermal stability with decomposition temperatures from 118 to 267 °C. The detonation performance for salts were calculated by using EXPLO 5, their detonation velocities are in the range from 6807 to 8614 m·s–1 and detonation pressures fall between 18.8 to 31.6 GPa. All the salts exhibit very low mechanical sensitivity, which indicates their potential application as insensitive energetic materials.

The Ingenious Synthesis of a Nitro-Free Insensitive High-Energy Material Featuring Face-to-Face and Edge-to-Face π-Interactions.

Density, detonation property, and sensitivity may be the most valued features when evaluating an energetic material. By reasoning structure–property relationships, a nitro-free planar energetic material with high nitrogen and oxygen content, 7-hydroxy-difurazano[3,4-b:3′,4′-f]furoxano[3″,4″-d]azepine (4), was synthesized using a unique and facile approach. The structure was fully characterized by IR and NMR spectra, elemental analysis, differential scanning calorimetry (DSC), and single-crystal X-ray diffraction. The expected properties of 4, including a high density of 1.92 g cm−3, high detonation velocity of 8,875 m s−1, and low mechanical sensitivities (impact sensitivity, 21 J and friction sensitivity, >360 N), confirm our strategy. Interestingly, the single-crystal structures of 4 reveal expected face-to-face and edge-to-face π-interactions in the crystal stacking. The remarkable differences in crystal stacking of 4 provide unequivocal evidence that face-to-face π-π interactions contribute significantly to closer assembly and higher density.

Experimental investigations into stress sensitivity in three Chinese coal samples by NMR

ABSTRACT The coal reservoirs have low mechanical strength and strong stress sensitivity. The study of stress sensitivity is of great significance to the efficient development of coalbed methane (CBM). In order to reveal the stress and strain characteristics of coal reservoirs, the low-field nuclear magnetic resonance (NMR) experiments with variable confining pressures were carried out on three coal samples from China. Based on the T2 spectrum of coal samples under different confining pressures, the pore distribution, connectivity, and porosity variation rules of the coal samples were analyzed. Results show that the peaks of mesopore, macropore-fissure in the coal samples are well developed; however, the micropore peaks are poorly developed. There are differences in the stress deformation of pores and fractures in coals. With increasing confining pressures from 0 to 16 MPa, the peak of fractures decrease most obvious, and the peak of mesopore and macropore-fissure are relatively obvious, while the peak of the small pores is not significantly reduced. With the confining pressure increases, the total NMR porosity of coal decreases as the rule of negative exponential function, which is mainly controlled by changes of the porosity of seepage pore. The effect of adsorption pore on porosity changes is not obvious.

Runaway reaction and thermal hazards simulation of 4-amino-1,2,4-triazole picrate by HP-DSC and ARC

4-Amino-1,2,4-triazole picrate (4-ATPA) is a type of ionic liquids, as well as an explosive with sound thermal stability and low mechanical sensitivity. However, under upset conditions such as high temperature and pressure, an unpredictable explosion would occur and result in huge casualties and property losses. The purpose of this research was to evaluate the thermal hazard and runaway reaction of 4-ATPA through high-pressure differential scanning calorimetry and accelerating rate calorimeter. The kinetic parameters of decomposition reaction under non-isothermal and different pressure conditions were calculated based on the experiment results. Experimental results showed that the β and test pressure had no effect on the amount of heat release. Adiabatic experiments indicated that 4-ATPA had a high onset temperature at 196.8 °C. The maximum self-heating rate (3567.9 °C min−1) and pressure rise rate (202.0 bar min−1) revealed the vulnerability of 4-ATPA to suffer a disastrous explosion. Moreover, the apparent activation energy and pre-exponential factor were evaluated as 110.2 kJ mol−1 and 1.8 × 10−15 s−1 by ASTM E698 method. The correctness of the thermodynamic calculation formula under adiabatic conditions is verified by ARC tests. Finally, the thermal hazard risk of 4-ATPA was classified as unacceptable based on the risk classification criteria.