Lower Impact Sensitivity Research Articles

Synthesis of a Novel Double Salt: Ammonium 3,4‐Diamino‐1,2,4‐triazolium Styphnate

Nitrogen‐rich double salt ammonium 3,4‐diamino‐1,2,4‐triazoliumstyphnate (NH4·DATr·TNR) (2) with good thermal stability was successfully synthesized by reacting 3,4‐diamino‐1,2,4‐triazolium chloride aqueous solution with styphnic acid methanol solution under the reaction medium of aqueous ammonia. The title double salt was characterized by elemental analysis (EA), Fourier transformation infrared spectrum (FT‐IR), and X‐ray single‐crystal diffraction. It crystallizes in the monoclinic crystal system with space group P21/n. Its density is 1.780 g·cm–3. Compound 2 is thermal stable below 200 °C by the differential scanning calorimetry (DSC) test. The non‐isothermal kinetics parameters were calculated by the Kissinger's method and Ozawa‐Doyle's method, respectively. In addition, compound 2 showed low friction and impact sensitivities.

Preparation and Properties of CL‐20 based Composite by Direct Ink Writing

AbstractDirect ink writing (DIW) is a new trend in the micro‐scale charging of energetic materials. In this study, a CL‐20 based composite was prepared using DIW, and its properties were characterized. Results indicated that the particles of the composite are found at the sub‐micron level, and a single layer measures at 2.4 μm. The composite has high density and low impact sensitivity, and its critical detonation size is around 1×0.4 mm. This feature will contribute to the detonation at the micro levelto a certain degree.

Preparation and Characterization of Cyclotrimethylenetrinitramine (RDX) with Reduced Sensitivity

The internal defects and shape of cyclotrimethylenetrinitramine (RDX) crystal are critical parameters for the preparation of reduced sensitivity RDX (RS-RDX). In the current study, RDX was re-crystallized and spheroidized to form the high-quality RDX that was further characterized by purity, apparent density, size distribution, specific surface area, impact sensitivity, and shock sensitivity. The effects of re-crystallization solvent on the growth morphology of RDX crystal were investigated by both theoretical simulation and experiment test, and consistent results were obtained. The high-quality RDX exhibited a high purity (≥99.90%), high apparent density (≥1.811 g/cm3), spherical shape, and relatively low impact sensitivity (6%). Its specific surface area was reduced more than 30%. Compared with conventional RDXs, the high-quality RDX reduced the shock sensitivities of PBXN-109 and PBXW-115 by more than 30%, indicating that it was a RS-RDX. The reduced sensitivity and good processability of the high-quality RDX would be significant in improving the performances of RDX-based PBXs.

A computational study on new oxidizers as replacements for ammonium perchlorate: tetranitroacetimidic acid and tetranitroacetamide

High energetic materials tetranitroacetimidic acid (TNAA) and tetranitroacetamide (NTNAA) with positive oxygen balance (OB = 30%) are highly potential replacements for ammonium perchlorate (AP). Tautomerization from TNAA to NTNAA is feasible, reflected by the activation energy of 160.2∼170.0 kJ/mol. No transition state appears on the C–NO2 bond breaking, which triggers pyrolysis of two compounds. The C–NO2 bond dissociation energies are 116.1∼167.2 kJ/mol and 120.4∼174.6 kJ/mol for TNAA and NTNAA, respectively. The chemical stabilities of TNAA and NTNAA are higher than that of the insensitive explosive 1,1-diamino-2,2-dinitroethylene. TNAA and NTNAA possess lower impact sensitivities (h50 ≥ 77.51 cm) than AP does. Detonation properties of the composite explosives containing TNAA or NTNAA are comparable with that of the composite explosives containing AP. The acceptable stabilities, highly positive OB, environmentally friendly decomposition products, and the comparable ability to improve detonation performance of composite explosives show that TNAA and NTNAA are potential replacements for AP as an oxidizer used in composite explosives.

Synthesis of 1-Amino-2,4-Dinitroimidazole Optimized by Online Infrared Spectroscopy and its Energetic Properties.

The optimization of the reaction conditions (solvent, reaction time, and aminating agent) for the synthesis of 1-amino-2,4-dinitroimidazole (3) by monitoring the reaction with online infrared spectroscopy is reported in this study. First, the thermal characteristics of 3 were studied by using differential scanning calorimetry (DSC; using heating rates of 2.5, 5, 10, and 20 K min-1 ), thermogravimetric analysis (TG), and the thermal explosion method. The Kissinger and Ozawa methods were used to calculate the average activation energy for the formation of 3; with logarithmic frequency factors (ln A) of 21.04 and 9.62, and activation energies (Ea ) of 98.68 and 102.28 kJ mol-1 , respectively. Compound 3 and its reaction precursors 2,4-dinitroimidazole (1) and 1,4-dinitroimidazole were characterized by single-crystal X-ray diffraction. Compound 3 is shown to have good energetic properties, as determined through EXPLO5 v6.02 and actual measurement. Furthermore, this energetic material is found to have low impact sensitivity (IS>40 J) and friction sensitivity (FS>360 N).

Synthesis and Properties of 5-(3-Amino-1, 2, 5-oxadiazol-4-yl)tetrazol-1-ol and Its Ammonium and Hydroxylammonium Salts

5-(3-Amino-1, 2, 5-oxadiazol-4-yl)tetrazol-1-ol (4) as well as its ammonium salt (5), and hydroxylammonium salt (6) were synthesized with high yield from malononitrile as raw material via diazotization, addition, and cyclization reactions. Their structures were characterized by infrared (IR) spectra, nuclear magnetic resonance (NMR), elemental analyses, and X-ray single-crystal diffraction(XRD). The impact and friction sensitivities of compounds 4, 5 and 6 were tested using the drop hammer method and friction sensitivity tester. The thermal stabilities of compounds 4, 5 and 6 were studied by DSC. Results show that a large number of intramolecular and intermolecular hydrogen bonds for compounds 4, 5 and 6 are formed. These hydrogen bonds have an important influence on their structure, density, thermal properties and sensitivities, especially all hydrogens in the molecule of compound 6 participate in hydrogen bond formation, resulting in compound 6 has a relatively high density (1.786 g·cm-3). Compounds 4, 5 and 6 exhibit low impact and friction sensitivity and good thermal stabiliy and can be used as environmentally friendly and new-generation insensitive energetic materials.

Theoretical design of bicyclo[2.2.1]heptane derivatives for high-energy density compounds with low impact sensitivity

For new high-energy density compounds, a series of new bicyclo[2.2.1]heptane derivatives were designed and studied by density functional theory (DFT) method. The heat of formation (HOF) was evaluated by the isodesmic reaction. The densities and the heats of sublimation were predicted by the electrostatic potential analysis at B3PW91/6-31G(d,p) and B3LYP/6-311++G(2df,2p) levels, respectively. The detonation performances were predicted by the Kamlet-Jacobs equations. The bond dissociation energies (BDE) and impact sensitivity that is evaluated by the free space per molecule were also studied to give a better understanding of the stability. Results show that HOFs increase with the increasing number of N atoms. When the number of NO2 groups is larger than 4, HOFs generally increase with the increasing number of NO2 groups. Even though solid-phase HOF is decreasing, detonation energy is always rising with Oxygen Balance (OB) closing to zero-OB, and positive value of OB will largely reduce detonation energy. Detonation velocity and detonation pressure of the designed compounds are in the range of 5.62–9.46km/s and 11.72–41.44GPa, respectively. And detonation velocity and detonation pressure always increase with the increasing number of N atoms or NO2 groups except when OB is positive value. BDEs of all designed compounds are larger than 20kcal/mol shows that all designed compounds have a reasonable thermal stability. The calculated impact sensitivities show that all designed HEDCs have acceptable sensitivity. Especially impact sensitivity of C7, D7, E7, F6andG6 are expected to be very close to Tetryl (h50=25cm). Considering the thermal stability, impact sensitivity and detonation performance, A8, B8, C7, C8, D7, E7, F6andG6 might be interesting candidates for use as HEDCs.

“One‐Step” Synthesis of Ionic Ferrocenyl Compounds of Ferrocenylmethyldimethylamine. Characterization, Migration, and Catalytic Properties During Combustion

AbstractAlkylferrocene‐based burning rate catalysts exhibit high migration tendency and volatility during prolonged storage and fabrication process of the solid propellants. To retard the migration problems, eight ionic compounds composed of ferrocenylmethyldimethylammonium cation paired with a common energetic anion, were synthesized by “one‐step” procedure. The compounds were characterized by FT‐IR, NMR, and UV/Vis spectroscopy as well as elementary analysis. Their crystal structures were confirmed by single‐crystal X‐ray diffraction. The TG and DSC analyses indicated that they exhibit high thermal stability. Cyclic voltammetry studies suggested that most of them show reversible or quasi‐reversible redox waves. The anti‐migration results revealed that 1–4 are low‐migratory compounds, but 5 exhibits high migration trends. The TG curves at 70 °C for 24 h showed that all of them have low volatility. They have from high to low impact sensitivity depending on the anions of the compounds. They all exhibit significant effect on the thermal decomposition of ammonium perchlorate (AP) and some of them accelerate the thermal degradation of 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX). Among them 4 is the best one. Unexpectedly, compound 5, with 1H‐tetrazolate as anion, can decompose into its original reactants at the temperature just higher than its melting point and could show smart‐material functionality in solid propellants.

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

AbstractThe 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−1from 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.

Furazans with Azo Linkages: Stable CHNO Energetic Materials with High Densities, Highly Energetic Performance, and Low Impact and Friction Sensitivities.

Various highly energetic azofurazan derivatives were synthesized by simple and efficient chemical routes. These nitrogen-rich materials were fully characterized by FTIR spectroscopy, elemental analysis, multinuclear NMR spectroscopy, and high-resolution mass spectrometry. Four of them were further confirmed structurally by single-crystal X-ray diffraction. These compounds exhibit high densities, ranging from 1.62 g cm(-3) up to a remarkably high 2.12 g cm(-3) for nitramine-substituted azofurazan DDAzF (2), which is the highest yet reported for an azofurazan-based CHNO energetic compound and is a consequence of the formation of strong intermolecular hydrogen-bonding networks. From the heats of formation, calculated with Gaussian 09, and the experimentally determined densities, the energetic performances (detonation pressure and velocities) of the materials were ascertained with EXPLO5 v6.02. The results suggest that azofurazan derivatives exhibit excellent detonation properties (detonation pressures of 21.8-46.1 GPa and detonation velocities of 6602-10 114 m s(-1) ) and relatively low impact and friction sensitivities (6.0-80 J and 80-360 N, respectively). In particular, they have low electrostatic spark sensitivities (0.13-1.05 J). These properties, together with their high nitrogen contents, make them potential candidates as mechanically insensitive energetic materials with high-explosive performance.

GAP/CL-20-Based Compound Explosive: A New Booster Formulation Used in a Small-Sized Initiation Network

ABSTRACTWith ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and glycidyl azide polymer (GAP) as the solid filler and binder, respectively, GAP/CL-20-based compound explosives were designed and prepared. Using micro injection charge technology, the compound explosives were packed into small grooves to explore their application in a small-sized initiation network. The detonation reliability, detonation velocity, mechanical sensitivity, shock sensitivity, and brisance of the explosive were measured and analyzed. The results show that when the solid content of CL-20 is 82 wt%, the explosive charged in the groove has a smooth surface from a macroscopic view. From a microscopic view, a coarse surface is bonded with many CL-20 particles by GAP binder. The GAP/CL-20-based explosive charge successfully generates detonation waves in a groove larger than 0.6 mm × 0.6 mm. When the charge density in the groove is 1.68 g·cm−3 (90% theoretical maximum density), the detonation velocity reaches 7,290 m·s−1. Moreover, this kind of explosive is characterized by low impact and shock sensitivity.

Additives Effects on Crystal Morphology of Dihydroxylammonium 5,5ʹ-Bistetrazole-1,1ʹ-diolate by Molecular Dynamics Simulations

Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) is a newly synthesized explosive with excellent comprehensive properties: high energy storage, low impact sensitivity, and low toxicity. To understand and improve the crystal morphology of TKX-50, we reported the polymer consistent force field to simulate the crystal morphology of TKX-50 by growth morphology (GM) method. We then used this force field in molecular dynamics (MD) simulations to predict the influences of additives on crystal facets of TKX-50. The calculated results indicate that ethanol, ethylene glycol, and acetic acid are more favorable to the spheroidization of TKX-50, which provides a theoretical support for the additive selection of crystalline system. Furthermore, we added the selected additives in the recrystallization system of TKX-50. The recrystallized samples possessed a small aspect ratio and were close to spherical in shape, which indicates that the experimental results are consistent with the simulated results.

Theoretical study of the effect of N-oxides on the performances of energetic compounds.

In order to study the effects of N-oxide on structure and performance, six categories of energetic compounds were systemically investigated. The results indicated that the C-C bonds in the rings were shortened, and the C-N bonds close to the N → O bond were elongated when N atoms was oxidized to form N → O bonds. N → O bonds can increase the densities of most categories of compounds, and the increment will increase with the number of N → O bonds. As to their detonation performances, almost all categories of compounds had an increased trend, except for some NO2-, NHNO2- and ONO2-substituted compounds. The contribution of 1,2,3,4-tetrazine and 1,2,4,5-tetrazine to performances was better than that of pyrazine and [1,2,5] oxadiazolo [3,4-b] pyrazine on the whole, and the groups, especially energetic groups, made a huge contribution to performance. When R was a NH2 or ONO2 group, all compounds had lower impact sensitivities, and thus represent candidates for novel energetic compounds. However, other than the sixth category of compounds, all compounds had higher impact sensitivities when R was a NO2 or NHNO2 group, and have little significance in application.

Two-sided effects of strong hydrogen bonding on the stability of dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50)

Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) is a recently synthesized energetic ionic salt (EISs) with some excellent properties including high energy content, high density, low impact sensitivity and low toxicity, and therefore is a promising alternative energetic material. In contrast to commonly applied energetic CHON materials, TKX-50 features strong intermolecular hydrogen bonds (HBs). However, the effects of these strong HBs on its important properties remain unclear. We report herein the two-sided effects of the strong HBs on the stability of TKX-50, through ab initio simulations on shear deformation and thermal decomposition. That is, on the one hand, the strong HBs in TKX-50 lead to a layer-like arrangement of the cations and dianions in the (010) planes with the adjacent layers connected only by two types of weakest HBs, which facilitates the conversion of external kinetic energy into interlayer sliding, and contributes to low impact sensitivity; on the other hand, the extensive HBs in TKX-50 act as a potential source to facilitate H-transfer (including proton transfer), which accelerates subsequent thermal decomposition, and thus deteriorates the thermal stability of TKX-50 relative to its notably low impact sensitivity. These two-sided effects of the strong HBs in a TKX-50 crystal should be useful to understand properties of other EISs, in which strong HBs are universal, and enrich the knowledge of the sensitivity mechanism of energetic materials.

Computational investigation on a series of heteroaromatic nitrogen-rich compounds

Density functional theory calculations were performed to calculate the detonation performance, frontier molecular orbitals, and impact sensitivity of a series of heteroaromatic nitro-rich compounds. The results show that all the title compounds exhibit high-positive solid-phase heats of formation. The detonation velocities and pressures of the title compounds were predicted via the Kamlet–Jacobs equation. Thirteen compounds have larger D and P than HMX because of the big crystal densities and solid HOFs. The analysis of frontier molecular orbitals shows that two compounds may be kinetically more stable and chemically less active than other compounds. In addition, most of the compounds were found to have lower impact sensitivity than HMX.

Molecular design of prismane-based potential energetic materials with high detonation performance and low impact sensitivity

To develop new energetic materials, the eleven nitroester substitution derivatives of prismane were investigated at the B3LYP/6-311G** level of density functional theory (DFT). The gas phase heats of formation were calculated by isodesmic reactions and the solid-state heats of formation were obtained by the Politzer approach using the heats of sublimation for the designed compounds. The detonation velocities and pressures of all molecules were calculated by Kamlet–Jacobs equations based on molecular density and heat of detonation. The results show that the nitroester group in prismane is helpful for enhancing molecular detonation properties and power index. Among all molecules, 1,2,3,4-tetrnitroesterprismane has excellent detonation properties (detonation pressure = 40.05 GPa, detonation velocity = 9.28 km/s) and large power index value. The molecular stabilities were evaluated by calculating bond dissociation energies and characteristic heights ( H 50 ). The results indicate that the bond dissociation energies of all molecules are above 80 kJ/mol, and all molecules have a larger H 50 value than hexanitrohexaazaisowurtzitane (CL-20, 12 cm). The obtained structure–property relationships may provide basic information for the molecular design of novel high-energy materials.

Preparation and characterization of nano NC/HMX composite particles

Abstract Nano nitrocellulose/cyclotetramethylene tetranitramine (NC/HMX) composite particles were precipitated from their co-solutions by the spray drying method. The nano composite samples were characterized by scanning electron microscope, transmission electron microscope and X-ray diffraction. Impact sensitivity and thermal decomposition properties of nano composites were also measured and analyzed. Results show that the product particles are close to spherical in shape and range from 0.5 μm to 5 μm in size. In the product particles, β-HMX particles with size ranging from 50 nm to 100 nm are uniformly and discretely dispersed in NC binders. The drop height of nano NC/HMX composite particles (66.1 cm) is more than triple as high as that of raw HMX (21.6 cm), exhibiting considerably low impact sensitivity. Moreover, nano composite particles are easier to decompose and decomposed more rapidly than do raw HMX under the thermal stimulus due to the lower peak temperature and activation energy and higher reaction rate. Therefore, nano composites are expected to be candidates filled in high burning rate propellants.

Energetic salts based on furazan-functionalized tetrazoles: routes to boost energy.

Based on the backbone of the furazan-tetrazole structure, routes were developed to improve the properties of energetic materials. Two types of high-density energetic salts were designed, prepared, and fully characterized. Single-crystal X-ray analyses support the structural characteristics for two amino salts. A majority of the salts exhibited good detonation properties, high thermal stabilities, and relatively low impact and friction sensitivities. Hydroxylammonium and hydrazinium salts, 1-3 and 1-4, which have relatively high densities (1.84 and 1.74 g cm(-3,) , respectively), acceptable impact and friction sensitivities (14 J, 160 N and 28 J, 360 N), and good detonation pressures (38.3 and 32.2 GPa) and velocities (9323 and 9094 m s(-1) ), have performance properties superior to 1,3,5-trinitro-1,3,5-triazinane (RDX) and triaminotrinitrobenzene (TATB).

Anisotropic Impact Sensitivity and Shock Induced Plasticity of TKX-50 (Dihydroxylammonium 5,5′-bis(tetrazole)-1,1′-diolate) Single Crystals: From Large-Scale Molecular Dynamics Simulations

Dihydroxylammonium 5,5′-bis(tetrazole)-1,1′-diolate (TKX-50) is a newly synthesized energetic material with high energy storage, low impact sensitivity, and low toxicity. These features make it a viable candidate to replace such commonly used energetic materials as RDX and CL-20 in the next generation of explosives. Sensitivity determines the engineering application of energetic materials (EMs) and has been widely studied for various EMs. To understand the origin of the anisotropic sensitivity and properties of this new synthesized EM, we report a flexible classical force field for TKX-50 developed to reproduce the molecular properties (geometry, vibrational frequencies and torsion barriers) and the crystal properties (cell parameters and lattice energy). We then used this force field in molecular dynamics (MD) simulations to predict such thermodynamic and mechanical properties as isothermal compressibility, thermal expansion, elastic moduli, and heat capacity. Furthermore, we carried out large scale (∼a half million atoms) MD simulations to investigate the mechanical response to shocks in the [100], [010] and [001] directions. The predicted Hugoniot elastic limits (HELs) are 6.1 GPa for [100], 14.2 GPa for [010] and 9.1 GPa for [001] shocks. Thus, single crystal TKX-50 shows anisotropic impact sensitivity with [010] as the most sensitive direction and [100] as least sensitive. The plastic deformations in shock compression along the [100] direction primary arise from the (001)/[210] and (010)/[001] slip systems of. For the [010] shock, the primary slip systems are (100)/[021] and (001)/[210]. However, no obvious slip system was observed for [001] shock.

Molecular design of N–NO2substituted cycloalkanes derivatives Cm(N–NO2)mfor energetic materials with high detonation performance and low impact sensitivity

Cycloalkane derivatives Cm(N–NO2)mexhibit notable detonation properties and remarkable stability for potential energetic materials.