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Mechanical and thermal hazards are critical for chemical compounds. Foremost, the design of novel energetic materials that are stable, insensitive, but have a detonation performance superior to in-service materials is of great interest. However, a single source of safety data for hazardous materials with explosophoric functionalities is still missing. Herein, an experimental database on thermal stability, impact, and friction sensitivity for 150 CHNOFCl compounds is presented. Mechanical sensitivity is discussed in detail: particle size and shape effects, instrument design, and experimental protocol are considered. The entire dataset was analyzed using the simple descriptors of molecular structure. Mechanical sensitivity was found to be linearly correlated with the maximal heat of explosion for certain classes of compounds (nitrobenzenes, furazans, pyrazoles, etc.). Consideration of all species shows that previously proposed sensitivity increase with an energy content rise is relevant, although it is not strict line, as was assumed, but rather a widened “strip”. A new parameter, safety factor, is proposed to combine two types of sensitivity data. With this factor, the limiting values of mechanical sensitivity at a given energy content are provided that represent the state-of-art development of energetic materials and may be used for screening and design of novel compounds.
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... 10,11 Recently, we released an extensive data set of mechanical and thermal sensitivity data for 150 energetic species. 7 The data set contains some well-known explosives, and we briefly discussed the scatter of literature data for these species. The most likely reason for these inconsistencies is the difference in the experimental setups itself. ...
... It could lead to varied outcomes, especially for lowly sensitive compounds with high melting points. 7,14 The reproducibility of the mechanical sensitivities reported in the modern literature for newly synthesized energetics is the main topic of this communication. While there is a thorough study devoted to a single compound 15 with indication of various disturbing factors, to the best of our knowledge, this question has not been discussed systematically on a range of chemicals. ...
... We can use the approach suggested in a prior study. 7 It relies on the representation of experimental data in coordinates of integrated sensitivity (socalled safety factor) versus the thermodynamic measure of energetic potential (viz., maximal heat of explosion, ρQ max ). The inversely proportional dependency between these two parameters has been widely discussed in the literature. ...
Article
Mechanical stress is an important trigger of reactions in chemicals. Historically, the standard testing protocols for impact and friction sensitivity have been developed mainly for energetic materials and explosives. As a result, the structure− mechanical safety data is available for common explosives and is constantly reported for newly synthesized energetic compounds. The present work is motivated by the widely held among practitioners idea of high variability of mechanical sensitivity data, the advancements of new heterocyclic and high-nitrogen chemistry, and clear need in benchmark reference data set for QSPR modeling. We started from literature analysis and have already noted that many chemical papers lack the details required to replicate their findings regarding mechanical sensitivity. Next, we prepared over 100 species that have been previously synthesized and whose sensitivity had been reported by other researchers. The scatter within the literature and present study's results is illustrated and analyzed. Finally, we proposed a data set of 83 chemicals, which have the most reliable mechanical sensitivity data. This benchmark data set is recommended to be used for modeling of mechanical hazards of reactive chemicals. The logics of how this data set can be expanded in future is given; it might involve the collaborative efforts by different groups.
... Nevertheless, most of the leaders shown in Fig. 1a have the drawbacks limiting its real-life applications, mainly sensitivity and stability issues. Thus, the sensitivity to impact and friction reaches the level of primary explosives for DDF and [1,2,5] oxadiazolo [3,4-e] [1,2,3,4]tetrazine 4,6-dioxide (FTDO) [8]. ...
... Because of its specifics, researchers in energetic materials field usually do not operate with "big data", but rather have datasets with hundreds of compounds (e.g, [8,9]). Nevertheless, the increased computational capabilities allow the feature extraction and further directed synthesis of target energetic compounds. ...
... Vuppuluri et al. [75] show that cocrystal design can improve the energetic performance. They synthesized solvate of 2,4,6,8,10,4,6,8,10, and hydrogen peroxide. At the same density (1.4 g cm − 3 ), HP solvate of CL-20 shows 300 m s − 1 higher experimental detonation velocity as compared to pristine nitramine. ...
Article
Energetic materials are important class of functional compounds that combine the beauty of extreme high-energy chemistry with rigorous constraints on safety and performance. As a result, the development of energetic materials is a challenging process that require the best of computational, chemical synthesis, and material design techniques. This review discusses the state-of-art of the energetics field, and then highlights the most recent synthetic advancements that go beyond – regioisomerism impact, almost all-nitrogen species, new mesoionic ring fragments, and compounds bearing elements other than traditional CHNO. The computational advancements are summarized further: the material genome approaches and high-throughput virtual screening. Next, the material science and crystal engineering design tools are reviewed, from cocrystal design and host-guest inclusion to various polymer coating techniques. Overall, we showcase the complexity of interdisciplinary problem of energetic materials design, that entraps the original mostly organic chemical field, but then material science and crystal engineering, and now targets the computational discovery and machine learning.
... They are higher than the onset of decomposition temperature of 290 • C for trinitrotoluene (TNT) ( [24], pp. 1894-1986 [25]), a conventional explosive. The peak decomposition temperatures of compound 1 and 2 were 332.8 • C and 328.2 • C, respectively. ...
... They are higher than the onset of decomposition temperature of 290 °C for trinitrotoluene (TNT) ( [24], pp. 1894-1986, [25]), a conventional explosive. The peak decomposition temperatures of compound 1 and 2 were 332.8 °C and 328.2 °C, respectively. ...
... Density measured by a gas pycnometer at 25 • C.5 Ref[24], pp. 1894-1986[25]. ...
Article
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The innovative synthesis of 3,8-dibromo-2,9-dinitro-5,6-dihydrodiimidazo [1,2-a:2′,1′-c]pyrazine and 3,9-dibromo-2,10-dinitro-6,7-dihydro-5H-diimidazo [1,2-a:2′,1′-c][1,4]diazepine is described in this study. The tricyclic fused molecular structures are formed by the respective amalgamation of piperazine and homopiperazine with the imidazole ring containing nitro. Compound 1 and 2 possess excellent high-density physical properties (ρ1 = 2.49 g/cm3, ρ2 = 2.35 g/cm3) due to the presence of a fused ring structure and Br atom. In addition to their high density, they have high decomposition temperatures (Td > 290 °C) which means that they have excellent thermal stability and can be used as potential heat-resistant explosives. Low mechanical sensitivities (IS > 40 J, FS > 360 N) are observed. The twinning structure of 2 was resolved by X-ray diffraction. Non-covalent interaction analysis, Hirshfeld surfaces, 2D fingerprint plot, and Electrostatic potential analysis were used to understand the intramolecular interactions in relation to physicochemical properties. The unique structures of this type of compound provide new potential for the evolution of energetic materials.
... (2) Why is TFO·HCl more mechanically sensitive and can even explode at impact? To answer both questions, it is useful to analyze the calculated 26 ± 5 (d) b >360 (10%) 2,4,6-trinitrotoluene 62 30 ± 5 (e) >360 (0%) pyrazine 1,4-dioxide 63 6.9 ± 1.2 (d) c >360 (0%) a The positive reaction of explosion is marked as (e), and the decomposition is designated as (d). b No explosion is observed even at a maximal load of 100 J. c Explosions are registered at ≥25 J. ...
... Furthermore, the energetic potential of a molecule has been repeatedly shown to be a descriptor of the compound's sensitivity (the greater energy, the higher the sensitivity). 62,71,72 Table 3 shows the calculated detonation parameters of studied hydroxylamines. For detonation velocity, we show the value computed using the calculated or experimental density; the difference is not high and acceptable for ranking of the material. ...
Article
Organic derivatives of hydroxylamine are important reagents in modern chemistry, but their thermal stability and related hazards have not yet been systematically studied. In the present study, we report a detailed thermal analysis of N-hydroxysuccinimide (NHS), N-hydroxyphthalimide (NHPI), 1,4-piperazine diol (PipzDiol), 1,3,5-trihydroxy-1,3,5-triazinan-1-ium chloride (formaldoxime trimer hydrochloride, TFO·HCl), and tris-oxime TRISOXH3. Then, we suggest the effective kinetic parameters and mechanisms of thermal decomposition. All these NOH-containing chemicals exhibit the exothermic decomposition when examined under conditions that retard material vaporization (such as DSC at elevated pressure or in hermetic crucibles). The application of Yoshida-type rules points to a certain hazard associated with TFO·HCl, TRISOXH3, and PipzDiol. Small-scale mechanical sensitivity testing validated the DSC-based hypothesis: TFO·HCl explodes at certain drop energies, and two other species decompose under impact. The standard drop energies corresponding to 50% probability of initiation are within 14–26 J. Overall, the reactive chemistry of the analyzed hydroxylamines may result in certain risks when they are stimulated by temperature or impact. Even for well-known reagents such as NHS, the amount of heat liberated in the course of decomposition is considerable (about 1300 J g–1). 1,3,5-Trihydroxy-1,3,5-triazinan-1-ium chloride by the amount of decomposition enthalpy (2200 ± 300 J g–1) and the level of the impact sensitivity (16 ± 5 J) can be compared with explosives, but it is less thermally stable, decomposing above 100 °C. The calculation of virtual detonation performance of this salt shows much higher stored energy as compared to other studied hydroxylamines. We propose the calculation of the detonation parameters for screened compounds as an alternative way of explosive hazard identification.
... Furazan 1 shows high impact sensitivity, which is comparable with that of nitrate esters (pentaerythritol tetranitrate, PETN: IS = 3 J) [24]. This compound is also sensitive to friction, its value is between sensitivity of priming explosives (lead azide <5 N) [25] and nitrate esters, (PETN: 70 N) [23]. ...
... The data of X-ray powder diffraction for compound 1 (Fig. 5) T m , melting point; T dec , onset decomposition temperature; d, density at ambient temperature; HOF, enthalpy of formation; IS, impact sensitivity; FS, friction sensitivity; D, calculated detonation velocity; P C-J , calculated detonation pressure (using PILEM software [26]). а [24], b [22], c [27], d [28]. ...
Article
The synthesis verification of 3-amino-4-azido-1,2,5-oxadiazole and its structural characterization (IR, NMR, X-Ray, elemental analysis) are reported. Its thermal behavior (TG-DSC), standard enthalpy of formation, sensitivity to mechanical stimuli, detonation parameters were studied. Our study unveils wide application perspectives of 3-amino-4-azidofurazan as a precursor to novel energetic materials for future insights and an eco-friendly primary explosive.
... The first fluorine-containing group, which was introduced in energetic materials (HEMs) during structural design, was -C(NO 2 ) 2 F [5][6][7][8][9][10][11]. Notably, -C(NO 2 ) 3 changing in HEMs with -C(NO 2 ) 2 F or -C(NO 2 )F 2 groups has led to the development of energetic materials, possessing markedly higher stability and decreased sensitivity to mechanical impact [12,13]. 2 of 22 Currently, the known perspective energetic fluorinated groups used in the new energetic structures are -C(NO 2 ) 2 F and -C(NO 2 ) 2 F 2 [14][15][16][17][18][19][20][21], -NF 2 and -C(NO 2 ) 2 NF 2 [22][23][24][25][26][27][28][29][30][31], and -SF 5 [32][33][34][35][36]. It was learned that introducing even the simplest fluorine "C-F" group instead of "C-H" sometimes substantially improves practical HEM properties; i.e., it lowers sensitivity and increases the density of traditional explosives, leading to upgrading energetic properties. ...
Article
Full-text available
We performed a theoretical investigation of the fluorinated compounds’ morphology and stability. The research was conducted using the widely adopted DFT approach, specifically the B3LYP method and the cc-pVTZ basis set, aiming to design high-energy materials that exhibit low sensitivity, toxicity, instability, and reduced proneness to decomposition or degradation over a short period. In the paper, we presented the investigation results for the compounds whose total energy is the lowest. Their thermal and chemical stability was evaluated based on stability indicators such as cohesion, chemical hardness, and softness. The oxygen–fluorine balance is assessed to determine the sensitivity of these advanced materials. The density, detonation pressure, and velocity of the selected conformers were theoretically obtained to reveal the influence of -CF3, -OCF3, and cyclic -O(CF2)nO- fragments on the energetic properties of nitroaromatics as well as their stability and resistance to shock stimuli. The results enable the prediction of advanced energetic materials that achieve a favorable balance between power and stability. Based on the results achieved, we put forward CF3N2, OCF3N2, C2F6N2, 1CF2N2/O2CF2N2, and 2CF4N2/O2C2F4N2 for practical usage because these compounds possess greater stability compared to tetryl and better explosive properties than TNT.
... In the past decade, thermal analysis has been widely used in a wide range of fields, including inorganic substances [18], pigments [19], explosives [20][21][22], energetic materials [23][24][25][26], polymers [27][28][29][30][31][32], nanocomposites [33], and biomass materials [34,35]. The main techniques used for sample measurements are differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). ...
Article
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In recent years, various kinds of civil explosive detonation accidents have occurred frequently around the world, resulting in substantial human casualties and significant property losses. It is generally believed that thermal stimulation plays a critical role in triggering the detonation of explosives; consequently, the study of the thermal hazards of explosives is of great significance to many aspects of safety emergency management practices in the production, transportation, storage, and use of explosives. It is known that the thermal stability of the ammonium perchlorate-aluminium system and the ammonium nitrate-aluminium system has been extensively investigated previously in the literature. However, there is a paucity of research on the thermal hazard characteristics of non-ideal explosives under varying oxygen balance conditions within the academic sphere. Therefore, this research focused on the study of the thermal hazards of non-ideal explosives based on thermokinetic analysis. The thermal hazards of non-ideal explosive mixtures of ammonium perchlorate and aluminium and of ammonium nitrate and aluminium were studied by thermal analysis kinetics. The thermokinetic parameters were meticulously studied through differential scanning calorimetry (DSC) analysis. The results showed that the peak reaction temperature and activation energy of the ammonium perchlorate-aluminium system were significantly higher than those of the ammonium nitrate-aluminium system. Under the condition of zero oxygen balance, the peak reaction temperature of the ammonium nitrate-aluminium system was 259 °C (heating rate 5 °C/min), and the activation energy was 84.7 kJ/mol. Under the same conditions, the peak reaction temperature and activation energy of the ammonium perchlorate-aluminium system were 292 °C (heating rate 5 °C/min) and 94.9 kJ/mol, respectively. These results indicate that the ammonium perchlorate-aluminium system has higher safety under the same thermal stimulation conditions. Furthermore, research on both non-ideal explosive systems reveals that the activation energy is at its peak under negative oxygen balance conditions, recorded at 104.2 kJ/mol (ammonium perchlorate-aluminium) and 86.2 kJ/mol (ammonium nitrate-aluminium), which indicates a higher degree of safety. Therefore, the investigation into the thermal hazards of non-ideal explosive systems under different oxygen balance conditions is of utmost importance for the enhancement and improvement of safety emergency management practices.
... Note: A recent reassessment of experimentally determined impact sensitivity for a range of common energetic materials has highlighted once more the variability of results depending on method and apparatus (10 J, RDX, and 13 J, NTO, as average over ten trials by Muravyev et al., vs. 3.5 to 7.5 J and 25 to >120 J, respectively, for the BAM tester. 37 It is therefore not surprising that the initiation of synthesis-grade NTO is within the range of the Sheffield drop-weight apparatus (5.5 J, RDX; extrapolated 11 J, NTO, assuming an unchanged curvature of the probability to initiation -impact energy function). ...
Article
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We report the preparation of a co-crystal formed between the energetic molecule 3-nitro-1,2,4-triazol-5-one (NTO) and 4,4'-bipyridine (BIPY), that has been structurally characterised by high-pressure single crystal and neutron powder diffraction data up to 5.93 GPa. No phase transitions or proton transfer were observed up to this pressure. At higher pressures the crystal quality degraded and the X-ray diffraction patterns showed severe twinning, with the appearance of multiple crystalline domains. Computational modelling indicates that the colour changes observed on application of pressure can be attributed to compression of the unit cell that cause heightened band dispersion and band gap narrowing that coincides with a shortening of the BIPY π⋯π stacking distance. Modelling also suggests that the application of pressure induces proton migration along an N-H⋯N intermolecular hydrogen bond. Impact-sensitivity measurements show that the co-crystal is less sensitive to initiation than NTO, whereas computational modelling suggests that the impact sensitivities of NTO and the co-crystal are broadly similar.
... k Detonation pressure. l Ref.62 m Ref. 63 n Ref. 64 o Ref.65 ...
Article
A comparative study of experimentally established structures, stability and energetic performance for ammonium and hydrazinium salts of 4H-[1,2,3]triazolo[4,5-c][1,2,5]oxadiazole (triazolofurazan, TF) as well as its N-oxide and N-nitroimide was performed. The...
... The heat of explosion, oxygen balance, and functional group are highly predictive of explosive handling sensitivity. Based on these correlations, the energy-sensitivity rule is made a consensus in this field, which indicates that it is quite difficult to create more powerful yet safer energetic molecules [4,5]. Indeed, the sensitivity is significantly contributed by the powder properties at the crystal scale. ...
... The heat of explosion, oxygen balance, and functional group are highly predictive of explosive handling sensitivity. Based on these correlations, the energy-sensitivity rule is made a consensus in this field, which indicates that it is quite difficult to create more powerful yet safer energetic molecules [4,5]. Indeed, the sensitivity is significantly contributed by the powder properties at the crystal scale. ...
... An accurate prediction of thermal decomposition temperature (T d ) is still a challenge in the energetic materials (EMs) community, complicating evaluation of the potential industrial and military applications in the design of new compounds [1][2][3][4][5]. Recently, machine learning (ML) technologies have become an area of heightened research interest for quantitative relationships exploration between molecular structure and T d , regardless of the intricate physical and chemical mechanisms involved in the decomposition process [6][7][8][9][10][11][12][13]. ...
... materials (EMs) community, complicating evaluation of the potential industrial and military applications in the design of new compounds. [1][2][3][4][5] Recently, machine learning (ML) technologies have become an area of heightened research interest for quantitative relationships exploration between molecular structure and Td, regardless of the intricate physical and chemical mechanisms involved in the decomposition process. [6][7][8][9][10][11][12][13] In the afore-mentioned works, the selection of descriptors is of paramount importance. ...
... Modern trends in the development of energetics concentrated on contradictory requirements of performance increase and safety improvement. 4,5 First studies of the cocrystallization approach for energetics has already shown a possibility to decrease the mechanical hazards, 6 improve stability, 7 and raise energetic potential. 8 It should be noted that energetic materials are typically crowded molecules enriched with explosophoric functionalities. ...
Article
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Pyrazine 1,4-dioxide (PZDO) is a chemical frequently employed as a coformer in cocrystal design. It has two N-oxide fragments that signify potential hazards, but we found no information about it in prior literature. Therefore, we investigate the thermal behavior, thermochemical properties, and mechanical sensitivity of the title compound. We demonstrate that the material explodes in standard impact tests at a certain drop energy. By the level of its computed energetic potential, PZDO approaches benchmark trinitrotoluene. We screened ten energetic materials for cocrystal formation with PZDO using thermal analysis methods and predicted three novel cocrystals. However, we failed to grow the X-ray quality crystals by the conventional approach due to significantly differing solubility of PZDO and other components in common solvents. Two suitable coarse cocrystals of 3,4-dinitropyrazole/PZDO and 3,5-dinitropyrazole/PZDO were finally prepared by resublimation (vacuum recondensation of preformed comelt), and its X-ray structure is reported. Overall, we characterize PZDO as an energetic material and highlight the potential risks associated with the compound. The preparation of cocrystals via the gas phase route, although laborious, may be effective when the traditional (via solution) approach fails.
... 6 Unfortunately, wide applications of BCHMX are hindered due to its high impact sensitivity (IS ∼ 8 J, similar to that of HMX). 10 Note that the latter fact was attributed to a low N−NO 2 bond dissociation energy, predicted at the B3LYP level of theory to be 159 kJ mol −1 in comparison with its counterparts for RDX (173 kJ mol −1 ) and HMX (186 kJ mol −1 ). 11 In order to cope with sensitivity issues, BCHMX was tested as a component of energetic compositions. ...
Article
Theoretical studies of the decomposition mechanism of energetic materials quite often scrutinize only the primary thermolysis reactions. However, the secondary reactions are crucial, inter alia, for proper building of the combustion models and understanding the autocatalytic processes. In the present study, we applied predictive DLPNO–CCSD(T) calculations to elucidate the kinetics and decomposition mechanism of a novel promising energetic material, 1,3,4,6-tetranitrooctahydroimidazo [4,5-d] imidazole (BCHMX). We identified eight previously unknown BCHMX conformers, both cis and trans in accordance to the spatial position of the H atoms bonded to a carbon bridge. Among them, the relative enthalpies of cis isomers lie in the narrow range ∼10 kJ mol–1 rendering them thermally accessible in the course of decomposition. The radical N–NO2 bond cleavage via one of the novel conformers is the dominant primary decomposition channel of BCHMX with the kinetic parameters Ea = 168.4 kJ mol–1 and log(A, s–1) = 18.5. We also resolved several contradictory assumptions on the mechanism and key intermediates of BCHMX thermolysis. To get a deeper understanding of the decomposition mechanism, we examined a series of unimolecular and bimolecular secondary channels of BCHMX. Among the former reactions, the C–C bond unzipping followed by another radical elimination of a nitro group is the most energetically favorable pathway with an activation barrier ∼113 kJ mol–1. However, contrary to the literature assumptions, the bimolecular H atom abstraction from a pristine BCHMX molecule by a primary nitramine radical product, not the nitro one, followed by another NO2 radical elimination, is the most important bimolecular secondary thermolysis reaction of BCHMX at lower temperatures. The isokinetic temperature of the bimolecular and unimolecular secondary reactions is ∼620 K. Unimolecular reactions might be important in dilute solutions, where bimolecular reactions are suppressed. The secondary reactions considered in the present work might be pertinent in the case of related energetic nitramines (e.g., RDX, HMX, and CL-20).
... However, the presence of reactive nitro functional groups (in B4−B6) reduces the ΔE LUMO−HOMO value and is expected to have less stability than other derivatives. Muravyev et al.70 proposed safety factor (SF) as a new parameter that indicates the mechanical sensitivity of explosives based on their density and the maximum heat of explosion (Q max ) data. ...
... [5][6][7][8][9] One of the most expected outcome in the design of novel high-energy substances is a balance between high detonation performance and acceptable sensitivity to various kinds of impact. 10 For this aim, several synthetic strategies were developed and used to date. One of the promising tools in this regard includes a preparation of nitrogen-rich energy salts. ...
Article
Modeling of the structure of molecules and simulation of crystal structure followed by the calculation of the enthalpies of formation for 21 salts of three high-energy tetrazole 1N-oxides: 5-nitro-1-hydroxy-1H-tetrazole 1a-1g,...
Article
The initial decomposition reactions of 1,3,5-trinitrobenzene (TNB), picric acid (PA), 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitroaniline (TNA) and 2,4,6-trinitrophenylmethylnitramine (Tetryl) were studied using ReaxFF-lg molecular dynamics simulations, and the substituent effect on the thermal decomposition behaviours of nitrobenzene compounds was evaluated through the reactant number, initial decomposition pathway, products and cluster analysis. The results show that the introduction of substituents could promote the decomposition of the reactants, increase the frequency of the nitro-nitrito isomerization reaction and intermolecular H or O atom transfer reaction, and reduce the frequency of the direct nitro dissociation reaction. Notably, these effects were most obvious in the case of TNT. Owing to the introduction of substituents, the number of hydrogen-containing products (HO2N, H2, H2O and NH3) increased. Different functional groups can also lead to variations in the quantities of decomposition products and cluster distribution. The decomposition process of the five nitrobenzenes was examined in detail through the analysis of intermediate products, revealing the distinct influence of the substituent groups. These findings contribute to an enhanced understanding of how different substituent groups influence the energy release mechanisms of energetic compounds.
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A new high-energy compound 5-((1,4-dihydro-5H-tetrazol-5-ylidene)amino)[1,2,3]-triazolo[4,5-c][1,2,5]oxadiazol-5-ium-4-ide was synthesized. It consists of a triazolofurazan core and a tetrazole cycle linked by a nitrogen bridge. Thermal stability of this compound (Tonset = 174 °C) and its dipotassium salt (Tonset = 199 °C) were studied. The structure of the compound was confirmed by X-ray diffraction.
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The design of novel high energy density materials (HEDMs) is still one of the significant challenges in the field of applied chemistry. Newly discovered scaffolds are rare, but they open...
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Novel energetic materials (EM) often combine two intrinsically counter trends, viz., a high energy density and mediocre safety parameters, like thermal stability and sensitivity toward mechanical stimuli. A rational design of promising EMs requires a proper understanding of their thermal stability at both macroscopic and molecular levels. In the present contribution, we studied in detail the thermal stability of 4,4’-dinitro-3,3’-diazenofuroxan (DDF), an ultrahigh-performance energetic material with a reliable experimental detonation velocity being very close to 10 km s-1. To this end, we employed a set of complementary thermoanalytical (DSC and TGA in the solid state along with advanced thermokinetic models, optical microscopy, and gas products detection) and theoretical techniques (DLPNO-CCSD(T) quantum chemical calculations). According to the DSC measurements, the solid-state thermolysis of DDF turned out to be a complex three-step process. The decomposition commences at ~85°C and the most intense heat release occurs at ~130°C depending on the heating rate. In order to proper describe the kinetics of DDF thermolysis beyond the simple Kissinger and Friedman methods, we applied a “top-down” kinetic approach resulting in the formal model comprised of three independent stages. A flexible Kolmogorov-Johnson-Mehl-Avrami-Erofeev equation was applied for the first decomposition stage along with the extended Prout-Tompkins equation for the second and third processes, respectively. The formal exponent in the former equation turned out to be close to a second order, thus suggesting a two-dimensional nuclei-growth model for the first stage. We rationalized this fact with the aid of optical microscopy experiments tracking the changes in the morphology of a solid DDF sample. Then, we complemented the formal macroscopic kinetics with some mechanistic patterns of the primary decomposition channels from quantum chemical calculations. The three reactions involving all important moieties of the DDF molecule turned out to compete very closely: viz., the nitro-nitrite isomerization, radical C(heterocycle)−N(bridge) bond scission and molecular decomposition comprised of the consequent N−O and C−C bond scissions in a furoxane ring. The DLPNO-CCSD(T) activation barriers of all these reactions were close to ~230 kJ mol-1. Most importantly, the calculations provide some mechanistic details missing in thermoanalytical experiment and formal kinetic models. Apart from this, we also determined a mutually consistent set of thermochemical and phase change data for DDF.
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Oxygen balance is a crucial index of energetic materials that indicates the efficiency of redox process during energy release. In this work, a straightforward synthesis including N-amination and azo-coupling oxidative...
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The thermal stability of N-methyl derivatives of 7H-difurasanofuroxanoazepine and 7H-trifurazanoazepine in non-isothermal and isothermal modes has been studied. Formal-kinetic regularities of decomposition and temperature dependences of reaction rate constants have been determined. The thermal stability methyl, propargyl, cyanomethyl, allyl and amine derivatives of azepines is compared.
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The effects of void defect sizes on the hotspot formation and pyrolysis mechanism of high-energy cocrystal 4,40,5,50-tetranitro-2,20-bi-1H-imidazole/ 2,4,6-triamino-5-nitropyrimidine-1,3-dioxide (TNBI/TANPDO) were quantitatively assessed by ReaxFF-lg molecular dynamics simulations. Nano-size defects can...
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Synthetic electrochemistry may establish direct routes to a preparation of a plethora of organic substances, which are hardly accessible by conventional experimental techniques. Herein, we present an electrochemically‐driven method for an assembly of a broad range of rare heterocyclic mesoionic entities –1,2,3‐triazole 1‐imines. These nitrogen heterocycles were prepared through a transition‐metal‐ and exogenous oxidant‐free strategy using a C/Ni electrode pair. Over 30 examples of thus synthesized 1,2,3‐triazole 1‐imines illustrate selectivity and practical utility of this approach. Key solvent‐controlled reactivity patterns for the formation of the triazole imine scaffold were revealed indicating a modulation ability of the developed approach. These experimental findings were additionally justified based on cyclic voltammetry (CV) data and density functional theory (DFT) calculations. Moreover, according to differential scanning calorimetry (DSC) data, some of the prepared 1,2,3‐triazole 1‐imines correspond to the thermally stable species with an onset decomposition temperature up to 190 °C.
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The review is devoted to the key achievements of the Laboratory of Chemistry of Nitro Compounds at the Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences since its founding by Academician of the Russian Academy of Sciences V. A. Tartakovsky in 1971. The main attention is paid to the structural factors affecting the stability of polynitrogen-oxygen systems (PNO systems), design rules for new stabilized PNO systems, and new synthetic methods towards such systems. The synthesis of dinitramide salts, 1,2,3,4-tetrazine 1,3-dioxides, nitro-NNO-azoxy compounds, and other new classes of PNO systems is considered in detail. The advances in synthesis of new types of N-nitroamines are also considered.
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Впервые с помощью метода газовой электронографии (ГЭ) и квантово-химических расчётов исследована структура молекулы 3-циано-4-амино-1,2,5-оксадиазол-2-оксида (3-циано-4-аминофуроксана, ЦАФО) в газовой фазе и найдены равновесные параметры исследуемой молекулы. Проведено сравнение полученных данных с таковыми у родственных соединений, исследованных с помощью газовой электронографии и рентгеноструктурного анализа. Продемонстрировано, что наилучшее согласие с экспериментом получено на уровне теории B3LYP/aug-cc-pVTZ. Полученная информация о молекулярном строении свободного ЦАФО будет полезной для структурных исследований соединений, содержащих фуроксановые фрагменты.
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The determination of impact sensitivity for energetic materials traditionally relies on expensive and safety-challenged experimental means. This has instigated a shift towards scientific computations to gain insights into and predict...
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The sensitivity of energetic materials along different crystal directions is not the same and is anisotropic. In order to explore the difference in friction sensitivity of different surfaces, we calculated the structure, excess energy, surface energy, electronic structure, and the nitro group along (1 1 1), (1 1 0), (1 0 1), (0 1 1), (0 0 1), (0 1 0), and (1 0 0) surfaces of EDNA based on density functional theory. The analysis results showed that relative to other surfaces, the (0 0 1) surface has the shortest N-N average bond length, largest N-N average bond population, smallest excess energy and surface energy, widest band gap, and the largest nitro group charge value, which indicates that the (0 0 1) surface has the lowest friction sensitivity compared to other surfaces. Furthermore, the conclusions obtained by analyzing the excess energy are consistent with the results of the N-N bond length and bond population, band gap, and nitro charge. Therefore, we conclude that the friction sensitivity of different surfaces of EDNA can be evaluated using excess energy.
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Sensitivity is one of the most concerns of explosives but its underlying mechanism remains ambiguous. Here, 2,6-Diamino-3,5- dinitropyrazine -1-oxide (LLM-105) crystals with different morphology, including crosswise, needle, plate, block, diamond and spheric-like shape, were prepared by solution crystallization method and their crystal characteristics and sensitivity were investigated in detail. It is found that the H50 values (impact sensitivity) of LLM-105 vary at a very wide range of 33.8∼112.2 cm and are mainly influenced by particle morphology, crystal integrity, particle surface defects and roughness, but are almost independence of intracrystalline defects and particle sizes. The friction sensitivities of all samples are zero and not affected by crystal characteristics. The G50 values (shock sensitivity) are within a range of 0∼6.9 mm and increasing with decreasing particle sizes and crystal apparent density. Notably, LLM-105 crystals with a spherical shape, good integrity, smooth surface and fewer defects are insensitive to impact and shock impulse. The relationships between the crystal characteristics and sensitivity of LLM-105 are very complex and show some abnormal phenomena,which could be attributed to the crystal packing style and aggregated microstructures of LLM-105.
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In the present work, we studied in detail the thermochemistry, thermal stability, mechanical sensitivity, and detonation performance for 20 nitro-, cyano-, and methyl derivatives of 1,2,5-oxadiazole-2-oxide (furoxan), along with their bis-derivatives. For all species studied, we also determined the reliable values of the gas-phase formation enthalpies using highly accurate multilevel procedures W2-F12 and/or W1-F12 in conjunction with the atomization energy approach and isodesmic reactions with the domain-based local pair natural orbital (DLPNO) modifications of the coupled-cluster techniques. Apart from this, we proposed reliable benchmark values of the formation enthalpies of furoxan and a number of its (azo)bis-derivatives. Additionally, we reported the previously unknown crystal structure of 3-cyano-4-nitrofuroxan. Among the monocyclic compounds, 3-nitro-4-cyclopropyl and dicyano derivatives of furoxan outperformed trinitrotoluene, a benchmark melt-cast explosive, exhibited decent thermal stability (decomposition temperature >200 °C) and insensitivity to mechanical stimuli while having notable volatility and low melting points. In turn, 4,4′-azobis-dicarbamoyl furoxan is proposed as a substitute of pentaerythritol tetranitrate, a benchmark brisant high explosive. Finally, the application prospects of 3,3′-azobis-dinitro furoxan, one of the most powerful energetic materials synthesized up to date, are limited due to the tremendously high mechanical sensitivity of this compound. Overall, the investigated derivatives of furoxan comprise multipurpose green energetic materials, including primary, secondary, melt-cast, low-sensitive explosives, and an energetic liquid.
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The apparent simplicity of the drop-weight apparatus for explosive sensitivity testing hides the reality that it is actually a complex integrated test of both ignition and growth of deflagration. Although the drop-weight test is undeniably a useful screening test for explosive properties, a misunderstanding of the technique’s limitations has blinded many researchers to its limited wider applicability. This monograph discusses how the test actually works, the significant engineering difficulties with standardization between machines, which types of explosives are suited to the test and which are not, and finally offers a few suggestions for alternatives when a more quantified understanding of a material’s response is required for other applications.
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Energetic compounds 1–6, consisting of one or two furazan rings linked by azo or azoxy bridges and one or two nitro‐NNO‐azoxy substituents, were synthesized by nitration of the corresponding tert‐butyl‐NNO‐azoxy precursors with NO2BF4. Novel methods for the synthesis of 3,4‐bis(tert‐butyl‐NNO‐azoxy)furazan (7) and bis‐4,4′‐(tert‐butyl‐NNO‐azoxy)‐3,3′‐azoxyfurazan (21) were elaborated. The nitro‐NNO‐azoxy compounds obtained display high calculated detonation performance (vD=8.07–9.40 km s⁻¹ and PC‐J=27.4–43.4 GPa) that is superior to the corresponding nitrofurazans (DNF, DNAzF, DNAF). The replacement of nitrofurazans with the corresponding (nitro‐NNO‐azoxy)furazans increases the specific impulse of the model solid composite propellant formulations by 2–10 s, which is due to high calculated heats of formation (600–892 kcal kg⁻¹) and positive oxygen balance (0–20 %) of the latter compounds.
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Extensive density functional theory (DFT) calculation and data analysis on molecular and crystal level features of 60 reported energetic materials (EMs) allowed us to define key descriptors that are characteristics of these compounds’ thermostability. We see these descriptors as reminiscent of “Lipinski’s rule of 5”, which revolutionized the design of new orally active pharmaceutical molecules. The proposed descriptors for thermostable EMs are of a type of molecular design, location and type of the weakest bond in the energetic molecule, as well as specific ranges of oxygen balance, crystal packing coefficient, Hirshfeld surface hydrogen bonding, and crystal lattice energy. On this basis, we designed three new thermostable EMs containing bridged, 3,5-dinitropyrazole moieties, HL3, HL7, and HL9, which were synthesized, characterized, and evaluated in small-scale field detonation experiments. The best overall performing compound HL7 exhibited an onset decomposition temperature of 341 °C and has a density of 1.865 g cm–3, and the calculated velocity of detonation and maximum detonation pressure were 8517 m s–1 and 30.6 GPa, respectively. Considering HL7’s impressive safety parameters [impact sensitivity (IS) = 22 J; friction sensitivity (FS) = 352; and electrostatic discharge sensitivity (ESD) = 1.05 J] and the results of small-scale field detonation experiments, the proposed guidelines should further promote the rational design of novel thermostable EMs, suitable for deep well drilling, space exploration, and other high-value defense and civil applications.
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Safety, performance, cost efficient synthesis and toxicity are the most important aspects of modern explosives. Sensitivity measurements are performed in accordance with different protocols all around the world. Sometimes the BAM drop hammer does not accurately reflect the sensitivity of an energetic material, in particular the sensitivity of primary explosives. Therefore, we present here preliminary results obtained using the novel ball drop tester (BIT‐132), manufactured by OZM research, following MIL‐STD‐1751 A (method 1016). The ball drop impact sensitivity tester is a device in which a free‐falling steel ball is dropped onto an unconfined sample, and is expected to produce more realistic results than the currently commonly used BAM method. The results obtained using the probit analysis were compared to those from the BAM drop hammer and friction tester. The following sensitive explosives were investigated: HMTD, TATP, TAT, Tetrazene, MTX‐1, KDNBF, KDNP, K2DNABT, Lead Styphnate Monohydrate, DBX‐1, Nickel(II) Hydrazine Nitrate, Silver Acetylide, AgN3, Pb(N3)2 RD‐1333, AgCNO, and Hg(CNO)2.
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A supercritical antisolvent process has been applied to obtain the nitrocellulose nanoparticles with an average size of 190 nm from the nitrocellulose fibers of 20 μm in diameter. Compared to the micron-sized powder, nano-nitrocellulose is characterized with a slightly lower decomposition onset, however, the friction sensitivity has been improved substantially along with the burning rate increasing from 3.8 to 4.7 mm·s−1 at 2 MPa. Also, the proposed approach allows the production of stable nitrocellulose composites. Thus, the addition of 1 wt.% carbon nanotubes further improves the sensitivity of the nano-nitrocellulose up to the friction-insensitive level. Moreover, the simultaneous introduction of carbon nanotubes and nanosized iron oxide catalyzes the combustion process evidenced by a high-speed filming and resulting in the 20% burning rate increasing at 12 MPa. The presented approach to the processing of energetic nanomaterials based on the supercritical fluid technology opens the way to the production of nitrocellulose-based nanopowders with improved performance.
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A series of highly energetic organic salts comprising a tetrazolylfuroxan anion, explosophoric azido or azo functionalities, and nitrogen‐rich cations were synthesized by simple, efficient, and scalable chemical routes. These energetic materials were fully characterized by IR and multinuclear NMR (¹H, ¹³C, ¹⁴N, ¹⁵N) spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). Additionally, the structure of an energetic salt consisting of an azidotetrazolylfuroxan anion and a 3,6,7‐triamino‐7H‐[1,2,4]triazolo[4,3‐b][1,2,4]triazolium cation was confirmed by single‐crystal X‐ray diffraction. The synthesized compounds exhibit good experimental densities (1.57–1.71 g cm⁻³), very high enthalpies of formation (818–1363 kJ mol⁻¹), and, as a result, excellent detonation performance (detonation velocities 7.54–8.26 kms⁻¹ and detonation pressures 23.4–29.3 GPa). Most of the synthesized energetic salts have moderate sensitivity toward impact and friction, which makes them promising candidates for a variety of energetic applications. At the same time, three compounds have impact sensitivity on the primary explosives level (1.5–2.7 J). These results along with high detonation parameters and high nitrogen contents (66.0–70.2 %) indicate that these three compounds may serve as potential environmentally friendly alternatives to lead‐based primary explosives.
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Simulations of SADT values based on the heat balance of the system are presented for azobisisobutyronitrile (AIBN). These simulations used kinetic parameters obtained from heat flow calorimetry experiments performed at temperatures in the stability range of low-temperature (L-T) polymorph of AIBN. Thermal Activity Monitor (TAM) data were collected in the range of 55–70 °C. The simulated SADT value for L-T AIBN amounts to 46 °C. This is very similar to the computed results obtained in the BAM project (Malow et al., 2015; Roduit et al., 2015; Moukhina, 2015; Kossoy et al., 2015) for the high-temperature (H-T) form of AIBN which amounts to 47 °C and is also in full agreement with the large scale experimentally found SADT of AIBN (47 °C) (Malow et al., 2015). The prerequisites for collecting proper kinetic data for the quasi-AC type energetic materials in which the phase change phenomena (polymorphic transformation or melting) precedes the decomposition are discussed. The apparent paradox when the application of incorrect kinetics applied in narrow α or T ranges may sometimes result in the correct predictions of such safety parameters, such as SADT, is also explained.
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Computers teach themselves to make molecules Chemical reaction databases that are automatically filled from the literature have made the planning of chemical syntheses, whereby target molecules are broken down into smaller and smaller building blocks, vastly easier over the past few decades. However, humans must still search these databases manually to find the best way to make a molecule. This involves many steps and choices. Some degree of automation has been achieved by encoding 'rules' of synthesis into computer programs, but this is time consuming owing to the numerous rules and subtleties involved. Here, Mark Waller and colleagues apply deep neural networks to plan chemical syntheses. They trained an algorithm on essentially every reaction published before 2015 so that it could learn the 'rules' itself and then predict synthetic routes to various small molecules not included in the training set. In blind testing, trained chemists could not distinguish between the solutions found by the algorithm and those taken from the literature.
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High‐nitrogen‐content compounds have attracted great scientific interest and technological importance because of their unique energy content, and they find diverse applications in many fields of science and technology. Understanding of structure–property relationship trends and how to modify them is of paramount importance for their further improvement. Herein, the installation of oxygen‐rich modules, C(NO2)3, C(NO2)2F, or C(NO2)2NF2, into an endothermic framework, that is, the combination of a nitropyrazole unit and tetrazole ring, is used as a way to design novel energetic compounds. Density, oxygen balance, and enthalpy of formation are enhanced by the presence of these oxygen‐containing units. The structures of all compounds were confirmed by XRD. For crystal packing analysis, it is proposed to use new criterion, ΔOED, that can serve as a measure of the tightness of molecular packing upon crystal formation. Overall, the materials show promising detonation and propulsion parameters.
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We present a proof of concept that machine learning techniques can be used to predict the properties of CNOHF energetic molecules from their molecular structures. We focus on a small but diverse dataset consisting of 109 molecular structures spread across ten compound classes. Up until now, candidate molecules for energetic materials have been screened using predictions from expensive quantum simulations and thermochemical codes. We present a comprehensive comparison of machine learning models and several molecular featurization methods - sum over bonds, custom descriptors, Coulomb matrices, Bag of Bonds, and fingerprints. The best featurization was sum over bonds (bond counting), and the best model was kernel ridge regression. Despite having a small data set, we obtain acceptable errors and Pearson correlations for the prediction of detonation pressure, detonation velocity, explosive energy, heat of formation, density, and other properties out of sample. By including another dataset with 309 additional molecules in our training we show how the error can be pushed lower, although the convergence with number of molecules is slow. Our work paves the way for future applications of machine learning in this domain, including automated lead generation and interpreting machine learning models to obtain novel chemical insights.
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The key steps of the synthesis of two high energy compounds, namely, 4-(2,2,2-trinitroethyl)-2,6,8,10,12-pentanitrohexaazaisowurtzitane and 4,10-bis(2,2,2-trinitroethyl)-2,6,8,12-tetranitrohexaazaisowurtzitane, were optimized. Their enthalpy of formation, density, impact and friction sensitivity, and thermal stability were experimentally determined.
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The design of novel energetic materials with improved performance, optimized parameters, and environmental compatibility remains a challenging task. In this study, new high‐energy materials based on isomeric dinitrobi‐1,2,5‐oxadiazole structures comprising nitrofurazan and nitrofuroxan subunits were synthesized. Due to planarity and strong noncovalent interactions, these materials display high density values as determined by single‐crystal X‐ray diffraction. The thermal, impact, and friction sensitivities of both isomers are similar to that of nitroesters. Their high detonation performance along with the combined benefits of high density, high heat of formation, and good oxygen balance make the synthesized compounds promising as explosives and highly‐energetic oxidizers.
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FOX-7, first synthesized two decades ago, is a promising insensitive energetic compound. Enthalpy of formation is among the most important parameters that influence, e.g., the detonation velocity, a crucial performance indicator of an energetic material. Very surprisingly, despite the fact that FOX-7 has been known for almost 20 years, its accurate standard-state (crystalline) formation enthalpy is still a controversy. It has been reported several times (often without any experimental details and primary data) to be ~ -30 – -32 kcal/mol. However, the paper in JCED we comment here proposed the value of ~-49 kcal/mol. Given the fact that all previous studies report the combustion calorimetry values, which are crucially sensitive to purity of the compound and combustion conditions, in the present contribution, we tried to obtain an independent benchmark using complementary methods. We combined easier and more robust techniques: viz., highly accurate quantum chemical computations for the gas phase thermochemistry and mass loss data for enthalpy of sublimation. We carefully estimated the accuracy of both approaches on model systems and finally obtained the value of FOX-7 formation enthalpy to be -28.8 kcal/mol. This raises serious doubts on the results of the paper discussed.
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The nitrogen-rich energetic compound 5-amino-3,4-dinitropyrazole (5-ADP) was investigated using complementary experimental techniques. X-ray diffraction indicates the strong intermolecular hydrogen bonding in 5-ADP crystals. Compound exhibits low impact sensitivity (23 J) and insensitivity to friction. The activation energy of thermolysis determined to be 230±5 kJ mol−1 from DSC measurements. Accelerating rate calorimetry indicates the lower thermal stability (173 °C) of 5-ADP than that of RDX, which is probably the main concern about using this compound. 5-ADP also exhibits good compatibility with common energetic materials (viz. TNT, RDX, ammonium perchlorate), including an active binder. The burning rate of 5-ADP monopropellant is higher than that of benchmark HMX, while the pressure exponent 0.51±0.04 is surprisingly low. Addition of ammonium perchlorate does not affect the pressure exponent of 5-ADP, while the burning rate increases. The 5-amino-3,4-dinitropyrazole exhibits a notable combination of combustion performance, low sensitivity, and good compatibility, which renders it as a promising energetic material.
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Liquid and supercritical CO2 and TFE have been systematically studied as media for CL-20 recrystallization to estimate their potential for the selective preparation of ultrafine particles. It has been found that the polymorphic composition of produced microcrystals can be efficiently controlled by the alteration of the solvent system and the micronization method used. Thus, the application of CO2 as an anti-solvent in both SAS and GAS methods results in the formation of α-CL-20–CO2 solvates, regardless of the process conditions. The use of TFE as an active medium for the GAS and RESS methods allows for selective preparation of uniform ultrafine β- or ε-CL-20 particles under mild conditions. The developed ε-CL-20 production method favorably differs from the known analogues by its tolerance to the quality of the initial substrate (crude CL-20), increased environmental and industrial safety, ease of product isolation, and the ability to control the particle morphology and crystalline phase.
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A smooth synthesis of 4H-[1,2,3]triazolo[4,5-c][1,2,5]oxadiazole 5-oxide 1 and its energetic salts (ammonium, hydroxylammonium, guanidinium, triaminoguanidinium) is reported. The compounds synthesized were characterized by multinuclear nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy, mass spectrometry, elemental analysis, differential scanning calorimetry, single-crystal, and powder X-ray diffraction. All the compounds possess a beneficially high enthalpy of formation (88.9–168.0 kcal·mol–1). These data, in combination with the experimentally determined densities (1.702–1.934 g·cm–1), were used to calculate the detonation pressures (33.9–43.1 GPa) and velocities (8.86–9.31 km·s–1). The majority of the synthesized energetic salts had moderate impact and friction sensitivity, which made them promising candidates for various energy applications, including their use as components of solid composite propellants. It was shown that compounds 1 and 2c–f had higher energetic characteristics as components of solid composite propellants (the specific impulse was higher by 5–10 s) than HMX or CL-20 in propellant formulations.
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A computer simulation of cocrystal structures of [1,2,5]oxadiazolo[3,4-e][1,2,3,4]tetrazine-4,6-dioxide (FTDO) with benzotrifuroxan (BTF) in ratios of (1 : 1), (2 : 1) and (3 : 1) was performed, and their thermodynamic stability and physical–chemical characteristics were calculated. According to calculations, the (3 : 1) cocrystal is thermodynamically most stable. Therefore, it is the most preferable for cocrystallization, and we successfully obtained a cocrystal only for the (3 : 1) ratio. The cocrystal was characterized by X-ray diffraction and vibrational spectroscopy. In the vibrational spectra, some new bands were observed compared with the parent compounds spectra. In addition, some bands of pure FTDO and BTF disappeared, which is typical for a molecular complex formation. The thermal decomposition and sensitivity to impact and friction of the cocrystal were investigated. The impact sensitivity (2.8 J) turned out to be equal to the sensitivity of the less sensitive component (BTF). In addition, the sensitivity to friction (14 N) decreased by three times compared with the highly sensitive FTDO, which is unusual for cocrystals of high-energy compounds. The (3 : 1) cocrystal had a high density of 1.888 (calc.) and 1.865 g cm⁻³ (exp.). The calculated detonation velocity (9.14 km s⁻¹) and Chapman–Jouguet pressure (38.08 GPa) are high, and indicate favorable prospects for using this cocrystal.
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Several energy-rich bifuroxans incorporating nitro and azido functionalities have been synthesized and thoroughly characterized by IR and multinuclear NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction and differential scanning calorimetry. N-oxide regiochemistry was employed to design the tunable azido(nitro)bifuroxans with different physicochemical and energetic properties. All synthesized compounds have high enthalpies of formation (449-777 kJ mol-1) and attractive performance evidenced by high detonation velocity (8.95-9.75 km s-1) and Champan-Jouguet pressure (35-45 GPa). The most powerful energetic material in this series is 4,4’-dinitro-3,3’-bifuroxan. This hydrogen-free molecule (C4N6O8) exhibits an outstanding heat of explosion value of 15.3 kJ cm-1 far exceeding the top energetic material hexanitrohexaazaisowurtzitane CL-20. At the same time, the impact and friction sensitivities of 4,4ʹ-dinitro-3,3ʹ-bifuroxan deemed acceptable for practical use. Overall, 4,4’-dinitro-3,3’-bifuroxan breaks a general trend called “energy-sensitivity rule” representing a linear increase of mechanical sensitivity with a growth of energetic content of the molecule and, thus, offers a great promise for future applications.
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A three-step method was developed for converting both ethoxycarbonylmethyl groups of 4,4'-bis[3-(ethoxycarbonylmethyl)-1Н-1,2,4-triazol-5-yl]azofurazan into fluorodinitromethyl groups, enabling the preparation of the target 4,4'-bis[3-(fluorodinitromethyl)-1Н-1,2,4-triazol-5-yl]azofurazan in 74% overall yield.
Article
Highly efficient design on the levels of molecule and crystal, as well as formulation, is highly desired for accelerating the development of energetic materials (EMs). Sensitivity is one of the most important characteristics of EMs and should be compulsorily considered in the design. However, owing to multiple factors responsible for the sensitivity, it usually undergoes a low predictability. Thus, it becomes urgent to clarify which factors govern the sensitivity and what is the importance of these factors. The present article focuses upon the progress of the molecular and crystal correlations on the sensitivity, and the molecule-based numerical models for sensitivity prediction in the past decades. On the molecular level, composition, geometric structure, electronic structure, energy and reactivity can be correlated with the sensitivity; while the sensitivity can be also related with molecular packing pattern, intermolecular interaction, crystal morphology, crystal size and distribution, crystal surface/interface and crystal defect on the crystal level. And most of these factors, in particle on the crystal level, have been employed as variables in numerical models for predicting sensitivity of categorized EMs. Besides, we stress that more attention should be paid to the sensitivity correlations on the inherent structures of EMs, molecule and crystal packing, because they can be readily dealt by molecular simulations nowadays, facilitating to reveal the physical nature of sensitivity.
Article
High endothermicity is one of the most important factors in the design of high-performance energetic materials for a new generation rocket technologies. Taking this into account, in this work, novel highly energetic cage compounds were synthesized by incorporation of a high-enthalpy N-azidomethyl moiety into the polynitro hexaazaisowurtzitane backbone. All obtaned compounds were fully characterized by high-resolution mass spectrometry, IR and multinuclear NMR (1Н, 13С, 14N, 15N) spectroscopy. For two of them, 4-azidomethyl-2,6,8,10,12-pentanitrohexaazaisowurtzitane and 4,10-bis(azidomethyl)-2,6,8,12-tetranitrohexaazaisowurtzitane, density and structural features were established by X-ray diffractometry. Enthalpies of formation were determined experimentally by combustion calorimetry. Thermal stability measurements and testing to Impact and friction sensitivity were also carried out. The synthesized compounds exhibit a high level of heat resistance (decomposition onset 180–205 °C) and density (1.85–1.93 g∙сm–3). Their enthalpies of formation on a unit of mass (up to 2210 kJ∙kg–1) are the highest among hexaazaisowurtzitane derivatives known and are 2−2.5 times surpass that of CL-20. The combination of these attractive properties makes the new materials promising energetic components in propellant compositions.
Conference Paper
Safety, performance and toxicity are the most important aspects of modern explosives. Sensitivity measurements are carried out in different manners all around the world, often making a comparison of the results difficult. Due to this, we present our first results on the novel ball drop tester (BIT-132), manufactured by OZM research, following MIL-STD-1751A (method 1016). The sensitivity tester is a device, dropping a free-falling steel ball onto an unconfined sample, assumed to produce results more realistic than currently used methods like the BAM drophammer. Eleven common primary explosives such as lead azide, lead styphnate, silver azide, KDNBF, K 2 DNABT, tetrazene and others, as well as the secondary explosives PETN, RDX, TKX-50 and FOX-7 were chosen for evaluation. The results according to the Probit analysis were compared to the energies observed by the BAM drophammer. The differences between the results of both methods as well as advantages and disadvantages are discussed.
Article
Among energetic materials, there is a significant challenge facing researchers to seek an optimal balance between high performance and safety. By combination of furoxan and 1,2,4- oxadiazole backbones and C-NO2 moieties, a promising energetic molecule, bis(4-nitro-1,2,5-oxadiazole-2-oxid-3-yl)-azo-1,2,4-oxadiazole (6) was prepared and characterized by IR, multinuclear NMR spectroscopy, elemental analysis, DSC measurement and single crystal X-ray diffraction. It has a high density (1.92 g cm-3), acceptable thermal stability (182 °C) and high heat of formation (1188.8 kJ mol-1/ 2.8 kJ g-1). The calculated detonation performance (D = 9666 m s-1, P = 42.8 GPa) is comparable to that of CL-20 (9706 m s-1, 45.2 GPa). More importantly, it shows desirable impact and friction sensitivity (IS: 12 J, FS: 180 N), which is less sensitivie than HMX (IS: 7.4 J, FS: 120 N). Furthermore, a detonation test of compound 6 was conducted. The results indicate that compound 6 is more powerful than the commonly used secondary explosive RDX (D = 8795 m s-1, P = 34.9 GPa). The combination of advanced performances and desirable safety make this substance a potential secondary explosive.
Article
Methods for the syntheses of a series of high-energy 4(10)-2-fluoro-2,2-dinitroethyl and 4(10)-2,2-dinitroethyl derivatives of polynitrohexaazaisowurtzitanes were developed. The enthalpy of formation, molecular crystalline density, sensitivity to mechanical impact, and thermal stability were experimentally determined for two compounds.
Article
Thermal stability of energetic materials, being of the utmost importance for safety issues, is often considered in terms of kinetics, e.g., the Arrhenius parameters of the decomposition rate constant. The latter, in turn, are commonly determined using conventional thermoanalytical procedures with the use of simple Kissinger or Ozawa methods for kinetic data processing. However, thermal decomposition of energetic materials typically occurs via numerous exo- and endothermal processes including fast parallel reactions, phase transitions, autocatalysis, etc. This leads to numerous drawbacks of simple approaches. In this paper, we proposed a new methodology for characterization of thermochemistry and thermal stability of melt-cast energetic materials, which is comprised of complementary set of experimental and theoretical techniques in conjunction with a suitable kinetic model. With the aid of the proposed methodology, we studied in detail a novel green oxidizer, tetranitroacetimidic acid (TNAA). The experimental mass loss kinetics in the melt was perfectly fitted with a model comprised of zero-order reaction (sublimation or evaporation) and first-order thermal decomposition of TNAA with the effective Arrhenius parameters Ea = 41.0 ± 0.2 kcal mol-1 and log(A / s-1) = 20.2 ± 0.1. We rationalized the experimental findings on the basis of highly accurate CCSD(T)-F12 quantum chemical calculations. Computations predict that thermolysis of TNAA involves an intricate interplay of multiple decomposition channels of the three tautomers, which are equilibrated via either monomolecular reactions or concerted double hydrogen atom transfer in the H-bonded dimers; the calculated Arrhenius parameters of the effective rate constant coincide well with experiment. Most importantly, calculations provide detailed mechanistic evidence missing in the thermoanalytical experiment and explain formation of the experimentally observed primary products N2O and NO2. Along with kinetics and mechanism of decomposition, the proposed the approach yielding accurate thermochemistry and phase change data of TNAA.
Article
The discovery of novel explosophoric building blocks for the construction of energetic compounds is extremely rare. Here, based on the comparative experimental properties and computational analysis of compounds where nitroaryl backbone bonded with various nitrogen/oxygen-rich groups, it is shown that those compounds that have azasydnone group, possess the highest density, detonation performance and thermal stability than their corresponding nitro, azido and tetrazole-analogs. All of these properties, as well as the oxygen balanced content of the “green” nitrogen rich endothermic unit make it attractive explosophoric building block for the field of energetic materials chemistry.
Article
The key to successfully design high-performance and insensi-tive energetic compounds for practical applications is through adjusting the molecular organization including both fuel and oxidizer. Now a superior hydrogen-free 5/6/5 fused ring energet-ic material, 1,2,9,10-tetranitrodipyrazolo[1,5-d:5',1'-f][1,2,3,4]tetrazine (6) obtained from 4,4',5,5'-tetranitro-2H,2'H-3,3'-bipyrazole (4) by N-amination and N-azo coupling reac-tions is described. The structures of 5 and 6 were confirmed by single crystal X-ray diffraction measurements. Compound 6 has a remarkable room temperature experimental density of 1.955 g cm-3 and shows excellent detonation performance. In addition, it has a high decomposition temperature of 233 oC. These fascinating properties which are comparable to those of CL-20 make it very attractive in high performance applications.
Article
The safety properties of hazardous materials, viz., thermal stability and sensitivity to mechanical stimuli (typically, to impact and friction) are of utmost importance for industrial applications. Direct experimental measurements of these values are demanding in terms of both methodology and experimental effort necessary to meet existing standards. It is therefore very tempting to obtain all these values from a single set of readily available experimental data using simple models and/or empirical correlations. benchmarking of the three approaches proposed b Zhao et al. [1] for estimations of SADT, ignition temperature, and impact sensitivities on various hazardous materials revealed that only the ignition temperature estimations in accordance with Eq. (3) are reasonable. In turn, the Eqs. (2) and (4) miss the impor-tant underlying physical grounds. Their use in evaluation of hazards should be avoided.
Article
A workable cost-efficient synthetic method for the construction of nitro substituted tetrazole-N-aryl/heteroaryl derivatives is discussed here. The energetic functional groups-NO2,-NHNO2 and-N3 are reliably inserted into the molecular backbone, making the tetrazole-N-aryl derivatives highly energetic and insensitive to heat and impact. For example, the tetrazole derivatives 7 and 8, bearing a-NO2 or a-NHNO2 group, exhibit energetic properties close to RDX, but with enhanced insensitivity. Most of the synthesized compounds show exothermic decomposition and are consequently useful for energetic material applications.
Article
[Figure not available: see fulltext.] Regioselective introduction of nitro groups was studied in the case of pyrazoles containing a 1- or 5-tetrazole substituent at position 3(5). All the possible isomeric C-mononitropyrazoles were synthesized. The reduction of these compounds gave the respective 3(5)-amino-5(3)-tetrazolylpyrazoles, which were nitrated to 3(5)-nitramino-4-nitro-5(3)-tetrazolylpyrazoles. The reaction of 1-(nitropyrazol-3(5)-yl)tetrazoles with hydroxylamine-O-sulfonic acid produced the respective N-amino derivatives.
Article
The reaction of 3-amino-5-nitro-1,2,4-triazole with nitrous acid produces the corresponding diazonium salt. When the diazonium salt is treated with nitroacetonitrile, a subsequent condensation and cyclization reaction occurres to produced 4-amino-3,7-dinitrotriazolo-[5,1-c][1,2,4] triazine (DPX-26). X-ray crystallographic analysis shows that the DPX-26 has a density of 1.86 g cm−3, while it is calculated to have a heat of formation of 398.3 kJ mol−1. DPX-26 is predicted to approach the explosive performance of RDX but displays significantly better safety properties. Oxidation of DPX-26 using hypofluorous acid produces 4-amino-3,7-dinitrotriazolo-[5,1-c][1,2,4] triazine 4-oxide (DPX-27), which is also predicted to be a high-performance material with enhanced safety properties.
Article
Thermal decomposition of a novel promising high-performance explosive dihydroxylammonium 5,5’-bistetrazole-1,1’-diolate (TKX-50) was studied using a number of thermal analysis techniques (thermogravimetry, differential scanning calorimetry, and accelerating rate calorimetry, ARC). To obtain more comprehensive insight into kinetics and mechanism of TKX-50 decomposition, a variety of complementary thermoanalytical experiments were performed under various conditions. Non-isothermal and isothermal kinetics were obtained at both atmospheric and low (up to 0.3 Torr) pressures. The gas products of thermolysis were detected in-situ using IR spectroscopy, and the structure of solid-state decomposition products was determined by X-ray diffraction and scanning electron microscopy. Diammonium 5,5’-bistetrazole-1,1’-diolate (ABTOX) was directly identified to be the most important intermediate of the decomposition process. The important role of bistetrazole diol (BTO) in the mechanism of TKX-50 decomposition was also rationalized by thermolysis experiments with the mixtures of TKX-50 and BTO. Several widely used thermoanalytical data processing techniques (Kissinger, isoconversional, formal kinetic approaches, etc.) were independently benchmarked against the ARC data, which are more germane to the real storage and application conditions of energetic materials. Our study revealed that none of the reported before Arrhenius parameters can properly describe the complex two-stage decomposition process of TKX-50. On the contrary, we showed the superior performance of the isoconversional methods combined with isothermal measurements, which yielded the most reliable kinetic parameters of TKX-50 thermolysis. In contrast with existing reports, the thermal stability of TKX-50 was determined in the ARC experiments to be lower than that of hexogen, but close to that of hexanitrohexaazaisowurtzitane (CL-20).
Article
Continuing advances in energetic pyrazole construction foster further its rational use. This work establishes an approach for the first synthesis of nitropyrazole that bear both furazan and trinitromethyl moieties. The approach to the in