Positive Oxygen Balance Research Articles

Benzofuroxan‐Based Energetic Materials with Alternating Nitro and Hydroxyl Groups: Synthesis, Characterization, and Energetic Properties

AbstractDue to its good stability, density and oxygen balance, the benzofuroxan fused ring framework has attracted particular attention in the field of high energy density materials. The planar structure of the benzofuroxan facilitates the straightforward derivatization with explosophores and contributes to molecular stability. In this work, a benzofuroxan scaffold was utilized to develop a highly dense energetic material, namely 5,7‐dihydroxy‐4,6‐dinitrobenzo[c][1,2,5]oxadiazole 1‐oxide (DHDNBF). The successive inclusion of explosophores like nitro (−NO2) and oxidative functionality like hydroxyl (−OH) on benzofuroxan resulted in an impressive density (ρ=1.91 g cm−3) and a positive oxygen balance (6.20 %) in DHDNBF (2). Furthermore, the hydroxy groups on DHDNBF enable the formation of dicationic energetic salts 3–7, contributing to additional modifications in the overall performance. Energetic salts 3, 4, and 5 exhibit significantly higher densities ranging from 1.84 (5) to 1.87 (3) g cm−3 and possess a favorable oxygen balance approaching zero or equal to zero. A marked improvement in thermal stabilities was observed in all the energetic salts (3–7) compared to their neutral counterparts, DHDNBF. Energetic salts 4 (Dv=8459 m s−1, P=32.10 GPa) and 5 (Dv=8539 m s−1, P=30.37 GPa) possess good energetic performance, comparable to that of well‐known explosives such as LLM‐105 (Dv=8560 m s−1, P=33.4 GPa). Overall, the favorable characteristics of energetic salts 4 and 5 make them potential candidates for use as benzofuroxan‐based secondary and primary explosives, respectively, in various military and civilian applications.

Study on Oxygen Balance Regulation of TKX‐50 Based on Emulsion Method

AbstractDuring the process of external work, the energy of the negative oxygen balanced 5,5′‐Bi‐tetrazolium‐1,1′dioxyhydroxylammonium salt (TKX‐50) is not fully released, resulting in low energy utilization efficiency and the generation of harmful gases that pollute the environment. Based on this, in order to adjust the oxygen balance of TKX‐50, nano TKX‐50/AP composites with positive, zero and negative oxygen balance were prepared by emulsion method. The morphology of nano TKX‐50/AP composite was similar to that of hedgehog‐like spherical‐like particles, with many dense pores formed on the surface, and the average particle size was about 30 μm. During the composite process, part of TKX‐50 reacted with AP to form 5,5′‐bistetrazole‐1,1′dioxidamide (ABTOX). The first thermal decomposition peak temperature of zero‐oxygen balance TKX‐50/AP composite was 236.0°C, which was slightly reduced compared with that of TKX‐50. The second thermal decomposition peak temperature was 275.1°C, which was 22.2°C higher than that of TKX‐50. The heat release of zero‐oxygen balance TKX‐50/AP composite reached 2206 J g−1, which increased by 35.9% compared to TKX‐50, and the energy utilization efficiency was also greatly improved. The drop height of 50% explosion probability (H50) of zero‐oxygen balance TKX‐50/AP composite was 63.5 cm, and the explosion probability of friction sensitivity was 72%. Compared with TKX‐50, it increased by 15.1 cm and decreased by 28%, respectively. The results showed that the mechanical safety performance of TKX‐50 had been improved.

First Alliance of Pyrazole and Furoxan Leading to High-Performance Energetic Materials.

Nitrogen heterocyclic scaffolds retain their leading position as valuable building blocks in material science, particularly for the design of small-molecule energetic materials. However, the search for more balanced combinations of directly linked heterocyclic cores is far from being exhausted and aims to reach ideally balanced high-energy substances. Herein, we present the synthetic route to novel pyrazole-furoxan framework enriched with nitro groups and demonstrate a promising set of properties, viz., good thermal stability, acceptable mechanical sensitivity, and high detonation performance. In-depth crystal analysis showed that the isomers having lower-impact sensitivity values in both types of regioisomeric pairs are those with the exocyclic furoxan oxygen atom being closer to the pyrazole ring. Owing to the favorable combination of high crystal densities (1.83-1.93 g cm-3), positive oxygen balance to CO (up to +13.9%), and high enthalpies of formation (322-435 kJ mol-1), the synthesized compounds show high calculated detonation velocities (8.4-9.1 km s-1) and excellent metal accelerating abilities. The incorporation of the 3-nitrofuroxan moiety increases the thermal stability (by ca. 20 °C) and decreases the mechanical sensitivity of target hybrid materials in both types of regioisomeric pairs. Simultaneously, the detonation performance of 3-nitrofuroxans is almost identical to that of 4-nitrofuroxans, highlighting the potential of the regioisomeric tunability in the future design of energetic materials.

Polynitro-1,2,4-triazole Energetic Materials with N-Amino Functionalization.

Trinitromethyl and N-amino groups were innovatively incorporated into the framework of 1,2,4-triazole, resulting in 1-amino-5-nitro-3-(trinitromethyl)-1,2,4-triazole (2). Ammonium and hydrazinium salts of 1-amino-5-nitro-3-(dinitromethyl)-1,2,4-triazole were synthesized by acidification, extraction, and neutralization with bases from the potassium salt. All of the newly prepared energetic compounds were comprehensively characterized by using infrared spectroscopy, elemental analysis, nuclear magnetic resonance spectroscopy, and single crystal X-ray diffraction. Compound 2 exhibits favorable properties such as positive oxygen balance (OBCO2 = 5.8%), high density (1.88 g cm-1), good detonation performances (vD = 8937 m s-1, P = 35.5 GPa), and appropriate friction sensitivity (FS = 144 N). The potassium salt 3 demonstrates good thermal decomposition temperature (181 °C) and high density (1.98 g cm-1), while the ammonium salt and hydrazinium salt also display good thermal decomposition temperatures of 183 and 176 °C, respectively. Among these compounds, the ammonium salt exhibits the lowest mechanical sensitivities (FS = 144 N, IS = 6 J).

Acceleration Ability of Mixtures of Explosives with a Positive and Negative Oxygen Balance

Acceleration Ability of Mixtures of Explosives with a Positive and Negative Oxygen Balance

Theoretical study of a series of 1,2-diazete based trinitromethyl derivatives as potential energetic compounds.

Explosive properties of novel potential high energy density materials of a series of 1,2-diazete-based molecules with trinitromethyl functional group were investigated computationally. All the sixty seven molecules were optimised to obtain their molecular geometries and electronic structures. Electrostatic potential analysis was also carried out in the determination of different parameters. The calculations indicate that the majority of the compounds have high positive heat of formations, high density and good detonation performance greater than that of traditional energetic materials like RDX and HMX. They are also having comparable values of impact sensitivity. These features promise their potential to be used as energetic materials for future applications. Most of the designed molecules are having high positive oxygen balance values so that the study of these molecules can also be extended as potential candidates for oxidisers in solid propellants. Optimisation and vibrational frequency analysis of the studied molecules were done with density functional theory using B3LYP/aug-cc-pVDZ as the basis set to zero imaginary frequencies using Gaussian 09. Electrostatic potential analysis were carried using the Multiwfn program.

Trinitroethyl hydrazides of dicarbonic acids – Energetic compounds with high oxygen and nitrogen content

AbstractMany currently used energetic materials need to be replaced with new compounds due to toxicity or other drawbacks. Among these is the oxidizer ammonium perchlorate, often used in solid state propellants, which itself, as well as its combustion products, poses health and environmental issues. Herein, three new polynitro energetic compounds are presented containing trinitroethyl moieties. Starting from easily available starting materials, such as malonic acid ethylester, diglycolic and diaminodiacetic acid, simple and straightforward syntheses were performed to obtain first the corresponding hydrazides and subsequently the trinitroethyl hydrazides in good yields and high purity. These compounds have a positive oxygen balance (assuming to the formation of CO), a high oxygen and nitrogen content and moderate densities. Full characterization was performed by NMR spectroscopy, vibrational analysis and elemental analysis. By using the Gaussian program package, the heats of formation were calculated and the energetic parameters were estimated utilizing the EXPLO5 computer code.

Pushing the Limit of Oxygen Balance on a Benzofuroxan Framework: K2DNDP as an Extremely Dense and Thermally Stable Material as a Substitute for Lead Azide.

Because of environmental and health impacts, there is an ongoing necessity to develop sustainable primary explosives to replace existing lead-based analogues. Now we describe a potential primary explosive, dipotassium 4,6-dinitro-5,7-dioxidobenzo[c][1,2,5]oxadiazole 1-oxide (K2DNDP), which exhibits an excellent thermal stability (Tdec = 281 °C), positive oxygen balance (+4.79%), and a calculated crystal density of ρ = 2.274 g cm-3 at 100 K. Its physicochemical properties concomitantly with its straightforward synthesis make it a potential replacement for lead-based initiators.

Influence of the Nano-Iron Oxide Adsorption-Enhanced Microstructured Charcoal Additives on the ANFO’s Properties

The article presents the results of the third research stage on the potential microstructured charcoal additives in ANFO. The charcoal powder was liquid adsorption-treated with Fe in various ratios. Adding MC-Fe to ANFO changed the exothermic peak’s position from ca. 280 °C to 250 °C due to lower activation energy, which influenced the kinetics of the reaction. Bruceton’s test indicated that the MC-Fe addition to ANFO resulted in ca. 10% lower initiation energy in comparison with pure ANFO. However, the energy level did not influence the potential applicability of the additives. The fumes analysis indicated a lower concentration of CO for all tested samples; however, the concentration of NOx rose. The thermodynamic calculations confirmed the experimental results, which could be explained by the increased positive oxygen balance. Moreover, all analyses showed that the most promising blasting properties referred to the ANFO sample containing the microstructured charcoal additive of a C:Fe ratio of 4:1. Therefore, further research will be dedicated to advanced studies between the chemical composition of this specific ANFO sample and its physicochemical and blasting properties.

Perchlorate-Free Energetic Oxidizers Enabled by Ionic Cocrystallization.

The search for a suitable replacement for the ubiquitous oxidizer ammonium perchlorate (AP) is a top priority to enable more sustainable solid rocket motors. The oxidizing salts ammonium nitrate (AN) and ammonium dinitramide (ADN) are regarded as potential green replacements for AP, but suffer from a plethora of handling and processing issues including poor stability and a needle-like crystal morphology which inhibits dense packing; these prevent their widespread use. In the present work, ionic cocrystallization is leveraged to produce the first cocrystals of these oxidizing salts with an energetic coformer and the first such cocrystals to maintain a positive oxygen balance. The azole-based energetic molecule 5,5'-dinitro-2H,2H'-3,3″-bi-1,2,4-triazole (DNBT) is successfully cocrystallized with AN to yield the cocrystal 2AN:DNBT. Differential scanning calorimetry data confirms that AN, which in its pure form suffers from a problematic solid-state phase transition, is stabilized in the cocrystal. Application of this cocrystallization strategy to ADN produces 2ADN:DNBT, which has the highest oxygen balance of any organic cocrystal.

Microplastic pollution associated with reduced respiration in seagrass (Zostera marina L.) and associated epiphytes

Seagrasses provide crucial ecosystem services of relevance for the marine environment. However, anthropogenic activities are causing global seagrass decline. Increasing microplastic (MP) concentrations have been recognized as a novel threat to many marine organisms, but their effects on marine plants remain underexplored. Here, we investigate the effects of microplastic (polyethylene (PE) and polypropylene (PP)) exposure on the photosynthesis and respiration of the seagrass Zostera marina L. and its associated epiphytes. Measurements were conducted on seagrass leaves with and without epiphyte cover, as well as on epiphytes scraped off the leaf surface. Net gas exchange and pH drift measurements were used to determine rates of photosynthesis and respiration, as well as the ability of leaves and epiphytes to utilize bicarbonate. In addition, variable chlorophyll fluorescence imaging was employed to quantify the photosynthetic capacity of seagrass leaves. Our results show a limited effect of short-term (14 days) microplastic exposure on seagrass leaves and their associated epiphytes, although the photosynthetic activity and respiration rates were gradually reduced for bare seagrass leaves with increasing microplastic concentrations (25-1000 mg MP L-1). A >50% reduction in dark respiration of bare leaves was found at the highest MP exposure, while respiration rates of leaves with epiphytes and separated epiphytes were reduced by maximally ~45 and 30% upon MP exposure, respectively. Short-term microplastic exposure did not alter i) the ability to utilize bicarbonate, ii) the maximum quantum yield of PSII (FV/FM), nor iii) the light utilization efficiency of Z. marina leaves and associated epiphytes. The compensation irradiance decreased for all investigated specimens, and seagrass leaves (with and without epiphytes) were able to retain a positive net oxygen balance throughout all treatments. We speculate that the observed decrease in photosynthetic activity and respiration was caused by leachates from microplastics. Our findings thus indicate that seagrass Z. marina largely possess resilience toward microplastic pollution at its current level.

Linear furoxan assemblies incorporating nitrobifuroxan scaffold: En route to new high-performance energetic materials

Energetic materials science is undergoing a global renaissance aiming to reach an ideal combination between reliable synthetic strategies, high performance and acceptable molecular stabilities. In this work, design and synthesis of novel energetic non-hydrogen furoxan assemblies has been successfully realized. Fine tunability of molecular composition in a series of furoxan-based materials was achieved by the variation of a number of heterocyclic rings and employing N-oxide regioisomerism strategy. Using this approach, advanced energetic regioisomeric azo-bridged bifuroxan assemblies 6 and 7 as well as 3,4′-dinitro-3′,4-bifuroxan 8 with the excellent overall performance were synthesized. Calculations of Hirshfeld surfaces and molecular electrostatic potentials were conducted to better understand the relationship between the molecular structure and mechanical sensitivity in the synthesized series of energetic materials. It was found, that the supramolecular aggregation of 3,4′-dinitro-3′,4-bifuroxan 8 molecules in crystal is more anisotropic that is commonly believed to be more favorable pattern for the low sensitive substances. All target materials have high densities (1.88–1.95 g cm−3), acceptable thermal stabilities (up to 165 °C), high enthalpies of formation (1.6–2.4 kJ g−1) and positive oxygen balance to CO (up to + 25%). As a result, these compounds exhibit high detonation velocities (9.1–9.5 km s−1), excellent heats of explosion (6.6–7.2 kJ g−1) and combustion performance (Isp = 269–281 s). Therefore, these furoxan-based advanced energetic materials unveil new opportunities in search of next-generation functional organic materials for various applications.

Energetic Coordination Polymers Based on Copper Furazans and 1,2,3-Triazoles: Tuning the Oxygen Balance with Nitramino Functionalities

Four novel energetic complexes comprising furazan/nitramino groups were synthesized through a simple hydrothermal method. Owing to the introduction of an oxygen-containing nitramino group, Cu(DNAF)(NH3)3 (ECP-1), Cu(DNAF)(H2O)3 (ECP-2), Cu(ANFZ)2(H2O)5 (ECP-3), and Cu2(TA)2(H2O)6 (ECP-4) (DNAF = 4,5-dinitraminofurazan, ANFZ = 4-amino-3-nitraminofurazan, TA = 5-nitro-4-nitramino-1,2,3-triazole) possess relatively high oxygen contents and oxygen balance, indicating efficient energy release during the self-sustained redox process. In addition, these energetic coordination polymers (ECPs) possess exceptional crystal density and insensitivity to external stimuli. Compared to the energetic complexes reported previously, the oxygen balance and contents of nitrogen and oxygen atoms of ECP-1–ECP-4 remain at a relatively higher level (OB > −20%, N+O% > 60%), ECP-2 and ECP-4 have excellent positive oxygen balance (10.5% and 5.5%, respectively), and ECP-4 has the highest density (2.22 g/cm3) among these four coordination polymers.

Characterization of Electrospinning Prepared Nitrocellulose (NC)-Ammonium Dinitramide (ADN)-Based Composite Fibers.

Nanoscale composite energetic materials (CEMs) based on oxidizer and fuel have potential advantages in energy adjustment and regulation through oxygen balance (OB) change. The micro- and nanosized fibers based on nano nitrocellulose (NC)-ammonium dinitramide (ADN) were prepared by the electrospinning technique, and the morphology, thermal stability, combustion behaviors, and mechanical sensitivity of the fibers were characterized by means of scanning electron microscope (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), gas pressure measurement of thermostatic decomposition, laser ignition, and sensitivity tests. The results showed that the prepared fibers with fluffy 3D macrostructure were constructed by the overlap of micro/nanofibers with the energetic particles embedded in the NC matrix. The first exothermic peak temperature (Tp) of the samples containing ADN decreased by 10.1 °C at most compared to that of ADN, and the pressure rise time of all the samples containing ADN moved forward compared to that of the sample containing NC only. Furthermore, ADN can decrease the ignition delay time of NC-based fibers under atmosphere at room temperature from 33 ms to 9 ms and can enhance the burning intensity of NC-based fibers under normal pressure. In addition, compared to the single high explosive CL-20 or RDX, the mechanical sensitivities of the composite materials containing high explosive CL-20 or RDX were much decreased. The positive oxygen balance of ADN and the intensive interactions between ADN and NC can reduce the ignition delay time and promote the burning reaction intensity of NC-based composite fibers, while the mechanical sensitivities of composite fibers could be improved.

Trinitromethyl-triazolone (TNMTO): a highly dense oxidizer.

A scalable synthesis of 5-(trinitromethyl)-2,4-dihydro-3H-1,2,4-triazol-3-one (TNMTO) is possible from commercially available 2-methylpyrimidine-4,6-diol. It exhibits high density (1.90 g cm-3) with comparably low thermal stability (Td = 80 °C) and positive oxygen balance (OBco = 20.51%, OBCO2 = 0.0%). TNMTO has an attractive combination of detonation properties (P = 35.01 GPa, D = 8997 ms-1) and propulsive properties (Isp(neat) = 251.85 s, ρIsp(neat) = 478.52 gs cm-3, ). These are superior to ammonium dinitroamide (ADN), 2,2,2-tetranitroacetimidic acid (TNAA) and ammonium perchlorate (AP), making it a potential green oxidizer in solid rocket propulsion.

Bis-(2-difluoroamino-2,2-dinitroethyl)nitramine – Energetic oxidizer and high explosive

• Bis-(2-difluoramino-2,2-dinitroethyl)nitramine ( 1 ) is synthesized. • 1 has a very high density of 2.032 g cm −3 at 298 K. • Thermochemical and kinetic data is reported. • Specific impulse is improved over standard AP-based formulations. • 1 reaches the detonation performance level of landmark CL-20. There is an urgent demand for novel energetic materials with improved performance to serve as oxygen suppliers (oxidizers) and high-energy additives. Synthesis and characterization of compound that combines both of the above roles, bis-(2-difluoroamino-2,2-dinitroethyl)nitramine ( 1 ), is reported. 1 was synthesized by difluoroamination of bis(2,2-dinitroethyl)nitramine in good yield. The analysis of X-ray diffraction data shows that NF 2 -groups has a significant contribution into a very high density of 1 , 2.032 g cm −3 at 298 K. The positive oxygen balance (+8%) makes it an attractive oxidizer, the rocket specific impulse is improved to 277 s vs 265 s for standard ammonium perchlorate-based formulation. Furthermore, the detonation performance of 1 reaches the level of most powerful explosive, CL-20. As a way to tune the melt-casting temperature and decrease the high friction sensitivity of 1 , its eutectics with trinitrotoluene were proposed.

Enhancement of Energetic Performance through the Construction of Trinitromethyl Substituted β-Bis(1,2,4-oxadiazole).

Halogen-free substitutions of ammonium perchlorate (AP), which meet the requirements of high density, high performance, and acceptable stability, have been a subject of scientific research for many years. In this work, by regrouping atoms in trinitromethyl substituted bis(1,2,4-oxadiazole), a novel oxidizer, trinitromethyl substituted β-bis(1,2,4-oxadiazole) (3), was designed and synthesized. It possesses an improved density (ρ = 2.002 g cm-3 at 170 K, ρ = 1.942 g cm-3 at 298 K) and thermal stability (Td = 142.8 °C) in comparison to its regioisomer 5,5'-bis(trinitromethyl)-3,3'-bi(1,2,4-oxadiazole) (E). The properties for 3 were studied by both experimental and theoretical methods. The high positive oxygen balance of +7.3% and high specific impulse of 250 s also make compound 3 a promising candidate for an energetic oxidizer.

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

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

Renaissance of dinitroazetidine: novel hybrid energetic boosters and oxidizers.

Nitrogen-oxygen organic materials constitute an important family of multipurpose high-energy materials. However, the preparation of energetic boosters and oxidizers for various civil and space technologies remains a challenging task and such materials usually require special precautions and fine tunability of their functional properties. To find a balance between energy and safety while retaining the oxidizing ability of target energetic materials, novel hybrid organic compounds comprising furoxan and 3,3-dinitroazetidine scaffolds enriched with additional nitro groups were synthesized. The prepared 3-(3,3-dinitroazetidinoyl)-4-nitrofuroxan and 3,3-dinitro-1-(2,2,2-trinitroethyl)azetidine have high nitrogen-oxygen contents (75-79%), positive oxygen balance to CO (up to +10.3%) and good experimental densities (1.75-1.80 g cm-3). A combination of superior detonation performance (D = 8.3-8.5 km s-1 and P = 32-33 GPa) and moderate mechanical sensitivity enables the application potential of these energetic materials as booster explosives or oxidizers. Additionally, their functional properties remain essentially competitive with other oxygen-rich energetic materials (pentaerythritol tetranitrate, ammonium dinitramide, and tetranitratoethane). Hirshfeld surface calculations supported by energy framework plots were also performed to better understand the relationship between the molecular structure and stability/sensitivity. This work unveils novel directions in the construction of balanced energetic boosters and oxidizers for various applications.

Detonation properties and impact sensitivities of trinitromethane derivatives of three-membered heterocyclic ring compounds

We have carried out the design and theoretical investigation of a series of trinitromethane derivatives of three-membered heterocyclic ring compounds – aziridine, 1H-azirine, diaziridine, 1H-diazirine, triaziridine, 1H-triazirene, oxaziridine, oxadiaziridine, dioxaziridine, oxirane, and dioxirane – in search for new high energy density materials (HEDM). We have estimated the properties relevant to HEDMs of the proposed molecules using Density Functional Theory (B3LYP/aug-cc-pVDZ). The results show that most of the molecules have a high value of solid-phase heat of formation, crystal density, detonation velocity and pressure with satisfying values for impact sensitivities. We have identified some of these molecules, 1-(triinitromethyl)diaziridine, 2-(trinitromethyl)-1-nitro-1H-azirine, and (2-(trinitromethyl)-3-nitrooxirane) are potential candidates of energetic molecules among the 60 molecules we investigated. As most of them are having a high positive oxygen balance, they can be recommended for use as oxidisers in solid propellants.