Wenquan Zhang

Bis(borano)hypophosphite-based ionic liquids as ultrafast-igniting hypergolic fuels

A family of hydride-rich bis(borano)hypophosphite-based ionic liquids was developed, which showed good water stability at room temperature and unexpected hypergolic reactivity with oxidizers. These ionic fluids have exhibited the shortest ignition delay times so far, demonstrating their application potential as hypergolic fuels or additives in liquid bipropellants.

A promising high-energy-density material

High-energy density materials represent a significant class of advanced materials and have been the focus of energetic materials community. The main challenge in this field is to design and synthesize energetic compounds with a highest possible density and a maximum possible chemical stability. Here we show an energetic compound, [2,2′-bi(1,3,4-oxadiazole)]-5,5′-dinitramide, is synthesized through a two-step reaction from commercially available reagents. It exhibits a surprisingly high density (1.99 g cm−3 at 298 K), poor solubility in water and most organic solvents, decent thermal stability, a positive heat of formation and excellent detonation properties. The solid-state structural features of the synthesized compound are also investigated via X-ray diffraction and several theoretical techniques. The energetic and sensitivity properties of the explosive compound are similar to those of 2, 4, 6, 8, 10, 12-(hexanitrohexaaza)cyclododecane (CL-20), and the developed compound shows a great promise for potential applications as a high-energy density material.High energy density materials are of interest, but density is the limiting factor for many organic compounds. Here the authors show the formation of a high density energetic compound from a two-step reaction between commercially available compounds that exhibit good heat thermal stability and detonation properties.

Super-base-derived hypergolic ionic fuels with remarkably improved thermal stability

Two series of super-base-derived hypergolic ionic liquid materials were synthesized and fully characterized by 1H and 13C NMR, IR spectroscopy, and high resolution mass spectrometry (HRMS). Their physicochemical properties such as thermal properties, density, viscosity, heats of formation, specific impulse, and ignition delay time were intensively characterized or calculated. Among fourteen new organic ionic materials, eleven salts are liquids at room temperature, which all exhibit good stability to heat and expected hypergolic properties upon contact with WFNA. The densities of these ionic compounds range from 1.00 to 1.22 g cm−3, and their heats of formation vary between −38.0 and 478.6 kJ mol−1. Surprisingly, most of these new ionic liquids exhibited an unexpected thermal stability of >280 °C, in which salt 1 gave the Td value of 310 °C, which is superior to those of any known hypergolic ionic liquids. As a new class of hypergolic fuels, these novel ionic liquid materials have some unique advantages compared to traditional propellant fuels like hydrazine and its derivatives, including extremely low vapour pressure, short ID time, high thermal stability, etc., thereby demonstrating their potential applications as green fuels in liquid bipropellant formulations.

Towards Safer Rocket Fuels: Hypergolic Imidazolylidene-Borane Compounds as Replacements for Hydrazine Derivatives

Currently, toxic and volatile hydrazine derivatives are still the main fuel choices for liquid bipropellants, especially in some traditional rocket propulsion systems. Therefore, the search for safer hypergolic fuels as replacements for hydrazine derivatives has been one of the most challenging tasks. In this study, six imidazolylidene-borane compounds with zwitterionic structure have been synthesized and characterized, and their hypergolic reactivity has been studied. As expected, these compounds exhibited fast spontaneous combustion upon contact with white fuming nitric acid (WFNA). Among them, compound 5 showed excellent integrated properties including wide liquid operating range (-70-160 °C), superior loading density (0.99 g cm(-3) ), ultrafast ignition delay times with WFNA (15 ms), and high specific impulse (303.5 s), suggesting promising application potential as safer hypergolic fuels in liquid bipropellant formulations.

Stabilization of the Pentazolate Anion in a Zeolitic Architecture with Na20N60 and Na24N60 Nanocages

The experimental detection and synthesis of pentazole (HN5 ) and its anion (cyclo-N5- ) have been actively pursued for the past hundred years. The synthesis of an aesthetic three-dimensional metal-pentazolate framework (denoted as MPF-1) is presented. It consists of sodium ions and cyclo-N5- anions in which the isolated cyclo-N5- anions are preternaturally stabilized in this inorganic open framework featuring two types of nanocages (Na20 N60 and Na24 N60 ) through strong metal coordination bonds. The compound MPF-1 is indefinitely stable at room temperature and exhibits high thermal stability relative to the reported cyclo-N5- salts. This finding offers a new approach to create metal-pentazolate frameworks (MPFs) and enables the future exploration of interesting pentazole chemistry and also related functional materials.

Nitrato-Functionalized Task-Specific Ionic Liquids as Attractive Hypergolic Rocket Fuels

Hypergolic ionic liquids (HILs) as potential replacements for hydrazine derivatives have attracted increasing interest over the last decade. Previous studies on HILs have mostly concentrated on the anionic innovations of ionic liquids to shorten the ignition delay (ID) time, but little attention has been paid to cationic modifications and their structure-property relationships. In this work, we present a new strategy of cationic functionalization by introducing the energetic nitrato group into the cationic units of HILs. Interestingly, the introduction of oxygen-rich nitrato groups into the cationic structure significantly improved the combustion performance of HILs with larger flame diameters and duration times. The density-specific impulse (ρIsp ) of these novel HILs are all above 279.0 s g cm-3 , much higher than that of UDMH (215.7 s g cm-3 ). In addition, the densities of these HILs are in the range of 1.22-1.39 g cm-3 , which is much higher than that of UDMH (0.79 g cm-3 ), showing their higher loading capacity than hydrazine-derived fuels in a propellant tank. This promising strategy of introducing nitrato groups into the cationic structures has provided a new platform for developing high-performing HILs with improved combustion properties.

Towards N-alkylimidazole-borane-based hypergolic fuels

Over the past few decades, toxic and highly volatile hydrazine derivatives have been the main fuel choices for liquid bipropellants, especially in traditional hypergolic rocket engines. The search for new hypergolic fuels as replacements for hydrazine derivatives is of great interest to researchers. In this study, a series of N-alkylimidazole borane compounds has been synthesized and characterized. Interestingly, these compounds display promising applications as potential hypergolic fuels owing to their excellent physiochemical properties including low melting points, high thermal stability, low viscosities, and unique hypergolic reactivity. Compared with popular hypergolic ionic liquids, the cost-effective and scaling-up advantages of these materials highlight their promising potential as high-performance fuels in liquid bipropellant formulations.

Green primary energetic materials based on N-(3-nitro-1-(trinitromethyl)-1H-1,2,4-triazol-5-yl)nitramide

In this study, a series of high-energy-density materials (1·2H2O–9) based on N-(3-nitro-1-(trinitromethyl)-1,2,4-triazol-5-yl)nitramide were synthesized and structurally characterized using 1H NMR, 13C NMR, IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The crystal results demonstrated that potassium 3-nitro-5-(nitroimino)-1-(trinitromethyl)-1,2,4-triazolate hydrate (2·H2O) exhibits an infinite two-dimensional (2D) metal–organic framework (MOF) containing the coordination group NO2 and metal cation K+. Additionally, this 2D MOF exhibited a high oxygen content (46.41%) and a positive oxygen balance (14.77%). Heats of formation and the detonation properties of the newly prepared compounds were calculated using the Gaussian 09 and EXPLO 5 programs, respectively. Energetic evaluation indicated that these compounds demonstrate good detonation performances, all of which outperform traditional primary explosives mercury fulminate, lead azide, 2-diazo-4,6-dinitrophenol, and in some cases, even exceed the performance of high explosive RDX. Therefore, the high detonation parameters of the compounds enable these potential primary explosives to trigger the whole detonation easily. Furthermore, several attractive properties, such as an excellent density (2.00 g cm−3), an impact sensitivity of 2 J, a friction sensitivity of 32 N, and a low amount of toxic detonation products, make 2·H2O an eco-friendly primary explosive.

Synthesis of 1-(2H-tetrazol-5-yl)-5-nitraminotetrazole and its derivatives from 5-aminotetrazole and cyanogen azide: a promising strategy towards the development of C–N linked bistetrazolate energetic materials

A series of C–N linked bistetrazolate nitramino compounds, i.e., 1-(2H-tetrazol-5-yl)-5-nitraminotetrazole (2) and its energetic salts (3–8), were successfully prepared from readily available 5-aminotetrazole. All new energetic compounds were fully characterized by IR and NMR spectra and elemental analysis, and six of them (1, 3–7) were further determined by single-crystal X-ray diffraction analysis. The nitrogen contents of these energetic bistetrazolate compounds, ranging from 59.3% (3) to 74.8% (7), are much higher than those of the commonly used high explosives such as RDX (N: 37.8%), HMX (N: 37.8%) and CL-20 (N: 38.3%). And theoretical calculations by using the Gaussian 09 program package demonstrate that compounds 1–8 have high positive heats of formation, of which the heats of formation of ammonium salt 4 (3.60 kJ g−1), aminonitroguanidinium 5 (3.11 kJ g−1) and dihydrazinium salt 7 (3.25 kJ g−1) are approximately eight times higher than those of RDX (0.39 kJ g−1) and HMX (0.39 kJ g−1), and four times higher than that of CL-20 (0.83 kJ g−1). The high nitrogen contents and high heats of formation have endowed these energetic compounds with prominent detonation performance. It is noteworthy that compound 7 exhibits an excellent calculated detonation velocity of 9822 m s−1 superior to that of CL-20 (9730 m s−1), while the impact and friction sensitivities of 7 (IS = 8 J, FS = 192 N) are comparable to those of HMX (IS = 7 J, FS = 112 N). The good detonation properties with moderate sensitivities demonstrate that compound 7 is a promising candidate for application as a high-performance energetic material.

Synthesis and Properties of Triaminocyclopropenium Cation Based Ionic Liquids as Hypergolic Fluids

A novel family of hydrophobic triaminocyclopropenium cation based ionic liquids have been synthesized, and their structures and physicochemical properties characterized by NMR and IR spectroscopy, elemental analysis, differential scanning calorimetry, and hypergolic tests. The experimental results showed that all of these ionic liquids exhibited the expected hypergolic reactivity with the oxidizer white fuming nitric acid. Among them, the hypergolic ionic liquid based on the cyanoimidazolylborohydride anion showed excellent integrated properties, including high decomposition temperature (194 °C), high density (0.95 g cm-3 ), moderate viscosity (44 MPa s), ultrafast ignition delay time (6 ms), and high specific impulse (301.9 s); this demonstrates its potential as an environmentally friendly alternative to toxic hydrazine derivatives.