Preparation of the 1-Methylimidazole Borane/Tetrazole System for Hypergolic Fuels

Based on the acid–base neutralization, the (1-methylimidazolium)(tetrazol-1-yl)borane was successfully synthesized by taking advantage of the acidity of the tetrazole and the basicity of the 1-methylimidazole borane complex. Through HRMS, NMR, and FT−IR, the structure of synthetic compounds was characterized in detail. Concerning about the (1-methylimidazolium)(tetrazol-1-yl)borane, it had an ignition−delay time of about 25 ms and a density specific impulse over 351 s·g/cm³, making it a suitable candidate for green hypergolic fuels. Moreover, it also demonstrated that introducing tetrazole into the borane could be an appropriate strategy to adjust the performance of the energy of those borane compounds.

Synthesis of asymmetric [bis(imidazolyl)-BH2]+-cation-based ionic liquids as potential rocket fuels

As potential hypergolic fuels, hypergolic ionic liquids have attracted much attention since their development. Herein, a series of hypergolic ionic liquids based on asymmetric [bis(imidazolyl)-BH2]+ cations were synthesized. The asymmetric structure of these hypergolic ionic liquids was further confirmed by NMR, infrared (IR), and high-resolution mass spectrometry-electron spray ionization (HRMS-ESI). Moreover, these hypergolic ionic liquids possess a high density of over 1.00 g cm-3, a comprehensive liquid range from -60 °C to 20 °C, and a density-specific impulse performance ranging from 305.4 to 357.8 s g cm-3, which is superior to that of unsymmetrical dimethylhydrazine. Remarkably, (1-allyl-1H-imidazol-3-ium-1-yl)(1-methyl-1H-imidazol-3-ium-1-yl) dihydroboronium dicyandiamide had the best ignition-delay time (18 ms), a high density (1.114 g cm-3), and a high value for heat of formation (400 kJ mol-1/1.48 kJ g-1). This work provides the possibility of a promising and green hypergolic fuel as rocket propellant.

Improved photocatalytic efficiency of TiO2 by doping with tungsten and synthesizing in ionic liquid: precise kinetics-mechanism and effect of oxidizing agents

The degradation of nitroaromatics/toxic energetic compounds contaminated water is a major cause of concern. W-doped TiO₂ nanoparticles (NPs) were synthesized in ionic liquid, ethyl methyl imidazolium dicyanamide (EMIM-DCA) by a solvothermal method. The developed NPs were sintered at 500 °C and characterized by UV-Vis-DRS, FT-IR, FE-SEM, XRD, XPS, and BET techniques. The 30-40-nm-sized NPs were subjected to photocatalytic degradation of the toxic energetic compound, tetryl (2,4,6-trinitrophenylmethylnitramine) under UV-Vis light. Various operating parameters such as the effect of concentration of catalyst, pH of feed phase, oxidizing agents, and recycling of catalyst were studied in detail. For the first time, the degradation-mechanism pathway and kinetics of tetryl were evaluated. The degradation products were precisely analyzed by using HPLC, GC-MS, and TOC techniques. The USEPA has prescribed a drinking water limit of 0.02 mg L^-1, and it was found that 0.5 g of 4% W-TiO₂ could totally degrade tetryl (50 mg L^-1) within 8 h. The kinetic rate constant of 4% W-TiO₂ was 0.356 h^-1, whereas pure TiO₂ showed 0.207 h^-1.

Carbon Nanostructures Derived through Hypergolic Reaction of Conductive Polymers with Fuming Nitric Acid at Ambient Conditions

Hypergolic systems rely on organic fuel and a powerful oxidizer that spontaneously ignites upon contact without any external ignition source. Although their main utilization pertains to rocket fuels and propellants, it is only recently that hypergolics has been established from our group as a new general method for the synthesis of different morphologies of carbon nanostructures depending on the hypergolic pair (organic fuel-oxidizer). In search of new pairs, the hypergolic mixture described here contains polyaniline as the organic source of carbon and fuming nitric acid as strong oxidizer. Specifically, the two reagents react rapidly and spontaneously upon contact at ambient conditions to afford carbon nanosheets. Further liquid-phase exfoliation of the nanosheets in dimethylformamide results in dispersed single layers exhibiting strong Tyndall effect. The method can be extended to other conductive polymers, such as polythiophene and polypyrrole, leading to the formation of different type carbon nanostructures (e.g., photolumincent carbon dots). Apart from being a new synthesis pathway towards carbon nanomaterials and a new type of reaction for conductive polymers, the present hypergolic pairs also provide a novel set of rocket bipropellants based on conductive polymers.

Review of State-of-the-Art Green Monopropellants: For Propulsion Systems Analysts and Designers

Current research trends have advanced the use of “green propellants” on a wide scale for spacecraft in various space missions; mainly for environmental sustainability and safety concerns. Small satellites, particularly micro and nanosatellites, evolved from passive planetary-orbiting to being able to perform active orbital operations that may require high-thrust impulsive capabilities. Thus, onboard primary and auxiliary propulsion systems capable of performing such orbital operations are required. Novelty in primary propulsion systems design calls for specific attention to miniaturization, which can be achieved, along the above-mentioned orbital transfer capabilities, by utilizing green monopropellants due to their relative high performance together with simplicity, and better storability when compared to gaseous and bi-propellants, especially for miniaturized systems. Owing to the ongoing rapid research activities in the green-propulsion field, it was necessary to extensively study and collect various data of green monopropellants properties and performance that would further assist analysts and designers in the research and development of liquid propulsion systems. This review traces the history and origins of green monopropellants and after intensive study of physicochemical properties of such propellants it was possible to classify green monopropellants to three main classes: Energetic Ionic Liquids (EILs), Liquid NOx Monopropellants, and Hydrogen Peroxide Aqueous Solutions (HPAS). Further, the tabulated data and performance comparisons will provide substantial assistance in using analysis tools—such as: Rocket Propulsion Analysis (RPA) and NASA CEA—for engineers and scientists dealing with chemical propulsion systems analysis and design. Some applications of green monopropellants were discussed through different propulsion systems configurations such as: multi-mode, dual mode, and combined chemical–electric propulsion. Although the in-space demonstrated EILs (i.e., AF-M315E and LMP-103S) are widely proposed and utilized in many space applications, the investigation transpired that NOx fuel blends possess the highest performance, while HPAS yield the lowest performance even compared to hydrazine.

Model development and design criteria of hypergolic imidazolium ionic liquids from ignition delay time and viscosity viewpoints

The relationships between ID time, viscosity and molecular structure of hypergolic imidazolium ILs are discussed to specify ideal structural characteristics.

Synthesis and Properties of Azide-Functionalized Ionic Liquids as Attractive Hypergolic Fuels

Hypergolic ionic liquids (ILs) have shown a great promise as viable replacements for toxic and volatile hydrazine derivatives used as propellant fuels, and hence, have attracted increasing interest over the last decade. To take advantage of the reactivity and high energy density of the azido group, a family of low-cost and easily prepared azide-functionalized cation-based ILs, including fuel-rich anions, such as nitrate, dicyanamide, and nitrocyanamide anions, were synthesized and characterized. All the dicyanamide- and nitrocyanamide-based ILs exhibited spontaneous combustion upon contact with 100 % HNO₃ . The densities of these hypergolic ILs varied in the range 1.11-1.29 g cm^-3 , and the density-specific impulse, predicted based on Gaussian 09 calculations, was between 289.9 and 344.9 s g cm^-3 . The values of these two key physical properties are much higher than those of unsymmetrical dimethylhydrazine (UDMH). Among the studied compounds, compound IL-3b, that is, 1-(2-azidoethyl)-1-methylpyrrolidin-1-ium dicyanamide, shows excellent integrated properties including the lowest viscosity (30.9 M Pa s), wide liquid operating range (-70 to 205 °C), shortest ignition-delay time (7 ms) with 100 % HNO₃ , and superior density specific impulse (302.5 s g cm^-3 ), suggesting promising applications with potential as bipropellant formulations.

Rational Design and Facile Synthesis of Boranophosphate Ionic Liquids as Hypergolic Rocket Fuels

The design and synthesis of new hypergolic ionic liquids (HILs) as replacements for toxic hydrazine derivatives have been the focus of current academic research in the field of liquid bipropellant fuels. In most cases, however, the requirements of excellent ignition performances, good hydrolytic stabilities, and low synthetic costs are often contradictory, which makes the development of high-performance HILs an enormous challenge. Here, we show how a fuel-rich boranophosphate ion was rationally designed and used to synthesize a series of high-performance HILs with excellent comprehensive properties. In the design strategy, we introduced the {BH₃ } moiety into the boranophosphate ion for improving the self-ignition property, whereas the complexation of boron and phosphite was used to improve the hydrolytic activity of the borohydride species. As a result, these boranophosphate HILs exhibited wide liquid operating ranges (>220 °C), high densities (1.00-1.10 g cm^-3 ), good hydrolytic stabilities, and short ignition delay times (2.3-9.7 milliseconds) with white fuming nitric acid (WFNA) as the oxidizer. More importantly, these boranophosphate HILs could be readily prepared in high yields from commercial phosphite esters, avoiding complex and time-consuming synthetic routes. This work offers an effective strategy of designing boranophosphate HILs towards safer and greener hypergolic fuels for liquid bipropellant applications.

Piperidinium ionic liquids as electrolyte solvents for sustained high temperature supercapacitor operation

A supercapacitor with a piperidinium ionic liquid and an LiTFSI electrolyte operates for 10 000+ cycles at 100 °C.

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 (ρI_sp ) 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.

Theoretical performance evaluation of hypergolic ionic liquid fuels with storable oxidizers

The density specific impulse of 14 hypergolic ionic liquids with various oxidizers has been theoretically evaluated and found to be higher than the conventional fuel, UDMH.

Cyanotetrazolylborohydride (CTB) anion-based ionic liquids with low viscosity and high energy capacity as ultrafast-igniting hypergolic fuels

Hypergolic CTB-based ionic liquids exhibited remarkable low viscosity, high density, and ultra-short IDs (as short as 1.4 ms).