Replacement of Toxic Hydrazines in Satellite Propulsion with Greener Dinitramide-Based Energetic Ionic Liquid Candidates.

Satellite propulsion uses liquid mono or bi-propellants composed of a hydrazine in combination with a strong oxidant. However, hydrazines are highly toxic. As a result, many research efforts for more environmentally compatible propellants have been made over the past decade. In this study we evidence green formulations that retain high propulsive performances. They are based on the dinitramide anion. From an initial library of 37 ammonium dinitramides 3 best candidates were selected after evaluation of their potential syntheses, calculated theoretical performances, experimental synthesis optimizations and decomposition temperatures. These three salts were then formulated to obtain acceptable sensitivities and melting points, which eventually led to only one formulation being retained: a 40 : 60 mixture of dimethylammonium dinitramide and ammonium dinitramide phlegmatized by 10 % of glycerol.

An ab Initio Study of High-Energetic Trioxatriazinane Derivatives: Conformational Analysis, Nitrogen Inversion, Heats of Formation, Dissociation Reaction, and Dimerization.

High-energetic materials belong to two main classes: propellants and explosives. The still rather unexplored family of 1,3,5,2,4,6-trioxatriazinanes, N3O3R3, has a representative of each class. We have selected three compounds, R = H, R = CH3 and R = NO2, this last compound being known as TNTOTA, "trinitro-trioxa-triazinane". Of these compounds we have studied the conformational analysis, the nitrogen inversion, the heats of formation, and the dissociation reaction into the three monomers. In addition, the corresponding 1,3,2,4-dioxadiazetidines (N2O2R2) have also been studied.

On the Feasibility of Rugose Lipid Microparticles in Pressurized Metered Dose Inhalers with Established and New Propellants.

Pressurized metered dose inhalers (pMDIs) require optimized formulations to provide stable, consistent lung delivery. This study investigates the feasibility of novel rugose lipid particles (RLPs) as potential drug carriers in pMDI formulations. The physical stability of RLPs was assessed in three different propellants: the established HFA-134a and HFA-227ea and the new low global-warming-potential (GWP) propellant HFO-1234ze. A feedstock containing DSPC and calcium chloride was prepared without pore forming agent to spray dry two RLP batches at inlet temperatures of 55 °C (RLP55) and 75 °C (RLP75). RLPs performance in pMDI formulations was compared to two reference samples that exhibit significantly different performance when suspended in propellants: well-established engineered porous particles and particles containing 80% trehalose and 20% leucine (80T20L). An accelerated stability study at 40 °C and relative humidity of 7% ± 5% was conducted over 3 months. At different time points, a shadowgraphic imaging technique was used to evaluate the colloidal stability of particles in pMDIs. Field emission electron microscopy with energy dispersive X-ray spectroscopy was used to evaluate the morphology and elemental composition of particles extracted from the pMDIs. After 2 weeks, all 80T20L formulations rapidly aggregated upon agitation and exhibited significantly inferior colloidal stability compared to the other samples. In comparison, both the RLP55 and RLP75 formulations, regardless of the propellant used, retained their rugose structure and demonstrated excellent suspension stability comparable with the engineered porous particles. The studied RLPs demonstrate great potential for use in pMDI formulations with HFA propellants and the next-generation low-GWP propellant HFO-1234ze.

Highly Scalable and Inherently Safer Preparation of Di, Tri and Tetra Nitrate Esters Using Continuous Flow Chemistry.

Nitrate esters are important organic compounds having wide application in energetic materials, medicines and fuel additives. They are synthesized through nitration of aliphatic polyols. But the process safety challenges associated with nitration reaction makes the production process complicated and economically unviable. Herein, we have developed a continuous flow process wherein polyol and nitric acid are reacted in a microreactor to produce nitrate ester continuously. Our developed process is inherently safer and efficient. The process was optimized for industrially important nitrate esters containing two, three and four nitro groups. Substrates include glycol dinitrates: 1,2-propylene glycol dinitrate (PGDN), ethylene glycol dinitrate (EGDN), diethylene glycol dinitrate (DEGDN), triethylene glycol dinitrate (TEGDN); trinitrates: trimethylolethane trinitrate (TMETN), 1,2,4-butanetriol trinitrate (BTTN); and tetranitrates: erythritol tetranitrate (ETN). The optimized process for each molecule provided yield >90 % in a short residence time of 1 min corresponding to a space time yield of >18 g/h/mL of reactor volume.

Preparation of Ferrocene-Terminated Dendrimers for the Thermal Decomposition of Ammonium Perchlorate.

As a common oxidizer, ammonium perchlorate (AP) is an important component in composite solid propellants (CSPs). Ferrocene (Fc)-based compounds are often selected as burning rate catalysts (BRCs) to catalyze AP decomposition owing to their excellent catalytic behavior. However, one of the drawbacks of Fc-based BRCs is migration in CSPs. In this study, five Fc-terminated dendrimers are designed and synthesized to improve the anti-migration properties, and their chemical structures are confirmed systemically by the related spectra characterization techniques. Moreover, the redox performance, catalytic effect on AP decomposition, combustion performance, and mechanical properties in CSPs are also studied. The shapes of the prepared propellant samples are observed via scanning electron microscopy. The obtained Fc-based BRCs have good redox performance, a positive effect on promoting AP decomposition, excellent combustion catalytic performance, and good mechanical properties. Meanwhile, they have a higher anti-migration ability than catocene (Cat) and Fc. This study demonstrates that Fc-terminated dendrimers have great potential to be applied as anti-migration BRCs in CSPs.

Nitration of Chitin Monomer: From Glucosamine to Energetic Compound.

The nitration of chitin monomer in a mixture of nitric acid and acetic anhydride was conducted and a highly nitrated (3R,4R,6R)-3-acetamido-6-((nitrooxy)methyl)tetrahydro-2H-pyran-2,4,5-triyl trinitrate (1) was obtained. Its structure was fully characterized using infrared spectroscopy, NMR spectroscopy, elemental analysis, and X-ray diffraction. Compound 1 possesses good density (ρ: 1.721 g·cm-3) and has comparable detonation performance (Vd: 7717 m·s-1; P: 25.6 GPa) to that of nitrocellulose (NC: Vd: 7456 m·s-1; P: 23 GPa; Isp = 239 s) and microcrystalline nitrocellulose (MCNC; Vd: 7683 m·s-1; P: 25 GPa; Isp = 250 s). However, Compound 1 has much lower impact sensitivity (IS: 15 J) than the regular nitrocellulose (NC; IS: 3.2 J) and MCNC (IS: 2.8 J). Compound 1 was calculated to exhibit a good specific impulse (Isp: 240 s), which is comparable with NC (Isp: 239 s) and MCNC (Isp: 250 s). By replacing the nitrocellulose with Compound 1 in typical propellants JA2, M30, and M9, the specific impulse was improved by up to 4 s. These promising properties indicate that Compound 1 has a significant potential as an energetic component in solid propellants.

Trace Detection and Chemical Analysis of Homemade Fuel-Oxidizer Mixture Explosives: Emerging Challenges and Perspectives.

The chemical analysis of homemade explosives (HMEs) and improvised explosive devices (IEDs) remains challenging for fieldable analytical instrumentation and sensors. Complex explosive fuel-oxidizer mixtures, black and smokeless powders, flash powders, and pyrotechnics often include an array of potential organic and inorganic components that present unique interference and matrix effect difficulties. The widely varying physicochemical properties of these components as well as external environmental interferents and background challenge many sampling and sensing modalities. This review provides perspective on these emerging challenges, critically discusses developments in sampling, sensors, and instrumentation, and showcases advancements for the trace detection of inorganic-based explosives.

Application of fractional calculus methods to viscoelastic behaviours of solid propellants.

A three-branch viscoelastic model based on fractional derivatives is proposed for the viscoelastic behaviours of solid propellants. The simulation results show a satisfactory agreement with the stress relaxation modulus and complex modulus of solid propellants. As a comparison, the static modulus is also characterized by traditional viscoelastic model with integer-order derivatives. Results show that the application of the fractional derivatives to the viscoelastic constitutive model can effectively reduce the number of the required parameters while giving an accurate prediction of viscoelastic behaviours of solid propellants. Moreover, a simple and effective direct search method based on simulated annealing and Powell's mothed is proposed for the data fitting. This article is part of the theme issue 'Advanced materials modelling via fractional calculus: challenges and perspectives'.

The Study of HEMs Based on the Mechanically Activated Intermetallic Al12Mg17 Powder.

In this work, Al-Mg intermetallic powders were characterized and obtained by melting, casting into a steel chill and subsequent mechanical activation in a planetary mill. The method for producing Al12Mg17 intermetallic powder is presented. The dispersity, morphology, chemical composition, and phase composition of the obtained powder materials were investigated. Certain thermodynamic properties of high-energy materials containing the Al-Mg powder after mechanical activation of various durations were investigated. The addition of the Al-Mg powders to the high-energy composition (synthetic rubber SKDM-80 + ammonium perchlorate AP + boron B) can significantly increase the burning rate by approximately 47% and the combustion heat by approximately 23% compared with the high-energy compositions without the Al-Mg powder. The addition of the Al12Mg17 powder obtained after 6 h of mechanical activation provides an increase in the burning rate by 8% (2.5 ± 0.1 mm/s for the mechanically activated Al12Mg17 powder and 2.3 ± 0.1 mm/s for the commercially available powder) and an increase in the combustion heat by 3% (7.4 ± 0.2 MJ/kg for the mechanically activated Al-Mg powder and 7.1 ± 0.2 MJ/kg for the commercially available powder). The possibility of using the Al-Mg intermetallic powders as the main component of pyrotechnic and special compositions is shown.

Single-Walled Carbon Nanotubes (SWCNTs) as Solid-Contact in All-Solid-State Perchlorate ISEs: Applications to Fireworks and Propellants Analysis.

Herein, we present reliable, robust, stable, and cost-effective solid-contact ion-selective electrodes (ISEs) for perchlorate determination. Single-walled carbon nanotubes (SWCNTs) were used as solid-contact material and indium (III) 5, 10, 15, 20-(tetraphenyl) porphyrin chloride (InIII-porph) as an ion carrier. The sensor exhibited an improved sensitivity towards ClO4- ions with anionic slope of -56.0 ± 1.1 (R2 = 0.9998) mV/decade over a linear range 1.07 × 10-6 - 1.0 × 10-2 M and detection limit of 1.8 × 10-7 M. The short-term potential stability and the double-layer capacitance were measured by chronopotentiometric and electrochemical impedance spectroscopy (EIS) measurements, respectively. The sensor is used for ClO4- determination in fireworks and propellant powders. The results fairly agree with data obtained by ion chromatography.

Continuous Monitoring of Shelf Lives of Materials by Application of Data Loggers with Implemented Kinetic Parameters.

The evaluation of the shelf life of, for example, food, pharmaceutical materials, polymers, and energetic materials at room or daily climate fluctuation temperatures requires kinetic analysis in temperature ranges which are as similar as possible to those at which the products will be stored or transported in. A comparison of the results of the evaluation of the shelf life of a propellant and a vaccine calculated by advanced kinetics and simplified 0th and 1st order kinetic models is presented. The obtained simulations show that the application of simplified kinetics or the commonly used mean kinetic temperature approach may result in an imprecise estimation of the shelf life. The implementation of the kinetic parameters obtained from advanced kinetic analyses into programmable data loggers allows the continuous online evaluation and display on a smartphone of the current extent of the deterioration of materials. The proposed approach is universal and can be used for any goods, any methods of shelf life determination, and any type of data loggers. Presented in this study, the continuous evaluation of the shelf life of perishable goods based on the Internet of Things (IoT) paradigm helps in the optimal storage/shipment and results in a significant decrease of waste.

Nitroguanidine (NQ) (2016).

1-Nitroguanine (NG), also known as picrate, guanidine nitro, and N'-nitroguanidine, is used by the military as a propellant. Oral rodent LD50 data are generally >5000 mg/kg. NG is neither an eye nor a skin irritant, and it is not a skin sensitizer. NG is not genotoxic. No inhalation data are available; however, there are data from both 14- and 90-day oral (feed) toxicity studies in male and female Sprague Dawley rats at dosages up to 1000 mg/kg/day. There were no deaths on these studies and the only effect considered possibly related to treatment was decreased weight in females at the high-dose level in the 90-day study. Mice at similar dosages were even less affected. The NOAEL for both rats and mice (oral) was 316 mg/kg/day. There was no evidence of developmental toxicity in Sprague-Dawley rats administered NG by oral gavage, and the free-standing NOAEL was 1000 mg/kg with material toxicity. In Wistar rats, there was high mortality (50%) at 500 mg/kg NG administered by oral gavage; there was decreased body weight, feed consumption, and notable clinical signs in the dams at this dose level. Fetal toxicity could not be determined in this group. NG demonstrated maternal toxicity at 1000 mg/kg in rabbits; however, there were no evident differences in the rate of fetal malformations across the test groups. A NOAEL of 316 mg/kg was identified for maternal and fetal toxicity in this study. In a two-generation study, it was concluded the NG did not cause reproductive or fertility effects at dosages up to 1000 mg/kg/day. Absorption was rapid, non-dose dependent, and resulted in an apparent volume of distribution (VD) of between 0.66 (IV) and 0.85-0.87 (oral) l/kg. Elimination was primarily through the urine as unchanged compound. Human experience with NG dates back 100 years; however, no actual studies on humans have been reported. Non-military uses include automotive airbags, anti-corrosive coatings, and pharmaceutical manufacturing. The point of departure for Workplace Environmental Exposure Level (WEEL) derivations was 316 mg/kg, and a WEEL of 7 mg/m3 as an 8-h time-weighted average (TWA) was recommended.

Manganese-Mediated Linkage of Perchlorate to Aminotetrazoles Produces Twice the Energy Density of the Unmetalated Salt.

New regimes of energy density in energetic materials may be achieved by replacement of oxidizing nitro groups with stronger oxidants such as oxychlorine species. We report the energetic material 1,3-di-tert-butyltetrazolium-5-imidoperchloratomanganese(II) 2, which crystallizes as an oligomeric cubane cluster. Bomb calorimetry on the amorphous, solvent-free phase gives an energy density of at least 40±3 MJ L- , higher than hydrocarbon combustion in air, more than twice that of traditional energetic nitramines, and ≈70 % higher than that of the unmetalated tetrazolium perchlorate salt without metal linkage. The effects of solid-state structure, charge, and lattice energy on the energy of 2 are discussed.

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.

Energetic Salts Based on Tetrazole N-Oxide.

Energetic materials (explosives, propellants, and pyrotechnics) are used extensively for both civilian and military applications and the development of such materials, particularly in the case of energetic salts, is subject to continuous research efforts all over the world. This Review concerns recent advances in the syntheses, properties, and potential applications of ionic salts based on tetrazole N-oxide. Most of these salts exhibit excellent characteristics and can be classified as a new family of highly energetic materials with increased density and performance, alongside decreased mechanical sensitivity. Additionally, novel tetrazole N-oxide salts are proposed based on a diverse array of functional groups and ions pairs, which may be promising candidates for new energetic materials.

Application of a nanostructured supramolecular solvent for the microextraction of diphenylamine and its mono-nitrated derivatives from unburned single-base propellants.

A supramolecular solvent made up of nano-sized inverted hexagonal aggregates of 1-octanol is proposed for the microextraction of diphenylamine and its mono-nitrated derivatives in unburned single-base propellants. The procedure included the extraction of sub-gram quantities (30 mg) of homogenized propellant with 1.5 mL of the supramolecular solvent. Several conditions affecting extraction efficiency, for example the concentrations of the major components of the supramolecular solvent (tetrahydrofuran and alkanol), alkanol type, solvent pH, and extraction time, were investigated and optimized. The main forces for the microextraction of analytes in the nanostructured supramolecular solvent include both dispersion and hydrogen bond interactions. This mixed-mode mechanism resulted in high extraction efficiencies reaching low method detection limits (0.005-0.012 mg/g) without the need for extract evaporation. Under the optimum conditions, recoveries in samples ranged between about 82.6 and 98.7%. Compared to the reference method, the proposed method is simple and rapid, delivering accurate and precise results, and can be applied for routine determination of diphenylamine and its derivatives in propellants. The precision of the method, expressed as relative standard deviation, was about 4.3-10.9%.

Cyanoborohydride-based ionic liquids as green aerospace bipropellant fuels.

In propellant systems, the most common bipropellants are composed of two chemicals, a fuel (or reducer) and an oxidizer. Currently, the choices for propellant fuels rely mainly on hydrazine and its methylated derivatives, even though they are extremely toxic, highly volatile, sensitive to adiabatic compression (risk of detonation), and, therefore, difficult to handle. With this background, the search for alternative green propellant fuels has been an urgent goal of space science. In this study, a new family of cyanoborohydride-based ionic liquids (ILs) with properties and performances comparable to hydrazine derivatives were designed and synthesized. These new ILs as bipropellant fuels, have some unique advantages including negligible vapor pressure, ultra-short ignition delay (ID) time, and reduced synthetic and storage costs, thereby showing great application potential as environmentally friendly fuels in bipropellant formulations.

Amine-boranes: green hypergolic fuels with consistently low ignition delays.

Complexation of amines with borane converts them to hypergols or decreases their ignition delays (IDs) multifold (with white fuming nitric acid as the oxidant). With consistently low IDs, amine-boranes represent a class of compounds that can be promising alternatives to toxic hydrazine and its derivatives as propellants. A structure-hypergolicity relationship study reveals the necessary features for the low ID.

Nitryl cyanide, NCNO2.

The elusive nitryl cyanide, NCNO2, has been synthesized and characterized. It was prepared in good yield, isolated by fractional condensation, characterized by NMR and vibrational spectroscopy, and studied by theoretical calculations. Nitryl cyanide holds promise as a high energy density material (HEDM) and might also prove useful as a HEDM building block. The simplicity and inherent stability of nitryl cyanide, together with the known multitude of nitriles in interstellar space, suggest that the compound might also be a potential candidate for observations in atmospheric and interstellar chemistry.

Preparation of Polydopamine Functionalized HNIW Crystals and Application in Solid Propellants.

The application of hexanitrohexaazaisowurtzitane (HNIW) as an oxidizer in solid propellants aligns with the pursuit of high-energy materials. However, the phase transformation behavior and high impact sensitivity of HNIW are its limitations. Due to the strong adhesion and mild synthesis conditions, polydopamine (PDA) has been employed to modify HNIW. However, the method suffers from a slow coating process and a non-ideal coating effect under short reaction time. Herein, oxygen-accelerated dopamine in situ polymerization coating method was developed. It was found that oxygen not only reduced the coating time but also contributed to forming a dense and uniform PDA layer. HNIW@PDA coated in oxygen for 6 h exhibited the most favorable performance, with a delay of 20.8 °C in the phase transition temperature and a reduction of 145.45% in the impact sensitivity. The -OH groups on the surface of PDA enhanced the interaction between HNIW and polymer binders, resulting in a 20.36% reduction in the dewetting percentage. The lower content of PDA in HNIW@PDA (1.17%) resulted in minimal variation in the heat of explosion for HNIW@PDA-based HTPB propellant (6287 kJ/kg) in comparison to HNIW-based HTPB propellant (6297 kJ/kg). Hence, HNIW@PDA-based propellants are expected to offer an alternative with promising safety and mechanical performance compared to existing HNIW-based propellants, thus facilitating the application of HNIW in high-energy propellants. This work presents a low-cost method for efficiently inhibiting the phase transformation of polycrystalline explosives and reducing the impact sensitivity. It also offers a potential approach to enhance the interfacial interaction between nitro-containing explosives and polymer binders.