Energetic Ionic Salts Research Articles

Ionization and separation as a strategy for significantly enhancing the thermal stability of an instable system: a case for hydroxylamine-based salts relative to that for pure hydroxylamine.

Energetic ionic salts (EISs) are attracting extensive attention because of their ready preparation and some excellent properties and performances that are comparable to those of common explosives with neutral molecules. Hydroxylamine (HA) is protonated or ionized as H-HA+ and preferred to be introduced into EISs to form HA-based EISs with almost all kinds of anions since these EISs possess higher packing densities and thus more excellent detonation performances than others with the same anions. Moreover, relative to that of pure HA, the thermal stability of HA-based EISs is significantly enhanced. This significantly enhanced thermal stability can extend the application of HA via deprotonation of H-HA+ back to HA; however, the mechanism for stabilization of HA by salification remains unclear. Herein, we employed thermodynamic and kinetic calculations and molecular dynamics simulations to reveal the thermal stability mechanisms of many currently synthesized HA-based EISs and some previously reported EISs with inorganic anions as well as those of pure HA and its aqueous solution. As a result, we have found that the enhanced stability of HA-based EISs is mainly due to the ionization and separation of HA molecules themselves. That is, H-HA+, as an ionized product, is more molecularly stable than HA, with significantly strengthened covalent bonds. The separation of H-HA+ ions or HA molecules makes decomposition more difficult as decomposition initiation varies from bimolecular to unimolecular reactions of HA, with a significant increase in the energy barrier. We have, therefore, proposed a strategy for the stabilization of unstable systems, such as neutral N-rich energetic compounds, by ionization and separation to strengthen these systems and change the decomposition mechanism by increasing the energy barriers of trigger steps such that these barriers become more difficult to overcome, respectively.

Enhanced Intermolecular Hydrogen Bonds Facilitating the Highly Dense Packing of Energetic Hydroxylammonium Salts

The energy and performance of energetic materials can be improved by increasing their crystal packing density. Thus, we propose a strategy involving salification with hydroxylammonium cations (HA+) to increase the packing coefficients (PCs) and packing densities of energetic ionic salts (EISs). Structural analyses and theoretical calculations of the observed EISs indicate that the strong intermolecular hydrogen bonds (HBs) between HA+ and anions are primarily responsible for the increase in EIS density. Such strong HBs usually exist in HA+-based energetic salts and rarely in other EISs but are absent in energetic crystals with neutral molecules. Such HBs induce high PCs and relatively high crystal packing densities by compensating for the relatively lower molecular density of HA+ compared with other cations. Moreover, in combination with HBs in common explosives, we find a simple dependence showing that the shorter the strongest HB corresponds to the higher PC, suggesting that the strongest HB can be rega...

Pyrolysis of Energetic Ionic Salts Based on Nitrogen-rich Heterocycles

Energetic ionic salts based on nitrogen-rich heterocycles are expected to usher in a new era in the fields of propellants, explosives, and pyrotechnics owing to their excellent combustion characteristics, green nature, and the ability to tailor them based on requirements. The review focuses on an important aspect of these compounds, other than the synthesis procedure and physico-chemical characterisation, that is frequently overlooked, i.e. the decomposition pathways and the associated chemical kinetic parameters, which are essential to elucidate and simulate their combustion characteristics. The reaction mechanisms of four major families of energetic ionic salts, explored by various experimental and numerical techniques, are reported in detail.

Two Energetic Ionic Salts of en·PA·H2O and en·TNR: Preparation, Structural Characterization, and Properties

AbstractEnergetic salts of en·PA·H2O and en·TNR were synthesized by using ethylenediamine and picric acid (PA) or 2,4,6‐trinitroresorcinol (TNR) as raw materials, and their structures were characterized by elemental analysis and FT‐IR spectroscopy. Single crystals of the title salts were obtained and their structures were determined by single‐crystal X‐ray diffraction. The thermal decomposition behaviors were investigated by DSC and TG‐DTG technologies, furthermore the non‐isothermal kinetic parameters and enthalpies of formation for the salts were calculated. Their combustion heats were measured by oxygen bomb calorimetry and their enthalpies of formation were also calculated based on the combustion heat data. In addition, the detonation pressure (P) and detonation velocities (D) of the salts were predicted by using the K‐J equations. The results indicated that the title salts have potential applications in the field of energetic materials.

Two-sided effects of strong hydrogen bonding on the stability of dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50)

Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) is a recently synthesized energetic ionic salt (EISs) with some excellent properties including high energy content, high density, low impact sensitivity and low toxicity, and therefore is a promising alternative energetic material. In contrast to commonly applied energetic CHON materials, TKX-50 features strong intermolecular hydrogen bonds (HBs). However, the effects of these strong HBs on its important properties remain unclear. We report herein the two-sided effects of the strong HBs on the stability of TKX-50, through ab initio simulations on shear deformation and thermal decomposition. That is, on the one hand, the strong HBs in TKX-50 lead to a layer-like arrangement of the cations and dianions in the (010) planes with the adjacent layers connected only by two types of weakest HBs, which facilitates the conversion of external kinetic energy into interlayer sliding, and contributes to low impact sensitivity; on the other hand, the extensive HBs in TKX-50 act as a potential source to facilitate H-transfer (including proton transfer), which accelerates subsequent thermal decomposition, and thus deteriorates the thermal stability of TKX-50 relative to its notably low impact sensitivity. These two-sided effects of the strong HBs in a TKX-50 crystal should be useful to understand properties of other EISs, in which strong HBs are universal, and enrich the knowledge of the sensitivity mechanism of energetic materials.

A New Energetic Material and its Risk Research

Bis (1, 5‐diamino‐4‐methyl‐tetrazolium) azotetrazolate (BMDATZT) was synthesized with high yield in this work. The yield is 97.46%. The structure was characterized by IR, 1H NMR, and MS. The single crystal of BMDATZT•2H2O was first cultivated. The heat of formation, detonation pressure, and detonation velocity were first calculated. The crystalline density of BMDATZT•2H2O is 1.573 g/cm3. BMDATZT has high detonation pressure and detonation velocity (P =25.06 GPa, D = 7.805 km s−1), which are higher than those of 2,4,6‐Trinitrotoluene (TNT). Its thermal and mechanical sensitivities are moderate. Therefore, it is a kind of insensitive nitrogen‐rich energetic ionic salt with good performance, and it has potential application prospect in gas generating agent, explosive and solid propellant.

Nitrogen-rich salts of 1-aminotetrazol-5-one: oxygen-containing insensitive energetic materials with high thermal stability

Energetic ionic salts based on ATO exhibit a good balance between low sensitivity and high detonation performance.

Preparation, Structural Characterization, and Thermal Analysis of Nitrogen‐rich Energetic Ionic Salts based on 4‐Amino‐3‐hydrazino‐5‐mercapto‐1, 2,4‐triazole

AbstractTwo heterocyclic‐based energetic ionic salts were synthesized from 4‐amino‐3‐hydrazino‐5‐mercapto‐1, 2,4‐triazole (1), which was used as proton bases reacting with nitric or perchloric acid. They were characterized by elemental analysis, IR spectroscopy, and single‐crystal X‐ray diffraction. In addition, their combustion heats were measured by oxygen bomb calorimetry and their heats of formation were predicted based on the combustion heats data. The non‐isothermal kinetics parameters were calculated by Kissinger's method and Ozawa‐Doyle's method, respectively. The critical temperature of thermal explosion and the thermodynamic parameters were also obtained by DSC results. The energetic properties and thermal analyses confirmed that the two salts maybe have potential application in the field of energetic materials.

Synthesis and Characterization of the Nitrophenol Energetic Ionic Salts of 5,6,7,8‐Tetrahydrotetrazolo[1,5‐b][1,2,4]triazine

AbstractNitrophenol energetic ionic salts based on the 5,6,7,8‐tetrahydrotetrazolo[1,5‐b][1,2,4]triazine (TZTN, 1) cation and nitrophenol anions have been synthesized in high yields by neutralization reactions. All the salts were characterized by X‐ray single‐crystal diffraction technology, IR spectroscopy, elemental analysis, and DSC measurements. The heats of formation of 2–4 were calculated by using isodesmic reactions. The calculated detonation pressures of these salts range from 29.7 to 32.6 GPa and their detonation velocities fall between 8337 and 8613 m s–1; these properties make them competitive energetic materials. In addition, the sensitivities towards impact, friction, and flame were tested, and the results indicated that salts 2 and 3 have acceptable sensitivities, whereas salt 4 shows relatively high sensitivity towards impact and flame.

A theoretical study of 3,5-diazido-1,2,4-triazole: the role of the hydrogen bonding interaction in stabilizing the molecular system

3,5-Diazido-1, 2, 4-triazole (DATZ) is a compound that has a good thermal stability and can be used to produce high energetic ionic salts. The conformations of DATZ were searched by the molecular dynamics simulations and optimized by the molecular mechanics and dispersion-corrected density functional theory methods. The dimer and trimer of DATZ were constructed from the most stable monomer. The hydrogen bonding interactions, which were found to be critically important in increasing the stability of the dimer and trimer, were investigated with the help of the natural bond orbital and the quantum theory of atoms in molecules analyses. The changes in thermodynamic functions, stabilization interaction energies, and hydrogen-bonding energies show that the trimer is most likely the existing form of DATZ. The intramolecular, intermolecular, and water catalytic proton transfer processes were simulated to investigate the proton transfer mechanism. The intermolecular transfer process requires the lowest activation energy (42.56 kJ mol−1) and is the most likely process of proton transfer. DATZ is not only a proton acceptor but also a proton donor. Its weak acidity was quantified as pKa = 10.16. The solvation energy estimated using the conductor-like polarizable continuum model in water is the largest (−99.96 kJ mol−1), revealing that DATZ is more stable in water than in another seven solvents.

Comparative Theoretical Studies on Energetic Ionic Salts Composed of Heterocycle-Functionalized Nitraminofurazanate-Based Anions and Triaminoguanidinium Cation

Density functional theory and volume-based thermodynamics calculations have been performed to study the crystal densities, heats of formation (HOFs), energetic properties, thermodynamics of formation, and impact sensitivity for the salts composed of heterocycle-functionalized nitraminofurazanate-based anions and triaminoguanidinium cation. The results show that the triaminoguanidinium nitraminofurazanate-based salts have high densities and positive HOFs. The substitution of the oxygen-containing substituent (−NO2 or −C(NO2)3) is helpful for enhancing the densities and detonation properties of the nitraminofurazanate-based salts, and the substitution of −C(NO2)3 exhibits the best performance. Incorporating the conjugated bridge −N═N– or −N═N–N═N– into the heterocycle-functionalized nitraminofurazanate-based salts is favorable for improving the density and detonation properties of its salt. The tetrazole-functionalized salts exhibit the best detonation properties among the three salt series. The calculated ...

Synthesis, Characterization, and Thermal Analysis of Two Energetic Ionic Salts Based on 3,4‐Diamino‐1,2,4‐triazole (DATr)

AbstractTwo energetic ionic salts DATr·NTO (2) and DATr·TNR (3) of 3,4‐diamino‐1,2,4‐triazole (DATr) (1) were synthesized by reaction of 3,4‐diamino‐1,2,4‐triazole with either 3‐nitro‐1,2,4‐triazole‐5‐one (NTO) or 2,4,6‐trinitro‐resorcinol (TNR) in aqueous solution. Their structures were characterized by FT IR spectroscopy (FT‐IR) and X‐ray single‐crystal diffraction analysis. Their molecular structure and crystal structure were determined. They belong to the monoclinic crystal system, space group P21/c. The crystal density is 1.693 g·cm–3 and 1.738 g·cm–3, respectively. The thermal decomposition characteristics of the title compounds were investigated using differential scanning calorimetry (DSC) and thermogravimetry/differential thermogravimetry (TG/DTG) technologies. Furthermore, the sensitivity properties were determined by standard methods.

Progress in Synthesis of Energetic Ionic Salts of Triazole and Tetrazole Compounds

Progress in Synthesis of Energetic Ionic Salts of Triazole and Tetrazole Compounds

Energetic Ionic Materials: How Green Are They? A Comparative Life Cycle Assessment Study

Recently, several energetic ionic salts and liquids have been proposed as novel high-energy materials, propellants, and explosives. The life cycle environmental impacts of these new energetic salts have not been previously studied. Environmental impacts arise both from release of these energetic materials themselves as well as from their synthesis. In this work, for the first time, we report the results of cradle-to-gate life cycle environmental impacts of production of energetic ionic salt 1,2,3-triazolium nitrate and compare it with traditional energetic material 2,4,6-trinitrotoluene (TNT). The results indicate that the production processes of ionic salt have a significantly higher environmental footprint than conventional energetic materials. The above result was consistent across all nine impact categories analyzed and can be directly attributed to energy intensive steps needed to prepare the ionic salt and its precursors. The findings suggest that ionic energetic materials have higher environmental ...

Structure–property relationships of energetic nitrogen-rich salts composed of triaminoguanidinium or ammonium cation and tetrazole-based anions

Density functional theory and volume-based thermodynamics calculations have been performed to study the crystal densities, heats of formation (HOFs), energetic properties, and thermodynamics of formation for a series of ionic salts composed of triaminoguanidinium or ammonium cations and tetrazole-based anions. Substitution with NF2, CH2NF2, CF2NF2, or C(NO2)2NF2 groups increased the densities of the salts. The densities of the tetrazole-based salts are affected not only by different substituents but also by different cations. The CN or N3 groups are effective substituents for increasing the HOFs of the salts. The triaminoguanidinium cation is more effective than the ammonium cation for increasing the HOF of the tetrazole-based salts. Substitution with NO2, NF2, or C(NO2)2NF2 groups enhances the explosive properties of the salts. The thermodynamics of formation of the salts reveal that all of the tetrazole-based salts with the triaminoguanidinium or ammonium cation could be synthesized using the proposed reactions. Our calculated methods provide a straightforward and inexpensive route for screening a large number of potentially energetic ionic salts.

First-Principle Studies on the Pressure-Induced Structural Changes in Energetic Ionic Salt 3-Azido-1,2,4-triazolium Nitrate Crystal

Periodic first-principle calculations have been performed to study the effect of high pressure on the geometrical and electronic structures of the energetic ionic salt 3-azido-1,2,4-triazolium nitrate (ATAN) under hydrostatic pressure of 0–300 GPa. The local density approximation with CA-PZ functional has been adopted because the crystal structure optimized with it agrees better with the experimental results than with other functionals at the ambient pressure. When the hydrostatic compression is exerted upon the ATAN crystal, the unit cell parameters, density, total energy, interatomic distances, bond angles, atom charges, bond populations, band structure, and density of states of ATAN crystal change regularly with the increase in pressure except at 200 GPa where the structural transformations occur. Although the azido group bends gradually and slowly to form a five-membered tetrazole ring, the H atom in the adjacent cation transfer to the terminal N atom of the azido group and a new covalent bond forms a...

Densities, Heats of Formation, Energetic Properties, and Thermodynamics of Formation of Energetic Nitrogen-Rich Salts Containing Substituted Protonated and Methylated Tetrazole Cations: A Computational Study

We have performed density functional theory and volume-based thermodynamics calculations to study the effects of different substituents and energetic anions on the densities, heats of formation, energetic properties, and thermodynamics of formation for a series of energetic nitrogen-rich salts composed of the substituted protonated and methylated tetrazole cations with nitrate, dinitroamide, azide, and perchlorate anions. The volumes of the cations and anions were estimated to get the crystal densities of the salts from electronic structure calculations. The heats of formation (HOFs) of cations, anions, and lattice energies of the salts were calculated separately to obtain the HOFs of the salts based on Born−Haber energy cycles. According to the densities and HOFs, the detonation velocities and detonation pressures of the salts were predicted by the Kamlet−Jacobs equations. Finally, the lattice enthalpies and entropies were used to construct a thermodynamic cycle for salt formation to predict the possibility to synthesize the salts. This procedure provides a straightforward and inexpensive route to screen a large number of potential energetic ionic salts.

Energetic salts of azotetrazolate, iminobis(5-tetrazolate) and 5, 5′-bis(tetrazolate)

Energetic ionic salts of azotetrazolate (AT), iminobis(5-tetrazolate) (IBT) and 5, 5'-bis(tetrazole) (BT) were synthesized; 1-methyl-4-aminotriazolium azotetrazolate has a layered structure and exhibits a heat of formation of +4360 kJ kg(-1).