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Ammonium DiNitramide (ADN) is one of the most promising green energetic oxidizers for future rocket propellant formulations. In the present work, we report a detailed theoretical study on structural, elastic, and vibrational properties of the emerging oxidizer under hydrostatic compression using various dispersion correction methods to capture weak intermolecular (van der Waals and hydrogen bonding) interactions. The calculated ground state lattice parameters, axial compressibilities, and equation of state are in good accord with the available experimental results. Strength of intermolecular interactions has been correlated using the calculated compressibility curves and elastic moduli. Apart from this, we also observe discontinuities in the structural parameters and elastic constants as a function of pressure. Pictorial representation and quantification of intermolecular interactions are described by the 3D Hirshfeld surfaces and 2D finger print maps. In addition, the computed infra-red (IR) spectra at ambient pressure reveal that ADN is found to have more hygroscopic nature over Ammonium Perchlorate (AP) due to the presence of strong hydrogen bonding. Pressure dependent IR spectra show blue- and red-shift of bending and stretching frequencies which leads to weakening and strengthening of the hydrogen bonding below and above 5 GPa, respectively. The abrupt changes in the calculated structural, mechanical, and IR spectra suggest that ADN might undergo a first order structural transformation to a high pressure phase around 5-6 GPa. From the predicted detonation properties, ADN is found to have high and low performance characteristics (DCJ = 8.09 km/s and PCJ = 25.54 GPa) when compared with ammonium based energetic oxidizers (DCJ = 6.50 km/s and PCJ = 17.64 GPa for AP, DCJ = 7.28 km/s and PCJ = 18.71 GPa for ammonium nitrate) and well-known secondary explosives for which DCJ = ~8-10 km/s and PCJ = ~30-50 GPa, respectively. [ABSTRACT FROM AUTHOR]

Dinitramide anion (DA) is one of the most notable discoveries in the field of energetic materials. Some of the important DA-based compounds are ammonium dinitramide (ADN), potassium dinitramide, silver dinitramide, sodium dinitramide, lithium dinitramide, guanidium dinitramide, etc. apart from several others. All DA-based energetic compounds have wide range of applications ranging from basic chemistry, engineering and to other allied areas. However, ADN is one of the important DA-based compound, and major researches are going over ADN to use it in rocket/ missile for green propulsion. DA-based compounds are generally used in the development of high-performance solid/ liquid propellants, pyrotechnics compositions and for lethal explosives. Other uses of DA compounds are in the chemical synthesis and in various types of industrial processes. In the present paper, an overview has been presented over the crystal structure, physical and chemical properties of all the synthesised DA-based compounds which are documented till date. The present study will be helpful in understanding various application areas of DA-based compounds and their future uses. [ABSTRACT FROM AUTHOR]

In the molecule of neutral bis[(1H-tetrazol-5-yl)methyl]nitramide, (I), C4H6N10O2, there are two intramolecular N—H...O hydrogen bonds. In the crystal, N—H...N hydrogen bonds link molecules, forming a two-dimensional network parallel to (-201) and weak C—H...O, C—H...N hydrogen bonds, and intermolecular π–π stacking completes the three-dimensional network. The anion in the molecular salt, triaminoguanidinium 5-({[(1H-tetrazol-5-yl)methyl](nitro)amino}methyl)tetrazol-1-ide, (II), CH9N6+·C4H5N10O2−, displays intramolecular π–π stacking and in the crystal, N—H...N and N—H...O hydrogen bonds link the components of the structure, forming a three-dimensional network. In the crystal of diammonium bis[(tetrazol-1-id-5-yl)methyl]nitramide monohydrate, (III), 2NH4+·C4H4N10O22−·H2O, O—H...N, N—H...N, and N—H...O hydrogen bonds link the components of the structure into a three-dimensional network. In addition, there is intermolecular π–π stacking. In all three structures, the central N atom of the nitramide is mainly sp2-hybridized. Bond lengths indicate delocalization of charges on the tetrazole rings for all three compounds. Compound (II) was found to be a non-merohedral twin and was solved and refined in the major component.

In this work, by using density functional theory, the adsorption of Nitramide (NH2NO2) molecule on the surface of pristine, B, As and B&As doped (4,4) armchair aluminum nitride nanotube (AlNNTs) is investigated. From optimized structures the adsorption energy, deformation energy, natural bond orbital (NBO), atom in molecule (AIM), quantum parameters, reduced density gradient (RDG) and molecular electrostatic potential (MEP) are calculated. The calculated results indicate that the adsorption energy values of NH2NO2 on the surface of pristine, As, B and B&As doped AlNNTs complex are negative and favorable in viewpoint of thermodynamic. Moreover the adsorption of NH2NO2 molecule on the surface of B&As doped AlNNTs is more stable and favorable than other models. It is notable that with doping B&As atoms in AlNNTs the deformation energy of NH2NO2 and nanotube are less than other models. The results of AIM and RDG outcomes demonstrate that nature of binding NH2NO2…AlNNTs is covalent bond type, indicates strong interactions. The results of NBO & Mullikan partial charge transfer, HOMO-LUMO, total charge transfer parameters (ΔN) and molecular electrostatic potential (MEP) display that the charge transfer occurred from NH2NO2 molecule toward nanotube surface and electrical properties of system change significantly from original state. The results of this study reveal that the B&As doped AlNNTs is a good adsorbent for NH2NO2 molecule. [ABSTRACT FROM AUTHOR]

The compound N-(5-(4-chlorobenzyl)-1,3,5-triazinan-2-ylidene)nitramide (C10H12ClN5O2, M = 269.70) was synthesized and structurally confirmed by 1H NMR, 13C NMR, HRMS and single-crystal x-ray diffraction. The crystal belongs to the monoclinic system with space group P21/c. The title compound consisted of a benzene ring and a 1,3,5-triazine ring. All carbon atoms in the benzene ring were nearly coplanar with a dihedral (C6−C5−C10 and C7−C8−C9) angle of 1.71°and all non-hydrogen atoms of the 1,3,5-triazine ring were not planar, but exhibited a half-chair conformation. The crystal structure was stabilized by a strong intramolecular hydrogen bonding interaction N(3)−H(3)···O(2) and three intermolecular hydrogen bonding interactions, N(2)−H(2)···O(1), N(2)−H(2)···N(4) and N(3)−H(3)···Cl(1). The preliminary bioassay showed that the title compound showed not only aphicidal activity against Sitobion miscanthi (inhibition rate: 74.1%) and Schizaphis graminum (77.5%), but also antifungal activities against Pythium aphanidermatum (62.0%). These results provide valuable guidelines for the design and synthesis of novel aphid control agents and fungicides.

Abstract Ammonium dinitramide (ADN; [NH 4 ]+[N(NO 2) 2 ]−) is the most promising oxidizer for use with future green solid and liquid propellants for spacecraft applications. To allow the effective development and use of ADN-based propellants, it is important to understand ADN reaction mechanisms. This work presents a detailed chemical kinetics model for the liquid phase reactions of ADN based on quantum chemical calculations. The thermal corrections, entropies, and heat capacities of chemical species were calculated from the partition function using statistical machinery based on the G4 level of theory. Rate coefficients were also determined to allow the application of transition state theory and variational transition state theory to reactions identified in our previous study. The new model employed herein simulates the thermal decomposition of ADN under specific heating conditions and successfully predicts heats of reaction and the gases that result from decomposition under those conditions. The thermal behavior predicted from the new model was an excellent match with the experimental behavior observed from thermal analysis using differential scanning calorimetry and Raman spectroscopy. The new kinetic model reveals the mechanism for the decomposition of ADN. [ABSTRACT FROM AUTHOR]

A series of new energetic salts based on N,N′-methylenebis(N-(4-(dinitromethyl)-1,2,5-oxadiazol-3-yl)nitramide) was synthesized and fully characterized by NMR and IR spectroscopy, and elemental analysis. Their excellent vD (7995–8885 m s−1) and acceptable sensitivities (IS, 1–5 J; FS, 40–120 N) make them good candidates as metal-free green primary explosives (with the exception of 3). [ABSTRACT FROM AUTHOR]

The dissolution properties of 2-oxo-1,3,5-trinitro-1,3,5-triazacyclohexane (Keto-RDX) in dimethyl sulfoxide (DMSO) were studied by using a RD496-2000 Calvet microcalorimeter at four different temperatures under atmospheric pressure. The heat effects, molar enthalpies (ΔdissH), and differential enthalpies (ΔdifH) of dissolution were determined. Furthermore, the corresponding kinetic equations describing the dissolution processes at the four experimental temperatures are dα/dt = 10−2.43 (1 − α)0.63 (T = 298.15 K), dα/dt = 10−2.41 (1 − α)0.67 (T = 303.15 K), dα/dt = 10−2.40 (1 − α)0.75 (T = 308.15 K), and dα/dt = 10−2.38 (1 − α)0.76 (T = 313.15 K). The determined values of the activation energy E and pre-exponential factor A for the dissolution process are 5.99 kJ mol−1 and 10−1.38 s−1, respectively. [ABSTRACT FROM AUTHOR]

Ammonium Dinitramide (ADN) in its generic form has a long needle shaped structure, which hinders higher solid loading. Therefore, it is of utmost importance to optimize its crystal morphology into octagonal shapes. Moreover, the low critical humidity level of ADN renders it unusable in a humid climate. Hence, encapsulation with a hydrophobic polymer is necessary. In the present work, ADN was synthesized by nitration of potassium sulfamate with mixed acid nitration. The product was then mixed with toluene, graphene, citryl ammonium butyl, Cab-o-sil, and coating polymer (Polystyrene or HTPB) and treated with ultrasound to obtain semi-spherical ADN-coated particles. The method offers a reduction in operating temperature and elimination of ADN melting in the shape-altering process. In addition, the ADN product has a similar particle size and thermal stability compared to those in a conventional ADN melt-prilling method. The ADN product investigated under SEM confirms the particle morphological change from long needles into semi-spherical shapes. The particle size obtained, in the micrometer range, is ideal for higher theoretical maximum density. Furthermore, the ultrasound-treated ADN particles show significant reduction in moisture absorption, from 68% to 16% at 65% relative humidity. The DSC result shows no degradation of thermal stability of the coated particles. [ABSTRACT FROM AUTHOR]

New technologies are developed in the project RHEFORM to enable the replacement of hydrazine with liquid propellants based on ammonium dinitramide (ADN). The replacement of hydrazine with green propellants will make space propulsion more sustainable and better suitable for the requirements of future missions. In the RHEFORM project investigation on the composition of the propellants are conducted to enable the use of materials for catalysts and combustion chambers which are not subject to the International Traffic in Arms Regulations (ITAR). New igniters are under development aiming at a reduction of required energy and a more prompt ignition. Two different types of igniters are considered: improved catalytic igniters and thermal igniters. The technologies developed in RHEFORM will be implemented in two thruster demonstrators, aiming at a technology readiness level (TRL) of 5. In the present work the results obtained in the first half of the project are presented. [ABSTRACT FROM AUTHOR]

The aims of this work is to scrutinize the structural, physical and electrical properties of nitroamine (NH2NO2) adsorption on the outer and inner surface of pristine and C-replacing boron nitride nanosheet (BN nanosheet), using density functional theory methods at cam-B3LYP/6-31G (d) level of theory. Inspections of determined results represent that the adsorption of nitramide on the outer surface of pristine and C-replaced BN nanosheet is exothermic and on the inner surface it is endothermic. The deformation energy of system displays that the geometry and structure of BN nanosheet and nitramide in the BN nanosheet/NH2NO2 complex change significantly from the original state, whereas the quantum parameters and gap energy of the BN nanosheet/NH2NO2 system alter slightly from the original state. The nuclear magnetic resonance and molecular electrostatic potential consequences exhibit that in the BN nanosheet/NH2NO2 complex, the highest density of electrons is concentrated surrounding the NH2NO2 molecule. [ABSTRACT FROM AUTHOR]

In the molecule of neutral bis¬[(1H-tetrazol-5-yl)methyl]nitramide, (I), C4H6N10O2, there are two intra-molecular N-H⋯O hydrogen bonds. In the crystal, N-H⋯N hydrogen bonds link molecules, forming a two-dimensional network parallel to (201) and weak C-H⋯O, C-H⋯N hydrogen bonds, and intermolecular π-π stacking completes the three-dimensional network. The anion in the molecular salt, triaminoguanidinium 5-({[(1H-tetrazol-5-yl)methyl](nitro)amino}methyl)tetrazol-1-ide, (II), CH9N6+⋅C4H5N10O2-, displays intramolecular π-π stacking and in the crystal, N-H⋯N and N-H⋯O hydrogen bonds link the components of the structure, forming a three-dimensional network. In the crystal of diammonium bis[(tetrazol-1-id-5-yl)methyl]nitramide monohydrate, (III), 2NH4+⋅C4H4N10O22-⋅H2O, O-H⋯N, N-H⋯N, and N-H⋯O hydrogen bonds link the components of the structure into a three-dimensional network. In addition, there is intermolecular π-π stacking. In all three structures, the central N atom of the nitramide is mainly sp²-hybridized. Bond lengths indicate delocalization of charges on the tetrazole rings for all three compounds. Compound (II) was found to be a non-merohedral twin and was solved and refined in the major component. [ABSTRACT FROM AUTHOR]

Silver dinitramide AgN(NO) was prepared, and its structure was characterized by UV-Visible absorption spectra, Fourier transform infrared (FT-IR) spectra and Fourier transform Raman spectra. Its thermal decomposition process was investigated by differential scanning calorimetry and thermogravimetric analysis coupled with the gas analysis by FT-IR (EGA-FT-IR). The intermediate and final products of thermal decomposition were analyzed by FT-IR, Raman spectra and X-ray diffraction. Kissinger method and Ozawa methods were used to calculate apparent activation energy E , the pre-exponential constant lg A and linear correlation coefficient r. The results showed that the degradation process of AgN(NO) could be divided into two stages. The first one with a mass loss of 21.86 % took place in 408-483 K, in which NO was released and the intermediate product of thermal decomposition was AgNO. The second stage with a mass loss of 28.24 % occurred in 483-800 K. In this process, gases NO and O were evolved and Ag was the final product of thermal decomposition. Kissinger method results: E = 66.59 kJ mol, lg A = 7.21 min and r = 0.9913. Ozawa method results: E = 70.53 kJ mol, r = 0.9987. [ABSTRACT FROM AUTHOR]

Low toxicity ammonium dinitramide (ADN)-based aerospace propulsion systems currently show promise with regard to applications such as controlling satellite attitude. In the present work, the decomposition and combustion processes of an ADN-based monopropellant thruster were systematically studied, using a thermally stable catalyst to promote the decomposition reaction. The performance of the ADN propulsion system was investigated using a ground test system under vacuum, and the physical properties of the ADN-based propellant were also examined. Using this system, the effects of the preheating temperature and feed pressure on the combustion characteristics and thruster performance during steady state operation were observed. The results indicate that the propellant and catalyst employed during this work, as well as the design and manufacture of the thruster, met performance requirements. Moreover, the 1 N ADN thruster generated a specific impulse of 223 s, demonstrating the efficacy of the new catalyst. The thruster operational parameters (specifically, the preheating temperature and feed pressure) were found to have a significant effect on the decomposition and combustion processes within the thruster, and the performance of the thruster was demonstrated to improve at higher feed pressures and elevated preheating temperatures. A lower temperature of 140 °C was determined to activate the catalytic decomposition and combustion processes more effectively compared with the results obtained using other conditions. The data obtained in this study should be beneficial to future systematic and in-depth investigations of the combustion mechanism and characteristics within an ADN thruster. [ABSTRACT FROM AUTHOR]

In this article, the effect of catalytic bed thermal characteristics on the combustion processes of ammonium dinitramide (ADN)-based environmentally friendly propellant within the monopropellant thruster are analyzed. The thermal characteristics are described by considering the thruster outer wall radiation, thermal non-equilibrium temperature models, and thermal dispersion effect in the catalytic bed. This is filled with highly effective catalyst particles through the computational fluid dynamic simulation software called ANSYS Fluent. The results of spray hitting the wire mesh are achieved through an experiment, and the process of the liquid propellant evaporation is also considered. Profiles describing thermal characteristics of the catalytic bed by the user-defined function (UDF) are utilized to achieve the heat transfer characteristics by considering the non-equilibrium temperature models with thermal dispersion effect. The P1 radiation model takes into account the influence of the high temperature generated by the decomposition and combustion processes within the ADN thruster. The results demonstrate that the thermal characteristics have significant effects on the decomposition and combustion processes. Meanwhile, the influence of the thermal dispersion effect, decomposition and composition mechanisms, as well as the influence of the methanol mass fraction on the heat transfer are tested to provide an in-depth understanding of the operating mechanism within the ADN thruster. [ABSTRACT FROM AUTHOR]

The thermal decomposition of a high-energy oxidizer viz., guanylurea dinitramide (GUDN) has been studied by non-isothermal thermogravimetry (TG) and thermogravimetry combined with mass spectrometry (TG-MS). Isoconversional method of Vyazovkin (VZ) was used to investigate the dependence of activation energy ( E a ) on conversion (α). A strong dependence of E a on α, where the E a increases steadily for up to an α of ∼0.6 followed by a marginal increase and reaches ∼435.0 kJ mol −1 at the end of the reaction. E a has also been determined for GUDN using Kissinger’s method. A comparison of the results from Kissinger and isoconversional method shows that the activation energies from these methods are comparable. Using the model free isoconversional method, the isothermal conversion as a function of time at two different temperatures was also computed. The evolved gases during the decomposition of GUDN were analyzed by TG-MS which revealed the formation of ions corresponding to N 2 , O 2 , NH 3 , H 2 O, N 2 , NO, methane diimine, isocyanic acid, N 2 O, NO 2 and urea. [ABSTRACT FROM AUTHOR]

High pressure differential scanning calorimetry (HP-DSC) has been used to study thermal decomposition of energetic materials, i.e., trinitrotoluene, cyclotrimethylenetrinitramine, and ammonium dinitramide. HP-DSC runs have been performed in the range of 0.1–14 MPa both in inert and oxidative environments to determine the effect of pressure on vaporization/dissociation, melting, and decomposition processes. Results reveal that the melting point linearly increase with pressure with the slope 0.12–0.15 °C/MPa. Decomposition pathways and DSC effects are highly affected by pressure, as evaluated by changes in the peak temperature, reaction heat effect, and kinetic parameters. Activation energy and pre-exponential factor values were defined for separated decomposition stages of compounds, and found to vary with pressure. Vaporization/dissociation of starting material along with secondary reactions are proposed to be the main processes affected by pressure. Obtained results reveal that HP-DSC technique is useful in determining kinetic parameters and heat effect under elevated pressures, where energetic materials are usually applied. [ABSTRACT FROM AUTHOR]

Reactions of oxidative nucleophilic substitution of alkyl iodides with lithium perchlorate and dinitramide were studied. The reactions of alkyl iodides and lithium perchlorate, proceeding in the presence of nitronium tetrafluoroborate as an oxidant, furnished a series of new alkyl perchlorates, including those containing an adamantyl fragment. Spectral properties of alkyl perchlorates were studied in detail for the first time. The reactions of oxidative nucleophilic substitution of iodoacetic ester and lithium dinitramide, proceeding upon treatment with nitronium tetrafluoroborate or ozone, resulted in the substitution of an iodine atom with the nitrate anion. [ABSTRACT FROM AUTHOR]

The development of new ionic salt as green propellants is one of intense investigations to replace toxic N,N'-dimethylhydrazine. A new energetic salt N,N',N"-tri(propan-2-ylidene)methanetriamium dinitramide (NTAGDN) based on dinitramide was synthesized by reacting silver dinitramide with triaminoguanidinium chloride. The structure of this new energetic salt was confirmed by single-crystal X-ray diffraction, elemental analysis, Fourier transform infrared spectrometry, ultraviolet-visible spectrophotometry, and nuclear magnetic resonance spectroscopy. NTAGDN crystallizes in the orthorhombic space group R3-. Thermal decomposition was studied by differential scanning calorimetry, differential thermal analysis, and thermogravimetric tandem infrared spectrometry. Results indicated that NTAGDN exhibited excellent resistance to thermal decompositions of up to 470 K and incurred an 80.54% mass loss between 450 and 523 K via exothermic decomposition. The kinetic parameters of NTAGDN thermal decomposition were also obtained from the differential thermal analysis data by Kissinger's method with Ea = 125.46 kJ·mol-1. Moreover, based on the Kamlet-Jacobs formula, the detonation velocity and detonation pressure of NTAGDN were calculated as 6.3 km·s-1 and 15 GPa, respectively. [ABSTRACT FROM AUTHOR]

The working processes of the ADN-based liquid thruster are complex, utilizing catalytic decomposition in a catalyst bed and high-pressure combustion in the combustion chamber. The present study examines the experimental performance of high-pressure combustion in an ADN-based liquid thruster. Using the Tunable Diode Laser Absorption Spectroscopy (TDLAS) method, flow parameters such as gas temperature and the characteristic species concentration of CO in the combustion chamber were measured instantaneously under the atmospheric environment. The effects of propellant inlet pressure and the catalyst bed preheated temperature on the combustion process were evaluated. It was found that both an increase in the propellant inlet pressure and an increase in the catalyst bed preheated temperature led to an increase in the gas temperature and a decrease of the CO mole fraction in the combustion chamber. In a hot fire test in the vacuum chamber, the performance of the model thruster under steady operation was tested. The results showed that with the increase of propellant inlet pressure, the combustion chamber pressure and the combustion chamber wall temperature also increase. However, although the increase of the catalyst bed preheated temperature also led to the increase of the combustion chamber wall temperature, the combustion chamber pressure remained nearly constant. These results provide a better understanding of the mechanisms of high-pressure combustion with ADN-based liquid propellants, which is beneficial to the development of green aerospace propulsion techniques. [ABSTRACT FROM AUTHOR]

The influence of solutions on ammonium dinitramide (ADN) crystal morphology was investigated using a combined experimental and molecular dynamics simulation approach. Scanning electron microscopy showed that ADN recrystallized from acetone, propanol, dimethyl sulfoxide (DMSO), and ethanol exhibited a lamellar structure, in contrast to the polyhedron structure obtained with isopropanol/NaF. X-ray diffraction analysis revealed that ADN crystals are mainly composed of six crystal faces (010, 011, 110, 100, 121, 031), and acetone, propanol, DMSO, and ethanol result in crystals in which growth at face (100) dominated. Molecular dynamics simulations indicated that the accessible surfaces and lattice energy ( E) vary with the crystal faces. The interaction energy between solutions and crystal faces ( E) was dependent on both crystal faces and solution components, as was the attachment energy ( E). The relative standard deviation R of the growth rate of the crystal faces was ordered as follows: acetone (0.117) > propanol (0.098) > DMSO (0.094) > ethanol (0.087) > isopropanol (0.078) > isopropanol/NaF (0.073). A larger R resulted in a lamellar structure, while a smaller R gave more homogeneous growth rates that resulted in polyhedron crystals. [ABSTRACT FROM AUTHOR]

Ammonium dinitramide (ADN) monopropellant is currently the most promising among all ‘green propellants’. In this paper, the decomposition and combustion process of liquid ADN-based ternary mixtures for propulsion are numerically studied. The R–R distribution model is used to study the initial boundary conditions of droplet distribution resulting from spray hit on a wire mesh based on PDA experiment. To simulate the heat-transfer characteristics between the gas–solid phases, a two-temperature porous medium model in a catalytic bed is used. An 11-species and 7-reactions chemistry model is used to study the catalytic and combustion processes. The final distribution of temperature, pressure, and other kinds of material component concentrations are obtained using the ADN thruster. The results of simulation conducted in the present study are well agree with previous experimental data, and the demonstration of the ADN thruster confirms that a good steady-state operation is achieved. The effects of spray inlet mass flux and porosity on monopropellant thruster performance are analyzed. The numerical results further show that a larger inlet mass flux results in better thruster performance and a catalytic bed porosity value of 0.5 can exhibit the best thruster performance. These findings can serve as a key reference for designing and testing non-toxic aerospace monopropellant thrusters. [ABSTRACT FROM AUTHOR]

The dissolution properties of ammonium dinitramide (ADN) in N-methyl pyrrolidone (NMP) were studied with a RD496-2000 Calvet microcalorimeter at four different temperatures under atmospheric pressure. The heat effects were determined for ADN in NMP. The molar enthalpies and the differential molar enthalpies for ADN in NMP were also obtained at the same time. The corresponding kinetic equations that describe the four dissolution processes are discussed. [ABSTRACT FROM AUTHOR]

Ammonium dinitramide (ADN) is a promising new oxidizer for solid propellants because it possesses both high oxygen balance and high energy content, and does not contain halogen atoms. A necessary characteristic of solid propellants is chemical stability under various conditions. This study focused on the thermal decomposition mechanism of ADN under pressurized conditions. The pressure was adjusted from 0.1 to 6 MPa, while ADN was heated at a constant rate. The exothermal behavior and the decomposition products in the condensed phase during heating were measured simultaneously using pressure differential scanning calorimetry (PDSC) and Raman spectrometry. PDSC analyses showed the multiple stages of exotherms after melting. The exothermal behavior at low temperatures varied with pressure. Analysis of the decomposition products indicated that ammonium nitrate (AN) was generated during decomposition of ADN at all pressures. At normal pressure, AN was produced at the same time as start of exotherm. However, the temperature at which the ratio of ADN in chemical species in the condensed phase began to decrease under high pressure was higher than that at atmospheric pressure despite the existence of significant exotherm. At initial stage, thermal decomposition of ADN that does not generate AN was thought to be promoted by increased pressure. [ABSTRACT FROM AUTHOR]

Highlights: [•] Development of a condensed-phase kinetic mechanism for NH4NO3 decomposition. [•] Validation against original TGA-XRD-DSC experiments and literature data. [•] Impact of heating rate on reactions pathways and N-selectivity. [•] Impact of gas-phase reactions involving nitramide and nitric acid. [ABSTRACT FROM AUTHOR]

Singlet, triplet and ionized states of the energetic molecule 1,1-diamino-2,2-dinitroethylene, known as FOX-7 or DADNE, were investigated using the symmetry-adapted-cluster configuration interaction (SAC-CI) ab initio wave function. The 20 computed singlet transitions, with 2 exceptions, were bright. The most intense singlet transitions were of the n→π type-typical of molecules having nitro groups. Fast intersystem crossing (ISC) from the 1A, 2A and 8A bright singlet transitions is possible. Other feasible ISC processes are discussed. The computed singlet and ionization spectra have similar features when compared to nitramide and N,N-dimethylnitramine molecules, which have only a nitro group. The ionization energies of the first 20 states have differences in comparison with Koopmans' energy values that can reach 3 eV. Moreover, the character of the first ionized states, dominated by single ionizations, is not the same when compared with the character resulting from application of Koopmans' theorem. [ABSTRACT FROM AUTHOR]

Abstract: A comprehensive multi-phase combustion model has been developed to study the physiochemical processes involved in the combustion of ammonium dinitramide (ADN). The numerical model is based on the conservation equations of mass, species concentration, and energy, and takes into account finite-rate chemical kinetics in both condensed and gas phases. Based on an extensive review of the literature on ADN thermal decomposition, three global decomposition reactions in the condensed phase of ADN are included. A detailed chemical kinetics scheme involving 34 species and 165 reactions is employed in the gas phase. Detailed combustion-wave structures and burning rate characteristics of ADN are described. The optimized gas-phase kinetics mechanism was able to predict the multi-stage flame structure. Good agreements between the predicted and measured profiles of temperature and species mole fractions were obtained at different pressures. Reasonable agreements between calculated and measured values of propellant burning rates and surface temperatures were obtained over a broad range of pressure from 0.7 to 350atm. The burning rate increases with pressure, except in the mid range of ∼60–100atm. The coupled condensed- and gas-phase analysis employed in the current model is able to capture this irregular/unstable combustion behavior in the mid range, where the burning rate decreases with the increase in pressure. [Copyright &y& Elsevier]

The enthalpy of dissolution of FOX-12 in dimethyl sulfoxide (DMSO) was measured by means of a RD496-III Calvet microcalorimeter at 298.15 K. Empirical formulae for the calculation of the enthalpy of dissolution ( $$ \Updelta_{\text{diss}} H $$ ), relative partial molar enthalpy ( $$ \Updelta_{\text{diss}} H_{\text{partial}} $$ ), and relative apparent molar enthalpy ( $$ \Updelta_{\text{diss}} H_{\text{apparent}} $$ ) were obtained from the experimental data of the enthalpies of dissolution of FOX-12 in DMSO. The kinetic equation that describes the dissolution process of FOX-12 in DMSO at 298.15 K is determined as $$ \frac{{{\text{d}}\alpha }}{{{\text{d}}t}} = 8.5 \times 10^{ - 3} (1 - \alpha )^{0.59} $$ . [ABSTRACT FROM AUTHOR]

The enthalpies of dissolution of N-guanylurea dinitramide (GUDN) in dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP) were measured using an RD496-2000 Calvet microcalorimeter at 298.15 K under atmospheric pressure, respectively. Empirical formulae for the calculation of the enthalpy of dissolution (Δ H), relative partial molar enthalpy (Δ H), and relative apparent molar enthalpy (Δ H) were obtained from the experimental data of the dissolution processes of GUDN in DMSO and NMP. Furthermore, the corresponding kinetic equations describing the two dissolution processes were d α/d t = 10(1 − α) for the dissolution of GUDN in DMSO, and d α/d t = 10(1 − α) for the dissolution of GUDN in NMP. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) and the dispersion corrected DFT have been used to investigate the hygroscopicity of ammonium dinitramide (ADN). Calculation results show that the gaseous ADN has a strong hydrogen bond. But the ionic pair structure NH · N(NO) is stabilized upon the addition of water molecules. Natural bond orbital calculations suggest that the intra- and intermolecular orbital interactions LP(O) → σ*(N-H) or LP(O) → σ*(O-H) make the system stabilized as a whole. En energy decomposition analysis reveals that the interactions between ADN and HO are dominated by the electrostatic and orbital interactions. The formation reactions become more spontaneous with the increasing number of water molecules but can be weakened by the growing temperature from 200 to 400 K. Moreover, the molecular dynamic method is applied to explore a more realistic cluster model to study the interactions between ADN and HO. [ABSTRACT FROM AUTHOR]

Ammonium dinitramide (ADN) is one of the several promising new solid propellant oxidizers. ADN is of interest because its oxygen balance and energy content are high, and it also halogen-free. One of the most important characteristics of a propellant oxidizer, however, is stability and ADN is known to degrade to ammonium nitrate (AN) during storage, which will affect its performance. This study focused on the effects of aging on the thermal decomposition mechanism of ADN. The thermal behaviors of ADN and ADN/AN mixtures were studied, as were the gases evolved during their decomposition, using differential scanning calorimetry (DSC), thermogravimetry-differential thermal analysis-infrared spectrometry (TG-DTA-IR), and thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS). The results of these analyses demonstrated that the decomposition of ADN occurs via a series of distinct stages in the condensed phase. The gases evolved from ADN decomposition were NO, NO, N, and HO. In contrast, ADN mixed with AN (to simulate aging) did not exhibit the same initial reaction. We conclude that aging inhibits early stage, low temperature decomposition reactions of ADN. Two possible reasons were proposed, these being either a decrease in the acidity of the material due to the presence of AN, or inhibition of the acidic dissociation of dinitramic acid by NO. [ABSTRACT FROM AUTHOR]

Information on synthesis methods and properties of N, N′-dinitrourea and its salts, which were reported virtually simultaneously by different authors in different publications, is summarized and systematized. Merits and drawbacks of various approaches for the synthesis of the target products are discussed. The reactivity of N, N′-dinitrourea and its salts in the reactions of nucleophilic substitution and condensation is discussed. [ABSTRACT FROM AUTHOR]

N-Guanylurea-dinitramide (FOX-12) is a very insensitive energetic material intended to be used in the composition of next-generation insensitive munitions. To help predict the environmental behavior and fate of FOX-12, we conducted a study to determine its photodegradability and biodegradability. When dissolved in water, FOX-12, a guanylurea-dinitramide salt, also named GUDN, dissociated instantly to produce the dinitramide moiety and guanylurea, as demonstrated by high-performance liquid chromatography (HPLC) analysis. When an aqueous solution of FOX-12 was subjected to photolysis using a solar-simulated photoreactor, we found a rapid removal of the dinitramide with concurrent formation of N2O, NO2-, and NO3-. The second component, guanylurea, was photostable. However, when FOX-12 was incubated aerobically with the soil isolate Variovorax strain VC1 and protected from light, the dinitramide component of FOX-12 was recalcitrant but guanylurea degraded effectively to ammonia, guanidine, and presumably CO2. When FOX-12 was incubated with strain VC1 in the presence of light, both components of FOX-12 degraded, giving similar products to those described above. We concluded that the new insensitive explosive FOX-12 can be effectively degraded by a joint photomicrobial process and, therefore, should not cause persistent contamination of surface waters. [ABSTRACT FROM AUTHOR]

The mechanism for sublimation of NH4N(NO2)2(ADN) has been investigated quantum-mechanicallywithgeneralized gradient approximation plane-wave density functional theorycalculations; the solid surface is represented by a slab model andthe periodic boundary conditions are applied. The calculated latticeconstants for the bulk ADN, which were found to consist of NH4+[ON(O)NNO2]−units,instead of NH4+[N(NO2)2]−, agree quite well with experimental values.Results show that three steps are involved in the sublimation/decompositionof ADN. The first step is the relaxation of the surface layer with1.6 kcal/mol energy per NH4ON(O)NNO2unit; thesecond step is the sublimation of the surface layer to form a molecular[NH3]–[HON(O)NNO2] complex with a 29.4kcal/mol sublimation energy, consistent with the experimental observationof Korobeinichev et al.(10) The last stepis the dissociation of the [H3N]–[HON(O)NNO2] complex to give NH3and HON(O)NNO2with the dissociation energy of 13.9 kcal/mol. Direct formationof NO2(g) from solid ADN costs a much higher energy, 58.3kcal/mol. Our calculated total sublimation enthalpy for ADN(s) →NH3(g) + HON(O)NNO2) (g), 44.9 kcal/mol viathree steps, is in good agreement with the value, 42.1 kcal/mol predictedfor the one-step sublimation process in this work and the value 44.0kcal/mol computed by Politzer et al.(11) usingexperimental thermochemical data. The sublimation rate constant forthe rate-controlling step 2 can be represented as ksub= 2.18 × 1012exp (−30.5 kcal/mol/RT)s–1, which agrees well with available experimentaldata within the temperature range studied. The high pressure limitdecomposition rate constant for the molecular complex H3N···HON(O)NNO2can be expressed by kdec= 3.18 × 1013exp (−15.09kcal/mol/RT) s–1. In addition, water molecules werefound to increase the sublimation enthalpy of ADN, contrary to thatfound in the ammonium perchlorate system, in which water moleculeswere shown to reduce pronouncedly the enthalpy of sublimation. [ABSTRACT FROM AUTHOR]

The spatial and electronic structure studies of nitramide NHNO suggest that the change in its molecular geometry upon transition from the gas phase to the condensed state is caused by an increase in the contribution of conjugation between functional groups. According to the analysis of the Bader atomic charges, the effects of such conjugation are to a considerable extent governed by intramolecular charge transfer from the amino to the nitro group. From estimation of the contribution of conjugation to the charge transfer it follows that conjugation remains in the isolated molecule. The influence of hydrogen bonding on the increase in the contribution of conjugation and the corresponding charge redistribution in the molecule was considered. Despite the presence of conjugation between functional groups, the planar configuration of the molecule in the crystal is not realized and the crystallographic twofold axis corresponds to superposition of two molecular configurations with C symmetry. [ABSTRACT FROM AUTHOR]

Abstract: The reaction mechanism of the fast selective catalytic reduction (SCR) of NO x has been investigated by means of a microkinetic model based on DFT calculations. First, potential additional reaction mechanisms are presented that include the intermediate formation of Z−[NO x ]+ (x =1, 2) from the decomposition of N2O y (y =3, 4) on a Brønsted acid. The formed reacts with ammonia to nirosamine or nitramide. The DFT results are applied in a microkinetic model together with prior studies of Brüggemann et al. The simulated conversion of NO x is in agreement with experimental data over a wide range of temperature. The activity of the H-ZSM5 for the fast SCR is based on the reaction sequence via Z−[NO x ]+, the decomposition of nitrosamine and nitramide, and the reaction of nitrous and nitric acid with adsorbed ammonia at low temperatures. Ammonia blocks the active sites at low temperatures while thermodynamic limitations of the surface species N2O y restrict the conversion at high temperatures. Heat of formations and reaction rate constants were adjusted within the accuracy of the applied method for important elementary steps to cope with experimental data. [Copyright &y& Elsevier]

A large set of quasi-classical, direct dynamics trajectory simulations were performed for decomposition of 1,5-dinitrobiuret (DNB) over a temperature range from 4000 to 6000 K, aimed at providing insight into DNB decomposition mechanisms. The trajectories revealed various decomposition paths and reproduced the products (including HNCO, N2O, NO2, NO, and water) observed in DNB pyrolysis experiments. Using trajectory results as a guide, structures of intermediate complexes and transition states that might be important for decomposition were determined using density functional theory calculations. Rice-Ramsperger--Kassel--Marcus (RRKM) theory was then utilized to examine behaviors of the energized reactant and intermediates and to determine unimolecular rates for crossing various transition states. According to RRKM predictions, the dominant initial decomposition path of energized DNB corresponds to elimination of HNNO2H via a conceited mechanism where the molecular decomposition is accompanied with intramolecular H-atom transfer from the central nitrogen to the terminal nitro oxygen. Other important paths correspond to elimination of NO2 and H2NNO2. NO2 elimination is a simple N-N bond scission process. Formation and elimination of nitramide is, however, dynamically complicated, requiring twisting a - NHNO2 group out of the molecular plane, followed by an intramolecular reaction to form nitramide before its elimination. These two paths become significant at temperatures above 1500 K, accounting for > 17% of DNB decomposition at 2000 K. This work demonstrates that quasi-classical trajectory simulations, in conjunction with electronic structure and RRKM calculations, are able to extract mechanisms, kinetics, dynamics and product branching ratios for the decomposition of complex energetic molecules and to predict how they vary with decomposition temperature. [ABSTRACT FROM AUTHOR]

Abstract: ONIOM calculation was carried out to investigate the isomerization and dissociation reactions of nitramide (NA) encapsulated inside an armchair (5,5) single-walled carbon nanotubes [NA@CNT(5.5)]. Results demonstrated that the activation energy barriers of the N–N bond dissociation and the nitro–nitrite isomerization of NA significantly decreased when NA was encapsulated inside CNT(5,5), suggesting that the CNT(5,5) can promote the two initial reactions. However, the H-migration reaction of NA was hindered by the encapsulation inside CNT(5.5) in view of the increase in the barrier height. The encapsulated inside CNT(5,5) resulted in the exchange of the order of energy barriers for the N–N bond dissociation and H-migration isomerization. The H-migration reaction was kinetically favorable for the isolated NA, but the N–N bond dissociation was the most energetically favorable for the NA@CNT(5.5). Results also showed that, in the encapsulated state, the H-migration reaction could compete vigorously with the N–N bond dissociation due to their close activation energies. Furthermore, we found that the relative energies of the intermediates formed by the isomerization and dissociation of NA were also modified by the encapsulation inside CNT(5,5). [Copyright &y& Elsevier]

Symmetry-adapted-cluster configuration interaction (SAC-CI) wave functions were employed to compute 16 singlet and 13 triplet vertical transitions, and 14 ionized states including relative intensities of the nitramide molecule, H2NNO2. This molecule is the simplest neutral closed-shell molecule which has an N–NO2 bond and is a member of the nitramine family, R,R′N(NO2), an important class of energetic materials with practical applications. The present nitramide results showed strong similarities with the ones of the N, N-dimethylnitramine molecule, which has also an N–NO2 bond and was previously studied using the SAC-CI method. Experimental ultraviolet and photoelectron band spectra of the nitramide molecule could be successfully assigned. All the singlet transitions have valence character. The computed singlet and triplet transitions, excepting a singlet one, result from excitation originating in the four highest occupied molecular orbitals, which have close energies. Most of the singlet and triplet transitions involved mixing of singly excited configurations. The strongest computed transition, at 6.8 eV, is a mixture of two nπNO2 → π* configurations corresponding to excitations from the highest occupied molecular orbital (HOMO) to the first two virtual orbitals and has an optical oscillator strength value of 0.2665. The computed ionized states described the whole measured spectrum, have excellent agreement when compared with the measured ionization potentials and revealed an inversion of the ordering of the first states not expected according to Koopmanns’ theorem, thereby showing the limitations of the latter. [ABSTRACT FROM AUTHOR]

Abstract: The thermal decomposition of two highly energetic materials, mononitrobiuret (MNB) and 1,5-dinitrobiuret (DNB), was investigated by thermogravimetric analysis and differential scanning calorimetry. Mass spectrometry and IR spectroscopy were used to identify the gaseous products. Decomposition appears in both cases to be initiated by the release of nitramine. The gaseous products after the exothermic decomposition are similar for MNB and DNB, but the decomposition temperature of MNB is significantly higher and leads to the formation of urea, biuret (imidodicarbonic diamide), triuret (diimidotricarbonic diamide), tetrauret (triimidotetracarbonic diamide), and cyanuric acid (S-triazine-2,4,6(1H,3H,4H)-trione). [Copyright &y& Elsevier]