Hexanitrohexaazaisowurtzitane Research Articles

Hydrogen peroxide – A promising oxidizer for rocket propulsion and its application in solid rocket propellants

This paper discusses the potential use of hydrogen peroxide as oxidizer for solid rocket propulsion. While hydrogen peroxide is a liquid in normal conditions, it may be used in solid rocket motor grains. Use of hydrogen peroxide of HTP class (High Test Peroxide) is proposed. It has been known for many decades but its utilization has been historically limited to liquid propellants. Until recently is application even in liquid state in rocket propulsion for space and defence has been limited due to storability and safety issues. With the availability of new grades of HTP with higher purity and concentrations, enhanced performance, safety and storability are possible. This results in HTP being considered for a wide range of rocket propulsion systems: as oxidizer in bipropellant and hybrid propulsion systems, as well a monopropellant. To ensure proper analysis of the potential of using HTP in next-generation solid rocket propellants, this paper reviews existing rocket propulsion applications of HTP. Modern use requires high performance and common current composite propellant compositions utilize ammonium perchlorate (AP) as oxidizer, what has several disadvantages, which are discussed. Alternative oxidizing compounds include ammonium dinitiramide (ADN), ammonium nitrate (AN), hydrazinium nitroformate (HNF), hexanitrohexaazaisowurtzitane (HNIW) and several other secondary explosives. Key properties of solid propellant oxidizers are listed and discussed. The need for further alternatives, despite numerous recent advances in solid rocket oxidizer technology is justified. The global push forward high performance green propulsion is one of the main motivations behind considering HTP for solid rocket propulsion. Theoretical performance of solid rocket motors using solid grains containing a high mass fraction of HTP is presented. This includes performance considering several fuels and additives and different oxidizer loadings. Up to date concepts of using hydrogen peroxide in solid propellants are reviewed. Solid cryogenic propellants using hydrogen peroxide are mentioned, but focus is given to solid propellants which could ensure flexible operations, thus use in state-of-the-art solid rocket motors. Challenges of HTP application as an oxidizer for solid propulsion are listed. This includes a discussion concerning its reactivity, thus limited compatibility with organic materials. Recommendations for further experimental work are proposed. Potential technology applications are listed with explanations why these particular niches may benefit from utilization of the new solid propellant technology.

Two novel heterobimetallic metal-organic frameworks for the enhanced catalytic thermolysis and laser ignition of CL-20

The study of multiple complex catalytic mechanisms is currently one of the great scientific issues for the application of high-energy solid propellants. Two novel heterobimetallic metal-organic frameworks (MOFs), Ba4Pb4(CH3CO2)8 [(CH6CO2)4Pb](CH3CO2)4 (PbBa-MOF) and Ba2Ni(CO2H)6(OH2)4 (NiBa-MOF), were prepared via the solvothermal method, and their structures and composition were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR) techniques and N2 adsorption/desorption experiment. The thermal decomposition characteristics of the two MOFs and their catalytic performances on the hexanitro hexaazaisowurtzitane (CL-20) thermolysis were also studied by differential scanning calorimetr (DSC) and thermogravimetric-fourier transform infrared spectroscopy-mass spectrum (TG-FTIR-MS) methods. The results showed that the NiBa-MOF presented a lower initial decomposition temperature than the PbBa-MOF, and the difference of the MOFs structures affected the starting point of thermal decomposition. Compared with the pure CL-20, the thermolysis peak temperature and apparent activation energy (Ea) of the CL-20/PbBa-MOF mixture were decreased by 2.2 °C and 23.76 kJ‧mol−1, respectively. The Ea of CL-20/NiBa-MOF mixture was lower and 42.01 kJ‧mol−1, indicating the better catalytic activity of NiBa-MOF. The thermolysis catalytic mechanisms were studied by analyzing the transformation of gas products during the pyrolysis of mixtures. The effect of these two MOFs on the CL-20 thermolysis is primarily owing to the strong attraction of metal cations to electronics, bimetallic synergistic catalysis, and the release of active free radicals. Furthermore, the laser ignition and flame propagation features showed that these two MOFs reduced the minimum ignition power density and ignition delay time of the CL-20, and the flame becomes brighter and more luminous. The influence of the two MOFs on the flame bright spot of CL-20 based mixtures was described.

Preparation and performances characterization of HNIW/NTO-based high-energetic low vulnerable polymer-bonded explosive

To satisfy the energy and security requirements of the explosives, it is necessary to develop high-energetic low vulnerable explosive. As the representatives of high-energetic explosives and low vulnerable explosives, hexanitrohexaazaisowurtzitane (HNIW) and 3-nitro-1,2,4-triazole-5-one (NTO) are used to research high-energetic low vulnerable polymer-bonded explosive (PBX) in this study. Based on the formulation of PAX-11 (94 mass% HNIW, 2.4 mass% CAB, 3.6 mass% BDNPA/F), some HNIW is replaced by NTO to reduce the vulnerability of the PBX during this work. Solution−water suspension method was used to prepare a series PBXs with different formulations. The explosion probability method, differential scanning calorimeter and accelerating rate calorimeter are used to evaluate the hazards of different PBX molding powders. And the thermal vulnerabilities, mechanical properties and energy levels of PBX columns are assessed by slow cook-off tests, tensile strengthes and detonation velocities, respectively. Moreover, finite element numerical simulations are adopted to study the transient temperature distributions, ignition time and ignition locations of the PBX columns during slow cook-off. The investigated results show that when the mass fraction of HNIW and NTO is 50% and 44%, respectively, the PBX passes the slow cook-off test and the detonation velocity reaches 8685 m s−1. To balance the energy and vulnerability of the PBXs, we obtain a high-energetic low vulnerable PBX formulation (50 mass% HNIW, 44 mass% NTO, 2.4 mass% CAB, 3.6 mass% BDNPA/F, 0.5 mass% additional graphite) which can be used in the warhead of the high-explosive anti-tank cartridge.

Scale-Up of a Semi-Batch Draft Tube Baffled Crystallizer for Hexanitrohexaazaisowurtzitane Based on Experiments and Computational Fluid Dynamics Simulation

In this study, experimental work was carried out for the production of microsized hexanitrohexaazaisowurtzitane (HNIW) in a 500 L draft tube baffled (DTB) crystallizer. Acetone and isopropanol were...

Pyrolysis pathway redirection of HNIW by nano-aluminum

The pyrolysis behavior of hexanitrohexaazaisowurtzitane (HNIW) and HNIW/nano-Aluminum are investigated by non-isothermal differential scanning calorimetry/thermogravimetry/Pyrolysis-mass spectrometry/Fourier transform infrared spectroscopy (DSC/TG/Py-MS/FTIR) coupling analysis. The result shows that nano-Al improves the thermal stability of HNIW by swinging the very beginning of pyrolysis from synchronous bond cleavage of the highly strained molecular to the formation of HONO free radical corresponding with the increment of apparent activation energy. After the initial stage, nano-Al catalyzes the pyrolysis pathway to primary cleavage of C–N bond and releasing hyperbaric unstable N2O, which sequentially reacts with other gaseous products and Al.

Molecular dynamics investigation on the morphology of HNIW affected by the growth condition

ABSTRACTThe crystal morphology of Hexanitrohexaazaisowurtzitane (HNIW) in vacuum and ethyl acetate was investigated by attachment energy (AE) model through molecular dynamics (MD). The simulated solvent-affected outcome agrees well with the experimental crystal habit cultivated from ethyl acetate. The influence of model size on the modified AE was discussed, and a reasonable model size was obtained. The model size can be broadened to calculate the morphology of other compounds. The radial distribution function (RDF) analyses and diffusion coefficient analyses were performed to explore the adsorption and diffusion behaviors of ethyl acetate molecules on HNIW surfaces. The simulation results can provide some guidance for the further crystallization process of HNIW.

Investigation of the effect of the CAB/A3 system on HNIW-based PBXs using molecular dynamics.

The influences of the temperature and the BDNPA/BDNPF (A3) content on the mechanical properties of and the binding energies between hexanitrohexaazaisowurtzitane (HNIW) and cellulose acetate butyrate (CAB)/A3 were studied via molecular dynamics simulations. The morphology of HNIW in acetone was simulated using an attachment energy (AE) model to elucidate the HNIW surfaces that are present under real-world conditions. The simulation results were consistent with the experimentally derived ones, and they indicated that the exposed HNIW surfaces were (0 0 1), (1 1 0), and (1 1 -1). The mechanical properties of CAB with different amounts of A3 were calculated at different temperatures, and the results showed that the amount of A3 was a stronger influence than the temperature on the mechanical properties. The binding energies between CAB/A3 and the exposed HNIW surfaces were calculated. Based on the binding energy and the area of each exposed surface, the weighted-average binding energy was calculated and then used instead of the total binding energy to evaluate the effect of the temperature and the A3 content on the binding energy. The average binding energy was found to be highest when the temperature was 313 K and the mass fraction of A3 was 0.15.

Bis(dinitropyrazolyl)methanes as Stable High Energy Materials

The development of high energy materials (HEMs) with both high explosive performance and decreased sensitivity is a main theme of current research for energetic materials. Polynitroazoles are good building blocks for new energetic materials because of their stable chemical properties. Two new bis(dinitropyrazolyl)methanes as potential insensitive HEMs were prepared via either the coupling of dinitropyrazole or the nitration of bis(mononitropyrazolyl)methane. Their insensitive properties are also reported and compared to those of RDX (trinitrohexahydro‐s‐triazine) and HNIW (CL‐20, hexanitrohexaazaisowurtzitane).

Thermally Induced Polymorphic Transformation of Hexanitrohexaazaisowurtzitane (HNIW) Investigated by in-situ X-ray Powder Diffraction

Thermally Induced Polymorphic Transformation of Hexanitrohexaazaisowurtzitane (HNIW) Investigated by in-situ X-ray Powder Diffraction

Study of Deactivation of Pd(OH)2/C Catalyst in Reductive Debenzylation of Hexabenzylhexaazaisowurtzitane

AbstractThe conversion of hexabenzylhexaazaisowurtzitane (HBIW) to 2,6,8,12‐tetraacetyl‐4,10‐dibenzyl‐2,4,6,8,10,12‐hexaazaisowurtzitane (TADB) is the major challenge in the production of hexanitrohexaazaisowurtzitane (HNIW) which only proceeds over supported palladium catalyst in a reductive debenzylation reaction. The catalyst is quickly deactivated during the debenzylation reaction. In this study, the change in Pd content in the catalyst during the reaction was measured. It was demonstrated that a portion of the palladium particles in the catalyst was leached during the reaction. The H2 chemisorption isotherm on the catalyst at 303 K showed that the volume of chemisorbed H2 on spent catalyst was significantly less than that on fresh catalyst. The N2 physisorption isotherm on the catalyst at 77 K revealed that the surface area of spent catalyst was less than that of fresh catalyst. Moreover, the FESEM‐EDS and TEM images and also wide‐angle XRD patterns demonstrated that the mean sizes of palladium crystallites and particles in spent catalyst were larger than those in the fresh catalyst. These results demonstrated that the leaching of palladium particles and the aggregation of palladium particles in catalyst play active roles in the deactivation of catalyst in the debenzylation of HBIW.

Estimation of the kinetic parameters for thermal decomposition of HNIW and its adiabatic time-to-explosion by Kooij formula

Abstract A differential/integral method to estimate the kinetic parameters (apparent activation energy Ea and pre-exponential factor A) for thermal decomposition reaction of energetic materials based on Kooij formula are applied to study the nonisothermal decomposition reaction kinetics of hexanitrohexaazaisowurtzitane (HNIW) by analyzing nonisothermal DSC curve data. The apparent activation energy (Ea) obtained by the integral isoconversional non-isothermal method based on Kooij formula is used to check the constancy and validity of apparent activation energy by the differential/integral method based on Kooij formula. The most probable mechanism function of thermal decomposition reaction of HNIW is determined by a logical choice method. The equations for calculating the critical temperatures of thermal explosion (Tb) and adiabatic time-to-explosion (tTIad) based on Kooij formula are used to calculate the values of Tb and tTIad to evaluate the thermal safety and heat-resistant ability of HNIW. All the original data needed for analyzing the kinetic parameters are from nonisothermal DSC curves. The results show that the kinetic model function in differential form and the values of Ea and A of decomposition reaction of HNIW are 3(1 − α)[−ln(1 − α)]2/3, 152.73 kJ mol−1 and 1011.97 s−1, respectively, and the values of self-accelerating decomposition temperature (TSADT), Tb and tTIad are 486.55 K, 493.11 K and 52.01 s, respectively.

BTATz–HNIW–CMDB propellants

The high nitrogen compound 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine and the high energy density material hexanitrohexaazaisowurtzitane (HNIW), were used as substitute of hexogen (RDX) in the composite modified double base (CMDB) propellant formulations, the propellant samples were prepared, the thermal behaviors, nonisothermal reaction kinetics, and thermal safety were carried out, and the eight important parameters were calculated and obtained as the self-accelerating decomposition temperature (T SADT), thermal ignition temperature (T TIT), critical temperatures of thermal explosion (T b), critical temperature of hot-spot initiation (T cr,hot-spot), characteristic drop height of impact sensitivity (H 50), critical thermal explosion ambient temperature (T acr), safety degree (S d), and thermal explosion probability (P TE). It shows that the content of HNIW has a large effect on the decomposition reaction mechanism of the CMDB propellant, when the content of HNIW is 10 %, the decomposition reaction are controlled by the random nucleation and subsequent growth (n = l), and the reaction mechanism obeys Mampel law; but when the content of HNIW is 20 %, the decomposition reaction are controlled by the chemical reaction (n = 1/4). The mechanism can not be changed by the catalysts, and they just make the apparent activation energy change slightly. For the sample, from BC01 to BC04, the values of T SADT and T TIT making an upward tendency, show the resistivity to heat: BC04 > BC03 > BC02 > BC01; the values of T acr and S d, BC01 are the maximum and BC02 are the minimum, show the heat sensitivity: BC01 > BC03 > BC04 > BC02. For the same radius, the thermal safety of the sphere sample is greater than that of the infinite cylinder one.

DFT studies on a high-energy density cage compound 1, 3, 5, 7, 9, 11-hexo(N(CH3)NO2)-2, 4, 6, 8, 10, 12-hexaazatetracyclo[5, 5, 0, 0, 0] dodecane

The infrared and Raman spectra, heat of formation (HOF) and thermodynamic properties were investigated by B3LYP/6-31G** method for a new designed polynitro cage compound 1,3,5,7,9,11-hexo(N(CH3)NO2)-2,4,6,8,10,12-hexaazatetracyclo[5,5,0,0,0]dodecane. The detonation velocity (D) and pressure (P) were predicted by the Kamlet–Jacobs equations based on the theoretical density and condensed HOF. The bond dissociation energies and bond orders for the weakest bonds were analysed to investigate the thermal stability of the title compound. The computational result shows that the detonation velocity and pressure of the title compound are superior to those of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), but inferior to those of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) and hexanitrohexaazaisowurtzitane (HNIW). And the analysis of thermal stability shows that the first step of pyrolysis is the rupture of the N7–NO2 bond. The crystal structure obtained by molecular mechanics belongs to the P21 space group, with the lattice parameters Z = 2, a = 11.8246 Å, b = 10.4632 Å, c = 15.9713 Å, ρ = 1.98 g cm−3.

Computational studies on a high density cage compound hexanitrohexaazaisowurtzitane derivative

A newly designed polynitro cage compound with a framework of hexanitrohexaazaisowurtzitane (HNIW) was investigated by density functional theory (DFT) calculations. The molecular structure was optimized at the B3LYP/6-31G** level. IR spectrum, heat of formation (HOF), and thermodynamic properties were also predicted. The detonation velocity and pressure were evaluated by using the Kamlet–Jacobs equations, based on the theoretical density and condensed HOF. The bond dissociation energies (BDEs) and bond orders for the weakest bonds were analyzed to investigate the thermal stability of the title compound. The results show that the first step of pyrolysis is the rupture of the N8–NO2 bond. The crystal structure obtained by molecular mechanics belongs to the P21 space group, with the following lattice parameters: Z = 2, a = 11.10 Å, b = 15.15 Å, c = 10.77 Å, ρ = 1.872 g cm−3. The designed compound has high thermal stability and good detonation properties, and is a promising high-energy-density compound.

Effects of binders and graphite on the sensitivity of ε-HNIW

In order to optimize formulations of PBX based on Hexanitrohexaazaisowurtzitane (HNIW) and meet the application in mixed explosive, the mold powder of HNIW coated by varied binders was obtained by aqueous suspension technology. Several particle sizes of graphite were added as additive with a 0.5 % mass ratio. The experiment results showed that fluorine resin (FPM) was better than polyurethane and cis-butadiene rubber when the mass percentage of binders was fixed at 4 %. The characteristic height of HNIW/FPM (96/4) mold powder was at 28 cm (2.5 kg hammer), while that of the neat HNIW was at 15 cm merely, and the friction explosion probability fell from 100 to 70 %. The addition of flake graphite with proper grain size would reduce the mechanical sensitivity of HNIW and improved the fluxion property of HNIW-based mold powders. The thermal stability characteristic of HNIW FPM (96/4) and HNIW/FPM/G (96/4/0.5) were studied by thermogravimetric analysis (TG) at 10 °C min−1, the peak decomposition temperatures were at 251 and 250 °C, which were closed to that of neat HNIW(249 °C) and also identified superior thermal stability of compound.

Thermal Decomposition Study of HNIW by Synchrotron Photoionization Mass Spectrometry

AbstractThermal decomposition of hexanitrohexaazaisowurtzitane (HNIW) was investigated through tuneable vacuum ultraviolet photoionization with molecular‐beam sampling mass spectrometry (MBMS). According to photoionization efficiency (PIE) spectroscopic results, the initial decomposition products of HNIW were identified including HCN, CO, NO, HNCO, N2O, CO2 (a little), NO2, C2H2N2, C3H3N3, C4H3N3, C3H4N4, C5H4N4, C5H5N5 and C6H6N6. The possible ionization energies of C2H2N2, C4H3N3, C3H4N4 and C6H6N6 were analyzed on basis of the PIE spectra. The data were compared with those of thermogravimetry‐mass spectrometry (TG‐MS) and thermogravimetry‐Fourier transform‐infrared spectroscopy (TG‐FT‐IR). The kinetic parameters for the formation of HNCO, HCN and CO2 were calculated from the current curves of species by TG‐FT‐IR spectroscopy, typically the apparent activation energy (Ea) and prefactor (A) for HNCO were Ea=161.3 ± 2.5 kJ mol−1 and A=38.9 ± 0.6 s−1 with an optimal mechanism function f(α)=(1−α). Global thermal decomposition reaction and Arrhenius equation of HNIW were suggested at the end.

Synthesis of Waterborne Polyurethane for Coating on HNIW

The waterborne polyurethane (WPU) was synthesized from isophorone diisocyanate (IPDI), polypropylene glycol (PPG), dimethylolpropionic acid (DMPA) and 1,4-butanediol (BDO) under acetone reflux. The cast films obtained from it were characterized by Fourier transform infrared (FTIR), nuclear magnetic resonance (1H NMR) and differential scanning calorimetry (DSC). The curve of DSC presented a bimodal profile. It showed that the waterborne polyurethane resin degraded obviously at about 305°C and 381°C, which was an endothermic course. The scanning electron microscopy (SEM) micrographs revealed that hexanitrohexaazaisowurtzitane (HNIW) was coated with waterborne polyurethane by means of water volatilization. The impact sensitivity experimental results indicated that the characteristic height H50 of HNIW coated with waterborne polyurethane increased from 25.1cm to 34.2cm. That is, the waterborne polyurethane can decrease the impact sensitivity of HNIW.

Thermal Decomposition of Hexanitrohexaazaisowurtzitane and Its Residues

Hexanitrohexaazaisowurtzitane (HNIW) particles were heated isothermally at (204.0±0.5), (208.0±0.5), (212.0±0.5), and (216.0±0.5) ℃ for 10, 20, 30, 40, 50, and 60 min under (2.0±0.1) MPa pressure in an argon atmosphere. Residues obtained at (208.0±0.5) ℃ were studied by elemental analysis, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetry-differential scanning calorimetry-mass spectrometry (TG-DSC-MS) and thermogravimetry-Fourier transform infrared (TG-FTIR) spectroscopy. Results showed that after isothermal decomposition of HNIW crystals at about 210.0 ℃ for 60 min residues were formed with an average molecular formula of C2H2N2O. Unreacted HNIW is present in the residue and is more thermally unstable than the original HNIW. We confirmed that HNIW crystals decomposed stepwise under isothermal conditions. Three stages were found to exist during the thermal decomposition of HNIW residues. The first decomposition stage consists of an initial decomposition of unreacted HNIW, the second stage comprises an elimination reaction of five-membered ring amides and nitrogen heterocyclic compounds and in the third stage five-membered ring amides are degraded and secondary reactions involving NO2 occur. The main gaseous products in every stage are discussed.

Thermal Decomposition Kinetics of Hexanitrohexaazaisowurtzitane by Mass Spectrometry

Thermal decomposition of hexanitrohexaazaisowurtzitane (HNIW) was studied by mass spectroscopy (MS) with low impacting electron energy. Non-isothermal kinetics treating method for ion curves in mass spectroscopy was established. The mechanism of HNIW thermal decomposition was analyzed according to the Arrhenius curves of ion products. The results showed that the apparent activation energy of the HNIW thermal decomposition was 145.1 kJ·mol-1. Between 130 and 150 ℃, ion products are mainly produced by electron impact, and activation energy is between 28 and 41 kJ·mol-1. Between 213 and 228 ℃, ion products are mainly produced by thermal decomposition, and activation energy is between 143 and 179 kJ·mol-1. The kinetic compensation effect occurs in thermal decomposition of HNIW between 213 and 228 ℃, and the compensation effect equation is lnA=0.252Ea-0.645. The main reactions of HNIW thermal decomposition are as HNIW.438→6NO2+2HCN+HNIW.108, HNIW.438→6NO2+3HCN+HNIW.81, HNIW.438→6NO2+4HCN+HNIW.54.

Dissociation Mechanism of HNIW Ions Investigated by Chemical Ionization and Electron Impact Mass Spectroscopy

AbstractChemical Ionization (CI) with Collision‐Induced Dissociation (CID) spectroscopy and Electron Impacting (EI) with metastable Mass analyzed Ion Kinetic Energy (MIKE) spectroscopy have been applied to study ionic dissociations of Hexanitrohexaazaisowurtzitane (HNIW). Similarities and differences between EI/MIKE and CI/CID mass spectra of HNIW were analyzed. In EI mass spectra, the ions [HNIW−n NO2]+ (n=2–5), such as the ion at m/z 347, were less frequent (1–2% relative abundance), but in CI mass spectra, these ions were very abundant. For some ions of large molar mass from HNIW, their dissociations pathways from parent ions to daughter ions were built according to CID and MIKE spectra. Molecular ions of HNIW with a protonated nitro group at five‐member ring seem more stable than at six‐member ring. The HNIW ions losing five of six nitro groups are very stable based on CID spectra, which agrees with some research results for thermal decomposition of HNIW in literature.