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1

N-N Bond Lengths and Initiation Reactivity of Nitramines

Zeman Svatopluk, Atalar Taner, Růžička Aleš

Central European Journal of Energetic Materials

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2020

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Vol. 17, no. 2

169--200

EN

For the 16 selected nitramines, it is shown that an increase in the energy content of these molecules (represented by enthalpies of formation) is connected with an increase in the lengths of the longest N–N bonds in the molecules. These lengths are directly proportional to the activation energies of the low-temperature thermal decomposition of the pure nitramines in all states of matter for this reaction. Raising the energy content also leads to reductions in the rate constants of thermal decomposition. Both of these facts are in contrast to expectations and also with similar published findings concerning thermal decomposition of nitramines in solution, which can be explained by the solvation effect and termination of the emerging aza-radicals in solutions. The calculated dissociation energies of the weakest N–N bonds yielded a relatively good reciprocal conformity with the lengths of the longest N–N bonds of the nitramines studied, especially when using the UB3LYP/6-31G* method. The relationship between the impact sensitivity of these nitramines and the lengths of their longest N–N bond is not completely clear. Such lengths cannot be a measure of impact reactivity, because the longest N–N bond might be stabilized in some cases by suitable intermolecular interactions with adjacent molecules in the crystal lattice.

2

Determination of the Mechanical and Thermal Properties, and Impact Sensitivity of Pressed HMX-based PBX

Li Yuxiang, Wu Peng, Hua Cheng, Wang Jun, Huang Bing, Chen Jin, Qiao Zhiqiang, Yang Guangcheng

Central European Journal of Energetic Materials

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2019

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Vol. 16, no. 2

295--315

EN

Submicron- and nano-explosives have attracted growing attention, while the mechanism of how particle size influences the impact sensitivity is not completely understood. In the present work, HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) based PBXs (plastic bonded explosives) of three particle size distributions (1-2 and 10-20 μm, and 100-300 nm) and two pressed densities (91%TMD and 79%TMD) were characterized and tested with a range of techniques to determine their mechanical and thermal properties and impact sensitivities. The results demonstrated that with decreased particle size, the mechanical strength as well as the thermal conductivity were dramatically improved, and the impact sensitivity was significant decreased. The structure of impacted samples suggested that the ignition mechanism is dependant on the particle size. Samples with higher density were more sensitive to impact, as the impact force acting on these samples was higher. The correlation between particle size and impact sensitivity is discussed in detail.

3

An Insensitive Booster Explosive: DAAF Surface-coated with Viton A

Li X., Wu B., Liu S., An C., Wang J.

Central European Journal of Energetic Materials

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2018

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Vol. 15, no. 3

445--455

EN

3,3’-Diamino-4,4’-azoxyfurazan (DAAF) is the principal component of an insensitive booster explosive; refined DAAF and DAAF surface-coated with Viton A were prepared. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) were employed to characterize the morphology, composition, and thermal decomposition of these samples. The impact sensitivity and theoretical detonation velocity of DAAF-based composites were also measured and analyzed. The results showed that DAAF surface-coated with Viton A was successfully obtained, and the impact sensitivity of DAAF/Viton A composites was much lower than that of crude DAAF. In addition, DAAF/Viton A composites exhibited better thermal stability compared to crude DAAF and refined DAAF. The theoretical detonation velocity of DAAF/Viton A composites and TATB/Viton A composites are roughly the same. Therefore, there is still great potential for DAAF to be used as the main explosive component of a booster explosive.

4

A Novel Method for the Prediction of the Impact Sensitivity of Quaternary Ammonium-based Energetic Ionic Liquids

Keshavarz M. H., Esmaeilpour K., Khoshandam H., Keshavarz Z., Atabak H. H., Damiri S., Afzali A.

Central European Journal of Energetic Materials

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2017

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Vol. 14, no. 3

520--533

EN

Impact sensitivity is an important safety parameter for the assessment of the hazards of working with new energetic compounds including ionic molecular energetic materials. This paper introduces two novel simple correlations to assess the impact sensitivity of quaternary ammonium-based energetic ionic liquids, which are based on the elemental composition of cations and anions divided by the molecular weight of a desired ionic liquid as well as the contribution of specific cations and anions. For 72 ionic molecular systems as a training set, the root mean square (rms) deviations of predictions for these models relative to experiment are 11 J and 6 J, respectively. The reliability of the models has also been tested for a further three ionic compounds containing complex structures, which give rms deviations of 12 J and 6 J, respectively, with respect to the measured data. The results of the current study indicate that the accuracy of this novel method for the prediction of the impact sensitivity of quaternary ammonium-based energetic ionic liquids is not necessarily enhanced by greater complexity.

5

The Relationship between Impact Sensitivity of Nitroaromatic Energetic Compounds and their Electrostatic Sensitivity

Zohari N., Seyed-Sadjadi S. A., Marashi-Manesh S.

Central European Journal of Energetic Materials

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2016

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Vol. 13, no. 2

427--443

EN

This study presents a linear relationship between the impact sensitivity of nitroaromatic energetic compounds and their electric spark sensitivity. The methodology assumes that the impact sensitivity of a nitroaromatic energetic compound with the general formula CaHbNcOd can be expressed as a function of the electrostatic sensitivity, the number of NH2 group substitutions in the 2,4,6-trinitrophenyl ring and non-additive structural parameters. The root mean square and absolute standard deviation of a newly introduced correlation were respectively found to be 2.4 and 2.0 for 27 nitroaromatic energetic compounds. The proposed new correlation was also tested for 7 additional nitroaromatic energetic compounds, which have complex molecular structures such as 1-(2,4,6-trinitrophenyl)-5,7-dinitrobenzotriazole and 1,3,7,9-tetranitrophenoxazine.

6

Considerations on Energy Deposition with the BAM-Fallhammer

Von Oertzen A., Lehmann T.

Central European Journal of Energetic Materials

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2016

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Vol. 13, no. 2

273--288

EN

The BAM-Fallhammer is a mechanical device to test the impact sensitivity of explosives and to determine a sensitiveness level. By its construction it transforms potential energy into kinetic energy of an impacting hammer, then hitting the sample. Ideally the entire potential energy is available at the moment of impact and the supporting base is infinitely rigid. By this study we want to quantify how much a real Fallhammer deviates from the ideal concept, and what the differences between different Fallhammers in different laboratories are. This information has never been collected in a consistent way. The aim of the authors is to develop guidance on the mechanical properties of the Fallhammer, which can be used for different purposes such as internal quality control, validation of the correct functioning of the Fallhammer, preparation of Round-Robin tests and similar. An established and verified mechanical status of a Fallhammer would greatly improve the quality and comparability of results and Round-Robin tests on the impact sensitivity of explosives.

7

Process Optimization and Characterization of an HMX/Viton Nanocomposite

Shi X., Wang C., Wang J., Li X., An C., Wang J., Ji W.

Central European Journal of Energetic Materials

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2015

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Vol. 12, no. 3

487--495

EN

HMX/Viton A nanocomposites were prepared by a spray drying process using different processing parameters, which included the dry gas inlet temperature, the air flow rate, and the solution feed flow rate. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the nanocomposites. The effects of the processing parameters on the morphology of the samples were investigated and are discussed. The thermal decomposition behaviour and impact sensitivity of the raw HMX and HMX/Viton A nanocomposites were also measured and compared. Optimal morphology and dispersion of the coated samples was achieved when the dry gas inlet temperature and the air and solution feed flow rates were 55 °C, 660 L/h and 1.5 mL/min, respectively. Under these optimal processing conditions, the nanocomposites were spherical in shape, ranged from 0.2-2 μm in size, and were composed of many tiny particles of 50-100 nm in size. The crystal phase of the nanocomposites was the same as that of raw HMX. Compared with those of raw HMX, the melting point and impact sensitivity of the nanocomposites were lower and the thermal decomposition rate was slightly higher.

8

Preparation and Characterization of CL-20/EPDM by a Crystal Refinement and Spray Drying Method

Ji W., Li X., Wang J.

Central European Journal of Energetic Materials

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2015

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Vol. 12, no. 4

831--840

EN

A 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) based mixed explosive was prepared by a spray drying method using CL-20 suspended in hexane containing EPDM rubber (ethylene-propylene-diene monomer), and made into a stable suspension. The samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and their thermal stability and impact sensitivity were also measured. The results showed that the ethylene-propylene-diene-monomer rubber (EPDM) can be successfully coated on to the CL-20 crystal surface. Compared to refinement-spray CL-20, the impact sensitivity of CL-20/EPDM was significantly reduced. The characteristic drop height was increased from 28.12 to 39.78 cm. The thermal stability was better than refinement-spray CL-20.

9

Predicted Crystal Structures, Analysis, Impact Sensitivities and Morphology of Solid High-Energy Complexes: Alkaline-Earth Carbohydrazide Perchlorates

Liu Y., Zhang R., Feng C.-G., Yang L., Zhang T.-L.

Central European Journal of Energetic Materials

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2015

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Vol. 12, no. 2

229--248

EN

The crystal structures, density of states, energy gap, thermodynamic properties, impact sensitivities and morphology of beryllium carbohydrazide perchlorate ([Be(CHZ)3](ClO4)2), magnesium carbohydrazide perchlorate ([Mg(CHZ)3](ClO4)2), calcium carbohydrazide perchlorate ([Ca(CHZ)3] (ClO4)2), strontium carbohydrazide perchlorate ([Sr(CHZ)3](ClO4)2) and barium carbohydrazide perchlorate ([Ba(CHZ)3](ClO4)2) were investigated using the density functional theory (DFT) and crystal morphology theory. The results show that all of the complexes have six-coordinated distorted octahedra, which is different from previous works. This was rationalised by consideration of the intermolecular interactions in the crystal structures. Hence the crystal structure is now more reliable. The chemical reactions of the whole molecule may be triggered by an electron transition of CHZ or ClO4 −. Furthermore the energy gaps were observed, and the values of the impact sensitivities were inferred to have the following sequence: [Be(CHZ)3](ClO4)2 > [Mg(CHZ)3](ClO4)2 > [Sr(CHZ)3](ClO4)2 > [Ca(CHZ)3](ClO4)2 > [Ba(CHZ)3](ClO4)2. In addition, the thermodynamic equations at 25-1000 K were obtained. The positive values of the standard molar free enthalpies shows that carbohydrazide perchlorates are stable at 298.15 K. The (1 0 -1) and (0 0 2) faces are the most important growth directions of the crystal morphologies, and have the minimum growth rates. From the cleaved main growth faces, it can be deduced that surface active agents with active hydrogen atoms in the functional groups could be used as crystal-control reagents to control the crystal morphology for alkaline-earth carbohydrazide perchlorates.

10

Recent Advances in the Study of the Initiation of Nitramines by Impact Using Their 15N NMR Chemical Shifts

Jungová M., Zeman S., Yan Q.-L.

Central European Journal of Energetic Materials

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2014

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Vol. 11, no. 3

383--393

EN

The relationship between the 15N NMR chemical shifts of aza nitrogen atoms in twelve nitramines and the impact sensitivity of these compounds, expressed as the drop energy, Edr, has been analyzed from the point of view of recently published findings. This relationship appears to be the best method for identifying the key atoms at the reaction centre of a given molecule. These atoms might be taken as “chemical hot spots”. The absence of any solid state influence on the chemical shifts, which were here determined in solution, does not have a fundamental influence on the reaction centre identification. The relationship discussed here confirms the close molecular structural dependence for drop energies (impact sensitivities) obtained for individual energetic materials (EMs) by means of a standard impact tester (Julius Peters) with the detection of the 50% probability of initiation based on acoustic detection. The dependence of impact sensitivity on specific crystal surfaces, using samples of individual EMs obtained by screening, should be investigated more extensively.

11

Quantum Chemical Study of Aminonitrocyclopentanes as Possible High Energy Density Materials (HEDMs)

Bai J., Chi W. J., Li L. L., Yan T., Wen X. E., Li B. T., Wu H. S., Ma F. L.

Central European Journal of Energetic Materials

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2013

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Vol. 10, no. 4

467--480

EN

Nitro and amine groups were introduced into the cyclopentane skeleton, and the heats of formation, detonation performance, bond dissociation energies, and impact sensitivity for these aminonitrocyclopentanes were calculated in detail at the B3LYP/6-311G** level. The results show that all of the derivatives have negative heats of formation, which are influenced by the position of the substituent groups. Their stabilities were estimated and analyzed according to their bond dissociation energies and calculated characteristic H50 values. Most of the compounds were found to have a lower impact sensitivity than HMX. Furthermore, the detonation velocities and detonation pressures were predicted via the Kamlet-Jacobs equation. Of all these aminonitrocyclopentanes, E has the best detonation properties (ρ = 2.05 g/cm3, D = 9.11 m/s, P = 39.62 GPa) and can be considered as a candidate high energy density material.

12

Crystal Density Prediction, Charge Density Distribution and the Explosive Properties of the Highly Energetic Molecule 2-Methyl-5-nitramino-tetrazole: a DFT and AIM Study

Srinivasan P., Kumaradhas P.

Central European Journal of Energetic Materials

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2013

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Vol. 10, no. 1

53--68

EN

The ab initio crystal density, bond topological and explosive properties of the energetic molecule 2-methyl-5-nitraminotetrazole (MNAT) have been calculated by the MOLPAK/PMIN software and the AIM theory. The density predicted from the crystal structure simulation almost matches the experimental density. The geometrical parameters of the molecule lifted from the crystal structure are in very close agreement with the reported X-ray molecular structure. The bond topological analysis predicts a signifcantly low bond electron density, as well as a less Laplacian of electron density, for the N–NO2 bond. The Laplacian for the bond to the attached methyl group, the C(2)–N(2) bond, is also found to be less negative; the less negative values of the Laplacian confrms that these are the weakest bonds in the molecule. The impact sensitivity (h50) of the molecule has been calculated, and is almost equal to the reported experimental value. The sensitivity of the molecule was also estimated from the electrostatic imbalance parameter and has the value ν = 0.242. The isosurface of the electrostatic potential of the molecule displays a high negative electrostatic potential region around the tetrazole ring and the nitramine N–N bond, which are the possible reactive locations in the molecule.

13

Charge Density Distribution, Electrostatic Properties and Sensitivity of the Highly Energetic Molecule 2,4,6-Trinitro-1,3,5-triazine: A Theoretical Study

Srinivasan P., Maheshwari K., Jothi M., Kumaradhas P.

Central European Journal of Energetic Materials

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2012

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Vol. 9, nr 1

59-76

EN

Ab initio and density functional theory (DFT) calculations were carried out on the energetic propellant molecule 2,4,6-trinitro-1,3,5-triazine (TNTA) to understand its bond topology and its energetic properties using the theory of atoms in molecules (AIM). The DFT method predicts that the electron density ρ bcp (r) at the bond critical points of ring C-N bonds is ∼ 2.34 e Å -3 and the corresponding Laplacian ∇ 2 ρ bcp(r) is ∼ -24.4 e Å -5 ; whereas these values are found to be very small in the -NO2 group attached to C-N bonds [ρ bcp(r): ∼ 1.73 e Å -3 and Δ 2 ρ bcp (r): ∼ -14.5 e Å -5 ]. The negative Laplacian values of C-NO 2 bonds are significantly lower which indicates that the charges of these bonds are highly depleted. The C-NO2 bonds exhibit low bond order (∼ 0.8), as well as low (∼ 56.4 kcal/mol) bond dissociation energy. As we reported in our earlier studies, we found high bond charge depletion for these bonds, which are considered the weakest bonds in the molecule. The frontier orbital energies exhibit a wide band gap, which is larger than those of existing molecules TATB, TNT and TNB. The impact sensitivity (H 50 %) (4.2 m) and oxygen balance (2.77%) were calculated and compared with related structures. Large negative electrostatic potential regions were found near the nitro groups where reaction is expected to occur. The relation between charge depletion ∇ 2 ρ bcp(r) and the electrostatic potential at the bond midpoints V mid reveals the sensitive areas of the molecule.

14

Path to ε-HNIW with Reduced Impact Sensitivity

Elbeih A., Husarova A., Zeman S.

Central European Journal of Energetic Materials

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2011

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Vol. 8, nr 3

173-182

EN

New purification method was applied to obtain epsilon HNIW (ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, ε-HNIW) which has low impact sensitivity. The method is based on removing the impurities from a solution of alpha HNIW (ε-HNIW) by a chemical reaction to obtain pure epsilon form. For comparison, selected different published methods for recrystallization of HNIW to obtain the epsilon form were studied. All the selected methods are based on solvent-antisolvent technique. The optimum parameters, such as type of solvent and anti-solvent, volume ratio of solvent to anti-solvent, rate of addition, speed of stirring, etc., were applied to enhance the crystal size and shape of ε-HNIW. Checking the polymorphs of the obtained HNIW was done by Fourier transform infrared spectroscopy (FTIR). The thermal stability of the prepared samples was studied by using differential thermal analysis technique (DTA). Qualitative analysis of the crystal size and shape was done using scanning electron microscope (SEM) devise. Quantitative measurement of the crystals sizes for the studied samples was determined by Laser scattering particle size distribution analyzer. Impact sensitivity was measured by falling hammer test. The results indicate that all the applied methods of recrystallization give ε-HNIW. The impact sensitivity of HNIW decreases by obtaining small particles with regular shape. All the used published methods produce ε-HNIW with higher impact sensitivity than other nitramines. While the obtained crystals from the new method has regular smooth surface, with small particle size and its impact sensitivity is lower than RDX and HMX.

15

Computational Characterization of a Potential Energetic Compound: 1,3,5,7-Tetranitro-2,4,6,8-tetraazacubane

Politzer P., Lane P., Murray J. S.

Central European Journal of Energetic Materials

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2011

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Vol. 8, nr 1

39-52

EN

The high densities and (strain-induced) enthalpies of formation of cage-type molecules have drawn attention to their polynitro derivatives as potential energetic materials. Several such compounds have been synthesized, including octanitrocubane and hexanitrohexaazaisowurtzitane. One that has not yet been prepared but has evoked continuing interest is 1,3,5,7-tetranitro-2,4,6,8- tetraazacubane. Some years ago, on the basis of a very high estimated density (about 2.19 g/cm3), it was predicted to have detonation properties greatly superior to those of HMX. We have now used computational procedures developed since that time to reassess the expected detonation performance of this compound. We find: density, 1.940 g/cm3; solid phase enthalpy of formation at 298 K, 757 cal/g; detonation velocity, 9.8 mm/µs; detonation pressure, 444 kbar; impact sensitivity, h50 ∼ 40 cm. These are all better than the corresponding values for HMX, but not by as much as had been estimated earlier.

16

A quantum chemical study on thermolysis initiation mechanisms and impact sensitivity of energetic materials

Xu X., Xiao H., Fan J., Chen Z.

Central European Journal of Energetic Materials

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2005

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Vol. 2, nr 4

5-21

EN

Thermolysis initiation mechanisms of polynitro compounds, tetrazole derivatives and their metallic salts, and cage high energy density compounds have been investigated using quantum chemical approaches. Our calculations showed that the trigger bonds whose breaking initiate a decomposition or an explosion were C-NO2 or N-NO2 bonds for nitro derivatives of benzene and aminobenzenes, CL-20 and polynitroadamantanes. Explosion of nitro derivatives of phenol and toluene were most likely triggered by the isomerization reactions involving the H-shift. Due to larger strain energy, the trigger bond was found to be the C-C bond in the framework of polynitrocubanes. Regarding tetrazoles and their metallic salts, opening of the tetrazole ring, i.e., scission of the N-N bond, followed by formation of N2 molecules, initiate explosive reactions. We found for energetic materials having similar molecular structures and following similar thermal decomposition mechanisms, the bond orders of the trigger bond and the activation energy to break the bond were directly related to the impact sensitivity. We thus proposed two criteria used to evaluate the relative ordering of impact sensitivity for energetic materials with similar structures: the smaller the bond order, the more sensitive an energetic material, which was called the principle of the smallest bond order (PSBO). And the higher the activation energy, the less sensitive a material was. We demonstrated that in most cases the PSBO was equivalent to the activation energy criterion. The former was more convenient and easier to obtain while the latter could be applied more universally.