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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.

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Application of BCHMX in Shaped Charges against RHA Targets Compared to Different Nitramine Explosives

Elbeih A., Elshenawy T., Zeman S., Akstein Z.

Central European Journal of Energetic Materials

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2018

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Vol. 15, no. 1

3--17

EN

In this work, a new bicyclic nitramine, cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole (bicyclo-HMX or BCHMX), has been tested for its performance as a shaped charge explosive filler in comparison with three other interesting cyclic nitramines. Four shaped charges were prepared using different nitramine-based plastic bonded explosives (PBXs), and their performance was measured experimentally in terms of the penetration depth into laminated rolled homogeneous armour (RHA) targets. The explosive fillers were highly pressed PBXs based on RDX, HMX, BCHMX and CL-20, bonded by Viton A binder. The Autodyn numerical hydrocode was implemented to determine the shaped charge jet’s characteristics and its penetration depth. The experimental and calculated detonation characteristics of the explosives used are reported. Relationships between the detonation characteristics of the explosives and the jet characteristics were observed. The results show that CL-20 is the most powerful explosive, with the largest penetration depth into the RHA target, while BCHMX explosive has a relatively enhanced penetration depth with respect to RDX explosive. The results of the Autodyn code calculations are consistent with the experimental measurements, with a maximum difference of 6.6%.

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Concerning the Shock Sensitivities of Certain Plastic Bonded Explosives Based on Attractive Cyclic Nitramines

Zeman S., Elbeih A. E., Hussein A., Elshenawy T., Pelikán V., Yan Q-L.

Central European Journal of Energetic Materials

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2017

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Vol. 14, no. 4

775--787

EN

Plastic bonded explosives (PBXs) based on ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-HNIW), 1,3,5-trinitro-1,3,5-triazinane (RDX), β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (β-HMX) and cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole (BCHMX) were prepared using a hydroxyl-terminated polybutadiene as a binder (HTPB) and cured with hexamethylene di-isocyanate (HMDI). Recently published data for analogous PBXs with a polyisobutylene binder (i.e. a C4 matrix) are also included. All of these PBXs were tested using the Small Scale Water Gap Test according to STANAG 4490, the results of which are directly proportional to the impact and friction sensitivities of the PBXs studied. Reciprocal ratios between the shock sensitivity of these PBXs and their performance were found using the volume heat of explosion as a variable; a semi-logarithmic analogue, using a representative of the detonation pressure (product ρD2) as a variable, has shown an opposite trend for three of these PBXs. A semi-logarithmic relationship between the shock sensitivity of the PBXs and the impact sensitivity of their pure nitramine fillers has confirmed the higher shock reactivity of the C4 PBXs filled with both technical ε-HNIW and RS-ε-HNIW, while for the HTPB PBXs filled with technical grade ε-HNIW, the shock sensitivity found was as expected. The shape and size of the particles should not be a reason for the increased resistance to shock of HMX-C4.

4

Recent advances in the study of the initiation of energetic materials rusing characteristics of their thermal decomposition. Part I, Cyclic nitramines

Zeman S., Yan Q.-L., Vlček M.

Central European Journal of Energetic Materials

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2014

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Vol. 11, no. 2

173--189

EN

Arrhenius parameters, Ea and log A, of 17 cyclic nitramines, derived from the Russian vacuum manometric method (SMM) and compatible thermoanalytical methods, have been used in this study. The detonation velocity, D, at maximum theoretical crystal density, of the nitramines in this study was taken as a characteristic of their detonation. On the basis of known relationships between their Ea and D2 values (modified Evans-Polanyi-Semenov equation), the specific influence of some physicochemical properties on their thermal decomposition was shown. A new logarithmic relationship was found between the rate constant k, of the unimolecular thermal decomposition of the nitramines studied at 230 °C, and their D values. A fundamental characteristic of this new relationship rests on the equivalency of the primary fission processes in the low-temperature thermal decomposition and on the detonation initiation of the nitramines under study. Both these relationships confirm the problems encountered in the kinetic specification of the thermal decomposition of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12hexaazaisowurtzitane (HNIW, CL-20) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). These problems, and also the possible influence of the pre-decomposition states on the thermal decomposition of the nitramines studied, are discussed.

5

Recent Advances in the Study of the Initiation of Energetic Materials Using the Characteristics of Their Thermal Decomposition Part II. Using Simple Differential Thermal Analysis

Zeman S., Yan Q.-L., Elbeih A.

Central European Journal of Energetic Materials

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2014

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Vol. 11, no. 3

395--404

EN

Simple Differential Thermal Analysis (DTA), with evaluation of its output by the Kissinger method, was used in the case of emulsion explosives and, as an advanced application, for several plastic bonded explosives (PBXs). In both of these kinds of explosive the square of their detonation velocities, D2, is used as their performance characteristic. A relationship between the slope of the Kissinger equation, EaT-1, and the D2 values makes it possible to formulate a possible mechanism for the initiation of emulsion explosives. Regarding PBXs, it would seem possible to postulate a change in the detonation chemistry of plastic bonded nitramines, depending on the pressure and temperature in the zone of the detonation wave, particularly in the case of CL-20 fillers. Binders with aromatic building units in their macromolecular structure seem to be less-favoured in terms of their thermal reactivity and performance than the final PBXs. These findings document the advantages of the above-mentioned application of simple DTA.

6

Characteristics of Melt Cast Compositions Based on cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5 d] imidazole (BCHMX)/TNT

Elbeih A., Zeman S.

Central European Journal of Energetic Materials

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2014

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Vol. 11, no. 4

501--513

EN

cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5 d]imidazole (BCHMX) is a new bicyclic nitramine which has been prepared using a two-stage synthetic method. In this work, a new melt cast composition based on BCHMX/TNT (60/40 by wt.) was prepared. For comparison purposes, Composition B based on RDX (1,3,5-trinitro1,3,5-triazacyclohexane)/TNT (60/40 by wt.), and HMX (1,3,5,7-tetranitro-1,3,5,7tetraazacyclooctane)/TNT (60/40 by wt.) were also studied. Impact and friction sensitivities of these compositions and of the individual explosives were determined. The detonation velocities were measured experimentally. The performance of the compositions prepared was studied by measuring the brisance using the Kast method. The detonation parameters of the compositions and the individual explosives were calculated using the EXPLO5 thermodynamic code. The results show that mixing these nitramines with TNT decreases their sensitivities. BCHMX/TNT is more sensitive to impact and friction than Composition B while it has higher detonation parameters, at the same level as HMX/TNT. In comparison, BCHMX/TNT has the highest relative brisance of the compositions studied. It is postulated that the higher performance characteristics of BCHMX and compositions based on it, in comparison with those of HMX, are due to a higher positive heat of formation for this nitramine.

7

Thermal Decomposition of Azidonitramines

Stepanov R. S., Kruglyakova L. A., Astachov A. M.

Central European Journal of Energetic Materials

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2007

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Vol. 4, nr 1-2

151-156

EN

The kinetic laws and mechanism of the thermal decomposition of azidonitramines in gaseous phase, melt, and in solutions are discovered. Homolysis is established to be the first order reaction, the limiting stage has Arrhenius's parameters Ea = 144.8-166.5 kJ mole–1, lgA = 13.53-14.97, what is not adequate for monofunctional alkylazides and alkylnitramines. The thermolysis of azidogroup initiates the decomposition. Nitraminogroup in β- or α-position to azidogroup increases the decomposition rate by 1-2 orders correspondingly as compared with δ-position.

8

Electric Spark Sensitivity of Nitramines. Part I. Aspects of Molecular Structure

Zeman S., Pelikán W., Majzlík J., Friedl Z., Kočí J.

Central European Journal of Energetic Materials

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2006

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Vol. 3, nr 3

27-44

EN

An ESZ KTTV instrument of a new, relatively simple construction has been applied to determination of electric spark sensitivity (EES) of 16 nitramines. Results obtained are compared with those from measurements by means of an older RDAD instrument. Attention was focused both on the relationships between the EES values from both the instruments and theoretical B3LYP/6-311+G(d,p) N-NO2 bond dissociation energies, B3LYP/6-31G(d,p) Mulliken net charges of the nitro group, heats of fusion and 15N NMR chemical shifts of the nitrogen atoms of the most reactive nitro groups, respectively. It is stated a larger difference between results of both instruments. The EES values from both the instruments correlate with such characteristics of molecular structure which correspond to the primarily leaving nitro group in the nitramine molecule. It has been found that these relationships for ESZ KTTV results are strongly affected by molecular structure factors. It is also pointed out that the dislocations in the crystals should have some relation to electric spark sensitivity.

9

Structure and Rearrangement of Ring Substituted N0Methyl-N-phenylnitramines

Daszkiewicz Z., Zaleski J., Nowakowska E. M., Kyzioł J. B.

Polish Journal of Chemistry

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2002

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Vol. 76 / nr 8

1113-1125

EN

The mechanism of the acid catalyzed nitramine rearrangement must account for the unusual sensitivity of the reaction of N-methyl-N-phenylnitramine derivatives to the ring substituents. Spectral analyses indicate the lack of interaction between the nitramino group and the second substituent through the aromatic ring. X-ray analyses confirm the spectral data: there is no conjugation between the aromatic and nitramine sextets of _-electrons. X-ray structural data also indicate that the nitramino group cannot behave as the basic centre. A reconsideration of the rearrangement rate constants of the series of ring substituted N-methyl-N-phenylnitramines lead to the conclusion that migration of the N-nitro group precedes protonation. The influence of the substituents on the reaction rates is determined by their influence on the basicity of the imino nitrogen in an intermediate. The CIDNP effect, observed in the rearrangement, results from the transformation of mobile nitrito group into the stable nitro substituent.