New aspects of initiation reactivities of energetic materials demonstrated on nitramines

Theoretical insight into density and stability differences of RDX, HMX and CL-20

In this work, density and stability differences of RDX, HMX and CL-20 are exploited and addressed through static calculations from views of monomolecular parameters, intermolecular interactions (by the proposed BEC method) and crystal packing.

Review of the molecular and crystal correlations on sensitivities of energetic materials

Highly efficient design on the levels of molecule and crystal, as well as formulation, is highly desired for accelerating the development of energetic materials (EMs). Sensitivity is one of the most important characteristics of EMs and should be compulsorily considered in the design. However, owing to multiple factors responsible for the sensitivity, it usually undergoes a low predictability. Thus, it becomes urgent to clarify which factors govern the sensitivity and what is the importance of these factors. The present article focuses upon the progress of the molecular and crystal correlations on the sensitivity, and the molecule-based numerical models for sensitivity prediction in the past decades. On the molecular level, composition, geometric structure, electronic structure, energy and reactivity can be correlated with the sensitivity; while the sensitivity can be also related with molecular packing pattern, intermolecular interaction, crystal morphology, crystal size and distribution, crystal surface/interface and crystal defect on the crystal level. And most of these factors, in particle on the crystal level, have been employed as variables in numerical models for predicting sensitivity of categorized EMs. Besides, we stress that more attention should be paid to the sensitivity correlations on the inherent structures of EMs, molecule and crystal packing, because they can be readily dealt by molecular simulations nowadays, facilitating to reveal the physical nature of sensitivity.

Models for predicting impact sensitivity of energetic materials based on the trigger linkage hypothesis and Arrhenius kinetics

In order to predict the impact sensitivity of high explosives, we designed and evaluated several models based on the trigger linkage hypothesis and the Arrhenius equation. To this effect, we calculated the heat of detonation, temperature of detonation, and bond dissociation energy for 70 energetic molecules. The bond dissociation energy divided by the temperature of detonation proved to be a good predictor of the impact sensitivity of nitroaromatics, with a coefficient of determination (R²) of 0.81. A separate Bayesian analysis gave similar results, taking model complexity into account. For nitramines, there was no relationship between the impact sensitivity and the bond dissociation energy. None of the models studied gave good predictions for the impact sensitivity of liquid nitrate esters. For solid nitrate esters, the bond dissociation energy divided by the temperature of detonation showed promising results (R² = 0.85), but since this regression was based on only a few data points, it was discredited when model complexity was accounted for by our Bayesian analysis. Since the temperature of detonation correlated with the impact sensitivity for nitroaromatics, nitramines, and nitrate esters, we consider it to be one of the leading predictive factors of impact sensitivity for energetic materials.

The Safety Properties of a Potential Kind of Novel Green Primary Explosive: Al/Fe₂O₃/RDX Nanocomposite

Green primary explosives have gained wide attention for environmental protection. A potential novel lead-free primary explosive, Al/Fe₂O₃/RDX hybrid nanocomposite was prepared by ultrasonic mixing, and its safety properties are discussed in detail. Results showed that their sensitivity and safety properties were a function of the specific surface area and proportions of their ingredients. Their impact sensitivity fell and their static discharge, flame, and hot bridge wire sensitivities rose as the specific surface area of nano-Fe₂O₃ increased. As the amount of Al/Fe₂O₃ nanothermite was increased, its impact sensitivity fell and its flame sensitivity rose; their static discharge and hot bridge wire sensitivities, however, followed an inverted “U” type change trend and were determined by both the particle size of the ingredients and the resistance of the nanocomposite. Their firing properties in an electric detonator depended on the proportion of the constituents. Thus, green nanoscale primary explosives are appropriate for a range of initiatory applications and can be created by adjusting their specific surface area and the amount of their constituents.

Assessment of two new nitrogen-rich tetrazine derivatives as high performance and safe energetic compounds

This work introduces two novel nitrogen-rich derivatives of tetrazine, i.e. 1,2-bis (6-nitro-1,2,4,5-tetrazin-3-yl)diazene and 1,2-bis(6-nitro-1,2,4,5-tetrazin-3-yl)hydrazine, as high performance and safe energetic compounds.

Electric-field-induced structural and electronic changes and decomposition of an energetic complex: a computational study on zinc carbohydrazide perchlorate crystals

The effects of electric field on the structure and decomposition mechanism of an energetic transition metal complex were theoretically studied for the first time.

First-principles study of electric field effects on the structure, decomposition mechanism, and stability of crystalline lead styphnate

The electric field effects on the structure, decomposition mechanism, and stability of crystalline lead styphnate have been studied using density functional theory. The results indicate that the influence of external electric field on the crystal structure is anisotropic. The electric field effects on the distance of the Pb-O ionic interactions are stronger than those on the covalent interactions. However, the changes of most structural parameters are not monotonically dependent on the increased electric field. This reveals that lead styphnate can undergo a phase transition upon the external electric field. When the applied field is increased to 0.003 a.u., the effective band gap and total density of states vary evidently. And the Franz-Keldysh effect yields larger influence on the band gap than the structural change induced by external electric field. Furthermore, lead styphnate has different initial decomposition reactions in the presence and absence of the electric field. Finally, we find that its sensitivity becomes more and more sensitive with the increasing electric field.

Theoretical investigations on heat of formation, detonation performance, and pyrolysis mechanism of 1,3,5,7,9,11-hexo(nitramine)-2,4,6,8,10,12- hexaazatetracyclo[5,5,0,0,0]dodecane

The B3LYP/6-311G(d,p) method was used to investigate IR and Raman spectra, heat of formation, and thermodynamic properties of a newly designed polynitro cage compound 1,3,5,7,9,11-hexo(nitramine)-2,4,6,8,10,12-hexaazatetracyclo[5,5,0,0,0]dodecane. The detonation and pressure were evaluated by using the Kamlet−Jacobs equations based on the theoretical density and condensed heat of formation. The bond dissociation energies and bond orders for the weakest bonds were analyzed to investigate the thermal stability of the title compound. The results show that the N9−NO2 bond is predicted to be the trigger bond during pyrolysis. There exists an essentially linear relationship between the Wiberg bond indices of N−NO2 bonds and the charges –QNO2 on the nitro groups. The crystal structure obtained by molecular mechanics belongs to the P21 space group, with lattice parameters Z = 2, a = 10.9220 Å, b = 13.6669 Å, c = 9.4659 Å, and ρ = 2.05 g cm−3.

Predicting Heats of Explosion of Nitroaromatic Compounds through NBO Charges and 15N NMR Chemical Shifts of Nitro Groups

This work presents a new quantitative model to predict the heat of explosion of nitroaromatic compounds using the natural bond orbital (NBO) charge and 15N NMR chemical shifts of the nitro groups (15NNitro) as structural parameters. The values of the heat of explosion predicted for 21 nitroaromatic compounds using the model described here were compared with experimental data. The prediction ability of the model was assessed by the leave-one-out cross-validation method. The cross-validation results show that the model is significant and stable and that the predicted accuracy is within 0.146 MJ kg−1, with an overall root mean squared error of prediction (RMSEP) below 0.183 MJ kg−1. Strong correlations were observed between the heat of explosion and the charges (R2 = 0.9533) and 15N NMR chemical shifts (R2 = 0.9531) of the studied compounds. In addition, the dependence of the heat of explosion on the presence of activating or deactivating groups of nitroaromatic explosives was analyzed. All calculations, including optimizations, NBO charges, and 15NNitro NMR chemical shifts analyses, were performed using density functional theory (DFT) and a 6-311+G(2d,p) basis set. Based on these results, this practical quantitative model can be used as a tool in the design and development of highly energetic materials (HEM) based on nitroaromatic compounds.

Theoretical investigations on the structure, density, thermodynamic and performance properties of amino-, methyl-, nitroso- and nitrotriazolones

We have studied herein the effect of position and the number of -NO, -NO2, -NH2 and -CH3 groups on the structure, stability, impact sensitivity, density, thermodynamic and detonation properties of triazolones by performing density functional theory calculations at the B3LYP/aug-cc-pVDZ level. The optimized structures, vibrational frequencies and thermodynamic values for triazolones have been obtained in their ground state. Kamlet-Jacob equations were used to calculate the detonation velocity and detonation pressure of model compounds. The detonation properties of NNTO (D 8.75 to 9.10 km/s, P 34.0 to 37.57 GPa), DNTO (D 8.80 to 9.05 km/s, P 35.55 to 38.27 GPa), ADNTO (D 9.01 to 9.42 km/s and P 37.81 to 41.10 GPa) and ANNTO (D 8.58 to 9.0 km/s, P 30.81 to 36.25 GPa) are compared with those of 1,3,5-trinitro-1,3,5-triazine (RDX) (D 8.75 km/s, P 34.70 Gpa) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) (D 8.96 km/s, P 35.96 GPa). The designed compounds satisfy the criteria of high energy materials.

A DFT study of aminonitroimidazoles

Density functional theory (DFT) calculations at the B3LYP/aug-cc-pVDZ level were performed to explore the geometric and electronic structures, band gaps, thermodynamic properties, densities and performances of aminonitroimidazoles. The calculated performance properties, stabilities and sensitivities of the model compounds appear to be promising compared with those of the known explosives 2,4-dinitro-1H-imidazole (2,4-DNI), 1-methyl-2,4,5-trinitroimidazole (MTNI), hexahydro-1,3,5-trinitro-1,3,5-triazinane (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocane (HMX). The position of the NH(2) or the number of NO(2) groups on the diazole presumably determines the structure, heat of formation, stability, sensitivity, density and performance of the compound.

Contemplation on spark sensitivity of certain nitramine type explosives

Spark sensitivity of explosives is an important subject. Presently, some correlations are sought between the spark sensitivity and certain molecular orbital characteristics of some nitramine type explosives. For that purpose certain semi-empirical and DFT calculations have been carried out. Investigations have revealed that the nitramines considered undergo decomposition in the electric field mainly via their anionic states.

Simple method for prediction of activation energies of the thermal decomposition of nitramines

A novel general method has been introduced to predict activation energies of thermal decomposition of nitramines as an important class of energetic compounds. It is shown that the activation energies of acyclic nitramines can be expressed as a function of optimized elemental composition. The resultant relationship as a core correlation can be corrected for cyclic nitramines that contain more than five member ring. R(2) value or the coefficient of determination of the new correlation is 0.94. The new correlation has the root mean square (rms) and the average deviations of 5.67 and 3.98 kJ/mol, respectively, for 14 nitramines with different molecular structures. The new method is also tested for some cyclic and acyclic nitramines with complex molecular structures, e.g. two new nitramines 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW) and 4,10-dinitro-2,4,6-tetroxa-4,10-diaazaisowurtzitane (TEX), so that it can predict relatively good results as compared to the experimental values.

Some properties of explosive mixtures containing peroxides Part II. Relationships between detonation parameters and thermal reactivity of the mixtures with triacetone triperoxide

This study concerns mixtures of triacetone triperoxide (3,3,6,6,9,9-hexamethyl-1,2,4,5,7,8-hexoxonane, TATP) and ammonium nitrate (AN) with added water (W), as the case may be, and two dry mixtures of TATP with urea nitrate (UN). Relative performances (RP) of the mixtures and their individual components, relative to TNT, were determined by means of ballistic mortar. Thermal reactivity of these mixtures was examined by means of differential thermal analysis and the data were analyzed according to the modified Kissinger method (the peak temperature was replaced by the temperature of decomposition onset in this case). The reactivity, expressed as the EaR(-1) slopes of the Kissinger relationship, correlates with the squares of the calculated detonation velocities for the charge density of 1000 kg m(-3) of the studied energetic materials. Similarly, the relationships between the EaR(-1) values and RP have been found. While the first mentioned correlation (modified Evans-Polanyi-Semenov equation) is connected with the primary chemical micro-mechanism of the mixtures detonation, the relationships in the second case should be connected with the thermochemical aspects of this detonation.

Theoretical prediction of electric spark sensitivity of nitroaromatic energetic compounds based on molecular structure

A new simple correlation is introduced for predicting electric spark sensitivity of nitroaromatic compounds. This approach is based on the number of carbons and hydrogens as well as the ratio of hydrogens to oxygens and the presence of certain groups, i.e. alkyl or alkoxy groups, attached to an aromatic ring. The model is optimized using a set of 17 polynitroaromatic explosives as training set and then it is applied to 14 explosives from a variety of chemical families as test set in order to assess the predictive capability of new method. Predicted results are reasonably close to the measured values for both training and test sets.

Decomposition of some polynitro arenes initiated by heat and shock Part I. 2,4,6-Trinitrotoluene

Samples of 2,4,6-trinitrotoluene (TNT) exposed to heat or to shock and residues after their detonation have been analyzed chromatographically (LC-UV and LC/MS). It was found that the main identified decomposition intermediates are identical in all the three cases. 4,6-Dinitro-2,1-benzoisoxazole and 2,4,6-trinitrobenzaldehyde are the most reactive from them. It has been stated that the chemical micro-mechanism of the primary fragmentations of shock-exposed TNT molecules and/or its detonation transformation should be the same as in the case of its low-temperature thermal decomposition.