New Correlation between Electric Spark and Impact Sensitivities of Nitramine Energetic Compounds for Assessment of Their Safety

Electric spark and impact sensitivities of nitramine energetic compounds are two important sensitivity parameters, which are closely related to many accidents in working places. For nitramines, in contrast to electric spark sensitivity, their impact sensitivity can be easily measured or predicted by various methods. A new approach is introduced to correlate electric spark and impact sensitivities of nitramine energetic compounds by the use of three structural parameters. The predicted results of the novel model for 20 nitramines are compared with two of the best available models, which are based on complex quantum mechanical approach and the measured values of activation energies of thermolysis. The root‐mean‐square (rms) and maximum deviations of the new model are 1.06 and 2.41 J, respectively. For further 14 nitramines, where the measured electric spark or impact sensitivities were not available, the estimated electric spark sensitivities by the new model are close to those predicted based on experimental data of activation energies of thermolysis.     

Reliable Prediction of Shock Sensitivity of Energetic Compounds based on Small‐scale Gap Test through Their Electric Spark Sensitivity

The sensitivity of an energetic compound gives its vulnerability to accidental detonation, which is caused by an unintended stimulus. Shock and electric spark sensitivities of energetic compounds are two important sensitivity parameters for assessment of their safety in working places. Several correlations are introduced for reliable prediction of shock sensitivities of energetic compounds at 90, 95, and 98 % of theoretical maximum density (TMD) according to NSWC using Navy small‐scale gap test through their electric spark sensitivities. For 11 explosives, where experimental data of both shock and electric spark sensitivities were available, the predicted results at 90 % of TMD are compared with the quantum mechanical approach. The root‐mean‐square (rms) deviations of the new and complex quantum mechanical methods at 90 % TMD are 2.38 and 3.95 kbar, respectively, which confirmed the high reliability of the new method. For high explosives with 90, 95, and 98 % TMD, it will be shown that the predicted results of the new method are also much more reliable than one of the best available empirical approaches. A correlation between shock sensitivities on the basis of aluminum gaps with different thicknesses and the pressure required to initiate material pressed to 90 % TMD is also derived.     

Correlation between Shock Sensitivity of Nitramine Energetic Compounds based on Small‐scale Gap Test and Their Electric Spark Sensitivity

Electric spark sensitivity and shock sensitivity based small‐scale gap test for nitramine energetic compounds are two important sensitivity parameters, which are needed for assessment of their safety in working places. A novel method is introduced for reliable prediction of electric spark or shock sensitivity of a desired nitramine energetic compound when reliable data for one of the sensitivity is available. A novel correlation with a high value of correlation coefficient (R² = 0.998) is derived between electric spark and shock sensitivities of 20 cyclic and acyclic nitramines. For these nitramines, the predicted results of electric spark sensitivities of the novel model are compared with two of the best available models. The root‐mean‐square (rms) and maximum deviations of the new model are 0.20 and 0.51 J, respectively, which are much less than two comparative methods. The reliability of the new method for prediction of electric spark sensitivity of further 14 nitramines is also compared with one of the best available methods, where the measured electric spark or shock sensitivities were not available in literature.     

A novel method for risk assessment of electrostatic sensitivity of nitroaromatics through their activation energies of thermal decomposition

This study presents a novel relationship between electric spark sensitivity of nitroaromatic energetic compounds and their activation energies of thermal decomposition. The new correlation can help to elucidate the mechanism of initiation of energetic materials by electric spark. It can be used to predict the magnitude of electric spark sensitivity of new nitroaromatics, which is difficult to measure. The methodology assumes that electric spark sensitivity of a nitroaromatic energetic compound with general formula C_aH_bN_cO_d can be expressed as a function of its activation energy of thermal decomposition as well as optimized elemental composition and the contribution of specific molecular structural parameters. The new correlation has the root mean square and the average deviations of 1.43 and 1.17 J, respectively, for 22 nitroaromatic energetic compounds with different molecular structures. The proposed new method is also tested for eight nitroaromatic energetic compounds, which have complex molecular structures, e.g., 1,3,7,9-tetranitrophenoxazine, 2,4,6-tris(2,4,6-trinitrophenyl)-1,3,5-triazine, and 1-(2,4,6-trinitrophenyl)-5,7-dinitrobenzotriazole.     

Impact sensitivity and activation energy of pyrolysis for tetrazole compounds

Calculations with both DFT‐B3LYP and semiempirical quantum chemical PM3 methods are carried out on a series of tetrazole derivatives and their metal salts to investigate the relationship between the relative order of impact sensitivity and activation energy of thermal decomposition. The results show that the relative order of sensitivity for the titled compounds can be predicted by examining the activation energy for breaking down of tetrazole ring. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 350–357, 2000     

Furazans with Azo Linkages: Stable CHNO Energetic Materials with High Densities,Highly Energetic Performance,and Low Impact and Friction Sensitivities

Various highly energetic azofurazan derivatives were synthesized by simple and efficient chemical routes. These nitrogen‐rich materials were fully characterized by FTIR spectroscopy, elemental analysis, multinuclear NMR spectroscopy, and high‐resolution mass spectrometry. Four of them were further confirmed structurally by single‐crystal X‐ray diffraction. These compounds exhibit high densities, ranging from 1.62 g cm^?3 up to a remarkably high 2.12 g cm^?3 for nitramine‐substituted azofurazan DDAzF ( 2 ), which is the highest yet reported for an azofurazan‐based CHNO energetic compound and is a consequence of the formation of strong intermolecular hydrogen‐bonding networks. From the heats of formation, calculated with Gaussian 09, and the experimentally determined densities, the energetic performances (detonation pressure and velocities) of the materials were ascertained with EXPLO5 v6.02. The results suggest that azofurazan derivatives exhibit excellent detonation properties (detonation pressures of 21.8–46.1 GPa and detonation velocities of 6602–10 114 m s^?1) and relatively low impact and friction sensitivities (6.0–80 J and 80–360 N, respectively). In particular, they have low electrostatic spark sensitivities (0.13–1.05 J). These properties, together with their high nitrogen contents, make them potential candidates as mechanically insensitive energetic materials with high‐explosive performance.     

Theoretical evaluation of sensitivity and thermal stability for high explosives based on quantum chemistry methods: A brief review

Over the past 20 years, a number of scientists have conducted numerous fundamental investigations based on quantum chemistry theory into various mechanistic processes that seems to contribute to the sensitivity of energetic materials. A large number of theoretical methods that have been used to predict their mechanical and spark sensitivity are summarized in this article, in which the advantages and disadvantages of these methods, together with their scope of use are clarified. In addition, the theoretical models for thermal stability of explosives are briefly introduced as a supplement. It has been concluded that the current ability to predict sensitivity is merely based on a series of empirical rules, such as simple oxygen balance, molecular properties, and the ratios of C and H to oxygen for different classes of explosive compounds. These are valid only for organic classes of explosives, though some special models have been proposed for inorganic explosives, such as azides. An exact standard for sensitivity should be established experimentally by some new techniques for both energetic compounds and their mixtures. © 2013 Wiley Periodicals, Inc.     

Relationship between Electric Spark Sensitivity of Cyclic Nitramines and Their Molecular Electronic Properties

On the basis of the structural and electronic properties of 14 different cyclic nitramine molecules, two types of formulas are employed to predict their electric spark sensitivity. One contains the minimum Mulliken charges of nitro group, the ratio of hydrogen to oxygen, and the ratio of carbon to oxygen; the other contains the lowest unoccupied molecular orbital energy, the ratio of hydrogen to oxygen, and the ratio of carbon to oxygen. Using these two types of formulas, we calculate the electric spark sensitivity of these 14 cyclic nitramine molecules, and compare them with the experimental data and previous theoretical values. And our investigations show that the former type of formula is better than the latter on predicting the electric spark sensitivity for cyclic nitramine molecules.     

Magnesium Azotetrazole‐1,1′‐dioxide: Synthesis and Promising Properties of Green Insensitive Energetic Materials

Magnesium azotetrazole‐1,1′‐dioxide ( 1 ) was first prepared and intensively characterized by single‐crystal X‐ray diffraction, IR spectroscopy, mass spectrometry, elemental analysis, and DSC measurements. The heat of formation was calculated using the atomization energy method based on quantum chemistry and the heat of detonation was also predicted. The NBO analysis was performed for inspecting charge distributions. The sensitivities towards impact and friction were tested using the BAM standard. The high detonation performance (5289 kJ · kg^–1), good thermal stabilities (245.5 °C) and excellent insensitivity (39.2 J and >360 N) as well as clean decomposition products supports it of great interest as a promising candidate of green insensitive energetic materials.     

A New Method for Assessment of Performing Mechanical Works of Energetic Compounds by the Cylinder Test

A new method is introduced for assessment of performing mechanical works of energetic compounds by cylinder wall velocities of CHNOFCl energetic compounds on the basis of the cylinder test. Four suitable decomposition paths are used to evaluate the number of moles of gaseous detonation products per gram of explosive, the average molecular weight of these gases, and the heat of detonation in calories per gram by considering different decomposition products HF, HCl, CO, N₂, H₂O, H₂, and CO₂. For CHNO and fluoro energetic compounds, the predicted cylinder wall velocities of these compounds give more reliable results than one of the best available empirical methods. The predicted root mean square (rms) deviations of cylinder wall velocities of the new model for some chloro explosives at actual radial expansions 0.6 and 1.9 mm are 0.010 and 0.062 km · s^–1, which show high reliability of the new method.     

硝基芳烃对黑呆头鱼毒性定量构效关系的研究

用CNDO/2法计算50种硝基芳烃化合物的净电荷(Q_C、Q_N及Q_-NO2);使用MNDO法计算其中42种化合物的E_LUMO、E_HOMO、生成热之差△(△H_f)及偶极矩μ。定量分析了7种量化参数与黑呆头鱼毒性96h-LC₅₀的构效关系,通过统计分析,得到如下模式:式中:-1gLC₅₀=11. 35-1. 28E_LUMO-9.17Q_N+0. 46E_HOMO-0.12μ n=35,r=0.920,s=0.298。应用所得方程及量化参数讨论所研究系列化合物在鱼体内的毒性作用。     

Note on the use of the vacuum stability test in the study of initiation reactivity of attractive cyclic nitramines in Formex P1 matrix

The zero-order reaction rates (specific rate constants) of isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) were measured by means of the Czech vacuum stability test, STABIL. The PBXs are based on 1,3,5-trinitro-1,3,5-triazinane (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole (BCHMX), and ε 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-HNIW, ε-CL-20) with 13 wt% of the Formex P1 type matrix, i.e., a matrix of the explosive with pentaerythritol tetranitrate (PETN) bound by 13 wt% of a mixture of 25 wt% of styrene–butadiene rubber and 75 wt% of an oily material. Dependencies were found between the specific rate constants mentioned and the detonation velocities of PBXs, and consequently between these constants and the impact and electric spark sensitivities of pure explosive fillers, i.e., RDX, HMX, HNIW, BCHMX, and PETN. It is stated that the higher impact or electric spark sensitivity of their pure explosive fillers corresponds to the higher thermal reactivity of the given PBXs.     

1,5‐Di(nitramino)tetrazole: High Sensitivity and Superior Explosive Performance

Highly energetic 1,5‐di(nitramino)tetrazole and its salts were synthesized. The neutral compound is very sensitive and one of the most powerful non‐nuclear explosives to date. Selected nitrogen‐rich and metal salts were prepared. The potassium salt can be used as a sensitizer in place of tetracene. The obtained compounds were characterized by low‐temperature X‐ray diffraction, IR and Raman spectroscopy, multinuclear NMR spectroscopy, elemental analysis, and DSC. Calculated energetic performances using the EXPLO5 code based on calculated (CBS‐4M) heats of formation and X‐ray densities support the high energetic performances of the 1,5‐dinitraminotetrazolates as energetic materials. The sensitivities towards impact, friction, and electrostatic discharge were also explored.     

Improved prediction of heats of formation of energetic materials using quantum mechanical calculations

We present simple atom and group-equivalent methods that will convert quantum mechanical energies of molecules to gas phase heats of formation of CHNO systems. In addition, we predict heats of sublimation and vaporization derived from information obtained from the quantum-mechanically calculated electrostatic potential of each isolated molecule. The heats of sublimation and vaporization are combined with the aforementioned gas phase heats of formation to produce completely predicted condensed phase heats of formation. These semiempirical computational methods, calibrated using experimental information, were applied to a series of CHNO molecules for which no experimental information was used in the development of the methods. These methods improve upon an earlier effort of Rice et al. [Rice, B. M.; Pai, S. V.; Hare, J. Combust. Flame 1999, 118, 445] through the use of a larger basis set and the application of group equivalents. The root-mean-square deviation (rms) from experiment for the predicted group-equivalent gas phase heats of formation is 3.2 kcal/mol with a maximum deviation of 6.5 kcal/mol. The rms and maximum deviation of the predicted liquid heats of formation are 3.2 and 7.4 kcal/mol, respectively. Finally, the rms and maximum deviation of predicted solid heats of formation are 5.6 and 12.2 kcal/mol, respectively, an improvement in the rms of approximately 40% compared to the earlier Rice et al. predictions using atom equivalents and a smaller basis set (B3LYP/6-31G*).     

Correlation between Molecular Structure of Ferrocene Derivative and Impact Sensitivity of Fine‐AP/Ferrocene Derivative Mixture

On the basis of investigation of molecular structure characteristics of model ferrocene derivatives, the correlation between stability and molecular structure of double‐core ferrocene derivatives (DFDs) was studied. Then, the relation of stability of DFDs and impact sensitivity of fine‐AP/DFD mixtures was investigated. The results showed that the DFDs with methylene bridge group were more stable than those with methylethylidene bridge group. The stability order of the five DFDs was DEFM>EDFM≈BDFM>GFP>TBPF. The impact sensitivities of the fine‐AP/DFD mixtures were in inverse proportion to the stabilities of the DFDs.     

Long–term Drifts in Sensitivity Caused by Biofouling of an Amperometric Oxygen Sensor

Changes in oxygen sensitivity of an poly(o‐phenylenediamine) (PoPD) coated gold electrode was determined by constructing calibration curves in vitro. Oxygen sensitivities recorded in the presence of biofoulants were significantly different from those recorded in buffer; however, PoPD demonstrated its effectiveness in providing some resistance to changes in oxygen sensitivity over time compared to a bare electrode. Three sets of PoPD‐coated electrodes were calibrated in simple electrolyte of phosphate buffered saline; each set yielding an average oxygen sensitivity of 0.58±0.03 μA/ppm, 0.68±0.01 μA/ppm, and 0.48±0.01 μA/ppm (n=4), which shows the electrode to electrode variation in the PoPD‐coating/electrode. These sets were correspondingly exposed to bovine serum albumin, fibrinogen, rat brain homogenate. Exposure to these biofoulants resulted in decreases in sensitivity ranging from 26–35 % after immediate exposure. Furthermore, long‐term exposure to some biofoulants causes significant decreases in sensitivity over a time period of 14 days. We also estimated through in vitro exposure to rat brain homogenate the errors that might be associated with current methods of calibration. Sensitivities to oxygen determined by precalibration resulted in a 50 % error from the sensitivity found in vitro; the error from postcalibration after rinsing resulted in 25 % error.     

Highly Energetic,Low Sensitivity Aromatic Peroxy Acids

The synthesis, structure, and energetic materials properties of a series of aromatic peroxy acid compounds are described. Benzene‐1,3,5‐tris(carboperoxoic) acid is a highly sensitive primary energetic material, with impact and friction sensitivities similar to those of triacetone triperoxide. By contrast, benzene‐1,4‐bis(carboperoxoic) acid, 4‐nitrobenzoperoxoic acid, and 3,5‐dinitrobenzoperoxoic acid are much less sensitive, with impact and friction sensitivities close to those of the secondary energetic material 2,4,6‐trinitrotoluene. Additionally, the calculated detonation velocities of 3,5‐dinitrobenzoperoxoic acid and 2,4,6‐trinitrobenzoperoxoic acid exceed that of 2,4,6‐trinitrotoluene. The solid‐state structure of 3,5‐dinitrobenzoperoxoic acid contains intermolecular O‐H???O hydrogen bonds and numerous N???O, C???O, and O???O close contacts. These attractive lattice interactions may account for the less sensitive nature of 3,5‐dinitrobenzoperoxoic acid.     

Synthesis and photochemical properties of azidohemicyanine

Photochemical activity of azidohemicyanine (1-methyl-4-(4-azidostyryl)quinolinium iodide) was predicted by quantum chemical calculations and confirmed experimentally. The azidohemicyanine, which was synthesized, is characterized by a long-wavelength absorption band (LWAB) in the spectral region 350–500 nm with a maximum at 417 nm; it decomposes with a quantum yield of 0.84±0.17 upon irradiation within the LWAB, the quantum yield being independent of the presence of oxygen. The reaction products identified by ESI mass spectrometry include the corresponding primary amine as well as azo, hydrazo, nitroso, and nitro compounds, some of them are unidentified. The azidohemicyanine possesses the longest-wavelength visible light sensitivity among aromatic azides known so far. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1402–1408, July, 2008.