Svatopluk Zeman

Sensitivities of High Energy Compounds

The article presents a survey of the development trends in studies of sensitivity (initiation reactivity) of energetic materials (EMs) over the last nine years, focusing mainly on impact and shock sensitivities. Attention is given to the initiation by heat, laser, electrostatic discharge, impact and shock, including the influence of hydrostatic compression, crystal defects, molecular structure and desensitizing admixtures on the initiation reactivity. Problems of the initiation of nitromethane are examined with a special accent. It is stated that one of the best-developed theories for such studies is Dlotts Model of the Multiphonon Up-Pumping. Also significant is the model based on Non-Equilibrium Zeldovich–von Neuman–Doring theory. Very important are approaches devised by Politzer and Murray, updated by Price et al. as a hybrid model of prediction of the impact sensitivity of CHNO explosives. The physical organic chemistry approach to the sensitivity problem (POC model) is discussed with special emphasis. In this way it has been found that the electron structure and close neighborhood of the primarily leaving nitro group are dominant factors in the initiation by shock, electric spark and heat of polynitro compounds.

The relationship between kinetic data of the low-temperature thermolysis and the heats of explosion of organic polynitro compounds

Abstract A linear relationship between the activation energies of the initial stage of non-autocatalysed, low-temperature thermolysis and the heats of explosion of organic polynitro compounds is presented. This was derived from discussions on a set of problems concerning the identity of primary chemical processes of the thermal decomposition and detonation of organic explosives. The necessary kinetic data of thermal decomposition for the studied compounds were taken from the results obtained by the Soviet manometric method (SMM) and the Rogers method of differential scanning calorimetry (DSC). The data obtained from differential thermal analysis (DTA), i.e., Piloyan activation energies of the initial exothermal decomposition of some of the above mentioned compounds, were used as a supplement. It is also shown that the kinetic data obtained by DTA according to Kissinger are not applicable to the study of the micromechanism of the initiation of detonation.

The relationship between differential thermal analysis data and the detonation characteristics of polynitroaromatic compounds

Abstract The thermal stabilities of 37 polynitroaromatic compounds are specified by means of non-isothermal DTA. The initial temperatures of the exotherms TD, as well as the Piloyan decomposition activation energies, E, of the compounds are determined. A relationship is derived between ET−1D and the detonation characteristics of the compounds being measured. It is shown that allocation of the measured compounds to separate forms of the determined relationship is, in addition to thermochemical factors, also determined by the electron configuration and steric conditions in the reaction center of the given molecule.

Modified Evans–Polanyi–Semenov relationship in the study of chemical micromechanism governing detonation initiation of individual energetic materials

Abstract The paper deals with basic problems of the study of the thermal reactivity of individual energetic materials with special attention on the compatibility of results obtained using different methods. It is shown that the activation energies for thermal decomposition of these materials, obtained under comparable conditions, correlate with the respective detonation heats through a modified Evans–Polanyi–Semenov equation. These correlation relationships apply within groups of molecules with closely related structures and underline the importance of the bond that is primarily split in the molecule for the detonation of a given material. They also indicate that the primary fragmentation processes during low-temperature thermal decomposition are the same as those controlling the detonation reaction. It is shown that the correlation relationships found are also valid in the case of electric spark initiation.

Cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), its properties and initiation reactivity

Using the (15)N NMR chemical shifts of nitrogen atoms in nitramino groups of cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (bicyclo-HMX or BCHMX) and additional 10 nitramines, we have assessed its reactivity in detonation, under the influence of impact, and by action of electric spark. It is stated that the thermal stability of BCHMX is higher than that of 1,3,5-trinitro-1,3,5-triazinane (RDX). The longest NN bond in the BCHMX molecule (1.412(4)A) is the cause for its higher impact reactivity, which is at the level of that of penterythritol tetranitrate (PETN). In the experimentally determined detonation velocity, BCMX can be slightly better performing than RDX. From the standpoint of friction sensitivity, BCHMX is similar to 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). Attention was also focused on the solubility-temperature dependence of BCHMX in acetone, acetonitrile, ethyl acetate, dimethyl sulfoxide, tetrahydrofurane, and nitromethane. X-ray crystallographic study of BCHMX (C(4)H(6)N(8)O(8), M(r)=294.17), has been carried out at the temperature of 150K with the following results: a=8.5430(8), b=6.9480(6), c=8.7780(8)A, alpha=90.0(7) degrees , beta=102.452(11) degrees , gamma=90.0(9) degrees , V=508.777(8)A(3), Z=2, D(x)=1.920 g cm(-3), lambda(Mo Ka)=0.71073A, micro=0.169 cm(-1), F(000)=856, final R=0.0414 for 1254 independent observed reflections. In the BCHMX crystal there were found more short contacts in the molecular crystal of BCHMX data of Gilardi creating extensive supramolecular architecture.

Thermal stabilities of polynitroaromatic compounds and their derivatives

Abstract The thermal stabilities of 33 polynitroaromatic compounds and their derivatives were determined using non-isothermal differential thermal analysis (DTA). For twelve of these, the thermal stabilities of their mixtures with 1,3,5-trinitrobenzene was also determined. The results obtained are discussed from a molecular structural point of view. The results obtained from DTA measurements are compared with the published data which were derived from the results of the application of the manometric method to the study of the thermal reactivity of polynitroaromatic compounds. The differences which exist between the conclusions reached on basis of DTA application, on the one hand, and those obtained on the basis of the application of the manometric method, on the other hand, are discussed. Using the published relationship for the calculation of the temperature limit (Tmax) for the use of polynitroaromatic compounds as secondary thermostable explosives, Tmax values are calculated for the compounds being measured. A relationship is derived between Tmax and TD the initial exothermal decomposition temperature obtained from the DTA of the studied compounds.

Kinetic data from low-temperature thermolysis in the study of the microscopic initiation mechanism of the detonation of organic polynitro compounds

Abstract Seventy-three organic polynitro compounds and one nitroso compound were subjected to thermal decomposition; the process was followed using the Soviet manometric method (SMM) or DSC. From the kinetic data of the initial stage of the decomposition, corresponding values were calculated of the natural logarithm of equilibrium constants of the activated complex (In K≠). A relationship was found and discussed between the values ln K≠ and ln D, where D is a detonation velocity at maximum theoretical density of the above-mentioned compounds. Taking into account the previously published relationships, i.e. the relationships existing between thermochemical kinetic characteristics from DTA and detonation characteristics of polynitroaromates, it is concluded that the chemical mechanisms of primary thermolytical processes and initial detonation reactions of organic polynitro compounds are identical. Attention was also paid to the influence exercised by the solvent upon kinetic parameters of thermolysis in the above-mentioned compounds; it is proved that polynitroaromates can in no way be classified as inert solvents.

Relationship between detonation characteristics and 15N NMR chemical shifts of nitramines

Abstract The paper presents 15N NMR chemical shifts δ of twenty three nitramines out of which 1-nitro-1-azaethylene (DIGEN), 1,3-dinitro-1,3-diazacyclobutane (TETROGEN) and 1,3,5,7,9-pentanitro-1,3,5,7,9-pentaazacyclodecane (DECAGEN) have not been synthesized yet. The corresponding δ values of these three substances have been predicted. The relationship has been confirmed between squares of detonation velocities or, as the case may be, the detonation heats and δ values of nitrogen atoms in nitro group of the nitramines. This relationship represents a certain form of Evans-Polanyi-Semenov equation and such it directly specifies the most reactive nitro group of nitramine molecule in the detonation and, hence, the N-NO2 bond primarily split in this process.

Some predictions in the field of the physical thermal stability of nitramines

Abstract Eight linear and seven cyclic nitramines predominantly with methylenenitramine grouping were studied by means of the differential scanning calorimetry (DSC). For eleven of them the characteristics of fusion were specified. Linear relationships were found between the onset or peak temperatures of melting of these compounds and the melting points of their aliphatic structural analogues (i.e. homomorphs). A similar relationship between the corresponding heats of fusion ΔHm, tr was specified. On the basis of these facts the melting points (in K) and the ΔHm, tr values (in kJ mol−1) were predicted for N-nitromethyleneimine, DIGEN (368.5–371.5 and 23.45), 2,4-dinitro-2,4-diazacyclobutane, TETROGEN (433.8-436.1 and 26.33), 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane, OCTOGEN (463.4–465.2 and 32.10), 1,3,5,7,9-pentanitro-1,3,5,7,9-pentaazacyclodecane, DECAGEN (600.3 and 34.93) and trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecaline, TNTAD (555.6–556.1 and 46.40).

Kinetic compensation effect and thermolysis mechanisms of organic polynitroso and polynitro compounds

Abstract The present study starts from the published values of the Arrhenius parameters E a and log A of thermolysis in the condensed state of seven nitrosamines and one hundred organic polynitro compounds. On the basis of the linear relationship between E a and log A , the set studied has been divided into several reaction series, each of which is characterized by a mechanism of primary thermolysis. For compounds with intense intermolecular interactions in a crystal, the classification mentioned is codetermined by the stabilizing effect of the crystal lattice. In the context of this effect, the absence of an effect of solid-liquid transition on thermal reactivity of octogen (HMX) has been confirmed. The idea also presented is that, in the primary homolysis in thermolyses of polynitro compounds, there takes place a mutual interaction of molecules of the given compound, which is analogous to termination interactions of nitroarenes in radical polymerizations.