B. L. Korsunskii

Phase transformations of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane: the role played by water, dislocations, and density

A comparative study of the kinetics and mechanisms of the α → γ and ɛ → γ polymorphic transitions in polycrystalline haxanitrohexaazaisowurtzitane was performed using electron and optical microscopy, calorimetry, IR spectroscopy, and quantitative X-ray phase analysis. The kinetics of both processes is complex because of the morphology of the crystals, their defect structure, and impurities. As distinct from the ɛ → γ process, which always occurs as a single crystal-polycrystal transition (through nucleation by the dislocation mechanism with subsequent movement of the phase separation front), the α → γ process can also follow the quasi-homogeneous mechanism and occur as a single crystal-single crystal transition.

Thermal decomposition of [1,2,5]Oxadiazolo[3,4-e][1,2,3,4]-Tetrazine-4,6-di-N-Oxide

The thermal decomposition of [1,2,5]oxadiazolo[3,4-e][1,2,3,4]-tetrazine-4,6-di-N-oxide (furazano tetrazine dioxide, FTDO) in the solid state, melt, and dinonyl phthalate solution is studied. The kinetic and thermodynamic parameters of the process are determined. These results enable to estimate the thermal stability of FTDO. The composition of the gaseous reaction products and the elemental composition of the condensed product are determined. On the basis of kinetic, analytical, and spectral data, the mechanism of the process, including the formation of the N-nitrosofurazanoaziridine intermediate, is discussed.

The thermal decomposition of azidopyridines

The thermal decomposition of new heteroaromatic polyazides 2,6-diazido-3,5-dicyanopyridine, 2,4,6-triazido-3,5-dicyanopyridine, and 2,3,4,5-tetraazido-6-cyanopyridine was studied by thermogravimetry, volumetry, mass-spectrometry, and IR spectroscopy. Reaction kinetic parameters were determined. The only gaseous product of the thermal decomposition of all the azides studied was nitrogen, its degree of purity was 99.0–99.8 vol %. 2,6-Diazido-3,5-dicyanopyridine and 2,4,6-triazido-3,5-dicyanopyridine had thermal stability and thermal decomposition parameters close to those of the majority of aromatic azides. The mechanism of thermal decomposition of these azides includes the splitting off of the nitrogen molecule at the initial limiting process stage. Subsequent intermolecular reactions with the participation of nitrenes result in the formation of an amorphous substance containing polyconjugated fragments with sp2 hybridization, which form planar two-dimensional networks. 2,3,4,5-Tetraazido-6-cyanopyridine has very low thermal stability; the rate of nitrogen release during its decomposition is almost 1000 times higher than with 2,6-diazido-3,5-dicyanopyridine and 2,4,6-triazido-3,5-dicyanopyridine at comparable temperatures. This was explained by the presence of the ortho azido group (there is no ortho arrangement of azido groups in 2,6-diazido-3,5-dicyanopyridine and 2,4,6-triazido-3,5-dicyanopyridine).

Synthesis and thermal decomposition of ditetrazol-5-ylamine

Ditetrazol-5-ylamine (DTA) was synthesized from cyanuric chloride in four steps. The thermal decomposition of DTA in the solid state was studied by thermogravimetry, volumetry, mass spectrometry, IR spectroscopy, and calorimetry. Under isothermal conditions at 200–242 °C, thermal decomposition obeys the first order autocatalytic kinetics. The kinetic and activation parameters of DTA decomposition were determined. The composition of gaseous reaction products and the structure of condensed residue were studied. The thermal effect of thermal DTA decomposition is 281.4 kJ mol−1. The nitrogen content in a mixture of gaseous products formed by the reaction in a temperature interval of 200–242 °C exceeds 97 vol.%.

Kinetics and mechanism of a polymorphous transition in polycrystalline ε-hexanitrohexaazaisowurtzitane

Optical and electron microscopy, calorimetry, IR spectroscopy, and XRD analysis were used to study the ε → γ polymorphous transition in polycrystalline hexanitrohexaazaisowurtzitane. The kinetics of the process is extremely complex due to the intrinsic morphological features and defects in individual crystals in the polycrystalline sample. A limiting phenomenon, which manifests itself in a sharp slowdown of the process at a critical temperature, was revealed. The polymorphous transformation is triggered by dehydration, the removal of the residual water from the crystal. It was demonstrated that dislocations play an important role in the process under study.

Thermal decomposition of 2,4,6-triazido-1,3,5-triazine

The thermal decomposition of 2,4,6-triazido-1,3,5-triazine in the melt and a dinonyl phthalate solution is studied by thermogravimetry, manometry, mass spectrometry, and IR spectroscopy. The kinetic and activation parameters of the process are determined. The only gaseous product of the reaction is nitrogen. This fact, along with the structure of the condensed residue formed during the thermal decomposition of 2,4,6-triazido-1,3,5-triazine in the melt, are indicative of the abstraction of a nitrogen molecule from an azide group at the initial stage and of the subsequent reactions leading to the formation of a planar network of polyconjugated bonds between C and N atoms. For the thermal decomposition of 2,4,6-triazido-1,3,5-triazine in solution the preexponential factor and activation energy are found to be 1012.8 s–1 and 34100 cal/mol, respectively, which are characteristic of the thermal decomposition of most azides. To explain why these parameters are substantially higher for the reaction in the melt (1017.4 s–1 and 42300 cal/mol), it is assumed that, in this case, the process proceeds by the polymerization (polycondensation) mechanism to form twodimensional networks, with the apparent kinetic parameters being effective quantities. Based on these data, it is concluded that the high sensitivity of 2,4,6-triazido-1,3,5-triazine to external influences is of kinetic nature.

Steady regimes of exothermic autocatalytic reaction in a continued stirred-tank reactor

A continued stirred-tank reactor with an exothermic autocatalytic reaction running in it is modeled. In contrast to the simple kinetic law formulated in terms of a first-order equation, a variety of possible types of thermal isoclines, including isoles, are found for the autocatalytic process in the dimensionless “degree of conversion-temperature” coordinates. A bifurcation curve separating the domains of existence of one and three steady states is constructed in the Se-Da coordinates.

A kinetic model of the structural transformation of a molecular crystal initiated by the escape of mobile defects

A diffusion model of the polymorphic transformation of a molecular crystal accompanied by the escape of mobile defects is suggested. The model describes both bulk and frontal regimes of the process. The frontal regime is possible when the concentration of mobile defects exceeds some threshold value, the existence of which explains spread of times of the beginning of the polymorphic transition in a crystal. The temperature dependence of the rate of a polymorphic process wave was obtained. Internal crystal microstresses that appeared in a phase transition wave were theoretically estimated.

Modeling of the Dynamics of a Well-Stirred Reactor with Parallel Exothermic Reactions

The dynamics of a well-stirred reactor in which two parallel exothermic first-order reactions occur was modeled. Phase portraits of the system were plotted, the possibility of realization of oscillatory regimes was revealed, and the stability of the steady states involved was examined. Two types of limit cycle extinction, smooth and sharp, were demonstrated to exist.

Density evolution of the energy-rich compound furazano[3,4-e]tetrazine-4,6-dioxide as stability indicator during prolonged storage

Pycnometric method, powder X-ray diffraction analysis, and IR spectroscopy were used to study the fundamental aspects of how the density of energy-rich compound furazano[3,4-e]tetrazine-4,6-dioxide varies during its prolonged storage. It was shown that the density grows during the first stage with length of up to 14 days due to the recrystallization. In further storage during eight years, the density gradually falls due to the buildup of stresses in the crystal lattice, created by thermal decomposition products. The degree of decomposition at 22°C during 8 years, evaluated by extrapolation of the Arrhenius dependence, is 0.24%. The observed decrease in the density is attributed to the anomalously weak hampering effect of the crystal lattice.