T. S. Larikova

Comparative Investigation of Thermal Decomposition of Various Modifications of Hexanitrohexaazaisowurtzitane (CL-20)

The thermal decomposition kinetics of different polymorphs of CL-20 (α, γ and e) has been investigated by thermogravimetry, IR spectroscopy and optical and electronic microscopy. The reactions proceed with self-acceleration and can be described by a kinetic law of first order with autocatalysis. Already at the earliest stages of decomposition (≤1%) phase transitions take place from αγ and from eγ. For this reason the observed decomposition is related to the decomposition of γ-CL-20. On the other hand, the kinetics of decomposition depends on the initial polymorphic state, so that the thermal decomposition increases in the series: α<γ<e. Experiments with different samples of α-CL-20 demonstrate that different rates of decomposition are observed for the same polymorph depending on the mean size and the size distribution of the crystals and their morphological features. In some cases the thermal stability of α-CL-20 can be increased by previous annealing. It is concluded that the thermal decomposition of CL-20 is purely a solid-state process. Microscopical and spectroscopical analysis of the condensed CL-20 decomposition product (formed after prolonged heating at high temperature) show that it has a network structure and consists mainly of carbon and nitrogen.

Kinetics of thermal decomposition of hexanitrohexaazaisowurtzitane

Thermal decomposition of hexanitrohexaazaisowurtzitane (HNIW) in the solid state and in solution was studied by thermogravimetry, manometry, optical microscopy, and IR spectroscopy. The kinetics of the reaction in the solid state is described by the first-order equation of autocatalysis. The rate constants and activation parameters of HNIW thermal decomposition in the solid state and solution were determined. The content of N2 amounts to approximately half of the gaseous products of HNIW thermolysis. The thermolysis of HNIW and its burning are accompanied by the formation of a condensed residue. During these processes, five of six nitro groups of the HNIW molecule are removed, and one NO2 group remains in the residue, which contains amino groups and no C−H bonds.

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.%.

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.

Thermal decomposition of 2,4,6-triazidopyridine

The thermal decomposition of 2,4,6-triazidopyridine in the melt is studied using thermogravimetry, manometry, mass spectrometry, and IR spectroscopy. In the temperature range of 120–160°C, the process obeys the first-order kinetic law, being described by the Arrhenius equation k [s–1] = 1012.8 ± 0.4exp[–(31200 ± 1500)]/RT with values of the parameters typical of the thermal decomposition of aromatic and heterocyclic azides. The reaction produces nitrogen, as the only gaseous product. Unlike the other heterocyclic azides, the decomposition of which is characterized by anomalously high values of the Arrhenius parameters, the thermal decomposition of 2,4,6-triazidopyridine yields a condensed product having a system of polyconjugated bonds with higher force characteristics. It is concluded that the decomposition of 2,4,6-triazidopyridine proceeds by a mechanism in which the rate-limiting step is the dissociation of the nitrogen molecule from the azide group to form a nitrene.

Thermal decomposition of 2,4,6-triazidopyrimidine in the melt

The kinetics and the products of thermal decomposition of 2,4,6-triazidopyrimidine in the melt were investigated by thermogravimetry, manometry, mass-spectrometry, and IR spectroscopy. The kinetic and activation parameters of the processes were found. Nitrogen was the only gaseous product of the reaction. The structure of the solid reaction product was determined. A mechanism of thermal decomposition of 2,4,6-triazidopyrimidine, including elimination of a nitrogen molecule to give nitrene in the initial step, was proposed. The unusually high pre-exponential factor in the Arrhenius equation (1016.7±0.7 s–1) was attributed to a significant contribution of polymerization (polycondensation) to the overall process, resulting in the formation of carbon—nitrogen two-dimensional networks.

Thermal decomposition ofC-iodotetrazoles

Thermal decomposition of 1-substitutedC-iodotetrazoles in melt and solutions has been investigated. Thermal stabilities, kinetic and activation parameters, and compositions of products of thermolysis ofC-iodotetrazolcs depend on the substituent nature. The scheme of thermolysis ofC-iodotetrazoles has been suggested.