Mechanism, Kinetics and Thermodynamics of Decomposition for High Energy Derivatives of [1,2,4]Triazolo[4,3-b][1,2,4,5]tetrazine

This paper presents the data of research studies on the mechanisms, kinetics and thermodynamics of decomposition of three high-energy compounds: [1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine-3,6-diamine (TTDA), 3-amino-6-hydrazino[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine (TTGA) and 3,6-dinitroamino[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine (DNTT). The points of change of the reaction mechanisms under thermal effects with different intensities from 0.1 to 2000 s−1 have been established. The values of activation and induction energies for the limiting stages of decomposition have been obtained. The formation of nanostructured carbon nitride (α-C3N4) in condensed decomposition products, cyanogen (C2N2) and hydrogen cyanide (HCN) in gaseous products have been shown. Concentration-energy diagrams for the reaction products have been compiled. The parameters of heat resistance and thermal safety proved to be: 349.5 °C and 358.2 °C for TTDA; 190.3 °C and 198.0 °C for TTGA; 113.4 °C and 114.1 °C for DNTT. The energy and thermodynamic properties have also been estimated. This work found the activation energy of the decomposition process to be 129.0 kJ/mol for TTDA, 212.2 kJ/mol for TTGA and 292.2 kJ/mol for DNTT. The average induction energy of the catalytic process (Ecat) for TTGA was established to be 21 kJ/mol, and for DNTT-1500–1700 kJ/mol. The induction energy of the inhibition process (Eing) of TTDA was estimated to be 800–1400 kJ/mol.


Introduction
High-energy compounds (HECs) are used in many areas of civil industry, such as the synthesis of superhard materials like diamond and ceramics, in car airbags, in mining, recycling of waste rubber products and in other areas. At the same time, the sensitivity of HEC to external influences limits scenarios of their use in various fields of technology. In this regard, the search for insensitive HECs remains an urgent task. Many creative teams have demonstrated in their works that polynitrogen-containing heterocyclic compounds, such as nitro-, amino-and nitroamino-derivatives of imidazole, pyrazole, oxadiazoles, triazoles, tetrazole, triazines and tetrazines (Scheme 1) and condensed structures based on these heterocycles, have the required balance of energy properties and sensitivity to external influences [1][2][3][4][5][6][7][8][9][10][11][12]. The experimental data obtained indicate the expediency of performing exploratory work, and analyzing the mechanisms of decomposition of polynitrogen heterocyclic compounds, which can primarily be focused on the synthesis of promising materials, for example, polymer ceramics. In this field, derivatives of [1,2,4]triazolo [4,3b] [1,2,4,5]tetrazine [13][14][15][16][17][18][19][20][21] can find a practical application as HECs; however, the formation of volatile cyanides during decomposition of these compounds raises concerns regarding their toxicological safety.
The characteristics of some compounds presented are described in the literature (Table 1). On the one hand, the mechanisms and directions of chemical reactions are the main physico-chemical characteristics for HECs. On the other hand, experimental studies aimed at carrying out such measurements have many technical and fundamental limitations. Therefore, the problems of constructing energy diagrams of slow decay and explosive transformation processes directly from the data of experimental observations require nontrivial solutions. In order to identify the energy potential and regulate the energy release in the considered range of substances, research studies of chemical reactions occurring under various thermal conditions have been carried out.

Results
The frequency, structure and elemental composition of the synthesized compounds were confirmed by 1 H and 13 C NMR, IR and RAMAN spectroscopy, chromato-mass spectrometry and elemental analysis. The crystal structure was determined by powder X-ray Molecules 2022, 27, 6966 3 of 28 diffraction methods. The monophase of the sample was confirmed by X-ray phase analysis and Raman spectroscopy.

Thermodynamics Calculation Results
For the substances under consideration, thermodynamic calculations were carried out using classical methods [31][32][33][34][35] and semi-empirical methods of quantum chemistry. Table 2 shows the values obtained from thermodynamic calculations. From the results obtained, it can be assumed that the expected density in calculations by the group contribution method is close to real substances. The molecular volume method shows highly inflated results and does not take into account the packing coefficient. In addition, it is worth noting that each of the polymorphic modifications will have its own density values.
Below, Figure 1 shows the obtained PV diagrams of decomposition products of the studied HEC. The diagrams ( Figure 1) characterize various processes and directions of chemical reactions during decomposition of the compounds under study. In addition, studies of the composition of reaction products under various conditions have been carried out. P-V diagrams of reaction products for explosive transformation processes (deflagration, explosive burning, normal detonation and recompressed detonation) are shown in Figure 1a,c,e; P-V diagrams of reaction products for slow thermal decomposition and combustion processes are shown in Figure 1b,d,f. The course of reactions in slow thermal decomposition modes of decomposition and combustion is characteristic of the conditions realized in the cells of thermal analysis at heating rates up to the limit values of the thermal stability of the substance under study.

Results
The frequency, structure and elemental composition of the synthesized compounds were confirmed by 1 H and 13 C NMR, IR and RAMAN spectroscopy, chromato-mass spectrometry and elemental analysis. The crystal structure was determined by powder X-ray diffraction methods. The monophase of the sample was confirmed by X-ray phase analysis and Raman spectroscopy.

Thermodynamics Calculation Results
For the substances under consideration, thermodynamic calculations were carried out using classical methods [31][32][33][34][35] and semi-empirical methods of quantum chemistry. Table 2 shows the values obtained from thermodynamic calculations. From the results obtained, it can be assumed that the expected density in calculations by the group contribution method is close to real substances. The molecular volume method shows highly inflated results and does not take into account the packing coefficient. In addition, it is worth noting that each of the polymorphic modifications will have its own density values. P-V diagrams of reaction products for explosive transformation processes (deflagration, explosive burning, normal detonation and recompressed detonation) are shown in Figure 1 a, c, e; P-V diagrams of reaction products for slow thermal decomposition and combustion processes are shown in Figure 1 b, d, f. The course of reactions in slow thermal decomposition modes of decomposition and combustion is characteristic of the conditions realized in the cells of thermal analysis at heating rates up to the limit values of the thermal stability of the substance under study.
The purpose of the experimental part of this work is to determine substances' decomposition temperatures under various conditions and the kinetics and their heat resistance, with the subsequent connection of the obtained values and reaction products to theoretical models. [1,2,4]Triazolo [4,3-b] [1,2,4,5]tetrazine-3,6-diamine (TTDA) was synthesized by a well-known technique [29,36].

Structure and Chemical Composition of Synthesized Substances
The characteristics determined in our study were as follows: Dark brown powder (Figure 2 a, d, g). 1 Н NMR (DMSO-d6, 500 MHz): δ/ppm 6.82, 7.60 (both s, 4Н, 2 NH2). 13   The purpose of the experimental part of this work is to determine substances' decomposition temperatures under various conditions and the kinetics and their heat resistance, with the subsequent connection of the obtained values and reaction products to theoretical models. [1,2,4,5]tetrazine-3,6-diamine (TTDA) was synthesized by a wellknown technique [29,36].

Structure and Chemical Composition of Synthesized Substances
The characteristics determined in our study were as follows: Dark brown powder (Figure 2a, [1,2,4,5]tetrazine (TTGA) was synthesized by a well-known method [18].

X-ray Diffraction Studies
The studies were carried out on a laboratory X-ray powder diffractometer in a standard configuration.
X-ray diffraction analysis conditions: pressure 730-740 mmHg, temperature 22-24 • C; source-X-ray tube with copper anode (working radiation of K series: K α1 , K α2 and K β for copper corresponds to wavelengths of 1.5406 Å, 1.5444 Å and 1.3920 Å (working energy of quanta~8keV); detector-semiconductor with cooling Peltier; geometry-Bregg-Brentano (θ-2θ); scanned angle range=0. 8 The interplane distances (d) measured by powder X-ray diffraction method, as well as their processing by Le Bail [37] and Pawley [38], made it possible to characterize the crystal lattice of the studied substances. Table 3 shows the results of the analysis. Table 3. Crystal structure of energetic compounds.

Sample c [%] Ds [Å] Symmetry Group
Unit Cell Parameter The solution of the crystal structure of the samples was performed by sequential analysis of radiographs. Determination of interplanar distances was performed by the method of full-profile analysis. The accepted initial conditions for calculating X-ray diffractions data are: the crystallographic model is the result of primary X-ray diffraction; the radiation source is an X-ray tube with a copper anode (K α1 =1.5406 Å), a semiconductor detector, a pseudo-Voigt and Pearson-VII profile function, the simulated range is 2Θ-2-60 • , the initial half-width parameter is FWHM 0.01.
Indexing was carried out by the Monte Carlo method and using standard dichotomy algorithms: DICVOL06 [39] and THREOR [40]. Refinement of the unit cell parameters was performed by the methods of Le Bail [37] and Pawley [38], the results are summarized in Table 3. Statistical characteristics of the analysis were entered into the final CIF files. All characteristics of the crystalline compounds, including the electronic structure, were obtained for the first time in this work.  [1,2,4,5]tetrazine derivatives were performed by derivatography methods with synchronous registration of mass loss data using microweights (TGA) and heat flux from the substance using thermocouples (DTA). The studies were carried out as follows: a weight of 5 mg was placed in a ceramic crucible, which was installed in a heating element and heated at various speeds of 2.5, 4, 6, 10, 15, 30 and 100 K/min, with data accumulation statistics 190 points/K, 80 points/K, 48 points/K and 30 points/K, respectively, in the temperature range from 300 to 770 K, at a dynamic flow rate of nitrogen gas, 40.    Tables 4 and 5 show the temperature characteristics of the decomposition processes of samples of [1,2,4]triazolo [4,3-b] [1,2,4,5]tetrazine derivatives at different heating rates. The measurements were obtained by the methods of derivatography: DTA (Table 4), TGA (Table 5).
Data from differential thermogravimetric analysis were used to analyze the points of intensive decomposition. Thermogravimetry results and differential thermocouple readings were used to evaluate the processes occurring without significant loss of mass. Standard indium samples were used as the calibration of the heat flow measurement.          We associate the appearance of the first decomposition peaks at slow heating rates with three processes:

1.
Decomposition in the gas phase as the most probable process. Moreover, the higher the accumulation of gases, the greater the thermal effect of the reaction. This is due to the ability of substances to sublimate. 2.
The first stage of decomposition in the solid phase, due to the separation of substituents from the base of azolotetrazine. This hypothesis arose as a result of the analysis of the magnitude of the shift of the peak of the rate of the solid-phase decomposition process, which is inhibited by the reaction products. In contrast to the generally accepted hypotheses about the catalytic effect of the gas phase of decomposition products, we have recorded inhibition in azolotetrazine compounds.

4.
The presence of impurities similar in molecular structure, but less heat-resistant than the main phase.
These processes can occur both jointly and separately. We divided the contribution of each of the stages, taking into account the parameters of the decomposition kinetics: the activation energy (and adiabatic induction energy) and the rate constant of the chemical reaction, supplemented with data on the composition of the products of the gas phase during the reaction. A more detailed analysis was carried out by the DTGA method ( Figure 6) and the construction of integral decomposition curves (Figure 7).
These processes can occur both jointly and separately. We divided the contribution of each of the stages, taking into account the parameters of the decomposition kinetics: the activation energy (and adiabatic induction energy) and the rate constant of the chemical reaction, supplemented with data on the composition of the products of the gas phase during the reaction. A more detailed analysis was carried out by the DTGA method (Figure 6) and the construction of integral decomposition curves (Figure 7).  After preliminary data processing, the studied samples can be characterized as follows.
The TTDA sample has a good temperature resistance of~350 • C, energy release kinetics, residual heat release and low mass loss before decomposition. The mass fraction of condensed products after completion of the decomposition process is more than 40%, which indicates the insufficiency of the oxidizer in the molecule and the purge gas and, possibly, the incomplete course of the decomposition reaction in the main stage ( Figure 3).
The TTGA sample showed the greatest reactivity and an increase in pressure in the chamber; it is obvious that the thermal decomposition of this sample proceeds in the explosive combustion mode. However, the momentum of the formed gases does not have high values. The substance has a temperature resistance up to 180 • C (Figure 4). The mass fraction of condensed residues is less than 15%. In the DTA cell, the conditions of reactive action on the sensing element were implemented, characterizing the pulse of gas flows.
Samples of DNTT when decomposed in DTA cells showed the highest caloric content, reactivity and momentum (rapid increase in pressure in the chamber). Clearly, this substance, compared to the others presented for analysis, has the lowest activation energy and induction period of adiabatic decomposition, and the highest adiabatic induction energy and number of simultaneous acts of molecular decay. In the DTA cell, at heating rates of more than 2.5 min −1 , the substance decomposes in the form of an explosive transformation with the spread of reaction products and the formation of condensed products that are scattered around the cell by the gases released. In this regard, the mass fraction of the condensed residue is not measured precisely (Figures 5 and 6). The substance is characterized by low temperature resistance up to 120 • C and thermal stability. The total mass fraction of condensed residues during decomposition in nitrogen could not be recorded. A different picture is observed when the rate of thermal exposure decreases to 1-2.5 min −1 . Three-stage decomposition is observed, which is accompanied by low energy release and the formation of a large number of condensed reaction products, and conditions of slow thermal decomposition are realized. Table 6 shows the characteristics obtained at a standard heating rate of 10 • C/min. After preliminary data processing, the studied samples can be characterized as follows.
The TTDA sample has a good temperature resistance of ~350 °C, energy release kinetics, residual heat release and low mass loss before decomposition. The mass fraction of condensed products after completion of the decomposition process is more than 40%, which indicates the insufficiency of the oxidizer in the molecule and the purge gas and, possibly, the incomplete course of the decomposition reaction in the main stage ( Figure  3).
The TTGA sample showed the greatest reactivity and an increase in pressure in the chamber; it is obvious that the thermal decomposition of this sample proceeds in the explosive combustion mode. However, the momentum of the formed gases does not have high values. The substance has a temperature resistance up to 180 °C (Figure 4). The mass

Characteristics of Gaseous Reaction Products at the Peak of Decomposition
The studies were carried out using mass spectrometry methods with various sample inputs: the gas phase from the differential thermal analysis cell through a pulse valve, the formation of the gas phase in a high-vacuum chamber with various types of ionization (field, laser and spark) with the direct connection of the mass spectrometer channel to the decomposition chamber. The mass spectrometer consisted of an electron-spark ionizer, a quadrupole mass filter and a detector in the form of a Faraday cup.
The speed of registration of mass spectra varied from 10 to 100 Da/s, the number of points of the profile line varied from 250 to 10, according to the registration speeds. The energy of the electron beam in the ionizer varied from 90 eV (focus 70 eV) to 25 eV (focus 15 eV) and complete shutdown of the ionizer.
HTDMS: a sample weighing 2-3 mg was placed in a special cell located in a sealed vacuum chamber connected to the mass spectrometer channel. The procedure for pumping the gas medium to a residual pressure of 10 −5 Pa was carried out, and the procedures for degassing the sample and registering the thermodynamic background were performed. The heating rate varied from 30 to 2000 K/s and the recorded heating range from 320 to 1200 K. The statistics of data accumulation in the mass spectrometer ranged from 50 µs/Dalton to 1 s/Dalton. The final measurement results are shown in Figures 8-10.     As thermodynamic calculations and experimental measurements have shown, during the decomposition of substances of this class, the formation of gaseous nitrogen (N, N2), hydrogen cyanide (HCN), cyanogen (C2N2) and other substances that in some way inhibiting the decomposition process under slow exposure is observed. A similar result was obtained by the HTDMS method. In azolotetrazines containing nitro groups, there is a decrease in the concentration of hydrogen cyanide and cyane, an increase in the concentration of oxide (CO) and carbon dioxide (CO2), as well as nitrogen oxides (NO, NO2). This fact somewhat distinguishes the gas-dynamic properties of the products of explosive transformation reactions in such compounds from classical explosives.

Characteristics of Condensed Reaction Products after Decomposition
After the decomposition of polynitrogen compounds that do not contain a large number of nitro groups, presumably polymer carbon nitride (CN)n is formed, which according to known data [22][23][24][25][26][27][28] has a layered crystal structure similar to hexagonal graphite.
The obtained results of elemental (C15N23H3*H2O), spectral, X-ray phase ( Figure 11) and X-ray diffraction analysis (Table 7) confirm the assumptions made.
Processing of the obtained diffraction data was carried out by the method of fullprofile analysis. As a result, micromorphometric characteristics were determined: the size of the coherent scattering region (crystallite), microdistorsion, condensed products of decomposition reactions of the studied azolotetrazine derivatives. The results are shown in Table 7 and Figure 12. As thermodynamic calculations and experimental measurements have shown, during the decomposition of substances of this class, the formation of gaseous nitrogen (N, N 2 ), hydrogen cyanide (HCN), cyanogen (C 2 N 2 ) and other substances that in some way inhibiting the decomposition process under slow exposure is observed. A similar result was obtained by the HTDMS method. In azolotetrazines containing nitro groups, there is a decrease in the concentration of hydrogen cyanide and cyane, an increase in the concentration of oxide (CO) and carbon dioxide (CO 2 ), as well as nitrogen oxides (NO, NO 2 ). This fact somewhat distinguishes the gas-dynamic properties of the products of explosive transformation reactions in such compounds from classical explosives.

Characteristics of Condensed Reaction Products after Decomposition
After the decomposition of polynitrogen compounds that do not contain a large number of nitro groups, presumably polymer carbon nitride (CN)n is formed, which according to known data [22][23][24][25][26][27][28] has a layered crystal structure similar to hexagonal graphite.
The obtained results of elemental (C 15 N 23 H 3 *H 2 O), spectral, X-ray phase ( Figure 11) and X-ray diffraction analysis (Table 7) confirm the assumptions made.     The formed products have a nanocrystalline structure, and the higher reaction rate results in more porous condensed carbon nitride residue. The large porosity in this case TTDA TTGA DNTT Figure 11. X-ray diffraction data of a powdered sample of the α-phase of carbon nitride.
Processing of the obtained diffraction data was carried out by the method of fullprofile analysis. As a result, micromorphometric characteristics were determined: the size of the coherent scattering region (crystallite), microdistorsion, condensed products of decomposition reactions of the studied azolotetrazine derivatives. The results are shown in Table 7 and Figure 12.    The formed products have a nanocrystalline structure, and the higher reaction rate results in more porous condensed carbon nitride residue. The large porosity in this case TTDA TTGA DNTT The formed products have a nanocrystalline structure, and the higher reaction rate results in more porous condensed carbon nitride residue. The large porosity in this case affects the color; the highly porous product has a light beige shade of brown. The product of low porosity is brown and dark brown. Compound

Discussion
The analysis was carried out separately for two stages of the process:
Solid-phase decay assisted with gas.
All calculations were performed within the recommended ICTAC [41] methods for calculating thermodynamics and kinetics based on the results of thermal analysis.
For the fundamental analysis of the kinetics of thermal decomposition and thermodynamic characteristics of the process, the methods of Kissenger [42], FWO [43,44], KAS [45], Friedman [46], Frank-Kamenetsky [47], Zhang [48,49] and Gibbs [32,33] were used. Figure 13a-d show the results of determining the inflection point and changing the mechanism from slow thermal decomposition to explosive chemical reactions for the compounds under study. Formulas (9), (13) and (14) were used for the calculation.
affects the color; the highly porous product has a light beige shade of brown. The product of low porosity is brown and dark brown.
Compound NyHx(CN)n absorption bands found, cm

Discussion
The analysis was carried out separately for two stages of the process: 1. Gas phase decay; 2. Solid-phase decay assisted with gas.
All calculations were performed within the recommended ICTAC [41] methods for calculating thermodynamics and kinetics based on the results of thermal analysis.
For the fundamental analysis of the kinetics of thermal decomposition and thermodynamic characteristics of the process, the methods of Kissenger [42], FWO [43,44], KAS [45], Friedman [46], Frank-Kamenetsky [47], Zhang [48,49] and Gibbs [32,33] were used. Figure 13a-d show the results of determining the inflection point and changing the mechanism from slow thermal decomposition to explosive chemical reactions for the compounds under study. Formulas (9), (13) and (14) were used for the calculation. (c) (d) Figure 13. Points of change in the mechanism of chemical reactions in the studied compounds for: TTDA (a,b); TTGA (c) and DNTT (d). DTA-I-parameters of the process of intensive decomposition (maximum exothermic effect) carried out by the method of differential thermal analysis; DTG-Iparameters of the intensive decomposition process (maximum exothermic effect) carried out by thermogravimetric analysis; DTA-II-parameters of the slow decomposition process (previous exothermic effect) carried out by differential thermal analysis; DTG-II-parameters of the slow decomposition process (previous exothermic effect) carried out by thermogravimetric analysis.      Figure 14 shows the inhibition and catalysis energies (autocatalysis) for the compounds under study, and Figure 15 shows the concentration-energy diagrams of reaction products obtained from calculations and experimental measurements for the compounds under study.  (c) (d) Figure 14. Changes in the induction energy of intensive decomposition processes depending on the catalytic contribution (taking into account gas-phase decomposition and in the absence of gasphase decomposition) for: TTDA (a); TTGA (b) and DNTT (c,d). It is worth noting that the process of decomposition reactions is multi-stage. Two stages of decomposition are distinguishable, and in some cases three. Moreover, the lower the rate of thermal exposure, the more distinguishable are the stages of the process.
Kinetic studies have shown that the first stage of decomposition of azolotetrazine It is worth noting that the process of decomposition reactions is multi-stage. Two stages of decomposition are distinguishable, and in some cases three. Moreover, the lower the rate of thermal exposure, the more distinguishable are the stages of the process.
Kinetic studies have shown that the first stage of decomposition of azolotetrazine derivatives has a significantly lower rate of decomposition reactions than the second, which indicates greater stability of the base. Nevertheless, the decomposition of the base practically has an explosive character (Tables 8-14) with a transition to detonation, which negatively affects safety indicators.
The presented sequence of decomposition reactions and the decomposition scheme of [1,2,4]triazolo [4,3-b] [1,2,4,5]tetrazine derivatives made it possible to analyze in more detail the mechanism of chemical interactions of decomposition reaction products under different effects.
Inhibition of the decomposition process occurs in the presence of up to 30 masses% of the total mass of the gas phase for each of the substances in a mixture with a solid, then a sharp explosive decomposition occurs without significant participation of inhibitors. The onset of this effect is observed with the accumulation of gases, i.e., with slow thermal exposure and thermal aging. Before the onset of the phase state under consideration, the kinetics of decomposition obey the Arrhenius law without correction for inhibitors. These, apparently, are the molecules of the substances themselves in the gas phase and cyanides. It can be assumed that due to the presence of a significant number of amino groups and nitrogen-containing fragments, the radicals of primary gas-phase decomposition bind, which is indicated not only by an increase in the temperature of thermal solid-phase decomposition, but also by the data obtained on compliance with the Arrhenius law during decomposition of this class of substances after heat treatment, as a result of which substances have a higher resistance to sublimation and the transition to the gas phase.
The results of calculations of thermal stability and autocatalysis of decomposition reactions in the studied derivatives of [1,2,4]triazolo [4,3-b] [1,2,4,5]tetrazine obtained by Formulas (15)-(19) (chapter 4.2) are shown in Table 15. ∆G*, ∆H*, ∆S* are the Gibbs energy, enthalpy, and the entropy of the decomposition process respectively; T SADT is the temperature of the beginning of the autocatalytic decomposition process; Tm is the thermal explosion temperature.
Positive values of ∆G*, ∆H*, ∆S* of the limiting stage of decomposition indicate the absence of spontaneous reactions. Nevertheless, in each of the samples there are at least 3 points of change of the reaction mechanism.

Materials and Methods
In this paper, various methods were used to study the mechanisms for chemical decomposition of HECs, the sequence of which allowed us to exclude the non-triviality of solving the problem of directions of chemical reactions. Studies of the molecular and crystalline structure of the synthesized compounds, carried out by using nuclear magnetic resonance, time-of-flight mass spectrometry, vibrational spectroscopy and powder X-ray diffraction methods made it possible to decipher their structures without complex sample preparation operations: unfortunately, the cultivation of high-quality single crystals is not always possible. In addition, studies of the structure of powders allowed us to determine the actual chemical composition of substances used in the study of the mechanisms and kinetics of decomposition. The methods of derivatography and high-temperature dynamic mass spectrometry were used to study the kinetics of decomposition and the mechanisms of chemical interactions. In order to exclude non-triviality in the form of exothermic phase transitions, thermorentgenography methods have been applied. The mono phase of the samples has been confirmed by the X-ray phase analysis. The thermodynamic calculations made it possible to characterize the properties of reaction products in a wide range of their states, from sublimation of matter to compressed cold plasma. Comparisons of computational and theoretical concepts and experimentally measured values, characterizing the composition of reaction products and the mechanisms of their interactions, are carried out.
Analysis of the difference in the activation and induction energies of decomposition in the gas and solid phases enabled us to establish the energy of catalysis (inhibition) of the decomposition process. The use of thermorentgenography methods allows one to refute the hypothesis of an isothermal phase transition under thermal influences.

Thermodynamics of Decomposition Processes
In this paper, the problem of thermodynamic equilibrium was solved directly from the basic laws of thermodynamics, and the system was characterized by a maximum of entropy. The system of equations was compiled on the basis of an analytical relationship between the entropy value of the unit mass of the working fluid and the thermodynamic parameters that determine the composition and conditions of the equilibrium existence of the system [31,32].
The entropy of a multicomponent system was estimated as follows: where k-number of components of the gas phase; L-number of condensed phases; ng, ncmolar content of substances, mol/kg; Si 0 , Sl 0 -entropy of substances in the standard state, J/(mol·K); T-temperature, K; v-specific volume, m 3 /kg.
Under the accepted assumptions, the entropy of a substance in a condensed state does not depend on pressure, therefore Sl = Sl 0 .
Total enthalpy dH, [J/kg]. The enthalpy of the whole system is also the sum of the The obtained materials were recrystallized and purified from impurities.

Thermodynamics of Decomposition Processes
In this paper, the problem of thermodynamic equilibrium was solved directly from the basic laws of thermodynamics, and the system was characterized by a maximum of entropy. The system of equations was compiled on the basis of an analytical relationship between the entropy value of the unit mass of the working fluid and the thermodynamic parameters that determine the composition and conditions of the equilibrium existence of the system [31,32].
The entropy of a multicomponent system was estimated as follows: where k-number of components of the gas phase; L-number of condensed phases; n g , n c -molar content of substances, mol/kg; S i 0 , S l 0 -entropy of substances in the standard state, J/(mol·K); T-temperature, K; v-specific volume, m 3 /kg.
Under the accepted assumptions, the entropy of a substance in a condensed state does not depend on pressure, therefore S l = S l 0 . Total enthalpy dH, [J/kg]. The enthalpy of the whole system is also the sum of the enthalpy of its constituent phases.
The enthalpy of individual substances is calculated from the temperature of 298.15K, accepted as standard, and includes the enthalpy of formation of substances as a measure of their chemical energy where C pi -is the specific heat capacity of an individual substance at constant pressure, J/(mol·K). The mass fraction of condensed phases Z is the ratio of the mass of all condensed substances to the mass of the system as a whole.
The composition of the decay products was characterized when solving the Lagrange function, in the form: