Vol 42, No 9 (2023)

The thermal stability of N-cyanomethyl derivatives of 7H-difurasanofuroxanoazepine and 7H-trifurazanoazepine in nonisothermal and isothermal modes is studied. The formal kinetic regularities of the decomposition and temperature dependences of the reaction rate constants are determined. The thermal stability of cyanomethyl, allyl, and amine derivatives of azepines is compared.

For the first time, a comparative study is carried out of the macrokinetic parameters of the combustion of powder and granular mixtures of Ti + C when diluted by metal powders. The burning rates of powder mixtures (Ti + C) + 20% Me (Me = Ni, Cu) turned out to be higher than those of Ti + C mixtures, despite the lower temperature of combustion. This contradicts the theoretical models of the dependence of the combustion rate on the maximum temperature in condensed heterogeneous media. When diluting a Ti + C mixture with Ti or TiC powders, such a contradiction does not occur. The data obtained are explained using the convective-conductive model of combustion by the strong influence of the impurity gas release from titanium ahead of the combustion front. The values of the time of the transition of combustion between the granules and the burning rate of the material inside the granules, as well as a quantitative assessment of the decelerating effect of impurity gases in powder mixtures, are obtained using the values of combustion rates of the mixtures with granules of different sizes. For the (Ti + C) + 20% Ni mixture, the ignition time of the granules turned out to be less than 1 ms. The efficiency of the combustion transition between granules in the presence of a hot Ni melt is explained by comparing the combustion parameters of granular mixtures of Ti + C diluted with other metal powders and titanium carbide.

Mathematical models of the dynamic behavior of a multivelocity heterogeneous reacting medium in a plug flow reactor are formulated. The correctness of the mathematical model is studied. A particular analytical solution of the system is obtained, which can be used as a test to check the accuracy of the numerical solution of the model system. The possibility of extending this modeling technique to more complex regimes of exothermic chemical interaction in multivelocity mixed media is shown. A numerical study of the oscillatory regime of the displacement reactor is carried out.

It is experimentally shown that in the studied range of reagent ratios of propane/oxygen mixtures (C3H8 : O2 = 1 : 1–1 : 5), an increase in the oxygen content leads to a decrease the intensity of the stabilized cool propane flame. It is established that with an increase in the oxygen content, the selectivity of the formation of formaldehyde and acetaldehyde increases, and the selectivity of the formation of methanol decreases, which can be explained by the competition of the reactions of their formation.

The nonideal detonation of ternary mixtures of nitromethane (NM) and ammonium perchlorate (AP) with a large excess of aluminum (Al) is numerically modelled. A theoretical model developed earlier, in which the exothermic transformation of the mixture proceeds in three stages, including the decomposition of NM and AP, as well as the diffusion combustion of Al, is used. The calculation results are in close agreement with the experimental data on the detonation velocity recorded in steel tubes with a diameter of 18 mm, varying in a wide range of the NM content and Al/AP ratio in the mixtures. The values of the coefficients of the conversion rates of NM and AP, which are used in modeling the detonation of triple mixtures, are determined from the closest agreement of the calculations with the experiments on the charge diameter effect on the detonation velocity of a mixture of NM with 54% AP. The pressure exponents were set equal to 1. When changing the ratio of components, the calculations carried out with the same conversion rate coefficients closely agree with the experimental data. This is the reason why the selected values are used to calculate the detonation of triple mixtures. The low conversion rate of AP in comparison with NM leads to the length of the detonation wave reaction zone increasing up to 10 mm. The share of burnt AP is slightly less than half in mixtures with an Al/AP ratio of 1 : 1, and slightly more than one-third with an Al/AP ratio of 2 : 1.

Proflavine (PF)—2,6-diaminoacridine—is a mutagen and, as one of the dyes of the acridine series, it is able to form complexes with DNA, which leads both to the appearance of optical activity in the long-wave absorption band of the dye and to a change in optical activity in the UV region of the spectrum, where the absorption of nitrogenous bases of DNA is observed. An experimental study of optical activity in the form of circular dichroism (CD) spectra shows that in the visible region of the spectrum, optical activity is caused by the exciton chromophore-chromophore interaction of dye molecules that have formed a complex with an asymmetric helical DNA molecule. The appearance of an additional CD in the UV region is related to the exciton interaction of short-wavelength optical transitions of dye molecules with similar frequencies of the UV transitions of nucleic bases. The decomposition of the CD spectra into components makes it possible to isolate the contribution from the interaction of long-wavelength dye transitions with the short-wavelength (UV) transitions of the neighboring chromophores. In particular, a contribution was found from the interaction of the magnetic transition moment of chromophores in higher vibrational states with the dipole transition moments of the neighboring chromophores. This previously undescribed effect is related to the violation of the symmetry plane of the aromatic system of the dye in higher vibrational states; it is absent in the region of the zero vibrational band. The constructed decomposition procedure makes it possible to separate from the total CD spectra the contributions of the optical interactions previously described theoretically, which potentially allows us to estimate the geometric parameters of the complex.

The equations of multimoment hydrodynamics, supplemented by stochastic components, are used to study the chaotic distortion of a regular flow in the wake of a sphere. The mutual influence of the Reynolds number and the intensity of weak disordered perturbations in the incident flow, characterized by the turbulence coefficient, is investigated. The calculations show that the turbulent flow pattern is formed due to the excessive growth of disordered perturbations in the unstable recirculating zone in the near wake behind the sphere. The transition from laminar to turbulent motion has a considerable length on the Reynolds number scale. The turbulence coefficient is a key factor influencing the formation of a turbulent flow pattern. Low values of the turbulence coefficient can block the occurrence of turbulence even at arbitrarily high values of the Reynolds number. On the contrary, high values of the turbulence coefficient can initiate turbulence even at relatively low values of the Reynolds number. The degree of the development of turbulence is interpreted in terms of randomness coefficients depending on the Reynolds number and the turbulence coefficient. The previously formulated idea on the nature of turbulence is confirmed. The regular component of turbulence is formed as a result of unstable motion of coherent structures. Excessively expanding disordered perturbations form the chaotic component of turbulence.