ТЕОРЕТИЧЕСКИЕ ИССЛЕДОВАНИЯ СИНТЕЗА МЕТАСТАБИЛЬНЫХ (НЕРАВНОВЕСНЫХ) ПРОДУКТОВ В ВОЛНЕ БЕЗГАЗОВОГО ГОРЕНИЯ

Abstract

The first part of the article considers the obtaining of nonequilibrium products in the combustion waves. The basic theoretical concepts are provided for the synthesis of metastable phases in binary systems. The multiple wave process in eutectic systems is explained by the properties of synthesis and the decomposition of unstable phases. This phenomenon is observed in the systems, the equilibrium phase diagram of which has a simple eutectic form, i.e., does not have the stable phases: Al-Ge, Al-Si, Al-S, etc. During slow cooling the final products represent the initial materials, during fast cooling there is the quenching of metastable phases produced in a combustion wave, in particular for the Al-Ge system. These facts indicate that this multiple wave process is caused by the synthesis and disintegration of nonequilibrium phases. There is a temperature above which the wave synthesis of metastable products takes place and below of which the wave disintegration occurs. In this case, the reaction product can be either stable or metastable depending on the initial conditions of the mixture and the combustion parameters. The thermodynamic analysis shows that the probability of producing a metastable product in the system increases with decreasing a scale of heterogeneity. At the mode change point of the chemical interaction there is a sudden change in the combustion characteristics: the temperature, the intensity of chemical conversion and the combustion rate. The calculated and known experimental data are compared. The method was developed to estimate the effective thermodynamic and kinetic constants, as well as the model parameters using experimental data. The second part of the article considers the development and study of a mathematical model for solid flame combustion in a two-component gasless system that forms a metastable phase. The model includes the heat balance equation and the chemical reaction equation that takes into account the processes of synthesis and decomposition of a metastable phase, as well as the boundary and initial conditions. The mathematical model was numerically studied. The characteristic modes were defined for wave processes. Three characteristic modes were found: separation, fusion and extinction. The modes differ in the arrangement of the synthesis fronts and the disintegration of products. The self-oscillation modes in this system are shown to be separated by a temperature boundary of the phase stability. In addition, the self-oscillation mode can not be realized when the synthesis (during bursts) and decomposition (in the period of depressions) coexist. The self-oscillation mode was found to exist in the area of the product decomposition as an intermediate mode between the stationary modes.