A. I. Kirdyashkin

Generation and transfer of an electric charge in self-propagating high-temperature synthesis using the Co-S system as an example

Based on experimental studies, it is shown that the propagation of a combustion wave in a Co-S powder mixture is accompanied by a complex of physical phenomena including acoustic noise, generation of the constant, pulse, and variable electromotive force in a frequency range greater than 1 MHz, and superequilibrium emission of electric-charge carriers. The volt-ampere characteristic of the emission current in the combustion wave, which has a negative-resistance site, is obtained. Combustion occurs under conditions of mutual influence of the physical phenomena observed.

Acoustic emission during self-propagating high-temperature synthesis

It was established experimentally that during SHS, reaction systems (Ni-Al, Ti-B, Mo-B, etc.) generated acoustic oscillations in the frequency range from 5 Hz to 1.1 MHz with a pulse power of up to 17 W. It was found that the combustion of different systems is characterized by an individual set of dynamic parameters of acoustic emission in the modes of low ordered discrete pulses and highly ordered self-oscillations. It is shown that the spatial zone of acoustic emission is localized near the combustion wave. Analysis of the acoustic emission mechanisms of SHS is performed.

Modeling of combustion of premixed mixtures of gases in an expanding channel with allowance for radiative heat losses

Characteristics of the radiative heat flux from an expanding microchannel with combustion of a premixed mixture of gases are theoretically studied within the framework of a onedimensional diffusion-thermal model. The results obtained are generalized to the case of gas combustion in a porous medium consisting of a number of individual regularly packed microchannels. It is demonstrated that the radiative heat flux from subsurface layers of the porous body should be taken into account in calculating the efficiency of radiative porous burners and in modeling flame stabilization inside the porous medium.

Technological Combustion of Mineral-Based Powder Systems in the Production of Porous Composites

The paper reports results from experimental studies of the combustion of ilmenite- and quartz-based powder mixtures and formation of products in the combustion reactions. The reaction regimes involving the formation of porous microheterogeneous compositions Al2O3–metal-like alloy were studied. It is shown that the mechanisms of hot-spot combustion and formation of an anisotropic macrostructure of the reaction products are interrelated. Key words: combustion, hot-spot reaction, minerals, ceramics.

Influence of initial parameters of reacting systems on the porosity structure of self-propagating high-temperature synthesis products

The effects of the particle size of powder components, the relative density of the sample, and the degree of dilution of the mixture by thermally inert materials on the pore structure of self-propagating high-temperature synthesis products obtained in the combustion process involving melt were experimentally studied using the (Ti + 26% Si)-Al2O3 system as an example. Special techniques of quantitative metallographic analysis allowing for the analysis of materials with complex pore space structure were used.

Synthesis and investigation of porous Ni-Al substrates for solid-oxide fuel cells

Self-propagating high-temperature synthesis (SHS) is applied for the production of porous supporting Ni-Al bases of solid-oxide fuel cells. The effect of synthesis conditions and the composition of source powders on the phase composition, microstructure, gas permeability, corrosion resistance, and other properties of obtained Ni-Al samples is investigated. The possibility is shown for the formation of solid-oxide fuel cells (SOFCs) on the surface of porous Ni-Al plates. The cells have the structure Ni-ZrO3:Y2O3 anode/ZrO3:Y2O3 electrolyte/La0.8Mn0.2SrO3 cathode and provide a specific power of 400 mW/cm2 at a temperature of 800°C.

Electroimpulsive activation of self-propagating high-temperature synthesis in powder mixtures

The effect of frequency electroimpulsive treatment on the self-propagating high-temperature synthesis reaction in a powder mixture is studied with the use of the Ni-Al system as an example. The longitudinal direction of the electric field applied to the sample and of the electric current relative to the direction of combustion-wave propagation was used. It is established that under the action of electrotreatment, the linear combustion rate increases by a factor of 1.3-1.6, the structure is transformed, and the completeness of chemical transformation increases. It is shown that the effects observed are of a nonthermal nature.

Formation of self-propagating high-temperature synthesis products in a magnetic field

The combustion of compressed Ni+16% Al, Ni+50% Al, Co+30% S, Ti+58% FeB, Ti+20% C, and FeO+10% Fe+18% Al mixtures in a constant magnetic field is studied. The depth of conversion is found to increase and the geometric dimensions of the phase components of the reaction end products to coarsen under the influence of the field in the systems containing a ferromagnetic metal. The changes in the reaction product are related to additional mass transport behind the self-propagating high-temperature synthesis wave.

Porous SHS-Ceramics

In the work, interrelations between morphology of porous metalloceramics and thermal modes of SHS wave have been revealed on the basis of complex investigations including high-speed microvideo filming and dynamic pyrometry of processes, the physical and chemical analysis of products by the example of various intermetallic and hybrid (Ni, Co, Сr-Al, Ti-B-Cu, Ti-Si), metallothermic (FeTiO3-Al, Si, C; FeO-Al2O3-MgO-Al, etc.) systems.

On the Theory of Electrical Phenomena in Combustion of Heterogeneous Systems with Condensed Products

The effect of the electromotive force arising in combustion of heterogeneous systems with condensed products is explained. A convective mechanism of arising regions with different charge densities due to charge transfer by the gas filtered in the pores is formulated on the basis of the developed physical concepts, estimates, and analysis of experimental data. Key words: combustion, electron emission, filtration, electromotive force.