V. D. Kitler

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.

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.

Interphase convection in the contact interaction of metals under nonisothermal conditions

Experimental data on the contact interaction of heterogeneous metal plates upon heating by a pulse infrared radiation laser are reported. It is shown that in the contact zone, melting and microconvective mixing of metals occur owing to high temperature and concentration gradients. The calculations suggest that the use of pulse laser heating allows one to reproduce the thermophysical conditions of the SHS process quite exactly. Based on the data obtained, the activating role of microconvection in SHS processes is assumed. Taking into account the additional convective mass transfer allows one to explain the discrepancy between the calculated and observed parameters of the synthesis wave.

Combustion of TiAl alloy in nitrogen

It has been shown that Ti–Al–N ternary compounds, belonging to MAX phases (ceramic materials that can be processed as metals) can be produced by combustion of a granular powder of T65Yu35 (TiAl) alloy in nitrogen flow at a pressure close to atmospheric pressure. Combustion is accompanied by transfer of part of the aluminum through the gas phase. The propagation velocity of the combustion zone and the maximum temperature increase with increasing flow rate.

Features of self-propagating high-temperature synthesis of spinel pigments

The method of self-propagating high-temperature synthesis (SHS) was used to synthesize spinel ceramic pigments. Producing aluminum-nickel and aluminum-cobalt pigments in a finely dispersed state is a complex stepwise (combined) process involving a reduction stage and simultaneous natural air filtration. In the case of small-diameter samples, a flat combustion front is observed and in large samples, the front is formed of many hot spots. The dependence of combustion rate on porosity is presented. The maximum combustion rate of these systems are recorded for porosity of 50–60%. Powdered SHS pigments were obtained for the first time.

Investigation of SHS processes using laser hardening

Using the titanium-boron system as an example, a procedure for ultrafast hardening (106–107 K/sec) of the SHS reaction using pulse laser radiation is developed. The dynamic scheme of the component interaction is obtained on the basis of metallographical and micro X-ray spectrum analysis. It is shown that under conditions of high-speed heating mass transfer on the interfaces has a pronounced convective character, ensuring an increased interaction rate.