Influence of Inert Particles on the Physical Regularities of Bulk Synthesis of Composite
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INFLUENCE OF INERT PARTICLES ON THE PHYSICAL REGULARITIES OF BULK SYNTHESIS OF COMPOSITE N. V. Bukrina and A. G. Knyazeva
UDC 544.4
The physical phenomena accompanying the bulk synthesis of a composite from pure elements with addition of inert particles are analyzed. Among the main reasons, a change in thermophysical properties (heat capacity and thermal conductivity coefficient), as well as a decrease in the total heat release in a chemical reaction, are highlighted. The complex of chemical reactions is described by a total reaction with effective formal kinetic parameters. The kinetic law takes into account strong inhibition of the reaction by the layer of the synthesized product which prevents the interaction of the reagents. The effective thermophysical properties of the mixture in the reactor depend on the properties of the components and the volume fraction of inert particles. It is shown that the addition of refractory particles to the mixture leads to a slowdown in the stage of the ignition process and a more complete conversion due to the heat stored in the inert particles. Keywords: high-temperature synthesis, inert particles, intermetallic compound, mathematical modeling.
INTRODUCTION At present, the processes of high-temperature bulk synthesis are widely used to obtain composite materials. The result of the process depends on many parameters that reflect the influence of the initial data, preparation method, geometric conditions of synthesis, method of initiating the reaction, and kinetics of the accompanying physical and chemical processes. The experiments [1, 2] have shown that high reaction rates of the high-temperature bulk synthesis of an intermetallic compound from the initial elements significantly the control of the structural and phase state formation of the final product. One of the ways to reduce the synthesis temperature and improve main indicators of the material efficiency under experimental conditions is the introduction of inert refractory particles into the reaction mixture [3]. In the synthesis, non-reactive refractory particles are mainly used, which, on the one hand, change the thermophysical properties of the mixture, and on the other hand, can act as nucleation centers during reaction processes and subsequent crystallization. The particles can be used to control heat transfer during ignition. The method of synthesis of composites with the addition of inert particles differs significantly from the synthesis method, when strengthening inclusions are synthesized simultaneously with the intermetallic matrix [4–6]. First, the particles absorb heat and then, they support the reaction. In this case, the liquid phase accelerates the compound formation reaction. Second, an additional exothermal effect arises during the synthesis of inclusions. In this case, the liquid-phase process prevails. By adding inert particles to the reaction mixture, it is possible to avoid an uncontrolled increase in temperature and to carry out the synthesis mainly in the solid phase. An analysis of qualitative
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