The kinetics and mechanism of combusted Zr–B–Si mixtures and the structural features of ceramics based on zirconium boride and silicide

Abstract

The study focuses on investigation of the combustion kinetics and mechanisms, as well as the phase- and structure formation processes, during elemental synthesis of ceramics based on zirconium diboride and silicide doped with aluminum. The effect of the degree of dilution with an inert component and initial temperature T0 on the combustion kinetics of the Zr–Si–Al–B mixture is studied. An increase in T0 in the range of 298–700K causes a directly proportional rise in the combustion temperature Tc and rate Uc, which demonstrates that staging of the reactions of formation of zirconium boride and silicide remains invariant. The effective activation energy Eeff of the combustion process is 225kJ/mol, suggesting that the liquid-phase processes have a decisive effect on the reaction kinetics. The interaction of zirconium with boron and silicon runs through the Zr–Si–Al–B melt that is formed in the combustion zone. Staging of chemical transformations during phase and structure formation of SHS products is studied. The primary ZrB2 grains crystallize from the melt in the combustion zone; the ZrSi silicide phase is formed with a delay of no longer than 0.5s. Compact ceramics with composition ZrB2–ZrSi–ZrSi2–ZrSiAl2 synthesized by forced SHS- pressing showing a great potential for high-temperature applications both as a construction material and as a precursor for ion-plasma deposition of coatings.