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 T 0 on the combustion kinetics of the Zr–Si–Al–B mixture is studied. An increase in T 0 in the range of 298–700 K causes a directly proportional rise in the combustion temperature T c and rate U c , which demonstrates that staging of the reactions of formation of zirconium boride and silicide remains invariant. The effective activation energy E eff of the combustion process is 225 kJ/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 ZrB 2 grains crystallize from the melt in the combustion zone; the ZrSi silicide phase is formed with a delay of no longer than 0.5 s. Compact ceramics with composition ZrB 2 –ZrSi–ZrSi 2 –ZrSiAl 2 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.