Solid-state reactions  of SiC–TiO₂–MgO system and phase relations in SiC–SiO₂–TiC–TiO₂–MgO system

Abstract

Preliminary experiments revealed solid-state reactions in the SiC–TiO₂–MgO system that resulted in forming TiC compound, providing, thus, a new reaction system for the formation of TiC–SiC ceramic matrix composites. This system's high-temperature physicochemical reaction and the phase equilibrium relations of TiC–SiC with salt compounds in the SiC–TiO₂–MgO system will be examined in this paper. The obtained findings may significantly contribute to the composition of TiC–SiC ceramic composites. Solid-state reactions in the SiC–TiO₂–MgO system were investigated during experimental procedures employing thermodynamic computing. Chemical kinetics of some reactions were highlighted and discussed, including mutual displacement reaction of SiC + TiO₂ = TiC + SiO₂ to form TiC, the acid-based reaction of MgO with SiO₂ or TiO₂ to form Mg-silicates (Mg₂SiO₄, MgSiO₃) or Mg-titanates (Mg₂TiO₄, MgTiO₃, MgTi₂O₅), the reduction reaction of 2TiO₂ + C = Ti₂O₃ + + CO (g) with the involvement of excessive TiO₂. The appearance of Ti₂O₃ may also be due to significant surface defects of rutile TiO₂ (110) derived from its bulk Ti³⁺ defects. However, Mg-silicates and Mg-titanates were not found in the design of the current SiC–TiO₂–MgO system but the oxide design of the MgO–TiO₂–SiO₂ system. As the SiC–TiO₂–MgO ternary system was extended to the SiC–SiO₂–TiC–TiO₂–MgO quinary system, the phase relations form a combination of the TiC–SiC phase relations with all salts of the TiO₂–MgO–SiO₂ system. Experiments confirmed the formation of TiC and its coexistence with SiC and all binary compounds of the TiO₂–MgO–SiO₂ system, specifying an interaction in the SiC–SiO₂–MgO–TiO₂–TiC system. The phase relations of the quinary system were established, followed by constructing its phase diagram relations at 1400 °C, which would be beneficial for the compositional design of TiC–SiC, TiC–ceramic, and SiC–ceramic composites