Solid-State Reactions of SiC-TiO.sub.2-MgO System and Phase Relations in SiC-SiO.sub.2-TiC-TiO.sub.2-MgO System

Preliminary experiments revealed solid-state reactions in the SiC-TiO.sub.2-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-TiO.sub.2-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-TiO.sub.2-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 + TiO.sub.2 = = TiC + SiO.sub.2 to form TiC, the acid-based reaction of MgO with SiO.sub.2 or TiO.sub.2 to form Mg-silicates (Mg.sub.2SiO.sub.4, MgSiO.sub.3) or Mg-titanates (Mg.sub.2TiO.sub.4, MgTiO.sub.3, MgTi.sub.2O.sub.5), the reduction reaction of 2TiO.sub.2 + C = Ti.sub.2O.sub.3 + CO (g) with the involvement of excessive TiO.sub.2. The appearance of Ti.sub.2O.sub.3 may also be due to significant surface defects of rutile TiO.sub.2 (110) derived from its bulk Ti.sup.3+ defects. However, Mg-silicates and Mg-titanates were not found in the design of the current SiC-TiO.sub.2-MgO system but the oxide design of the MgO-TiO.sub.2-SiO.sub.2 system. As the SiC-TiO.sub.2-MgO ternary system was extended to the SiC-SiO.sub.2-TiC-TiO.sub.2-MgO quinary system, the phase relations form a combination of the TiC-SiC phase relations with all salts of the TiO.sub.2-MgO-SiO.sub.2 system. Experiments confirmed the formation of TiC and its coexistence with SiC and all binary compounds of the TiO.sub.2-MgO-SiO.sub.2 system, specifying an interaction in the SiC-SiO.sub.2-MgO-TiO.sub.2-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.