Effect of temperature and Ar flow rate on Ti3SiC2 formation from TiSiO4 powders coated with pyrolytic carbon

In this study, equilibrium thermodynamic analysis was initially carried out for TiO₂:SiO₂:C molar ratio of 1:1:4 at 1600 K, 1700 K and 1800 K as a function of Ar/solid reactant ratio. It was predicted that single phase Ti₃SiC₂ is formed when a critical Ar/solid reactant ratio is exceeded. This behavior is ascribed to the reduction of partial pressures of gaseous reaction products of SiO and CO. Subsequently, formation of Ti₃SiC₂ phase from carbon coated TiSiO₄ powders by carbothermal reduction was investigated as a function temperature, isothermal holding time and Ar flow rate. Carbothermal reduction experiments at 1800 K and at a Ar flow rate of 250 cm³/min for 60 min showed that the optimal C content was determined to be 27.47 wt.%. The ternary carbide compound was not detected within 120 min at 1600 K and 1700 K, but a major TiOC phase along with a minor SiC phase. Whereas at 1800 K, the ternary carbide phase was observed and its amount increased from 6.80 wt.% at 0 min to 38.91 wt.% at 75 min above which it gradually decomposed into the binary carbides. The experiments carried out for various Ar flow rate at 1800 K for 75 min revealed that the highest ternary carbide content (47.84 wt.%) was obtained at a Ar flow rate of 425 cm³/min. The thermodynamic and experimental results indicate that Ti₃SiC₂ formation takes place via the reaction of pre-formed TiC and SiC phases with the remaining SiO₂.