Synthesis and reaction mechanism of Ti3SiC2 ternary compound by carbothermal reduction of TiO2 and SiO2 powder mixtures

The present study aims to investigate synthesis of Ti₃SiC₂ from TiO₂ and SiO₂ powder mixtures by carbothermal reduction method. Equilibrium TiO₂–SiO₂–C ternary phase diagram was used to predict the conditions for the formation of Ti₃SiC₂ at 1800 K under Ar atmosphere. A reactant mixture with a TiO₂:SiO₂ molar ratio of 1.5 and a C content of 68.75 mol% (26.86 wt%) was initially selected among the thermodynamically favorable reactant compositions for the experimental studies. Two different C sources, graphite flakes and pyrolytic C coating, were used to synthesize Ti₃SiC₂ at 1800 K under Ar atmosphere. When graphite flakes were used, the products contained a trace amount of Ti₃SiC₂ phase along with major TiC and minor SiC phases. Whereas, pyrolytic C coating on the oxide particles resulted in the products with much higher Ti₃SiC₂ contents owing to the close contact between the reactants. Optimal C concentration for the C coated oxide mixtures with a TiO₂:SiO₂ molar ratio of 1.5 was determined to be 30.05 wt% under the experimental conditions studied. Ti₃SiC₂ content of the products obtained from this reactant was observed to increase with reaction time to 31 wt% at 75 min beyond which it gradually decreased. XRD studies indicated that the product with the highest ternary carbide content also contained TiC and a trace amount of SiC. SEM-EDS analyses showed that this sample essentially consisted of spherical fine TiC particles and Ti₃SiC₂ nanolaminates. Equilibrium thermodynamic analysis of the TiO₂–SiO₂–C system suggested that the reaction of solid Ti₂O₃ with SiO and CO gases may play a dominant role in the formation of Ti₃SiC₂.