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.