KINETICS AND PHASE EVOLUTION DURING CARBOTHERMAL SYNTHESIS OF TITANIUM CARBIDE FROM ULTRAFINE TITANIA CARBON MIXTURE/

The kinetics and phase evolution of the TiC formation process by carbo thermal reduction of ultrafine titania/carbon mixture were investigate d using thermogravimetric analysis (TGA), X-ray diffraction (XRD) and oxygen analysis. Titania (TiO2) first lowered its oxidation state to T i3O5 via an unidentified phase (possibly one of the Magneli phases). T hen Ti3O5 was further reduced to Ti2O3, followed by the formation of t itanium oxycarbide (TiCxOy) phase and its purification toward high pur ity TiC thereafter. Ti2O3 was the oxide phase with the lowest oxidatio n state before forming TiCxOy phase. In the isothermal TGA trace, the formation of Ti3O5 showed a diffusion-controlled process; possibly car bon diffusion limited the solid state reaction. The formation of Ti2O3 and TiCxOy was interpreted to be associated with CO gas-assisted redu ction reaction, based on constant reaction rate for each process. The activation energy for the formation of Ti2O3 (from Ti3O5) and TiCxOy ( from Ti2O3) phase were calculated to be 415.6 and 264.3 kJ mol(-1), re spectively. The TiC powder synthesized at 1550 degrees C for 4 h in fl owing argon atmosphere showed fine particle size (0.3-0.6 mu m) with o xygen content of 0.7 wt% and lattice parameter of 0.4328 nm while inte rparticle agglomeration was moderate. (C) 1998 Chapman & Hall.