THERMODYNAMIC STUDY OF THE TI-C-O SYSTEM IN THE TEMPERATURE-RANGE 1400-1600-K

The reduction of TiO2 (rutile) by carbon has been studied in a graphite furnace. Pressure measurements of CO in equilibrium with the solid phases βTi3O5, TiCxOy and C (graphite) have been performed. The temperature dependence of the carbon monoxide pressure is given by the equation: log10Pco(atm) = - 18600 T + 11.72 (1400 - 1600 K). At 1580 K, the results of the isothermal studies together with those of X-ray and chemical analysis of quenched specimens are consistent with the following equation: Ti3O5 + 6.02 C ⇌ TiC0.67O0.33 + 4.01 CO. The standard free energies of formation of the compounds have been calculated: ΔGf15800 TiC0.67O0.33 = -60 578 cal mol-1ΔGf15800 TiC1.0 = -39 419 cal mol-1. In the presence of free carbon, the composition and lattice parameter of the f.c.c. titanium oxycarbide vary from TiC0.67O0.33 (a = 4.305 A ̊) to TiC1.0 (a = 4.331 A ̊) while the carbon monoxide pressure decreases from 700 to 10-5 Torr. © 1979.