Thermodynamic study of the TiCO system in the temperature range 1400 – 1600 K

The reduction of TiO 2 (rutile) by carbon has been studied in a graphite furnace. Pressure measurements of CO in equilibrium with the solid phases βTi 3 O 5 , TiC x O y and C (graphite) have been performed. The temperature dependence of the carbon monoxide pressure is given by the equation: log 10 P co (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: Ti 3 O 5 + 6.02 C ⇌ TiC 0.67 O 0.33 + 4.01 CO The standard free energies of formation of the compounds have been calculated: ΔG f 1580 0 TiC 0.67 O 0.33 = −60 578 cal mol −1 ΔG f 1580 0 TiC 1.0 = −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 TiC 0.67 O 0.33 ( a = 4.305 A ̊ ) to TiC 1.0 ( a = 4.331 A ̊ ) while the carbon monoxide pressure decreases from 700 to 10 −5 Torr.