Formation of titanium carbonitride phases via the reduction of TiO2 with carbon in the presence of nitrogen

The reduction of rutile (TiO2) with carbon was studied in a range of nitrogen atmospheres. The effect of the reactivity of carbon on the reducibility of TiO2 to titanium carbonitride phase (TiCxNy) was investigated over a range of temperatures between 1173 K and 1773 K. The present study also reports the effect of the presence of ammonia, CO, and hydrogen gases on the reduction reaction equilibrium of TiO2 to carbonitride (TiCN). The compositional dependence of the lattice parameter of TiCN phase on the concentrations of interstitial atoms, C, N, and O is also discussed. The mechanism of TiCN phase formation from TiO2 has been established on the basis of a predominance area diagram in the Ti-C-N-O system derived from the Gibbs free energy data at 1573 K and 1 atm of N-2 gas. The derived values of the activation energies for simultaneous reduction-nitridation of TiO2 to TiCN are discussed in the light of interstitial ion diffusion through the B1 (NaCl type) structure. The dependence of TiC lattice parameter on the concentrations of N and O at the interstitial sublattice sites is also established. The apparent values of the activation energies were found to be in the range of 220 kJ to 240 kJ mol(-1) for both types of reducing agents: graphite and activated charcoal. (C) 1999 Kluwer Academic Publishers.