Formation of titanium carbonitride phases via the reduction of TiO sub 2 with carbon in the presence of nitrogen

摘要

The reduction of rutile (TiO sub 2 ) with carbon was studied in a range of nitrogen atmospheres. The effect of the reactivity of carbon on the reducibility of TiO sub 2 to titanium carbonitride phase (TiC sub x N sub y ) was investigated over a range of temperatures between 1173-1773K. The present study also reports the effect of the presence of ammonia, CO, and hydrogen gases on the reduction reaction equilibrium of TiO sub 2 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 TiO sub 2 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 1573K and 1 atm of N sub 2 gas. The derived values of the activation energies for simultaneous reduction-nitridation of TiO sub 2 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 220-240 kJ mol exp -1 for both types of reducing agents: graphite and activated charcoal.