Carbothermal reduction and nitridation of titanium dioxide in the H2-N2 gas mixture
This article examines carbothermal reduction/nitridation of rutile in a H2–N2 gas mixture in the temperature-programmed and isothermal experiments in a fixed-bed reactor. The aim of this investigation was to establish the reduction/nitridation sequence, the reaction degree, and the rate of synthesis of titanium oxycarbonitride under different experimental conditions. The off-gas composition was monitored using an infrared sensor (CO, CO2, and CH4) and a dew point analyzer (H2O). Extents of reduction and nitridation were determined from the off-gas composition and LECO analysis. Phase composition of reduced samples was analyzed using powder X-ray diffraction (XRD). Rate and extent of conversion of titanium oxides to titanium oxycarbonitride increased with increasing temperature. The conversion of titania into titanium oxycarbonitride at 1150°C was completed in 180 min; the conversion time decreased to 30 min at 1300°C. Increasing temperature resulted in formation of titanium oxycarbonitride with higher TiC content. Porosity had a minor effect on the reduction/nitridation of titania with the tendency to increase the reduction rate with increasing porosity. Reduction/nitridation of titania at 1150°C followed the sequence: TiO2→Ti5O9→Ti4O7→Ti3O5→TiOxCyNz.