Phase evolution and reaction mechanism during reduction-nitridation process of titanium dioxide with ammonia

Titanium nitride powders were synthesized from titanium dioxide at 1173-1373 K in ammonia atmosphere. The reduction-nitridation products with various fractions obtained at various temperatures were analyzed by X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscopy, and selected area electron diffraction. The reaction sequence from TiO2 to TiN in ammonia atmosphere was changed by increasing the reaction temperature. The reaction sequence at 1173 K was found as TiO2 -> TiN1-xOx -> TiN. When the reaction temperature was above 1273 K, the reaction sequence changed to as follows: TiO2 -> Ti9O17 -> TiN1-xOx -> TiN. Ti3O5 was not found as an intermediate phase on account of its instability in NH3 atmosphere. The morphology of the synthesized TiN is closely related to that of the raw materials.