Formation of nonstoichiometric titanium oxides nanoparticles TinO2n–1 upon heat-treatments of titanium hydroxide and anatase nanoparticles in a hydrogen flow

Abstract

Titania powders with anatase structure and crystallite size ranged from 20 to 27 nm were produced from titanium hydroxide by hydrothermal synthesis. The nanopowders and the initial hydroxide were isothermally heat-treated in a hydrogen flow at temperatures of 00–1000°C for times ranging from 1 to 27.5 h. It was found that the thermal treatment of titanium hydroxide in a reducing atmosphere at 800–900°C yields TiO₂ with rutile structure. An unusual thermal stability of the metastable structure of anatase was observed in the case of nanocrystalline TiO₂ powders up to a temperature of 900°C at which the anatase–rutile phase transition is observed. It was found that the nonstoichiometry of rutile and anatase powders changes upon a thermal treatment in a hydrogen flow. The heat-treatment in a hydrogen flow at 1000°C for 1 h was shown to lead to the formation of nanoparticles of the Magneli phase with the composition corresponding to Ti9O17 irrespective of the chemical nature of the precursor. The increase of the heat-treatment time at this temperature leads to the appearing of the Magneli phases with the compositions corresponding to Ti₈O₁₅ and Ti₉O₁₇ and Ti₂O₃ and Ti₃O₅ suboxides in addition to the Ti₉O₁₇ main phase.