Reduction of TiO2 assisted by a microwave plasma at atmospheric pressure

The reduction of rutile-TiO2 thin foils by microwave plasma created in a resonant cavity at atmospheric pressure gives a TiO/Ti2O3/Ti3O5 sequence at 973 K for a 5%H2-He mixture. The efficiency of the reduction process is strongly affected by a slight change of the gas composition. The intensity of the Hα transition measured by optical emission spectroscopy was used to determine experimental conditions where the temperature of the substrate could be adjusted between 980 and 1090 K without changing the hydrogen concentration close to the surface substrate. In these conditions, no titanium layer could be detected by grazing angle X-ray diffraction. A TiO/Ti2O3 sequence is observed with an anatase-rutile transition that occurs above a treatment temperature of 1020 K. The overall reduction rate is close to 1 μm h−1 under the chosen conditions. The evolution of the thickness of the Ti2O3 layer below 1060 K demonstrates that the deoxidation mechanism is not simply related to the atomic hydrogen concentration in the gas phase.