Phase structure and thermal evolution in mixed oxide TiO2-ZrO2 powders obtained by the sol-gel process

In this work we present the phase structure evolution, with long annealing times, of mixed oxides powders in the TiO2-ZrO2 system, obtained by the sol-gel method. Several compositions were synthesized via the catalytic hydrolysis of titanium and zirconium butoxides, HNO3 was added to adjust the pH=3. Pure zirconia and titania were also prepared. Long thermal treatments were applied from 100-1000degreesC, increasing the temperature every 100degreesC. These samples were heated during 20 h at each temperature. By combining XRD, DTA and FTIR the main changes on the phase crystallization were analyzed. Pure titania show the formation of anatase from the fresh sample, with heating a progressive transformation occurs to rutile phase. The mixed oxides over the composition range 50-100 wt % ZrO2, produce an amorphous powder up to 600degreesC. The samples rich in titania, can incorporate ZrO2 only into the rutile lattice forming a solid solution. In the middle region, the continuous increasing of zirconia favors the crystallization of ZTss at 700degreesC. At the rich-end zirconia, the formation of a monoclinic zirconia solid solution (Zmss) was observed, and the crystallization temperature of ZTss diminishes up to 500degreesC. Tetragonal zirconia was not observed. Finally, pure zirconia show the coexistence of the monoclinic and tetragonal polymorphs over a wide temperature range, 400-900degreesC. Photocatalytic activity of ZrTiO4 and the parent oxides, was evaluated monitoring the degradation of 2,4-dinitroaniline by UV-VIS spectroscopy; and the energy band gap was calculated.