Phase Structure and Thermal Evolution in Mixed Oxide TiO₂-ZrO₂ Powders Obtained by the Sol-Gel Process

Abstract

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 100–1000°C, increasing the temperature every 100°C. 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 600°C. 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 700°C. 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 500°C. Tetragonal zirconia was not observed. Finally, pure zirconia show the coexistence of the monoclinic and tetragonal polymorphs over a wide temperature range, 400–900°C.

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.