Phase transformation of hydrous-zirconia fine particles containing cerium hydroxide

Monoclinic hydrous-zirconia fine particles that contained cerium(IV) hydroxide (Ce(OH)(4)) were heated from 200 degrees C to 600 degrees C, to investigate the phase transformation to CeO2-doped tetragonal ZrO2. Both ZrOCl2.8H(2)O and CeCl3.7H(2)O were dissolved in aqueous solutions and then boiled to prepare the hydrous-zirconia particles. The Ce(OH)(4)-containing hydrous-zirconia particles were prepared by adding aqueous ammonia into the boiled solutions. The monoclinic-to-tetragonal (m --> t) phase transformation of the Ce(OH)(4)-containing hydrous zirconias was observed at 300 degrees C using X-ray diffraction (XRD). XRD and Brunauer-Emmett-Teller (BET) specific surface area measurements revealed that the Ce(OH)(4)-containing hydrous zirconias had a tendency to transform from the monoclinic phase to the tetragonal phase at lower temperatures as the primary particle size of the hydrous zirconia decreased and the Ce(OH)(4) content increased. These tendencies for the m --> t phase transformation agree with the conclusions that have been derived from thermodynamic and kinetic considerations.