Structural and textural study on ZrO 2-Y 2O 3 powders

Abstract

Microporous gels of ZrO 2, ZrO 2·2mol% Y 2O 3 and ZrO 2·5mol%Y 2O 3 were treated in air and under vacuum at temperatures ranging from 450 to 1300 °C. X-ray and electron diffraction results seem to indicate that both, pure and doped zirconia gels crystallize in the cubic form of ZrO 2. On lengthening of the thermal treatment at 450 °C or after treatment at higher temperatures, the transformations cubic→tetragonal→monoclinic occur, but those are delayed as the yttria content in the sample increases. In some treatment conditions, cubic and tetragonal phases can also been retained to some extent in pure zirconia. Moreover, a rhombohedral deformation of the cubic cell along the 〈111〉 directions has been observed in some crystals of pure zirconia samples. Textural degradation takes place in both, pure and doped zirconia, due to particle growth and also the loss of porosity and therefore, the observed structural stabilization does not improve textural stability. The differences in the texture of pure and doped samples have been related to dehydration and crystal growth processes, and to the properties of primary particles in the gels.