The preparation and characterization of soft-agglomerated ZrO2-SiO2 nanocrystalline composite by supercritical CO2

Zirconia silica (50/50 vol.%) nanocomposites were prepared by supercritical CO2 method at 15 MPa and 150 degrees C. The characterization of synthesized powders was carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM) scanning electron microscopy (SEM) and BET. The results of XRD showed that the nanocomposite powders have mostly the tetragonal phase of zirconia (t-ZrO2) at 1000 degrees C, however it was determined the tetragonal (major), monoclinic (minor) of zirconia and cristobalite (major) phases of silica were present at 1500 degrees C. The crystallite sizes of the t-ZrO2 were in the range of 8-30 nm with increasing temperature from 1000 degrees C to 1500 degrees C. The surface area of samples at 1000 degrees C was 171 m(2)/g. In addition, the agglomeration degree (N = d(BET)(3)/d(XRD)(3)) of powders at 1000 degrees C was 4, which was an indication of the soft agglomeration of powders. The stabilization of the t-ZrO2 up to 1500 degrees C was attributed to the confinement of ZrO2 particles by the surrounding cristobalite phase of silica in the structure. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.