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 °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 °C, however it was determined the tetragonal (major), monoclinic (minor) of zirconia and cristobalite (major) phases of silica were present at 1500 °C. The crystallite sizes of the t-ZrO2 were in the range of 8–30 nm with increasing temperature from 1000 °C to 1500 °C. The surface area of samples at 1000 °C was 171 m2/g. In addition, the agglomeration degree (N=dBET3/dXRD3) of powders at 1000 °C was 4, which was an indication of the soft agglomeration of powders. The stabilization of the t-ZrO2 up to 1500 °C was attributed to the confinement of ZrO2 particles by the surrounding cristobalite phase of silica in the structure.