The phase formation and stability of tetragonal ZrO2 prepared in a silica bath

Tetragonal zirconia (ZrO2) precursor powders were obtained in a silica bath using zirconium (IV) nitrate and tetraethyl orthosilicate (TEOS) as starting materials in an ethanol–water solution using co-precipitation process mixing at 348 K and pH=7 for 10 min. The phase formation and stability of ZrO2 freeze dried precursor powders prepared in a silica bath were investigated using differential scanning calorimetry/thermogravimetry (DSC/TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and an energy dispersive spectrometer (EDS). DSC results revealed tetragonal ZrO2 (t-ZrO2) formation at 1165 K. After the zirconia freeze dried precursor powders were calcined between 1173 K and 1473 K for 2 h, XRD patterns showed the calcination powders all to be a single tetragonal phase. The crystallite size of the tetragonal zirconia was only 3.3 nm when the freeze-dried precursor powders were calcined at 1173 K for 10 min. In addition, the crystallite size of t-ZrO2 increased but was still smaller than 20 nm when the freeze dried precursor powders were calcined at 1473 K for 120 min. The TEM observed results were also confirmed with XRD analysis.