Phase formation and crystallite size of tetragonal zirconia nanocrystals calcined between 825 and 875 °c

Research has been carried out to study the effect of calcination temperature in the range of 825-875 °C on the phase formation and crystallite size of tetragonal zirconia (t-ZrO2) to know when the phase transformation occurs. The raw material was zircon (ZrSiO4) powder, synthesized from the basic material of zircon sand (ZrSiO4) originating from Kereng Pangi, Central Kalimantan. Amorphous zirconia was produced from the zircon powder, which was subjected to reaction with NaOH, annealing at 700 °C for 3 hours, reaction with HCl, annealing for 1 hour at 100 °C, and titration using 10% NH4OH base. The precursors used to obtain t-ZrO2 powders were amorphous zirconia (ZR-A) and 700 °C zirconia (TZR-700). The TZR-700 precursor was obtained by heating the ZR-A precursor for 3 hours at 700 °C. Then, the ZR-A and TZR-700 powders were calcined at 825, 850, and 875 °C to produce the t-ZrO2 nanocrystals. Size and morphology characterization of the nanocrystals included XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy), and PSA (Particle Size Analysis). XRD data for all precursors and calcination temperatures showed the presence of pure tetragonal zirconia. Further analysis of XRD data showed that the crystal size increased with increasing calcination temperature, i.e., 9, 10, and 13 nm for precursor ZR-A and 10, 11, and 14 nm for precursor TZR-700 at the designated calcination temperatures. Meanwhile, PSA data showed that the average particle size of each precursor also increased with increasing calcination temperature. The scanning electron microscope (SEM) observation was in line with the results of XRD and PSA analyses.