Effect of calcination temperature and holding time on crystal structure and size of tetragonal ZrO₂

This study investigates the synthesis of tetragonal zirconia (t-ZrO₂) from natural zircon sand via alkali fusion, focusing on the effects of calcination temperature (800, 900, and 1000°C) and holding time (3, 5, 7, and 12 h) on the crystal structure and crystallite size. X-ray diffraction (XRD) analysis revealed that at 800°C, the lattice parameter a and unit cell volume initially decreased with increasing holding time and then increased, indicating a shift from stress relaxation and defect elimination to crystal growth and phase stabilization at longer holding times. In contrast, at 1000°C, both the lattice parameter a and unit cell volume consistently decreased with longer holding times, reflecting enhanced atomic diffusion, reduction of oxygen vacancies, and stabilization of the tetragonal phase. The crystallite size steadily increased with temperature and holding time, ranging from approximately 7 to 17 nm. These results indicate that holding time and temperature play crucial roles in the formation of t-ZrO₂. Moreover, the crystallite size of t-ZrO₂ showed an increase of about 21% when the holding time was extended from 3 to 12 h at 1000°C. The observed trends reflect the complex interactions between the kinetic effects and thermodynamic stability in shaping the crystal structure and size evolution during alkali fusion synthesis.