Synthesis of nanocrystalline zirconia using sol-gel and precipitation techniques

Nanocrystalline zirconia samples having predominantly tetragonal crystalline phase were synthesized using sol-gel and conventional precipitation techniques from zirconium hydroxide obtained by the hydrolysis of both zirconium propoxide and zirconium oxychloride precursors. Thermal drying of zirconium hydroxide gel in an oven (110 degrees C, 12 h) results in lower crystallite size (11-13 nm) as compared to drying under vacuum (50 mbar, 70 degrees C), which shows higher crystallite size (20-21 nm) during both sol-gel and conventional precipitation synthesis. The progressive transformation of tetragonal to monoclinic phase of zirconia with increasing calcination temperature was observed to be related to the critical crystallite size and lattice strain. Sol-gel synthesis was found to be advantageous because of the stabilization of tetragonal phase at higher temperature, whereas complete phase transformation was observed in the samples prepared by precipitation method at 600-700 degrees C temperature. Sol-gel synthesis resulted in spherical-shaped particles whereas cubic-/rectangular-shaped particles of varying sizes were predominantly formed by conventional precipitation synthesis.