Nanocrystallization and phase transformation in monodispersed ultrafine zirconia particles from various homogeneous precipitation methods

Monodispersed ultrafine (nano- to micrometer) zirconia precursor powders we re synthesized by three different physicochemical methods: (I) forced hydro lysis, (II) homogeneous precipitation in inorganic salt solutions, and (III ) hydrolysis/condensation of alkoxide, The forced hydrolysis method; produc ed monoclinic nanocrystalline particles (cube shaped) of nanometer scale, w hich depended largely on the initial salt concentration. Methods II and III , both involving the use of alcohol as a solvent, exhibited a faster partic le formation rate and generated amorphous ultrafine (submicrometer) monodis persed microspheres, indicating that the presence of alcohol may have stimu lated particle nucleation due to its low dielectric property (and, thus, th e low solubility of nucleus species in mixed water-alcohol solutions). Nucl eation and growth of the particles in solutions are discussed based on the measurements obtained by small-angle X-ray scattering (SAXS) and dynamic li ght scattering (DLS), High-temperature X-ray diffraction (HTXRD) and TGA/DT A studies elucidated the differences in phase transformation for different types of powders. The most interesting finding was the nonconventional mono clinic nanocrystal nucleation and growth that occurred prior to transformat ion to the tetragonal phase (at 1200 degrees C) during the heat treatment o f the nanocrystalline powders produced by the forced hydrolysis.