Hydrous zirconium dioxide: interfacial properties,the formation of monodisperse spherical particles,and its crystallization at high temperatures

The characteristics of hydrous zirconia gels obtained by hydrolysis of highly acidic ZrOCl₂ · 8H₂O solutions at 100C are described. Under adequate conditions, monodisperse spherical hydrous zirconia is obtained. The role of sulphate and chloride ions is described. The gel has a large water content, indicating only modest crosslinking. Crystallization upon heating takes place with the formation of both monoclinic and tetragonal zirconia polymorphs; X-ray line widening studies do not indicate a particle size-crystal structure correlation. On the basis of this observation and using Stranki's rule, the crystallization sequence upon heating is rationalized. Surface properties of hydrous zirconia are discussed on the basis of electrophoretic measurements, and compared with those of baddeleyte. The site binding model is not very adequate to describe these systems, and the existence of a very thin gel-like region at the baddeleyte-water interface is postulated.