Sol-gel chemistry of transition metal oxides

Preparation of monodispersed colloidal particles

Chemistry of zirconia and its use in chromatography

Mechanisms of tetragonal phase stabilisation, at room temperature, in nanocrystalline ( 1 μm) are reviewed in detail. The merits, demerits and scope of each individual model are outlined. The analysis of the literature shows that, although the mechanism of tetragonal phase stabilisation in bulk ZrO2 is well understood, the room temperature tetragonal phase stabilisation mechanism in undoped, nanocrystalline ZrO2 is controversial. Various proposed models, based on surface energy (nanocrystallite size), strain energy, internal and external hydrostatic pressure, structural similarities, foreign surface oxides, anionic impurities, water vapour and lattice defects (oxygen ion vacancies), are discussed in detail. It is proposed that generation of excess oxygen ion vacancies within the nanocrystalline ZrO2 is primarily responsible for the room temperature tetragonal phase stabilisation, below a critical size. Hence, the mechanism of ...

Mechanisms of room temperature metastable tetragonal phase stabilisation in zirconia

https://ris.utwente.nl/ws/files/6792250/Mercera90zirconia.pdf

Zirconia as a support for catalysts: Evolution of the texture and structure on calcination in air

The characteristics of hydrous zirconia gels obtained by hydrolysis of highly acidic ZrOCl2 · 8H2O solutions at ∼100‡C 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.

G. Rigotti

Papers

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