Colloidal ceramics gels from

The formation of ordered two- and three-dimensional microstructuies in dispersions and in liquid systems has an influence on a broad range of products and processes. For example, microcapsules, vesicles, and liposomes can be used for controlled drug dehvery, for the contaimnent of inks and adhesives, and for the isolation of toxic wastes. In addition, surfactants continue to be important for enhanced oil recovery, ore beneficiation, and lubrication. Ceramic processing and sol-gel techniques for the fabrication of amorphous or ordered materials with special properties involve a rich variety of colloidal phenomena, ranging from the production of monodispersed particles with controlled surface chemistry to the thermodynamics and dynamics of formation of aggregates and microciystallites. 

Analysis of relaxation curves from fluids is of particular interest for the characterization of pores in rocks [Dav 1, Fori, Kle 1 ] and other porous materials such as packs of beads or grains, ceramics, zeolites, foods, colloids, emulsions, gels, suspensions, and is of interest to the retrieval of biochemical and biophysical information [Labi]. Because longitudinal and transverse relaxation rates can be significantly increased in the vicinity of solid-liquid interfaces, the relaxation behaviour of H and other nuclei of fluids confined in porous media can provide important information about porosity, pore-size distribution, and pore connectivity [Hiirl, Kiel, Kle2]. 

Figure 37.6 Additive and subtractive models of coloration and examples of CMYK and RGB ceramic pigments obtained in the author s laboratory by colloidal sol-gel route (from TEOS, NH4VO3, or PreOii dissolved in HNO3, SnCl2, zirconium acetate, and nitrate salts of...

The sol-gel process involves the transition of a system from a liquid "sol" (mostly colloidal) into a solid "gel" phase (11). By applying this methodology, it is possible to fabricate ceramic or glass materials in a wide variety of forms ultrafine or spherical-shaped powders, thin film coatings, ceramic fibers, microporous inorganic membranes, monolithic ceramics and glasses, or extremely porous aerogel materials. 

The earliest routes for forming ceramics from sol-gel solutions involved the precipitation of metal oxide particles from solutions. These form a true colloidal suspension a sol. Upon destabilization of this sol, aggregation takes place and a rigid network is formed a gel. A gel is intermediate between a solid and a liquid. The term sol—gel has since been used by the materials science community to describe, albeit erroneously, virtually all chemical processing of ceramics from solutions (e.g., metal oxide particle precipitation or metalorganic decomposition). This discussion focuses on the gel aspects of sol—gel synthesis and not on the sol aspects, which are treated separately in this book. 

The sol-gel process is a versatile solution process for making ceramic and glass materials involving the transition of a system from a colloidal suspension (sol) into a solid phase (gel) ". The resulting porous gel can be chemically purified and consolidated at high temperatures. In the classical sol-gel process, the precursor (e.g. a metal enolate or a metal aUcoxide) is exposed to a series of hydrolysis and polymerization reactions to form... 

The preparation of the required microporous ceramic layers is possible by the sol-gel route from stable colloidal dispersions with individual nanoparticles of less than 10 nm. Different types of ceramic nanofilters have been prepared from such aqueous or organic sols of the following oxides y-alumina, zirconia, ° hafnia," and titania. ... 

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