Hydrolysis and condensation of metal

To date, it has been difficult to produce monodisperse spherical powders from metal alkoxides with low valence, such as Al and Fe, because the hydrolysis and condensation of metal alkoxides in alcohol are too rapid to allow control of particle size, size distribution, and morphology. Many previous studies reported (28-30) that alkoxide-... 

Controlled hydrolysis and condensation of metal alkoxide precursors, followed by drying at ambient pressure and temperalure. 

Sol-gel processing can be used to prepare a variety of materials, including glass, powders, films, fibers, and monoliths. Traditionally, the sol-gel process generally involves hydrolysis and condensation of metal alkoxides. Metal alkox-ides are good precursors because they readily undergo hydrolysis that is, the hydrolysis step replaces an alkoxide with a hydroxide group from water and a free alcohol is formed. Once hydrolysis has occurred, the sol can react further... 

For coordinatively saturated metals the hydrolysis and condensation of metal alkoxides M(OR)2 corresponds to the nucleophilic substitution of alkoxy ligands by hydroxylated species XOH ... 

I 7 6 Properties, Synthesis and Applications of Highly Dispersed Medal Oxide Catalysts 16.3.1.1 Hydrolysis and Condensation of Metal Alkoxides... 

The formation of colloidal particles can be obtained from hydrolysis and condensation of metal salts in aqueous media. The aqueous chemistry of metal salts is quite complicated owing to the occurrence of hydrolysis reactions which convert the ions to new ionic species or to precipitates. When dissolved in water a metal cation becomes solvated by the surrounding water molecules according to... 

A quite different approach from that of colloidal sols in the preparation of sol-gel derived membranes utilizes polymeric sols. In this category of sols the dispersed phase results from the hydrolysis and condensation of metal organic precursors in organic media. In most cases this process deals with the polymerization of metal alkoxides in alcohol according to the following reactions ... 

The hydrolysis and condensation of metal alkoxides M OR)z leads to oligomers in which metal atoms tend to acquire their maximum coordination number. The formation of these species can be controlled by the hydrolysis ratio h = H2O/M. 

Sol-gel chemistry is based on the hydrolysis and condensation of metal alkoixdes. These reactions correspond to the nucleophilic substitution of alkoxy ligands by hydroxylated species XOH as follows M(OR)z + x XOH —[M(OR)z-x(OX)x] + x ROH where X stands for H (hydrolysis) or M (condensation). 

The sol-gel method is generally employed for the synthesis of metal oxide NPs as well as oxide nanocomposites. The sol-gel process involves the hydrolysis and condensation of metal precnrsors [43,44]. Further condensation and polymerization will lead to three-dimensional metal oxide networks forming the gel. The sol-gel process can be either in aqueous or non-aqueous medium. In the aqueous sol-gel process, oxygen for the formation of the oxide is supplied by water molecules. In the... 

Inorganic sol-gel route Metaloxane polymer Inorganic polymers interconnected by van der Waals or hydrogen bonding Hydrolysis and condensation of metal alkoxides... 

Hydrolysis and condensation of metal alkoxides are commonly used for the sol-gel synthesis of metal oxides. Oxo-polymers are first formed. They then aggregate and give rise to an oxide network after drying and densification. The chemical m ification of alkoxide precursors leads to the formation of new molecular species with completely different structures, functionalities and reactivities. The sol-gel route therefore offers good... 

Solution chemistry of metal alkoxide precursors discusses hydrolysis and condensation of metal alkoxides and chemically modified aikoxides in nonaqueous solvents. 

Since the hydrolysis and condensation of metal alkoxides are extremely sensitive to water, the thickness of electrodeposited non-sihcon sol-gel films is also dependent on the content of water in the deposition solution, as shown in Figure 12.8. A critical water content was observed for both anodic and cathodic electrodeposition, at which the film deposited had the highest thickness. Almost no film was electrodeposited when the water content was very low, about <10 ppm. This indicates that both anodic and cathodic electrodeposition are based on the electrolysis of water. However, it is still unclear why the thickness of the film decreased as the water content was higher than 100 ppm. One possible explanation is that the sol-gel precursor underwent condensation in the solution forming oligomers that were not active enough for further film deposition. 

In contrast to conventional sol-gel processes, which are based on the hydrolysis and condensation of metal precursors in an aqueous alcohol-mixed solvent, the nonhydrolytic sol-gel reaction proceeds by reactions of the metal precursors in organic media [16]. This nonhydrolytic sol-gel process has unique advantages... 

The reactions involved in sol-gel technique based on the hydrolysis and condensation of metal alkoxides (M(OR)x) can be described as follows ... 

Sol-gel chemistry is based on the hydrolysis and condensation of metal alkoxides M(OR)z. These reactions can be described as nucleophilic substitutions or additions. The reactivity of metal alkoxides toward hydrolysis therefore increases as the electronegativity of the metal atom decreases and its size increases. Silicon alkoxides are not very sensitive toward hydrolysis and condensation. Reaction rates have to be increased via acid or base catalysis. Most other alkoxides are highly sensitive to... 

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