Polymeric sol-gel route

The aim of this contribution is to present data on the preparation of catalysts containing as embedding species a large family of eolloids such as colloids of ruthenium, platinum, or palladium-gold alloys and triflate derivatives such as lanthanum and silver triflate or tert-butyldimethylsilyltrifluoromethanesulfonate (BMSTM). Silica, zirconia and tantalum oxides were used as carrier. All these preparations considered the polymeric sol-gel route using as starting materials silicon, zirconium or tantalum alcoxides. 

The XRD pattern of the calcined 8YSZ powder obtained by polymeric sol-gel route is shown in Figure 1, indicating the powder with a pure cubic structure . Average domain (r) of the powder was estimated by Scherrer equation" ... 

This work reports the development of a polymeric/sol-gel route for the deposition of silicon carbide and silicon oxycarbide thin films for applications such as heat-, corrosion-, and wear-resistant coatings, coatings on fibers for controlling the interaction with the matrix in ceramic matrix composites, or films in electronic and optoelectronic devices. This method, in which the pre-ceramic films are converted to a ceramic coating either by a conventional high temperature annealing or by ion irradiation, is alternative to conventional methods such as chemical or physical vapor deposition (CVD, PVD), molecular beam epitaxy, sputtering, plasma spray, or laser ablation, which are not always practical or cost efficient. 

The sol-gel processing of materials can refer to a multitude of reaction processes which employ a wide variety of chemical precursors to prepare many different products [30]. According to Kakihana, there are essentially three different kinds of sol-gel routes (i) colloidal sol-gel route (ii) inorganic sol-gel routes and (iii) polymeric sol-gel routes [2]. The primary goal in aU of these sol-gel processes is the preparation of a homogeneous precursor solution from which a homogeneous sohd compound can be obtained. This classification of sol-gel routes is shown in Table 8.1. 

Polymeric sol-gel route In-situ polymerizable complex Organic polymers interconnected by coordinate, van der Waals or hydrogen bonding Polymerization between a-hydro carbo lic acid and polyhydro alcohol in the presence of metal complexes... 

Porous membranes have been prepared by the sol-gel process from a variety of metal oxides and composite oxides. The sol-gel process is divided into two main routes the polymeric sol-gel route and the colloidal sol-gel route [3]. A metal alkoxide or inorganic salt is hydrolyzed and a simultaneous condensation reaction occurs to form polymeric or colloidal sols. In the colloidal sol route. 

ColomerM.T., Jurado J.R. Structural, microstructural, and electrical transport properties 0fTiO2-RuOa ceramic materials obtained by polymeric sol-gel route. Chem. Mater. 2000 12 923-930 Conde A., Duran A., de DamboreneaM. Polymeric sol-gel coatings as protective layers ofaluminium alloys. Progr. Org. Coat. 2003 46 288-296... 

Figure 7-4. Microporous structures of membrane top-layers resulting from the irtteraction of branched clusters in the polymeric sol-gel route (a) ultramicroporous or microporous layers resulting from weakly (interpenetrated) or highly (non-interpenetrated) branched clusters (b) role of surfactants to prevent clusters interpenetration and to allow an increase of pore volume.

Mechanistic studies are particularly needed for the hydrolysis and polymerization reactions that occur in sol-gel processing. Currently, little is known about these reactions, even in simple systems. A short list of needs includes such rudimentary data as the kinetics of hydrolysis and polymerization of single alkoxide sol-gel systems and identification of the species present at various stages of gel polymerization. A study of the kinetics of hydrolysis and polymerization of double alkoxide sol-gel systems might lead to the production of more homogeneous ceramics by sol-gel routes. Another major area for exploration is the chemistry of sol-gel systems that might lead to nonoxide ceramics. 

Figure 2S, Scheme of sol-gel routes. Colloidal sol-gel route and polymeric gel route (Burggraaf, Keizer and van Hassel (1989a, b). 

Quasi-solid state dye-sensitized solar cells (DSCs) have been constructed using a new polymeric ionic fluid as the electrolyte.119 The electrolyte was synthesized by the sol-gel route using MTMSPI+I as the precursor that was made by derivatizing methylimidazolium with triethyoxysilane. Condensation of this material in the presence of formic acid and in the absence of water led to Si-O-Si-O-type polymerization and formation of a polysilsesquioxane-type structure. When this material was mixed with iodine, it served as a redox electrolyte for DSCs. The DSCs made this way are robust and easy to assemble but their efficiency of 3.1% is relatively low. However, possible improvement lies in modification of the organic groups attached to the polysilsesquioxane backbone. 

We give a brief description of the general principles of the sol-gel technique, with special emphasis on fiber making via this technique. Essentially the sol-gel route of making any glass or ceramic involves the formation of the appropriate glass or ceramic structure by chemical polymerization of suitable compounds in... 

Preparation of metal oxides by the sol—gel route proceeds through three basic steps (/) partial hydrolysis of metal alkoxides to form reactive monomers (2) the polycondensation of these monomers to form coUoid-like oligomers (sol formation) and (i) additional hydrolysis to promote polymerization and cross-linking leading to a three-dimensional matrix (gel formation). Although presented herein sequentially, these reactions occur simultaneously after the initial processing stage. 

Organic or inorganic entities as well as polymer particles can also be used as template agents in the preparation of porous ceramic membranes following either the polymeric or the colloidal sol-gel route. The strategy to control microstructure in porous material is illustrated in Fig. 7.13. The template agents are trapped during matrix formation and eliminated in a second step with the aim to define the pore size in the final material. 

M.R. Mohammadi, D.J. Fray, M.C. Cordero-Cabrera, Sensor performance of nanostructured Ti02 thin films derived from particulate sol-gel route and polymeric fugitive agents , Sensors and Acmators B Chemical, 124, 74-83, (2007). 

The preparation of a material from a nanoobject can be performed by the sol-gel route, by which it is included it as a host compound in a polymerizing mixture of water, solvent and a silica source (TMOS (tetramethoxysilane), TEOS (tetraethoxysilane)) (Fig. 6). The resulting solid is a biphasic system at the molecular scale but also sometimes at the macrometer scale. As a consequence the two components can be separated by physical means. 

In real life. Si alkoxides are often available as complexes in solution in their parent alcohol and are typically polymerized to a smaller or larger extent. Even if some monolithic but quite dense aerogel-like materials can be synthesized through ultrasonic-assisted solventless sol-gel routes (Chap. 20) [31, 32], their polymerization is mostly carried out in an organic solvent through simultaneous hydrolysis (2.2) and po ycondensation of water (2.3) and alcohol (2.4) so that water becomes a reactant added in controlled proportion to drive the hydrolysis reaction (2.2). 

The third sol-gel route involves the formation of an organic polymeric network. 

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