Colloidal sol-gel route

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

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. 

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. 

Colloidal sol-gel route Colloid Particles interconnected by van der Waals or hydrogen bonding Mostfy from oxide or hydroxide sok... 

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. 

Figure 7-12. Synthesis and thermal pathways followed for the preparation of a -alumina mesoporous membrane by the colloidal sol-gel route.

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 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. ... 

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 main problem raised by these preparations is to adapt the proeedure to the solvent compatible with the embedding materials. Both the colloids and the triflate derivatives are soluble in a limited number of solvents, mostly not the alcohols generally used in such preparations. Therefore, the protocol procedure described in this contribution followed a specific sol-gel route for each hybrid catalyst. During these preparations we investigated i) the formation of the sol by hydrolysis of the alcoxide in the selected solvent ii) the addition of the stabilized colloid or triflate derivative in the formed sol iii) the addition of a surfactant in the case of triflates iv) the gelation, and finally v) the drying and calcining of the materials. 

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 colloid-like oligomers (sol formation) and (3) 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. 

Because the interparticle interactions in those sols are dominated by physical forces such as van der Waals forces, electrostatic forces and Brownian motion, the colloidal sol-gel method is termed a physical gel route [2]. The next two sections are restricted to two chemical gel routes (i) inorganic polymerization and (ii) organic polymerizahon. 

Route C Colloidal Sol-Gel Synthesis from Inorganic Precursors... 

Four different sol-gel routes can be used to prepare various kinds of sulfide materials. Sol-gel synthesis of sulfides usually follows colloidal chemical processing, except route A. It is very important to control the sizes of colloidal particles. As-S and Ge-S glass films could be prepared by sol-gel processing for planar waveguides, for IR optical applications. The sol-gel synthesis of multicomponent sulfide glasses needs further study, perhaps based on the Ge-S system. Route D can also be used for synthesis of multicomponent sulfides. 

The sol-gel process is one of the most appropriate methods for the preparation of functional oxide layers. There are two sol-gel routes one is based on colloid chemistry in aqueous media, and the other on the chemistry of metal organic precursors in organic solvents. Figure 2.8 shows the sol-gel process for membrane formation. 

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