Silicon ethoxides

The relative rates of reaction for the hydrolysis and condensation dictate the structure and properties of an alkoxide gel. These reaction rates are schematically described in Figure 8.18 [43] for the example of a silicon ethoxide. In acidic solutions, hydrolysis is achieved by a bimolecular displacement mechanism that substitutes a hydronium ion (H" ) for an alkyl [44]. Under these conditions the hydroljreis is rapid compared to the condensation of the hydrolyzed monomers and promotes the development of larger and more linear molecules, as is described in Figure 8.19. Under basic conditions, hydrolysis occurs by nucleophilic substitution of hydrojgrl ions (OH ) for alkyl groups [45]. Here the condensation is rapid relative to hydrolysis, promoting the precipitation of three-dimensional colloidal particles as shown in Figure 8.17(b) and 8.19. 

FIGURE 8J.8 Schanatic comparison between the rates of hydrolysis and condensation for silicon ethoxide solutions. Redrawn fiom Schaeffer [43],... 

Oxidation of Silicon Ethoxide Vapor in Air at 1100°C Properties Specific surface area 78 mVg, XRD pattern available [1086]. 

PZC/IEP of Silica Obtained by Oxidation of Vapor of Silicon Ethoxide in Air at 1100°C... 

Oxidation of Alkoxides in Air Vapors of aluminum iec-butoxide and silicon ethoxide (premixed or sequentially delivered) were oxidized in air at 700-1400°C for various times (64-170ms) and different. VFOj/SiO, ratio (mass%). 

From Titanium Isopropoxide and Silicon Ethoxide in Ethanol Properties BET specihc surface area 320-357 mVg [2030], specihc surface area 380 ni 7g [2374]. 

Synthetic titania was dispersed in a mixture of 100 cm of ethanol and 1 crn of 2% ammonia. Three additions of silicon ethoxide, 0.6 cm each, were made in 15 min intervals. The suspension was stirred for a further 12 h, and the particles were washed. 

Beilstein Handbook Reference) AI3-15098 BRN 1422225 Dynasil A EINECS 201-083-8 ES 100 ES 28 Ethyl orthosilicate Ethyl silicate Ethyl silicate, ((EtO)4Si) Etylu krzemian HSDB 534 NSC 4790 Orthosilicic acid, tetraethyl ester Silane, tetraethoxy- Silester Silicate d ethyle Silicate tetraethylique Silicic acid, tetraethyl ester Silicic acid H4Si04), tetraethyl ester Silicon ethoxide Silicon tetraethoxide Silikan L TEOS Tetraethoxysilane ... 

By improving the different parameters that play a role in monolithicity, preparation refinements can be found. A base-catalyzed alkoxide solution leads to fine particles of silica with a specific surface area of 250-350 m2/g. This powder is mixed with fluorinated silicon ethoxide solution. Both filler and fluorine allow one to obtain monolithic silica gels [60]. 

Aerogels of titania, titania-silica, and titania-vanadia were prepared with titanium butoxide, silicon ethoxide, and vanadium triisopropoxide as precursors. The titania and titania-silica aerogels were then used as supports for vanadia, introduced by the incipient wetness impregnation of vanadium triisopropoxide and the subsequent calcination at 773 K. 

Hydroxide suspensions of mullite with partially stabilized zirconia were prepared from metal alkoxide starting materials. Zirconium isoamyloxide and yttrium isopropoxide were mixed in the proper proportions for the partially stabilized zirconia. Aluminum isopropoxide and silicon ethoxide were added in the proper proportions for mullite. These solutions were refluxed for 4 to 8 h and then hydrolyzed to a pH of 0.5 using HNO3. The solutions were then neutralized to a pH of 8 using NH4OH. The resulting suspensions then contained the proper amount of each component as a hydroxide to form the mullite partially-stabilized zirconia matrix materials. With MgO as a stabilizer, procedures were identical to the above, except that MgO ethoxide was used instead of yttrium isopropoxide. Batch sizes were 25 to 100 g of final material. 

Fig. 6. Suggested reaction mechanism for silicatein-mediated catalysis of polysiloxane synthesis from silicon ethoxides at neutral pH. The mechanism suggested is closely analogous to that known for the structurally similar proteolytic enzymes explanation in text. Reprinted from [7],...

The reaction of silicon ethoxide with acetic anhydride was investigated as early as 1866 by Friedel and Crafts who reported the preparation of triethoxy silicon monoacetate. The reaction has been reinvestigated by Post and Hofrichter as well as by Narain and Mehrotra. ... 

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