Tetra ethoxysilane

Further examination has shown that the acid content should be small in order for the solution to become spinnable in the course of hydrolysis and polycondensation. It has been found (4 ) that very large concentrations at more than 0.15 in the [HCl]/[Metal alkoxide] ratio of acid catalyst produce round-shaped particles in the tetra-ethoxysilane (7) and tetramethoxysilane solutions, and so no spinnability appears. 

The sol-gel process involves hydrolysis of alkoxide precursors under acidic or basic conditions, followed by condensation and polycondensation of the hydroxylated units, which lead to the formation of porous gel. Typically a low molecular weight metal alkoxide precursor molecule such as tetramethoxy silane (TMOS) or tetra ethoxysilane (TEOS) is hydrolyzed first in the presence of water, acid catalyst, and mutual solvent... 

Synonyms Tetraethyl orthosilicate tetra-ethoxysilane ethyl orthosilicate silicic acid, tetraethyl ester... 

Tetraalkoxysilanes (usually tetramethoxysilane, TMOS, bp 121 °C, or tetra-ethoxysilane, TEOS, bp 169 °C) for hydrolytic gelling can be made by reaction of SiCl4 (Section 17.8.2) with the relevant alcohol ... 

Okubo et al. [40,41] treated Vycor glass membranes with tetra-ethoxysilane which was initially adsorbed and finally decomposed on the pore wall by heat treatment. The pore size was expected to be decreased by this treatment. As a result of this modification the permeation decreased and the permeation as a function of temperature increased (compared with that of the non-modified glass) for the gases He, O2, N2, Ar, H2 and CO2 and became activated. The authors argue that surface diffusion carmot explain this result and suggest that the modified system is in the transition region of Knudsen to molecular sieving (micropore diffusion). 

T. Okubo and H. Inoue, Single gas permeation through porous glass modified with tetra ethoxysilane. AIChE /., 35 (1989) 845-848. 

Preliminary studies indicated that extensive water was formed as a reaction product when the metal-organic compounds were decomposed via an oxygen discharge. This water could be chemically incorporated into the oxide films when the substrates were held below a certain temperature which depended on the organic evaporation rate and the hygroscopic nature of the substrate. For instance, with NaCl substrates, the silica films were found to be free of water above 180°C. with a tetra-ethoxysilane evaporation rate of 0.015 cc./hour (5). The presence of silicic acid was detected below 180°C. by infrared transmission studies. 

Clays have also been pillared with polyoxometalate ions, such [(PW11VO40)4-].261 Other layered materials can also be pillared. Zirconium phosphate has been pillared with chromium(III) oxide.262 A layered titanate has been pillared with silica.263 The need for a separate pillaring step has been avoided in the preparation of some porous lamellar silicas which are structurally similar to pillared clays.264 Eight to twelve carbon diamines were used with tetra-ethoxysilane in ethanol with added water to make them in 18 h at room temperature. The template was recovered by solvent extraction before the silica was calcined. 

Another approach is the nucleophilic displacement of chloride from chloro-propyl-silica with a pyridine-substituted porphyrin. These materials are active in the epoxidation of alkenes, where iodosylbenzene is the preferred oxidant, and in the oxidation of alkanes to alcohols and ketones. The copolymerisation of a porphyrin containing four attached trimethoxysilane groups with tetra-ethoxysilane, leading to an active hybrid silica-porphyrin, offers another route to these important catalysts. 

In order to understand the roles that biomolecules play in the fabrication of nano- and micro-structured biosilica, organic material associated with biosilica was identified, isolated and studied. In addition to some earlier studies, the following recent findings are of particular importance. Several proteins isolated from plants, diatom species (silafFins) and sponges (silicateins) have previously been shown to facilitate the in vitro polymeri tion of silica from a silicon catecholate complex, tetramethoxysilane (TMOS) and tetra-ethoxysilane (TEOS), respectively. Bioextracts from plants Equisetum talmateia and Equisetum arvense have been isolated from biosilica. These... 

From the viscosity versus time data collected for each system, the molecular weight and cluster size can be calculated as a function of time to the gel point using the equations derived in the first few sections of this chapter. From these calculations, it is possible to model the evolution of the gel structure dynamically. In Fig. 11, the evolution of an HF-catalyzed gel as a function of time is presented, starting with the unhydrolyzed monomer molecule tetra-ethoxysilane at time zero and proceeding, in stages, to the final gel structure at 16 minutes. Also presented is the effect of normal drying, in which the fractal characteristics of the individual clusters are all but eliminated. 

TEOS Tetraethyl orthosiUcate Si(OC2H5)4, also termed silicon tetra ethoxysilane a common Si02 sol-gel precursor... 

The reverse microemulsion method is based on the controlled hydrolysis of tetra-ethoxysilane (TEOS) molecules and their ammonia catalysed condensation like the Stober method, but the reaction milieu is in this case a stable and macroscopically isotropic dispersion of a surfactant and water in a hydrocarbon. In this system the hydrolysis is confined inside the aqueous nuclei where precursors condense to form the nanoparticles. Optimized synthetic protocols and experimental conditions allow one to obtain nanoparticle samples in the dimensional range of about 15-200 nm [70, 76] (Fig. 11). 

Figure 3-23 Octahedron produced by the hydrolytic condensation of tetra-ethoxysilane (TEOS).

IR spectra were used to study a-Si02 films produced by plasma-enhanced CVD from an SiH4-02 mixture. Film thicknesses were measured in terms of bands at 800 and 1050 cm" " IR bands due to vSi-OH and vSi-O-Si were used to characterise Si02 films deposited from 02/tetra-ethoxysilane plasmas. ... 

Heunish analysed the thermal decomposition products of tetra-ethoxysilane (ethylsilicate) on columns comprising polypropylene glycol on silanized Chromosorb P at 40°C using a thermal conductivity detector. The main impurities in the sample were ethyl alcohol, acetaldehyde, ethylene and ethane. 

The most common tetraalkoxysilanes used in the sol-gel process are tetra-ethoxysilane (Si(OC2H5)4) and tetramethoxysilane (Si(OCHj)4), which are abbreviated in the literature as TEOS and TMOS, respectively. The traditional method of preparing tetraalkoxysilanes is by reacting tetra-chlorosilane with alcohol [3]. When anhydrous ethanol is used, the product is TEOS with hydrogen chloride as a by-product ... 

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