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Published in Eli Ruckenstein, Hangquan Li, Chong Cheng, Solution and Surface Polymerization, 2019
To obtain mechanically and thermally improved polymer materials, hybrids, consisting of an organic polymer matrix and inorganic oxide, have been prepared and investigated.1–8 A low-temperature sol-gel process of an organometallic precursor, such as silicate, titanate, or aluminate, has been a convenient technique for the synthesis of the inorganic constituent of these hybrids. Tetraethylorthosilicate (TEOS) is the most common precursor employed because it yields a glassy silica network by hydrolysis and condensation under mild conditions. Some of these hybrids prepared by in situ hydrolysis and polycondensation of silicon alkoxide in the presence of an organic polymer exhibited high improvements in mechanical properties.9,10 Recently, some interesting hybrids of silicon oxide and conjugated polymers have been reported that exhibited improved electroluminescence efficiency.11,12 When silicon oxide was employed in the preparation of light-emitting-diode devices, their durability was improved.11,12
Sol–Gel Processing
Published in M. N. Rahaman, Ceramic Processing and Sintering, 2017
The most commonly used precursors for the sol–gel processing of silica are tetraethoxysilane, Si(OC2H5)4, abbreviated TEOS, which is also referred to as tetraethylorthosilicate or silicon tetraethoxide, and tetramethoxysilnae, Si(OCH3)4, abbreviated TMOS, which is also referred to as tetramethyorthosilicate or silicon tetramethoxide. The physical properties of these two precursors are given in Table 5.3.
Sol–Gel Processing
Published in Mohamed N. Rahaman, Ceramic Processing, 2017
The most commonly used precursors for the sol–gel processing of silica are tetraethyoxysilane, Si(OC2H5)4, abbreviated TEOS, which is also referred to as tetraethylorthosilicate or silicon tetra- ethoxide, and tetramethoxysilane, Si(OCH3)4, abbreviated TMOS, which is also referred to as tetramethyorthosilicate or silicon tetramethoxide. The physical properties of these two precursors are given in Table 5.3.
Green synthesis of SiO2 from Equisetnm arvense plant for synthesis of SiO2/ZIF-8 MOF nanocomposite as photocatalyst
Published in Journal of Coordination Chemistry, 2023
Babak Azari, Afshin Pourahmad, Babak Sadeghi, Masoud Mokhtary
TEOS (tetraethyl orthosilicate)/TMOS (tetramethyl orthosilicate) is used to produce silica powders with extremely high purity [23]. However, their preparations are very expensive, which limits their usage. Silica-rich plant materials such as rice husk [24], wheat hull and wheat hull ash [25], bagasse ash [26], lemon grass [27], etc. can be used as an alternative source to prepare purified silica in an almost amorphous form, considered as a cheap source for the production of various silicon-based materials.
Titania-silica Composite with Photocatalytic Properties and Its Application on Brazilian Granite and Sandstone
Published in International Journal of Architectural Heritage, 2023
Danielle Grossi, Dolores Ribeiro Ricci Lazar, Eliane Aparecida Del Lama, Valter Ussui
Tetraethyl orthosilicate, also known as TEOS, is one of the most commonly used products for consolidating stone, mainly sandstone and granite. It is resistant to ultraviolet radiation, which makes it ideal for use in outdoor areas (Wheeler 2005). It forms relatively strong silicon-oxygen bonds that have high thermal and oxidative stability, presenting good results on stones with moderate degradation. On very degraded stones, however, this product fails to show a good consolidation capacity (Price 2006). The deposition of silica gel via the application of TEOS causes two simultaneous reactions. The first is hydrolysis of the alkoxy group, which separates the ethanol molecules. This reaction can be accelerated by either acid or alkaline catalysis, used in the preparation of most commercial products. Water is essential to this reaction and the subsequent formation of silica gel. Due to this characteristic, TEOS is not effective in arid climates, because the water may evaporate before the gel forms. The second reaction is the condensation of unstable silanols (-Si-OH) to form an amorphous gel (Snethlage and Sterflinger 2011). A major advantage of TEOS is that the other product formed in the reaction is ethanol, which evaporates completely and causes no damage to the stone. Some types of TEOS have water-repellent properties due to the presence of alkyl groups (including methyl, ethyl, i-butyl, and n-octyl) attached directly to silicon. In general, the alkyl groups, formed by siloxanes of varying degrees of cross-linking and molecular weights, may contain reactive alkoxy groups. Diluents include water and organic solvents, such as alcohol or mineral spirits. When water-based, these products interfere with curing of joints, grouts, pointing, plastic repairs and alkoxysilane-based consolidants. Because of this, a pause time of 8 weeks is recommended between the application of the consolidant and the water repellent. The advantages of using a water-repellent consolidant include reduced maintenance time and cost (Wheeler 2005).