Tetraethyl orthosilicate, formally named tetraethoxysilane (TEOS), ethyl silicate is the organic

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one elemen ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

Si(OC₂H₅)₄. TEOS is a colorless liquid. It degrades in water. TEOS is the of

orthosilicic acid Orthosilicic acid () is an inorganic compound with the formula . Although rarely observed, it is the key compound of silica and silicates and the precursor to other silicic acids . Silicic acids play important roles in biomineralization and t ...

, Si(OH)₄. It is the most prevalent

alkoxide In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organic substituent. Alkoxides are strong bases and, wh ...

of silicon. TEOS is a tetrahedral molecule. Like its many analogues, it is prepared by

alcoholysis In chemistry, solvolysis is a type of nucleophilic substitution (S1/S2) or elimination where the nucleophile is a solvent molecule. Characteristic of S1 reactions, solvolysis of a chiral reactant affords the racemate. Sometimes however, the st ...

silicon tetrachloride Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colourless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications. Preparation Silic ...

: :SiCl₄ + 4 EtOH → Si(OEt)₄ + 4 HCl where Et is the

ethyl group In organic chemistry, an ethyl group (abbr. Et) is an alkyl substituent with the formula , derived from ethane (). ''Ethyl'' is used in the International Union of Pure and Applied Chemistry's nomenclature of organic chemistry for a saturated t ...

, C₂H₅, and thus EtOH is

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a hyd ...

Applications

TEOS is mainly used as a crosslinking agent in

silicone A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cooking ...

polymers and as a precursor to silicon dioxide in the semiconductor industry. TEOS is also used as the silica source for synthesis of some

zeolites Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a metal ion or H+. These po ...

. Other applications include coatings for carpets and other objects. TEOS is used in the production of

aerogel Aerogels are a class of synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure. The result is a solid with extremely low ...

. These applications exploit the reactivity of the Si-OR bonds. TEOS has historically been used as an additive to alcohol based rocket fuels to decrease the heat flux to the chamber wall of regeneratively cooled engines by over 50%. TEOS is used in

steel casting Steel casting is a specialized form of casting involving various types of steel cast to either final/net or near-net shape. Steel castings are used when iron castings cannot deliver enough strength or shock resistance.Oberg, p. 1332 Examples ...

industry as a inorganic binder and stiffener for making silica-based ceramic molding forms (see also

sodium silicate Sodium silicate is a generic name for chemical compounds with the formula or ·, such as sodium metasilicate , sodium orthosilicate , and sodium pyrosilicate . The anions are often polymeric. These compounds are generally colorless transparent ...

). As inorganic binder for coatings ( passivation) of different materials such as steel, glass, brass, and even wood in order to make surfaces water-, oxygen- and high-temperature resistant. As additive to solid polymers to enchance adhesiveness to glass, steel or wood. As a binder for porcelian teeth crowns. As precursor to siloxanes.

Other reactions

TEOS easily converts to silicon dioxide upon the addition of water: :Si(OC₂H₅)₄ + 2 H₂O → SiO₂ + 4 C₂H₅OH An idealized equation is shown, in reality the silica produced is hydrated. This hydrolysis reaction is an example of a sol-gel process. The side product is ethanol. The reaction proceeds via a series of condensation reactions that convert the TEOS molecule into a mineral-like solid via the formation of Si-O-Si linkages. Rates of this conversion are sensitive to the presence of

acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...

s and bases, both of which serve as

catalyst Catalysis () is the process of increasing the reaction rate, rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the ...

s. The

Stöber process The Stöber process is a chemical process used to prepare silica () particles of controllable and uniform size for applications in materials science. It was pioneering when it was reported by Werner Stöber and his team in 1968, and remains today ...

allows the formation of monodisperse and

mesoporous silica Mesoporous silica is a form of silica that is characterised by its mesoporous structure, that is, having pores that range from 2 nm to 50 nm in diameter. According to IUPAC's terminology, mesoporosity sits between microporous (50 ...

. At elevated temperatures (>600 °C), TEOS converts to silicon dioxide: :Si(OC₂H₅)₄ → SiO₂ + 2 (C₂H₅)₂O The volatile coproduct is

diethyl ether Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable liq ...

Storage

TEOS is stored in hermetic steel vessels at temperatures up to 30°С.

Safety

TEOS has low toxicity by ingestion. While

tetramethoxysilane Tetramethyl orthosilicate (TMOS) is the chemical compound with the formula Si(OCH3)4. This molecule consists of four methoxy groups bonded to a silicon atom. The basic properties are similar to the more popular tetraethyl orthosilicate, which is ...

is highly damaging to eyes since it deposits silica, TEOS is much less so due to lower hydrolysis rate of the ethoxy groups.{{Cite web , url=https://www.mathesongas.com/pdfs/msds/MAT09230.pdf , title=Archived copy , access-date=2015-03-26 , archive-date=2015-04-02 , archive-url=https://web.archive.org/web/20150402095230/https://www.mathesongas.com/pdfs/msds/MAT09230.pdf , url-status=dead

References

External links

NIST Standard Reference Database 69, June 2005 Release: NIST Chemistry WebBook
Ethoxides Silicate esters