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 element ...
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(OC
2H
5)
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 ...
, 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, whe ...
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 ste ...
of
silicon tetrachloride:
:SiCl
4 + 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 ...
, C
2H
5, 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 ...
.
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, cookin ...
polymers and as a precursor to
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
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 p ...
. 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
A siloxane is a functional group in organosilicon chemistry with the Si−O−Si linkage. The parent siloxanes include the oligomeric and polymeric hydrides with the formulae H(OSiH2)''n''OH and (OSiH2)n. Siloxanes also include branched compoun ...
.
Other reactions
TEOS easily converts to
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
upon the addition of water:
:Si(OC
2H
5)
4 + 2 H
2O → SiO
2 + 4 C
2H
5OH
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 se ...
s and bases, both of which serve as
catalyst
Catalysis () is the process of increasing the 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 catalyst recyc ...
s. The
Stöber process allows the formation of
monodisperse and
mesoporous silica.
At elevated temperatures (>600 °C), TEOS converts to
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
:
:Si(OC
2H
5)
4 → SiO
2 + 2 (C
2H
5)
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 li ...
.
Storage
TEOS is stored in hermetic steel vessels at temperatures up to 30°С.
Safety
TEOS has low toxicity by ingestion. While
tetramethoxysilane 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