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 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 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
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 ...
:
:SiCl
4 + 4 EtOH → Si(OEt)
4 + 4 HCl
where Et is the
ethyl group, 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 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. 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 industry as a inorganic binder and stiffener for making silica-based
ceramic molding
The ceramic molding process is a production method which guarantees the precision required, and also gives a good surface finish, using a high temperature method to better structure and shape parts. This process also gives a low grade of toleration ...
forms (see also
sodium silicate).
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 compou ...
.
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
acids 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
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
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