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 tec ...
, 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 organyl 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 ster ...
of
silicon tetrachloride
Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colorless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications. It is a part of the ...
:
: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
The International Union of Pure and Applied ...
, C
2H
5, and thus EtOH is
ethanol
Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
.
Applications
TEOS is mainly used as a crosslinking agent in
silicone
In Organosilicon chemistry, organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (, where R = Organyl group, organic group). They are typically colorless oils or elastomer, rubber ...
polymers and as a precursor to
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
in the semiconductor industry.
TEOS is also used as the silica source for synthesis of some
zeolites
Zeolites are a group of several Microporous material, microporous, crystalline aluminosilicate minerals commonly used as commercial adsorption, adsorbents and Catalysis, catalysts. They mainly consist of silicon, aluminium, oxygen, and have the ge ...
. Other applications include coatings for carpets and other objects. TEOS is used in the production of
aerogel
Aerogels are a class of manufacturing, 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 wit ...
. 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 an inorganic binder and stiffener for making silica-based
ceramic molding file:Old-Babylonian clay mould for ceramic plaques, from Southern Mesopotamia, Iraq.jpg, alt=whitish mould, Clay mould for ceramic (fired clay) plaques, from Southern Mesopotamia, Iraq
Ceramic molding is a versatile and precise manufacturing proces ...
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 tra ...
).
and as an inorganic binder for coatings (
passivation) of different materials such as steel, glass, brass, and wood in order to make surfaces resistant to water, oxygen and high temperatures.
. Further applications of TEOS include its use as an additive to solid polymers to enhance their adhesion to glass, steel or wood,
as a binder for porcelain
teeth crowns,
and as a precursor to
siloxane
In organosilicon chemistry, a siloxane is an organic compound containing a functional group of two silicon atoms bound to an oxygen atom: . The parent siloxanes include the oligomeric and polymeric hydrides with the formulae and . Siloxanes ...
s.
Other reactions
TEOS easily converts to
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
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
An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...
s and bases, both of which serve as
catalyst
Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
s. The
Stöber process
The Stöber process is a chemical process used to prepare silica () particles of controllable and monodisperse, uniform size for applications in materials science. It was pioneering when it was reported by Werner Stöber and his team in 1968, and ...
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 , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
:
: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 with the chemical formula , sometimes abbreviated as . It is a colourless, highly Volatility (chemistry), volatile, sweet-smelling ("ethereal odour"), extremely flammable liquid. It belongs ...
.
Safety
Inhalation of TEOS induces eye and nose irritation, and eye contact with the liquid is irritating. High exposure to TEOS can lead to
pulmonary edema
Pulmonary edema (British English: oedema), also known as pulmonary congestion, is excessive fluid accumulation in the tissue or air spaces (usually alveoli) of the lungs. This leads to impaired gas exchange, most often leading to shortness ...
, but hazards can be reduced by atmospheric humidity and vapor pressure conditions.
[{{Cite web , last=PubChem , title=Ethyl silicate , url=https://pubchem.ncbi.nlm.nih.gov/source/hsdb/534 , access-date=2024-05-15 , website=pubchem.ncbi.nlm.nih.gov , language=en] The mechanism of irritation is similar to that of
tetramethyl orthosilicate
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 i ...
.
References
External links
NIST Standard Reference Database 69, June 2005 Release: NIST Chemistry WebBook
Ethoxy compounds
Silicate esters