tetraethyl orthosilicate; ethyl silicate; silicic acid tetraethyl ester; silicon ethoxide; TEOS; tetraethyl silicate
3D model (JSmol)
|Molar mass||208.33 g mol−1|
|Density||0.933 g/mL at 20 °C|
|Melting point||−77 °C (−107 °F; 196 K)|
|Boiling point||168 to 169 °C (334 to 336 °F; 441 to 442 K)|
|reacts with water, soluble in ethanol, and 2-propanol|
|Vapor pressure||1 mmHg|
|Main hazards||Flammable, Harmful by inhalation|
|Flash point||45 °C (113 °F; 318 K)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|6270 mg/kg (rat, oral)|
LCLo (lowest published)
|1000 ppm (rat, 4 hr)
700 ppm (guinea pig, 6 hr)
1740 ppm (guinea pig, 15 min)
1170 ppm (guinea pig, 2 hr)
|US health exposure limits (NIOSH):|
|TWA 100 ppm (850 mg/m3)|
|TWA 10 ppm (85 mg/m3)|
IDLH (Immediate danger)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Tetraethyl orthosilicate, formally named tetraethoxysilane and abbreviated TEOS, is the chemical compound with the formula Si(OC2H5)4. TEOS is a colorless liquid that degrades in water. TEOS is the ethyl ester of orthosilicic acid, Si(OH)4. It is the most prevalent alkoxide of silicon.
- SiCl4 + 4 EtOH → Si(OEt)4 + 4 HCl
TEOS is mainly used as a crosslinking agent in silicone 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. 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 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 acids and bases, both of which serve as catalysts. The Stöber process allows the formation of monodisperse and mesoporous silica.
At elevated temperatures (>600 °C), TEOS converts to silicon dioxide:
- Si(OC2H5)4 → SiO2 + 2 (C2H5)2O
The volatile coproduct is diethyl ether.
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