Tetraethyl orthosilicate

• Tetraethylorthosilicate
• Tetraethyl
• Tetraethoxysilane
• Of silicic acid
• Ethyl silicate
• TEOS

Colorless liquid with a pungent odor

Liquid

0.94 g · cm -3

-85.5 ° C

168 ° C.

Insoluble in water

1.3928 (20 ° C)

Attention

10 ml · m -3, 85 mg · m-3

6270 mg · kg -1 ( LD50, rat, oral)

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Tetraethylorthosilicate, TEOS briefly known as tetraethoxysilane, of silicic acid or ethyl silicate, is an ethyl ester of ortho silicic acid.

Use

It is used in sol-gel processes, as the silica precursor for the production of the colloidal sol-gel systems. In water, the compound is substantially insoluble. A mixture of ethanol and water is therefore mostly used as the reaction medium. In neutral TEOS hydrolyzed in water very slowly (several hours) to ortho silicic acid and ethanol:

The ortho silicic acid formed further decomposes into silica by formation of Si -O -Si bonds and release of water:

Significantly faster the hydrolysis is carried out in acidic or alkaline, as both significantly catalyze the reaction. In ammoniacal monodisperse silica particles can be obtained from a TEOS / ethanol mixture which contains some water. The so-called Stöber process can be adjusted by the choice of concentrations, temperatures, and the amount of ammonia, the particle size in the range of about 20-500 nm. The method is used for example for the production of photonic crystals and artificial opals.

Production

TEOS is prepared industrially by alcoholysis of silicon tetrachloride with ethanol.