Aluminium silicate (or aluminum silicate) is a name commonly applied to chemical compounds which are derived from
aluminium oxide, Al
2O
3 and
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 ...
, SiO
2 which may be
anhydrous or hydrated, naturally occurring as
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
s or synthetic. Their chemical formulae are often expressed as xAl
2O
3·ySiO
2·zH
2O. It is known as
E number E559.
Examples
* Al
2SiO
5, (Al
2O
3·SiO
2), which occurs naturally as the minerals
andalusite
Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5. This mineral was called andalousite by Delamétehrie, who thought it came from Andalusia, Spain. It soon became clear that it was a locality error, and that the spe ...
,
kyanite
Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks gener ...
and
sillimanite
Sillimanite is an aluminosilicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist Benjamin Silliman (1779–1864). It was first described in 1824 for an occurrence in Chester, Connecticut.
Occurrence ...
which have different crystal structures.
* Al
2Si
2O
5(OH)
4, (Al
2O
3·2SiO
2·2H
2O), which occurs naturally as the mineral
kaolinite and is also called aluminium silicate dihydrate.
[Handbook of Inorganic Compounds, Dale L. Perry, Taylor & Francis, 2011, ] It is a fine white powder and is used as a filler in paper and rubber and also used in paints.
* Al
2Si
2O
7, (Al
2O
3·2SiO
2), called metakaolinite, formed from kaolin by heating at .
* Al
6Si
2O
13, (3Al
2O
3·2SiO
2), the mineral
mullite
Mullite or porcelainite is a rare silicate mineral formed during contact metamorphism of clay minerals. It can form two stoichiometric forms: 3 Al2 O32 SiO2 or 2Al2O3 SiO2. Unusually, mullite has no charge-balancing cations present. As a result, th ...
, the only thermodynamically stable intermediate phase in the Al
2O
3-SiO
2 system at atmospheric pressure.
[Ceramic and Glass Materials: Structure, Properties and Processing, James F. Shackelford, R. H. Doremus, Springer, 2008, ] This also called '3:2 mullite' to distinguish it from 2Al
2O
3·SiO
2, Al
4SiO
8 '2:1 mullite'.
* 2Al
2O
3·SiO
2, Al
4SiO
8 '2:1 mullite'.
Aluminium silicate composite materials, fibres
Aluminium silicate is a type of fibrous material made of aluminium oxide and silicon dioxide, (such materials are also called aluminosilicate fibres). These are glassy solid solutions rather than chemical compounds. The compositions are often described in terms of % weight of
alumina, Al
2O
3 and
silica
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 ...
, SiO
2. Temperature resistance increases as the % alumina increases. These fibrous materials can be encountered as loose wool, blanket, felt, paper or boards.
[Concise Encyclopedia of Composite Materials, ed. Anthony Kelly, MIT Press, 1989, ]
References
External links
Aluminum silicatesat the University of Waterloo, Canada
{{Authority control
Silicates
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name i ...
Silicates
Orthorhombic minerals
E-number additives