Aluminum silicate (or aluminium silicate) is a name commonly applied to chemical compounds which are derived from
aluminium oxide
Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several Aluminium oxide (compounds), aluminium oxides, and specifically identified as alum ...
, Al
2O
3 and
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 ...
, 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 substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...
s or synthetic. Their chemical formulae are often expressed as xAl
2O
3·ySiO
2·zH
2O. It is known as
E number
E numbers, short for Europe numbers, are codes for substances used as food additives, including those found naturally in many foods, such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...
E559.
Main representatives
Andalusite,
kyanite, and
sillimanite are the principal aluminium silicate minerals. The
triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three Phase (matter), phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at ...
of the three
polymorphs is located at a temperature of and a pressure of . These three minerals are commonly used as
index minerals in
metamorphic rocks.
* Al
2SiO
5, (Al
2O
3·SiO
2), which occurs naturally as the minerals
andalusite,
kyanite and
sillimanite which have distinct crystal structures.
* 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, 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'.
The above list mentions
ternary materials (Si-Al-O).
Kaolinite is a quaternary material (Si-Al-O-H). Also called aluminium silicate dihydrate, kaolinite occurs naturally as a mineral. Its formula is Al
2Si
2O
5(OH)
4, (Al
2O
3·2SiO
2·2H
2O).
[Handbook of Inorganic Compounds, Dale L. Perry, Taylor & Francis, 2011, ]
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 , 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 abundant f ...
, 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
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 is also used for an ...
Silicates
Orthorhombic minerals
E-number additives