Aluminium silicate

Aluminium silicate (or aluminum silicate) is a name commonly applied to chemical compounds which are derived from aluminium oxide, Al2O3 and silicon dioxide, SiO2 which may be anhydrous or hydrated, naturally occurring as minerals or synthetic. Their chemical formulae are often expressed as xAl2O3·ySiO2·zH2O. It is known as E number E559.

This article is about neutral chemical compounds composed solely of aluminium, silicon, and oxygen. For related charged compounds containing counterions, see Aluminosilicate.
Aluminium silicate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.032.036
E number E559 (acidity regulators, ...)
UNII
  • InChI=1S/2Al.O3Si.2O/c;;1-4(2)3;;/q2*+1;-2;; ☒N
    Key: PZZYQPZGQPZBDN-UHFFFAOYSA-N ☒N
  • O=[Al]O[Si](=O)O[Al]=O
Properties
Al
2SiO
5
Molar mass 162.0456 g mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Main representatives
Phase diagram of Al2SiO5
(aluminosilicates).[2]

Andalusite, kyanite, and sillimanite are the principal aluminium silicate minerals.[3][4][5] The triple point of the three polymorphs is located at a temperature of 500 °C (932 °F) and a pressure of 0.4 GPa (58,000 psi). These three minerals are commonly used as index minerals in metamorphic rocks.

  • Al2SiO5, (Al2O3·SiO2), which occurs naturally as the minerals andalusite, kyanite and sillimanite which have distinct crystal structures.
  • Al2Si2O7, (Al2O3·2SiO2), called metakaolinite, formed from kaolin by heating at 450 °C (842 °F).[6]
  • Al6Si2O13, (3Al2O3·2SiO2), the mineral mullite, the only thermodynamically stable intermediate phase in the Al2O3-SiO2 system at atmospheric pressure.[7] This also called '3:2 mullite' to distinguish it from 2Al2O3·SiO2, Al4SiO8 '2:1 mullite'.
  • 2Al2O3·SiO2, Al4SiO8 '2:1 mullite'.[7]

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 Al2Si2O5(OH)4, (Al2O3·2SiO2·2H2O).[6]

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, Al2O3 and silica, SiO2. Temperature resistance increases as the % alumina increases. These fibrous materials can be encountered as loose wool, blanket, felt, paper or boards.[8]

References
  1. Whitney, D.L. (2002). "Coexisting andalusite, kyanite, and sillimanite: Sequential formation of three Al2SiO5 polymorphs during progressive metamorphism near the triple point, Sivrihisar, Turkey". American Mineralogist. 87 (4): 405–416. doi:10.2138/am-2002-0404.
  2. Whitney, D.L. (2002). "Coexisting andalusite, kyanite, and sillimanite: Sequential formation of three Al2SiO5 polymorphs during progressive metamorphism near the triple point, Sivrihisar, Turkey". American Mineralogist. 87 (4): 405–416. doi:10.2138/am-2002-0404.
  3. "Andalusite, Handbook of Mineralogy" (PDF). Archived (PDF) from the original on 2012-05-16.
  4. "Kyanite" (PDF). Handbook of Mineralogy. Archived (PDF) from the original on 2012-02-24.
  5. "Sillimanite" (PDF). Handbook of Mineralogy. Archived (PDF) from the original on 2011-11-19.
  6. Handbook of Inorganic Compounds, Dale L. Perry, Taylor & Francis, 2011, ISBN 978-1-4398-1461-1
  7. Ceramic and Glass Materials: Structure, Properties and Processing, James F. Shackelford, R. H. Doremus, Springer, 2008, ISBN 978-0-387-73361-6
  8. Concise Encyclopedia of Composite Materials, ed. Anthony Kelly, MIT Press, 1989, ISBN 0-262-11145-4
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