Aluminium oxide



Aluminium oxide
Identifiers
CAS number 1344-28-1
Properties
Molar mass 101.96 g/mol
Density 3.97 g cm−3, solid
Melting point

2054 °C

Boiling point

2980 °C [1]

Solubility in water insoluble
Structure
Coordination
geometry 		octahedral
Thermochemistry
Std enthalpy of
formation ΔfHo298 		−1675.7 kJ mol−1
Standard molar
entropy So298 		50.92 J mol−1 K−1
Hazards
MSDS External MSDS
EU classification Not listed.
Flash point non-flammable
Related Compounds
Other anions aluminium hydroxide
Other cations boron trioxide
gallium oxide
indium oxide
thallium oxide
Supplementary data page
Structure and
properties 		εr, etc.
Thermodynamic
data 		Phase behaviour
Solid, liquid, gas
Spectral data MS
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Aluminium oxide is an amphoteric oxide of aluminium with the refractory material.[3]

Natural occurrence

sapphires are gem-quality forms of corundum with their characteristic colors due to trace impurities in the corundum structure.

Properties

Aluminium oxide is an electrical abrasive and as a component in cutting tools.[3]

Aluminium oxide is responsible for metallic aluminium's resistance to weathering. Metallic aluminium is very reactive with atmospheric hardness.

Aluminium oxide was taken off the United States Environmental Protection Agency's chemicals lists in 1988. Aluminium oxide is on EPA's TRI list if it is a fibrous form.[citation needed]

Crystal structure

The most common form of crystalline alumina, α-aluminium oxide, is known as corundum. Corundum has a trigonal Bravais lattice with a space group of R-3c (number 167 in the International Tables). The oxygen ions nearly form a hexagonal close-packed structure with aluminium ions filling two-thirds of the octahedral interstices.

Production

Aluminium Bayer process:

Al2O3 + 3 H2O + 2 NaOH → 2NaAl(OH)4

The Fe2O3 does not dissolve in the base. The SiO2 dissolves as silicate Si(OH)62-. Upon filtering, Fe2O3 is removed. When the Bayer liquor is cooled, Al(OH)3 precipitates, leaving the silicates in solution. The mixture is then calcined (heated strongly) to give aluminium oxide:[3]

2Al(OH)3 + heat → Al2O3 + 3H2O

The formed Al2O3 is alumina.

Uses

  Annual world production of alumina is approximately 45 million tonnes, over 90% of which is used in the manufacture of aluminium metal.[3]. The major uses of speciality aluminium oxides are in refractories, ceramics, polishing and abrasive applications. Large tonnages are also used in the manufacture of zeolites, coating titania pigments and as a fire retardant/smoke suppressant.

In lighting and photography, alumina is a medium for sodium vapor lamps.[citation needed] Aluminium oxide is also used in preparation of coating suspensions in compact fluorescent lamps.

Health and medical applications include it as a material in hip replacements,[3] in water filters (derived water treatment chemicals such as sodium aluminate, are one of the few methods available to filter water-soluble fluorides out of water), and even in toothpaste formulations.

Aluminium oxide is also used for its strength. Most pre-finished wood flooring now uses aluminium oxide as a hard protective Mohs scale of mineral hardness).

It is widely used as a coarse or fine polishing and scratch-repair kits. Its polishing qualities are also behind its use in toothpaste.

Aluminium oxide is widely used in the fabrication of superconducting devices, particularly SQUID), where it is used to form highly resistive quantum tunnelling barriers.

See also

References

This article needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (November 2007)
  1. ^ Mallinckrodt Baker, MSDS. Aluminum Oxide: Material Safety Data Sheet (A28440).
  2. ^ "Aloxite", ChemIndustry.com database, retrieved 24 February 2007
  3. ^ a b c d e Alumina (Aluminium Oxide) – The Different Types of Commercially Available Grades. The A to Z of Materials. Retrieved on 2007-10-27.
 
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