Alumina - Definition


Alumina - Definition

**Properties**
General
Name	Aluminium oxide Aluminum oxide (US)
Chemical Formula	Al₂O₃
Appearance	White crystalline powder or solid
Physical
Formula weight	101.96 amu
Melting point at SP	2303 K
Boiling point at SP	3250 K
Density	3.97 &times 10³ kg/m³
Crystal structure	Trigonal (hex)
Solubility	Insoluble
Thermochemistry
Δ_fH⁰_liquid	−1620.57 kJ/mol
Δ_fH⁰_solid	−1675.69 kJ/mol
S⁰_{liquid, 1 bar}	67.24 J/mol·K
S⁰_solid	50.9 J/mol·K
Safety
Ingestion	Low hazard
Inhalation	May cause irritation or lung damage
Skin	Low hazard
Eyes	Low hazard
SI units were used where possible.

Aluminium oxide (or aluminum oxide) (Al₂O₃) is a chemical compound of aluminium and oxygen. It is also referred to as alumina for short, a name commonly used in the mining, ceramic and materials science communities.

Aluminium oxide is the main component of bauxite, the principal ore of aluminium. Industrially, bauxite is purified to aluminium oxide via the Bayer process, and then converted to aluminium metal in the Hall-Heroult process.

The gems ruby and sapphire are mostly aluminium oxide, given their characteristic colors by trace impurities.

Aluminium oxide is responsible for metallic aluminium's resistance to weathering. Metallic aluminium is very reactive with atmospheric oxygen, and a thin layer of aluminium oxide quickly forms on any exposed aluminium surface. This layer protects the metal from further oxidation. The thickness and properties of this oxide layer can be enhanced using a process called anodising.

Aluminium oxide is an excellent thermal and electrical insulator. In its crystalline form, called corundum, its hardness makes it suitable for use as an abrasive and as a component in cutting tools.

Powdered aluminium oxide is frequently used as a medium for chromatography.

In August, 2004, scientists in the United States working for 3M developed a technique for making an alloy of alumina and rare earth elements to produce a strong glass.

Aluminium oxide was taken off the EPA's chemicals lists in 1988.

See also