Aluminium oxide
:
Alumina redirects here. It may also refer to
Alumina Limited.
| Aluminium oxide | | |
| General |
|---|
| Other names | Alumina,
Aluminium(III) Oxide |
| Molecular formula | Al2O3 |
| Molar mass | 101.96 g/mol |
| CAS number | [] |
| Properties |
|---|
| Density and phase | 3.97 g/cm3, solid |
| Solubility in water | Insoluble. |
>| Melting point2054°C |
| Boiling point | ~3000°C |
| Thermal Conductivity | 18 W/m·K |
| Structure |
|---|
Coordination
geometry | Octahedron. |
| Crystal structure | Cubic. |
| Thermodynamic data |
|---|
Standard enthalpy
of formation Î"fHosolid | -1675.7 kJ/mol |
Standard molar entropy
Sosolid | 50.92 J/(mol K) |
| Heat capacity Cp | 79.04 J/(mol K) |
| Hazards |
|---|
| MSDS | External MSDS |
| EU classification | Not listed. |
| NFPA 704 | |
| Flash point | Non-flammable. |
| Supplementary data page |
|---|
Structure and
properties | n, εr = 9.5, etc.
Refractive index at
different wavelengths |
Thermodynamic
data | Phase behaviour
Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds |
|---|
| Other s | Aluminium hydroxide |
| Other s | Boron trioxide
Gallium oxide
Indium oxide
Thallium oxide |
| Related compounds | Aluminium hydroxide |
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 a
chemical compound of
aluminium and
oxygen with the
chemical formula 23. It is also commonly referred to as
alumina in the
mining,
ceramic and
materials science communities.
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.
Aluminium oxide is responsible for metallic aluminium's resistance to
weathering. Metallic aluminium is very reactive with atmospheric
oxygen, and a thin
passivation 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. A number of
alloys, such as
aluminium bronzes, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance.
Aluminium oxide was taken off the
EPA's chemicals lists in
1988.
Corundum is the naturally occurring
mineral form of aluminium oxide.
Rubies and
sapphires are gem-quality forms of corundum with their characteristic colors due to trace impurities in the corundum structure.
Aluminium
oxide, also known as alumina, is the main component of
bauxite, the principal
ore of
aluminium. The largest manufacturers in the world of alumina are Alcoa, Alcan and Rusal. Companies which specialise in the production of speciality aluminium oxides and aluminium hydroxides include Alcan and
Almatis. The bauxite ore is made up of impure Al
2O
3, Fe
2O
3, and SiO
2. These are then purified by the Bayer Process:
Al
2O
3 + 3H
2O + 2NaOH + heat â†' 2NaAl(OH)
4The Fe
2O
3 does not dissolve in the base. The SiO
2 dissolves as silicate Si(OH)
6-6. Upon filtering, Fe
2O
3 is removed. With the addition of an acid, Al(OH)
3 precipitates. The silicate remains in solution. Then:
2Al(OH)
3 + heat â†' Al
2O
3 + 3H
2O
The formed Al
2O
3 is alumina.
In 1961, GE developed "
Lucalox", a transparent alumina used in
sodium vapor lamps.
In August
2004, scientists in the
United States working for
3M developed a technique for making an
alloy of aluminium oxide and
rare earth elements to produce a strong
glass called
transparent alumina.
Annual world production of alumina is approximately 60 million tonnes, over 90% of which is used in the manufacture of aluminium metal. Major uses for aluminium hydroxide include the manufacture of water treatment chemicals such as aluminium sulphate, Poly Aluminium Chloride and sodium aluminate. Large tonnnages are also used in the manufacture of zeolites, coating titania pigments and as a fire retardants/smoke suppressant. The major uses of speciality aluminium oxides are in refractories, ceramics, polishing and abrasive applications. Minor uses include use in toothpaste formulations, and as a medium for
chromatography. In this latter application alumina is available in the so-called
Brockmann types neutral, basic (
pH 9.5) and acidic (pH 4.5 when in water). Aluminium oxide also used in preparation of coating suspensions in
compact floroscent light lamps.
*
International Chemical Safety Card 0351*
PhysicsWeb article on Transparent alumina*
alumina grades commercial supplierAlcan * [
1]Alcan Specialty Aluminas *[
2]
