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{{Chembox new| Name = Aluminium oxide| ImageFile = Corundum-unit-cell-3D-balls.png| Section1 = {{Chembox Identifiers| CASNo = 1344-28-1 -->
| Section2 = {{Chembox Properties| MolarMass = 101.96 g/mol| Density = 3.97 g cm−3, solid| Solubility =
insoluble| MeltingPt = 2054 °C| BoilingPt = 2980 °C -->
| Section3 = {{Chembox Structure| Coordination = [octahedral -->
| Section4 = {{Chembox Thermochemistry| DeltaHf = −1675.7 kJ mol−1| Entropy = 50.92 J mol−1 K−1 -->
| Section7 = {{Chembox Hazards| EUClass = Not listed.| FlashPt = non-flammable -->
| Section8 = {{Chembox Related| OtherAnions = aluminium hydroxide
[gallium oxide
indium oxide
thallium oxide-->-->
Aluminium oxide is an
amphoteric oxide of
aluminium with the chemical formula 23. It is also commonly referred to as
alumina in the
mining, ceramic and
materials science communities.
Properties
Aluminium oxide is an electrical
Electrical insulation but has a relatively high thermal conductivity. In its most commonly occurring crystalline form, called
corundum or α-aluminum oxide, 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 alumina 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. The alumina generated by anodising is typically amorphous, but discharge assisted oxidation processes such as plasma electrolytic oxidation result in a significant proportion of crystalline alumina in the coating, enhancing its hardness.
Aluminium oxide was taken off the
United States Environmental Protection Agency's chemicals lists in 1988. Aluminum oxide is on EPA's TRI list if it is a fibrous form.
Natural occurrence
Corundum is the naturally occurring
crystalline form of aluminium oxide.
ruby and
sapphires are gem-quality forms of corundum with their characteristic colors due to trace impurities in the corundum structure.
Crystal structure
The most common form of crystalline alumina, α-aluminum oxide, is known as corundum and has a
close-packing (HCP) lattice structure.
Industrial Fabrication Process
Aluminium oxide, also known as alumina, is the main component of
bauxite, the principal ore of
aluminium. The largest manufacturing 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, Inc.. The bauxite ore is made up of impure Al2O3, Fe2O3, and SiO2. These are then purified by the
Bayer process:
Al2O3 + 3H2O + 2NaOH + heat → 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. The silicate remains in solution. Then:
2Al(OH)3 + heat → Al2O3 + 3H2O
The formed Al2O3 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.
As discussed above (in the "Properties" section), alumina can be grown as a
coating on aluminium by
anodising or by plasma electrolytic oxidation.
Uses
Annual world production of alumina is approximately 65 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 tonnages 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 is also used in preparation of coating suspensions in compact fluorescent lamps.
Al2O3 is also used in fluoride water filters. It is one of the few methods available to filter water soluble fluorides out of water.
Aluminum oxide is also used as a material in
hip replacements.
Commercial uses
Because of aluminium oxide's position on the
Mohs scale of mineral hardness, (9), it is very widely used as an abrasive as a significantly less expensive replacement for industrial diamonds. Many types of
sandpaper use aluminium oxide crystals. In addition, its low heat retention and specific heat makes it widely used in almost all grinding operations, particularly metalworking tools.
Aluminium oxide is used in certain
CD/
DVD cleaning kits. Alumina will polish the media surface, leaving it clean and relatively
scratch-free.
Alumina is also the
byproduct of hydrogen generation for the purposes of fuel generation when water is added to pellets comprised of aluminum and gallium. The other byproduct of the reaction is gallium.
Most pre-
finished wood flooring now uses aluminum oxide as a hard protective
coating.
See also
- Bayer process
- List of Alumina Refineries
References
-->
External links
- International Chemical Safety Card 0351
- PhysicsWeb article on Transparent alumina
{{Chembox new| Name = Aluminium oxide| ImageFile = Corundum-unit-cell-3D-balls.png| Section1 = {{Chembox Identifiers| CASNo = 1344-28-1 -->
| Section2 = {{Chembox Properties| MolarMass = 101.96 g/mol| Density = 3.97 g cm−3, solid| Solubility =
insoluble| MeltingPt = 2054 °C| BoilingPt = 2980 °C -->
| Section3 = {{Chembox Structure| Coordination = [octahedral -->
| Section4 = {{Chembox Thermochemistry| DeltaHf = −1675.7 kJ mol−1| Entropy = 50.92 J mol−1 K−1 -->
| Section7 = {{Chembox Hazards| EUClass = Not listed.| FlashPt = non-flammable -->
| Section8 = {{Chembox Related| OtherAnions =
aluminium hydroxide
[gallium oxideindium oxide
thallium oxide-->-->
Aluminium oxide is an amphoteric oxide of aluminium with the chemical formula 23. It is also commonly referred to as
alumina in the
mining, ceramic and materials science communities.
Properties
Aluminium oxide is an electrical
Electrical insulation but has a relatively high thermal conductivity. In its most commonly occurring crystalline form, called
corundum or α-aluminum oxide, 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 alumina 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. The alumina generated by anodising is typically
amorphous, but discharge assisted oxidation processes such as
plasma electrolytic oxidation result in a significant proportion of crystalline alumina in the coating, enhancing its hardness.
Aluminium oxide was taken off the
United States Environmental Protection Agency's chemicals lists in
1988. Aluminum oxide is on EPA's TRI list if it is a fibrous form.
Natural occurrence
Corundum is the naturally occurring crystalline form of aluminium oxide. ruby and
sapphires are gem-quality forms of corundum with their characteristic colors due to trace impurities in the corundum structure.
Crystal structure
The most common form of crystalline alumina, α-aluminum oxide, is known as corundum and has a
close-packing (HCP) lattice structure.
Industrial Fabrication Process
Aluminium
oxide, also known as alumina, is the main component of bauxite, the principal ore of aluminium. The largest manufacturing 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, Inc.. The bauxite ore is made up of impure Al2O3, Fe2O3, and SiO2. These are then purified by the
Bayer process:
Al2O3 + 3H2O + 2NaOH + heat → 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. The silicate remains in solution. Then:
2Al(OH)3 + heat → Al2O3 + 3H2O
The formed Al2O3 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.
As discussed above (in the "Properties" section), alumina can be grown as a
coating on aluminium by
anodising or by
plasma electrolytic oxidation.
Uses
Annual world production of alumina is approximately 65 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 tonnages 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 is also used in preparation of coating suspensions in compact fluorescent lamps.
Al2O3 is also used in fluoride water filters. It is one of the few methods available to filter water soluble fluorides out of water.
Aluminum oxide is also used as a material in
hip replacements.
Commercial uses
Because of aluminium oxide's position on the
Mohs scale of mineral hardness, (9), it is very widely used as an
abrasive as a significantly less expensive replacement for industrial diamonds. Many types of
sandpaper use aluminium oxide crystals. In addition, its low heat retention and specific heat makes it widely used in almost all grinding operations, particularly
metalworking tools.
Aluminium oxide is used in certain CD/
DVD cleaning kits. Alumina will polish the media surface, leaving it clean and relatively
scratch-free.
Alumina is also the byproduct of hydrogen generation for the purposes of fuel generation when water is added to
pellets comprised of aluminum and
gallium. The other byproduct of the reaction is gallium.
Most pre-finished wood flooring now uses aluminum oxide as a hard protective coating.
See also
References
-->
External links
- International Chemical Safety Card 0351
- PhysicsWeb article on Transparent alumina
Aluminium oxide - Wikipedia, the free encyclopedia
Aluminium oxide is an amphoteric oxide of aluminium with the chemical formula Al 2 O 3. It is also commonly referred to as alumina or aloxite [2] in the mining, ceramic and ...
Green Aluminium Oxide Abrasive Paper Roll - UK
Green Aluminium Oxide Abrasive uses a heavy E weight paper backing which is electro-coated and fully resin-over-resin bonded with aluminium oxide grit for an ultra long life. 5 ...
Yellow Aluminium Oxide Abrasive Paper Roll - UK
Yellow Aluminium Oxide Abrasive uses a heavy E weight paper backing which is electro-coated and fully resin-over-resin bonded with aluminium oxide grit for an ultra long life. 10 ...
Aluminium Oxide
Aluminum oxide for research or production. Small quantities available ... Single crystal sapphire possesses a unique combination of excellent optical, physical and chemical ...
aluminium oxide - Hutchinson encyclopedia article about aluminium ...
White solid formed by heating aluminium hydroxide. It is an amphoteric oxide, since it reacts readily with both acids and alkalis, and it is used as a refractory (furnace lining ...
ALUMINUM OXIDE
1. Product Identification Synonyms: AluminAR® CC-10; Aluminum oxide; Alumina; activated Alumina; alpha-Alumina CAS No.: 1344-28-1
Safety (MSDS) data for aluminium oxide
Safety (MSDS) data for aluminium oxide ... Glossary of terms on this data sheet. The information on this web page is provided to help you to work safely, but it is intended to be ...
Materials — Aluminum Oxide (Al2O3) Properties
Aluminum oxide (Al2O3) typical commercially available polycrystalline ceramic mechanical, thermal and electrical characteristics for this hard, strong, refractory, wear and ...
aluminium oxide - definition of aluminium oxide by the Free Online ...
Noun: 1. aluminium oxide - any of various forms of aluminum oxide occurring naturally as corundum
Aluminium: Production Method 1
Pure aluminium oxide is not used for electrolysis. Its melting point is too high, and it is not a good conductor. Instead it is dissolved at about 5 ...
