Aluminium oxide (British English) or aluminum oxide (American English)
is a chemical compound of aluminium and oxygen with the chemical
formula Al2O3. It is the most commonly occurring of several aluminium
oxides, and specifically identified as aluminium(III) oxide. It is
commonly called alumina (regardless of whether the element is spelled
aluminum or aluminium), and may also be called aloxide, aloxite, or
alundum depending on particular forms or applications. It occurs
naturally in its crystalline polymorphic phase α-Al2O3 as the mineral
corundum, varieties of which form the precious gemstones ruby and
sapphire. Al2O3 is significant in its use to produce aluminium metal,
as an abrasive owing to its hardness, and as a refractory material
owing to its high melting point.
1 Natural occurrence
5.7 Composite fiber
5.8 Abrasion protection
6 See also
8 External links
Corundum is the most common naturally occurring crystalline form of
aluminium oxide. Rubies and sapphires are gem-quality forms of
corundum, which owe their characteristic colors to trace impurities.
Rubies are given their characteristic deep red color and their laser
qualities by traces of chromium. Sapphires come in different colors
given by various other impurities, such as iron and titanium.
Aluminium oxide in its powdered form.
Al2O3 is an electrical insulator but has a relatively high thermal
conductivity (30 Wm−1K−1) for a ceramic material. Aluminium
oxide is insoluble in water. In its most commonly occurring
crystalline form, called corundum or α-aluminium oxide, its hardness
makes it suitable for use as an abrasive and as a component in cutting
Aluminium oxide is responsible for the resistance of metallic
aluminium to weathering. Metallic aluminium is very reactive with
atmospheric oxygen, and a thin passivation layer of aluminium oxide
(4 nm thickness) 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 aluminium oxide generated by
anodising is typically amorphous, but discharge assisted oxidation
processes such as plasma electrolytic oxidation result in a
significant proportion of crystalline aluminium oxide in the coating,
enhancing its hardness.
Aluminium oxide was taken off the United States Environmental
Protection Agency's chemicals lists in 1988.
Aluminium oxide is on the
Toxics Release Inventory
Toxics Release Inventory list if it is a fibrous form.
Aluminium oxide is an amphoteric substance, meaning it can react with
both acids and bases, such as hydrofluoric acid and sodium hydroxide,
acting as an acid with a base and a base with an acid, neutralising
the other and producing a salt.
Al2O3 + 6 HF → 2 AlF3 + 3 H2O
Al2O3 + 2 NaOH + 3 H2O → 2 NaAl(OH)4 (sodium aluminate)
Corundum from Brazil, size about 2×3 cm.
The most common form of crystalline aluminium oxide is known as
corundum, which is the thermodynamically stable form. The oxygen
ions form a nearly hexagonal close-packed structure with the aluminium
ions filling two-thirds of the octahedral interstices. Each Al3+
center is octahedral. In terms of its crystallography, corundum adopts
Bravais lattice with a space group of R-3c (number 167 in
the International Tables). The primitive cell contains two formula
units of aluminium oxide.
Aluminium oxide also exists in other phases, including the cubic γ
and η phases, the monoclinic θ phase, the hexagonal χ phase, the
orthorhombic κ phase and the δ phase that can be tetragonal or
orthorhombic. Each has a unique crystal structure and
properties. Cubic γ-Al2O3 has important technical applications. The
so-called β-Al2O3 proved to be NaAl11O17.
Molten aluminium oxide near the melting temperature is roughly 2/3
tetrahedral (i.e. 2/3 of the Al are surrounded by 4 oxygen neighbors),
and 1/3 5-coordinated, very little (<5%) octahedral Al-O is
present. Around 80% of the oxygen atoms are shared among three or
more Al-O polyhedra, and the majority of inter-polyhedral connections
are corner-sharing, with the remaining 10–20% being
edge-sharing. The breakdown of octahedra upon melting is
accompanied by a relatively large volume increase (~20%), the density
of the liquid close to its melting point is 2.93 g/cm3.
Aluminium hydroxide minerals are the main component of bauxite, the
principal ore of aluminium. A mixture of the minerals comprise bauxite
ore, including gibbsite (Al(OH)3), boehmite (γ-AlO(OH)), and diaspore
(α-AlO(OH)), along with impurities of iron oxides and hydroxides,
quartz and clay minerals. Bauxites are found in laterites. Bauxite
is purified by the Bayer process:
Al2O3 + H2O + NaOH → NaAl(OH)4
Al(OH)3 + NaOH → NaAl(OH)4
Except for SiO2, the other components of bauxite do not dissolve in
base. Upon filtering the basic mixture, Fe2O3 is removed. When the
Bayer liquor is cooled, Al(OH)3 precipitates, leaving the silicates in
NaAl(OH)4 → NaOH + Al(OH)3
The solid Al(OH)3
Gibbsite is then calcined (heated to over
1100 °C) to give aluminium oxide:
2 Al(OH)3 → Al2O3 + 3 H2O
The product aluminium oxide tends to be multi-phase, i.e., consisting
of several phases of aluminium oxide rather than solely corundum.
The production process can therefore be optimized to produce a
tailored product. The type of phases present affects, for example, the
solubility and pore structure of the aluminium oxide product which, in
turn, affects the cost of aluminium production and pollution
For its application as an electrical insulator in integrated circuits,
where conformal growth of thin film is a prerequisite and the
preferred growth mode is atomic layer deposition, Al2O3 films were
prepared by the chemical exchange between trimethylaluminum Al(CH3)3
2 Al(CH3)3 + 3 H2O → Al2O3 + 6 CH4
H2O in the above reaction was subsequently replaced by ozone (O3) as
the active oxidant and the following reaction took place:
2 Al(CH3)3 + O3 → Al2O3 + 3 C2H6
The Al2O3 films prepared using O3 show 10–100 times lower leakage
current density compared with those prepared by H2O.
Known as alundum (in fused form) or aloxite in the mining,
ceramic, and materials science communities, aluminium oxide finds wide
use. Annual world production of aluminium oxide in 2015 was
approximately 115 million tonnes, over 90% of which is used in the
manufacture of aluminium metal. The major uses of speciality
aluminium oxides are in refractories, ceramics, polishing and abrasive
applications. Large tonnages of aluminium hydroxide, from which
alumina is derived, are used in the manufacture of zeolites, coating
titania pigments, and as a fire retardant/smoke suppressant.
Over 90% of the aluminium oxide, normally termed Smelter Grade Alumina
(SGA), produced is consumed for the production of aluminium, usually
by the Hall–Héroult process. The remainder, normally called
speciality alumina is used in a wide variety of applications which
reflect its inertness, temperature resistance and electrical
Being fairly chemically inert and white, aluminium oxide is a favored
filler for plastics.
Aluminium oxide is a common ingredient in
sunscreen and is sometimes also present in cosmetics such as blush,
lipstick, and nail polish.
Many formulations of glass have aluminium oxide as an ingredient.
Aluminium oxide catalyses a variety of reactions that are useful
industrially. In its largest scale application, aluminium oxide is the
catalyst in the
Claus process for converting hydrogen sulfide waste
gases into elemental sulfur in refineries. It is also useful for
dehydration of alcohols to alkenes.
Aluminium oxide serves as a catalyst support for many industrial
catalysts, such as those used in hydrodesulfurization and some
Aluminium oxide is widely used to remove water from gas streams.
Aluminium oxide is used for its hardness and strength. It is widely
used as an abrasive, including as a much less expensive substitute for
industrial diamond. Many types of sandpaper use aluminium oxide
crystals. In addition, its low heat retention and low specific heat
make it widely used in grinding operations, particularly cutoff tools.
As the powdery abrasive mineral aloxite, it is a major component,
along with silica, of the cue tip "chalk" used in billiards. Aluminium
oxide powder is used in some CD/
DVD polishing and scratch-repair kits.
Its polishing qualities are also behind its use in toothpaste.
Main article: Alumina effect pigment
Aluminium oxide flakes are used in paint for reflective decorative
effects, such as in the automotive or cosmetic industries.
Aluminium oxide has been used in a few experimental and commercial
fiber materials for high-performance applications (e.g., Fiber FP,
Nextel 610, Nextel 720). Alumina nanofibers in particular have
become a research field of interest.
Aluminium oxide can be grown as a coating on aluminium by anodizing or
by plasma electrolytic oxidation (see the "Properties" above). Both
the hardness and abrasion-resistant characteristics of the coating
originate from the high strength of aluminium oxide, yet the porous
coating layer produced with conventional direct current anodizing
procedures is within a 60-70 Rockwell hardness C range  which is
comparable only to hardened carbon steel alloys, but considerably
inferior to the hardness of natural and synthetic corundum. Instead,
with plasma electrolytic oxidation, the coating is porous only on the
surface oxide layer while the lower oxide layers are much more compact
than with standard DC anodizing procedures and present a higher
crystallinity due to the oxide layers being remelted and densified to
obtain α-Al2O3 clusters with much higher coating hardness values
circa 2000 Vickers hardness.
Aluminium oxide output in 2005
Alumina is used to manufacture tiles which are attached inside
pulverized fuel lines and flue gas ducting on coal fired power
stations to protect high wear areas. They are not suitable for areas
with high impact forces as these tiles are brittle and susceptible to
This section needs additional citations for verification. Please help
improve this article by adding citations to reliable sources.
Unsourced material may be challenged and removed. (August 2014) (Learn
how and when to remove this template message)
In lighting, transparent aluminium oxide is used in some sodium vapor
Aluminium oxide is also used in preparation of coating
suspensions in compact fluorescent lamps.
In chemistry laboratories, aluminium oxide is a medium for
chromatography, available in basic (pH 9.5), acidic (pH 4.5
when in water) and neutral formulations.
Health and medical applications include it as a material in hip
replacements and birth control pills.
It is used as a dosimeter for radiation protection and therapy
applications for its optically stimulated luminescence
Aluminium oxide is an electrical insulator used as a substrate
(silicon on sapphire) for integrated circuits but also as a tunnel
barrier for the fabrication of superconducting devices such as single
electron transistors and superconducting quantum interference devices
Aluminum oxide being a dielectric with relatively large band gap is
used as an insulating barrier in capacitors.
Insulation for high-temperature furnaces is often manufactured from
aluminium oxide. Sometimes the insulation has varying percentages of
silica depending on the temperature rating of the material. The
insulation can be made in blanket, board, brick and loose fiber forms
for various application requirements.
Small pieces of aluminium oxide are often used as boiling chips in
It is also used to make spark plug insulators.
Using a plasma spray process and mixed with titania, it is coated onto
the braking surface of some bicycle rims to provide abrasion and wear
Most ceramic eyes on fishing rods are circular rings made from
aluminium oxide.
Aluminium oxide nanoparticle
Charged Aerosol Release Experiment (CARE)
List of alumina refineries
^ Patnaik, P. (2002). Handbook of Inorganic Chemicals. McGraw-Hill.
^ Raymond C. Rowe; Paul J. Sheskey; Marian E. Quinn (2009). "Adipic
acid". Handbook of Pharmaceutical Excipients. Pharmaceutical Press.
pp. 11–12. ISBN 978-0-85369-792-3.
^ a b Material Properties Data: Alumina (Aluminum Oxide) Archived
2010-04-01 at the Wayback Machine.. Makeitfrom.com. Retrieved on
^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton
Mifflin Company. ISBN 0-618-94690-X.
^ a b "NIOSH Pocket Guide to Chemical Hazards #0021". National
Institute for Occupational Safety and Health (NIOSH).
^ a b c d e "Alumina (
Aluminium Oxide) – The Different Types of
Commercially Available Grades". The A to Z of Materials. Archived from
the original on 10 October 2007. Retrieved 2007-10-27.
^ Elam, J. W. (October 2010). Atomic Layer Deposition Applications 6.
The Electrochemical Society. ISBN 9781566778213.
^ Campbell, Timothy; Kalia, Rajiv; Nakano, Aiichiro; Vashishta, Priya;
Ogata, Shuji; Rodgers, Stephen (1999). "Dynamics of Oxidation of
Aluminium Nanoclusters using Variable Charge Molecular-Dynamics
Simulations on Parallel Computers" (PDF). Physical Review Letters. 82
(24): 4866. Bibcode:1999PhRvL..82.4866C.
doi:10.1103/PhysRevLett.82.4866. Archived (PDF) from the original on
^ "EPCRA Section 313 Chemical List For Reporting Year 2006" (PDF). US
EPA. Retrieved 2008-09-30. [dead link]
^ a b I. Levin; D. Brandon (1998). "Metastable Alumina Polymorphs:
Crystal Structures and Transition Sequences". Journal of the American
Ceramic Society. 81 (8): 1995–2012.
doi:10.1111/j.1151-2916.1998.tb02581.x. Archived from the original on
^ a b c Paglia, G. (2004). "Determination of the Structure of
γ-Alumina using Empirical and First Principles Calculations Combined
with Supporting Experiments" (free download). Curtin University of
Technology, Perth. Retrieved 2009-05-05.
^ Wiberg, E.; Holleman, A. F. (2001). Inorganic Chemistry. Elsevier.
^ a b Skinner, L.B.; et al. (2013). "Joint diffraction and modeling
approach to the structure of liquid alumina". Phys. Rev. B. 87 (2):
024201. Bibcode:2013PhRvB..87b4201S. doi:10.1103/PhysRevB.87.024201.
Archived from the original on 2013-02-24.
^ Paradis, P.-F.; et al. (2004). "Non-Contact Thermophysical Property
Measurements of Liquid and Undercooled Alumina". Jap. J. Appl. Phys.
43 (4): 1496–1500. Bibcode:2004JaJAP..43.1496P.
Bauxite and Alumina Statistics and Information". USGS. Archived
from the original on 6 May 2009. Retrieved 2009-05-05.
^ Higashi GS, Fleming (1989). "Sequential surface chemical reaction
limited growth of high quality Al2O3 dielectrics". Appl. Phys. Lett.
55 (19): 1963–65. Bibcode:1989ApPhL..55.1963H.
^ Kim JB; Kwon DR; Chakrabarti K; Lee Chongmu; Oh KY; Lee JH (2002).
"Improvement in Al2O3 dielectric behavior by using ozone as an oxidant
for the atomic layer deposition technique". J. Appl. Phys. 92 (11):
6739–42. Bibcode:2002JAP....92.6739K. doi:10.1063/1.1515951.
^ Kim, Jaebum; Chakrabarti, Kuntal; Lee, Jinho; Oh, Ki-Young; Lee,
Chongmu (2003). "Effects of ozone as an oxygen source on the
properties of the Al2O3 thin films prepared by atomic layer
deposition". Mater Chem Phys. 78 (3): 733–38.
^ "Aloxite". ChemIndustry.com database. Archived from the original on
25 June 2007. Retrieved 24 February 2007.
^ Evans, K. A. (1993). "Properties and uses of aluminium oxides and
aluminium hydroxides". In Downs, A. J. The Chemistry of Aluminium,
Indium and Gallium. Blackie Academic. ISBN 075140103X.
^ Akers, Michael J. (2016-04-19). Sterile Drug Products: Formulation,
Packaging, Manufacturing and Quality. CRC Press.
^ Hudson, L. Keith; Misra, Chanakya; Perrotta, Anthony J.; Wefers,
Karl and Williams, F. S. (2002) "Aluminum Oxide" in Ullmann's
Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim.
^ Mallick, P.K. (2008). Fiber-reinforced composites materials,
manufacturing, and design (3rd ed., [expanded and rev. ed.] ed.). Boca
Raton, FL: CRC Press. pp. Ch.2.1.7.
^ Joseph H., Osborn. "understanding and specifying anodizing: what a
manufacturer needs to know". OMW Corporation. Archived from the
original on 2016-11-20. Retrieved 2014. Check date values in:
^ Li, Q; Liang, J; Wang, Q. "Modern Surface Engineering Treatments,
chapter 4 Plasma Oxidation Coatings on Lightweight Metals" (PDF).
INTECH 2013. Archived (PDF) from the original on 2016-03-04.
^ "GE Innovation Timeline 1957–1970". Archived from the original on
16 February 2009. Retrieved 2009-01-12.
^ "DailyMed - JUNEL FE 1/20- norethindrone acetate and ethinyl
estradiol, and ferrous fumarate". dailymed.nlm.nih.gov. Archived from
the original on 2017-03-13. Retrieved 2017-03-13.
^ Belkin, A.; et., al. (2017). "Recovery of Alumina Nanocapacitors
after High Voltage Breakdown". Sci. Rep. Bibcode:2017NatSR...7..932B.
^ Farndon, John (2001). Aluminum. Marshall Cavendish.
ISBN 9780761409472. Archived from the original on
Wikimedia Commons has media related to
CDC - NIOSH Pocket Guide to Chemical Hazards
Mixed oxidation states
Antimony tetroxide (Sb2O4)
Cobalt(II,III) oxide (Co3O4)
Europium(II,III) oxide (Eu3O4)
Iron(II,III) oxide (Fe3O4)
Lead(II,IV) oxide (Pb3O4)
Manganese(II,III) oxide (Mn3O4)
Silver(I,III) oxide (Ag2O2)
Triuranium octoxide (U3O8)
Carbon suboxide (C3O2)
Mellitic anhydride (C12O9)
Praseodymium(III,IV) oxide (Pr6O11)
Terbium(III,IV) oxide (Tb4O7)
+1 oxidation state
Copper(I) oxide (Cu2O)
Dicarbon monoxide (C2O)
Dichlorine monoxide (Cl2O)
Gallium(I) oxide (Ga2O)
Lithium oxide (Li2O)
Potassium oxide (K2O)
Rubidium oxide (Rb2O)
Silver oxide (Ag2O)
Thallium(I) oxide (Tl2O)
Sodium oxide (Na2O)
Water (hydrogen oxide) (H2O)
+2 oxidation state
Aluminium(II) oxide (AlO)
Barium oxide (BaO)
Beryllium oxide (BeO)
Cadmium oxide (CdO)
Calcium oxide (CaO)
Carbon monoxide (CO)
Chromium(II) oxide (CrO)
Cobalt(II) oxide (CoO)
Copper(II) oxide (CuO)
Europium(II) oxide (EuO)
Germanium monoxide (GeO))
Iron(II) oxide (FeO)
Lead(II) oxide (PbO)
Magnesium oxide (MgO)
Manganese(II) oxide (MnO)
Mercury(II) oxide (HgO)
Nickel(II) oxide (NiO)
Nitric oxide (NO)
Palladium(II) oxide (PdO)
Silicon monoxide (SiO)
Strontium oxide (SrO)
Sulfur monoxide (SO)
Disulfur dioxide (S2O2)
Tin(II) oxide (SnO)
Titanium(II) oxide (TiO)
Vanadium(II) oxide (VO)
Zinc oxide (ZnO)
+3 oxidation state
Aluminium oxide (Al2O3)
Antimony trioxide (Sb2O3)
Arsenic trioxide (As2O3)
Bismuth(III) oxide (Bi2O3)
Boron trioxide (B2O3)
Cerium(III) oxide (Ce2O3)
Dibromine trioxide (Br2O3)
Chromium(III) oxide (Cr2O3)
Dinitrogen trioxide (N2O3)
Dysprosium(III) oxide (Dy2O3)
Erbium(III) oxide (Er2O3)
Europium(III) oxide (Eu2O3)
Gadolinium(III) oxide (Gd2O3)
Gallium(III) oxide (Ga2O3)
Holmium(III) oxide (Ho2O3)
Indium(III) oxide (In2O3)
Iron(III) oxide (Fe2O3)
Lanthanum oxide (La2O3)
Lutetium(III) oxide (Lu2O3)
Manganese(III) oxide (Mn2O3)
Neodymium(III) oxide (Nd2O3)
Nickel(III) oxide (Ni2O3)
Phosphorus trioxide (P4O6)
Praseodymium(III) oxide (Pr2O3)
Promethium(III) oxide (Pm2O3)
Rhodium(III) oxide (Rh2O3)
Samarium(III) oxide (Sm2O3)
Scandium oxide (Sc2O3)
Terbium(III) oxide (Tb2O3)
Thallium(III) oxide (Tl2O3)
Thulium(III) oxide (Tm2O3)
Titanium(III) oxide (Ti2O3)
Tungsten(III) oxide (W2O3)
Vanadium(III) oxide (V2O3)
Ytterbium(III) oxide (Yb2O3)
Yttrium(III) oxide (Y2O3)
+4 oxidation state
Americium dioxide (AmO2)
Carbon dioxide (CO2)
Carbon trioxide (CO3)
Cerium(IV) oxide (CeO2)
Chlorine dioxide (ClO2)
Chromium(IV) oxide (CrO2)
Dinitrogen tetroxide (N2O4)
Germanium dioxide (GeO2)
Hafnium(IV) oxide (HfO2)
Lead dioxide (PbO2)
Manganese dioxide (MnO2)
Neptunium(IV) oxide (NpO2)
Nitrogen dioxide (NO2)
Osmium dioxide (OsO2)
Plutonium(IV) oxide (PuO2)
Praseodymium(IV) oxide (PrO2)
Protactinium(IV) oxide (PaO2)
Rhodium(IV) oxide (RhO2)
Ruthenium(IV) oxide (RuO2)
Selenium dioxide (SeO2)
Silicon dioxide (SiO2)
Sulfur dioxide (SO2)
Tellurium dioxide (TeO2)
Terbium(IV) oxide (TbO2)
Thorium dioxide (ThO2)
Tin dioxide (SnO2)
Titanium dioxide (TiO2)
Tungsten(IV) oxide (WO2)
Uranium dioxide (UO2)
Vanadium(IV) oxide (VO2)
Zirconium dioxide (ZrO2)
+5 oxidation state
Antimony pentoxide (Sb2O5)
Arsenic pentoxide (As2O5)
Dinitrogen pentoxide (N2O5)
Niobium pentoxide (Nb2O5)
Phosphorus pentoxide (P2O5)
Protactinium(V) oxide (Pa2O5)
Tantalum pentoxide (Ta2O5)
Vanadium(V) oxide (V2O5)
+6 oxidation state
Chromium trioxide (CrO3)
Molybdenum trioxide (MoO3)
Rhenium trioxide (ReO3)
Selenium trioxide (SeO3)
Sulfur trioxide (SO3)
Tellurium trioxide (TeO3)
Tungsten trioxide (WO3)
Uranium trioxide (UO3)
Xenon trioxide (XeO3)
Iridium trioxide (IrO3)
+7 oxidation state
Dichlorine heptoxide (Cl2O7)
Manganese heptoxide (Mn2O7)
Rhenium(VII) oxide (Re2O7)
Technetium(VII) oxide (Tc2O7)
+8 oxidation state
Osmium tetroxide (OsO4)
Ruthenium tetroxide (RuO4)
Xenon tetroxide (XeO4)
Iridium tetroxide (IrO4)
Hassium tetroxide (HsO4)
Oxides are sorted by oxidation state. Category:Oxides