Distance measuring equipment and Aluminium oxide: Difference between pages

{{Short description|Chemical compound with formula Al2O3}}

{{About|aluminium(III) oxide, Al₂O₃|other uses|Aluminium oxides}}

{{chembox

| Watchedfields = changed

| verifiedrevid = 477315085

| Name = Aluminium(III) oxide<br>(Aluminium oxide)

| ImageFile = Corundum-3D-balls.png

| ImageSize = 250

| ImageFile2 = Aluminium oxide A.jpg

| OtherNames = Dialuminium trioxide

| IUPACName = Aluminium oxide

| SystematicName = Aluminium(III) oxide

| Section1 = {{Chembox Identifiers

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = LMI26O6933

| EC_number = 215-691-6

| ChEMBL = 3707210

| DTXSID = DTXSID1052791

| DrugBank = DB11342

| InChI = 1/2Al.3O/q2*+3;3*-2

| SMILES = [Al+3].[Al+3].[O-2].[O-2].[O-2]

| InChIKey = PNEYBMLMFCGWSK-UHFFFAOYAC

| PubChem = 9989226

| SMILES1 = [O-2].[O-2].[O-2].[Al+3].[Al+3]

| StdInChI_Ref = {{stdinchicite|correct|chemspider}}

| StdInChI = 1S/2Al.3O/q2*+3;3*-2

| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

| StdInChIKey = PNEYBMLMFCGWSK-UHFFFAOYSA-N

| CASNo_Ref = {{cascite|correct|CAS}}

| CASNo = 1344-28-1

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| ChemSpiderID=8164808

| RTECS = BD120000

}}

| Section2 = {{Chembox Properties

| Al=2 | O=3

| Appearance = white solid

| Odor = odorless

| Density =3.987 g/cm³

| Solubility = insoluble

| SolubleOther = insoluble in all solvents

| MeltingPtC = 2072

| MeltingPt_ref=<ref>{{cite book| author = Patnaik, P. |title =Handbook of Inorganic Chemicals| publisher = McGraw-Hill| year = 2002| isbn = 978-0-07-049439-8}}</ref>

| BoilingPtC = 2977

| BoilingPt_ref=<ref>{{cite book |author1=Raymond C. Rowe |author2=Paul J. Sheskey |author3=Marian E. Quinn | contribution =Adipic acid |title=Handbook of Pharmaceutical Excipients |year=2009 |pages = 11–12 |publisher=Pharmaceutical Press |isbn=978-0-85369-792-3}}</ref>

| ThermalConductivity = 30&nbsp;W·m⁻¹·K⁻¹<ref name="properties"/>

| RefractIndex = ''n''_ωおめが&nbsp;=&nbsp;1.768–1.772 <br>''n''_{εいぷしろん}&nbsp;=&nbsp;1.760–1.763 <br> [[Birefringence]] 0.008

| MagSus = −37.0×10⁻⁶ cm³/mol

| LogP =0.31860<ref name="chemsrc">{{Cite web|url=https://www.chemsrc.com/en/cas/1344-28-1_177878.html|title=Aluminum oxide_msds}}</ref>

}}

| Section3 = {{Chembox Structure

| CrystalStruct = [[Trigonal]], [[Pearson symbol|hR30]]

| SpaceGroup = R{{overline|3}}c (No. 167)

| Coordination = [[octahedral]]

| LattConst_a = 478.5 pm

| LattConst_c = 1299.1 pm

}}

| Section4 =

| Section5 = {{Chembox Thermochemistry

| DeltaHf = −1675.7&nbsp;kJ/mol<ref name=b1>{{cite book| author = Zumdahl, Steven S.|title =Chemical Principles 6th Ed.| publisher = Houghton Mifflin Company| year = 2009| isbn = 978-0-618-94690-7}}</ref>

| Entropy = 50.92&nbsp;J·mol⁻¹·K⁻¹<ref name=b1/>

}}

| Section6 = {{Chembox Pharmacology

| ATCCode_prefix = D10

| ATCCode_suffix = AX04

}}

| Section7 = {{Chembox Hazards

| PEL = OSHA 15 mg/m³ (total dust)<br/>OSHA 5 mg/m³ (respirable fraction)<br/>ACGIH/TLV 10 mg/m³

| GHSPictograms = {{GHS07}}

| FlashPt = Non-flammable

| NFPA-H = 0|NFPA-F = 0|NFPA-R = 0

| REL = none<ref name=NIOSH/>

| IDLH = N.D.<ref name=NIOSH>{{PGCH|0021}}</ref>

}}

| Section8 = {{Chembox Related

| OtherAnions = [[aluminium hydroxide]]<br/>[[aluminium sulfide]]<br/>[[aluminium selenide]]

| OtherCations = [[boron trioxide]]<br/>[[gallium(III) oxide]]<br/>[[indium oxide]]<br/>[[thallium(III) oxide]]}}

}}

'''Aluminium oxide''' (or '''aluminium(III) oxide''') is a [[chemical compound]] of [[aluminium]] and [[oxygen]] with the [[chemical formula]] {{chem2|Al2O3}}. It is the most commonly occurring of several [[Aluminium oxide (compounds)|aluminium oxides]], and specifically identified as '''aluminium oxide'''. It is commonly called '''alumina''' and may also be called '''aloxide''', '''aloxite''', or '''alundum''' in various forms and applications. It occurs naturally in its crystalline [[Polymorphism (materials science)|polymorphic]] [[phase (matter)|phase]] αあるふぁ-Al₂O₃ as the [[mineral]] [[corundum]], varieties of which form the precious [[gemstone]]s [[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.<ref name=azom>{{cite web|title = Alumina (Aluminium Oxide) – The Different Types of Commercially Available Grades|url = http://www.azom.com/details.asp?ArticleID=1389|publisher = The A to Z of Materials|access-date = 2007-10-27|archive-url = https://web.archive.org/web/20071010063029/http://www.azom.com/details.asp?ArticleID=1389|archive-date = 10 October 2007|url-status = dead|df = dmy-all|date = 2002-05-03}}</ref>

==Natural occurrence==

[[Corundum]] is the most common naturally occurring [[crystallinity|crystalline]] form of aluminium oxide.<ref>{{Cite book|url=https://books.google.com/books?id=9WyXTae58DgC&q=Corundum+is+the+most+common+naturally+occurring+crystalline+form+of+aluminium+oxide.&pg=PA46|title=Atomic Layer Deposition Applications 6|last=Elam|first=J. W.|date=October 2010|publisher=The Electrochemical Society|isbn=9781566778213|language=en}}</ref> [[ruby|Rubies]] and [[sapphire]]s are gem-quality forms of corundum, which owe their characteristic colours to trace impurities. Rubies are given their characteristic deep red colour and their [[laser]] qualities by traces of [[chromium]]. Sapphires come in different colours given by various other impurities, such as iron and titanium. An extremely rare δでるた form occurs as the mineral deltalumite.<ref>{{Cite web|url=https://www.mindat.org/min-47933.html|title = Deltalumite}}</ref><ref>{{Cite web|url=https://www.ima-mineralogy.org/Minlist.htm|title=List of Minerals|date=21 March 2011}}</ref>

==History==

The field of aluminium oxide ceramics has a long history. Aluminum salts were widely used in ancient and medieval times, such as in [[alchemy]]. Several older textbooks cover the history of the field.<ref>{{cite book|title=Alumina as a Ceramic Material|publisher=Wiley|year=1970|first=Walter|last=Gitzen}}</ref> <ref>{{Cite book |last1 = Dorre | first1 = Erhard| last2 = Hubner | first2 = Heinz| title = Alumina, Processing, Properties, and Applications | year = 1984 | publisher = Springer-Verlag | location = Berlin; New York

| pages = 344}}</ref> A 2019 textbook by Andrew Ruys contains a detailed timeline on the

history of aluminium oxide from ancient times to the 21st century.<ref>{{Cite book| last=Ruys

| first=Andrew J. | title=Alumina Ceramics: Biomedical and Industrial Applications | year=2019 | publisher=Elsevier | location=Duxford, UK | isbn=978-0-08-102442-3 | pages=558 }}</ref>

==Properties==

[[Image:Oxid hlinitý.PNG|thumb|left|alt=Aluminium oxide in its powdered form|Aluminium oxide in its powdered form]]

Al₂O₃ is an [[Insulator (electricity)|electrical insulator]] but has a relatively high [[thermal conductivity]] ({{nowrap|30 Wm⁻¹K⁻¹}})<ref name="properties">[http://www.makeitfrom.com/data/?material=Alumina Material Properties Data: Alumina (Aluminum Oxide)] {{webarchive|url=https://web.archive.org/web/20100401131344/http://www.makeitfrom.com/data/?material=Alumina |date=2010-04-01 }}. Makeitfrom.com. Retrieved on 2013-04-17.</ref> for a ceramic material. Aluminium oxide is insoluble in water. In its most commonly occurring crystalline form, called [[corundum]] or αあるふぁ-aluminium oxide, its hardness makes it suitable for use as an [[abrasive]] and as a component in [[cutting tools]].<ref name = azom/>

Aluminium oxide is responsible for the resistance of metallic aluminium to [[weathering]]. Metallic aluminium is very reactive with atmospheric oxygen, and a thin [[Passivation (chemistry)|passivation layer]] of aluminium oxide (4&nbsp;nm thickness) forms on any exposed aluminium surface in a matter of hundreds of picoseconds.{{better source needed|date=September 2019}}<ref>{{cite journal| url=http://cacs.usc.edu/papers/Campbell-nAloxid-PRL99.pdf| doi=10.1103/PhysRevLett.82.4866| title=Dynamics of Oxidation of Aluminium Nanoclusters using Variable Charge Molecular-Dynamics Simulations on Parallel Computers| year=1999| author=Campbell, Timothy| journal=Physical Review Letters| volume=82| page=4866| last2=Kalia| first2=Rajiv| last3=Nakano| first3=Aiichiro| last4=Vashishta| first4=Priya| last5=Ogata| first5=Shuji| last6=Rodgers| first6=Stephen| bibcode=1999PhRvL..82.4866C| issue=24| url-status=live| archive-url=https://web.archive.org/web/20100701230226/http://cacs.usc.edu/papers/Campbell-nAloxid-PRL99.pdf| archive-date=2010-07-01}}</ref> 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 bronze]]s, 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 EPA's [[Toxics Release Inventory]] list if it is a fibrous form.<ref name=TRI>{{cite web|title=EPCRA Section 313 Chemical List For Reporting Year 2006 |url=http://www.epa.gov/tri/chemical/chemical%20lists/RY2006ChemicalList.pdf |archive-url=https://wayback.archive-it.org/all/20080522232533/http://www.epa.gov/tri/chemical/chemical%20lists/RY2006ChemicalList.pdf |url-status=dead |archive-date=2008-05-22 |publisher=US EPA |access-date=2008-09-30 }}</ref>

===Amphoteric nature===

Aluminium oxide is an [[amphoteric]] substance, meaning it can react with both [[acids]] and [[base (chemistry)|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 [[Aluminium fluoride|AlF₃]] + 3 H₂O

:Al₂O₃ + 2 NaOH + 3 H₂O → 2 NaAl(OH)₄ ([[sodium aluminate]])

==Structure==

[[Image:Corindon azulEZ.jpg|thumb|180px|left|Corundum from [[Brazil]], size about 2×3&nbsp;cm.]]

The most common form of crystalline aluminium oxide is known as [[corundum]], which is the thermodynamically stable form.<ref name=Levin>{{cite journal |author=I. Levin |author2=D. Brandon |year=1999

|title=Metastable Alumina Polymorphs: Crystal Structures and Transition Sequences |journal=Journal of the American Ceramic Society |volume=81 |issue=8 |pages=1995–2012 |doi=10.1111/j.1151-2916.1998.tb02581.x }}</ref> The oxygen ions form a nearly [[Close-packing of equal spheres|hexagonal close-packed]] structure with the aluminium ions filling two-thirds of the octahedral interstices. Each Al³⁺ center is [[octahedral molecular geometry|octahedral]]. In terms of its [[crystallography]], corundum adopts a [[trigonal]] [[Bravais lattice]] with a [[space group]] of [[Hexagonal crystal family|R{{overline|3}}c]] (number 167 in the International Tables). The [[primitive cell]] contains two formula units of aluminium oxide.

Aluminium oxide also exists in other metastable phases, including the cubic γがんま and ηいーた phases, the monoclinic θしーた phase, the hexagonal χかい phase, the orthorhombic κかっぱ phase and the δでるた phase that can be tetragonal or orthorhombic.<ref name=Levin /><ref name=Paglia>{{cite news| author = Paglia, G. | title =Determination of the Structure of γがんま-Alumina using Empirical and First Principles Calculations Combined with Supporting Experiments| publisher = Curtin University of Technology, Perth| year = 2004| url = http://espace.library.curtin.edu.au/R?func=search-simple-go&ADJACENT=Y&REQUEST=adt-WCU20040621.123301|format=free download|access-date = 2009-05-05}}</ref> Each has a unique crystal structure and properties. Cubic γがんま-Al₂O₃ has important technical applications. The so-called βべーた-Al₂O₃ proved to be NaAl₁₁O₁₇.<ref name = "Wiberg&Holleman">{{cite book|author1=Wiberg, E. |author2=Holleman, A. F. |year = 2001| title = Inorganic Chemistry| publisher = Elsevier| isbn = 978-0-12-352651-9}}</ref>

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, with very little (<5%) [[octahedral]] Al-O present.<ref name="Skinner2013">{{cite journal|title=Joint diffraction and modeling approach to the structure of liquid alumina|doi=10.1103/PhysRevB.87.024201|year=2013|author=Skinner, L.B.|journal=Phys. Rev. B|volume=87|issue=2|page=024201|bibcode=2013PhRvB..87b4201S|display-authors=etal|doi-access=free}}</ref> 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.<ref name = "Skinner2013"/> The breakdown of octahedra upon melting is accompanied by a relatively large volume increase (~33%), the density of the liquid close to its melting point is 2.93 g/cm³.<ref>{{cite journal|title=Non-Contact Thermophysical Property Measurements of Liquid and Undercooled Alumina |doi=10.1143/JJAP.43.1496|year=2004|author=Paradis, P.-F.|journal= Jpn. J. Appl. Phys. |volume=43|issue=4| pages=1496–1500|bibcode = 2004JaJAP..43.1496P |s2cid=250779901 |display-authors=etal}}</ref> The structure of molten alumina is temperature dependent and the fraction of 5- and 6-fold aluminium increases during cooling (and supercooling), at the expense of tetrahedral AlO₄ units, approaching the local structural arrangements found in amorphous alumina.<ref>{{cite journal |last1=Shi |first1=C |last2=Alderman |first2=O L G |last3=Berman |first3=D |last4=Du |first4=J |last5=Neuefeind |first5=J |last6=Tamalonis |first6=A |last7=Weber |first7=R |last8=You |first8=J |last9=Benmore |first9=C J |title=The structure of amorphous and deeply supercooled liquid alumina |journal=Frontiers in Materials |date=2019 |volume=6 |issue=38 |pages=38 |doi=10.3389/fmats.2019.00038 |bibcode=2019FrMat...6...38S |doi-access=free }}</ref>

==Production==

{{See also|List of countries by aluminium oxide production}}

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がんま-AlO(OH)), and [[diaspore]] (αあるふぁ-AlO(OH)), along with impurities of [[iron oxide]]s and hydroxides, quartz and [[clay minerals]].<ref>{{cite web| url = http://minerals.usgs.gov/minerals/pubs/commodity/bauxite/|publisher = USGS| access-date = 2009-05-05| title = Bauxite and Alumina Statistics and Information| archive-url= https://web.archive.org/web/20090506220703/http://minerals.usgs.gov/minerals/pubs/commodity/bauxite/| archive-date= 6 May 2009 | url-status= live}}</ref> Bauxites are found in [[laterite]]s. Bauxite is typically purified using 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 solution.

: NaAl(OH)₄ → NaOH + Al(OH)₃

The solid Al(OH)₃ [[Gibbsite]] is then [[calcined]] (heated to over 1100&nbsp;°C) to give aluminium oxide:<ref name = azom/>

: 2&thinsp;Al(OH)₃ → Al₂O₃ + 3&thinsp;H₂O

The product aluminium oxide tends to be multi-phase, i.e., consisting of several phases of aluminium oxide rather than solely [[corundum]].<ref name=Paglia/> 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 control.<ref name=Paglia/>

==Applications==

Known as ''alpha alumina'' in [[materials science]], and as ''alundum'' (in fused form) or ''aloxite''<ref name="CI14835">{{cite news| url = http://www.chemindustry.com/chemicals/14835.html| title = Aloxite| publisher = ChemIndustry.com database| access-date = 24 February 2007| url-status = live| archive-url = https://web.archive.org/web/20070625100844/http://www.chemindustry.com/chemicals/14835.html| archive-date = 25 June 2007}}</ref> in [[mining]] and [[ceramic]] communities, aluminium oxide finds wide use. Annual global production of aluminium oxide in 2015 was approximately 115 million [[tonne]]s, over 90% of which was used in the manufacture of aluminium metal.<ref name="azom" /> 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 [[Titanium dioxide|titania]] pigments, and as a fire retardant/smoke suppressant.

Over 90% of aluminium oxide, termed ''smelter grade alumina'' (SGA), is consumed for the production of aluminium, usually by the [[Hall–Héroult process]]. The remainder, termed ''specialty alumina'', is used in a wide variety of applications which take advantage of its inertness, temperature resistance and electrical resistance.<ref>{{cite book|chapter = Properties and uses of aluminium oxides and aluminium hydroxides|first = K. A.|last = Evans|title = The Chemistry of Aluminium, Indium and Gallium|editor-first = A. J.|editor-last = Downs|publisher = Blackie Academic|year = 1993|isbn = 978-0751401035}}</ref>

===Fillers===

Being fairly chemically inert and white, aluminium oxide is a favored filler for plastics. Aluminium oxide is a common ingredient in [[sunscreen]]<ref>{{cite web |title=Alumina |url=https://incidecoder.com/ingredients/alumina |website=INCI Decoder |access-date=20 June 2023 |archive-url=https://web.archive.org/web/20230205144849/https://incidecoder.com/ingredients/alumina |archive-date=5 February 2023}}</ref> and is often also present in cosmetics such as blush, lipstick, and nail polish.<ref>{{cite web |title=Alumina (Ingredient Explained + Products) |url=https://skinsort.com/ingredients/alumina |website=SkinSort |access-date=15 October 2023 |archive-url=https://web.archive.org/web/20231015122803/https://skinsort.com/ingredients/alumina |archive-date=15 October 2023}}</ref>

===Glass===

Many formulations of [[glass]] have aluminium oxide as an ingredient.<ref>{{Cite book|url=https://books.google.com/books?id=C2_LBQAAQBAJ&q=some+glass+contain+aluminum+oxide&pg=PA73|title=Sterile Drug Products: Formulation, Packaging, Manufacturing and Quality|last=Akers|first=Michael J.|date=2016-04-19|publisher=CRC Press|isbn=9781420020564|language=en}}</ref> Aluminosilicate glass is a commonly used type of glass that often contains 5% to 10% alumina.

===Catalysis===

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 reaction|dehydration]] of [[Alcohol (chemistry)|alcohol]]s to [[alkene]]s.

Aluminium oxide serves as a [[catalyst support]] for many industrial catalysts, such as those used in [[hydrodesulfurization]] and some [[Ziegler–Natta]] polymerizations.

===Gas purification===

Aluminium oxide is widely used to remove water from gas streams.<ref>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. {{doi|10.1002/14356007.a01_557}}.</ref>

===Abrasion===

Aluminium oxide is used for its hardness and strength. Its naturally occurring form, [[corundum]], is a 9 on the [[Mohs scale of mineral hardness]] (just below diamond). 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 [[metalworking|cutoff]] tools. As the powdery abrasive mineral [[aloxite]], it is a major component, along with [[silica]], of the [[Cue stick|cue tip]] "chalk" used in [[Cue sports|billiards]]. Aluminium oxide powder is used in some [[Compact disc|CD]]/[[DVD]] [[polishing]] and scratch-repair kits. Its polishing qualities are also behind its use in toothpaste. It is also used in [[microdermabrasion]], both in the machine process available through dermatologists and estheticians, and as a manual dermal abrasive used according to manufacturer directions.

===Paint===

{{Main|Alumina effect pigment}}

Aluminium oxide flakes are used in paint for reflective decorative effects, such as in the automotive or cosmetic industries.{{citation needed|date=May 2019}}

===Composite fiber===

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).<ref name=mallick>{{cite book|last=Mallick|first=P.K.|title=Fiber-reinforced composites materials, manufacturing, and design|year=2008|publisher=CRC Press|location=Boca Raton, FL|isbn=978-0-8493-4205-9|pages=Ch.2.1.7|edition=3rd ed., [expanded and rev. ed.]}}</ref> Alumina [[nanofibers]] in particular have become a research field of interest.

===Armor===

Some body armors utilize alumina ceramic plates, usually in combination with aramid or UHMWPE backing to achieve effectiveness against most rifle threats. Alumina ceramic armor is readily available to most civilians in jurisdictions where it is legal, but is not considered military grade.<ref>{{cite web |title=Ballistic Resistance of Body Armor |url=https://www.ncjrs.gov/pdffiles1/nij/223054.pdf |website=US Department of Justice |publisher=NIJ |access-date=31 August 2018}}</ref> It is also used to produce bullet-proof alumina glass capable to withstand impact of [[.50 BMG]] calibre rounds.

===Abrasion protection===

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<ref>{{cite web|first=Joseph H.|last=Osborn|title=understanding and specifying anodizing: what a manufacturer needs to know|url=http://www.omwcorp.com/understandingano/anoindex.html|website=OMW Corporation|year=2014|url-status=dead|archive-url=https://web.archive.org/web/20161120010024/http://www.omwcorp.com/understandingano/anoindex.html|archive-date=2016-11-20|access-date=2018-06-02}}</ref> 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あるふぁ-Al2O3 clusters with much higher coating hardness values circa 2000 Vickers hardness.{{Citation needed|date=December 2019|reason=removed citation to content from predatory publisher}}

[[Image:2005alumina.PNG|thumb|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 breakage.

===Electrical insulation===

Aluminium oxide is an electrical [[insulator (electricity)|insulator]] used as a substrate ([[silicon on sapphire]]) for [[integrated circuits]] but also as a [[quantum tunneling|tunnel barrier]] for the fabrication of [[superconducting]] devices such as [[single-electron transistor]]s, superconducting quantum interference devices ([[SQUID]]s) and [[Superconducting quantum computing|superconducting qubits]].

For its application as an electrical insulator in integrated circuits, where the conformal growth of a thin film is a prerequisite and the preferred growth mode is [[atomic layer deposition]], Al₂O₃ films can be prepared by the chemical exchange between [[trimethylaluminium]] (Al(CH₃)₃) and H₂O:<ref>{{Cite journal|author=Higashi GS, Fleming |title= Sequential surface chemical reaction limited growth of high quality Al₂O₃ dielectrics |journal=Appl. Phys. Lett.|volume=55 |issue= 19|pages=1963–65 |year=1989 |doi=10.1063/1.102337|bibcode = 1989ApPhL..55.1963H }}</ref>

:2 Al(CH₃)₃ + 3 H₂O → Al₂O₃ + 6 CH₄

H₂O in the above reaction can be replaced by [[ozone]] (O₃) as the active oxidant and the following reaction then takes place:<ref>{{Cite journal|author1=Kim JB |author2=Kwon DR |author3=Chakrabarti K |author4=Lee Chongmu |author5=Oh KY |author6=Lee JH |title= Improvement in Al₂O₃ dielectric behavior by using ozone as an oxidant for the atomic layer deposition technique

| journal=J. Appl. Phys. |volume=92 |issue= 11| pages=6739–42 |year=2002 |doi=10.1063/1.1515951|bibcode = 2002JAP....92.6739K }}</ref><ref>{{Cite journal|author1=Kim, Jaebum |author2=Chakrabarti, Kuntal |author3=Lee, Jinho |author4=Oh, Ki-Young |author5=Lee, Chongmu |title= Effects of ozone as an oxygen source on the properties of the Al₂O₃ thin films prepared by atomic layer deposition |journal=Mater Chem Phys |volume=78 |issue= 3| pages=733–38 |year=2003 |doi=10.1016/S0254-0584(02)00375-9}}</ref>

: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.

Aluminium oxide, being a dielectric with relatively large [[band gap]], is used as an insulating barrier in [[capacitors]].<ref name="Belkin">{{cite journal |last1=Belkin |first1=A. |last2=Bezryadin |first2=A. |last3=Hendren |first3=L. |last4=Hubler |first4=A. |title=Recovery of Alumina Nanocapacitors after High Voltage Breakdown |journal=Scientific Reports |date=20 April 2017 |volume=7 |issue=1 |pages=932 |doi=10.1038/s41598-017-01007-9|pmid=28428625 |pmc=5430567 |bibcode=2017NatSR...7..932B }}</ref>

===Other===

In lighting, translucent aluminium oxide is used in some [[sodium vapor lamp]]s.<ref>{{cite web|url=http://www.ge.com/innovation/timeline/eras/science_and_research.html|title=GE Innovation Timeline 1957–1970|access-date=2009-01-12| archive-url= https://web.archive.org/web/20090216233917/http://www.ge.com/innovation/timeline/eras/science_and_research.html| archive-date= 16 February 2009 | url-status= live}}</ref> Aluminium oxide is also used in preparation of coating suspensions in [[compact fluorescent lamp]]s.

In chemistry laboratories, aluminium oxide is a medium for [[chromatography]], available in [[Base (chemistry)|basic]] (pH&nbsp;9.5), [[acid]]ic (pH&nbsp;4.5 when in water) and neutral formulations. Additionally, small pieces of aluminium oxide are often used as [[boiling chips]].

Health and medical applications include it as a material in [[hip replacement]]s<ref name="azom" /> and [[Oral contraceptive pill|birth control pills]].<ref>{{Cite web|url=https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=75bb0024-8f1a-4036-9acd-006ea430f3b7#|title=DailyMed - JUNEL FE 1/20- norethindrone acetate and ethinyl estradiol, and ferrous fumarate|website=dailymed.nlm.nih.gov|access-date=2017-03-13|url-status=live|archive-url=https://web.archive.org/web/20170313130132/https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=75bb0024-8f1a-4036-9acd-006ea430f3b7|archive-date=2017-03-13}}</ref>

It is used as a [[scintillator]]<ref>{{Cite journal|author=V.B. Mikhailik, H. Kraus |title= Low-temperature spectroscopic and scintillation characterisation of Ti-doped Al₂O₃|journal=Nucl. Instr. Phys. Res. A|volume=546 |issue= 3|pages=523–534 |year=2005 |doi=10.1016/j.nima.2005.02.033|bibcode= 2005NIMPA.546..523M}}</ref>

and [[dosimeter]] for radiation protection and therapy applications for its [[optically stimulated luminescence]] properties.{{citation needed|date=August 2014}}

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.

It is also used to make [[spark plug]] [[insulator (electricity)|insulator]]s.<ref>{{Cite book|url=https://archive.org/details/aluminiumtheeleme00john|url-access=registration|page=[https://archive.org/details/aluminiumtheeleme00john/page/19 19]|quote=Aluminium oxide is also used to make spark plug insulators.|title=Aluminium|last=Farndon|first=John|date=2001|publisher=Marshall Cavendish|isbn=9780761409472|language=en}}</ref>

Using a [[Plasma spraying|plasma spray]] process and mixed with [[Titanium dioxide|titania]], it is coated onto the braking surface of some [[bicycle]] rims to provide abrasion and wear resistance.{{Citation needed|date=March 2011}}

Most ceramic eyes on fishing rods are circular rings made from aluminium oxide.{{citation needed|date=August 2014}}

In its finest powdered (white) form, called Diamantine, aluminium oxide is used as a superior polishing abrasive in watchmaking and clockmaking.<ref>{{Cite book | title=Practical Watch Repair|pages=164 | last=de Carle|first=Donald|publisher=N.A.G. Press Ltd.|isbn=0719800307|language=en|year=1969 }}</ref>

Aluminium oxide is also used in the coating of stanchions in the motorcross and mountainbike industry.

This coating is combined with molybdenumdisulfate to provide long term lubrication of the surface.<ref>{{Cite web|url=http://www.kashima-coat.com/global/service/kashima-coat/|title = Kashima Coat - Products / Services &#124; Next-generation anodize boasting light weight, high lubrication, and superb wear resistance. The answer is Miyaki's Kashima Coat}}</ref>

* [[Aluminium oxide nanoparticle]]

* [[Bauxite tailings]]

* [[Beta-alumina solid electrolyte]], a [[fast ion conductor]]

* [[Charged Aerosol Release Experiment]] (CARE)

* [[List of alumina refineries]]

* [[Micro-pulling-down]]

* [[Transparent alumina]]

==References==

{{Reflist|30em}}

==External links==

{{Commons category|Aluminium oxide}}

* [https://www.cdc.gov/niosh/npg/npgd0021.html CDC - NIOSH Pocket Guide to Chemical Hazards]

{{Aluminium compounds}}

{{Oxides}}

{{oxygen compounds}}

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{{Authority control}}

{{DEFAULTSORT:Aluminium Oxide}}

[[Category:Acid catalysts]]

[[Category:Abrasives]]

[[Category:Aluminium compounds]]

[[Category:Amphoteric compounds]]

[[Category:Biomaterials]]

[[Category:Ceramic materials]]

[[Category:Oxides]]

[[Category:Refractory materials]]

[[Category:Sesquioxides]]