Editing Aluminium oxide (section)

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

Al<sub>2</sub>O<sub>3</sub> is an [[Insulator (electricity)|electrical insulator]] but has a relatively high [[thermal conductivity]] ({{nowrap|30 Wm<sup>−1</sup>K<sup>−1</sup>}})<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-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.
:Al<sub>2</sub>O<sub>3</sub> + 6 HF → 2 [[Aluminium fluoride|AlF<sub>3</sub>]] + 3 H<sub>2</sub>O
:Al<sub>2</sub>O<sub>3</sub> + 2 NaOH + 3 H<sub>2</sub>O → 2 NaAl(OH)<sub>4</sub> ([[sodium aluminate]])