Editing Passivation (chemistry) (section)

===Titanium===
[[File:Anodized titanium table.jpg|thumb|right|Relation between voltage and color for anodized titanium.]]
The surface of [[titanium]] and of titanium-rich alloys oxidizes immediately upon exposure to air to form a thin passivation layer of [[titanium oxide]], mostly [[titanium dioxide]].<ref name="Chen 2001">{{cite journal | last1=Chen | first1=George Zheng | last2=Fray | first2=Derek J. | last3=Farthing | first3=Tom W. | title=Cathodic deoxygenation of the alpha case on titanium and alloys in molten calcium chloride | journal=Metallurgical and Materials Transactions B | volume=32 | issue=6 | year=2001 | issn=1073-5615 | doi=10.1007/s11663-001-0093-8 | pages=1041–1052| bibcode=2001MMTB...32.1041C | s2cid=95616531 }}</ref> This layer makes it resistant to further corrosion, aside from gradual growth of the oxide layer, thickening to ~25&nbsp;nm after several years in air. This protective layer makes it suitable for use even in corrosive environments such as sea water. Titanium can be anodized to produce a thicker passivation layer. As with many other metals, this layer causes [[thin-film interference]] which makes the metal surface appear colored, with the thickness of the passivation layer directly affecting the color produced.