Editing Titanium (section)

=== Chemical properties ===
[[File:Titanium products.jpg|thumb|left|Titanium products: plate, tube, rod, powder]]
[[File:Titanium in water Pourbaix diagram.png|thumb|[[Pourbaix diagram]] for titanium in pure water, perchloric acid, or sodium hydroxide<ref name="medusa">Puigdomenech, Ignasi (2004) [https://web.archive.org/web/20130605034847/http://www.kth.se/che/medusa ''Hydra/Medusa Chemical Equilibrium Database and Plotting Software''], KTH Royal Institute of Technology.</ref>]]
Like [[aluminium]] and [[magnesium]], the surface of titanium metal and its alloys [[oxidize]] immediately upon exposure to air to form a thin non-porous [[Passivation (chemistry)|passivation]] layer that protects the bulk metal from further oxidation or corrosion.<ref name="EBC" /> When it first forms, this protective layer is only 1–2&nbsp;[[nanometre|nm]] thick but it continues to grow slowly, reaching a thickness of 25&nbsp;nm in four years.<ref name="Emsley2001p453" /> This layer gives titanium excellent resistance to corrosion against oxidizing acids, but it will dissolve in dilute [[hydrofluoric acid]], hot hydrochloric acid, and hot sulfuric acid.

Titanium is capable of withstanding attack by dilute [[sulfuric acid|sulfuric]] and [[hydrochloric acid]]s at room temperature, chloride solutions, and most organic acids.<ref name=LANL/> However, titanium is corroded by concentrated acids.<ref>{{cite journal |author1=Casillas, N. |author2=Charlebois, S. |author3=Smyrl, W.H. |author4=White, H.S. |year=1994 |title=Pitting corrosion of titanium |journal=J. Electrochem. Soc. |volume=141 |issue=3 |pages=636–642 |doi=10.1149/1.2054783 |bibcode=1994JElS..141..636C |url=https://apps.dtic.mil/dtic/tr/fulltext/u2/a274980.pdf |url-status=live |archive-url=https://web.archive.org/web/20200827231129/https://apps.dtic.mil/dtic/tr/fulltext/u2/a274980.pdf |archive-date=27 August 2020}}</ref> Titanium is a very reactive metal that burns in normal air at lower temperatures than the melting point. Melting is possible only in an inert atmosphere or vacuum. At {{convert|550|°C|°F}}, it combines with chlorine.<ref name=LANL/> It also reacts with the other halogens and absorbs hydrogen.<ref name=HistoryAndUse/>

Titanium readily reacts with oxygen at {{convert|1200|°C|°F}} in air, and at {{convert|610|°C|°F}} in pure oxygen, forming [[titanium dioxide]].<ref name="TICE6th" /> Titanium is one of the few elements that burns in pure nitrogen gas, reacting at {{convert|800|°C|°F}} to form [[titanium nitride]], which causes embrittlement.<ref name=titaniumindustry>{{cite book |title=Industrial Applications of Titanium and Zirconium|chapter-url= https://books.google.com/books?id=0Adr4zleybgC&pg=PA112 |page= 112|first= A.L. |last= Forrest |chapter= Effects of Metal Chemistry on Behavior of Titanium in Industrial Applications |year=1981}}</ref> Because of its high reactivity with oxygen, nitrogen, and many other gases, titanium that is evaporated from [[electrical filament|filaments]] is the basis for [[titanium sublimation pump]]s, in which titanium serves as a scavenger for these gases by chemically binding to them. Such pumps inexpensively produce extremely low pressures in [[ultra-high vacuum]] systems.