tI

Titanium (symbol Ti, atomic number 22) is a lustrous transition metal known for a high strength-to-weight ratio and exceptional corrosion resistance. It forms a protective oxide layer that passivates its surface, giving it remarkable durability in harsh environments. In chemistry, titanium most commonly exhibits a +4 oxidation state, though +3 and other valences occur in compounds.

Occurrence and production. Titanium is the ninth-most abundant element in Earth's crust, and its primary sources are the minerals ilmenite (FeTiO3) and rutile (TiO2). The main industrial production route is the Kroll process, in which titanium tetrachloride (TiCl4) is reduced with magnesium in a molten salt to yield metallic titanium, which is then refined by processes such as vacuum arc remelting. Alternative methods include the FFC Cambridge process.

Isotopes and properties. Five stable isotopes occur naturally: 46Ti, 47Ti, 48Ti, 49Ti, and 50Ti. Titanium has a melting point of about 1,668°C and a density of roughly 4.5 g/cm3, making it lighter than many structural metals while maintaining high strength. It resists corrosion from seawater and most acids, especially in the presence of its native oxide layer.

Applications and alloys. Titanium and its alloys are widely used in aerospace, automotive, chemical processing, and marine applications due to strength, lightness, and corrosion resistance. Ti-6Al-4V is a common alpha-beta alloy used in airframes and medical implants. Titanium is also biocompatible, used for implants and prosthetics, and is employed in jewelry for its stiffness, non-reactivity, and color retention.

History. The element was identified in 1791 by William Gregor in Cornwall and named titanium by Martin Heinrich Klaproth in 1795 after the Titans of Greek myth. Commercial metallic titanium emerged in the mid-20th century through the Kroll process.