scandium ← titanium → vanadium - ↑ Ti ↓ Zr 22Ti Periodic table
Appearance
silvery grey-white metallic
General properties
Name, symbol, number	titanium, Ti, 22
Pronunciation	/taɪˈteɪniəm/ tye-TAY-nee-əm
Element category	transition metal
Group, period, block	4, 4, d
Standard atomic weight	47.867(1)
Electron configuration	[Ar] 4s2 3d2
Electrons per shell	2, 8, 10, 2 (Image)
Physical properties
Phase	solid
Density (near r.t.)	4.506 g·cm−3
Liquid density at m.p.	4.11 g·cm−3
Melting point	1941 K, 1668 °C, 3034 °F
Boiling point	3560 K, 3287 °C, 5949 °F
Heat of fusion	14.15 kJ·mol−1
Heat of vaporization	425 kJ·mol−1
Molar heat capacity	25.060 J·mol−1·K−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1982 2171 (2403) 2692 3064 3558
Atomic properties
Oxidation states	4, 3, 2, 1[1] (amphoteric oxide)
Electronegativity	1.54 (Pauling scale)
Ionization energies (more)	1st: 658.8 kJ·mol−1
	2nd: 1309.8 kJ·mol−1
	3rd: 2652.5 kJ·mol−1
Atomic radius	147 pm
Covalent radius	160±8 pm
Miscellanea
Crystal structure	hexagonal
Magnetic ordering	paramagnetic
Electrical resistivity	(20 °C) 420 nΩ·m
Thermal conductivity	21.9 W·m−1·K−1
Thermal expansion	(25 °C) 8.6 µm·m−1·K−1
Speed of sound (thin rod)	(r.t.) 5,090 m·s−1
Young's modulus	116 GPa
Shear modulus	44 GPa
Bulk modulus	110 GPa
Poisson ratio	0.32
Mohs hardness	6.0
Vickers hardness	970 MPa
Brinell hardness	716 MPa
CAS registry number	7440-32-6
Most stable isotopes
Main article: Isotopes of titanium
iso NA half-life DM DE (MeV) DP 44Ti syn 63 y ε - 44Sc γ 0.07D, 0.08D - 46Ti 8.0% 46Ti is stable with 24 neutrons 47Ti 7.3% 47Ti is stable with 25 neutrons 48Ti 73.8% 48Ti is stable with 26 neutrons 49Ti 5.5% 49Ti is stable with 27 neutrons 50Ti 5.4% 50Ti is stable with 28 neutrons
v t e · r

Titanium ( /taɪˈteɪniəm/ ty-TAY-nee-əm) is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant (including sea water, aqua regia and chlorine) transition metal with a silver color.

Titanium was discovered in Cornwall, Great Britain, by William Gregor in 1791 and named by Martin Heinrich Klaproth for the Titans of Greek mythology. The element occurs within a number of mineral deposits, principally rutile and ilmenite, which are widely distributed in the Earth's crust and lithosphere, and it is found in almost all living things, rocks, water bodies, and soils.^[2] The metal is extracted from its principal mineral ores via the Kroll process^[3] or the Hunter process. Its most common compound, titanium dioxide, is a popular photocatalyst and is used in the manufacture of white pigments.^[4] Other compounds include titanium tetrachloride (TiCl₄), a component of smoke screens and catalysts; and titanium trichloride (TiCl₃), which is used as a catalyst in the production of polypropylene.^[2]

Titanium can be alloyed with iron, aluminium, vanadium, molybdenum, among other elements, to produce strong lightweight alloys for aerospace (jet engines, missiles, and spacecraft), military, industrial process (chemicals and petro-chemicals, desalination plants, pulp, and paper), automotive, agri-food, medical prostheses, orthopedic implants, dental and endodontic instruments and files, dental implants, sporting goods, jewelry, mobile phones, and other applications.^[2]

The two most useful properties of the metal form are corrosion resistance and the highest strength-to-weight ratio of any metal.^[5] In its unalloyed condition, titanium is as strong as some steels, but 45% lighter.^[6] There are two allotropic forms^[7] and five naturally occurring isotopes of this element, ⁴⁶Ti through ⁵⁰Ti, with ⁴⁸Ti being the most abundant (73.8%).^[8] Titanium's properties are chemically and physically similar to zirconium, because both of them have the same number of valence electrons and are in the same group in the periodic table.

Characteristics[link]

Physical properties[link]

A metallic element, titanium is recognized for its high strength-to-weight ratio.^[7] It is a strong metal with low density that is quite ductile (especially in an oxygen-free environment),^[2] lustrous, and metallic-white in color.^[9] The relatively high melting point (more than 1,650 °C or 3,000 °F) makes it useful as a refractory metal. It is paramagnetic and has fairly low electrical and thermal conductivity.^[2]

Commercial (99.2% pure) grades of titanium have ultimate tensile strength of about 63,000 psi (434 MPa), equal to that of common, low-grade steel alloys, but are 45% lighter.^[6] Titanium is 60% more dense than aluminium, but more than twice as strong^[6] as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys (e.g., Beta C) achieve tensile strengths of over 200,000 psi (1,400 MPa).^[10] However, titanium loses strength when heated above 430 °C (806 °F).^[11]

It is fairly hard (although not as hard as some grades of heat-treated steel), non-magnetic and a poor conductor of heat and electricity. Machining requires precautions, as the material will soften and gall if sharp tools and proper cooling methods are not used. Like those made from steel, titanium structures have a fatigue limit which guarantees longevity in some applications.^[9] Titanium alloys specific stiffnesses are also usually not as good as other materials such as aluminium alloys and carbon fiber, so it is used less for structures which require high rigidity.

The metal is a dimorphic allotrope whose hexagonal alpha form changes into a body-centered cubic (lattice) β form at 882 °C (1,620 °F).^[11] The specific heat of the alpha form increases dramatically as it is heated to this transition temperature but then falls and remains fairly constant for the β form regardless of temperature.^[11] Similar to zirconium and hafnium, an additional omega phase exists, which is thermodynamically stable at high pressures, but is metastable at ambient pressures. This phase is usually hexagonal (ideal) or trigonal (distorted) and can be viewed as being due to a soft longitudinal acoustic phonon of the β phase causing collapse of (111) planes of atoms.^[12]

Chemical properties[link]

The most noted chemical property of titanium is its excellent resistance to corrosion; it is almost as resistant as platinum, capable of withstanding attack by dilute sulfuric acid and hydrochloric acid as well as chlorine gas, chloride solutions, and most organic acids.^[3] However, it is soluble in concentrated acids.^[14] The Pourbaix diagram in the image shows that titanium is actually thermodynamically a very reactive metal.

However, it is slow to react with water and air, because it forms a passive and protective oxide coating that protects it from further reaction.^[2] When it first forms, this protective layer is only 1–2 nm thick but continues to slowly grow; reaching a thickness of 25 nm in four years.^[15]

Titanium readily reacts with oxygen at 1,200 °C (2,190 °F) in air, and at 610 °C (1,130 °F) in pure oxygen, forming titanium dioxide.^[7] As a result, the metal cannot be melted in open air since it burns before the melting point is reached. Melting is only possible in an inert atmosphere or in a vacuum. At 550 °C (1,022 °F), it combines with chlorine.^[3] It also reacts with the other halogens and absorbs hydrogen.^[4]

Titanium is one of the few elements that burns in pure nitrogen gas, reacting at 800 °C (1,470 °F) to form titanium nitride, which causes embrittlement.^[16]

Experiments have shown that natural titanium becomes radioactive after it is bombarded with deuterons, emitting mainly positrons and hard gamma rays.^[3]

Compounds[link]

TiN coated drill bit

The +4 oxidation state dominates titanium chemistry,^[17] but compounds in the +3 oxidation state are also common.^[18] Because of this high oxidation state, many titanium compounds have a high degree of covalent bonding.

Star sapphires and rubies get their asterism from the titanium dioxide impurities present in them.^[15] Titanates are compounds made with titanium dioxide. Barium titanate has piezoelectric properties, thus making it possible to use it as a transducer in the interconversion of sound and electricity.^[7] Esters of titanium are formed by the reaction of alcohols and titanium tetrachloride and are used to waterproof fabrics.^[7]

Titanium nitride (TiN), having a hardness equivalent to sapphire and carborundum (9.0 on the Mohs Scale),^[19] is often used to coat cutting tools, such as drill bits.^[20] It also finds use as a gold-colored decorative finish, and as a barrier metal in semiconductor fabrication.^[21]

Titanium tetrachloride (titanium(IV) chloride, TiCl₄, sometimes called "tickle"^[22]) is a colorless liquid which is used as an intermediate in the manufacture of titanium dioxide for paint.^[23] It is widely used in organic chemistry as a Lewis acid, for example in the Mukaiyama aldol condensation.^[24] Titanium also forms a lower chloride, titanium(III) chloride (TiCl₃), which is used as a reducing agent.^[25]

Titanocene dichloride is an important catalyst for carbon-carbon bond formation. Titanium isopropoxide is used for Sharpless epoxidation. Other compounds include titanium bromide (used in metallurgy, superalloys, and high-temperature electrical wiring and coatings) and titanium carbide (found in high-temperature cutting tools and coatings).^[4]

Occurrence[link]

2003 production of titanium dioxide^[26]

Producer	thousands of tonnes	% of total
Australia	1291.0	30.6
South Africa	850.0	20.1
Canada	767.0	18.2
Norway	382.9	9.1
Ukraine	357.0	8.5
Other countries	573.1	13.6
Total world	4221.0	100.0

Because of rounding, values do not sum to 100%.

Titanium is always bonded to other elements in nature. It is the ninth-most abundant element in the Earth's crust (0.63% by mass)^[27] and the seventh-most abundant metal. It is present in most igneous rocks and in sediments derived from them (as well as in living things and natural bodies of water).^[2][3] Of the 801 types of igneous rocks analyzed by the United States Geological Survey, 784 contained titanium.^[27] Its proportion in soils is approximately 0.5 to 1.5%.^[27]

It is widely distributed and occurs primarily in the minerals anatase, brookite, ilmenite, perovskite, rutile, titanite (sphene), as well in many iron ores.^[15] Of these minerals, only rutile and ilmenite have any economic importance, yet even they are difficult to find in high concentrations. Significant titanium-bearing ilmenite deposits exist in western Australia, Canada, China, India, Mozambique, New Zealand, Norway, and Ukraine.^[15] Large quantities of rutile are also mined in North America and South Africa and help contribute to the annual production of 90,000 tonnes of the metal and 4.3 million tonnes of titanium dioxide.^[15] Total reserves of titanium are estimated to exceed 600 million tonnes.^[15]

Titanium is contained in meteorites and has been detected in the sun and in M-type stars;^[3] the coolest type of star with a surface temperature of 3,200 °C (5,790 °F).^[28] Rocks brought back from the moon during the Apollo 17 mission are composed of 12.1% TiO₂.^[3] It is also found in coal ash, plants, and even the human body.

Isotopes[link]

Naturally occurring titanium is composed of 5 stable isotopes: ⁴⁶Ti, ⁴⁷Ti, ⁴⁸Ti, ⁴⁹Ti, and ⁵⁰Ti, with ⁴⁸Ti being the most abundant (73.8% natural abundance). Eleven radioisotopes have been characterized, with the most stable being ⁴⁴Ti with a half-life of 63 years, ⁴⁵Ti with a half-life of 184.8 minutes, ⁵¹Ti with a half-life of 5.76 minutes, and ⁵²Ti with a half-life of 1.7 minutes. All of the remaining radioactive isotopes have half-lives that are less than 33 seconds and the majority of these have half-lives that are less than half a second.^[8]

The isotopes of titanium range in atomic weight from 39.99 u (⁴⁰Ti) to 57.966 u (⁵⁸Ti). The primary decay mode before the most abundant stable isotope, ⁴⁸Ti, is electron capture and the primary mode after is beta emission. The primary decay products before ⁴⁸Ti are element 21 (scandium) isotopes and the primary products after are element 23 (vanadium) isotopes.^[8]

History[link]

Martin Heinrich Klaproth named titanium for the Titans of Greek mythology.

Titanium was discovered included in a mineral in Cornwall, United Kingdom, in 1791 by amateur geologist and pastor William Gregor, then vicar of Creed parish.^[29] He recognized the presence of a new element in ilmenite^[4] when he found black sand by a stream in the nearby parish of Manaccan and noticed the sand was attracted by a magnet.^[29] Analysis of the sand determined the presence of two metal oxides; iron oxide (explaining the attraction to the magnet) and 45.25% of a white metallic oxide he could not identify.^[27] Gregor, realizing that the unidentified oxide contained a metal that did not match the properties of any known element, reported his findings to the Royal Geological Society of Cornwall and in the German science journal Crell's Annalen.^[29]

Around the same time, Franz-Joseph Müller von Reichenstein produced a similar substance, but could not identify it.^[4] The oxide was independently rediscovered in 1795 by German chemist Martin Heinrich Klaproth in rutile from Hungary.^[29] Klaproth found that it contained a new element and named it for the Titans of Greek mythology.^[28] After hearing about Gregor's earlier discovery, he obtained a sample of manaccanite and confirmed it contained titanium.

The processes required to extract titanium from its various ores are laborious and costly; it is not possible to reduce in the normal manner, by heating in the presence of carbon, because that produces titanium carbide.^[29] Pure metallic titanium (99.9%) was first prepared in 1910 by Matthew A. Hunter at Rensselaer Polytechnic Institute by heating TiCl₄ with sodium at 700–800 °C in the Hunter process.^[3] Titanium metal was not used outside the laboratory until 1932 when William Justin Kroll proved that it could be produced by reducing titanium tetrachloride (TiCl₄) with calcium.^[30] Eight years later he refined this process by using magnesium and even sodium in what became known as the Kroll process.^[30] Although research continues into more efficient and cheaper processes (e.g., FFC Cambridge), the Kroll process is still used for commercial production.^[3][4]

Titanium sponge, made by the Kroll process

Titanium of very high purity was made in small quantities when Anton Eduard van Arkel and Jan Hendrik de Boer discovered the iodide, or crystal bar, process in 1925, by reacting with iodine and decomposing the formed vapors over a hot filament to pure metal.^[31]

In the 1950s and 1960s the Soviet Union pioneered the use of titanium in military and submarine applications (Alfa Class and Mike Class)^[32] as part of programs related to the Cold War.^[33] Starting in the early 1950s, titanium began to be used extensively for military aviation purposes, particularly in high-performance jets, starting with aircraft such as the F100 Super Sabre and Lockheed A-12.

In the USA, the Department of Defense realized the strategic importance of the metal^[34] and supported early efforts of commercialization.^[35] Throughout the period of the Cold War, titanium was considered a Strategic Material by the U.S. government, and a large stockpile of titanium sponge was maintained by the Defense National Stockpile Center, which was finally depleted in 2005.^[36] Today, the world's largest producer, Russian-based VSMPO-Avisma, is estimated to account for about 29% of the world market share.^[37]

In 2006, the U.S. Defense Agency awarded $5.7 million to a two-company consortium to develop a new process for making titanium metal powder. Under heat and pressure, the powder can be used to create strong, lightweight items ranging from armor plating to components for the aerospace, transport, and chemical processing industries.^[38]

Production and fabrication[link]

Titanium (mineral concentrate)

The processing of titanium metal occurs in 4 major steps:^[39] reduction of titanium ore into "sponge", a porous form; melting of sponge, or sponge plus a master alloy to form an ingot; primary fabrication, where an ingot is converted into general mill products such as billet, bar, plate, sheet, strip, and tube; and secondary fabrication of finished shapes from mill products.

Because the metal reacts with oxygen at high temperatures it cannot be produced by reduction of its dioxide.^[9] Titanium metal is therefore produced commercially by the Kroll process, a complex and expensive batch process. (The relatively high market value of titanium is mainly due to its processing, which sacrifices another expensive metal, magnesium.^[40]) In the Kroll process, the oxide is first converted to chloride through carbochlorination, whereby chlorine gas is passed over red-hot rutile or ilmenite in the presence of carbon to make TiCl₄. This is condensed and purified by fractional distillation and then reduced with 800 °C molten magnesium in an argon atmosphere.^[7]