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22 scandium ← titanium → vanadium - ↑ Ti ↓ Zr Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	titanium, Ti, 22
Chemical series	transition metals
Group, Period, Block	4, 4, d
Appearance	silvery metallic
Atomic mass	47.867(1)  g·mol−1
Electron configuration	[Ar] 3d2 4s2
Electrons per shell	2, 8, 10, 2
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
Heat capacity	(25 °C) 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
Crystal structure	hexagonal
Oxidation states	2, 3, 4 (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	140  pm
Atomic radius (calc.)	176  pm
Covalent radius	136  pm
Miscellaneous
Magnetic ordering	paramagnetic
Electrical resistivity	(20 °C) 0.420 µ Ω·m
Thermal conductivity	(300 K) 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.) 5090  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
Selected isotopes
Main article: Isotopes of physchim62/temp iso NA half-life DM DE (MeV) DP 44Ti syn 63 y ε - 44Sc γ 0.07D, 0.08D - 46Ti 8.0% Ti is stable with 24 neutrons 47Ti 7.3% Ti is stable with 25 neutrons 48Ti 73.8% Ti is stable with 26 neutrons 49Ti 5.5% Ti is stable with 27 neutrons 50Ti 5.4% Ti is stable with 28 neutrons
References

Titanium (IPA: /tʌɪˈteɪniəm/) is a chemical element; in the periodic table it has the symbol Ti and atomic number 22. It is a light, strong, lustrous, corrosion-resistant (including resistance to sea water and chlorine) transition metal with a white-silvery-metallic color. Titanium can be alloyed with other elements such as iron, aluminium, vanadium, molybdenum and others, to produce strong lightweight alloys for aerospace and other demanding applications. In powdered form it can be added to other materials, such as graphite composites. Its most common compound, titanium dioxide, is used in the manufacture of white pigments.^[1]

The element occurs within a number of mineral deposits, principally rutile and ilmenite, which are widely distributed in the Earth's crust. There are two allotropic forms^[2] and five naturally occurring isotopes of this element; ⁴⁶Ti through ⁵⁰Ti with ⁴⁸Ti being the most abundant (73.8%).^[3] One of the most useful properties of the metal form is that it has the highest strength-to-weight ratio of any metal (in its unalloyed condition, as strong as steel, but only 60% its density).^[4] Titanium's properties are chemically and physically similar to zirconium.

Contents 1 History 2 Characteristics 3 Occurrence 4 Production by isolation 5 Manufacture and fabrication 6 Applications 6.1 Medical applications 7 Compounds 8 Isotopes 9 Precautions 10 See also 11 References 12 External links

[edit] History

Titanium was discovered combined in a mineral in Cornwall, in England by amateur geologist William Gregor in 1791. Gregor, who was the vicar of Creed village, recognized the presence of a new element in ilmenite.^[1] He found the mineral in a black sand by a stream in the nearby parish of Manaccan and noticed it was attracted by a magnet. Analysis of the sand determined it was made of two metal oxides; iron oxide and one he could not identify. 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.^[5]

Around the same time, Franz Joseph Muller also produced a similar substance, but could not identify it.^[1] The oxide was independently rediscovered in 1795 by German chemist Martin Heinrich Klaproth in red tourmaline ore from Hungary. Klaproth found that it contained a new element and named it for the Titans of Greek mythology.^[5] After hearing about Gregor's earlier discovery, he obtained a sample of menachanite 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.^[5] Pure metallic titanium (99.9%) was first prepared in 1910 by Matthew A. Hunter by heating TiCl₄ with sodium in a steel bomb at 700–800 °C in the Hunter process.^[4] Titanium metal was not used outside the laboratory until 1946 when William Justin Kroll proved that it could be commercially produced by reducing titanium tetrachloride with magnesium in the Kroll process. Although research continues into more efficient and cheaper processes (FFC Cambridge, e.g.), the Kroll process is still used for commercial production.^[1][4]

In 1950–1960s the Soviet Union led the world in the refinement, processing, and use of titanium. In Western Europe and the US, a fledging industry existed, primarily driven by fluctuating demand side market forces. As a result, the refined titanium supply in the west was unreliable until the late 1960s.^[6] Indeed, titanium for the highly successful U.S. SR-71 reconnaissance aircraft was acquired from the Soviet Union at the height of the Cold War. Throughout the period of the Cold War, titanium was considered a Strategic Material by the US government, and a large stockpile of titanium sponge was maintained by the Defense National Stockpile Center, which was finally depleted in 2005.^[7] Today, the world's largest producer, Russian-based VSMPO-Avisma, is estimated to account for about 29% of the world market share.^[8]

[edit] Characteristics

Titanium is recognized for its excellent resistance to corrosion; it is almost as resistant as platinum, capable of withstanding attack by acids, moist chlorine gas, and by common salt solutions.^[2] Pure titanium is not soluble in water but is soluble in concentrated acids.^[9] A metallic element, it is also recognized for its high strength-to-weight ratio.^[2] It is a light, strong metal with low density that, when pure, is quite ductile (especially in an oxygen-free environment),^[10] lustrous, and metallic-white in colour. The relatively high melting point (over 1,649 °C or 3,000 °F) makes it useful as a refractory metal.

Commercially pure grades of titanium have ultimate tensile strengths of up to 80,000 psi (550 MPa), equal to that of high strength low alloy steels, but are 43% lighter. Titanium is 60% heavier than aluminium, but more than twice as strong as the most commonly used 6061-T6 aluminum alloy. Certain titanium alloys (e.g., Beta C) achieve tensile strengths of close to 200,000 psi (1.4 GPa). It is fairly hard (although by no means as hard as some grades of heat-treated steel) and can be tricky to machine due to the fact that it will 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.^[11]

This metal forms a passive and protective oxide coating (leading to corrosion-resistance) when exposed to elevated temperatures in air, but at room temperatures it resists tarnishing.^[10] When it first forms, this protective layer is only 1 to 2 nanometers thick but continues to slowly grow; reaching a thickness of 25 nanometers in four years.^[5] It burns when heated in air 610 °C (1,130 °F) or higher (forming titanium dioxide) and is also one of the few elements that burns in pure nitrogen gas (it burns at 800 °C or 1,472 °F and forms titanium nitride).^[2][12] Titanium is resistant to dilute sulfuric and hydrochloric acid, along with chlorine gas, chloride solutions, and most organic acids.^[4] It is paramagnetic (weakly attracted to magnets) and has fairly low electrical and thermal conductivity.^[10]

Experiments have shown that natural titanium becomes radioactive after it is bombarded with deuterons, emitting mainly positrons and hard gamma rays.^[4] The metal is a dimorphic allotrope with the hexagonal alpha form changing into the cubic beta form very slowly at around 880 °C (1,616 °F).^[4] When it is red hot the metal combines with oxygen, and when it reaches 550 °C (1,022 °F) it combines with chlorine.^[4] It also reacts with the other halogens and absorbs hydrogen. ^[1]

[edit] Occurrence

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) and the fourth-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).^[10][4] It is widely distributed and occurs primarily in the minerals anatase, brookite, ilmenite, perovskite, rutile, titanite (sphene), as well in many iron ores. Of these minerals, only rutile and ilmenite have significant economic importance, yet even they are difficult to find in high concentrations.^[1] Significant titanium-bearing ilmenite deposits exist in western Australia, New Zealand, Norway, Canada, and the Ukraine. 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. Total known reserves of titanium are estimated to exceed 600 million tonnes.^[5]

This metal is found in meteorites and has been detected in the sun and in M-type stars;^[4] the coolest type of star with a surface temperature of 3,200 °C (5,792 °F).^[5] Rocks brought back from the moon during the Apollo 17 mission are composed of 12.1% TiO₂.^[4] Titanium is also found in coal ash, plants, and even the human body.

[edit] Production by isolation

Because the metal reacts with air at high temperatures it cannot be produced by reduction of its dioxide. Titanium metal is therefore produced commercially by the Kroll process, a complex and expensive batch process developed in 1946 by William Justin Kroll. 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.^[2]

A newer process, the FFC Cambridge process,^[14] may replace the older Kroll process. This method uses the feedstock titanium dioxide powder (which is a refined form of rutile) to make the end product which is either a powder or sponge. If mixed oxide powders are used, the product is an alloy at a much lower cost than the conventional multi-step melting process. It is hoped that the FFC Cambridge Process will render titanium a less rare and expensive material for the aerospace industry and the luxury goods market, and will be seen in many products currently manufactured using aluminium and specialist grades of steel. 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, transportation and chemical processing industries. ^[15]

Titanium was purified to ultra high purity 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.^[16]

Pure titanium dioxide may be prepared by grinding its mineral ore and mixing it with potassium carbonate and aqueous hydrofluoric acid. This yields potassium fluorotitanate (K₂TiF₆) which is extracted with hot water and decomposed with ammonia, producing an ammoniacal hydrated oxide. This in turn is ignited in a platinum vessel, to give the anhydrous oxide.^[12]

Common titanium alloys are made by reduction. For example; cuprotitanium (rutile with copper added is reduced), ferrocarbon titanium (ilmenite reduced with coke in an electric furnace), and manganotitanium (rutile with manganese or manganese oxides) are reduced.^[12]

2TiFeO₃ + 7Cl2 + 6C (900 °C) → 2TiCl₄ + 2FeCl₃ + 6CO

TiCl₄ + 2Mg (1100 °C) → 2MgCl₂ + Ti

[edit] Manufacture and fabrication

Titanium bearing ore is initially reduced using the Kroll process to produce titanium sponge, the basic feedstock for melting and pouring a titanium ingot in a VAR (Vacuum Arc Furnace). Because titanium reacts with atmospheric gases, all transformation at temperature (other than cold working) must be done in vacuum or in an inert atmosphere (usually argon). The relatively high market value of titanium, notwithstanding effects of supply and demand, is a function of the cost of the processing, which exceeds the processing costs of other metallics, and not of scarcity.^[17] Once produced, the ingot is subsequently reduced and transformed through a variety of steps by forging, extruding and rolling into finished mill products, such as plates, sheets or billets and bars. Production methods are similar to those used for making steel and stainless steel.

The ASTM International recognizes 31 Grades of titanium metal and alloys, of which Grades 1 through 4 are commercially pure (unalloyed). These four are distinguished by their varying degrees of tensile strength, as a function of oxygen content, with Grade 1 being the most ductile (lowest tensile strength with an oxygen content of 0.18%), and Grade 4 the least (highest tensile strength with an oxygen content of 0.40%).^[11] The remaining grades are alloys, each designed for specific purposes, be it ductility, strength, hardness, electrical resistivity, creep resistance, resistance to corrosion from specific media, or a combination thereof.^[18]

In terms of fabrication, welding of titanium must be done in an inert atmosphere in order to shield it from contamination with atmospheric gases. Contamination will cause a variety of conditions, such as embrittlement, which will reduce the integrity of the assembly welds and lead to joint failure. Commercially pure flat product (sheet, plate) can be formed readily, but processing must take into account the fact that the metal has a "memory" and tends to spring back. This is especially true of certain high-strength alloys.^[19][20]

[edit] Applications

About 95% of titanium ore extracted from the Earth is destined for refinement into titanium dioxide (TiO₂), an intensely white permanent pigment used in paints, paper, toothpaste, and plastics.^[21] It is also used in cement, in gemstones, as an optical opacifier in paper,^[22] and a strengthening agent in graphite composite fishing rods and golf clubs. Recently, it has been put to use in air purifiers (as a filter coating), or in film used to coat windows on buildings which when exposed to UV light (either solar or man-made) and moisture in the air produces reactive redox species like hydroxyl radicals that can purify the air or keep window surfaces clean.^[23]

Titanium is used in steel as an alloying element (ferro-titanium) to reduce grain size and as a deoxidizer, and in stainless steel to reduce carbon content.^[10] Titanium is often alloyed with aluminium (to refine grain size), vanadium, copper (to harden), iron, manganese, molybdenum, and with other metals.^[24] Applications for titanium mill products (sheet, plate, bar, wire, forgings, castings) can be found in industrial, aerospace, recreational and emerging markets.

Due to excellent corrosion resistance to sea water, it is used to make propeller shafts and rigging and in the heat exchangers of desalination plants;^[4] in heater-chillers for salt water aquariums, fishing line and leader, and diver knives as well. It was the principal material used in the construction of many advanced Russian submarines.^[25] Titanium is used to manufacture the housings and other components of ocean-deployed surveillance and monitoring devices for scientific and military use.

Because of its high tensile strength (even at high temperatures),^[2] light weight, extraordinary corrosion resistance,^[4] and ability to withstand extreme temperatures, titanium alloys are used in aircraft, armour plating, naval ships, spacecraft, and missiles.^[1][4] For these applications, titanium alloyed with aluminum, vanadium, and other elements is used for a variety of components including critical structural parts, fire walls, landing gear, exhaust ducts (helicopters) and hydraulic systems. In fact, about two thirds of all titanium metal produced is used in aircraft engines and frames.^[11] An estimated 58 tons are used in the Boeing 777, 43 in the 747, 18 in the 737, 24 in the Airbus A340, 17 in the A330 and 12 in the A320. The A380 may use 77 tons, including about 11 tons in the engines.^[26] In engine applications, titanium is used for rotors, turbine blades, hydraulic system components and nacelles.

Titanium metal is used in automotive applications, particularly in automobile or motorcycle racing, where weight reduction is critical while maintaining high strength and rigidity. The metal is generally too expensive to make it marketable to the general consumer market, other than high end products. Late model Corvettes have been available with titanium exhausts,^[27] and racing bikes are frequently outfitted with titanium mufflers. Other automotive uses include piston rods and hardware (bolts, nuts, etc.).

Its inertness and ability to be attractively colored makes it a popular metal for use in body piercing.^[29] Titanium may be anodized to produce various colors.^[30] A number of artists work with titanium to produce artworks such as sculptures, decorative objects and furniture.

Titanium is used in many sporting goods; tennis rackets, golf clubs, lacrosse stick shafts, cricket helmet grills, bicycle. Titanium alloys are also used in spectacle frames. This results in a rather expensive, but highly durable and long lasting frame which is light in weight and causes no skin allergies. Many backpackers use titanium equipment, including cookware, eating utensils, lanterns and tent stakes. Though slightly more expensive than traditional steel or aluminium alternatives, these titanium products can be significantly lighter without compromising strength.

Titanium has occasionally been used in architectural applications: the 120-foot (40 m) memorial to Yuri Gagarin, the first man to travel in space, in Moscow, is made of titanium for the metal's attractive color and association with rocketry.^[31] The Guggenheim Museum Bilbao and the Cerritos Millennium Library were the first buildings in Europe and North America, respectively, to be sheathed in titanium panels. Other construction uses of titanium sheathing include the Frederic C. Hamilton Building in (Denver, Colorado).^[32]

[edit] Medical applications

Because it is biocompatible (non-toxic and is not rejected by the body), titanium is used in a gamut of medical applications including surgical implements and implants, such as hip balls and sockets (joint replacement) that can stay in place for up to 20 years. Titanium has the inherent property to osseointegrate, enabling use in dental implants that can remain in place for over 30 years. This property is also useful for orthopedic implant applications.^[5] These benefit from titanium's lower modulus of elasticity (Young's modulus) to more closely match that of the bone that such devices are intended to repair. As a result, skeletal loads are more evenly shared between bone and implant, leading to a lower incidence of bone degradation due to stress shielding and periprosthetic bone fractures which occur at the boundaries of orthopedic implants which act as stress risers. However, titanium alloys' stiffness is still more than twice that of bone, eventually leading to joint degradation.

Since titanium is non-ferromagnetic, patients with titanium implants can be safely examined with magnetic resonance imaging (convenient for long-term implants). Preparing titanium for implantation in the body involves subjecting it to a high-temperature plasma arc which removes the surface atoms, exposing fresh titanium that is instantly oxidized.^[5] Titanium is also used for the surgical instruments used in image-guided surgery, as well as wheelchairs, crutches, and any other product where high strength and low weight are important.

[edit] Compounds

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

Although titanium metal is relatively uncommon, due to the cost of extraction, titanium dioxide (also called titanium(IV), titanium white, or even titania) is cheap, nontoxic, readily available in bulk, and very widely used as a white pigment in paint, enamel, lacquer, plastic and construction cement. TiO₂ powder is chemically inert, resists fading in sunlight, and is very opaque: this allows it to impart a pure and brilliant white colour to the brown or gray chemicals that form the majority of household plastics.^[1] In nature, this compound is found in the minerals anatase, brookite, and rutile.^[10]

Paint made with titanium dioxide does well in severe temperatures, is somewhat self-cleaning, and stands up to marine environments.^[1] Pure titanium dioxide has a very high index of refraction and an optical dispersion higher than diamond.^[4] Star sapphires and rubies get their asterism from the titanium dioxide impurities present in them.^[5] 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.^[2] Esters of titanium are formed by the reaction of alcohols and titanium tetrachloride and are used to waterproof fabrics.^[2]

Titanium nitride (TiN) is often used to coat cutting tools, such as drill bits. It also finds use as a gold-coloured decorative finish, and as a barrier metal in semiconductor fabrication.

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

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).^[1]

[edit] Isotopes

Main article: Isotopes of titanium

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-lifes that are less than 33 seconds and the majority of these have half-lifes that are less than half a second.^[3]

The isotopes of titanium range in atomic weight from 39.99 amu (⁴⁰Ti) to 57.966 amu (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.^[3]

[edit] Precautions

Titanium is non-toxic even in large doses and does not play any natural role inside the human body. An estimated 0.8 milligrams of titanium is ingested by humans each day but most passes through without being absorbed. It does, however, has a tendency to bio-accumulate in tissues that contain silica. An unknown mechanism in plants may use titanium to stimulate the production of carbohydrates and encourage growth. This may explain why most plants contain about 1 part per million (ppm) of titanium, food plants have about 2 ppm and horsetail and nettle contain up to 80 ppm.^[5]

As a powder or in the form of metal shavings, titanium metal poses a significant fire hazard and, when heated in air, an explosion hazard. Water and carbon dioxide-based methods to extinguish fires are ineffective on burning titanium; Class D dry powder fire fighting agents must be used instead.^[1]

Salts of titanium are often considered to be relatively harmless but its chlorine compounds, such as TiCl₂, TiCl₃ and TiCl₄, have unusual hazards. The dichloride takes the form of pyrophoric black crystals, and the tetrachloride is a volatile fuming liquid. All of titanium's chlorides are corrosive.

[edit] See also

• Titanium coating
• Titanium compounds.
• Titanium in Africa
• Titanium minerals
• Links to external chemical sources

[edit] References

• Flower, Harvey M. (2000). "Materials Science: A moving oxygen story". Nature 407: 305. 
• Stwertka, Albert (1998). Guide to the Elements (Revised Edition). Oxford: Oxford University Press. ISBN 0-19-508083-1. 
• Winter, Mark (2006). Chemistry: Periodic table: Titanium. WebElements. Retrieved on 2006-12-10.

[edit] External links

{{Spoken Wikipedia|Titanium.ogg|2005-08-25}}

• A Cleaner, Cheaper Route to Titanium
• International Titanium Association
• Metallurgy of Titanium and its Alloys, Cambridge University
• The Titanium Information Group
• World Production of Titanium Concentrates, by Country

Category:Chemical elements Category:Transition metals Category:Titanium