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A strong, low-density, highly corrosion-resistant, lustrous white metallic element that occurs widely in igneous rocks and is used to alloy aircraft metals for low weight, strength, and high-temperature stability. Atomic number 22; atomic weight 47.87 melting point 1,660°C; boiling point 3,287°C; specific gravity 4.54; valence 2, 3, 4.
[From Latin Tītān, Titan. See Titan.]
Background
Titanium is known as a transition metal on the periodic table of elements denoted by the symbol Ti. It is a lightweight, silver-gray material with an atomic number of 22 and an atomic weight of 47.90. It has a density of 4510 kg/m3, which is somewhere between the densities of aluminum and stainless steel. It has a melting point of roughly 3,032°F (1,667°C) and a boiling point of 5,948°F (3,287 C). It behaves chemically similar to zirconium and silicon. It has excellent corrosion resistance and a high strength to weight ratio.
Titanium is the fourth most abundant metal making up about 0.62% of the earth's crust. Rarely found in its pure form, titanium typically exists in minerals such as anatase, brookite, ilmenite, leucoxene, perovskite, rutile, and sphene. While titanium is relatively abundant, it continues to be expensive because it is difficult to isolate. The leading producers of titanium concentrates include Australia, Canada, China, India, Norway, South Africa, and Ukraine. In the United States, the primary titanium producing states are Florida, Idaho, New Jersey, New York, and Virginia.
Thousands of titanium alloys have been developed and these can be grouped into four main categories. Their properties depend on their basic chemical structure and the way they are manipulated during manufacture. Some elements used for making alloys include aluminum, molybdenum, cobalt, zirconium, tin, and vanadium. Alpha phase alloys have the lowest strength but are formable and weldable. Alpha plus beta alloys have high strength. Near alpha alloys have medium strength but have good creep resistance. Beta phase alloys have the highest strength of any titanium alloys but they also lack ductility.
The applications of titanium and its alloys are numerous. The aerospace industry is the largest user of titanium products. It is useful for this industry because of its high strength to weight ratio and high temperature properties. It is typically used for airplane parts and fasteners. These same properties make titanium useful for the production of gas turbine engines. It is used for parts such as the compressor blades, casings, engine cowlings, and heat shields.
Since titanium has good corrosion resistance, it is an important material for the metal finishing industry. Here it is used for making heat exchanger coils, jigs, and linings. Titanium's resistance to chlorine and acid makes it an important material in chemical processing. It is used for the various pumps, valves, and heat exchangers on the chemical production line. The oil refining industry employs titanium materials for condenser tubes because of corrosion resistance. This property also makes it useful for equipment used in the desalinization process.
Titanium is used in the production of human implants because it has good compatibility with the human body. One of the most notable recent uses of titanium is in artificial hearts first implanted in a human in 2001. Other uses of titanium are in hip replacements, pacemakers, defibrillators, and elbow and hip joints.
Finally, titanium materials are used in the production of numerous consumer products. It is used in the manufacture of such things as shoes, jewelry, computers, sporting equipment, watches, and sculptures. As titanium dioxide, it is used as a white pigment in plastic, paper, and paint. It is even used as a white food coloring and as a sunscreen in cosmetic products.
History
Most historians credit William Gregor for the discovery of titanium. In 1791, he was working with menachanite (a mineral found in England) when he recognized the new element and published his results. The element was rediscovered a few years later in the ore rutile by M. H. Klaproth, a German chemist. Klaproth named the element titanium after the mythological giants, the Titans.
Both Gregor and Klaproth worked with titanium compounds. The first significant isolation of nearly pure titanium was accomplished in 1875 by Kirillov in Russia. Isolation of the pure metal was not demonstrated until 1910 when Matthew Hunter and his associates reacted titanium tetrachloride with sodium in a heated steel bomb. This process produced individual pieces of pure titanium. In the mid 1920s, a group of Dutch scientists created small wires of pure titanium by conducting a dissociation reaction on titanium tetraiodide.
These demonstrations prompted William Kroll to begin experimenting with different methods for efficiently isolating titanium. These early experiments led to the development of a process for isolating titanium by reduction with magnesium in 1937. This process, now called the Kroll process, is still the primary process for producing titanium. The first products made from titanium were introduced around the 1940s and included such things as wires, sheets, and rods.
While Kroll's work demonstrated a method for titanium production on a laboratory scale, it took nearly a decade more before it could be adapted for large-scale production. This work was conducted by the United States Bureau of Mines from 1938 to 1947 under the direction of R. S. Dean. By 1947, they had made various modifications to Kroll's process and produced nearly 2 tons of titanium metal. In 1948, DuPont opened the first large scale manufacturing operation.
This large scale manufacturing method allowed for the use of titanium as a structural material. In the 1950s, it was used primarily by the aerospace industry in the construction of aircraft. Since titanium was superior to steel for many applications, the industry grew rapidly. By 1953, annual production had reached 2 million lb (907,200 kg) and the primary customer for titanium was the United States military. In 1958, demand for titanium dropped off significantly because the military shifted its focus from manned aircraft to missiles for which steel was more appropriate. Since then, the titanium industry has had various cycles of high and low demand. Numerous new applications and industries for titanium and its alloys have been discovered over the years. Today, about 80% of titanium is used by the aerospace industry and 20% by non-aerospace industries.
Raw Materials
Titanium is obtained from various ores that occur naturally on the earth. The primary ores used for titanium production include ilmenite, leucoxene, and rutile. Other notable sources include anatase, perovskite, and sphene.
Ilmenite and leucoxene are titaniferous ores. Ilmenite (FeTiO3) contains approximately 53% titanium dioxide. Leucoxene has a similar composition but has about 90% titanium dioxide. They are found associated with hard rock deposits or in beaches and alluvial sands. Rutile is relatively pure titanium dioxide (TiO2). Anatase is another form of crystalline titanium dioxide and has just recently become a significant commercial source of titanium. They are both found primarily in beach and sand deposits.
Perovskite (CaTiO3) and sphene (CaTi-SiO5) are calcium and titanium ores. Neither of these materials are used in the commercial production of titanium because of the difficulty in removing the calcium. In the future, it is likely that perovskite may be used commercially because it contains nearly 60% titanium dioxide and only has calcium as an impurity. Sphene has silicon as a second impurity that makes it even more difficult to isolate the titanium.
In addition to the ores, other compounds used in titanium production include chlorine gas, carbon, and magnesium.
The Manufacturing
Process
Titanium is produced using the Kroll process. The steps involved include extraction, purification, sponge production, alloy creation, and forming and shaping. In the United States, many manufacturers specialize in different phases of this production. For example, there are manufacturers that just make the sponge, others that only melt and create the alloy, and still others that produce the final products. Currently, no single manufacturer completes all of these steps.
Extraction
Purification
Production of the sponge
Alloy creation
Byproducts/Waste
During the production of pure titanium a significant amount of magnesium chloride is produced. This material is recycled in a recycling cell immediately after it is produced. The recycling cell first separates out the magnesium metal then the chlorine gas is collected. Both of these components are reused in the production of titanium.
The Future
Future advances in titanium manufacture are likely to be found in the area of improved ingot production, the development of new alloys, the reduction in production costs, and the application to new industries. Currently, there is a need for larger ingots than can be produced by the available furnaces. Research is ongoing to develop larger furnaces that can meet these needs. Work is also being done on finding the optimal composition of various titanium alloys. Ultimately, researchers hope that specialized materials with controlled microstructures will be readily produced. Finally, researchers have been investigating different methods for titanium purification. Recently, scientists at Cambridge University announced a method for producing pure titanium directly from titanium dioxide. This could substantially reduce production costs and increase availability.
Where to Learn More
Books
Othmer, K. Encyclopedia of Chemical Technology. New York: Marcel Dekker, 1998.
U.S. Department of the Interior U.S Geological Survey. Minerals Yearbook Volume 1. Washington, DC: U.S. Government Printing Office, 1998.
Periodicals
Freemantle, M. "Titanium Extracted Directly from TiO2." Chemical and Engineering News (25 September 2000).
Eylon D. "Titanium for Energy and Industrial Applications." Metallurgical Society AIME (1987).
Other
WebElements Web Page. December 2001. <http://www.webelements.com>.
[Article by: Perry Romanowski]
A chemical element, Ti, atomic number 22, and atomic weight 47.90. It occurs in the fourth group of the periodic table, and its chemistry shows many similarities to that of silicon and zirconium. On the other hand, as a first-row transition element, titanium has an aqueous solution chemistry, especially of the lower oxidation states, showing some resemblances to that of vanadium and chromium. See also Periodic table; Transition elements.
The catalytic activity of titanium complexes forms the basis of the well-known Ziegler process for the polymerization of ethylene. This type of polymerization is of great industrial interest since, with its use, high-molecular-weight polymers can be formed. In some cases, desirable special properties can be obtained by forming isotactic polymers, or polymers in which there is a uniform stereochemical relationship along the chain. See also Polyolefin resins.
The dioxide of titanium, TiO2, occurs most commonly in a black or brown tetragonal form known as rutile. Less prominent naturally occurring forms are anatase and brookite (rhombohedral). Both rutile and anatase are white when pure. The dioxide may be fused with other metal oxides to yield titanates, for example, K2TiO3, ZnTiO3, PbTiO3, and BaTiO3. The black basic oxide, FeTiO3, occurs naturally as the mineral ilmenite; this is a principal commercial source of titanium.
Titanium dioxide is widely used as a white pigment for exterior paints because of its chemical inertness, superior covering power, opacity to damaging ultraviolet light, and self-cleaning ability. The dioxide has also been used as a whitening or opacifying agent in numerous situations, for example as a filler in paper, a coloring agent for rubber and leather products, a pigment in ink, and a component of ceramics. It has found important use as an opacifying agent in porcelain enamels, giving a finish coat of great brilliance, hardness, and acid resistance. Rutile has also been found as brilliant, diamondlike crystals, and some artificial production of it in this form has been achieved. Because of its high dielectric constant, it has found some use in dielectrics.
The alkaline-earth titanates show some remarkable properties. The dielectric constants range from 13 for MgTiO3 to several thousand for solid solutions of SrTiO3 in BaTiO3. Barium titanate itself has a dielectric constant of 10,000 near 120°C (248°F), its Curie point; it has a low dielectric hysteresis. These properties are associated with a stable polarized state of the material analogous to the magnetic condition of a permanent magnet, and such substances are known as ferroelectrics. In addition to the ability to retain a charged condition, barium titanate is piezoelectric and may be used as a transducer for the interconversion of sound and electrical energy. Ceramic transducers containing barium titanate compare favorably with Rochelle salt and quartz, with respect to thermal stability in the first case, and with respect to the strength of the effect and the ability to form the ceramic in various shapes, in the second case. The compound has been used both as a generator for ultrasonic vibrations and as a sound detector. See also Piezoelectricity.
In addition to important uses in applications such as structural materials, pigments, and industrial catalysis, titanium has a rich coordination chemistry. The formal oxidation of titanium in molecules and ions ranges from −II to +IV. The lower oxidation states of −II and −I occur only in a few complexes containing strongly electron-withdrawing carbon monoxide ligands.
The lower oxidation states of titanium are all strongly reducing. Thus, unless specific precautions are taken, titanium complexes are typically oxidized rapidly to the +IV state. Moreover, many titanium complexes are extremely susceptible to hydrolysis. Consequently, the handling of titanium complexes normally requires oxygen- and water-free conditions. See also Coordination chemistry.
A family of laptop computers from Apple that was introduced in 1991. PowerBook was the first Apple brand name for a series of portable computers, which lasted until 2006, when they were superseded by the MacBook Pro. Prior to the PowerBook, Apple introduced a portable computer that was not very widely used (see Macintosh Portable). The first color PowerBook was the 165C in 1993.
Like the Macintosh desktop evolution, the first PowerBooks used Motorola 68K CPUs and subsequently changed to PowerPC chips in 1995.
Very Popular
Throughout their history, the PowerBooks were very popular. In 2001, Apple introduced a thin, silver PowerBook in a titanium case that became a cult machine. The titanium model was followed by anodized aluminum cases in keeping with Apple's new look. The last PowerBook was the PowerBook G4 in 2006, which was superseded by the MacBook line, also maintaining the silver case design. See iBook, MacBook and Macintosh.
 |
| Introduced in 1994, this PowerBook model used a touchpad instead of the trackball found on earlier models. Except for a brief period in the mid-1990s when certain models were experiencing battery problems, Apple's PowerBooks were very popular. |
 |
| Introduced in 2001, the 99.5% pure titanium body and 15.2" wide screen set this G4-based PowerBook apart from the crowd. Only one inch thick and weighing five pounds, its thin, crisp look began a new era in Macintosh laptop design. |
For more information on titanium, visit Britannica.com.
A chemical element, atomic number 22, atomic weight 47.90, symbol Ti.
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| Name, symbol, number | titanium, Ti, 22 | |||||||||||||||||||||||||||||||||||||||||||||
| Chemical series | transition metals | |||||||||||||||||||||||||||||||||||||||||||||
| Group, period, block | 4, 4, d | |||||||||||||||||||||||||||||||||||||||||||||
| Appearance | silvery metallic |
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| Standard atomic weight | 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 ° |
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| Boiling point | 3560 K (3287 °C, 5949 ° |
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| 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 | |||||||||||||||||||||||||||||||||||||||||||||
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| Atomic properties | ||||||||||||||||||||||||||||||||||||||||||||||
| Crystal structure | hexagonal | |||||||||||||||||||||||||||||||||||||||||||||
| Oxidation states | 2, 3, 4 (amphoteric oxide) |
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| 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 µΩ·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 | ||||||||||||||||||||||||||||||||||||||||||||||
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| 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 (jet engines, missiles, and spacecraft), military, industrial process (chemicals and petro-chemicals, desalination plants, pulp and paper), automotive, agri-food, medical (prostheses, orthopaedic implants, dental implants), sporting goods, and other applications.[1] Titanium was discovered in England 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.[1] The metal is extracted from its
principal mineral ores via the Kroll process.[2] Its most common compound, titanium
dioxide, is used in the manufacture of white pigments.[3] Other compounds include titanium
tetrachloride (TiCl4) (used in smoke screens/skywriting and as a
The two most useful properties of the metal form are corrosion resistance, and the highest strength-to-weight ratio of any
metal.[4] In its unalloyed condition, titanium is as strong
as steel, but 45% lighter.[5] There are two allotropic forms[6] and five naturally occurring
Titanium was discovered combined in a mineral in Cornwall, England in 1791 by amateur geologist and pastor William Gregor, the then vicar of Creed parish. He recognized the presence of a new element in ilmenite[3] when he found black sand by a stream in the nearby parish of Manaccan and noticed the sand was attracted by a magnet. 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.[5] 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.[8]
Around the same time, Franz Joseph Muller also produced a similar substance, but could not identify it.[3] The oxide was independently rediscovered in 1795 by German chemist Martin Heinrich Klaproth in rutile from Hungary.[9] Klaproth found that it contained a new element and named it for the Titans of Greek mythology.[8] 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.[8] 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.[2] 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 what came to be known as 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.[3][2]
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.[10]
In the 1950s and 1960s the Soviet Union pioneered the use of titanium in military and
submarine applications (
In the USA, the DOD realized the strategic importance of the metal[13] and supported early efforts of commercialization.[14] 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.[15] Today, the world's largest producer, Russian-based VSMPO-Avisma, is estimated to account for about 29% of the world market share.[16]
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.[17]
In 2007 a Canadian Student named Ehsan Ghandhari discovered a new version of the Kroll process which reduced the use of magnesium and chlorine decreasing the weight and price. He later published a book on the discovery.
A metallic element, titanium is recognized for its high strength-to-weight ratio.[6] It is a light, strong metal with low density that, when pure, is quite ductile (especially in an oxygen-free environment),[18] lustrous, and metallic-white in color. The relatively high melting point (over 1,649 °C or 3,000 °F) makes it useful as a refractory metal.
Commercial (99.2% pure) grades of titanium have ultimate tensile strengths of about 63,000 psi, equal to that of steels alloys, but are 45% lighter.[5] Titanium is 60% heavier than aluminium, but more than twice as strong[5] as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys (e.g., Beta C) achieve tensile strengths of over 200,000 psi (1.4 GPa).[19] However, titanium loses strength when heated above 430 °C (800 °F).[5]
It is fairly hard (although not as hard as some grades of heat-treated steel) and is difficult to machine, as 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.[20]
The metal is a dimorphic allotrope with the hexagonal alpha form changing into the body-centered cubic (lattice) beta form at 882 °C (1,619 °F).[5] The heat capacity of the alpha form increases dramatically as it is heated to this transition temperature but then falls and remains fairly constant for the beta form regardless of temperature.[5]
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
While the following pourbaix diagram shows that titanium is thermodynamically a very reactive metal, it is slow to react with water and air.
![The Pourbaix diagram for titanium in pure water, perchloric acid or sodium hydroxide[22]](http://content.answers.com/main/content/wp/en/thumb/c/cd/240px-Titanium_in_water_porbiax_diagram.png)
This metal forms a passive and protective oxide coating (leading to increased corrosion-resistance) when exposed to elevated temperatures in air, but at room temperatures it resists tarnishing.[18] 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.[8]
Titanium burns when heated in air 610 °C (1,130 °F) or higher, forming titanium dioxide.[6] It 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, which causes embrittlement).[23] Titanium is resistant to dilute sulfuric and hydrochloric acid, along with chlorine gas, chloride solutions, and most organic acids.[2] It is paramagnetic (weakly attracted to magnets) and has fairly low electrical and thermal conductivity.[18]
Experiments have shown that natural titanium becomes
| Producer | Thousands of tons | % 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 | 100.1 |
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)[5] 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).[18][2] In fact, of the 801 types of igneous rocks analyzed by the United States Geological Survey, 784 contained titanium.[5] Its proportion in soils is approximately 0.5 to 1.5%.[5]
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 any economic importance, yet even they are difficult to find in high
concentrations.[3] Significant
titanium-bearing ilmenite deposits exist in western Australia, Canada,
Titanium is contained in meteorites and has been detected in the sun and in M-type stars;[2] the coolest type of star with a surface temperature of 3,200 °C (5,792 °F).[8] Rocks brought back from the moon during the Apollo 17 mission are composed of 12.1% TiO2.[2] It is also found in coal ash, plants, and even the human body.
The processing of titanium metal occurs in 4 major steps:[25] reduction of titanium ore into "sponge", a porous form; melting of sponge, or sponge plus a master alloy to form an ingot; primary fabrication, whereby 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. 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.[5]) 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.[6]
A more recently developed method, the FFC Cambridge process,[26] may eventually replace the Kroll process. This method uses titanium dioxide powder (which is a refined form of rutile) as feedstock to make the end product which is either a powder or sponge. If mixed oxide powders are used, the product is an alloy manufactured at a much lower cost than the conventional multi-step melting process. The FFC Cambridge Process may render titanium a less rare and expensive material for the aerospace industry and the luxury goods market, and could be seen in many products currently manufactured using aluminium and specialist grades of steel.
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.[23]
About 50 grades of titanium and titanium alloys are designated and currently used, although only a couple of dozen are readily available commercially.[27] 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%).[20] 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.[28]
The grades covered by ASTM and other alloys are also produced to meet Aerospace and Military specifications (SAE-AMS, MIL-T), ISO standards, and country-specific specifications, as well as proprietary end-user specifications for aerospace, military, medical and industrial applications.[29]
In terms of fabrication, all welding of titanium must be done in an inert atmosphere of argon or helium in order to shield it from contamination with atmospheric gases such as oxygen, nitrogen or hydrogen, and to prevent fires, as molten titanium is highly reactive to oxygen.[5] 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.[30][31] The metal can be machined using the same equipment and via the same processes as stainless steel.[5]
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.[18] Titanium is often alloyed with aluminium (to refine grain size), vanadium, copper (to harden),
