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Titanium

Titanium

Gist

Titanium is a lustrous, silver-colored transition metal with atomic number 22, symbolized as Ti. It's known for its high strength-to-weight ratio, corrosion resistance, and biocompatibility. Titanium is abundant in the Earth's crust and is used in various applications, including aerospace, medical implants, and industrial equipment.

Titanium: These alloys are mainly used in aircraft, spacecraft and missiles because of their low density and ability to withstand extremes of temperature. They are also used in golf clubs, laptops, bicycles and crutches. Power plant condensers use titanium pipes because of their resistance to corrosion.

Summary

Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in sea water, aqua regia, and chlorine.

Titanium was discovered in Cornwall, Great Britain, by William Gregor in 1791 and was named by Martin Heinrich Klaproth after the Titans of Greek mythology. The element occurs within a number of minerals, principally rutile and ilmenite, which are widely distributed in the Earth's crust and lithosphere; it is found in almost all living things, as well as bodies of water, rocks, and soils. The metal is extracted from its principal mineral ores by the Kroll and Hunter processes. The most common compound, titanium dioxide (TiO2), is a popular photocatalyst and is used in the manufacture of white pigments. 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.

Titanium can be alloyed with iron, aluminium, vanadium, and molybdenum, among other elements. The resulting titanium alloys are strong, lightweight, and versatile, with applications including aerospace (jet engines, missiles, and spacecraft), military, industrial processes (chemicals and petrochemicals, desalination plants, pulp, and paper), automotive, agriculture (farming), sporting goods, jewelry, and consumer electronics. Titanium is also considered one of the most biocompatible metals, leading to a range of medical applications including prostheses, orthopedic implants, dental implants, and surgical instruments.

The two most useful properties of the metal are corrosion resistance and strength-to-density ratio, the highest of any metallic element. In its unalloyed condition, titanium is as strong as some steels, but less dense. There are two allotropic forms and five naturally occurring isotopes of this element, 46Ti through 50Ti, with 48Ti being the most abundant (73.8%).

Details

Titanium (Ti) is a chemical element, a silvery gray metal of Group 4 (IVb) of the periodic table. Titanium is a lightweight, high-strength, low-corrosion structural metal and is used in alloy form for parts in high-speed aircraft. A compound of titanium and oxygen was discovered (1791) by the English chemist and mineralogist William Gregor and independently rediscovered (1795) and named by the German chemist Martin Heinrich Klaproth.

Element Properties

atomic number  :  22
atomic weight  :  47.867
melting point  :  1,660 °C (3,020 °F)
boiling point  :  3,287 °C (5,949 °F)
density  :  4.5 g/{cm}^{3} (20 °C)
oxidation states  :  +2, +3, +4.

Occurrence, properties, and uses

Titanium is widely distributed and constitutes 0.44 percent of Earth’s crust. The metal is found combined in practically all rocks, sand, clay, and other soils. It is also present in plants and animals, natural waters and deep-sea dredgings, and meteorites and stars. The two prime commercial minerals are ilmenite and rutile. The metal was isolated in pure form (1910) by the metallurgist Matthew A. Hunter by reducing titanium tetrachloride (TiCl4) with sodium in an airtight steel cylinder.

The preparation of pure titanium is difficult because of its reactivity. Titanium cannot be obtained by the common method of reducing the oxide with carbon because a very stable carbide is readily produced, and, moreover, the metal is quite reactive toward oxygen and nitrogen at elevated temperatures. Therefore, special processes have been devised that, after 1950, changed titanium from a laboratory curiosity to an important commercially produced structural metal. In the Kroll process, one of the ores, such as ilmenite (FeTiO3) or rutile (TiO2), is treated at red heat with carbon and chlorine to yield titanium tetrachloride, TiCl4, which is fractionally distilled to eliminate impurities such as ferric chloride, FeCl3. The TiCl4 is then reduced with molten magnesium at about 800 °C (1,500 °F) in an atmosphere of argon, and metallic titanium is produced as a spongy mass from which the excess of magnesium and magnesium chloride can be removed by volatilization at about 1,000 °C (1,800 °F). The sponge may then be fused in an atmosphere of argon or helium in an electric arc and be cast into ingots. On the laboratory scale, extremely pure titanium can be made by vaporizing the tetraiodide, TiI4, in very pure form and decomposing it on a hot wire in vacuum. (For treatment of the mining, recovery, and refining of titanium, see titanium processing. For comparative statistical data on titanium production, see mining.)

Pure titanium is ductile, about half as dense as iron and less than twice as dense as aluminum; it can be polished to a high lustre. The metal has a very low electrical and thermal conductivity and is paramagnetic (weakly attracted to a magnet). Two crystal structures exist: below 883 °C (1,621 °F), hexagonal close-packed (alpha); above 883 °C, body-centred cubic (beta). Natural titanium consists of five stable isotopes: titanium-46 (8.0 percent), titanium-47 (7.3 percent), titanium-48 (73.8 percent), titanium-49 (5.5 percent), and titanium-50 (5.4 percent).

Titanium is important as an alloying agent with most metals and some nonmetals. Some of these alloys have much higher tensile strengths than does titanium itself. Titanium has excellent corrosion-resistance in many environments because of the formation of a passive oxide surface film. No noticeable corrosion of the metal occurs despite exposure to seawater for more than three years. Titanium resembles other transition metals such as iron and nickel in being hard and refractory. Its combination of high strength, low density (it is quite light in comparison to other metals of similar mechanical and thermal properties), and excellent corrosion-resistance make it useful for many parts of aircraft, spacecraft, missiles, and ships. It also is used in prosthetic devices, because it does not react with fleshy tissue and bone. Titanium has also been utilized as a deoxidizer in steel and as an alloying addition in many steels to reduce grain size, in stainless steel to reduce carbon content, in aluminum to refine grain size, and in copper to produce hardening.

Although at room temperatures titanium is resistant to tarnishing, at elevated temperatures it reacts with oxygen in the air. This is no detriment to the properties of titanium during forging or fabrication of its alloys; the oxide scale is removed after fabrication. In the liquid state, however, titanium is very reactive and reduces all known refractories.

Titanium is not attacked by mineral acids at room temperature or by hot aqueous alkali; it dissolves in hot hydrochloric acid, giving titanium species in the +3 oxidation state, and hot nitric acid converts it into a hydrous oxide that is rather insoluble in acid or base. The best solvents for the metal are hydrofluoric acid or other acids to which fluoride ions have been added; such mediums dissolve titanium and hold it in solution because of the formation of fluoro complexes.

Compounds

In its compounds, titanium exhibits oxidation states of +2, +3, and +4, as in the oxygen compounds titanium monoxide, TiO, dititanium trioxide, Ti2O3, and titanium dioxide, TiO2, respectively. The +4 oxidation state is the most stable.

The chemistry of titanium in the +2 state is rather restricted. By contrast, many compounds are formed by titanium in the +3 state. One of the more important is the trichloride TiCl3, a crystalline form of which is particularly useful as a catalyst in the stereospecific polymerization of propylene to make the commercially valuable polymer polypropylene.

Of the compounds formed by titanium in its +4 state, the dioxide, TiO2, is the most important. This nontoxic, pure white powder is used extensively as a pigment in paints, enamels, and lacquers. It occurs in nature as the minerals brookite, octahedrite, anatase, and rutile.

Another compound of commercial significance is titanium tetrachloride, a colourless liquid used to obtain titanium metal. It is also utilized for skywriting and producing smoke screens and as a catalyst in many organic reactions.

Titanium combines directly with many nonmetals, such as hydrogen, the halogens, nitrogen, carbon, boron, silicon, and sulfur at elevated temperatures. The resulting nitride (TiN), carbide (TiC), and borides (TiB and TiB2) are interstitial compounds that are very stable, hard, and refractory.

Additional Information:

Appearance

A hard, shiny and strong metal.

Uses

Titanium is as strong as steel but much less dense. It is therefore important as an alloying agent with many metals including aluminium, molybdenum and iron. These alloys are mainly used in aircraft, spacecraft and missiles because of their low density and ability to withstand extremes of temperature. They are also used in golf clubs, laptops, bicycles and crutches.

Power plant condensers use titanium pipes because of their resistance to corrosion. Because titanium has excellent resistance to corrosion in seawater, it is used in desalination plants and to protect the hulls of ships, submarines and other structures exposed to seawater.

Titanium metal connects well with bone, so it has found surgical applications such as in joint replacements (especially hip joints) and tooth implants.

The largest use of titanium is in the form of titanium(IV) oxide. It is extensively used as a pigment in house paint, artists’ paint, plastics, enamels and paper. It is a bright white pigment with excellent covering power. It is also a good reflector of infrared radiation and so is used in solar observatories where heat causes poor visibility.

Titanium(IV) oxide is used in sunscreens because it prevents UV light from reaching the skin. Nanoparticles of titanium(IV) oxide appear invisible when applied to the skin.

Biological role

Titanium has no known biological role. It is non-toxic. Fine titanium dioxide dust is a suspected carcinogen.

Natural abundance

Titanium is the ninth most abundant element on Earth. It is almost always present in igneous rocks and the sediments derived from them. It occurs in the minerals ilmenite, rutile and sphene and is present in titanates and many iron ores.

Titanium is produced commercially by reducing titanium(IV) chloride with magnesium. Titanium(IV) oxide is produced commercially by either the ‘sulfate process’ or the ‘chloride process’, both of which use the mineral ilmenite as a starting material.

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