Titanium, symbol Ti, silver-white metallic element used principally to make light, strong alloys. Titanium is one of the transition elements of the periodic table (see Periodic Law). The atomic number of titanium is 22.
Titanium was discovered in 1791 in the mineral menachanite by the British clergyman William Gregor, who named the new element menachite. Four years later, the German chemist Martin Heinrich Klaproth rediscovered the element in the mineral rutile and named it titanium in allusion to the strength of the mythological Greek Titans. The metal was isolated in 1910.
Pure titanium is soluble in concentrated acids, such as sulfuric and hydrofluoric acids, and insoluble in water. The metal is extremely brittle when cold, but is readily malleable and ductile at a low red heat. Titanium melts at about 1668°C (about 3034°F), boils at about 3287°C (about 5949°F), and has a specific gravity of 4.5. The atomic weight of titanium is 47.87.
Titanium burns in oxygen at 610°C (1130°F) to form titanium dioxide, and it burns in nitrogen at 800°C (1472°F) to form titanium nitride, TiN. Titanium exhibits valences of 4, 3, and 2, and forms the salts titanium tetrachloride, TiCl4; titanium trichloride, TiCl3; and titanium dichloride, TiCl2. It ranks ninth in abundance among the elements in Earth’s crust but is never found in the pure state. It occurs as an oxide in the minerals ilmenite, FeTiO3; rutile, TiO2; and sphene, CaO · TiO2 · SiO2.
To obtain titanium oxide, the mineral is ground and mixed with potassium carbonate and aqueous hydrofluoric acid to yield potassium fluorotitanate, K2TiF6. The fluorotitanate is extracted with hot water and decomposed with ammonia. The resulting ammoniacal hydrated oxide, when ignited in a platinum vessel, yields titanium dioxide, TiO2. Titanium is obtained in the pure form by first treating the oxide with chlorine to form titanium tetrachloride, a volatile liquid, and then reducing the liquid with magnesium in a closed iron chamber to yield metallic titanium. The metal is then melted and cast into ingots.
Because of its strength and light weight, titanium is used in metallic alloys and as a substitute for aluminum. Alloyed with aluminum and vanadium, titanium is used in aircraft for fire walls, outer skin, landing-gear components, hydraulic tubing, and engine supports. The compressor blades, disks, and housings of jet engines are also made of titanium. A commercial jet transport uses between 318 and 1134 kg (700 and 2500 lb) of the metal. Titanium is also widely used in missiles and space capsules; the Mercury, Gemini, and Apollo capsules were made largely of titanium. Other common titanium alloys include ferrocarbon titanium, made by reduction of ilmenite with coke in an electric furnace; cuprotitanium, formed by reduction of rutile to which copper has been added; and manganotitanium, produced by reduction of rutile to which manganese or oxides of manganese have been added.
The relative inertness of titanium makes it available as a replacement for bone and cartilage in surgery and as a pipe and tank lining in the processing of foods. It is used in heat exchangers in desalinization plants because of its ability to withstand saltwater corrosion. In metallurgy, titanium alloys are employed as deoxidizers and denitrogenizers to remove oxygen and nitrogen from molten metals. Titanium dioxide, known as titanium white, is a brilliant white pigment used in paints, lacquers, plastics, paper, textiles, and rubber.
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