Titanium (Ti), 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.
Titanium is widely distributed and constitutes 0.44 percent of the 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.)