Titanium, a lustrous, silvery-white, metallic chemical element. Titanium is soft, strong, lightweight, ductile (capable of being drawn into a thin wire), and corrosion-resistant, and can combine with many other metals to form alloys. If titanium is continually exposed to temperatures of 1,000 F. (538 C.) or higher, it is capable of absorbing oxygen, hydrogen, and other gases.

At ordinary temperatures the metal exists as alpha titanium. When heated to 1,625 F. (885 C.), alpha titanium slowly undergoes a change in crystal structure and becomes beta titanium, which is somewhat harder, stronger, and less ductile at room temperature. The difference in physical properties of these forms is important in the formation and hardening of alloys. Each form is made chemically stable at high temperatures by being alloyed with other metals; the alpha form is usually alloyed with aluminum, and the beta with chromium, manganese, iron, molybdenum, or vanadium. For certain alloying purposes, alpha and beta titanium are combined. Titanium alloys are classed according to the crystal form present—alpha, beta, or alpha-beta.

Uses

A large percentage of the titanium produced is used to make titanium dioxide. Titanium dioxide is used as a white pigment in the manufacture of chemical-resistant paints, rubber, plastics, and floor coverings. It is also used as a coating for welding rods and in the manufacture of paper to improve the color, brightness, and printing surface. Pure titanium dioxide is heated with oxygen and hydrogen to produce titania, or synthetic rutile, a transparent gemstone.

Titanium metal and most of its alloys are used in structural parts of missiles, jet engines, high-speed aircraft, and spacecraft. The addition of a small percentage of titanium will increase the strength and ductility of copper, magnesium, and nickel. Certain titanium-iron alloys are used in steelmaking to remove oxygen and nitrogen. Because the metal is resistant to most acids and other corrosive substances, it is used in the manufacture of chemical processing equipment. The metal is also used for surgical instruments and orthopedic appliances (such as leg braces).

Occurrence and Production

Titanium was discovered in 1791 by the English mineralogist William Gregor. The element is widely distributed in the earth's crust. It is always found combined with other elements because it is highly reactive chemically. Titanium is usually found combined with oxygen in the ore rutile, and with iron and oxygen in the ore ilmenite. Most titanium metal is obtained from rutile by the Kroll process, in which the metal is chemically separated from the impurities in the absence of air. Ilmenite is used primarily for the production of titanium dioxide. The leading ilmenite-producing countries are Australia, Norway, the United States, India, Malaysia, and Ukraine. Australia, Sierra Leone, and South Africa produce most of the world's rutile.

Symbol: Ti. Atomic number: 22. Atomic weight: 47.88. Specific gravity: 4.54. Melting point: 3,020 F. (1,660 C.). Boiling point: 5,949 F. (3,287 C.). Titanium has five stable isotopes: Ti–46 through Ti–50. It belongs to Group IVB of the Periodic Table and can have a valence of +3 or +4.