Titanium

I

Introduction

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. 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.

II

Properties and Occurrence

Titanium is soluble in certain acids, and aqueous solutions of the metal can be prepared, but it is not directly dissolved by water. The metal is extremely brittle when cold, but is readily malleable and ductile at a low red heat. Titanium melts at about 1660° C (about 3020° F), boils at about 3287° C (about 5949° F), and has a relative density of 4.5. The atomic weight of titanium is 47.9.

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 the crust of the Earth 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, K₂TiF ₆. 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.

III

Uses

Because of its strength and light weight, titanium is used in metallic alloys and as a substitute for aluminium. Alloyed with aluminium and vanadium, titanium is used in aircraft for fire walls, outer skin, landing-gear components, hydraulic tubing, and engine supports. The compressor blades, discs, and housings of jet engines are also made of titanium. A commercial jet transport uses between 318 and 1,134 kg (700 and 2,500 lb) of the metal. A supersonic transport, flying at speeds between 2,410 and 3,220 km/h (about 1,500 and 2,000 mph), uses from 14 to 45 tonnes of titanium. 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 desalination plants because of its ability to withstand salt-water 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. Titanium dioxide has also been used as the main active component of a catalytic (see Catalyst) paint. Tiny particles of this titanium compound adsorb nitrogen oxides (noxious and polluting gases from vehicle exhausts and fossil-fuel power stations—see Air Pollution and Acid Rain) and use energy from the Sun to convert the nitrogen oxides into nitric acid. This acid is either diluted and washed away by rain, or the calcium carbonate particles in the paint neutralize the nitric acid to produce harmless calcium nitrate, water, and carbon dioxide.