Titanium, Modern Technology's Designer Metal
An Indispensable Element, Once Thought to be Rare and of Little Use
Discovered independently in the 1790s by W. Gregor in England and M. H. Klaproth in Germany, titanium was named by the latter after the children of Gaia, the earth goddess of Greek mythology. Its apparent rarity was largely due to the fact that isolation from its ores was difficult and there was little demand for the metal.
In fact, it is the seventh most abundant metal in the earth's crust, up to 100 times as plentiful as everyday metals such as copper, zinc and nickel and 400 times more common than lead. By the middle of the 20th century, however titanium proved to be a prize among the elements when it was found to have properties ideally suited to the demands of modern technology. Its ores are now mined to the extent of 3 million tonnes each year, while 100 thousand tonnes of the metal itself are produced annually.
Titanium Oxide, the Whitest Substance Known
Small concentrations of titanium are widespread in rocks, and it is a common contaminant of ores of iron. The powdered oxide formed by purification of rutile, the principal ore, is the whitest material known, and is the standard against which other white substances are compared. Until recently, the main pigment in white paint was lead carbonate. Unfortunately, this is poisonous and tends to darken with age, mainly as a result of reaction with sulphur compounds from burning fuels. The extreme whiteness of titanium oxide, combined with its lack of toxicity mean that this compound has now almost completely replaced white lead in paints.
Extraction of Titanium From its Ore
The pure metal resists corrosion by common acids and alkalis though traces of impurities such as carbon, oxygen and nitrogen markedly affect the properties, and make the metal brittle and more susceptible to corrosion. Extraction, therefore, is both expensive and complex, so that it is unlikely ever to replace iron in importance. Rutile is heated with carbon in a stream of chlorine gas to form liquid titanium chloride. This is then heated with sodium or magnesium metal in an atmosphere of the noble gas, argon, to produce pure titanium. The chlorine, magnesium and sodium are recycled.
A Low Density, High Strength Metal
In powdered form, titanium is used to produce sparks in many fireworks. Its density is greater than that of aluminium, but less than those of iron and copper. The lightness, combined with its strength and ability to withstand high temperatures make it virtually the designer material for the construction of aircraft parts, jet engines and spacecraft.
The metal also finds a use in architecture, where it provides the outer shell of certain buildings. It has the appearance of steel, but does not rust. The walls of the Glasgow Science Centre, for example, are clad in a titanium skin.
Medical Uses of Titanium
Almost by accident, new properties of titanium were discovered in the late 1960s, which suggested unique potential in the medical field. When titanium is fixed into contact with bone for more than a few months, the bone grows into it, a process known as osseointegration. No adverse reactions have been observed from the body's immune system, nor has the metal shown evidence of even the slightest toxicity. Neither is it corroded by body acids. In consequence, titanium is now seen as the ideal material for use in bone replacement and strengthening operations. The metal traditionally used for this has been stainless steel, though this is rigid and does not flex well with bone. Nor does it bond with bone in the same way as titanium.
Though pure titanium is too soft for use in hip-joint replacement, it is easily strengthened by alloying with other metals. Traditional hip replacement therapy remains effective for around five years, on average. Titanium joints last very much longer. Extensive use in dentistry and cleft palate repair has also been undertaken, many prostheses still performing their tasks after more than twenty years. The potentially fatal weakness, known as an aneurism, in which artery walls bulge dangerously, can be successfully treated with a titanium mesh implant.
As technology advances, the demands for this versatile metal of low density, high strength and zero toxicity will surely multiply.
Glasgow Science Centre
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