David Calder, of Nayland College, asks :-
Where does titanium come from?
Bryce Williamson, a chemist at the University of Canterbury, responded.
Titanium is a relatively light and strong silvery-grey metal with many useful properties. However, its plentiful and widely distributed ores are difficult to convert to metal, and its use is therefore generally reserved for specialty applications.
The ninth most abundant element in the Earth's crust, titanium is found in almost all rocks and soils. Its most common ores are rutile (titanium dioxide; TiO2) and ilmenite (titanium-iron oxide; TiFeO3), the latter forming a significant component of the black sands found on North Island west-coast beaches from Wanganui north. Deposits of these ores are found widely distributed throughout the world.
The usage of titanium has been limited by the fact that it is amongst the most difficult of all metals to obtain in pure form. The problem stems from its reactivity with carbon, nitrogen and oxygen at high temperatures, which means that it can't be extracted from its ores using the types of process commonly used for other metals. In fact, although titanium compounds have been known since 1795, it was not until 1910 that the New Zealand-born metallurgist Matthew Hunter, working in the United States, produced the first pure sample of the metal. To achieve this he used the unusual procedure of reacting titanium tetrachloride (TiCl4), a white liquid, with molten sodium metal in an air-tight steel container.
The commercial process now used to produce titanium metal involves a number of steps. First the ore (rutile or ilmenite) is reacted with carbon and chlorine at high temperature to produce titanium tetrachloride. This liquid is then purified by distillation before being reacted with molten magnesium to produce magnesium chloride (MgCl2) and metallic titanium.
Metallic titanium is nearly as strong as steel but less than half as heavy. It has excellent corrosion resistance and retains its strength at high temperatures. It therefore finds uses in the aerospace industries, especially in the production of high-speed military aircraft whose fuselages are heated to high temperatures by friction with the air. It is also physiologically inert and so is used in medical applications, for example as pins and screws to hold broken bones together and as plates to repair fractured cheeks and skulls. Other useful properties include remarkably low conductance of heat and electricity, as well as an ability to combine with other metals to form alloys.