Tellurium

Category: metalloid Atomic number: 52 Colour: silvery white Melting point: 449°C (841°F) Boiling point: 988°C (1,810°F) First identified: 1783

Tellurium is an element for which the future supply is uncertain. Traditionally, it was used in alloys – for instance with copper, lead and stainless steel – to make them harder, more workable or resistant. It can also be used to vulcanize rubber and to tint glass. But the real area of growth in demand has come from its use in rewritable CDs and DVDs and in the manufacture of solar panels, because it can capture energy efficiently in the form of the compound cadmium telluride.

The problem is that tellurium is obtained as a by-product of copper production – it is recovered from the ‘anode slime’ produced in the electrolytic refining process. Copper production has declined in recent years, and there have also been changes in the processes used (as different types of copper are extracted), and this has affected the supply of tellurium, pushing prices up considerably.

Tellurium is usually produced as a dark-grey powder, though as a metalloid it also has a shiny, silver metallic form. It is somewhat toxic – like selenium – and, when handled, it can give you a nasty case of garlic breath, as well as blacken your hands rather unpleasantly. Appropriately enough, it was discovered in Transylvania: the Austrian mineralogist Franz Joseph Müller von Reichenstein found a shiny ore, which turned out to be gold telluride rather than antimony or bismuth, as he had suspected. He proved it contained a new element, but his work wasn’t widely recognized until he sent a sample to German chemist Martin Klaproth, who agreed his findings were correct.

The planet Uranus had recently been discovered. Mindful of an ancient tradition that connected each of the seven known celestial bodies with a metal (for instance, the sun was associated with gold, the moon was supposed to nourish silver ores in the ground, Mars was connected with iron, and so on), Klaproth united the Ancient Greek tellus (for ‘Earth’) with the first part of Uranus’s name to come up with the term ‘tellurium’.