Zirconium

Category: transition metal Atomic number: 40 Colour: silvery white Melting point: 1,855°C (3,371°F) Boiling point: 4,409°C (7,968°F) First identified: 1789

For over two millennia, we have known of a gold-coloured gemstone called zargun in Arabic, or zircon in English. Artificial versions of this gemstone are made today – they are more sparkly and dense than diamonds, but not as hard. Indeed, they were originally thought to be inferior diamonds – it was only in 1789, when Martin Klaproth managed to separate zirconia (or zirconium oxide) out from a zircon, that the element was discovered, and in 1824 that Berzelius managed to isolate some actual zirconium. The metal is hard, light, silvery and highly resistant to corrosion. (It also sparkles rather beautifully if you drop filings or dust into a Bunsen-burner flame, like a more spectacular version of the iron filings experiment your teacher may have shown you at school.)

The ceramics industry uses zirconium in pigments for glazing pottery, and, more importantly (in the form of zirconium oxide), in ultra-strong ceramics that will withstand high temperatures. A crucible made from it can be dipped into cold water while it is red-hot without damage. These ultra-strong ceramics are also used for knives, golf irons and cutting tools. The oxide is used, in addition, in the production of cosmetics, deodorants and microwave filters.

However, the most important use of zirconium is in nuclear reactors. As a metal that doesn’t absorb neutrons, it is used in the cladding of nuclear fuel and other elements in nuclear reactors – however, zirconium can play an unfortunate part in nuclear accidents. At very high temperatures, the metal will react with steam, producing hydrogen (which explodes) and zirconium oxide (which causes the fuel rods that were previously contained in it to collapse) – this was part of what went wrong at Chernobyl in 1986. As the reactor heated up to unprecedented levels, the zirconium reaction created a loop in which the temperature became even more out of control, and the notorious accident was the result.