The A–Z of Zirconium from Fake Gems to a Fixture of Nuclear Plants,John Emsley Considers the Many Uses of Zirconium

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in your element The A–Z of zirconium From fake gems to a fixture of nuclear plants,John Emsley considers the many uses of zirconium.

ircon — zirconium silicate (ZrSiO4) of chromium produce green gems, cerium to chemists — is a semi-precious gives red ones, and those with neodymium Zgemstone (pictured) that has been are purple. Less frivolously, zirconia makes known since ancient times. When cut a useful barrier coating that is both tough and polished, a zircon crystal shines and resists chemical attack. A ceramic layer with an unusual brilliance because of of zirconia is used to protect the blades of its high refractive index; colourless jet engines and gas turbines and it also acts specimens look like diamonds. The metal as a thermal barrier. component of zircon was first identified When it comes to matters of life and by Martin Heinrich Klaproth when death, zirconium also plays its part. Zircon analysing a crystal of the substance in in rocks found in Australia in 2000 showed Berlin in 1789. In that same year, he also that life might have started much earlier discovered uranium, and today both of these than once thought. Dated to be 4.4 billion metallic elements are essential for nuclear years old, the oxygen isotope ratio of O16/O18 power generation. in these samples showed they could only A zirconium–tin alloy, known as have been formed when there was liquid Zircaloy, is used as the cladding for water on the surface of the Earth, and this uranium oxide fuel elements. Resistant was nearly 500 million years earlier than 2 to corrosion at high temperatures, this © WILDLIFE GMBH/ALAMY previously assumed . Turning to its darker material does not absorb neutrons and so side, ultrafine zirconium powder is used does not become radioactive. The nuclear used to make heat-resistant crucibles — in some cluster bombs to produce burning industry buys almost all the zirconium a red-hot zirconia crucible can be plunged particles that saturate a target area. metal that is produced and some nuclear into cold water without cracking. The metallic element itself is used in plants have kilometres of zirconium-based World production of pure zirconia is alloys — zirconium makes steel stronger and tubing. Even so, corrosion can still occur almost 25,000 tonnes per year, and it ends improves its machinability. It is also used in water-cooled reactors1 and sometimes up in cosmetics, antiperspirants, food for surgical implants and prosthetic devices this has led to accidents. Although the packaging, and even fake gems. The most because it is biocompatible — it has no metal is stable in contact with water below unexpected use of zirconia is in ultra- known biological role or toxicity. The metal 900 °C, above this temperature they react strong ceramics. Research in this area was remains stable at high temperatures, so it is to form the oxide and hydrogen gas. It was driven by the military who sought a tank used for space-vehicles that heat up on re- this process that led to the explosions at engine that was not made of metal, and entry to the Earth’s atmosphere. Zirconium Three Mile Island in the US in 1979, and so would need neither lubricating oil nor is more than twice as abundant as copper at Fukushima after the earthquake and a cooling system. Consequently, a new and zinc, and over ten times more abundant tsunami there in 2011. generation of tough, heat-resistant ceramics than lead. Because zirconium is regarded as The chief source of zirconium is zircon were developed that are stronger and completely non-toxic and environmentally and more than 1.5 million tonnes of this sharper than toughened steel and which benign, its use will probably continue to mineral are extracted each year, mainly in make excellent high-speed cutting tools grow. For example, it is being added to Australia and South Africa. Zircon sand for industry. Zirconia is found in some paints to replace the small amounts of lead is traditionally a refractory material — it everyday objects too, such as knives, scissors compounds that are still needed. ❐ maintains its strength at high temperatures and golf irons and, because of its durability — and, as such, is used to make heat- and biocompatibility, is also used to make JOHN EMSLEY is a science writer and resistant linings for furnaces, giant ladles dental veneers. author of Nature’s Building Blocks and for molten metal, and foundry moulds. Zirconia can adopt three different other books. Other zirconium compounds, such as its crystallographic forms; monoclinic, e-mail: [email protected]

oxide (ZrO2), also have high-temperature tetragonal and, the most admired of all, applications. Better known as zirconia, this cubic zirconia (often referred to as simply References material only melts above 2,500 °C and is CZ), which has the same crystal structure 1. Cox, B. J. Nucl. Mater. 336, 331–368 (2005). 2. Rasmussen, B. Contrib. Mineral. Petr. as diamond and even out-sparkles it. Fake 150, 146–155 (2005). gems made of CZ can be coloured by incorporating other metal oxides; traces Corrected online 3 October 2014 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La 254 NATURE CHEMISTRY | VOL 6 | MARCH 2014 | www.nature.com/naturechemistry

ADDENDUM In Your Element: The A–Z of zirconium John Emsley

Nature Chemistry 6, 254 (2014); published online 20 February 2014; corrected after print 3 October 2014.

In the version of this In Your Element article previously published, it should have stated that some passages in this essay are based on the zirconium chapter in the author’s book, Nature’s Building Blocks.

1026 NATURE CHEMISTRY | VOL 6 | NOVEMBER 2014 | www.nature.com/naturechemistry