Zirconium Zr

Discovery

Zircon had been prized as a gemstone since antiquity, but the new element hidden inside it was recognised only in 1789, when the German chemist Martin Heinrich Klaproth analysed zircon from Sri Lanka and identified a new oxide, zirconia.

In 1824 Jöns Jacob Berzelius obtained impure zirconium metal by reducing a zirconium compound with potassium. The metal readily picks up oxygen and nitrogen, so pure samples remained elusive for a century.

In 1925 the Dutch scientists Anton Eduard van Arkel and Jan Hendrik de Boer produced high-purity zirconium by decomposing zirconium iodide vapour on a hot filament, the "crystal bar" process. With the rise of nuclear power in the mid-twentieth century, zirconium became a strategic material.

Origin of the name

The name derives from the mineral zircon, a word usually traced to the Persian zargun, "gold-coloured". The symbol is Zr.

Main uses

• Nuclear reactors: zirconium alloys (Zircaloy) absorb very few neutrons and resist hot water, making them the standard cladding for fuel rods. The chemically near-identical element hafnium must be removed first, because hafnium is a strong neutron absorber.
• Ceramics: tough, hard zirconia is used for dental crowns, ceramic knives and joint-replacement parts; cubic zirconia is a well-known diamond simulant.
• Foundry and refractories: zircon sand withstands high temperatures in casting moulds and furnace linings, and it makes ceramic glazes on tiles and sanitaryware opaque white.
• Chemical plants: zirconium resists strong acids and is used for reactors and piping.

Isotopes

Natural zirconium has five isotopes, zirconium-90, -91, -92, -94 and -96, with zirconium-90 accounting for just over half. Zirconium-96 undergoes double beta decay so slowly that it is effectively stable. Zirconium-89, with a half-life of about 78 hours, is attached to antibodies for PET imaging research, and zirconium-93 is a long-lived fission product.

When zircon crystallises, it takes in uranium but almost no lead, which makes it ideal for uranium–lead dating. Zircon grains from the Jack Hills in Western Australia formed about 4.4 billion years ago and are the oldest known fragments of Earth's crust.

In everyday life

Zirconium is mined mainly from beach sands along with titanium minerals. The metal has low toxicity and good biocompatibility, and aluminium–zirconium compounds are found in some antiperspirants.

Fine zirconium powder, however, ignites easily in air. At very high temperatures zirconium also reacts with steam to produce hydrogen; this reaction contributed to the hydrogen explosions at the Fukushima Daiichi nuclear plant in 2011.