Zirconium (Zr)

Zirconium (symbol Zr) is the chemical element with atomic number 40: a transition metal, solid at 0 °C, with an atomic mass of 91.224 u. Discovered in 1789 (Martin Heinrich Klaproth).

Zirconium is a highly corrosion-resistant metal that lets neutrons pass without absorbing them. That is why it forms the cladding that encloses the fuel in nuclear reactors. Its mineral, zircon, holds the oldest fragments of Earth ever dated.

Key facts

Atomic number: 40
Symbol: Zr
French name: Zirconium
Atomic mass: 91.224 u
Molar mass: 91.224 g/mol
Family: Transition metals
Position: period 5, group 4, d-block
State at 0 °C: Solid
Melting point: 1,854.9 °C
Boiling point: 4,376.9 °C
Density: 6.52 g/cm³
Electronegativity (Pauling): 1.33
First ionization energy: 640 kJ/mol
Atomic radius: 155 pm
Electron configuration: [Kr] 4d² 5s²
Abundance in Earth's crust: 165 ppm (18th most abundant element)
Indicative price: 36 $/kg (order of magnitude)
Radioactive: no
Discovery: 1789, Martin Heinrich Klaproth

Origin of the name

From the Persian zargun, “gold-colored,” via zircon.

What does zirconium look like?

A shiny, grayish-white, fairly hard metal that coats itself with a thin protective oxide layer. As a powder, it ignites easily.

Where is zirconium found?

About 165 ppm of Earth's crust, more than copper. It is found mostly in beach sands rich in heavy minerals, as zircon, which strongly resists erosion.

Natural sources

Zircon
Baddeleyite

How is zirconium produced?

Zircon sands are mined by dredging, often along with ilmenite and rutile (titanium ores). About 1.2 to 1.5 million tonnes of zircon are produced each year. To make the metal, it is converted to chloride and then reduced with magnesium (the Kroll process); for nuclear use, the hafnium, which absorbs neutrons, must be removed.

Top producers

Australia
South Africa
Mozambique
China

What is zirconium used for?

Opacifier in tile and bathroom-fixture glazes (zircon's top use).
Nuclear fuel cladding made of Zircaloy alloy.
Heat-resistant foundry sands and molds.
Zirconia (ZrO₂) for dental crowns and ceramic knife blades.
Acid-resistant chemical equipment.

In everyday life

Glazed sink and tiles
Cubic zirconia jewelry (diamond simulant)
Ceramic knife
Antiperspirant (aluminium-zirconium salts)

Role in living things

No biological role. It is barely absorbed by the body and considered to have low toxicity, hence its use in implants and dental products.

Hazards of zirconium

The solid metal is harmless, but its powder is pyrophoric (it ignites spontaneously). At very high temperatures it reacts with steam and releases hydrogen, which caused the Fukushima explosions in 2011.

Cosmic origin

Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).

History of zirconium

Zircon has been known as a gemstone since antiquity; its name may come from the Persian zargun, “gold-colored.” In 1789, German chemist Martin Heinrich Klaproth identified a new oxide in it, and Jöns Jacob Berzelius isolated the impure metal in 1824. Pure, ductile metal was not obtained until 1925.

Did you know?

Zircon grains from the Jack Hills in Australia, 4.4 billion years old, are the oldest known fragments of Earth.
Cubic zirconia, crystallized zirconium oxide, is the most widespread diamond imitation.
Zirconium and hafnium are so chemically alike that hafnium stayed “hidden” inside zirconium until 1923.

Isotopes of zirconium

Four stable isotopes, plus zirconium-96, radioactive but practically eternal. Zirconium-89 lets doctors follow antibodies through the body with PET imaging.

zirconium-89: radioactive, half-life 3.27 days. Labels antibodies for PET imaging of cancers.
zirconium-90: 51.45% of natural zirconium, stable
zirconium-91: 11.22% of natural zirconium, stable
zirconium-92: 17.15% of natural zirconium, stable
zirconium-93: radioactive, half-life 1.61 × 10⁶ years. Long-lived fission product in nuclear waste.
zirconium-94: 17.38% of natural zirconium, stable
zirconium-95: radioactive, half-life 64 days
zirconium-96: 2.8% of natural zirconium, radioactive, half-life 2.35 × 10¹⁹ years

Related elements

Same family (transition metals): Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn), Yttrium (Y), Niobium (Nb), Molybdenum (Mo), Technetium (Tc), Ruthenium (Ru), Rhodium (Rh), Palladium (Pd), Silver (Ag), Cadmium (Cd), Hafnium (Hf), Tantalum (Ta), Tungsten (W), Rhenium (Re), Osmium (Os), Iridium (Ir), Platinum (Pt), Gold (Au), Mercury (Hg), Rutherfordium (Rf), Dubnium (Db), Seaborgium (Sg), Bohrium (Bh), Hassium (Hs).

Same column (group 4): Titanium (Ti), Hafnium (Hf), Rutherfordium (Rf).