Zirconium
[Kr] 4d² 5s² · 2 · 8 · 18 · 10 · 2
A metal nearly transparent to neutrons and therefore indispensable in nuclear power: fuel cladding is made of zirconium alloys. Its oxide is a ceramic harder than steel and the best stand-in for diamond.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 40
- Atomic mass
- 91.224 а.е.м.
- Electron configuration
- [Kr] 4d² 5s²
- Electrons per shell
- 2 · 8 · 18 · 10 · 2
- Block
- d-block
- Group
- Titanium group
- Period
- 5
- Electronegativity (Pauling)
- 1.33
- Electronegativity (Allen)
- 1.32
- Atomic radius
- 206 pm
- Covalent radius
- 175 pm
- Van der Waals radius
- 223 pm
- Ionisation energy 1
- 640.1 kJ/mol
- Ionisation energy 2
- 1 270 kJ/mol
- Ionisation energy 3
- 2 218 kJ/mol
- Ionisation energy 4
- 3 313 kJ/mol
- Ionisation energy 5
- 7 752 kJ/mol
- Electron affinity
- 41.1 kJ/mol
- Common oxidation states
- +4
- Oxidation states
- -2, +1, +2, +3, +4
Physical properties
- State at 25 °C
- solid
- Density
- 6.52 g/cm³
- Melting point
- 2 128 K · 1 854.9 °C
- Boiling point
- 4 650 K · 4 376.9 °C
- Speed of sound
- 3 800 m/s
Thermal properties
- Heat of fusion
- 14 kJ/mol
- Heat of vaporisation
- 573 kJ/mol
- Specific heat capacity
- 0.278 J/(g·K)
- Thermal conductivity
- 22.6 W/(m·K)
Mechanical properties
- Young's modulus
- 88 GPa
- Shear modulus
- 33 GPa
- Bulk modulus
- 91.1 GPa
- Poisson ratio
- 0.34
- Mohs hardness
- 5
- Brinell hardness
- 650 MPa
Electrical and magnetic properties
- Electrical resistivity
- 421 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- 0.61 K
Crystal structure
- Crystal structure
- hexagonal close-packed (hcp)
- Lattice constants
- a = 323.2 pm · c = 514.7 pm
Abundance
- In the crust
- 165 mg/kg
- In the ocean
- 2.6·10⁻⁵ mg/L
- In the universe
- 50 mg/kg
- In the human body
- 0.06 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 90Zr | 51.45 % | stable | — |
| 91Zr | 11.22 % | stable | — |
| 92Zr | 17.15 % | stable | — |
| 94Zr | 17.38 % | stable | — |
| 96Zr | 2.8 % | stable | — |
Zirconium-93, half-life 1.5 million years, is a long-lived fission product that matters in spent fuel management.
Discovery
- Year of discovery
- 1789
- Discovered by
- Martin Heinrich Klaproth
- Where
- Germany
- Origin of the name
- from the mineral zircon, ultimately Persian zargun (gold-coloured)
History
Klaproth isolated the oxide from Ceylonese zircon in 1789. Berzelius made the metal in 1824, but ductile pure zirconium waited until van Arkel and de Boer's iodide process in 1925.
Where it occurs
165 mg/kg of the crust. The main minerals are zircon and baddeleyite, mined from coastal sands in Australia and South Africa.
How it is produced
The Kroll process, as for titanium: chlorination and magnesium reduction. A mandatory step is separating hafnium, which always accompanies zirconium and, in contrast, devours neutrons.
Role in living things
No biological role and essentially not absorbed.
Safety
The metal is harmless and biocompatible. Zirconium powder is pyrophoric, and in a reactor overheating accident zirconium reacts with steam to release hydrogen — which is what caused the explosions at Fukushima.
Uses
- Nuclear fuel cladding — zircaloy is transparent to neutrons and survives water at 300 °C
- Chemical plant resistant to acids and alkalis
- Zirconia: ceramic knives, dental crowns, refractories
- Cubic zirconia as a diamond simulant
- Oxygen sensors in vehicle exhaust systems
Curiosities
- Zirconium and hafnium are chemically almost indistinguishable but opposite towards neutrons: one is transparent, the other absorbs.
- Zircon is the oldest known terrestrial mineral: crystals from Western Australia are 4.4 billion years old.
- The Fukushima explosions were hydrogen from zirconium cladding reacting with superheated steam.
- Cubic zirconia is nearly indistinguishable from diamond by eye, but noticeably softer and denser.