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Hafnium (Hf)
Hafnium (symbol Hf) is the chemical element with atomic number 72: a transition metal, solid at 0 °C, with an atomic mass of 178.49 u. Discovered in 1923 (Dirk Coster and George de Hevesy).
Hafnium is so chemically close to zirconium that it wasn't discovered until 1923, even though it was present in every zirconium ore. Yet the two are opposites when it comes to neutrons: zirconium lets them through, hafnium soaks them up. It also sits at the heart of the transistors in our processors.
Key facts
- Atomic number
- 72
- Symbol
- Hf
- French name
- Hafnium
- Atomic mass
- 178.49 u
- Molar mass
- 178.49 g/mol
- Family
- Transition metals
- Position
- period 6, group 4, d-block
- State at 0 °C
- Solid
- Melting point
- 2,232.9 °C
- Boiling point
- 4,602.9 °C
- Density
- 13.31 g/cm³
- Electronegativity (Pauling)
- 1.3
- First ionization energy
- 659 kJ/mol
- Atomic radius
- 155 pm
- Electron configuration
- [Xe] 4f¹⁴ 5d² 6s²
- Abundance in Earth's crust
- 3 ppm (47th most abundant element)
- Indicative price
- 900 $/kg (order of magnitude)
- Radioactive
- no
- Discovery
- 1923, Dirk Coster and George de Hevesy
Origin of the name
From Hafnia, the Latin name for Copenhagen.
What does hafnium look like?
A bright, ductile, silvery-gray metal, highly resistant to corrosion. It melts at around 2,230 °C.
Where is hafnium found?
About 3 ppm of Earth's crust. There is no hafnium ore as such: it replaces a few percent of the zirconium in zircon and baddeleyite.
Natural sources
- Zircon
- Baddeleyite
How is hafnium produced?
A by-product of purifying zirconium for the nuclear industry, which must be stripped of its hafnium. The very tricky separation is done by liquid-liquid extraction or distillation, then the metal is reduced with magnesium (the Kroll process).
Top producers
- France
- United States
- China
- Russia
What is hafnium used for?
- Control rods in nuclear reactors, especially on submarines.
- Hafnium oxide, the insulator in microprocessor transistors since 2007.
- Superalloys for aircraft turbines.
- Electrodes in plasma cutting torches.
In everyday life
- A computer or smartphone processor
- A plasma cutting torch
Role in living things
No biological role; not very toxic.
Hazards of hafnium
Not very toxic, but fine hafnium powder is pyrophoric and can ignite spontaneously.
Cosmic origin
- Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).
- Neutron stars: Created when two neutron stars collide — the “forge” of gold.
History of hafnium
Using his atomic theory, Niels Bohr predicted that element 72 would not be a rare earth but a cousin of zirconium. In 1923, in Copenhagen, Dirk Coster and George de Hevesy found it in zirconium ores using X-ray spectroscopy and named it after Hafnia, the city's Latin name.
Did you know?
- France is one of the world's leading hafnium producers, a by-product of its nuclear-grade zirconium.
- Hafnium and tantalum carbides are among the most heat-resistant materials known, melting at around 4,000 °C.
- Its resemblance to zirconium comes from the “lanthanide contraction,” which makes their atoms almost the same size.
Isotopes of hafnium
Hafnium has five stable isotopes plus a sixth, hafnium-174, that is weakly radioactive. Its isomer 178m2 stores an enormous amount of energy, which fueled (vain) dreams of “isomer bombs.”
- hafnium-174: 0.16% of natural hafnium, radioactive, half-life 2 × 10¹⁵ years
- hafnium-176: 5.26% of natural hafnium, stable
- hafnium-177: 18.6% of natural hafnium, stable
- hafnium-178: 27.28% of natural hafnium, stable
- hafnium-178m: radioactive, half-life 31 years. A highly energetic isomer at the center of a controversy over nuclear energy storage.
- hafnium-179: 13.62% of natural hafnium, stable
- hafnium-180: 35.08% of natural hafnium, stable
- hafnium-181: radioactive, half-life 42.4 days
- hafnium-182: radioactive, half-life 8.9 × 10⁶ years. Extinct today, it is used to date the formation of the planets' metallic cores.
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), Zirconium (Zr), Niobium (Nb), Molybdenum (Mo), Technetium (Tc), Ruthenium (Ru), Rhodium (Rh), Palladium (Pd), Silver (Ag), Cadmium (Cd), 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), Zirconium (Zr), Rutherfordium (Rf).