Hafnium (Hf)
Stable isotopes of hafnium available from ISOFLEX
| Isotope | Z(p) | N(n) | Atomic Mass | Natural Abundance | Enrichment Level | Chemical Form |
| Hf-174 | 72 | 102 | 173.940042 | 0.162% | 13.46% | Oxide |
| Hf-176 | 72 | 104 | 175.941406 | 5.260% | 84.60% | Oxide |
| Hf-177 | 72 | 105 | 176.943220 | 18.606% | 85.40% | Oxide |
| Hf-178 | 72 | 106 | 177.943698 | 27.297% | 92.40% | Oxide |
| Hf-179 | 72 | 107 | 178.945815 | 13.629% | 75.00% | Oxide |
| Hf-180 | 72 | 108 | 179.946549 | 35.100% | ≥94.60% | Oxide |
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Hafnium was discovered in 1923 by Dirk Coster and George Charles von Hevesy. Its name derives from the Latin name Hafnia, meaning “Copenhagen.”
Hafnium is generally similar to zirconium. It has gray crystals, good corrosion resistance and high strength. It occurs as a close-packed hexagonal alpha form and as a body-centered cubic beta modification. It has a magnetic susceptibility of 0.42 x 10-6 emu/g at 25 ºC. It is insoluble in water, dilute mineral acids and nitric acid at all concentrations, and is soluble in hydrofluoric acid, concentrated sulfuric acid and aqua regia. The metal in bulk form does not react with most reagents at ordinary temperatures; however, the powdered metal or hafnium sponge may readily burn in air after being ignited with a spark. When heated to 360 ºC under water pressure, the metal is oxidized to hafnium oxide, forming a thin, protective surface oxide layer. Reaction with hydrofluoric acid at ordinary temperatures yields hafnium tetrafluoride. In finely divided form, hafnium is pyrophoric, igniting in air spontaneously; however, bulk metal reacts slowly in oxygen or air above 400 ºC. Reaction with hydrogen occurs around 700 ºC.
Hafnium is used in control rods for nuclear reactors. It has high resistance to radiation, as well as very high corrosion resistance. Another major application is in alloys with other refractory metals, such as tungsten, niobium and tantalum.
Properties of Hafnium
| Name | Hafnium |
| Symbol | Hf |
| Atomic number | 72 |
| Atomic weight | 178.49 |
| Standard state | Solid at 298 ºK |
| CAS Registry ID | 7440-58-6 |
| Group in periodic table | 4 |
| Group name | None |
| Period in periodic table | 6 |
| Block in periodic table | d-block |
| Color | Gray steel |
| Classification | Metallic |
| Melting point | 2233 °C |
| Boiling point | 4602 °C |
| Vaporization point | 2233 ºC |
| Thermal conductivity | 23.0 W/(m·K) at 298.2 ºK |
| Electrical resistivity | 35.1 µΩ·cm at 25 ºC |
| Electronegativity | 1.3 |
| Specific heat | 0.14 kJ/kg K |
| Heat of vaporization | 630 kJ·mol-1 at 4602 ºC |
| Heat of fusion | 25.5 kJ·mol-1 mole |
| Density of liquid | 12 g/cm3 at 2233 °C |
| Density of solid | 13.31 g/cm3 |
| Electron configuration | [Xe]4f145d26s2 |
| Atomic radius | 1.442 Å |
| Common oxidation state | +4 (also exhibits oxidation states +2 and +3) |
Research
- Isotope geochemistry and revised geochronology of the Purrido Ophiolite (Cabo Ortegal Complex, NW Iberian Massif): Devonian magmatism with mixed sources and involved Mesoproterozoic basement
- Early formation of the Moon 4.51 billion years ago
- Geochemical, isotopic, and zircon (U-Pb, O, Hf isotopes) evidence for the magmatic sources of the volcano-plutonic Ollo de Sapo Formation, Central Iberia