Hafnium
Atomic Data
| Atomic Number | 72 |
| Symbol | Hf |
| Atomic Weight | 178.49 u |
| Density (STP) | 13.31 g/cm³ |
| Melting Point | 2232.85 °C (2506 K) |
| Boiling Point | 4602.85 °C (4876 K) |
| Electronegativity | 1.3 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d2 6s2 |
| Oxidation States | +4 |
| Phase at STP | Solid |
| Category | Transition Metal |
| Period / Group | 6 / 4 |
| CAS Number | 7440-58-6 |
Electron Configuration
[Xe] 4f14 5d2 6s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 14 | 60 |
| O | 5 | 5s | 2 | 62 |
| O | 5 | 5p | 6 | 68 |
| O | 5 | 5d | 2 | 70 |
| P | 6 | 6s | 2 | 72 |
| Total | 72 | 72 | ||
Isotopes of Hafnium
Hafnium has six naturally occurring stable isotopes. The most abundant is ¹⁸⁰Hf, comprising 35.08% of all naturally occurring Hafnium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Hafnium-174 | ¹⁷⁴Hf | 72 | 102 | 0.16 | Stable |
| Hafnium-176 | ¹⁷⁶Hf | 72 | 104 | 5.26 | Stable |
| Hafnium-177 | ¹⁷⁷Hf | 72 | 105 | 18.6 | Stable |
| Hafnium-178 | ¹⁷⁸Hf | 72 | 106 | 27.28 | Stable |
| Hafnium-179 | ¹⁷⁹Hf | 72 | 107 | 13.62 | Stable |
| Hafnium-180 | ¹⁸⁰Hf | 72 | 108 | 35.08 | Stable |
Abundance & Occurrence
Hafnium is present in Earth's crust at approximately 3 ppm by mass and at approximately 0.3 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Hafnium powder fire hazard: Finely divided hafnium powder is highly pyrophoric and flammable; it is classified as a dangerous fire and explosion hazard and must be handled under inert gas or water; metal fires require Class D agents only.
- Hafnium tetrachloride: HfCl4 reacts with water to produce HCl; it is corrosive to skin, eyes, and airways and must be handled in dry, ventilated conditions.
- Inhalation hazard: Hafnium metal dust and hafnium compound dusts are respiratory irritants; use respiratory controls and ventilation for powder handling and machining operations.
- General toxicity: Bulk hafnium metal has low acute systemic toxicity; the primary hazards are physical (fire/dust) rather than toxic.
Hafnium in the Real World
Real-World Uses
- Nuclear reactor control rods: Hafnium has an exceptionally high thermal neutron absorption cross-section and excellent corrosion resistance in hot water; hafnium rods are used in pressurised water reactors (PWRs) and submarine nuclear reactors to regulate the fission rate.
- Semiconductor gate dielectrics: Hafnium dioxide (HfO₂) replaced silicon dioxide as the transistor gate insulator at the 45 nm node (Intel, 2007) and smaller; its much higher dielectric constant reduces gate leakage current, enabling further transistor scaling in modern CPUs and memory chips.
- Superalloy additive for turbine blades: Hafnium (1–4%) is added to nickel-based superalloys used in single-crystal jet engine turbine blades; it improves grain boundary cohesion and oxidation resistance at temperatures above 1000 °C.
- Plasma torch electrodes: Hafnium inserts are used as the electrode in plasma cutting torches because hafnium forms a stable oxide at the tip that supports the plasma arc without rapid electrode erosion when cutting stainless steel and aluminium.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is hafnium used for?
Hafnium's most important use is in nuclear reactor control rods: it absorbs neutrons exceptionally well and resists corrosion in hot water, making it ideal for pressurised water reactor control rods. Hafnium oxide (hafnia) is used as a high-k dielectric gate insulator in modern transistors, replacing silicon dioxide as transistors shrink below 45 nm. Hafnium is also used in superalloys for jet turbine blades.
Why is hafnium used in nuclear reactors?
Hafnium has a large thermal neutron absorption cross-section (approximately 100 barns) and consists of several isotopes that all absorb neutrons. Unlike many neutron absorbers, hafnium's absorption products are also good absorbers, so it remains effective over long periods without needing frequent replacement. Combined with its excellent corrosion resistance in high-temperature water, these properties make hafnium alloys the preferred control rod material in submarine and naval reactors.
How was hafnium discovered?
Hafnium was discovered in 1922 by Dutch physicist Dirk Coster and Hungarian chemist Georg von Hevesy at the Institute for Theoretical Physics in Copenhagen (then led by Niels Bohr). They predicted its existence from Bohr's new quantum model of the atom and found it by X-ray spectroscopy in zirconium ores. The name comes from Hafnia, the Latin name for Copenhagen.
What is hafnium oxide used for in transistors?
As transistors shrank to nanometre scales, the traditional silicon dioxide gate dielectric became too thin (just a few atomic layers) and leaked current. Hafnium oxide (HfO2), with a much higher dielectric constant (k~25 vs ~3.9 for SiO2), provides the same capacitance with a much thicker layer, dramatically reducing leakage current. Intel introduced hafnium-based high-k gate dielectrics in 2007, a fundamental shift in transistor materials after 40 years of silicon dioxide.