Hafnium
transition metalProperties
| Property | Value |
|---|---|
| Atomic Mass | 178.49 amu |
| Category | transition metal |
| Group | 4 |
| Period | 6 |
| Electron Configuration | [Xe] 4f14 5d2 6s2 |
| Electronegativity | 1.3 (Pauling) |
| Oxidation States | 4 |
| Melting Point | 2506 K (2232.8 °C) |
| Boiling Point | 4876 K (4602.9 °C) |
| Density | 13.31 g/cm³ |
| Discovered By | Dirk Coster, George de Hevesy (1923) |
About Hafnium
Hafnium is the textbook case for why the lanthanide contraction matters. Sitting directly under zirconium in group 4, it ended up with almost the same ionic radius (about 0.78 Å for Hf⁴⁺ vs 0.84 Å for Zr⁴⁺), which means the two elements travel together through every mineral and every separation step. Commercial Hf is basically a byproduct of cleaning up Zr. The reason chemists bother is nuclear: Hf has a thermal-neutron capture cross-section near 100 barns while Zr is under 0.2, so reactor-grade zirconium for fuel cladding has to be hafnium-free, and the hafnium that gets stripped out becomes the control-rod material. The other modern story is HfO₂ — a high-κ dielectric (κ ≈ 25) that replaced silicon dioxide as the gate insulator in transistors below the 45 nm node, ending the long reign of SiO₂ gates.
Fun Fact
Hafnium hid in plain sight for over 150 years — it is so chemically identical to zirconium that all zirconium samples contained significant hafnium contamination without anyone knowing.
Common Uses
- Control rods in pressurized water reactors for neutron absorption
- High-κ HfO₂ gate dielectric in sub-45 nm CMOS transistors
- Hf-bearing nickel superalloys for turbine blade leading edges
- Plasma-cutting torch electrodes that resist oxygen erosion
- Refractory carbide coatings (HfC) on rocket nozzle throats