Hafnium

Hafnium is a chemical element with symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1923, making it the penultimate stable element to be discovered (rhenium was identified two years later). Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered.

Hafnium is used in filaments and electrodes. Some semiconductor fabrication processes use its oxide for integrated circuits at 45 nm and smaller feature lengths. Some superalloys used for special applications contain hafnium in combination with niobium, titanium, or tungsten.

Hafnium's large neutron capture cross-section makes it a good material for neutron absorption in control rods in nuclear power plants, but at the same time requires that it be removed from the neutron-transparent corrosion-resistant zirconium alloys used in nuclear reactors.

Isotopes of hafnium

Natural hafnium (Hf) consists of five stable isotopes (¹⁷⁶Hf, ¹⁷⁷Hf, ¹⁷⁸Hf, ¹⁷⁹Hf, and ¹⁸⁰Hf) and one very long-lived radioisotope, ¹⁷⁴Hf, with a half-life of 2×10¹⁵ years. In addition, there are 30 other known radionuclides, the most stable of which is ¹⁸²Hf with a half-life of 8.9×10⁶ years. No other radioisotope has a half-life over 1.87 days. Most isotopes have half-lives under 1 minute. There are also 27 known nuclear isomers, the most stable of which is ^178m2Hf with a half-life of 31 years.

Relative atomic mass: 178.49(2).

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