- Hafnium (Hf) is a transition metal with atomic number 72, belonging to Group 4 of the periodic table, directly beneath zirconium.
- Its electron configuration is [Xe] 4f¹⁴ 5d² 6s², reflecting its placement among the d-block elements. A hafnium atom contains seventy-two protons, seventy-two electrons, and about one hundred and six neutrons in its most stable isotopes.
- Naturally occurring hafnium is composed of several stable isotopes, the most abundant being hafnium-180 (¹⁸⁰Hf).
- Hafnium was discovered in 1923 by Dirk Coster and George de Hevesy in Copenhagen, Denmark. Using X-ray spectroscopy, they identified it in zirconium minerals. The element was named after Hafnia, the Latin name for Copenhagen. Hafnium’s discovery confirmed predictions made by Niels Bohr based on his quantum model of the atom, as it filled a gap in the periodic table where Mendeleev had left space.
- Physically, hafnium is a lustrous, silvery-gray metal that is ductile and corrosion-resistant. It has a high melting point of 2,233 °C (4,051 °F) and a boiling point of 4,603 °C (8,337 °F), properties that make it useful in high-temperature environments. It is very dense (13.31 g/cm³) and chemically resembles zirconium so closely that the two elements are difficult to separate. Their chemical similarity arises from the lanthanide contraction, which makes their ionic radii nearly identical.
- Chemically, hafnium is resistant to attack by acids and alkalis but reacts with halogens to form hafnium halides, such as hafnium tetrachloride (HfCl₄), which is important for metal purification. It forms a stable oxide, hafnium dioxide (HfO₂), a refractory material with a very high melting point and strong dielectric properties.
- Hafnium has several important applications. It is widely used in nuclear reactors because of its exceptional ability to absorb neutrons, making it ideal for control rods. Conversely, zirconium, its twin element, is used for nuclear fuel cladding because it does not absorb neutrons strongly, highlighting the importance of their separation. Hafnium is also used in high-temperature alloys, aerospace components, plasma torches, and semiconductor technology. In modern electronics, hafnium dioxide is employed as a high-k dielectric material in advanced transistors, replacing silicon dioxide to improve performance in microprocessors.
- Biologically, hafnium has no known essential role in living organisms and is generally considered to have low toxicity. However, fine hafnium dust can pose inhalation hazards and should be handled with care.
- Environmentally, hafnium is relatively rare, constituting about 0.0003% of Earth’s crust. It is always found in association with zirconium minerals, particularly zircon (ZrSiO₄), and is obtained as a by-product of zirconium refining. Its scarcity and specialized applications make it an important strategic material in nuclear and technological industries.
