page_title: Hafnium
section_title: Production
hierarchical_section_title: Hafnium / Production
caption_attribution_description: Basa Sunda: Hafnium murni (99,98%) dina tungtung éléktroda nu dipaké dina prosés electron beam melting (conto simpenan Ethan Currens, kénca), nu geus ngalaman oksidasi (katuhu), jeung kubus 1 cm3 pikeun babandingan (tengah). Dipoto luhureun lambar kaca bodas. Deutsch: Reine (99,9&#160;%), elektronenstrahlgeschmolzene Hafnium-Stücke, mit und ohne Oxidschicht, sowie für den Größenvergleich ein 1 cm3 Hafnium-Würfel. Die Metallstücke wurden auf einer weißen Glasplatte photographiert. English: Pure (99.98&#160;%), Melted tip of a hafnium consumable electrode used in an ebeam remelting furnace (sample from the collection of Ethan Currens), oxidized hafnium ebeam remelted ingot (color from thin film effects in the oxide layer), and additional 1 cm3 hafnium cube for comparison. The metal piece-photo was taken on a white glass plate. Español: Hafnio puro (99,98%): punta fundida de un electrodo consumible usado en una caldera de refusión por rayo de electrones (muestra de la colección de Ethan Currens), lingote refundido por rayo de electrones oxidado (el color se debe al efecto película en la capa de óxido) y un cubo de 1 cm³ para comparar Français: (1) Pointe fondue d'une électrode sacrificielle d'hafnium pur à 99,98&#160;% utilisé dans une fournaise appliquant la technologie electron beam melting (EBM) (échantillon de la collection d'Ethan Currens), (2) lingot refondu d'hafnium oxydé par application de l'EBM (la couleur est un phénomène d'optique provoqué par une mince couche d'oxyde) et (3) un cube de 1 cm3 d'hafnium. Les trois pièces se trouvent sur une plaque de verre blanc.
context_page_description: Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1923, by Coster and Hevesy, making it the last stable element to be discovered. 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.
context_section_description: The heavy mineral sands ore deposits of the titanium ores ilmenite and rutile yield most of the mined zirconium, and therefore also most of the hafnium.
  Zirconium is a good nuclear fuel-rod cladding metal, with the desirable properties of a very low neutron capture cross-section and good chemical stability at high temperatures. However, because of hafnium's neutron-absorbing properties, hafnium impurities in zirconium would cause it to be far less useful for nuclear-reactor applications. Thus, a nearly complete separation of zirconium and hafnium is necessary for their use in nuclear power. The production of hafnium-free zirconium is the main source for hafnium.
  The chemical properties of hafnium and zirconium are nearly identical, which makes the two difficult to separate. The methods first used — fractional crystallization of ammonium fluoride salts or the fractional distillation of the chloride — have not proven suitable for an industrial-scale production. After zirconium was chosen as material for nuclear reactor programs in the 1940s, a separation method had to be developed. Liquid-liquid extraction processes with a wide variety of solvents were developed and are still used for the production of hafnium. About half of all hafnium metal manufactured is produced as a by-product of zirconium refinement. The end product of the separation is hafnium(IV) chloride. The purified hafnium(IV) chloride is converted to the metal by reduction  with magnesium or sodium, as in the Kroll process.
  HfCl₄ + 2 Mg (1100 °C) → 2 MgCl₂ + Hf
  Further purification is effected by a chemical transport reaction developed by Arkel and de Boer: In a closed vessel, hafnium reacts with iodine at temperatures of 500 °C, forming hafnium(IV) iodide; at a tungsten filament of 1700 °C the reverse reaction happens, and the iodine and hafnium are set free. The hafnium forms a solid coating at the tungsten filament, and the iodine can react with additional hafnium, resulting in a steady turn over.
  Hf + 2 I₂ (500 °C) → HfI₄
  HfI₄ (1700 °C) → Hf + 2 I₂
caption: Melted tip of a hafnium consumable electrode used in an electron beam remelting furnace, a 1 cm cube, and an oxidized hafnium electron beam-remelted ingot (left to right)
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