Hafnium is a chemical element with the symbol Hf and atomic number 72. A shiny, silvery gray, tetravalent change metamorphosis metal, hafnium chemically looks like 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 second-last stable element to be discovered. Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered.
Hafnium is used in thin threads and electrodes. Some (element used to make electronic circuits) lie/construction processes use its oxide for electronic devicess 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 take and hold (to prevent release) cross section makes it a good material for neutron (mental concentration/picking up of a liquid) in control rods in nuclear power plants, but at the same time needs/demands that it be removed from the neutron-clear/open and honest (slow chemical breakdown of something/rust, etc.)-resistant zirconium mixtures (of metals) used in nuclear reactors.
Hafnium is a shiny, silvery, (able to be flattened or drawn into wire) metal that is (slow chemical breakdown of something/rust, etc.)-resistant and chemically almost the same as zirconium (due to its having the same number of valence electrons, being in the same group, but also to relativistic effects; the expected (act of something getting bigger, wider, etc.) of atomic radii from period 5 to 6 is almost exactly cancelled out by the lanthanide contraction). Hafnium changes from its alpha form, a six-sided close-packed (something made of crossed strips of wood, metal, etc.), to its beta form, a body-centered cubic (something made of crossed strips of wood, metal, etc.), at 2388 K. The physical properties of hafnium metal samples are very (much) affected by zirconium (dirt, dust, etc.), especially the nuclear properties, as these two elements are among the hardest to separate because of their chemical (thing that’s almost the same as another thing).
A important/famous physical difference between these metals is their density, with zirconium having about one-half the density of hafnium. The most famous nuclear properties of hafnium are its high thermal neutron take and hold (to prevent release) cross section and that the centers (of cells or atoms) of (more than two, but not a lot of) different hafnium isotopes easily soak up (like a towel) two or more neutrons each. In contrast with this, zirconium is practically clear/open and honest to thermal neutrons, and it is commonly used for the metal parts/pieces of nuclear reactors – especially the covering of their nuclear fuel rods.
Hafnium reacts in air to form a (serving or acting to prevent harm) film that stops further (slow chemical breakdown of something/rust, etc.). The metal is not easily attacked by acids but can be oxidized with halogens or it can be burnt in air. Like its sister metal zirconium, finely divided hafnium can (start a fire/catch on fire) in a sudden and unplanned way in air. The metal is resistant to (mainly studied) alkalis.
The chemistry of hafnium and zirconium is so almost the same that the two cannot be separated on the basis of different/disagreeing chemical reactions. The melting points and boiling points of the compounds and the (ability to be dissolved in something) in solvents are the major differences in the chemistry of these twin elements.
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 covering metal, with the desirable properties of a very low neutron capture (thin slice that can be looked at) and good chemical (firm and steady nature/lasting nature/strength) at high temperatures. However, because of hafnium’s neutron-soaking up (like a towel) properties, in zirconium would cause it to be far less useful for nuclear-reactor uses. So, 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 very hard to separate. The methods first used — fractional crystallization of ammonium fluoride salts or the fractional summary/(when something is boiled down) of the chloride — have not proven good 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 (something produced along with something else) of zirconium (good taste/good manners/improvement). The end product of the separation is hafnium(IV) chloride. The cleaned hafnium(IV) chloride is converted to the metal by reduction with magnesium or sodium, as in the Kroll process.
HfCl4 + 2 Mg (1100 Â°C) a’ 2 MgCl2 + Hf
Further cleaning is produced/made happen by a chemical transport reaction developed by Arkel and de Boer: In a closed vessel, hafnium reacts with iodine at temperatures of 500 Â°C, forming hafnium(IV) iodide; at a tungsten thin thread of 1700 Â°C the reverse reaction happens, and the iodine and hafnium are set free. The chemical forms a solid coating at the tungsten thin thread, and the iodine can react with added/more hafnium, resulting in a steady iodine turnover.
Hf + 2 I2 (500 Â°C) a’ HfI4
HfI4 (1700 Â°C) a’ Hf + 2 I2