Hafnium: Difference between revisions

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Hafnium is a chemical element; it has 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 1922, by Dirk Coster and George de Hevesy. Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered. The element is obtained only by separation from zirconium, with most of the world's hafnium production coming from processes that also produce zirconium. These processes make use of heavy mineral sands ore deposits, which include the minerals zircon, rutile, and ilmenite, among others.

Hafnium is most often used in alloys with nickel, and was used in larger quantities to produce the control rods used in nuclear reactors. 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. It is ductile, and is also used in filaments and electrodes. Some semiconductor fabrication processes use its oxide for integrated circuits at 45 nanometres (1.8×10⁻⁶ in) and smaller, and superalloys used for special applications can contain hafnium in combination with niobium, titanium, or tungsten.

Pure hafnium is not toxic, but is extremely flammable to the point of being pyrophoric—capable of spontaneous combustion in air. Several industrial processes involved in the production of hafnium have by-products that can be hazardous when released into the environment, and several hafnium compounds have hazards of their own. One nuclear isomer of hafnium, ^178m2Hf, was the source of a controversy for its potential use as a weapon, but it has never been successfully produced for practical use.

Characteristics

Physical characteristics

File:Hafnium bits.jpg

Pieces of hafnium

Hafnium is a shiny, silvery, ductile metal^[1] that is corrosion-resistant and chemically similar to zirconium^[2] in that they have the same number of valence electrons and are in the same group. Also, their relativistic effects are similar: The expected expansion of atomic radii from period 5 to 6 is almost exactly canceled out by the lanthanide contraction. Hafnium changes from its alpha form, a hexagonal close-packed lattice, to its beta form, a body-centered cubic lattice, at 2,388 K (2,115 °C; 3,839 °F).^[3] The physical properties of hafnium metal samples are markedly affected by zirconium impurities, especially the nuclear properties, as these two elements are among the most difficult to separate because of their chemical similarity.^[2]

A notable physical difference between these metals is their density, with zirconium having about one-half the density of hafnium. The most notable nuclear properties of hafnium are its high thermal neutron capture cross section, roughly three orders of magnitude greater than that of zirconium,^[1] and that the nuclei of several different hafnium isotopes readily absorb two or more neutrons apiece.^[2] Because zirconium is practically transparent to thermal neutrons, it is commonly used for the metal components of nuclear reactors—especially the cladding of their nuclear fuel rods.^[2]

Chemical characteristics

File:Hafnium(IV) oxide.jpg

Hafnium dioxide (HfO₂)

Hafnium reacts in air to form a protective film of hafnium oxide in the monoclinic phase that inhibits further corrosion.^[4] Despite this, the metal is attacked by hydrofluoric acid and concentrated sulfuric acid, and can be oxidized with halogens^[5] or burnt in air. Like its sister metal zirconium, finely divided hafnium can ignite spontaneously in air.^[1] The metal is resistant to concentrated alkalis.^[5]

As a consequence of lanthanide contraction, the chemistry of hafnium and zirconium is so similar that the two cannot be separated based on differing chemical reactions. The melting and boiling points of the compounds and the solubility in solvents are the major differences in the chemistry of these twin elements.^[6]

Isotopes

At least 40 isotopes of hafnium have been observed, ranging in mass number from 153 to 192.^[7] The five stable isotopes have mass numbers from 176 to 180 inclusive; the primordial ¹⁷⁴Hf has a very long half-life of 3.8×10¹⁶ years.^[8]

The extinct radionuclide ¹⁸²Hf has a half-life of 8.90 million years, and is an important tracker isotope for the formation of planetary cores.^[9] No other radioisotope has a half-life over 1.87 years.^[10]

The longest-lived nuclear isomer ^178m2Hf (31 years) was at the center of a controversy for several years regarding its potential use as a weapon. Because of its high energy compared to the ground state ¹⁷⁸Hf, the isomer was put under scrutiny as being capable of induced gamma emission, which could be weaponized to produce large amounts of gamma radiation all at once.^[11] Applications of the isomer have been frustrated due to the difficulty of producing it without the product being immediately destroyed^[12] as well as its extremely high cost.^[13]

Occurrence

File:Zircão.jpeg

Zircon crystal (2×2 cm) from Tocantins, Brazil

Hafnium is estimated to make up about between 3.0 and 4.8 ppm of the Earth's upper crust by mass.^[14]^: 5 ^[15] It does not exist as a free element on Earth, but is found combined in solid solution with zirconium in natural zirconium compounds such as zircon, ZrSiO₄, which usually has about 1–4% of the Zr replaced by Hf. Rarely, the Hf/Zr ratio increases during crystallization to give the isostructural mineral hafnon (Hf,Zr)SiO₄, with atomic Hf > Zr.^[16] An obsolete name for a variety of zircon containing unusually high Hf content is alvite.^[17]

A major source of zircon (and hence hafnium) ores is heavy mineral sands ore deposits, pegmatites, particularly in Brazil and Malawi, and carbonatite intrusions, particularly the Crown Polymetallic Deposit at Mount Weld, Western Australia. A potential source of hafnium is trachyte tuffs containing rare zircon-hafnium silicates eudialyte or armstrongite, at Dubbo in New South Wales, Australia.^[18]

Production

File:Hafnium ebeam remelted.jpg

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)

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.^[19] 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 of hafnium.^[2]

File:Hafnium pellets with a thin oxide layer.jpg

Hafnium oxidized ingots which exhibit thin-film optical effects

The chemical properties of hafnium and zirconium are nearly identical, which makes the two difficult to separate.^[20] The methods first used—fractional crystallization of ammonium fluoride salts^[21] or the fractional distillation of the chloride^[22]—did not prove suitable for an industrial-scale production. After zirconium was chosen as a 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 producing hafnium.^[23] Other methods to purify hafnium from zirconium include molten salt extraction and crystallization of fluorozirconates.^[24] 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.^[25] The purified hafnium(IV) chloride is converted to the metal by reduction with magnesium or sodium, as in the Kroll process.^[26]

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \ce{HfCl4{} + 2 Mg ->[1100~^\circ\text{C}] Hf{} + 2 MgCl2}}

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 (900 °F), forming hafnium(IV) iodide; at a tungsten filament of 1,700 °C (3,100 °F) the reverse reaction happens preferentially, and the chemically bound iodine and hafnium dissociate into the native elements. The hafnium forms a solid coating at the tungsten filament, and the iodine can react with additional hafnium, resulting in a steady iodine turnover and ensuring the chemical equilibrium remains in favor of hafnium production.^[6]^[27]

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \ce{Hf{} + 2 I2 ->[500~^\circ\text{C}] HfI4}}

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \ce{HfI4 ->[1700~^\circ\text{C}] Hf{} + 2 I2}}

Chemical compounds

Due to the lanthanide contraction, the ionic radius of hafnium(IV) (0.78 ångström) is almost the same as that of zirconium(IV) (0.79 angstroms).^[28] Consequently, compounds of hafnium(IV) and zirconium(IV) have very similar chemical and physical properties.^[28] Hafnium and zirconium tend to occur together in nature and the similarity of their ionic radii makes their chemical separation rather difficult. Hafnium tends to form inorganic compounds in the oxidation state of +4. Halogens react with it to form hafnium tetrahalides.^[28] At higher temperatures, hafnium reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon.^[28] Some hafnium compounds in lower oxidation states are known.^[29]

Hafnium(IV) chloride and hafnium(IV) iodide have some applications in the production and purification of hafnium metal. They are volatile solids with polymeric structures.^[6] These tetrahalides are precursors to various organohafnium compounds,^[30] and hafnium(IV) chloride in particular is used in microelectronics manufacturing as a source of hafnium oxide in atomic layer deposition, much in the same way as zirconium(IV) chloride.^[31]

The white hafnium oxide (HfO₂), with a melting point of 2,812 °C (3,085 K; 5,094 °F) and a boiling point of roughly 5,100 °C (5,400 K; 9,200 °F), is very similar to zirconia, but slightly more basic.^[6] Hafnium carbide is the most refractory binary compound known, with a melting point over 3,890 °C (4,163 K; 7,034 °F), and hafnium nitride is the most refractory of all known metal nitrides, with a melting point of 3,310 °C (3,583 K; 5,990 °F).^[28] Hafnium carbonitride has the highest known melting point for any material, which is confirmed to be above 4,000 °C (4,270 K; 7,230 °F) by experiment,^[32] while calculations predict its melting point to be 4,110 °C (4,380 K; 7,430 °F).^[33]

History

File:Moseley step ladder.jpg

Photographic recording of the characteristic X-ray emission lines of some elements

Hafnium's existence was predicted by Dmitri Mendeleev in 1869. In his report on The Periodic Law of the Chemical Elements, in 1869, Dmitri Mendeleev had implicitly predicted the existence of a heavier analog of titanium and zirconium. At the time of his formulation in 1871, Mendeleev believed that the elements were ordered by their atomic masses and placed lanthanum (element 57) in the spot below zirconium. The exact placement of the elements and the location of missing elements was done by determining the specific weight of the elements and comparing the chemical and physical properties.^[34]

The X-ray spectroscopy done by Henry Moseley in 1914 showed a direct dependency between spectral line and effective nuclear charge. This led to the nuclear charge, or atomic number of an element, being used to ascertain its place within the periodic table. With this method, Moseley determined the number of lanthanides and showed the gaps in the atomic number sequence at numbers 43, 61, 72, and 75.^[35]

The discovery of the gaps led to an extensive search for the missing elements. In 1914, several people claimed the discovery after Henry Moseley predicted the gap in the periodic table for the then-undiscovered element 72.^[36] Georges Urbain asserted that he found element 72 in the rare earth elements in 1907 and published his results on celtium in 1911.^[37] Neither the spectra nor the chemical behavior he claimed matched with the element found later, and therefore his claim was turned down after a long-standing controversy.^[38] The controversy was partly because the chemists favored the chemical techniques which led to the discovery of celtium, while the physicists relied on the use of the new X-ray spectroscopy method that proved that the substances discovered by Urbain did not contain element 72.^[38] In 1921, Charles R. Bury^[39]^[40] suggested that element 72 should resemble zirconium and therefore was not part of the rare earth elements group. By early 1923, Niels Bohr and others agreed with Bury.^[41]^[42] These suggestions were based on Bohr's theories of the atom which were identical to chemist Charles Bury,^[39] the X-ray spectroscopy of Moseley, and the chemical arguments of Friedrich Paneth.^[43]^[44]

Encouraged by these suggestions and by the reappearance in 1922 of Urbain's claims that element 72 was a rare earth element discovered in 1911, Dirk Coster and Georg von Hevesy were motivated to search for the new element in zirconium ores.^[45] Hafnium was discovered by the two in 1923 in Copenhagen, Denmark, validating the original 1869 prediction of Mendeleev.^[46]^[47]^[48] It was ultimately found in zircon in Norway through X-ray spectroscopy analysis.^[49] The place where the discovery took place led to the element being named for the Latin name for "Copenhagen", Hafnia, the home town of Niels Bohr.^[50]^[51]^[52] Today, the Faculty of Science of the University of Copenhagen uses in its seal a stylized image of the hafnium atom.^[53]

Hafnium was separated from zirconium through repeated recrystallization of the double ammonium or potassium fluorides by Valdemar Thal Jantzen and von Hevesey.^[21] Anton Eduard van Arkel and Jan Hendrik de Boer were the first to prepare metallic hafnium by passing hafnium tetraiodide vapor over a heated tungsten filament in 1924.^[22]^[27] This process for differential purification of zirconium and hafnium is still in use today.^[2]

In 1923, six predicted elements were still missing from the periodic table: 43 (technetium), 61 (promethium), 85 (astatine), and 87 (francium) are radioactive elements and are only present in trace amounts in the environment,^[54] thus making elements 75 (rhenium) and 72 (hafnium) the last two stable elements to be discovered. The element rhenium was found in 1908 by Masataka Ogawa, though its atomic number was misidentified at the time, and it was not generally recognised by the scientific community until its rediscovery by Walter Noddack, Ida Noddack, and Otto Berg in 1925. This makes it somewhat difficult to say if hafnium or rhenium was discovered last.^[55]

Applications

Much of the hafnium produced is used in the manufacture of control rods for nuclear reactors^[23] and as an additive in nickel alloys to increase their heat resistance.^[1]

Hafnium has limited technical applications due to a few factors. It is very similar to zirconium, a more abundant element that can be used in most cases, and pure hafnium wasn't widely available until the late 1950s, when it became a byproduct of the nuclear industry's need for hafnium-free zirconium. Additionally, hafnium is rare and difficult to separate from other elements, making it expensive. After the Fukushima disaster reduced the demand for hafnium-free zirconium, the price of hafnium increased significantly from around $500–$600/kg ($227-$272/lb) in 2014 to around $1000/kg ($454/lb) in 2015.^[56] Hafnium products, such as tubes and sheets of the metal, could be purchased at Template:Euro/kg ($170/lb) in 2009.^[1]

Nuclear reactors

The nuclei of several hafnium isotopes can each absorb multiple neutrons. This makes hafnium a good material for nuclear reactors' control rods. Its neutron capture cross section (Capture Resonance Integral I_o ≈ 2000 barns)^[57] is about 600 times that of zirconium (other elements that are good neutron-absorbers for control rods are cadmium and boron). Excellent mechanical properties and exceptional corrosion-resistance properties allow its use in the harsh environment of pressurized water reactors.^[23] The German research reactor FRM II uses hafnium as a neutron absorber.^[58] It is also common in military reactors, particularly in US naval submarine reactors, to slow reactor rates that are too high.^[59]^[60] It is seldom found in civilian reactors, the first core of the Shippingport Atomic Power Station (a conversion of a naval reactor) being a notable exception.^[61]

Alloys

File:Apollo AS11-40-5866.jpg

Hafnium-containing rocket nozzle of the Apollo Lunar Module in the lower right corner

Hafnium is used in alloys with iron, titanium, niobium, tantalum, and other metals. An alloy used for liquid-rocket thruster nozzles, for example the main engine of the Apollo Lunar Modules, is C103 which consists of 89% niobium, 10% hafnium and 1% titanium.^[62]

Small additions of hafnium increase the adherence of protective oxide scales on nickel-based alloys. It thereby improves the corrosion resistance, especially under cyclic temperature conditions that tend to break oxide scales, by inducing thermal stresses between the bulk material and the oxide layer.^[63]^[64]^[65] An alloy that includes as little as 1% hafnium can withstand temperatures that are 50 °C (90 °F) higher than the same alloy without hafnium.^[1]

Microprocessors

Hafnium-based compounds are employed in gates of transistors as insulators in the 45 nm (and below) generation of integrated circuits from Intel, IBM and others.^[66]^[67] Hafnium oxide-based compounds are practical high-κ dielectrics, allowing reduction of the gate leakage current which improves performance at such scales.^[68]^[69]^[70]

Isotope geochemistry

Isotopes of hafnium and lutetium are also used in isotope geochemistry and geochronological applications, in lutetium-hafnium dating. It is often used as a tracer of isotopic evolution of Earth's mantle through time.^[71] This is because ¹⁷⁶Lu decays to ¹⁷⁶Hf with a half-life of approximately 37 billion years.^[72]^[73]^[74]

In most geologic materials, zircon is the dominant host of hafnium (>10,000 ppm) and is often the focus of hafnium studies in geology.^[75] Hafnium is readily substituted into the zircon crystal lattice, and is therefore very resistant to hafnium mobility and contamination. Zircon also has an extremely low Lu/Hf ratio, making any correction for initial lutetium minimal. Although the Lu/Hf system can be used to calculate a "model age", i.e. the time at which it was derived from a given isotopic reservoir such as the depleted mantle, these "ages" do not carry the same geologic significance as do other geochronological techniques as the results often yield isotopic mixtures and thus provide an average age of the material from which it was derived.^[76]^[77]

Garnet is another mineral that contains appreciable amounts of hafnium to act as a geochronometer. The high and variable Lu/Hf ratios found in garnet make it useful for dating metamorphic events.^[78] Mass spectrometry also makes use of these ratios to date garnet formed through igneous events.^[79]

Other uses

Due to its heat resistance and its affinity to oxygen and nitrogen, hafnium is a good scavenger for oxygen and nitrogen in gas-filled and incandescent lamps. Hafnium is also used as the electrode in plasma cutting because of its ability to shed electrons into the air.^[80] Hafnium metallocene compounds can be prepared from hafnium tetrachloride and various cyclopentadiene-type ligand species. Perhaps the simplest hafnium metallocene is hafnocene dichloride. Hafnium metallocenes are part of a large collection of Group 4 transition metal metallocene catalysts that are used worldwide in the production of polyolefin resins like polyethylene and polypropylene.^[81] A pyridyl-amidohafnium catalyst can be used for the controlled iso-selective polymerization of propylene, which can then be combined with polyethylene to make a tougher recycled plastic.^[82]

The high energy content of ^178m2Hf was the concern of a DARPA-funded program in the US. This program eventually concluded that using the ^178m2Hf nuclear isomer of hafnium to construct high-yield weapons with X-ray triggering mechanisms—an application of induced gamma emission—was infeasible because of its expense and difficulty to manufacture.^[12] See hafnium controversy.^[13]

Hafnium diselenide is studied in spintronics thanks to its charge density wave and superconductivity.^[83]

Toxicity and safety

Template:Chembox Hafnium is a pyrophoric material, and as such fine particles can spontaneously combust upon exposure to air. Hafnium powder is often wetted with at least 25% water by weight to be considered safe - the metal is insoluble in water.^[84] Machining hafnium is particularly hazardous because of the potential for fine particles of the metal to be produced and immediately introduced to frictional force. Compounds that contain this metal are rarely encountered by most people.^[85] The pure metal is not considered toxic, though it has been observed to accumulate in the liver when injected into rats.^[1] Hafnium compounds should be handled as if they were toxic because the ionic forms of metals are normally at greatest risk for toxicity, and limited animal testing has been done for hafnium compounds.^[85] Hafnium tetrachloride and hafnium tetrabromide, which are often part of industrial processes that use the element, are of particular note, with both compounds releasing acidic fumes on contact with water (hydrochloric and hydrobromic acid, respectively). Additionally, hafnium tetrachloride has been observed as causing liver damage at high exposure levels.^[1]

People can be exposed to hafnium in the workplace by breathing, swallowing, skin, and eye contact. In the United States, the Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for exposure to hafnium and hafnium compounds in the workplace as TWA 0.5 mg/m³ over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set the same recommended exposure limit (REL).^[24] At levels of 50 mg/m³, hafnium is immediately dangerous to life and health.^[86]

Because the mineral zircon is often associated with traces of the radioactive elements uranium and thorium, the chemically destructive processes used to separate zirconium from hafnium have potential to release these radioactive elements and their decay products into the environment along with other reaction wastes. Additionally, synthesis pathways that involve liquid-liquid extraction introduce ammonium chloride and sulfate into reaction mixtures, which as effluent can reduce available oxygen in water sources or produce cyanides if it comes into contact with thiocyanate-containing compounds.^[1]

References

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External links

Hafnium at Los Alamos National Laboratory's periodic table of the elements
Hafnium at The Periodic Table of Videos (University of Nottingham)
Hafnium Technical & Safety Data
NLM Hazardous Substances Databank – Hafnium, elemental
Don Clark: Intel Shifts from Silicon to Lift Chip Performance – WSJ, 2007
Hafnium-based Intel 45nm Process Technology
CDC – NIOSH Pocket Guide to Chemical Hazards

Template:Periodic table (navbox) Template:Hafnium compounds

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@@ Line 3: / Line 3: @@
 {{Infobox hafnium}}
-'''Hafnium''' is a [[chemical element]]; it has [[Symbol (chemistry)|symbol]] '''Hf''' and [[atomic number]] 72. A [[lustre (mineralogy)|lustrous]], silvery gray, [[tetravalence|tetravalent]] [[transition metal]], hafnium chemically resembles [[zirconium]] and is found in many zirconium [[mineral]]s. Its existence was [[Mendeleev's predicted elements|predicted by Dmitri Mendeleev]] in 1869, though it was not identified until 1922, by [[Dirk Coster]] and [[George de Hevesy]]. Hafnium is named after {{lang|la|Hafnia}}, the [[Latin]] name for [[Copenhagen#Etymology|Copenhagen]], where it was discovered.
+'''Hafnium''' is a [[chemical element]]; it has [[Symbol (chemistry)|symbol]] '''Hf''' and [[atomic number]] 72. A [[lustre (mineralogy)|lustrous]], silvery gray, [[tetravalence|tetravalent]] [[transition metal]], hafnium chemically resembles [[zirconium]] and is found in many zirconium [[mineral]]s. Its existence was [[Mendeleev's predicted elements|predicted by Dmitri Mendeleev]] in 1869, though it was not identified until 1922, by [[Dirk Coster]] and [[George de Hevesy]]. Hafnium is named after {{lang|la|Hafnia}}, the [[Latin]] name for [[Copenhagen#Etymology|Copenhagen]], where it was discovered. The element is obtained only by separation from zirconium, with most of the world's hafnium production coming from processes that also produce zirconium. These processes make use of [[heavy mineral sands ore deposits]], which include the minerals [[zircon]], [[rutile]], and [[ilmenite]], among others.
-Hafnium is used in filaments and electrodes.  Some [[semiconductor]] fabrication processes use its oxide for [[integrated circuit]]s at 45 nanometers and smaller feature lengths. Some [[superalloy]]s used for special applications contain hafnium in combination with [[niobium]], [[titanium]], or [[tungsten]].
+Hafnium is most often used in [[Alloy|alloys]] with [[nickel]], and was used in larger quantities to produce the [[Control rod|control rods]] used in [[Nuclear reactor|nuclear reactors]]. Hafnium's large [[neutron cross section|neutron capture cross section]] makes it a good material for [[neutron]] absorption in control rods in [[nuclear power plant]]s, but at the same time requires that it be removed from the neutron-transparent corrosion-resistant [[zirconium alloy]]s used in [[nuclear reactor]]s. It is [[Ductility|ductile]], and is also used in filaments and [[Electrode|electrodes]].  Some [[semiconductor]] fabrication processes use [[Hafnium(IV) oxide|its oxide]] for [[integrated circuit]]s at {{Convert|45|nm}} and smaller, and [[superalloy]]s used for special applications can contain hafnium in combination with [[niobium]], [[titanium]], or [[tungsten]].
-Hafnium's large [[neutron capture]] [[cross section (physics)|cross section]] makes it a good material for [[neutron]] absorption in [[control rod]]s in [[nuclear power plant]]s, but at the same time requires that it be removed from the neutron-transparent corrosion-resistant [[zirconium alloy]]s used in [[nuclear reactor]]s.
+Pure hafnium is not [[Toxicity|toxic]], but is extremely [[Combustibility and flammability|flammable]] to the point of being [[Pyrophoricity|pyrophoric]]—capable of [[spontaneous combustion]] in air. Several industrial processes involved in the production of hafnium have [[By-product|by-products]] that can be hazardous when released into the environment, and several [[hafnium compounds]] have hazards of their own. One [[nuclear isomer]] of hafnium, <sup>178m2</sup>Hf, was the source of [[Hafnium controversy|a controversy]] for its potential use as a weapon, but it has never been successfully produced for practical use.
 ==Characteristics==
@@ Line 14: / Line 14: @@
 [[File:Hafnium bits.jpg|thumb|left|Pieces of hafnium]]
 <section begin=properties />
-Hafnium is a shiny, silvery, [[ductility|ductile]] [[metal]] that is [[corrosion]]-resistant and chemically similar to zirconium<ref name="ASTM" /> in that they have the same number of [[valence electron]]s and are in the same group. Also, their [[relativistic quantum chemistry|relativistic effects]] are similar: The expected expansion of atomic radii from period 5 to 6 is almost exactly canceled out by the [[lanthanide contraction]]. Hafnium changes from its alpha form, a hexagonal close-packed lattice, to its beta form, a body-centered cubic lattice, at {{convert|2388|K}}.<ref>{{cite journal |last1=O'Hara |first1=Andrew |last2=Demkov |first2=Alexander A. |title=Oxygen and nitrogen diffusion in α-hafnium from first principles |journal=[[Applied Physics Letters]] |date=2014 |volume=104 |issue=21 |page=211909 |doi=10.1063/1.4880657 |bibcode=2014ApPhL.104u1909O }}</ref>  The physical properties of hafnium metal samples are markedly affected by zirconium impurities, especially the nuclear properties, as these two elements are among the most difficult to separate because of their chemical similarity.<ref name="ASTM" /><section end=properties />
+Hafnium is a shiny, silvery, [[ductility|ductile]] [[metal]]<ref name=":2">{{Cite book |last1=Nielsen |first1=Ralph H. |url=https://onlinelibrary.wiley.com/doi/book/10.1002/14356007 |title=Ullmann's Encyclopedia of Industrial Chemistry |last2=Wilfing |first2=Gerhard |date=2003-03-11 |publisher=Wiley |isbn=978-3-527-30385-4 |edition= |pages=191–201 |language=en |chapter=Hafnium and Hafnium Compounds |doi=10.1002/14356007.a12_559.pub2}}</ref> that is [[corrosion]]-resistant and chemically similar to zirconium<ref name="ASTM" /> in that they have the same number of [[valence electron]]s and are in the same group. Also, their [[relativistic quantum chemistry|relativistic effects]] are similar: The expected expansion of atomic radii from period 5 to 6 is almost exactly canceled out by the [[lanthanide contraction]]. Hafnium changes from its alpha form, a hexagonal close-packed lattice, to its beta form, a body-centered cubic lattice, at {{convert|2388|K}}.<ref>{{cite journal |last1=O'Hara |first1=Andrew |last2=Demkov |first2=Alexander A. |title=Oxygen and nitrogen diffusion in α-hafnium from first principles |journal=[[Applied Physics Letters]] |date=2014 |volume=104 |issue=21 |page=211909 |doi=10.1063/1.4880657 |bibcode=2014ApPhL.104u1909O }}</ref>  The physical properties of hafnium metal samples are markedly affected by zirconium impurities, especially the nuclear properties, as these two elements are among the most difficult to separate because of their chemical similarity.<ref name="ASTM" /><section end=properties />
-A notable physical difference between these metals is their [[density]], with zirconium having about one-half the density of hafnium. The most notable [[nuclear physics|nuclear]] properties of hafnium are its high [[thermal neutron|thermal]] [[neutron capture cross section]] and that the nuclei of several different hafnium isotopes readily absorb two or more [[neutron]]s apiece.<ref name="ASTM" /> In contrast with this, zirconium is practically transparent to thermal neutrons, and it is commonly used for the metal components of nuclear reactors—especially the cladding of their [[nuclear fuel rod]]s.
+A notable physical difference between these metals is their [[density]], with zirconium having about one-half the density of hafnium. The most notable [[nuclear physics|nuclear]] properties of hafnium are its high [[thermal neutron|thermal]] [[neutron capture cross section]], roughly three [[Order of magnitude|orders of magnitude]] greater than that of zirconium,<ref name=":2" /> and that the nuclei of several different hafnium isotopes readily absorb two or more [[neutron]]s apiece.<ref name="ASTM" /> Because zirconium is practically transparent to thermal neutrons, it is commonly used for the metal components of nuclear reactors—especially the cladding of their [[nuclear fuel rod]]s.<ref name="ASTM" />
 ===Chemical characteristics===
 {{See also|Hafnium#Chemical compounds|label1=&sect;&nbsp;Chemical compounds}}
 [[File:Hafnium(IV) oxide.jpg|thumb|left|[[Hafnium(IV) oxide|Hafnium dioxide]] (HfO<sub>2</sub>)]]
-Hafnium reacts in air to form a [[Passivation (chemistry)|protective film]] that inhibits further [[corrosion]].  Despite this, the metal is attacked by hydrofluoric acid and concentrated sulfuric acid, and can be oxidized with [[halogen]]s or burnt in air.  Like its sister metal zirconium, finely divided hafnium can ignite spontaneously in air. The metal is resistant to concentrated [[alkali]]s.
+Hafnium reacts in air to form a [[Passivation (chemistry)|protective film]] of [[Hafnium(IV) oxide|hafnium oxide]] in the [[Monoclinic crystal system|monoclinic]] phase that inhibits further [[corrosion]].<ref>{{Cite journal |last1=Smeltzer |first1=W.W |last2=Simnad |first2=M.T |date=1957 |title=Oxidation of hafnium |url=https://linkinghub.elsevier.com/retrieve/pii/0001616057900457 |journal=Acta Metallurgica |language=en |volume=5 |issue=6 |pages=328–334 |doi=10.1016/0001-6160(57)90045-7|url-access=subscription }}</ref>  Despite this, the metal is attacked by hydrofluoric acid and concentrated sulfuric acid, and can be oxidized with [[halogen]]s<ref name=":4">{{Citation |last=Holmes |first=D.R. |title=Corrosion of Hafnium and Hafnium Alloys |date=2005-01-01 |work=Corrosion: Materials |pages=354–359 |editor-last=Cramer |editor-first=Stephen D. |url=https://dl.asminternational.org/handbooks/book/25/chapter/341178/Corrosion-of-Hafnium-and-Hafnium-Alloys |access-date=2025-10-07 |publisher=ASM International |language=en |doi=10.31399/asm.hb.v13b.a0003826 |isbn=978-1-62708-183-2 |editor2-last=Covino |editor2-first=Bernard S.|url-access=subscription }}</ref> or burnt in air.  Like its sister metal zirconium, finely divided hafnium can ignite spontaneously in air.<ref name=":2" /> The metal is resistant to concentrated [[alkali]]s.<ref name=":4" />
 As a consequence of [[lanthanide contraction]], the chemistry of hafnium and zirconium is so similar that the two cannot be separated based on differing chemical reactions. The melting and boiling points of the compounds and the [[solubility]] in solvents are the major differences in the chemistry of these twin elements.<ref name="Holl">{{cite book|publisher = [[Walter de Gruyter]]|date = 1985|edition = 91–100|pages=1056–1057|isbn = 978-3-11-007511-3|title = Lehrbuch der Anorganischen Chemie|first = Arnold F.|last = Holleman |author2 = Wiberg, Egon |author3=Wiberg, Nils |language = de|doi=10.1515/9783110206845|author-link2=Egon Wiberg}}</ref>
@@ Line 27: / Line 27: @@
 ===Isotopes===
 {{Main|Isotopes of hafnium}}
-At least 40 isotopes of hafnium have been observed, ranging in [[mass number]] from 153 to 192.<ref name=PRC108>{{cite journal |first1=K. |last1=Haak |first2=O. B. |last2=Tarasov |first3=P. |last3=Chowdhury |display-authors=et al. |title=Production and discovery of neutron-rich isotopes by fragmentation of <sup>198</sup>Pt |date=2023 |journal=Physical Review C |volume=108 |number=34608 |page=034608 |doi=10.1103/PhysRevC.108.034608|bibcode=2023PhRvC.108c4608H |s2cid=261649436 }}</ref> The five stable isotopes have mass numbers from 176 to 180 inclusive; the [[primordial radionuclide|primordial]] <sup>174</sup>Hf has a very long half-life of {{val|3.8|e=16}} years.<ref name=belli2024/>
+At least 40 isotopes of hafnium have been observed, ranging in [[mass number]] from 153 to 192.<ref name=PRC108>{{cite journal |first1=K. |last1=Haak |first2=O. B. |last2=Tarasov |first3=P. |last3=Chowdhury |display-authors=et al. |title=Production and discovery of neutron-rich isotopes by fragmentation of <sup>198</sup>Pt |date=2023 |journal=Physical Review C |volume=108 |number=34608 |article-number=034608 |doi=10.1103/PhysRevC.108.034608|bibcode=2023PhRvC.108c4608H |osti=1998848 |s2cid=261649436 }}</ref> The five stable isotopes have mass numbers from 176 to 180 inclusive; the [[primordial radionuclide|primordial]] <sup>174</sup>Hf has a very long half-life of {{val|3.8|e=16}} years.<ref name=belli2024/>
-The [[extinct radionuclide]] <sup>182</sup>Hf has a half-life of {{val|8.90|u=million years}}, and is an [[Hafnium–tungsten dating|important tracker isotope]] for the formation of [[planetary core]]s.<ref name=":0">{{cite journal | vauthors = Kleine T, Walker RJ | title = Tungsten Isotopes in Planets | journal = Annual Review of Earth and Planetary Sciences | volume = 45 | issue = 1 | pages = 389–417 | date = August 2017 | pmid = 30842690 | pmc = 6398955 | doi = 10.1146/annurev-earth-063016-020037 | bibcode = 2017AREPS..45..389K }}</ref> No other radioisotope has a half-life over 1.87 years.
+The [[extinct radionuclide]] <sup>182</sup>Hf has a half-life of {{val|8.90|u=million years}}, and is an [[Hafnium–tungsten dating|important tracker isotope]] for the formation of [[planetary core]]s.<ref name=":0">{{cite journal | vauthors = Kleine T, Walker RJ | title = Tungsten Isotopes in Planets | journal = Annual Review of Earth and Planetary Sciences | volume = 45 | issue = 1 | pages = 389–417 | date = August 2017 | pmid = 30842690 | pmc = 6398955 | doi = 10.1146/annurev-earth-063016-020037 | bibcode = 2017AREPS..45..389K }}</ref> No other radioisotope has a half-life over 1.87 years.<ref>{{NUBASE2020|access-date=6 October 2025}}</ref>
-The longest-lived [[nuclear isomer]] <sup>178m2</sup>Hf (31 years) was at the [[Hafnium controversy|center of a controversy]] for several years regarding its potential use as a weapon.
+The longest-lived [[nuclear isomer]] <sup>178m2</sup>Hf (31 years) was at the [[Hafnium controversy|center of a controversy]] for several years regarding its potential use as a weapon. Because of its high energy compared to the ground state <sup>178</sup>Hf, the isomer was put under scrutiny as being capable of [[induced gamma emission]], which could be weaponized to produce large amounts of [[Gamma ray|gamma radiation]] all at once.<ref>{{Cite journal |last=Thomsen |first=D. E. |date=1986 |title=Pumping up Hope for a Gamma Ray Laser |url=https://www.jstor.org/stable/3970900 |journal=Science News |volume=130 |issue=18 |pages=276 |doi=10.2307/3970900 |jstor=3970900 |issn=0036-8423|url-access=subscription }}</ref> Applications of the isomer have been frustrated due to the difficulty of producing it without the product being immediately destroyed<ref name=":3">{{Cite journal |last1=Hsu |first1=Hsiao-Hua |last2=Talbert |first2=Willard L. |last3=Ward |first3=Tom |date=5 March 2017 |title=The Creation and Destruction of Hf-178m2 Isomer by Neutron Interaction |url=https://www.osti.gov/biblio/1345954 |journal=Los Alamos National Lab |doi=10.2172/1345954 |osti=1345954 }}</ref> as well as its extremely high cost.<ref name="bomb">{{cite web |author=Peter Zimmerman |author-link=Peter Zimmerman |date=June 2007 |title=The Strange Tale of the Hafnium Bomb: A Personal Narrative |url=https://www.aps.org/publications/apsnews/200706/backpage.cfm |access-date=5 March 2016 |website=[[American Physical Society]]}}</ref>
 ===Occurrence===
 [[File:Zircão.jpeg|thumb|left|Zircon crystal (2×2 cm) from [[Tocantins]], [[Brazil]]]]
-Hafnium is estimated to make up about between 3.0 and 4.8 [[Parts per million|ppm]] of the [[Earth]]'s upper [[crust (geology)|crust]] by mass.<ref>{{Cite book |last1=Haygarth |first1=John C. |url=https://onlinelibrary.wiley.com/doi/10.1002/9781118788417.ch1 |title=Zirconium and Hafnium |last2=Graham |first2=Ronald A. |date=2013-09-30 |publisher=John Wiley & Sons, Inc. |isbn=978-1-118-78841-7 |editor-last=Mishra |editor-first=Brajendra |location=Hoboken, NJ, USA |pages=1–71 |language=en |doi=10.1002/9781118788417.ch1}}</ref>{{rp|5}} <ref name=CRC>ABUNDANCE OF ELEMENTS IN THE EARTH’S CRUST AND IN THE SEA, ''CRC Handbook of Chemistry and Physics,'' 97th edition (2016–2017), p. 14-17</ref> It does not exist as a free element on Earth, but is found combined in [[solid solution]] with zirconium in natural [[zirconium]] compounds such as [[zircon]], ZrSiO<sub>4</sub>, which usually has about 1–4% of the Zr replaced by Hf. Rarely, the Hf/Zr ratio increases during crystallization to give the isostructural mineral [[hafnon]] {{chem2|(Hf,Zr)SiO4}}, with atomic Hf > Zr.<ref>{{cite book|title = The Rock-Forming Minerals: Orthosilicates|first1 = William Alexander|last1 = Deer |author-link1=William Alexander Deer|last2 = Howie|first2= Robert Andrew |author-link2=Robert A. Howie|last3=Zussmann|first3=Jack|isbn=978-0-582-46526-8|date = 1982|publisher = [[Longman|Longman Group Limited]]|pages=418–442|volume=1A|url=https://books.google.com/books?id=Yi0SAQAAMAAJ&q=9780582465268}}</ref> An obsolete name for a variety of zircon containing unusually high Hf content is ''alvite''.<ref>{{cite journal|title = The Mineralogy of Hafnium|first = O. Ivan|last = Lee|journal = [[Chemical Reviews]]|date = 1928|volume = 5|issue=1|pages=17–37|doi = 10.1021/cr60017a002|url=https://archive.org/details/in.ernet.dli.2015.27353/page/n23/mode/2up}}</ref>
+Hafnium is estimated to make up about between 3.0 and 4.8 [[Parts per million|ppm]] of the [[Earth]]'s upper [[crust (geology)|crust]] by mass.<ref>{{Cite book |last1=Haygarth |first1=John C. |url=https://onlinelibrary.wiley.com/doi/10.1002/9781118788417.ch1 |title=Zirconium and Hafnium |last2=Graham |first2=Ronald A. |date=2013-09-30 |publisher=John Wiley & Sons, Inc. |isbn=978-1-118-78841-7 |editor-last=Mishra |editor-first=Brajendra |location=Hoboken, NJ, USA |pages=1–71 |language=en |doi=10.1002/9781118788417.ch1}}</ref>{{rp|5}} <ref name=CRC>ABUNDANCE OF ELEMENTS IN THE EARTH'S CRUST AND IN THE SEA, ''CRC Handbook of Chemistry and Physics,'' 97th edition (2016–2017), p. 14-17</ref> It does not exist as a free element on Earth, but is found combined in [[solid solution]] with zirconium in natural [[zirconium]] compounds such as [[zircon]], ZrSiO<sub>4</sub>, which usually has about 1–4% of the Zr replaced by Hf. Rarely, the Hf/Zr ratio increases during crystallization to give the isostructural mineral [[hafnon]] {{chem2|(Hf,Zr)SiO4}}, with atomic Hf > Zr.<ref>{{cite book|title = The Rock-Forming Minerals: Orthosilicates|first1 = William Alexander|last1 = Deer |author-link1=William Alexander Deer|last2 = Howie|first2= Robert Andrew |author-link2=Robert A. Howie|last3=Zussmann|first3=Jack|isbn=978-0-582-46526-8|date = 1982|publisher = [[Longman|Longman Group Limited]]|pages=418–442|volume=1A|url=https://books.google.com/books?id=Yi0SAQAAMAAJ&q=9780582465268}}</ref> An obsolete name for a variety of zircon containing unusually high Hf content is ''alvite''.<ref>{{cite journal|title = The Mineralogy of Hafnium|first = O. Ivan|last = Lee|journal = [[Chemical Reviews]]|date = 1928|volume = 5|issue=1|pages=17–37|doi = 10.1021/cr60017a002|url=https://archive.org/details/in.ernet.dli.2015.27353/page/n23/mode/2up}}</ref>
 A major source of zircon (and hence hafnium) ores is [[heavy mineral sands ore deposits]], [[pegmatite]]s, particularly in [[Brazil]] and [[Malawi]], and [[carbonatite]] intrusions, particularly the Crown Polymetallic Deposit at [[Mount Weld]], [[Western Australia]]. A potential source of hafnium is [[Trachyte|trachyte tuffs]] containing rare zircon-hafnium silicates [[eudialyte]] or [[armstrongite]], at [[Dubbo]] in [[New South Wales]], Australia.<ref>{{cite web|url = http://www.alkane.com.au/projects/nsw/dubbo/DZP%20Summary%20June07.pdf|title = The Dubbo Zirconia Project |last=Chalmers|first=Ian|date = June 2007|publisher = Alkane Resources Limited|access-date = 2008-09-10|archive-url = https://web.archive.org/web/20080228054038/http://www.alkane.com.au/projects/nsw/dubbo/DZP%20Summary%20June07.pdf|archive-date = 2008-02-28}}</ref>
@@ Line 43: / Line 43: @@
 [[File:Hafnium ebeam remelted.jpg|thumb|left|Melted tip of a hafnium consumable electrode used in an [[Electron-beam additive manufacturing|electron beam]] [[Electron-beam furnace|remelting furnace]], a 1&nbsp;cm cube, and an oxidized hafnium electron beam-remelted ingot (left to right)]]
-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.<ref>{{cite web|title = 2008 Minerals Yearbook: Zirconium and Hafnium|first = Joseph|last = Gambogi|publisher=[[United States Geological Survey]]|date=2010|access-date=2021-11-11|url = https://www.usgs.gov/centers/nmic/zirconium-and-hafnium-statistics-and-information}}</ref>
+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.<ref>{{cite web|title = 2008 Minerals Yearbook: Zirconium and Hafnium|first = Joseph|last = Gambogi|publisher=[[United States Geological Survey]]|date=2010|access-date=2021-11-11|url = https://www.usgs.gov/centers/nmic/zirconium-and-hafnium-statistics-and-information}}</ref> 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 of hafnium.<ref name="ASTM">{{cite book|url = https://books.google.com/books?id=dI_LssydVeYC|title = ASTM Manual on Zirconium and Hafnium|first = J. H.|last = Schemel|publisher = [[ASTM]]|date = 1977|isbn=978-0-8031-0505-8|pages=1–5|location =Philadelphia|volume=STP 639}}</ref>[[File:Hafnium pellets with a thin oxide layer.jpg|thumb|right|Hafnium oxidized ingots which exhibit [[thin-film optics|thin-film optical]] effects]]
-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 of hafnium.<ref name="ASTM">{{cite book|url = https://books.google.com/books?id=dI_LssydVeYC|title = ASTM Manual on Zirconium and Hafnium|first = J. H.|last = Schemel|publisher = [[ASTM]]|date = 1977|isbn=978-0-8031-0505-8|pages=1–5|location =Philadelphia|volume=STP 639}}</ref>
+The chemical properties of hafnium and zirconium are nearly identical, which makes the two difficult to separate.<ref name="Larsen">{{cite journal|title = Concentration of Hafnium. Preparation of Hafnium-Free Zirconia|first1 = Edwin M.|last1 = Larsen|last2 = Fernelius |first2=W. Conard |last3=Quill|first3=Laurence |journal = [[Ind. Eng. Chem. Anal. Ed.]]|date=1943|volume=15|pages=512–515|doi =10.1021/i560120a015|issue = 8|url=https://docecity.com/concentration-of-hafnium-preparation-of-hafnium-free-zirconi-5f1098025158d.html|url-access=subscription}}</ref> The methods first used—[[Fractional crystallization (chemistry)|fractional crystallization]] of ammonium fluoride salts<ref name="Ark1924a" /> or the fractional distillation of the chloride<ref name="Ark1924b" />—did not prove suitable for an industrial-scale production. After zirconium was chosen as a 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 producing hafnium.<ref name="Hend" /> Other methods to purify hafnium from zirconium include [[molten salt]] extraction and crystallization of [[Fluorozirconate glass|fluorozirconates]].<ref name=":1">{{Cite book |last1=Bingham |first1=Eula |url=https://books.google.com/books?id=1mk3lFVtBSQC |title=Patty's Toxicology |last2=Cohrssen |first2=Barbara |date=2012-07-31 |publisher=John Wiley & Sons |isbn=978-0-470-41081-3 |pages=456–467 |language=en}}</ref> About half of all hafnium metal manufactured is produced as a by-product of zirconium refinement. The end product of the separation is [[Hafnium tetrachloride|hafnium(IV) chloride]].<ref name="USGS1952">{{cite book|publisher = The first production plants Bureau of Mines|title = Minerals yearbook metals and minerals (except fuels)|date = 1952|chapter-url = http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?type=turn&entity=EcoNatRes.MinYB1952v1.p1172&isize=M|last = Griffith|first = Robert F.|chapter =Zirconium and hafnium|pages=1162–1171}}</ref> The purified hafnium(IV) chloride is converted to the metal by reduction with [[magnesium]] or [[sodium]], as in the [[Kroll process]].<ref name="Gilb">{{cite journal|title = Preliminary Investigation of Hafnium Metal by the Kroll Process|first = H. L.|last = Gilbert|author2=Barr, M. M.|journal = Journal of the Electrochemical Society|date =1955|volume =102|page=243|doi = 10.1149/1.2430037|issue = 5}}</ref>
-[[File:Hafnium pellets with a thin oxide layer.jpg|thumb|right|Hafnium oxidized ingots which exhibit [[thin-film optics|thin-film optical]] effects]]
-The chemical properties of hafnium and zirconium are nearly identical, which makes the two difficult to separate.<ref name="Larsen">{{cite journal|title = Concentration of Hafnium. Preparation of Hafnium-Free Zirconia|first1 = Edwin M.|last1 = Larsen|last2 = Fernelius |first2=W. Conard |last3=Quill|first3=Laurence |journal = [[Ind. Eng. Chem. Anal. Ed.]]|date=1943|volume=15|pages=512–515|doi =10.1021/i560120a015|issue = 8|url=https://docecity.com/concentration-of-hafnium-preparation-of-hafnium-free-zirconi-5f1098025158d.html|url-access=subscription}}</ref> The methods first used—[[Fractional crystallization (chemistry)|fractional crystallization]] of ammonium fluoride salts<ref name="Ark1924a" /> or the fractional distillation of the chloride<ref name="Ark1924b" />—have not proven suitable for an industrial-scale production. After zirconium was chosen as a 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 producing hafnium.<ref name="Hend" /> About half of all hafnium metal manufactured is produced as a by-product of zirconium refinement. The end product of the separation is [[Hafnium tetrachloride|hafnium(IV) chloride]].<ref name="USGS1952">{{cite book|publisher = The first production plants Bureau of Mines|title = Minerals yearbook metals and minerals (except fuels)|date = 1952|chapter-url = http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?type=turn&entity=EcoNatRes.MinYB1952v1.p1172&isize=M|last = Griffith|first = Robert F.|chapter =Zirconium and hafnium|pages=1162–1171}}</ref> The purified hafnium(IV) chloride is converted to the metal by reduction  with [[magnesium]] or [[sodium]], as in the [[Kroll process]].<ref name="Gilb">{{cite journal|title = Preliminary Investigation of Hafnium Metal by the Kroll Process|first = H. L.|last = Gilbert|author2=Barr, M. M.|journal = Journal of the Electrochemical Society|date =1955|volume =102|page=243|doi = 10.1149/1.2430037|issue = 5}}</ref>
 : <chem>HfCl4{} + 2 Mg ->[1100~^\circ\text{C}] Hf{} + 2 MgCl2</chem>
@@ Line 59: / Line 56: @@
 Due to the [[lanthanide contraction]], the [[ionic radius]] of hafnium(IV) (0.78&nbsp;ångström) is almost the same  as that of  [[zirconium]](IV) (0.79&nbsp;[[angstrom]]s).<ref name="lanl72" /> Consequently, compounds of hafnium(IV) and zirconium(IV) have very similar chemical and physical properties.<ref name="lanl72" /> Hafnium and zirconium tend to occur together in nature and the similarity of their ionic radii makes their chemical separation rather difficult. Hafnium tends to form [[inorganic chemistry|inorganic compounds]] in the oxidation state of +4. [[Halogen]]s react with it to form hafnium tetrahalides.<ref name="lanl72" /> At higher temperatures, hafnium reacts with [[oxygen]], [[nitrogen]], [[carbon]], [[boron]], [[sulfur]], and [[silicon]].<ref name="lanl72" /> Some hafnium compounds in lower oxidation states are known.<ref>{{Greenwood&Earnshaw2nd|pages=971–975}}</ref>
-[[Hafnium(IV) chloride]] and hafnium(IV) iodide have some applications in the production and purification of hafnium metal.  They are volatile solids with polymeric structures.<ref name="Holl" /> These tetrachlorides are precursors to various [[Organozirconium chemistry|organohafnium compounds]] such as hafnocene dichloride and tetrabenzylhafnium.
+[[Hafnium(IV) chloride]] and hafnium(IV) iodide have some applications in the production and purification of hafnium metal.  They are volatile solids with polymeric structures.<ref name="Holl" /> These tetrahalides are precursors to various [[Organozirconium chemistry|organohafnium compounds]],<ref>{{Citation |last1=Wailes |first1=P. C. |title=Chapter IV - Organometallic Compounds of Zirconium(IV) and Hafnium(IV) |date=1974-01-01 |work=Organometallic Chemistry of Titanium, Zirconium, and Hafnium |pages=109–171 |editor-last=Wailes |editor-first=P. C. |url=https://www.sciencedirect.com/science/article/pii/B9780127303505500071 |access-date=2025-10-06 |series=Organometallic Chemistry: A Series of Monographs |publisher=Academic Press |doi=10.1016/b978-0-12-730350-5.50007-1 |isbn=978-0-12-730350-5 |last2=Coutts |first2=R. S. P. |last3=Weigold |first3=H. |editor2-last=Coutts |editor2-first=R. S. P. |editor3-last=Weigold |editor3-first=H.|url-access=subscription }}</ref> and hafnium(IV) chloride in particular is used in [[microelectronics]] manufacturing as a source of [[Hafnium(IV) oxide|hafnium oxide]] in [[atomic layer deposition]], much in the same way as [[zirconium(IV) chloride]].<ref>{{Cite book |last=Tiec |first=Yannick Le |url=https://books.google.com/books?id=BsibWJW8USsC |title=Chemistry in Microelectronics |date=2013-02-28 |publisher=John Wiley & Sons |isbn=978-1-118-57812-4 |at=1.2.3.3.2 |language=en}}</ref>
-The white [[hafnium oxide]] (HfO<sub>2</sub>), with a melting point of {{convert|2,812|C|K F}} and a boiling point of roughly {{convert|5,100|C|K F|sigfig=2}}, is very similar to [[zirconia]], but slightly more basic.<ref name="Holl" /> [[Hafnium carbide]] is the most [[refractory]] [[binary compound]] known, with a melting point over {{convert|3,890|C|K F|0}}, and hafnium nitride is the most refractory of all known metal nitrides, with a melting point of {{convert|3,310|C|K F|0}}.<ref name="lanl72">{{cite web|url = http://periodic.lanl.gov/72.shtml |title = Los Alamos National Laboratory – Hafnium|access-date=2008-09-10}}</ref> This has led to proposals that hafnium or its carbides might be useful as construction materials that are subjected to very high temperatures.{{Citation needed|date=July 2025}} [[Hafnium carbonitride]] has the highest known melting point for any material, which is confirmed to be above {{convert|4000|C|K F}} by experiment,<ref>{{cite journal |last1=Buinevich |first1=V.S. |last2=Nepapushev |first2=A.A. |last3=Moskovskikh |first3=D.O. |last4=Trusov |first4=G.V. |last5=Kuskov |first5=K.V. |last6=Vadchenko |first6=S.G. |last7=Rogachev |first7=A.S. |last8=Mukasyan |first8=A.S. |date=2020-03-17 |title=Fabrication of ultra-high-temperature nonstoichiometric hafnium carbonitride via combustion synthesis and spark plasma sintering |journal=Ceramics International |language=en |publisher=Elsevier |volume=46 |issue=10 |pages=16068–16073 |doi=10.1016/j.ceramint.2020.03.158 |issn=0272-8842 |oclc=8596178549 |s2cid=216437833}}</ref> while calculations predict its melting point to be {{convert|4110|C|K F}}.<ref name="DaiYu2023">{{Cite journal |last1=Dai |first1=Yu |last2=Zeng |first2=Fanhao |last3=Liu |first3=Honghao |last4=Gao |first4=Yafang |last5=Yang |first5=Qiaobin |last6=Chen |first6=Meiyan |last7=Huang |first7=Rui |last8=Gu |first8=Yi |date=2023-10-15 |title=Controlled nitrogen content synthesis of hafnium carbonitride powders by carbonizing hafnium nitride for enhanced ablation properties |url=https://linkinghub.elsevier.com/retrieve/pii/S0272884223022666 |journal=Ceramics International |language=en |volume=49 |issue=20 |pages=33265–33274 |doi=10.1016/j.ceramint.2023.08.035 |issn=0272-8842 |eissn=1873-3956 |oclc=9997899259 |s2cid=260672783|url-access=subscription }}</ref>
+The white [[hafnium oxide]] (HfO<sub>2</sub>), with a melting point of {{convert|2,812|C|K F}} and a boiling point of roughly {{convert|5,100|C|K F|sigfig=2}}, is very similar to [[zirconia]], but slightly more basic.<ref name="Holl" /> [[Hafnium carbide]] is the most [[refractory]] [[binary compound]] known, with a melting point over {{convert|3,890|C|K F|0}}, and hafnium nitride is the most refractory of all known metal nitrides, with a melting point of {{convert|3,310|C|K F|0}}.<ref name="lanl72">{{cite web|url = http://periodic.lanl.gov/72.shtml |title = Los Alamos National Laboratory – Hafnium|access-date=2008-09-10}}</ref> [[Hafnium carbonitride]] has the highest known melting point for any material, which is confirmed to be above {{convert|4000|C|K F}} by experiment,<ref>{{cite journal |last1=Buinevich |first1=V.S. |last2=Nepapushev |first2=A.A. |last3=Moskovskikh |first3=D.O. |last4=Trusov |first4=G.V. |last5=Kuskov |first5=K.V. |last6=Vadchenko |first6=S.G. |last7=Rogachev |first7=A.S. |last8=Mukasyan |first8=A.S. |date=2020-03-17 |title=Fabrication of ultra-high-temperature nonstoichiometric hafnium carbonitride via combustion synthesis and spark plasma sintering |journal=Ceramics International |language=en |publisher=Elsevier |volume=46 |issue=10 |pages=16068–16073 |doi=10.1016/j.ceramint.2020.03.158 |issn=0272-8842 |oclc=8596178549 |s2cid=216437833}}</ref> while calculations predict its melting point to be {{convert|4110|C|K F}}.<ref name="DaiYu2023">{{Cite journal |last1=Dai |first1=Yu |last2=Zeng |first2=Fanhao |last3=Liu |first3=Honghao |last4=Gao |first4=Yafang |last5=Yang |first5=Qiaobin |last6=Chen |first6=Meiyan |last7=Huang |first7=Rui |last8=Gu |first8=Yi |date=2023-10-15 |title=Controlled nitrogen content synthesis of hafnium carbonitride powders by carbonizing hafnium nitride for enhanced ablation properties |url=https://linkinghub.elsevier.com/retrieve/pii/S0272884223022666 |journal=Ceramics International |language=en |volume=49 |issue=20 |pages=33265–33274 |doi=10.1016/j.ceramint.2023.08.035 |issn=0272-8842 |eissn=1873-3956 |oclc=9997899259 |s2cid=260672783|url-access=subscription }}</ref>
 ==History==
@@ Line 84: / Line 81: @@
 </ref> Today, the [[University of Copenhagen Faculty of Science|Faculty of Science]] of the [[University of Copenhagen]] uses in its [[Seal (emblem)|seal]] a stylized image of the hafnium atom.<ref>{{cite web|publisher = University of Copenghagen|access-date=2016-11-19|title = University Life 2005|url = http://universitetshistorie.ku.dk/filer/aarsberetning/universitetsliv_2005_uk.pdf/ |format=pdf|page=43}}</ref>
-Hafnium was separated from zirconium through repeated recrystallization of the double [[ammonium]] or [[potassium]] fluorides by [[Valdemar Thal Jantzen]] and von Hevesey.<ref name="Ark1924a">{{cite journal|title = Die Trennung von Zirkonium und Hafnium durch Kristallisation ihrer Ammoniumdoppelfluoride (The separation of zirconium and hafnium by crystallization of their double ammonium fluorides)|journal = [[Zeitschrift für Anorganische und Allgemeine Chemie]]|volume = 141|date = 1924|pages= 284–288|first1 = A. E.|last1 = van Arkel|last2 = de Boer|first2=J. H.|doi = 10.1002/zaac.19241410117|language = de |author-link1=Anton Eduard van Arkel |author-link2=Jan Hendrik de Boer |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015006985249|url-access = subscription}}</ref> [[Anton Eduard van Arkel]] and [[Jan Hendrik de Boer]] were the first to prepare metallic hafnium by passing hafnium tetraiodide vapor over a heated [[tungsten]] filament in 1924.<ref name="Ark1924b">{{cite journal|title = Die Trennung des Zirkoniums von anderen Metallen, einschließlich Hafnium, durch fraktionierte Distillation|trans-title=The separation of zirconium from other metals, including hafnium, by fractional distillation| journal = [[Zeitschrift für Anorganische und Allgemeine Chemie]]|volume = 141|issue=1|date = 1924-12-23|pages= 289–296|first1 = A. E.|last1 = van Arkel|author-link1=Anton Eduard van Arkel|last2 = de Boer|first2=J. H.|author-link2=Jan Hendrik de Boer|doi = 10.1002/zaac.19241410118|language = de|url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015006985249|url-access = subscription}}</ref><ref name="Ark1925">{{cite journal|title = Darstellung von reinem Titanium-, Zirkonium-, Hafnium- und Thoriummetall (Production of pure titanium, zirconium, hafnium and Thorium metal)|journal = Zeitschrift für Anorganische und Allgemeine Chemie|volume = 148|date = 1925|pages= 345–350|first = A. E.|last = van Arkel|author2 = de Boer, J. H.|doi = 10.1002/zaac.19251480133|language = de}}</ref> This process for differential purification of zirconium and hafnium is still in use today.<ref name="ASTM" />
+Hafnium was separated from zirconium through repeated recrystallization of the double [[ammonium]] or [[potassium]] fluorides by [[Valdemar Thal Jantzen]] and von Hevesey.<ref name="Ark1924a">{{cite journal|title = Die Trennung von Zirkonium und Hafnium durch Kristallisation ihrer Ammoniumdoppelfluoride (The separation of zirconium and hafnium by crystallization of their double ammonium fluorides)|journal = [[Zeitschrift für Anorganische und Allgemeine Chemie]]|volume = 141|date = 1924|pages= 284–288|first1 = A. E.|last1 = van Arkel|last2 = de Boer|first2=J. H.|doi = 10.1002/zaac.19241410117|language = de |author-link1=Anton Eduard van Arkel |author-link2=Jan Hendrik de Boer |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015006985249|url-access = subscription}}</ref> [[Anton Eduard van Arkel]] and [[Jan Hendrik de Boer]] were the first to prepare metallic hafnium by passing hafnium tetraiodide vapor over a heated [[tungsten]] filament in 1924.<ref name="Ark1924b">{{cite journal|title = Die Trennung des Zirkoniums von anderen Metallen, einschließlich Hafnium, durch fraktionierte Distillation|trans-title=The separation of zirconium from other metals, including hafnium, by fractional distillation| journal = [[Zeitschrift für Anorganische und Allgemeine Chemie]]|volume = 141|issue=1|date = 1924-12-23|pages= 289–296|first1 = A. E.|last1 = van Arkel|author-link1=Anton Eduard van Arkel|last2 = de Boer|first2=J. H.|author-link2=Jan Hendrik de Boer|doi = 10.1002/zaac.19241410118|bibcode=1924ZAACh.141..289V |language = de|url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015006985249|url-access = subscription}}</ref><ref name="Ark1925">{{cite journal|title = Darstellung von reinem Titanium-, Zirkonium-, Hafnium- und Thoriummetall (Production of pure titanium, zirconium, hafnium and Thorium metal)|journal = Zeitschrift für Anorganische und Allgemeine Chemie|volume = 148|date = 1925|pages= 345–350|first = A. E.|last = van Arkel|author2 = de Boer, J. H.|doi = 10.1002/zaac.19251480133|language = de}}</ref> This process for differential purification of zirconium and hafnium is still in use today.<ref name="ASTM" />
-Hafnium was one of the last two [[Stable isotope|stable]] elements to be discovered. The element [[rhenium]] was found in 1908 by [[Masataka Ogawa]], though its atomic number was misidentified at the time, and it was not generally recognised by the scientific community until its rediscovery by [[Walter Noddack]], [[Ida Noddack]], and [[Otto Berg (scientist)|Otto Berg]] in 1925. This makes it somewhat difficult to say if hafnium or rhenium was discovered last.<ref name=nipponium2022>{{cite journal |last1=Hisamatsu |first1=Yoji |last2=Egashira |first2=Kazuhiro |first3=Yoshiteru |last3=Maeno |date=2022 |title=Ogawa's nipponium and its re-assignment to rhenium |journal=Foundations of Chemistry |volume=24 |issue= |pages=15–57 |doi=10.1007/s10698-021-09410-x |doi-access=free }}</ref>
-In 1923, six predicted elements were still missing from the periodic table: 43 ([[technetium]]), 61 ([[promethium]]), 85 ([[astatine]]), and 87 ([[francium]]) are radioactive elements and are only present in trace amounts in the environment,<ref>{{cite journal|doi = 10.1016/S0016-7037(98)00282-8|title = Nature's uncommon elements: plutonium and technetium|first = David|last = Curtis |author2 = Fabryka-Martin, June |author3=Dixon, Pauland |author4=Cramer, Jan |journal = Geochimica et Cosmochimica Acta|volume = 63|date =1999|pages= 275–285|bibcode=1999GeCoA..63..275C|issue = 2|url = https://digital.library.unt.edu/ark:/67531/metadc704244/}}</ref> thus making elements 75 ([[rhenium]]) and 72 (hafnium) the last two unknown non-radioactive elements.
+In 1923, six predicted elements were still missing from the periodic table: 43 ([[technetium]]), 61 ([[promethium]]), 85 ([[astatine]]), and 87 ([[francium]]) are radioactive elements and are only present in trace amounts in the environment,<ref>{{cite journal|doi = 10.1016/S0016-7037(98)00282-8|title = Nature's uncommon elements: plutonium and technetium|first = David|last = Curtis |author2 = Fabryka-Martin, June |author3=Dixon, Pauland |author4=Cramer, Jan |journal = Geochimica et Cosmochimica Acta|volume = 63|date =1999|pages= 275–285|bibcode=1999GeCoA..63..275C|issue = 2|url = https://digital.library.unt.edu/ark:/67531/metadc704244/}}</ref> thus making elements 75 ([[rhenium]]) and 72 (hafnium) the last two [[Stable isotope|stable]] elements to be discovered. The element [[rhenium]] was found in 1908 by [[Masataka Ogawa]], though its atomic number was misidentified at the time, and it was not generally recognised by the scientific community until its rediscovery by [[Walter Noddack]], [[Ida Noddack]], and [[Otto Berg (scientist)|Otto Berg]] in 1925. This makes it somewhat difficult to say if hafnium or rhenium was discovered last.<ref name=nipponium2022>{{cite journal |last1=Hisamatsu |first1=Yoji |last2=Egashira |first2=Kazuhiro |first3=Yoshiteru |last3=Maeno |date=2022 |title=Ogawa's nipponium and its re-assignment to rhenium |journal=Foundations of Chemistry |volume=24 |issue= |pages=15–57 |doi=10.1007/s10698-021-09410-x |doi-access=free }}</ref>
 ==Applications==
-Most of the hafnium produced is used in the manufacture of [[control rod]]s for [[nuclear reactor]]s.<ref name="Hend">{{cite web|title = Hafnium|first = James B.|last = Hedrick|url = http://minerals.er.usgs.gov/minerals/pubs/commodity/zirconium/731798.pdf|publisher = United States Geological Survey|access-date = 2008-09-10|archive-date = 2012-02-20|archive-url = https://web.archive.org/web/20120220013853/http://minerals.er.usgs.gov/minerals/pubs/commodity/zirconium/731798.pdf|url-status = dead}}</ref>
+Much of the hafnium produced is used in the manufacture of [[control rod]]s for [[nuclear reactor]]s<ref name="Hend">{{cite web|title = Hafnium|first = James B.|last = Hedrick|url = https://minerals.er.usgs.gov/minerals/pubs/commodity/zirconium/731798.pdf|publisher = United States Geological Survey|access-date = 2008-09-10|archive-date = 2012-02-20|archive-url = https://web.archive.org/web/20120220013853/http://minerals.er.usgs.gov/minerals/pubs/commodity/zirconium/731798.pdf}}</ref> and as an additive in [[nickel alloys]] to increase their heat resistance.<ref name=":2" />
-Hafnium has limited technical applications due to a few factors. First, it's very similar to zirconium, a more abundant element that can be used in most cases. Second, pure hafnium wasn't widely available until the late 1950s, when it became a byproduct of the nuclear industry's need for hafnium-free zirconium. Additionally, hafnium is rare and difficult to separate from other elements, making it expensive. After the Fukushima disaster reduced the demand for hafnium-free zirconium, the price of hafnium increased significantly from around $500–$600/kg ($227-$272/lb) in 2014 to around $1000/kg ($454/lb) in 2015.<ref>{{cite web|last1=Albrecht|first1=Bodo|title=Weak Zirconium Demand Depleting Hafnium Stock Piles|url=http://www.kitco.com/ind/Albrecht/2015-03-11-Weak-Zirconium-Demand-Depleting-Hafnium-Stock-Piles.html|website=Tech Metals Insider|publisher=KITCO|access-date=4 March 2018|date=2015-03-11|archive-date=2021-04-28|archive-url=https://web.archive.org/web/20210428094638/https://www.kitco.com/ind/Albrecht/2015-03-11-Weak-Zirconium-Demand-Depleting-Hafnium-Stock-Piles.html|url-status=dead}}</ref>
+Hafnium has limited technical applications due to a few factors. It is very similar to zirconium, a more abundant element that can be used in most cases, and pure hafnium wasn't widely available until the late 1950s, when it became a byproduct of the nuclear industry's need for hafnium-free zirconium. Additionally, hafnium is rare and difficult to separate from other elements, making it expensive. After the Fukushima disaster reduced the demand for hafnium-free zirconium, the price of hafnium increased significantly from around $500–$600/kg{{Spaces}}($227-$272/lb) in 2014 to around $1000/kg{{Spaces}}($454/lb) in 2015.<ref>{{cite web|last1=Albrecht|first1=Bodo|title=Weak Zirconium Demand Depleting Hafnium Stock Piles|url=http://www.kitco.com/ind/Albrecht/2015-03-11-Weak-Zirconium-Demand-Depleting-Hafnium-Stock-Piles.html|website=Tech Metals Insider|publisher=KITCO|access-date=4 March 2018|date=2015-03-11|archive-date=2021-04-28|archive-url=https://web.archive.org/web/20210428094638/https://www.kitco.com/ind/Albrecht/2015-03-11-Weak-Zirconium-Demand-Depleting-Hafnium-Stock-Piles.html}}</ref> Hafnium products, such as tubes and sheets of the metal, could be purchased at {{Euro|250}}/kg{{Spaces}}($170/lb) in 2009.<ref name=":2" />
 ===Nuclear reactors===
@@ Line 102: / Line 97: @@
 Hafnium is used in [[alloy]]s with [[iron]], [[titanium]], [[niobium]], [[tantalum]], and other metals. An alloy used for [[liquid-propellant rocket|liquid-rocket]] thruster nozzles, for example the main engine of the [[Apollo Lunar Module]]s, is C103 which consists of 89% niobium, 10% hafnium and 1% titanium.<ref name="hightemp">{{cite web|url = https://www.cbmm.com/portug/sources/techlib/science_techno/table_content/sub_3/images/pdfs/016.pdf|title = Niobium alloys and high Temperature Applications|first = John|last = Hebda|publisher = CBMM|date = 2001|access-date = 2008-09-04|archive-url = https://web.archive.org/web/20081217080513/http://www.cbmm.com.br/portug/sources/techlib/science_techno/table_content/sub_3/images/pdfs/016.pdf|archive-date = 2008-12-17}}</ref>
-Small additions of hafnium increase the adherence of protective oxide scales on nickel-based alloys. It thereby improves the [[corrosion]] resistance, especially under cyclic temperature conditions that tend to break oxide scales, by inducing thermal stresses between the bulk material and the oxide layer.<ref>{{cite journal|title = Effect of hafnium on the structure and properties of nickel alloys|first = S. B.|last = Maslenkov |author2 = Burova, N. N. |author3=Khangulov, V. V. |journal = Metal Science and Heat Treatment|volume = 22|date = 1980|doi=10.1007/BF00779883|pages=283–285|issue = 4|bibcode = 1980MSHT...22..283M|s2cid = 135595958}}</ref><ref>{{cite journal|first = V. M.|last = Beglov |author2 = Pisarev, B. K. |author3=Reznikova, G. G. |title = Effect of boron and hafnium on the corrosion resistance of high-temperature nickel alloys|journal = Metal Science and Heat Treatment|volume = 34|date = 1992|doi = 10.1007/BF00702544|pages=251–254|issue = 4|bibcode = 1992MSHT...34..251B |s2cid = 135844921 }}</ref><ref>{{cite journal|first = R. F.|last = Voitovich|author2=Golovko, É. I.|title = Oxidation of hafnium alloys with nickel|journal = Metal Science and Heat Treatment|volume = 17|date = 1975|doi = 10.1007/BF00663680|pages=207–209|issue = 3|bibcode = 1975MSHT...17..207V|s2cid = 137073174}}</ref>
+Small additions of hafnium increase the adherence of protective oxide scales on nickel-based alloys. It thereby improves the [[corrosion]] resistance, especially under cyclic temperature conditions that tend to break oxide scales, by inducing thermal stresses between the bulk material and the oxide layer.<ref>{{cite journal|title = Effect of hafnium on the structure and properties of nickel alloys|first = S. B.|last = Maslenkov |author2 = Burova, N. N. |author3=Khangulov, V. V. |journal = Metal Science and Heat Treatment|volume = 22|date = 1980|doi=10.1007/BF00779883|pages=283–285|issue = 4|bibcode = 1980MSHT...22..283M|s2cid = 135595958}}</ref><ref>{{cite journal|first = V. M.|last = Beglov |author2 = Pisarev, B. K. |author3=Reznikova, G. G. |title = Effect of boron and hafnium on the corrosion resistance of high-temperature nickel alloys|journal = Metal Science and Heat Treatment|volume = 34|date = 1992|doi = 10.1007/BF00702544|pages=251–254|issue = 4|bibcode = 1992MSHT...34..251B |s2cid = 135844921 }}</ref><ref>{{cite journal|first = R. F.|last = Voitovich|author2=Golovko, É. I.|title = Oxidation of hafnium alloys with nickel|journal = Metal Science and Heat Treatment|volume = 17|date = 1975|doi = 10.1007/BF00663680|pages=207–209|issue = 3|bibcode = 1975MSHT...17..207V|s2cid = 137073174}}</ref> An alloy that includes as little as 1% hafnium can withstand temperatures that are {{Convert|50|C-change|F-change}} higher than the same alloy without hafnium.<ref name=":2" />
 ===Microprocessors===
@@ Line 111: / Line 106: @@
 |title=Zirconium and/or hafnium oxynitride gate dielectric
 |pubdate=2000-01-11
-}}</ref><ref>{{cite news|url = https://www.nytimes.com/2007/01/27/technology/27chip.html|title = Intel Says Chips Will Run Faster, Using Less Power|first = John|last = Markoff|newspaper = New York Times|date=2007-01-27|access-date=2008-09-10}}</ref> Hafnium oxide-based compounds are practical [[high-k dielectric]]s, allowing reduction of the gate leakage current which improves performance at such scales.<ref>{{cite news|last = Fulton III|first = Scott M.|title = Intel Reinvents the Transistor|publisher = BetaNews|date=January 27, 2007|url =http://www.betanews.com/article/Intel_Reinvents_the_Transistor/1169872301|access-date=2007-01-27}}</ref><ref>{{cite news|last = Robertson|first = Jordan|title = Intel, IBM reveal transistor overhaul|publisher = The Associated Press|date=January 27, 2007|url = https://www.washingtonpost.com/wp-dyn/content/article/2007/01/27/AR2007012700152.html|access-date=2008-09-10}}</ref><ref>{{Cite web |title=Atomic Layer Deposition (ALD) |url=https://semiengineering.com/knowledge_centers/manufacturing/process/deposition/atomic-layer-deposition/ |access-date=2023-04-30 |website=Semiconductor Engineering |language=en-US}}</ref>
+}}</ref><ref>{{cite news|url = https://www.nytimes.com/2007/01/27/technology/27chip.html|title = Intel Says Chips Will Run Faster, Using Less Power|first = John|last = Markoff|newspaper = New York Times|date=2007-01-27|access-date=2008-09-10}}</ref> Hafnium oxide-based compounds are practical [[high-kappa dielectric|high-κ dielectric]]s, allowing reduction of the gate leakage current which improves performance at such scales.<ref>{{cite news|last = Fulton III|first = Scott M.|title = Intel Reinvents the Transistor|publisher = BetaNews|date=January 27, 2007|url =http://www.betanews.com/article/Intel_Reinvents_the_Transistor/1169872301|access-date=2007-01-27}}</ref><ref>{{cite news|last = Robertson|first = Jordan|title = Intel, IBM reveal transistor overhaul|publisher = The Associated Press|date=January 27, 2007|url = https://www.washingtonpost.com/wp-dyn/content/article/2007/01/27/AR2007012700152.html|access-date=2008-09-10}}</ref><ref>{{Cite web |title=Atomic Layer Deposition (ALD) |url=https://semiengineering.com/knowledge_centers/manufacturing/process/deposition/atomic-layer-deposition/ |access-date=2023-04-30 |website=Semiconductor Engineering |language=en-US}}</ref>
 ===Isotope geochemistry===
-Isotopes of hafnium and [[lutetium]] (along with [[ytterbium]]) are also used in [[isotope geochemistry]] and [[geochronology|geochronological]] applications, in [[lutetium-hafnium dating]]. It is often used as a tracer of isotopic evolution of [[Mantle (geology)|Earth's mantle]] through time.<ref>{{cite journal|last1=Patchett|first1=P. Jonathan|title=Importance of the Lu-Hf isotopic system in studies of planetary chronology and chemical evolution|journal=Geochimica et Cosmochimica Acta|date=January 1983|volume=47|issue=1|pages=81–91|doi=10.1016/0016-7037(83)90092-3|bibcode=1983GeCoA..47...81P}}</ref> This is because <sup>176</sup>Lu decays to <sup>176</sup>Hf with a [[half-life]] of approximately 37 billion years.<ref>{{cite journal|last1=Söderlund|first1=Ulf|last2=Patchett|first2=P. Jonathan|last3=Vervoort|first3=Jeffrey D.|last4=Isachsen|first4=Clark E.|title=The 176Lu decay constant determined by Lu–Hf and U–Pb isotope systematics of Precambrian mafic intrusions|journal=Earth and Planetary Science Letters|date=March 2004|volume=219|issue=3–4|pages=311–324|doi=10.1016/S0012-821X(04)00012-3|bibcode=2004E&PSL.219..311S}}</ref><ref>{{cite journal|last1=Blichert-Toft|first1=Janne|author-link=Janne Blichert-Toft|last2=Albarède|first2=Francis|title=The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crust system|journal=Earth and Planetary Science Letters|date=April 1997|volume=148|issue=1–2|pages=243–258|doi=10.1016/S0012-821X(97)00040-X|bibcode=1997E&PSL.148..243B}}</ref><ref>{{cite journal|last1=Patchett|first1=P. J.|last2=Tatsumoto|first2=M.|title=Lu–Hf total-rock isochron for the eucrite meteorites|journal=Nature|date=11 December 1980|volume=288|issue=5791|pages=571–574|doi=10.1038/288571a0|bibcode=1980Natur.288..571P|s2cid=4284487}}</ref>
+Isotopes of hafnium and [[lutetium]] are also used in [[isotope geochemistry]] and [[geochronology|geochronological]] applications, in [[lutetium-hafnium dating]]. It is often used as a tracer of isotopic evolution of [[Mantle (geology)|Earth's mantle]] through time.<ref>{{cite journal|last1=Patchett|first1=P. Jonathan|title=Importance of the Lu-Hf isotopic system in studies of planetary chronology and chemical evolution|journal=Geochimica et Cosmochimica Acta|date=January 1983|volume=47|issue=1|pages=81–91|doi=10.1016/0016-7037(83)90092-3|bibcode=1983GeCoA..47...81P}}</ref> This is because <sup>176</sup>Lu decays to <sup>176</sup>Hf with a [[half-life]] of approximately 37 billion years.<ref>{{cite journal|last1=Söderlund|first1=Ulf|last2=Patchett|first2=P. Jonathan|last3=Vervoort|first3=Jeffrey D.|last4=Isachsen|first4=Clark E.|title=The 176Lu decay constant determined by Lu–Hf and U–Pb isotope systematics of Precambrian mafic intrusions|journal=Earth and Planetary Science Letters|date=March 2004|volume=219|issue=3–4|pages=311–324|doi=10.1016/S0012-821X(04)00012-3|bibcode=2004E&PSL.219..311S}}</ref><ref>{{cite journal|last1=Blichert-Toft|first1=Janne|author-link=Janne Blichert-Toft|last2=Albarède|first2=Francis|title=The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crust system|journal=Earth and Planetary Science Letters|date=April 1997|volume=148|issue=1–2|pages=243–258|doi=10.1016/S0012-821X(97)00040-X|bibcode=1997E&PSL.148..243B}}</ref><ref>{{cite journal|last1=Patchett|first1=P. J.|last2=Tatsumoto|first2=M.|title=Lu–Hf total-rock isochron for the eucrite meteorites|journal=Nature|date=11 December 1980|volume=288|issue=5791|pages=571–574|doi=10.1038/288571a0|bibcode=1980Natur.288..571P|s2cid=4284487}}</ref>
-In most geologic materials, [[zircon]] is the dominant host of hafnium (>10,000 ppm) and is often the focus of hafnium studies in [[geology]].<ref>{{cite journal|last1=Kinny|first1=P. D.|title=Lu-Hf and Sm-Nd isotope systems in zircon|journal=Reviews in Mineralogy and Geochemistry|date=1 January 2003|volume=53|issue=1|pages=327–341|doi=10.2113/0530327|bibcode=2003RvMG...53..327K}}</ref> Hafnium is readily substituted into the zircon [[Crystal structure|crystal lattice]], and is therefore very resistant to hafnium mobility and contamination. Zircon also has an extremely low Lu/Hf ratio, making any correction for initial lutetium minimal. Although the Lu/Hf system can be used to calculate a "[[Nd model ages|model age]]", i.e. the time at which it was derived from a given isotopic reservoir such as the [[depleted-mantle model|depleted mantle]], these "ages" do not carry the same geologic significance as do other geochronological techniques as the results often yield isotopic mixtures and thus provide an average age of the material from which it was derived.
+In most geologic materials, [[zircon]] is the dominant host of hafnium (>10,000 ppm) and is often the focus of hafnium studies in [[geology]].<ref>{{cite journal|last1=Kinny|first1=P. D.|title=Lu-Hf and Sm-Nd isotope systems in zircon|journal=Reviews in Mineralogy and Geochemistry|date=1 January 2003|volume=53|issue=1|pages=327–341|doi=10.2113/0530327|bibcode=2003RvMG...53..327K}}</ref> Hafnium is readily substituted into the zircon [[Crystal structure|crystal lattice]], and is therefore very resistant to hafnium mobility and contamination. Zircon also has an extremely low Lu/Hf ratio, making any correction for initial lutetium minimal. Although the Lu/Hf system can be used to calculate a "[[Nd model ages|model age]]", i.e. the time at which it was derived from a given isotopic reservoir such as the [[depleted-mantle model|depleted mantle]], these "ages" do not carry the same geologic significance as do other geochronological techniques as the results often yield isotopic mixtures and thus provide an average age of the material from which it was derived.<ref>{{Cite journal |last1=Inácio Alves |first1=Márcio |last2=Almeida |first2=Bruna Saar de |last3=Cardoso |first3=Letícia Muniz da Costa |last4=Santos |first4=Anderson Costa dos |last5=Appi |first5=Ciro |last6=Bertotti |first6=Anelise Losangela |last7=Chemale |first7=Farid |last8=Tavares Jr |first8=Armando Dias |last9=Alves Martins |first9=Maria Virginia |last10=Geraldes |first10=Mauro César |date=2019-06-23 |title=ISOTOPIC COMPOSITION OF Lu, Hf AND Yb IN GJ-01, 91500 AND MUD TANK REFERENCE MATERIALS MEASURED BY LA-ICP-MS: APPLICATION OF THE Lu-Hf GEOCHRONOLOGY IN ZIRCON |url=https://www.e-publicacoes.uerj.br/index.php/jse/article/view/43877 |journal=Journal of Sedimentary Environments |volume=4 |issue=2 |pages=220–248 |doi=10.12957/jse.2019.43877 |issn=2447-9462}}</ref><ref>{{Citation |last=Vervoort |first=Jeff |title=Lu-Hf Dating: The Lu-Hf Isotope System |date=2014 |encyclopedia=Encyclopedia of Scientific Dating Methods |pages=1–20 |editor-last=Rink |editor-first=W. Jack |url=https://link.springer.com/10.1007/978-94-007-6326-5_46-1 |access-date=2025-10-08 |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-94-007-6326-5_46-1 |isbn=978-94-007-6326-5 |editor2-last=Thompson |editor2-first=Jeroen|url-access=subscription }}</ref>
-[[Garnet]] is another mineral that contains appreciable amounts of hafnium to act as a geochronometer. The high and variable Lu/Hf ratios found in garnet make it useful for dating [[metamorphism|metamorphic]] events.<ref>{{cite journal|last1=Albarède|first1=F.|last2=Duchêne|first2=S.|last3=Blichert-Toft|first3=J.|last4=Luais|first4=B.|last5=Télouk|first5=P.|last6=Lardeaux|first6=J.-M.|journal=Nature|title=The Lu–Hf dating of garnets and the ages of the Alpine high-pressure metamorphism|date=5 June 1997|volume=387|issue=6633|pages=586–589|doi=10.1038/42446|bibcode=1997Natur.387..586D|s2cid=4260388}}</ref>
+[[Garnet]] is another mineral that contains appreciable amounts of hafnium to act as a geochronometer. The high and variable Lu/Hf ratios found in garnet make it useful for dating [[metamorphism|metamorphic]] events.<ref>{{cite journal|last1=Albarède|first1=F.|last2=Duchêne|first2=S.|last3=Blichert-Toft|first3=J.|last4=Luais|first4=B.|last5=Télouk|first5=P.|last6=Lardeaux|first6=J.-M.|journal=Nature|title=The Lu–Hf dating of garnets and the ages of the Alpine high-pressure metamorphism|date=5 June 1997|volume=387|issue=6633|pages=586–589|doi=10.1038/42446|bibcode=1997Natur.387..586D|s2cid=4260388}}</ref> [[Mass spectrometry]] also makes use of these ratios to date garnet formed through [[Igneous rock|igneous]] events.<ref>{{Cite journal |last1=Godet |first1=Antoine |last2=Guilmette |first2=Carl |last3=Smit |first3=Matthijs |last4=Maneta |first4=Victoria |last5=Fournier-Roy |first5=François |last6=Musiyachenko |first6=Kira |date=2025 |title=Insights into garnet growth in S-type granite from Lu–Hf dating and trace element mapping |journal=Contributions to Mineralogy and Petrology |language=en |volume=180 |issue=6 |article-number=36 |doi=10.1007/s00410-025-02211-x |bibcode=2025CoMP..180...36G |issn=0010-7999|doi-access=free }}</ref>
 ===Other uses===
-Due to its heat resistance and its affinity to oxygen and nitrogen, hafnium is a good scavenger for oxygen and nitrogen in gas-filled and [[incandescent lamp]]s. Hafnium is also used as the electrode in [[plasma cutting]] because of its ability to shed electrons into the air.<ref>{{cite journal|journal = Journal of Physics D: Applied Physics|volume = 30|date = 1997|pages=636–644|title = Properties of electric arc plasma for metal cutting|first = S.|last = Ramakrishnany|author2=Rogozinski, M. W.|doi = 10.1088/0022-3727/30/4/019|bibcode = 1997JPhD...30..636R|issue = 4 | s2cid=250746818 }}</ref>
+Due to its heat resistance and its affinity to oxygen and nitrogen, hafnium is a good scavenger for oxygen and nitrogen in gas-filled and [[incandescent lamp]]s. Hafnium is also used as the electrode in [[plasma cutting]] because of its ability to shed electrons into the air.<ref>{{cite journal|journal = Journal of Physics D: Applied Physics|volume = 30|date = 1997|pages=636–644|title = Properties of electric arc plasma for metal cutting|first = S.|last = Ramakrishnany|author2=Rogozinski, M. W.|doi = 10.1088/0022-3727/30/4/019|bibcode = 1997JPhD...30..636R|issue = 4 | s2cid=250746818 }}</ref> Hafnium [[metallocene]] compounds can be prepared from [[hafnium tetrachloride]] and various [[cyclopentadiene]]-type [[ligand]] species. Perhaps the simplest hafnium metallocene is hafnocene dichloride. Hafnium metallocenes are part of a large collection of Group 4 [[transition metal]] metallocene catalysts that are used worldwide in the production of [[polyolefin]] resins like [[polyethylene]] and [[polypropylene]].<ref>{{cite journal |last1=g. Alt |first1=Helmut |last2=Samuel |first2=Edmond |date=1998 |title=Fluorenyl complexes of zirconium and hafnium as catalysts for olefin polymerization |journal=Chem. Soc. Rev. |volume=27 |issue=5 |pages=323–329 |doi=10.1039/a827323z}}</ref> A pyridyl-amidohafnium catalyst can be used for the controlled iso-selective polymerization of propylene, which can then be combined with polyethylene to make a tougher recycled plastic.<ref>{{cite journal |last=Eagan |first=James |date=24 Feb 2017 |title=Combining polyethylene and polypropylene: Enhanced performance with PE/iPP multiblock polymers |url=https://zenodo.org/record/891450 |journal=Science |volume=355 |issue=6327 |pages=814–816 |bibcode=2017Sci...355..814E |doi=10.1126/science.aah5744 |pmid=28232574 |s2cid=206652330 |doi-access=free}}</ref>
-The high energy content of <sup>178m2</sup>Hf was the concern of a [[DARPA]]-funded program in the US. This program eventually concluded that using the above-mentioned <sup>178m2</sup>Hf [[nuclear isomer]] of hafnium  to construct high-yield weapons with X-ray triggering mechanisms—an application of [[induced gamma emission]]—was infeasible because of its expense. See ''[[hafnium controversy]]''.
+The high energy content of <sup>178m2</sup>Hf was the concern of a [[DARPA]]-funded program in the US. This program eventually concluded that using the <sup>178m2</sup>Hf [[nuclear isomer]] of hafnium to construct high-yield weapons with X-ray triggering mechanisms—an application of [[induced gamma emission]]—was infeasible because of its expense and difficulty to manufacture.<ref name=":3" /> See [[hafnium controversy]].<ref name="bomb"/>
-Hafnium [[metallocene]] compounds can be prepared from [[hafnium tetrachloride]] and various [[cyclopentadiene]]-type [[ligand]] species. Perhaps the simplest hafnium metallocene is hafnocene dichloride. Hafnium metallocenes are part of a large collection of Group 4 [[transition metal]] metallocene catalysts <ref>{{cite journal|journal = Chem. Soc. Rev.|date=1998|volume=27|issue=5|pages=323–329|title=Fluorenyl complexes of zirconium and hafnium as catalysts for olefin polymerization|doi=10.1039/a827323z|last1=g. Alt|first1=Helmut|last2=Samuel|first2=Edmond}}</ref> that are used worldwide in the production of [[polyolefin]] resins like [[polyethylene]] and [[polypropylene]].
+[[Hafnium diselenide]] is studied in [[spintronics]] thanks to its [[charge density wave]] and [[superconductivity]].<ref>{{cite journal |url=https://phys.org/news/2022-09-road-spin-polarized-currents.amp |publisher=[[Phys.org]] |title=A new road towards spin-polarized currents |date=September 7, 2022 |author=[[Helmholtz Association|Helmholtz Association of German Research Centres]] |journal=Nature Communications |volume=13 |issue=1 |page=4147 |doi=10.1038/s41467-022-31539-2 |pmid=35842436 |pmc=9288546 |access-date=September 8, 2023 |archive-date= March 1, 2026|archive-url=https://web.archive.org/web/20260301084832/https://phys.org/news/2022-09-road-spin-polarized-currents.amp |url-status=live}}</ref>
-A pyridyl-amidohafnium catalyst can be used for the controlled iso-selective polymerization of propylene which can then be combined with polyethylene to make a much tougher recycled plastic.<ref>{{cite journal |last=Eagan |first=James |date=24 Feb 2017 |title=Combining polyethylene and polypropylene: Enhanced performance with PE/iPP multiblock polymers |journal=Science |volume=355 |issue=6327 |pages=814–816 |doi=10.1126/science.aah5744|pmid=28232574 |bibcode=2017Sci...355..814E |s2cid=206652330 |url=https://zenodo.org/record/891450 |doi-access=free }}</ref>
+==Toxicity and safety==
+{{Chembox
-[[Hafnium diselenide]] is studied in [[spintronics]] thanks to its [[charge density wave]] and [[superconductivity]].<ref>{{cite journal|url=https://phys.org/news/2022-09-road-spin-polarized-currents.amp|publisher=[[Phys.org]]|title=A new road towards spin-polarized currents|date=September 7, 2022|author=[[Helmholtz Association|Helmholtz Association of German Research Centres]]|journal=Nature Communications|volume=13|issue=1|page=4147|doi=10.1038/s41467-022-31539-2|pmid=35842436|pmc=9288546|access-date=September 8, 2023|archive-date=September 9, 2022|archive-url=https://archive.today/20220909224109/https://phys.org/news/2022-09-road-spin-polarized-currents.amp|url-status=bot: unknown}}</ref>
+| Name = Hafnium powder
+| container_only = yes
+|Section7={{Chembox Hazards
+| ExternalSDS =
+| GHSPictograms = {{GHS02}}
+| GHSSignalWord = Danger
+| HPhrases = {{H-phrases|228|250}}
+| PPhrases = {{P-phrases|210|222|231+232|233|240|370+378}}<ref name=sigma1>{{Cite web|url=https://www.sigmaaldrich.com/US/pl/sds/aldrich/266752?userType=undefined |website=[[Sigma-Aldrich]] |access-date=6 October 2025 |date=27 October 2023 |title=Hafnium}}</ref>
+| NFPA-H = 0
+| NFPA-F = 4
+| NFPA-R = 0
+| NFPA-S =
+| NFPA_ref = <ref name=fishersci1>{{Cite web|url=https://www.fishersci.com/store/msds?partNumber=AA1020114&productDescription=HFNM+PWR+-325MSH+99.6+%28+EX+25G&vendorId=VN00024248&countryCode=US&language=en |title=Hafnium powder |website=[[Fisher Scientific]] |date=30 March 2024|access-date=6 October 2025}}</ref>
+ }}
+}}
+Hafnium is a [[pyrophoric]] material, and as such fine particles can spontaneously combust upon exposure to air. Hafnium powder is often wetted with at least 25% water by weight to be considered safe - the metal is insoluble in water.<ref>{{Cite web|url=https://cameochemicals.noaa.gov/chemical/3542 |title=Hafnium powder, wetted with not less than 25% water |website=CAMEO Chemicals |access-date=6 October 2025}}</ref> [[Machining]] hafnium is particularly hazardous because of the potential for fine particles of the metal to be produced and immediately introduced to [[friction]]al force. Compounds that contain this metal are rarely encountered by most people.<ref name=":5">{{cite web|url = https://www.osha.gov/SLTC/healthguidelines/hafnium/index.html|title = Occupational Safety & Health Administration: Hafnium|publisher = U.S. Department of Labor|access-date = 2008-09-10|archive-url = https://web.archive.org/web/20080313003040/https://www.osha.gov/SLTC/healthguidelines/hafnium/index.html|archive-date = 2008-03-13}}</ref> The pure metal is not considered toxic, though it has been observed to accumulate in the [[liver]] when injected into rats.<ref name=":2" /> Hafnium compounds should be handled as if they were toxic because the ionic forms of metals are normally at greatest risk for toxicity, and limited animal testing has been done for hafnium compounds.<ref name=":5" /> [[Hafnium tetrachloride]] and [[hafnium tetrabromide]], which are often part of industrial processes that use the element, are of particular note, with both compounds releasing acidic fumes on contact with water ([[Hydrochloric acid|hydrochloric]] and [[hydrobromic acid]], respectively). Additionally, hafnium tetrachloride has been observed as causing liver damage at high exposure levels.<ref name=":2" />
-==Precautions==
+People can be exposed to hafnium in the workplace by breathing, swallowing, skin, and eye contact. In the United States, the [[Occupational Safety and Health Administration]] (OSHA) has set the legal limit ([[permissible exposure limit]]) for exposure to hafnium and hafnium compounds in the workplace as TWA 0.5&nbsp;mg/m<sup>3</sup> over an 8-hour workday. The [[National Institute for Occupational Safety and Health]] (NIOSH) has set the same [[recommended exposure limit]] (REL).<ref name=":1" /> At levels of 50&nbsp;mg/m<sup>3</sup>, hafnium is [[IDLH|immediately dangerous to life and health]].<ref>{{Cite web|title = CDC – NIOSH Pocket Guide to Chemical Hazards – Hafnium|url = https://www.cdc.gov/niosh/npg/npgd0309.html|website = www.cdc.gov|access-date = 2015-11-03}}</ref>
-Care needs to be taken when [[machining]] hafnium because it is [[pyrophoric]]—fine particles can spontaneously combust when exposed to air. Compounds that contain this metal are rarely encountered by most people. The pure metal is not considered toxic, but hafnium compounds should be handled as if they were toxic because the ionic forms of metals are normally at greatest risk for toxicity, and limited animal testing has been done for hafnium compounds.<ref>{{cite web|url = https://www.osha.gov/SLTC/healthguidelines/hafnium/index.html|title = Occupational Safety & Health Administration: Hafnium|publisher = U.S. Department of Labor|access-date = 2008-09-10|archive-url = https://web.archive.org/web/20080313003040/https://www.osha.gov/SLTC/healthguidelines/hafnium/index.html|archive-date = 2008-03-13}}</ref>
-People can be exposed to hafnium in the workplace by breathing, swallowing, skin, and eye contact. The [[Occupational Safety and Health Administration]] (OSHA) has set the legal limit ([[permissible exposure limit]]) for exposure to hafnium and hafnium compounds in the workplace as TWA 0.5&nbsp;mg/m<sup>3</sup> over an 8-hour workday. The [[National Institute for Occupational Safety and Health]] (NIOSH) has set the same [[recommended exposure limit]] (REL). At levels of 50&nbsp;mg/m<sup>3</sup>, hafnium is [[IDLH|immediately dangerous to life and health]].<ref>{{Cite web|title = CDC – NIOSH Pocket Guide to Chemical Hazards – Hafnium|url = https://www.cdc.gov/niosh/npg/npgd0309.html|website = www.cdc.gov|access-date = 2015-11-03}}</ref>
+Because the mineral zircon is often associated with traces of the radioactive elements [[uranium]] and [[thorium]], the chemically destructive processes used to separate zirconium from hafnium have potential to release these radioactive elements and their [[Decay product|decay products]] into the environment along with other reaction wastes. Additionally, synthesis pathways that involve liquid-liquid extraction introduce [[ammonium chloride]] and [[Ammonium sulfate|sulfate]] into reaction mixtures, which as [[effluent]] can reduce available oxygen in water sources or produce [[Cyanide|cyanides]] if it comes into contact with [[thiocyanate]]-containing compounds.<ref name=":2" />
 ==References==

Hafnium: Difference between revisions

Latest revision as of 17:45, 2 May 2026

Contents

Characteristics

Physical characteristics

Chemical characteristics

Isotopes

Occurrence

Production

Chemical compounds

History

Applications

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Isotope geochemistry

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Hafnium: Difference between revisions

Latest revision as of 17:45, 2 May 2026

Characteristics

Physical characteristics

Chemical characteristics

Isotopes

Occurrence

Production

Chemical compounds

History

Applications

Nuclear reactors

Alloys

Microprocessors

Isotope geochemistry

Other uses

Toxicity and safety

References

Further reading

External links

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