U.S. Consumer Product Safety Commission

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/U.S._Consumer_Product_Safety_Commission 

 

U.S. Consumer Product Safety Commission

Consumer Product Safety Commission’s seal
Agency overview
Formed	October 24, 1972
Headquarters	Bethesda, Maryland, U.S.
Employees	500
Agency executives	Robert S. Adler, Acting Chairman Elliot F. Kaye, Commissioner Dana Baiocco, Commissioner Peter Feldman, Commissioner
Website	www.cpsc.gov

The United States Consumer Product Safety Commission (USCPSC, CPSC, or commission) is an independent agency of the United States government. The CPSC seeks to promote the safety of consumer products by addressing “unreasonable risks” of injury (through coordinating recalls, evaluating products that are the subject of consumer complaints or industry reports, etc.); developing uniform safety standards (some mandatory, some through a voluntary standards process); and conducting research into product-related illness and injury. In part due to its small size, the CPSC attempts to coordinate with outside parties—including companies and consumer advocates—to leverage resources and expertise to achieve outcomes that advance consumer safety. The agency was created in 1972 through the Consumer Product Safety Act. The agency reports to Congress and the President; it is not part of any other department or agency in the federal government. The CPSC has five commissioners, who are nominated by the president and confirmed by the Senate for staggered seven-year terms. Historically, the commission was often run by three commissioners or fewer. Since 2009, however, the agency has generally been led by five commissioners, one of whom serves as chairman. The commissioners set policy for the CPSC. The CPSC is headquartered in Bethesda, Maryland.

Leadership

The commissioners of the CPSC are appointed by the U.S. president and with the consent of the U.S. Senate. As with some other U.S. federal independent agencies, commissioners are selected as members of political parties. Although the president is entitled by statute to select the chairman (with the consent of the Senate), no more than three commissioners may belong to the same party. Thus, the president is generally expected to consult with members of the opposite party in the Senate to select members of the commission from the opposite party. The commissioners (including the chairman) vote on selecting the vice chairman, who becomes acting chairman if the chairman’s term ends upon resignation or expiration.

Chairmen

The commission is led by acting Chairman Robert S. Adler, a Democrat who had previously served as acting chairman during the interim period between Inez Tenenbaum and Elliot F. Kaye’s chairmanships. Adler’s immediate predecessor was Ann Marie Buerkle, who held that position for the majority of the 2017-to-2019 period. Although she was nominated to be full, rather than acting, chairman, the Senate never acted on her nomination. The commission has not had a Senate-confirmed chairman since Kaye stepped down as chair following a White House request after Donald Trump’s inauguration. In March 2020, President Trump nominated Nancy Beck, an official at the U.S. Environmental Protection Agency, to chair the commission. Beck previously worked for an association representing the U.S. chemical industry.

Chairmen since 2000

Name	Tenure	Position (acting or full)
Robert S. Adler	2019–	Acting
Ann Marie Buerkle	2017–2019	Acting
Elliot F. Kaye	2014–2017	Full
Robert S. Adler	2013–2014	Acting
Inez Tenenbaum	2009–2013	Full
Thomas Hill Moore	2009	Acting
Nancy Nord	2006–2009	Acting
Hal Stratton	2002–2006	Full
Ann Brown	1994–2001	Full

Current commissioners

Members of the U.S. Consumer Product Safety Commission in 2018: (Left to Right) Peter Feldman, Dana Baiocco, Ann Marie Buerkle, Robert Adler, and Elliot Kaye

As of November 2020, the commission had a 2-to-2 partisan split between Republicans and Democrats. (Commissioner Kaye continues to hold his seat after the October 2020 expiration of his term during a statutorily permitted 1-year holdover.)

Name	Position	Party	Appointed by	Sworn in	Term expires
Robert S. Adler	Acting Chairman	Democratic	Barack Obama	August 2009	October 27, 2021
	Commissioner
Elliot F. Kaye		Democratic		July 2014	October 27, 2020
Dana Baiocco		Republican	Donald Trump	June 2018	October 27, 2024
Peter Feldman				October 5, 2018	October 27, 2026

Scope

All-terrain vehicle safety poster

The CPSC regulates the manufacture and sale of more than 15,000 different consumer products, from cribs to all-terrain vehicles. Products excluded from the CPSC’s jurisdiction include those specifically named by law as under the jurisdiction of other federal agencies. For example, on-road automobiles are regulated by the National Highway Traffic Safety Administration, guns are regulated by the Bureau of Alcohol, Tobacco, Firearms, and Explosives, and drugs are regulated by the Food and Drug Administration.

Activities

The CPSC fulfills its mission by banning dangerous consumer products, establishing safety requirements for other consumer products, issuing recalls of products already on the market, and researching potential hazards associated with consumer products.

Recalls, voluntary & otherwise

The aspect of CPSC’s work that most U.S. citizens might recognize is the “recall,” formally a “corrective action” in which a company develops a “a comprehensive plan that reaches throughout the entire distribution chain to consumers who have the product” and addresses a potential or alleged failure of a product. Recalls are nearly always voluntary. While many recalls involve consumers returning consumer products to the manufacturer for a replacement or, more rarely, a refund, recalls have also involved tasks such as instructing users on how to clean an item or publishing a software patch. Most recalls recover very few consumer products, for a variety of hypothesized reasons. Industry and consumer advocates are often at odds over whether recalls need to be more effective, as many consumers may simply discard products that are the subject of recalls. Whether a consumer learns of a recall in the first place is a different question. One commissioner has called for companies to spend as much on recall advertising as the companies do on their advertising of the products before recalls.

Rulemaking

The CPSC makes rules about consumer products when it identifies a consumer product hazard that is not already addressed by an industry voluntary consensus standard, or when Congress directs it to do so. Its rules can specify basic design requirements, or they can amount to product bans, as in the case of small high-powered magnets, which the CPSC attempted to ban. For certain infant products, the CPSC regulates even when voluntary standards exist. The CPSC is required to follow a rigorous, scientific process to develop mandatory rules. Failing to do so can justify the revocation of a rule, as was the case in a Tenth Circuit decision vacating the CPSC’s ban on small high-powered magnets.

Information gathering & information sharing

The CPSC learns about unsafe products in several ways. The agency maintains a consumer hotline through which consumers may report concerns about unsafe products or injuries associated with products. Product safety concerns may also be submitted through SaferProducts.gov. The agency also operates the National Electronic Injury Surveillance System (NEISS), a probability sample of about 100 hospitals with 24-hour emergency rooms. NEISS collects data on consumer product related injuries treated in ERs and can be used to generate national estimates.

The agency also works with and shares information with other governments, both in the U.S. (with states and public health agencies) and with international counterparts.

Publicity & communication

Mannequin targeted in CPSC Fireworks Safety Demonstration 2017

The CPSC works on a variety of publicity campaigns to raise awareness of safety.

Fireworks

Annually, the CPSC blows up mannequins to demonstrate the dangers of improper use of fireworks.

Drowning prevention

In connection with the U.S. swimming season (the northern hemisphere’s summer, roughly May to September), the CPSC conducts the “Pool Safely” campaign to prevent drowning through methods such as building fences and supporting education programs. Other efforts include attempts to prevent suction entrapment, which can kill by trapping a swimmer underwater, by eviscerating a swimmer’s internal organs (when a suction tube lacks a cover), or otherwise.

Social media presence

The CPSC’s Twitter account, @USCPSC, has garnered attention for amusing memes. It has been variously described as “The US Government’s Best Twitter Account” and the “coolest government Twitter account.”

Enforcement

Since February 2015, the average civil penalty has been $2.9 million. In April 2018, Polaris Industries agreed to pay a record $27.25 million civil penalty for failing to report defective off-road vehicles.

Funding and staff

In 1972 when the agency was created, it had a budget of $34.7 million and 786 staff members. By 2008 it had 401 employees on a budget of $43 million, but the Consumer Product Safety Improvement Act passed in 2008 increases funding $136.4 million in 2014 with full-time employees to at least 500 by 2013. Funding dropped to $127 million as of the commission’s fiscal year 2019 appropriation, and it continues to have slightly more than 500 employees.

Mid-2000s reform following the “Year of the Recall”

The year 2007 was called the “Year of the Recall” by some CPSC-watchers in the United States. The CPSC worked with manufacturers and importers on a record 473 voluntary recalls that year, and other U.S. federal agencies promoted other widely noted recalls. CPSC recalls included many incidents with lead in toys and other children’s products.

Consumer Product Safety Improvement Act of 2008

These issues led to the legislative interest in the reform of the agency, and the final result of these efforts was the passage of the Consumer Product Safety Improvement Act in 2008. The bill increased funding and staffing for the CPSC, placed stricter limits on lead levels in children’s products (redefined from products intended for children age seven and under to children age twelve and under), restricted certain phthalates in children’s toys and child care articles, and required mandatory testing and certification of applicable products. The Danny Keysar Child Product Notification Act required the CPSC to create a public database of recalled products and to provide consumers with a postage-paid postcard for each durable infant or toddler product. This act was named after Danny Keysar, who died in a recalled crib. Danny’s parents, Linda E. Ginzel and Boaz Keysar, founded Kids In Danger and were instrumental in working with the CPSC to strengthen product safety standards.

Creation of public database

The public database (saferproducts.gov), constructed at a cost of around US$3 million and launched in March 2011, “publicizes complaints from virtually anyone who can provide details about a safety problem connected with any of the 15,000 kinds of consumer goods regulated by the CPSC.” While lauded by consumer advocates for making previously hidden information available, manufacturers have expressed their concern “that most of the complaints are not first vetted by the CPSC before they are made public,” meaning it could be abused and potentially used to target specific brands. As of mid-April 2011, the database was accruing about 30 safety complaints per day. By June 2018, the database had 36,544 reports, with an average of approximately 13.74 reports filed each day.

Controversies

Recall of inclined infant sleepers

In 2019, the CPSC recalled inclined sleepers sold by multiple companies (including Mattel Fisher-Price’s Rock ’n Play as well as Kids II’s and Dorel’s rocking sleepers sold under a variety of brand names). The recalled products were associated with more than 30 infant deaths according to contemporary news reports. The controversy was among those that were tied to Acting Chairman Ann Marie Burekle’s announcement of her intention to step down after waiting for years for the U.S. Senate to act on her nomination to serve an additional term and be formally elevated to full chairmanship.

Recall of jogging strollers in 2019 after settlement in 2018

The CPSC sued the maker of Britax jogging strollers, then settled with the company, in 2018. Reports attributed the change to the change in personnel after Republicans gained a majority on the commission, although some commentators noted the unusual circumstances of the commission suing over a product that met existing standards. The 2018 settlement included the company’s agreement to provide a replacement part to consumers. The replacement part—a bolt—itself was later recalled because it broke easily.

Attempt to ban small, high-powered magnets

In 2012, following reports of consumers (mostly children) ingesting small, high-powered magnets made of rare earth materials such as neodynium, the commission voted to block sales of Maxfield & Oberton’s Buckyballs-branded toys, and later voted to issue a rule that would amount to a ban on all similar toys. Later, however, a federal appellate court overturned the ban, finding that the Commission had moved forward without adequate data. The decision vacating the ban was written by later-Supreme Court Justice Neil Gorsuch.

Industry-sponsored travel in the early 2000s

On November 2, 2007, The Washington Post reported that between 2002 and the date of their report, former chairman Hal Stratton and current commissioner and former acting chairman Nancy Nord had taken more than 30 trips paid for by manufacturing groups or lobbyists representing industries that are under the supervision of the agency. According to the Post, the groups paid for over $60,000 travel and related expenses during this time.

Surviving challenges to the commission’s continued existence

The CPSC’s creation was not without controversy, and the agency survived attempts to close it in its first decades. In 1981, President Ronald Reagan’s head of the Office of Management & Budget, David Stockman, sought to end the authorization for the agency to move it inside the Department of Commerce. The agency was given a new lease on life following agreement among U.S. senators.

Hafnium

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Hafnium 

 

Hafnium
Pronunciation	/ˈhæfniəm/ ​(HAF-nee-əm)
Appearance	steel gray
Standard atomic weight Ar, std(Hf)	178.486(6)
Hafnium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Zr ↑ Hf ↓ Rf lutetium ← hafnium → tantalum
Atomic number (Z)	72
Group	group 4
Period	period 6
Block	d-block
Electron configuration	[Xe] 4f14 5d2 6s2
Electrons per shell	2, 8, 18, 32, 10, 2
Physical properties
Phase at STP	solid
Melting point	2506 K ​(2233 °C, ​4051 °F)
Boiling point	4876 K ​(4603 °C, ​8317 °F)
Density (near r.t.)	13.31 g/cm3
when liquid (at m.p.)	12 g/cm3
Heat of fusion	27.2 kJ/mol
Heat of vaporization	648 kJ/mol
Molar heat capacity	25.73 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 2689 2954 3277 3679 4194 4876
Atomic properties
Oxidation states	−2, 0, +1, +2, +3, +4 (an amphoteric oxide)
Electronegativity	Pauling scale: 1.3
Ionization energies	1st: 658.5 kJ/mol 2nd: 1440 kJ/mol 3rd: 2250 kJ/mol
Atomic radius	empirical: 159 pm
Covalent radius	175±10 pm
Spectral lines of hafnium
Other properties
Natural occurrence	primordial
Crystal structure	​hexagonal close-packed (hcp)
Speed of sound thin rod	3010 m/s (at 20 °C)
Thermal expansion	5.9 µm/(m⋅K) (at 25 °C)
Thermal conductivity	23.0 W/(m⋅K)
Electrical resistivity	331 nΩ⋅m (at 20 °C)
Magnetic ordering	paramagnetic
Molar magnetic susceptibility	+75.0×10−6 cm3/mol (at 298 K)
Young's modulus	78 GPa
Shear modulus	30 GPa
Bulk modulus	110 GPa
Poisson ratio	0.37
Mohs hardness	5.5
Vickers hardness	1520–2060 MPa
Brinell hardness	1450–2100 MPa
CAS Number	7440-58-6
History
Naming	after Hafnia. Latin for: Copenhagen, where it was discovered
Prediction	Dmitri Mendeleev (1869)
Discovery and first isolation	Dirk Coster and George de Hevesy (1922)
Main isotopes of hafnium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 172Hf syn 1.87 y ε 172Lu 174Hf 0.16% 2×1015 y α 170Yb 176Hf 5.26% stable 177Hf 18.60% stable 178Hf 27.28% stable 178m2Hf syn 31 y IT 178Hf 179Hf 13.62% stable 180Hf 35.08% stable 182Hf syn 8.9×106 y β− 182Ta

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

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

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

Characteristics

Physical characteristics

Pieces of hafnium

Hafnium is a shiny, silvery, ductile metal that is corrosion-resistant and chemically similar to zirconium (due to its having the same number of valence electrons, being in the same group, but also to relativistic effects; the expected expansion of atomic radii from period 5 to 6 is almost exactly cancelled 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 2388 K. 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.

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 and that the nuclei of several different hafnium isotopes readily absorb two or more neutrons apiece. 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 rods.

Chemical characteristics

Hafnium dioxide

Hafnium reacts in air to form a protective film that inhibits further corrosion. The metal is not readily attacked by acids but can be oxidized with halogens or it can be burnt in air. Like its sister metal zirconium, finely divided hafnium can ignite spontaneously in air. The metal is resistant to concentrated alkalis.

The chemistry of hafnium and zirconium is so similar that the two cannot be separated on the basis of differing chemical reactions. The melting points and boiling points of the compounds and the solubility in solvents are the major differences in the chemistry of these twin elements.

Isotopes

At least 34 isotopes of hafnium have been observed, ranging in mass number from 153 to 186. The five stable isotopes are in the range of 176 to 180. The radioactive isotopes' half-lives range from only 400 ms for ¹⁵³Hf, to 2.0 petayears (10¹⁵ years) for the most stable one, ¹⁷⁴Hf.

The nuclear isomer ^178m2Hf was at the center of a controversy for several years regarding its potential use as a weapon.

Occurrence

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

Hafnium is estimated to make up about 5.8 ppm of the Earth's upper crust by mass. 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)SiO
4, with atomic Hf > Zr. An obsolete name for a variety of zircon containing unusually high Hf content is alvite.^[12]

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.

Production

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.

Zirconium is a good nuclear fuel-rod cladding metal, with the desirable properties of a very low neutron capture cross-section and good chemical stability at high temperatures. However, because of hafnium's neutron-absorbing properties, hafnium impurities in zirconium would cause it to be far less useful for nuclear-reactor applications. Thus, a nearly complete separation of zirconium and hafnium is necessary for their use in nuclear power. The production of hafnium-free zirconium is the main source for hafnium.

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. The methods first used — fractional crystallization of ammonium fluoride salts or the fractional distillation of the chloride — have not proven suitable for an industrial-scale production. After zirconium was chosen as material for nuclear reactor programs in the 1940s, a separation method had to be developed. Liquid-liquid extraction processes with a wide variety of solvents were developed and are still used for the production of hafnium. About half of all hafnium metal manufactured is produced as a by-product of zirconium refinement. The end product of the separation is hafnium(IV) chloride. The purified hafnium(IV) chloride is converted to the metal by reduction with magnesium or sodium, as in the Kroll process.

HfCl₄ + 2 Mg (1100 °C) → 2 MgCl₂ + Hf

Further purification is effected by a chemical transport reaction developed by Arkel and de Boer: In a closed vessel, hafnium reacts with iodine at temperatures of 500 °C, forming hafnium(IV) iodide; at a tungsten filament of 1700 °C the reverse reaction happens, and the iodine and hafnium are set free. The hafnium forms a solid coating at the tungsten filament, and the iodine can react with additional hafnium, resulting in a steady iodine turnover.

Hf + 2 I₂ (500 °C) → HfI₄

HfI₄ (1700 °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). Consequently, compounds of hafnium(IV) and zirconium(IV) have very similar chemical and physical properties. 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. At higher temperatures, hafnium reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon. Some compounds of hafnium in lower oxidation states are known.

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. These tetrachlorides are precursors to various organohafnium compounds such as hafnocene dichloride and tetrabenzylhafnium.

The white hafnium oxide (HfO₂), with a melting point of 2,812 °C and a boiling point of roughly 5,100 °C, is very similar to zirconia, but slightly more basic. Hafnium carbide is the most refractory binary compound known, with a melting point over 3,890 °C, and hafnium nitride is the most refractory of all known metal nitrides, with a melting point of 3,310 °C. This has led to proposals that hafnium or its carbides might be useful as construction materials that are subjected to very high temperatures. The mixed carbide tantalum hafnium carbide (Ta
₄HfC
₅) possesses the highest melting point of any currently known compound, 4,263 K (3,990 °C; 7,214 °F). Recent supercomputer simulations suggest a hafnium alloy with a melting point of 4,400 K.

History

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

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.

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.

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. Georges Urbain asserted that he found element 72 in the rare earth elements in 1907 and published his results on celtium in 1911. 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. 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. By early 1923, several physicists and chemists such as Niels Bohr and Charles R. Bury suggested that element 72 should resemble zirconium and therefore was not part of the rare earth elements group. These suggestions were based on Bohr's theories of the atom, the X-ray spectroscopy of Moseley, and the chemical arguments of Friedrich Paneth.

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. Hafnium was discovered by the two in 1923 in Copenhagen, Denmark, validating the original 1869 prediction of Mendeleev. It was ultimately found in zircon in Norway through X-ray spectroscopy analysis. 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. Today, the Faculty of Science of the University of Copenhagen uses in its seal a stylized image of the hafnium atom.

Hafnium was separated from zirconium through repeated recrystallization of the double ammonium or potassium fluorides by Valdemar Thal Jantzen and von Hevesey. 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. This process for differential purification of zirconium and hafnium is still in use today.

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, thus making elements 75 (rhenium) and 72 (hafnium) the last two unknown non-radioactive elements.

Applications

Most of the hafnium produced is used in the manufacture of control rods for nuclear reactors.

Several details contribute to the fact that there are only a few technical uses for hafnium: First, the close similarity between hafnium and zirconium makes it possible to use zirconium for most of the applications; second, hafnium was first available as pure metal after the use in the nuclear industry for hafnium-free zirconium in the late 1950s. Furthermore, the low abundance and difficult separation techniques necessary make it a scarce commodity. When the demand for zirconium dropped following the Fukushima disaster, the price of hafnium increased sharply from around $500–600/kg in 2014 to around $1000/kg in 2015.

Nuclear reactors

The nuclei of several hafnium isotopes can each absorb multiple neutrons. This makes hafnium a good material for use in the control rods for nuclear reactors. Its neutron-capture cross-section (Capture Resonance Integral I_o ≈ 2000 barns) 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. The German research reactor FRM II uses hafnium as a neutron absorber. It is also common in military reactors, particularly in US naval reactors, but seldom found in civilian ones, the first core of the Shippingport Atomic Power Station (a conversion of a naval reactor) being a notable exception.

Alloys

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.

Small additions of hafnium increase the adherence of protective oxide scales on nickel-based alloys. It improves thereby 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.

Microprocessors

Hafnium-based compounds are employed in gate insulators in the 45 nm generation of integrated circuits from Intel, IBM and others. Hafnium oxide-based compounds are practical high-k dielectrics, allowing reduction of the gate leakage current which improves performance at such scales.

Isotope geochemistry

Isotopes of hafnium and lutetium (along with ytterbium) 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. This is because ¹⁷⁶Lu decays to ¹⁷⁶Hf with a half-life of approximately 37 billion years.

In most geologic materials, zircon is the dominant host of hafnium (>10,000 ppm) and is often the focus of hafnium studies in geology. 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.

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.

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 air.

The high energy content of ^178m2Hf was the concern of a DARPA-funded program in the US. This program determined that the possibility of using a nuclear isomer of hafnium (the above-mentioned ^178m2Hf) to construct high-yield weapons with X-ray triggering mechanisms—an application of induced gamma emission—was infeasible because of its expense.

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.

Precautions

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.

People can be exposed to hafnium in the workplace by breathing it in, swallowing it, skin contact, 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 mg/m³ 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 mg/m³, hafnium is immediately dangerous to life and health.