Neodymium is a chemical element with symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite. Neodymium is not found naturally in metallic form or unmixed with other lanthanides, and it is usually refined for general use. Although neodymium is classed as a rare earth, it is a fairly common element, no rarer than cobalt, nickel, or copper, and is widely distributed in the Earth's crust. Most of the world's commercial neodymium is mined in China.
Neodymium compounds were first commercially used as glass dyes in 1927, and they remain a popular additive in glasses. The color of neodymium compounds—due to the Nd3+ ion—is often a reddish-purple but it changes with the type of lighting, due to the interaction of the sharp light absorption bands of neodymium with ambient light enriched with the sharp visible emission bands of mercury, trivalent europium or terbium. Some neodymium-doped glasses are also used in lasers that emit infrared with wavelengths between 1047 and 1062 nanometers. These have been used in extremely-high-power applications, such as experiments in inertial confinement fusion.
Neodymium is also used with various other substrate crystals, such as yttrium aluminium garnet in the Nd:YAG laser. This laser usually emits infrared at a wavelength of about 1064 nanometers. The Nd:YAG laser is one of the most commonly used solid-state lasers.
Another important use of neodymium is as a component in the alloys used to make high-strength neodymium magnets—powerful permanent magnets. These magnets are widely used in such products as microphones, professional loudspeakers, in-ear headphones, high performance hobby DC electric motors, and computer hard disks, where low magnet mass (or volume) or strong magnetic fields are required. Larger neodymium magnets are used in high-power-versus-weight electric motors (for example in hybrid cars) and generators (for example aircraft and wind turbine electric generators).
|Standard atomic weight Ar, std(Nd)||144.242(3)|
|Neodymium in the periodic table|
|Atomic number (Z)||60|
|Electron configuration||[Xe] 4f4 6s2|
Electrons per shell
|2, 8, 18, 22, 8, 2|
|Phase at STP||solid|
|Melting point||1297 K (1024 °C, 1875 °F)|
|Boiling point||3347 K (3074 °C, 5565 °F)|
|Density (near r.t.)||7.01 g/cm3|
|when liquid (at m.p.)||6.89 g/cm3|
|Heat of fusion||7.14 kJ/mol|
|Heat of vaporization||289 kJ/mol|
|Molar heat capacity||27.45 J/(mol·K)|
|Oxidation states||+2, +3, +4 (a mildly basic oxide)|
|Electronegativity||Pauling scale: 1.14|
|Atomic radius||empirical: 181 pm|
|Covalent radius||201±6 pm|
Spectral lines of neodymium
|Crystal structure|| double hexagonal close-packed (dhcp)|
|Speed of sound thin rod||2330 m/s (at 20 °C)|
|Thermal expansion||α, poly: 9.6 µm/(m·K) (at r.t.)|
|Thermal conductivity||16.5 W/(m·K)|
|Electrical resistivity||α, poly: 643 nΩ·m|
|Magnetic ordering||paramagnetic, antiferromagnetic below 20 K|
|Magnetic susceptibility||+5628.0·10−6 cm3/mol (287.7 K)|
|Young's modulus||α form: 41.4 GPa|
|Shear modulus||α form: 16.3 GPa|
|Bulk modulus||α form: 31.8 GPa|
|Poisson ratio||α form: 0.281|
|Vickers hardness||345–745 MPa|
|Brinell hardness||265–700 MPa|
|Discovery||Carl Auer von Welsbach (1885)|
|Main isotopes of neodymium|
Neodymium, a rare-earth metal, was present in the classical mischmetal at a concentration of about 18%. Metallic neodymium has a bright, silvery metallic luster, but as one of the more reactive lanthanide rare-earth metals, it quickly oxidizes in ordinary air. The oxide layer that forms then peels off, exposing the metal to further oxidation. Thus, a centimeter-sized sample of neodymium completely oxidizes within a year.
Neodymium metal tarnishes slowly in air and it burns readily at about 150 °C to form neodymium(III) oxide:
Neodymium is a quite electropositive element, and it reacts slowly with cold water, but quite quickly with hot water to form neodymium(III) hydroxide:
Neodymium metal reacts vigorously with all the halogens:
Neodymium compounds include
Some neodymium compounds have colors that vary based upon the type of lighting.
Naturally occurring neodymium is a mixture of five stable isotopes, 142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant (27.2% of the natural abundance), and two radioisotopes, 144Nd and 150Nd. In all, 31 radioisotopes of neodymium have been detected as of 2010, with the most stable radioisotopes being the naturally occurring ones: 144Nd (alpha decay with a half-life (t1/2) of 2.29×1015 years) and 150Nd (double beta decay, t1/2 = 7×1018 years, approximately). All of the remaining radioactive isotopes have half-lives that are shorter than eleven days, and the majority of these have half-lives that are shorter than 70 seconds. Neodymium also has 13 known meta states, with the most stable one being 139mNd (t1/2 = 5.5 hours), 135mNd (t1/2 = 5.5 minutes) and 133m1Nd (t1/2 ~70 seconds).
The primary decay modes before the most abundant stable isotope, 142Nd, are electron capture and positron decay, and the primary mode after is beta minus decay. The primary decay products before 142Nd are element Pr (praseodymium) isotopes and the primary products after are element Pm (promethium) isotopes.
Neodymium was discovered by Baron Carl Auer von Welsbach, an Austrian chemist, in Vienna in 1885. He separated neodymium, as well as the element praseodymium, from a material known as didymium by means of fractional crystallization of the double ammonium nitrate tetrahydrates from nitric acid, while following the separation by spectroscopic analysis; however, it was not isolated in relatively pure form until 1925. The name neodymium is derived from the Greek words neos (νέος), new, and didymos (διδύμος), twin.
Double nitrate crystallization was the means of commercial neodymium purification until the 1950s. Lindsay Chemical Division was the first to commercialize large-scale ion-exchange purification of neodymium. Starting in the 1950s, high purity (above 99%) neodymium was primarily obtained through an ion exchange process from monazite, a mineral rich in rare-earth elements. The metal itself is obtained through electrolysis of its halide salts. Currently, most neodymium is extracted from bastnäsite, (Ce,La,Nd,Pr)CO3F, and purified by solvent extraction. Ion-exchange purification is reserved for preparing the highest purities (typically >99.99%). The evolving technology, and improved purity of commercially available neodymium oxide, was reflected in the appearance of neodymium glass that resides in collections today. Early neodymium glasses made in the 1930s have a more reddish or orange tinge than modern versions which are more cleanly purple, due to the difficulties in removing the last traces of praseodymium in the era when manufacturing relied upon fractional crystallization technology.
Neodymium is rarely found in nature as a free element, but rather it occurs in ores such as monazite and bastnäsite (these are mineral group names rather than single mineral names) that contain small amounts of all rare-earth metals. In these minerals neodymium is rarely dominant (as in the case of lanthanum), with cerium being the most abundant lanthanide; some exceptions include monazite-(Nd) and kozoite-(Nd). The main mining areas are in China, the United States, Brazil, India, Sri Lanka, and Australia. The reserves of neodymium are estimated at about eight million tonnes. Although it belongs to the rare-earth metals, neodymium is not rare at all. Its abundance in the Earth's crust is about 38 mg/kg, which is the second highest among rare-earth elements, following cerium. The world's production of neodymium was about 7,000 tonnes in 2004. The bulk of current production is from China. As of January 2010 the Chinese government has imposed strategic material controls on the element, raising some concerns in consuming countries and causing skyrocketing prices of neodymium and other rare-earth metals. As of late 2011, 99% pure neodymium was traded in world markets for US$300 to US$350 per kilogram, down from the mid-2011 peak of US$500/kg. The price of neodymium oxide fell from $200/kg in 2011 to $40 in 2015, largely due to illegal production in China which circumvented government restrictions. The uncertainty of pricing and availability have caused companies (particularly Japanese ones) to create permanent magnets and associated electric motors with fewer rare-earth metals; however, so far they have been unable to eliminate the need for neodymium.
Neodymium is typically 10–18% of the rare-earth content of commercial deposits of the light rare-earth-element minerals bastnäsite and monazite. With neodymium compounds being the most strongly colored for the trivalent lanthanides, it can occasionally dominate the coloration of rare-earth minerals when competing chromophores are absent. It usually gives a pink coloration. Outstanding examples of this include monazite crystals from the tin deposits in Llallagua, Bolivia; ancylite from Mont Saint-Hilaire, Quebec, Canada; or lanthanite from the Saucon Valley, Pennsylvania, United States. As with neodymium glasses, such minerals change their colors under the differing lighting conditions. The absorption bands of neodymium interact with the visible emission spectrum of mercury vapor, with the unfiltered shortwave UV light causing neodymium-containing minerals to reflect a distinctive green color. This can be observed with monazite-containing sands or bastnäsite-containing ore.
Neodymium magnets (actually an alloy, Nd2Fe14B) are the strongest permanent magnets known. A neodymium magnet of a few grams can lift a thousand times its own weight. These magnets are cheaper, lighter, and stronger than samarium–cobalt magnets. However, they are not superior in every aspect, as neodymium-based magnets lose their magnetism at lower temperatures and tend to rust, while samarium–cobalt magnets do not.
Neodymium magnets appear in products such as microphones, professional loudspeakers, in-ear headphones, guitar and bass guitar pick-ups, and computer hard disks where low mass, small volume, or strong magnetic fields are required. Neodymium magnet electric motors have also been responsible for the development of purely electrical model aircraft within the first decade of the 21st century, to the point that these are displacing internal combustion–powered models internationally. Likewise, due to this high magnetic capacity per weight, neodymium is used in the electric motors of hybrid and electric automobiles, and in the electricity generators of some designs of commercial wind turbines (only wind turbines with "permanent magnet" generators use neodymium). For example, drive electric motors of each Toyota Prius require one kilogram (2.2 pounds) of neodymium per vehicle.
Certain transparent materials with a small concentration of neodymium ions can be used in lasers as gain media for infrared wavelengths (1054–1064 nm), e.g. Nd:YAG (yttrium aluminium garnet), Nd:YLF (yttrium lithium fluoride), Nd:YVO4 (yttrium orthovanadate), and Nd:glass. Neodymium-doped crystals (typically Nd:YVO4) generate high-powered infrared laser beams which are converted to green laser light in commercial DPSS hand-held lasers and laser pointers.
The current laser at the UK Atomic Weapons Establishment (AWE), the HELEN (High Energy Laser Embodying Neodymium) 1-terawatt neodymium-glass laser, can access the midpoints of pressure and temperature regions and is used to acquire data for modeling on how density, temperature, and pressure interact inside warheads. HELEN can create plasmas of around 106 K, from which opacity and transmission of radiation are measured.
Neodymium glass solid-state lasers are used in extremely high power (terawatt scale), high energy (megajoules) multiple beam systems for inertial confinement fusion. Nd:glass lasers are usually frequency tripled to the third harmonic at 351 nm in laser fusion devices.
Neodymium glass (Nd:glass) is produced by the inclusion of neodymium oxide (Nd2O3) in the glass melt. Usually in daylight or incandescent light neodymium glass appears lavender, but it appears pale blue under fluorescent lighting. Neodymium may be used to color glass in delicate shades ranging from pure violet through wine-red and warm gray.
The first commercial use of purified neodymium was in glass coloration, starting with experiments by Leo Moser in November 1927. The resulting "Alexandrite" glass remains a signature color of the Moser glassworks to this day. Neodymium glass was widely emulated in the early 1930s by American glasshouses, most notably Heisey, Fostoria ("wisteria"), Cambridge ("heatherbloom"), and Steuben ("wisteria"), and elsewhere (e.g. Lalique, in France, or Murano). Tiffin's "twilight" remained in production from about 1950 to 1980. Current sources include glassmakers in the Czech Republic, the United States, and China.
The sharp absorption bands of neodymium cause the glass color to change under different lighting conditions, being reddish-purple under daylight or yellow incandescent light, but blue under white fluorescent lighting, or greenish under trichromatic lighting. This color-change phenomenon is highly prized by collectors. In combination with gold or selenium, beautiful red colors result. Since neodymium coloration depends upon "forbidden" f-f transitions deep within the atom, there is relatively little influence on the color from the chemical environment, so the color is impervious to the thermal history of the glass. However, for the best color, iron-containing impurities need to be minimized in the silica used to make the glass. The same forbidden nature of the f-f transitions makes rare-earth colorants less intense than those provided by most d-transition elements, so more has to be used in a glass to achieve the desired color intensity. The original Moser recipe used about 5% of neodymium oxide in the glass melt, a sufficient quantity such that Moser referred to these as being "rare-earth doped" glasses. Being a strong base, that level of neodymium would have affected the melting properties of the glass, and the lime content of the glass might have had to be adjusted accordingly.
Light transmitted through neodymium glasses shows unusually sharp absorption bands; the glass is used in astronomical work to produce sharp bands by which spectral lines may be calibrated. Another application is the creation of selective astronomical filters to reduce the effect of light pollution from sodium and fluorescent lighting while passing other colours, especially dark red hydrogen-alpha emission from nebulae. Neodymium is also used to remove the green color caused by iron contaminants from glass.
Neodymium is a component of "didymium" (referring to mixture of salts of neodymium and praseodymium) used for coloring glass to make welder's and glass-blower's goggles; the sharp absorption bands obliterate the strong sodium emission at 589 nm. The similar absorption of the yellow mercury emission line at 578 nm is the principal cause of the blue color observed for neodymium glass under traditional white-fluorescent lighting.
Neodymium and didymium glass are used in color-enhancing filters in indoor photography, particularly in filtering out the yellow hues from incandescent lighting.
Similarly, neodymium glass is becoming widely used more directly in incandescent light bulbs. These lamps contain neodymium in the glass to filter out yellow light, resulting in a whiter light which is more like sunlight.
The use of neodymium in automobile rear-view mirrors, to reduce the glare at night, has been patented.
Similar to its use in glasses, neodymium salts are used as a colorant for enamels.
|GHS signal word||Warning|
|H315, H319, H335|
Neodymium metal dust is combustible and therefore an explosion hazard. Neodymium compounds, as with all rare-earth metals, are of low to moderate toxicity; however, its toxicity has not been thoroughly investigated. Neodymium dust and salts are very irritating to the eyes and mucous membranes, and moderately irritating to skin. Breathing the dust can cause lung embolisms, and accumulated exposure damages the liver. Neodymium also acts as an anticoagulant, especially when given intravenously.
Neodymium magnets have been tested for medical uses such as magnetic braces and bone repair, but biocompatibility issues have prevented widespread application. Commercially available magnets made from neodymium are exceptionally strong, and can attract each other from large distances. If not handled carefully, they come together very quickly and forcefully, causing injuries. For example, there is at least one documented case of a person losing a fingertip when two magnets he was using snapped together from 50 cm away.
Another risk of these powerful magnets is that if more than one magnet is ingested, they can pinch soft tissues in the gastrointestinal tract. This has led to at least 1,700 emergency room visits and necessitated the recall of the Buckyballs line of toys, which were construction sets of small neodymium magnets.
A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance (in very low concentrations) to alter the electrical or optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that were in the crystal lattice of the base material. The crystalline materials are frequently either crystals of a semiconductor such as silicon and germanium for use in solid-state electronics, or transparent crystals for use in the production of various laser types; however, in some cases of the latter, noncrystalline substances such as glass can also be doped with impurities.Isotopes of neodymium
Naturally occurring neodymium (60Nd) is composed of 5 stable isotopes, 142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant (27.2% natural abundance), and 2 long-lived radioisotopes, 144Nd and 150Nd. In all, 33 radioisotopes of neodymium have been characterized up to now, with the most stable being naturally occurring isotopes 144Nd (alpha decay, a half-life (t1/2) of 2.29×1015 years) and 150Nd (double beta decay, t1/2 of 7×1018 years). All of the remaining radioactive isotopes have half-lives that are less than 12 days, and the majority of these have half-lives that are less than 70 seconds; the most stable artificial isotope is 147Nd with a half-life of 10.98 days. This element also has 13 known meta states with the most stable being 139mNd (t1/2 5.5 hours), 135mNd (t1/2 5.5 minutes) and 133m1Nd (t1/2 ~70 seconds).
The primary decay modes before the most abundant stable isotope, 142Nd, are electron capture and positron decay, and the primary mode after is beta decay. The primary decay products before 142Nd are element Pr (praseodymium) isotopes and the primary products after are element Pm (promethium) isotopes.Isotopes of samarium
Naturally occurring samarium (62Sm) is composed of five stable isotopes, 144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived radioisotopes, 147Sm (half life: 1.06×1011 y) and 148Sm (7×1015 y), with 152Sm being the most abundant (26.75% natural abundance). 146Sm is also fairly long-lived (6.8×107 y), but is not long-lived enough to have survived in significant quantities from the formation of the Solar System on Earth, although it remains useful in radiometric dating in the Solar System as an extinct radionuclide.Other than the naturally occurring isotopes, the longest-lived radioisotopes are 151Sm, which has a half-life of 88.8 years, and 145Sm, which has a half-life of 340 days. All of the remaining radioisotopes have half-lives that are less than two days, and the majority of these have half-lives that are less than 48 seconds. This element also has twelve known isomers with the most stable being 141mSm (t1/2 22.6 minutes), 143m1Sm (t1/2 66 seconds) and 139mSm (t1/2 10.7 seconds).
The long lived isotopes,146Sm, 147Sm, and 148Sm primarily decay by alpha decay to isotopes of neodymium. Lighter unstable isotopes of samarium primarily decay by electron capture to isotopes of promethium, while heavier ones decay by beta decay to isotopes of europium.
Isotopes of samarium are used in samarium–neodymium dating for determining the age relationships of rocks and meteorites.
151Sm is a medium-lived fission product and acts as a neutron poison in the nuclear fuel cycle. The stable fission product 149Sm is also a neutron poison.Janus laser
The Janus laser was a (then considered high power) two beam infrared neodymium doped silica glass laser built at Lawrence Livermore National Laboratory in 1974 for the study of inertial confinement fusion. Janus was built using about 100 pounds of Nd:glass laser material. Initially, Janus was only capable of producing laser pulses of about 10 joules of energy.Natural nuclear fission reactor
A natural nuclear fission reactor is a uranium deposit where self-sustaining nuclear chain reactions have occurred. This can be examined by analysis of isotope ratios. The existence of this phenomenon was discovered in 1972 at Oklo in Gabon by French physicist Francis Perrin. The conditions under which a natural nuclear reactor could exist had been predicted in 1956 by Paul Kazuo Kuroda. The conditions found were very similar to what was predicted.
Oklo is the only known location for this in the world and consists of 16 sites at which self-sustaining nuclear fission reactions are thought to have taken place approximately 1.7 billion years ago, and ran for a few hundred thousand years, averaging probably less than 100 kW of thermal power during that time.Neodymium(III) bromide
Neodymium(III) bromide is a compound of one neodymium atom and three bromine atoms. Neodymium(III) bromide is a powder at room temperature, and it can be any color between off-white and pale green. Neodymium(III) bromide is hygroscopic.Neodymium(III) chloride
Neodymium(III) chloride or neodymium trichloride is a chemical compound of neodymium and chlorine with the formula NdCl3. This anhydrous compound is a mauve-colored solid that rapidly absorbs water on exposure to air to form a purple-colored hexahydrate, NdCl3·6H2O. Neodymium(III) chloride is produced from minerals monazite and bastnäsite using a complex multistage extraction process. The chloride has several important applications as an intermediate chemical for production of neodymium metal and neodymium-based lasers and optical fibers. Other applications include a catalyst in organic synthesis and in decomposition of waste water contamination, corrosion protection of aluminium and its alloys, and fluorescent labeling of organic molecules (DNA).Neodymium(III) oxide
Neodymium(III) oxide or neodymium sesquioxide is the chemical compound composed of neodymium and oxygen with the formula Nd2O3. It forms very light grayish-blue hexagonal crystals. The rare-earth mixture didymium, previously believed to be an element, partially consists of neodymium(III) oxide.Neodymium-doped yttrium lithium fluoride
Neodymium-doped yttrium lithium fluoride (Nd:YLF) is a lasing medium for arc lamp-pumped and diode-pumped solid-state lasers. The YLF crystal (LiYF4) is naturally birefringent, and commonly used laser transitions occur at 1047 nm and 1053 nm.It is used in Q-switched systems in part due
to its relatively long fluorescence lifetime.
As with Nd:YAG lasers, harmonic generation is frequently
employed with Q-switched Nd:YLF
to produce shorter wavelengths. A common application
of frequency-doubled Nd:YLF pulses is to pump ultrafast
Ti:Sapphire chirped-pulse amplifiers.
Neodymium-doped YLF can provide higher pulse energies than Nd:YAG for repetition rates of a few kHz or less. Compared to Nd:YAG, the Nd:YLF crystal is very brittle
and fractures easily. It is also slightly water-soluble — a YLF laser rod may very
slowly dissolve in cooling water which surrounds it.Neodymium-doped yttrium orthovanadate
Neodymium-doped yttrium orthovanadate (Nd:YVO4) is a crystalline material formed by adding neodymium ions to yttrium orthovanadate. It is commonly used as an active laser medium for diode-pumped solid-state lasers. It comes as a transparent blue-tinted material. It is birefringent, therefore rods made of it are usually rectangular.
As in all neodymium-doped laser crystals, the lasing action of Nd:YVO4 is due to its content of neodymium ions, which may be excited by visible or infrared light, and undergo an electronic transition resulting in emission of coherent infrared light at a lower frequency, usually at 1064 nm (other transitions in Nd are available, and can be selected for by external optics).Neodymium aluminium borate
Neodymium aluminium borate is a chemical compound with the chemical formula NdAl3(BO3)4.Neodymium magnet
A neodymium magnet (also known as NdFeB, NIB or Neo magnet), the most widely used type of rare-earth magnet, is a permanent magnet made from an alloy of neodymium, iron and boron to form the Nd2Fe14B tetragonal crystalline structure. Developed independently in 1982 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet commercially available. They have replaced other types of magnets in many applications in modern products that require strong permanent magnets, such as motors in cordless tools, hard disk drives and magnetic fasteners.Nitto Denko
Nitto Denko Corporation (日東電工株式会社, Nittō Denkō Kabushiki-gaisha) is a Japanese company that produces tapes, vinyl, LCDs, insulation, and several other products. It was founded in Osaki, Tokyo in 1918 to produce electrical insulation and it survived World War II, despite the destruction of its central offices which has since moved to Osaka. Nitto is a member of the Mitsubishi UFJ Financial Group (MUFG) keiretsu.Praseodymium
Praseodymium is a chemical element with symbol Pr and atomic number 59. It is the third member of the lanthanide series and is traditionally considered to be one of the rare-earth metals. Praseodymium is a soft, silvery, malleable and ductile metal, valued for its magnetic, electrical, chemical, and optical properties. It is too reactive to be found in native form, and pure praseodymium metal slowly develops a green oxide coating when exposed to air.
Praseodymium always occurs naturally together with the other rare-earth metals. It is the fourth most common rare-earth element, making up 9.1 parts per million of the Earth's crust, an abundance similar to that of boron. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare-earth oxide residue he called didymium from a residue he called "lanthana", in turn separated from cerium salts. In 1885, the Austrian chemist Baron Carl Auer von Welsbach separated didymium into two elements that gave salts of different colours, which he named praseodymium and neodymium. The name praseodymium comes from the Greek prasinos (πράσινος), meaning "green", and didymos (δίδυμος), "twin".
Like most rare-earth elements, praseodymium most readily forms the +3 oxidation state, which is the only stable state in aqueous solution, although the +4 oxidation state is known in some solid compounds and, uniquely among the lanthanides, the +5 oxidation state is attainable in matrix-isolation conditions. Aqueous praseodymium ions are yellowish-green, and similarly praseodymium results in various shades of yellow-green when incorporated into glasses. Many of praseodymium's industrial uses involve its ability to filter yellow light from light sources.Promethium
Promethium is a chemical element with symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500-600 grams naturally occurring in Earth's crust at any given time, and one of only two such elements that are followed in the periodic table by elements with stable forms, a distinction shared with technetium. Chemically, promethium is a lanthanide. Promethium shows only one stable oxidation state of +3.
In 1902 Bohuslav Brauner suggested that there was a then-unknown element with properties intermediate between those of the known elements neodymium (60) and samarium (62); this was confirmed in 1914 by Henry Moseley who, having measured the atomic numbers of all the elements then known, found that atomic number 61 was missing. In 1926, two groups (one Italian and one American) claimed to have isolated a sample of element 61; both "discoveries" were soon proven to be false. In 1938, during a nuclear experiment conducted at Ohio State University, a few radioactive nuclides were produced that certainly were not radioisotopes of neodymium or samarium, but there was a lack of chemical proof that element 61 was produced, and the discovery was not generally recognized. Promethium was first produced and characterized at Oak Ridge National Laboratory in 1945 by the separation and analysis of the fission products of uranium fuel irradiated in a graphite reactor. The discoverers proposed the name "prometheum" (the spelling was subsequently changed), derived from Prometheus, the Titan in Greek mythology who stole fire from Mount Olympus and brought it down to humans, to symbolize "both the daring and the possible misuse of mankind's intellect". However, a sample of the metal was made only in 1963.
There are two possible sources for natural promethium: rare decays of natural europium-151 (producing promethium-147), and uranium (various isotopes). Practical applications exist only for chemical compounds of promethium-147, which are used in luminous paint, atomic batteries and thickness measurement devices, even though promethium-145 is the most stable promethium isotope. Because natural promethium is exceedingly scarce, it is typically synthesized by bombarding uranium-235 (enriched uranium) with thermal neutrons to produce promethium-147 as a fission product.Rare-earth magnet
Rare-earth magnets are strong permanent magnets made from alloys of rare-earth elements. Developed in the 1970s and 1980s, rare-earth magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as ferrite or alnico magnets. The magnetic field typically produced by rare-earth magnets can exceed 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla. There are two types: neodymium magnets and samarium–cobalt magnets. Magnetostrictive rare-earth magnets such as Terfenol-D also have applications, e.g. in loudspeakers. Rare-earth magnets are extremely brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from breaking, chipping, or crumbling into powder.
The development of rare-earth magnets began around 1966, when K. J. Strnat and G. Hoffer of the US Air Force Materials Laboratory discovered that an alloy of yttrium and cobalt, YCo5, had by far the largest magnetic anisotropy constant of any material then known. The term "rare earth" can be misleading, as these metals are not particularly rare or precious; they are about as abundant as tin or lead. However rare earth ores are unevenly distributed, with the major source being China, which has led countries to classify rare earth metals as strategically important. Recent Chinese export restrictions on these materials have led other countries to initiate research programs to develop strong magnets that do not require them.Samarium–neodymium dating
Samarium–neodymium dating is a radiometric dating method useful for determining the ages of rocks and meteorites, based on radioactive decay of a long-lived samarium (Sm) isotope to a radiogenic neodymium (Nd) isotope. Neodymium isotope ratios together with samarium-neodymium ratios are used to provide information on the source of igneous melts, as well as to provide age information. It is sometimes assumed that at the moment when crustal material is formed from the mantle the neodymium isotope ratio depends only on the time when this event occurred, but thereafter it evolves in a way that depends on the new ratio of samarium to neodymium in the crustal material, which will be different from the ratio in the mantle material. Samarium–neodymium dating allows us to determine when the crustal material was formed.
The usefulness of Sm–Nd dating stems from the fact that these two elements are rare earths and are thus, theoretically, not particularly susceptible to partitioning during sedimentation and diagenesis. Fractional crystallisation of felsic minerals changes the Sm/Nd ratio of the resultant materials. This, in turn, influences the rate at which the 143Nd/144Nd ratio increases due to production of radiogenic 143Nd.
In many cases, Sm–Nd and Rb–Sr isotope data are used together.Tarnish
Tarnish is a thin layer of corrosion that forms over copper, brass, silver, aluminum, magnesium, neodymium and other similar metals as their outermost layer undergoes a chemical reaction. Tarnish does not always result from the sole effects of oxygen in the air. For example, silver needs hydrogen sulfide to tarnish, although it may tarnish with oxygen over time. It often appears as a dull, gray or black film or coating over metal. Tarnish is a surface phenomenon that is self-limiting, unlike rust. Only the top few layers of the metal react, and the layer of tarnish seals and protects the underlying layers from reacting.
Tarnish actually preserves the underlying metal in outdoor use, and in this form is called patina. The formation of patina is necessary in applications such as copper roofing, and outdoor copper, bronze, and brass statues and fittings. Patina is the name given to tarnish on copper based metals.