Neodymium is achemical element; it hassymbolNd andatomic number 60. It is the fourth member of thelanthanide series and is considered to be one of therare-earth metals. It is ahard, slightlymalleable, silvery metal that quicklytarnishes in air and moisture. When oxidized, neodymium reacts quickly, producing pink, purple/blue, and yellow compounds in the +2, +3 and +4oxidation states. It is generally regarded as having one of the most complexspectra of the elements.[9] Neodymium was discovered in 1885 by the Austrian chemistCarl Auer von Welsbach, who also discoveredpraseodymium. Neodymium is present in significant quantities in the mineralsmonazite andbastnäsite. Neodymium is not found naturally in metallic form or unmixed with other lanthanides, and it is usually refined for general use. Neodymium is fairly common—about as common ascobalt,nickel, orcopper—and iswidely distributed in the Earth'scrust. Most of the world's commercial neodymium ismined in China, as is the case with many other rare-earth metals.
Neodymiumcompounds were first commercially used asglass dyes in 1927 and remain a popular additive. The color of neodymium compounds comes from the Nd3+ion and is often a reddish-purple. This color changes with the type of lighting because of the interaction of the sharp light absorption bands of neodymium with ambient light enriched with the sharp visible emission bands ofmercury, trivalenteuropium orterbium. Glasses that have beendoped with neodymium are used in lasers that emitinfrared with wavelengths between 1047 and 1062 nanometers. These lasers have been used in extremely high-power applications, such as ininertial confinement fusion. Neodymium is also used with various othersubstrate crystals, such asyttrium aluminium garnet in theNd:YAG laser.
Metallic neodymium has a bright, silvery metallic luster.[12] Neodymium commonly exists in twoallotropic forms, with a transformation from a double hexagonal to abody-centered cubic structure taking place at about 863 °C.[13] Neodymium, like most of the lanthanides, isparamagnetic at room temperature. It becomes anantiferromagnet upon cooling below 20 K (−253.2 °C).[14] Below this transition temperature it exhibits a set of complex magnetic phases[15][16] that have long spin relaxation times andspin glass behavior.[17] Neodymium is a rare-earthmetal that was present in the classicalmischmetal at a concentration of about 18%. To make neodymium magnets it is alloyed withiron, which is aferromagnet.[18]
Neodymium is the fourth member of thelanthanide series. In theperiodic table, it appears between the lanthanidespraseodymium to its left and the radioactive elementpromethium to its right, and above the actinideuranium. Its 60 electrons are arranged in theconfiguration [Xe]4f46s2, of which the six 4f and 6s electrons arevalence. Like most other metals in the lanthanide series, neodymium usually only uses three electrons as valence electrons, as afterwards the remaining 4f electrons are strongly bound: this is because the 4f orbitals penetrate the most through the inertxenon core of electrons to the nucleus, followed by 5d and 6s, and this increases with higher ionic charge. Neodymium can still lose a fourth electron because it comes early in the lanthanides, where the nuclear charge is still low enough and the 4f subshell energy high enough to allow the removal of further valence electrons.[19]
Neodymium has a melting point of 1,024 °C (1,875 °F) and a boiling point of 3,074 °C (5,565 °F). Like other lanthanides, it usually has theoxidation state +3, but can also form in the +2 and +4 oxidation states, and even, in very rare conditions, +0.[4] Neodymium metal quicklyoxidizes at ambient conditions,[13] forming an oxide layer likeiron rust that canspall off and expose the metal to further oxidation; a centimeter-sized sample of neodymium corrodes completely in about a year. Nd3+ is generally soluble in water. Like its neighborpraseodymium, it readily burns at about 150 °C to formneodymium(III) oxide; the oxide then peels off, exposing the bulk metal to the further oxidation:[13]
4Nd + 3O2 → 2Nd2O3
Neodymium is an electropositive element, and it reacts slowly with cold water, or quickly with hot water, to formneodymium(III) hydroxide:[20]
2Nd (s) + 6H2O (l) → 2Nd(OH)3 (aq) + 3H2 (g)
Neodymium metal reacts vigorously with all the stablehalogens:[20]
2Nd (s) + 3F2 (g) → 2NdF3 (s) [a violet substance]
2Nd (s) + 3Cl2 (g) → 2NdCl3 (s) [a mauve substance]
2Nd (s) + 3Br2 (g) → 2NdBr3 (s) [a violet substance]
2Nd (s) + 3I2 (g) → 2NdI3 (s) [a green substance]
Neodymium dissolves readily in dilutesulfuric acid to form solutions that contain the lilac Nd(III)ion. These exist as a [Nd(OH2)9]3+ complexes:[21]
Organoneodymium compounds are compounds that have a neodymium–carbon bond. These compounds are similar tothose of the other lanthanides, characterized by an inability to undergoπ backbonding. They are thus mostly restricted to the mostly ioniccyclopentadienides (isostructural with those of lanthanum) and the σ-bonded simple alkyls and aryls, some of which may bepolymeric.[23]
Naturally occurring neodymium (60Nd) is composed of five stableisotopes—142Nd,143Nd,145Nd,146Nd and148Nd, with142Nd being the most abundant (27.2% of thenatural abundance)—and tworadioisotopes with extremely long half-lives,144Nd (alpha decay with ahalf-life (t1/2) of2.29×1015 years) and150Nd (double beta decay,t1/2 ≈9.3×1018 years). In all, 35 radioisotopes of neodymium have been detected as of 2022[update], with the most stable radioisotopes being the naturally occurring ones:144Nd and150Nd. All of the remainingradioactive isotopes have half-lives that are shorter than twelve days, and the majority of these have half-lives that are shorter than 70 seconds; the most stableartificial isotope is147Nd with a half-life of 10.98 days.
Neodymium also has 15 knownmetastable isotopes, with the most stable one being139mNd (t1/2 = 5.5 hours),135mNd (t1/2 = 5.5 minutes) and133m1Nd (t1/2 ~70 seconds). The primarydecay modes before the most abundant stable isotope,142Nd, areelectron capture andpositron decay, and the primary mode after isbeta minus decay. The primarydecay products before142Nd arepraseodymium isotopes, and the primary products after142Nd arepromethium isotopes.[24] Four of the five stable isotopes are only observationally stable, which means that they are expected to undergo radioactive decay, though with half-lives long enough to be considered stable for practical purposes.[25] Additionally, some observationally stableisotopes of samarium are predicted to decay to isotopes of neodymium.[25]
Neodymium isotopes are used in various scientific applications.142Nd has been used for the production of short-livedisotopes of thulium andytterbium.146Nd has been suggested for the production of147Pm, which is a source of radioactive power. Several neodymium isotopes have been used for the production of other promethium isotopes. The decay from147Sm (t1/2 =1.06×1011 y) to the stable143Nd allows forsamarium–neodymium dating.[26]150Nd has also been used to studydouble beta decay.[27]
In 1751, the Swedish mineralogistAxel Fredrik Cronstedt discovered a heavy mineral from the mine atBastnäs, later namedcerite. Thirty years later, fifteen-year-oldWilhelm Hisinger, a member of the family owning the mine, sent a sample toCarl Scheele, who did not find any new elements within. In 1803, after Hisinger had become an ironmaster, he returned to the mineral withJöns Jacob Berzelius and isolated a new oxide, which they namedceria after thedwarf planetCeres, which had been discovered two years earlier.[29] Ceria was simultaneously and independently isolated in Germany byMartin Heinrich Klaproth.[30] Between 1839 and 1843, ceria was shown to be a mixture of oxides by the Swedish surgeon and chemistCarl Gustaf Mosander, who lived in the same house as Berzelius; he separated out two other oxides, which he namedlanthana anddidymia.[31][32][33] He partially decomposed a sample ofcerium nitrate by roasting it in air and then treating the resulting oxide with dilutenitric acid. The metals that formed these oxides were thus namedlanthanum anddidymium.[34] Didymium was later proven to not be a single element when it was split into two elements, praseodymium and neodymium, byCarl Auer von Welsbach inVienna in 1885.[35][36] Von Welsbach confirmed the separation byspectroscopic analysis, but the products were of relatively low purity. Pure neodymium was first isolated in 1925. The name neodymium is derived from the Greek wordsneos (νέος), new, anddidymos (διδύμος), twin.[13][37][38]
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 (>99%) neodymium was primarily obtained through anion exchange process frommonazite, a mineral rich in rare-earth elements.[13] The metal is obtained throughelectrolysis of itshalidesalts. Currently, most neodymium is extracted frombastnäsite and purified by solvent extraction. Ion-exchange purification is used for the highest purities (typically >99.99%). Since then, the glass technology has improved due to the improved purity of commercially available neodymium oxide and the advancement of glass technology in general. Early methods of separating the lanthanides depended on fractional crystallization, which did not allow for the isolation of high-purity neodymium until the aforementioned ion exchange methods were developed after World War II.[39]
Neodymium is rarely found in nature as a free element, instead occurring in ores such asmonazite andbastnäsite (which aremineral groups rather than single minerals) that contain small amounts of all rare-earth elements. Neodymium is rarely dominant in these minerals, with exceptions such as monazite-(Nd) and kozoite-(Nd).[40] The main mining areas are in China, United States, Brazil, India, Sri Lanka, and Australia.
The Nd3+ ion is similar in size to ions of the early lanthanides of thecerium group (those from lanthanum tosamarium andeuropium). As a result, it tends to occur along with them inphosphate,silicate andcarbonate minerals, such asmonazite (MIIIPO4) andbastnäsite (MIIICO3F), where M refers to all the rare-earth metals except scandium and the radioactivepromethium (mostly Ce, La, and Y, with somewhat less Pr and Nd).[41] Bastnäsite is usually lacking inthorium and the heavy lanthanides, and the purification of the light lanthanides from it is less involved than from monazite. The ore, after being crushed and ground, is first treated with hot concentrated sulfuric acid, which liberates carbon dioxide,hydrogen fluoride, andsilicon tetrafluoride. The product is then dried and leached with water, leaving the early lanthanide ions, including lanthanum, in solution.[41][failed verification]
Neodymium's per-particle abundance in theSolar System is 0.083ppb (parts per billion).[42][b] This figure is about two thirds of that ofplatinum, but two and a half times more than mercury, and nearly five times more than gold.[42] The lanthanides are not usually found in space, and are much more abundant in theEarth's crust.[42][43]
The world's production of neodymium was about 7,000 tons in 2004.[37] As of 2015 the bulk of production and reserves of rare-earths is in China.[44] 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.[45][46]
Neodymium is typically 10–18% of the rare-earth content of commercial deposits of the light rare-earth-element minerals bastnäsite and monazite.[13] 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 thetin deposits inLlallagua, Bolivia;ancylite fromMont Saint-Hilaire,Quebec, Canada; or lanthanite fromLower Saucon Township, Pennsylvania. As with neodymium glasses, such minerals change their colors under the differing lighting conditions. The absorption bands of neodymium interact with the visibleemission spectrum ofmercury 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.[47]
The demand for mineral resources, such asrare-earth elements (including neodymium) and other critical materials, has been rapidly increasing owing to the growing humanpopulation and industrial development. Recently, the requirement for a low-carbon society has led to a significant demand for energy-saving technologies such as batteries, high-efficiency motors, renewable energy sources, and fuel cells. Among these technologies, permanent magnets are often used to fabricate high-efficiency motors, with neodymium-iron-boron magnets (Nd2Fe14B sintered and bonded magnets; hereinafter referred to asNdFeB magnets) being the main type of permanent magnet in the market since their invention.[48] NdFeB magnets are used inhybrid electric vehicles,plug-in hybrid electric vehicles,electric vehicles,fuel cell vehicles,wind turbines,home appliances, computers, and many small consumer electronic devices.[49] Furthermore, they are indispensable for energy savings. Toward achieving the objectives of theParis Agreement, the demand for NdFeB magnets is expected to increase significantly in the future.[49]
Neodymium magnets (an alloy, Nd2Fe14B) are the strongestpermanent magnets known. A neodymium magnet of a few tens of grams can lift a thousand times its own weight, and can snap together with enough force to break bones. These magnets are cheaper, lighter, and stronger thansamarium–cobalt magnets. However, they are not superior in every aspect, as neodymium-based magnets lose their magnetism at lower temperatures[50] and tend to corrode,[51] while samarium–cobalt magnets do not.[52]
Neodymium magnets appear in products such asmicrophones, professionalloudspeakers,headphones,guitar andbass guitarpick-ups, and computerhard disks where low mass, small volume, or strong magnetic fields are required. Neodymium is used in the electric motors of hybrid and electric automobiles[49] and in the electricity generators of some designs of commercial wind turbines (only wind turbines with "permanent magnet" generators use neodymium).[53] For example, drive electric motors of eachToyota Prius require one kilogram (2.2 pounds) of neodymium per vehicle.[11] Permanentneodymium iron boride (Nd2Fe14B) magnets are often made with heavy rare earth elements likedysprosium andterbium assubstituents to improve their performance in heated conditions, since the magnets lose performance rapidly above room temperature.[54] Neodymium magnets are used in medical devices such as MRI and treatments for chronic pain and wound healing.[55]
A neodymium glasslight bulb, with the base and inner coating removed, under two different types of light:fluorescent on the left, andincandescent on the right.Didymium glasses
Neodymium glass (Nd:glass) is produced by the inclusion ofneodymium oxide (Nd2O3) in the glass melt. In daylight orincandescent light neodymium glass appears lavender, but it appears pale blue underfluorescent lighting. Neodymium may be used to color glass in shades ranging from pure violet through wine-red and warm gray.[56]
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.[57] Current sources include glassmakers in the Czech Republic, the United States, and China.[58]
The sharp absorption bands of neodymium cause the glass color to change under different lighting conditions, being reddish-purple underdaylight or yellowincandescent light, blue under whitefluorescent lighting, and greenish undertrichromatic lighting. In combination withgold orselenium, red colors are produced. 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 thesilica 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 thelime content of the glass might have needed adjustments.[59]
Light transmitted through neodymium glasses shows unusually sharpabsorption bands; the glass is used inastronomical work to produce sharp bands by whichspectral lines may be calibrated.[13] 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.[60] Neodymium is also used to remove the green color caused by iron contaminants from glass.[61]
Nd:YAG laser rod
Neodymium is a component of "didymium" (referring to mixture of salts of neodymium andpraseodymium) 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 inincandescent light bulbs. These lamps contain neodymium in the glass to filter out yellow light, resulting in a whiter light which is more like sunlight.[62] DuringWorld War I, didymium mirrors were reportedly used to transmitMorse code across battlefields.[63] Similar to its use in glasses, neodymium salts are used as a colorant forenamels.[13]
Certain transparent materials with a small concentration of neodymium ions can be used in lasers asgain media for infrared wavelengths (1054–1064 nm), e.g.Nd:YAG (yttrium aluminium garnet), Nd:YAP (yttrium aluminiumperovskite),[64]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 commercialDPSS hand-held lasers andlaser pointers.[65]
Trivalent neodymium ion Nd3+ was the first lanthanide from rare-earth elements used for the generation of laser radiation. The Nd:CaWO4 laser was developed in 1961.[66] Historically, it was the third laser which was put into operation (the first was ruby, the second the U3+:CaF laser). Over the years the neodymium laser became one of the most used lasers for application purposes. The success of the Nd3+ ion lies in the structure of its energy levels and in the spectroscopic properties suitable for the generation of laser radiation. In 1964 Geusic et al.[67] demonstrated the operation of neodymium ion in YAG matrix Y3Al5O12. It is a four-level laser with lower threshold and with excellent mechanical and temperature properties. For optical pumping of this material it is possible to use non-coherent flashlamp radiation or a coherent diode beam.[68]
Neodymium ions in various types of ionic crystals, and also in glasses, act as a laser gain medium, typically emitting 1064 nm light from a particular atomic transition in the neodymium ion, after being "pumped" into excitation from an external source.
The current laser at the UKAtomic 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 106K, from which opacity and transmission of radiation are measured.[69]
Probably because of similarities to Ca2+, Nd3+ has been reported[74] to promote plant growth. Rare-earth element compounds are frequently used in China asfertilizer.[75]
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. Ingested neodymium salts are regarded as more toxic if they are soluble than if they are insoluble.[87] Neodymium dust and salts are very irritating to the eyes andmucous membranes, and moderately irritating to skin. Breathing the dust can cause lungembolisms, and accumulated exposure damages the liver. Neodymium also acts as ananticoagulant, especially when given intravenously.[37]
Neodymium magnets have been tested for medical uses such as magnetic braces and bone repair, butbiocompatibility issues have prevented widespread applications.[88] 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. 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.[89]
Another risk of these powerful magnets is that if more than one magnet is ingested, they can pinch soft tissues in thegastrointestinal tract. This has led to an estimated 1,700 emergency room visits[90] and necessitated the recall of theBuckyballs line of toys, which were construction sets of small neodymium magnets.[90][91]
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