Neodymium
Chemical element with atomic number 60 (Nd)
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Neodymium is a chemical element; it has symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes in air and moisture. When oxidized, neodymium reacts quickly, producing pink, purple/blue, and yellow compounds in overwhelmingly the +3 oxidation state, although highly rare and reactive +2 and +4 compounds are known. It is generally regarded as having one of the most complex spectra of the elements.[9] Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach, who also discovered praseodymium. Neodymium is present in significant quantities in the 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. Neodymium is fairly common—about as common as cobalt, nickel, or copper—and is widely distributed in the Earth's crust. Most of the world's commercial neodymium is mined in China, as is the case with many other rare-earth metals.
Neodymium metal in a glass vial | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Neodymium | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Pronunciation | /ˌniːoʊˈdɪmiəm/ ⓘ | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Appearance | silvery white | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Standard atomic weight Ar°(Nd) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Neodymium in the periodic table | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Atomic number (Z) | 60 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Group | f-block groups (no number) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Period | period 6 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Block | f-block | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electron configuration | [Xe] 4f4 6s2 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electrons per shell | 2, 8, 18, 22, 8, 2 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Physical properties | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Phase at STP | solid | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Melting point | 1295 K (1022 °C, 1872 °F)[3] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Boiling point | 3347 K (3074 °C, 5565 °F) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Density (at 20° C) | 7.007 g/cm3 [3] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Specific heat capacity | 190.308 J/(kg·K) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
Vapor pressure
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| Atomic properties | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Oxidation states | common: +3 0,[4] +2,[5] +4[5] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electronegativity | Pauling scale: 1.14 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Ionization energies |
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| Atomic radius | empirical: 181 pm | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Covalent radius | 201±6 pm | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
_NIST_ASD_emission_spectrum.png) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Other properties | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Natural occurrence | primordial | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Crystal structure | double hexagonal close-packed (dhcp) (hP4) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Lattice constants |  c = 1.17968 nm (at 20 °C)[3] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Thermal expansion | 6.7×10−6/K (at 20 °C)[3][a] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Thermal conductivity | 16.5 W/(m⋅K) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electrical resistivity | poly: 643 nΩ⋅m | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Magnetic ordering | paramagnetic, antiferromagnetic below 20 K[6] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Molar magnetic susceptibility | +5628.0×10−6 cm3/mol (287.7 K)[7] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Young's modulus | 41.4 GPa | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Shear modulus | 16.3 GPa | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Bulk modulus | 31.8 GPa | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Speed of sound thin rod | 2330 m/s (at 20 °C) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Poisson ratio | 0.281 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Vickers hardness | 345–745 MPa | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Brinell hardness | 265–700 MPa | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| CAS Number | 7440-00-8 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| History | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Naming | after Greek νέος, "new", and δίδυμος, "twin" (of lanthanum) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Discovery | Carl Gustaf Mosander (1841) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| First isolation | Carl Auer von Welsbach (1885) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Named by | Carl Auer von Welsbach (1885) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Isotopes of neodymium | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Neodymium compounds were first commercially used as glass 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 of mercury, trivalent europium or terbium. Glasses that have been doped with neodymium are used in lasers that emit infrared with wavelengths between 1046 and 1062 nanometers. These lasers have been used in extremely high-power applications, such as in inertial confinement fusion. Neodymium is also used with various other substrate crystals, such as yttrium aluminium garnet in the Nd:YAG laser.
Neodymium alloys are used to make high-strength neodymium magnets, which are powerful permanent magnets.[10] These magnets are widely used in products like microphones, professional loudspeakers, in-ear headphones, high-performance hobby DC electric motors, and computer hard disk drives, where low magnet mass (or volume) or strong magnetic fields are required. Larger neodymium magnets are used in electric motors with high power-to-weight ratios (e.g., in hybrid cars) and generators (e.g., aircraft and wind turbine electric generators).[11]
Physical properties
Neodymium is a silvery-white metal with a density of 7.01 g/cm3 at room temperature.[12] Its freshly exposed surface has a metallic luster, which is lost as the metal tarnishes in air. It melts at approximately 1,024 °C (1,875 °F) and boils at 3,074 °C (5,565 °F).[13]
Measurements on high-purity polycrystalline neodymium give an electrical resistivity of approximately 65 μΩ·cm at 18 °C (64 °F).[14] Ultrasonic measurements have yielded ambient-pressure bulk and shear moduli of approximately 33 and 14 GPa, respectively, describing the metal's resistance to compression and shear deformation. Under increasing pressure, both compressional and shear sound velocities rise until about 5.4 GPa, after which they change little; this behavior has been associated with instability of the crystal structure.[15]
At room temperature and atmospheric pressure, neodymium has a double hexagonal close-packed (dhcp) structure. Its close-packed atomic layers repeat in an ABAC sequence, creating two distinct environments for the atoms: those in the A layers have approximately cubic local symmetry, whereas those in the B and C layers have hexagonal local symmetry. The hexagonal unit cell has lattice parameters of approximately a = 3.658 Å and c = 11.802 Å.[16] On heating at atmospheric pressure, this structure transforms into a body-centered cubic phase at about 863 °C (1,585 °F).[17][13]
Compression produces a different sequence of transformations. At room temperature, a face-centered cubic phase has been reported at about 3.8 GPa, followed by a distorted face-centered cubic phase above approximately 18 GPa.[15] At still higher pressures, a monoclinic structure has been identified above about 75 GPa and observed up to 153 GPa.[18]
Neodymium is paramagnetic at room temperature and develops antiferromagnetic order below approximately 19.9 K. Further cooling produces a succession of magnetic phases involving the two types of atomic site. The magnetic order is spatially modulated, rather than consisting of a simple alternation between oppositely directed moments. Neutron-scattering measurements have revealed magnetic patterns with characteristic lengths of approximately 4.2–6.3 nm. Their arrangement changes with temperature and with the strength and direction of an applied magnetic field.[16]
Experiments on crystalline neodymium films have also identified a self-induced spin-glass state. The magnetic arrangement lacks long-range order and evolves slowly with time, even though the atoms occupy an ordered crystal lattice.[19] On warming, these films can become more magnetically ordered: imaging near 5 K showed a glassy state, whereas at 11 K the same region contained extended, regularly ordered magnetic domains. This unusual transition has been attributed to a reduction in competing magnetic interactions as the temperature rises.[20]
Neodymium is also a constituent of mischmetal, a mixture of rare-earth metals whose traditional composition contains about 18% neodymium.[13] Alloying neodymium with iron and boron produces the ferromagnetic compound Nd2Fe14B, which forms the magnetic phase in neodymium permanent magnets.[21]
Chemical properties
Neodymium is the fourth member of the lanthanide series, between praseodymium and promethium in the periodic table. Its 60 electrons have the electron configuration [Xe]4f46s2, with four 4f electrons and two 6s electrons outside the closed-shell xenon core. Its most common oxidation state is +3.[12] Formation of the Nd3+ ion removes the two 6s electrons and one 4f electron, leaving the configuration [Xe]4f3. The remaining 4f electrons are more tightly bound, favoring the trivalent state.[22] Compounds containing neodymium in the +2 and +4 oxidation states are also known.[23][24]
The metal tarnishes in air. Its surface oxide can flake away, exposing fresh metal and allowing oxidation to continue.[13] On burning in oxygen, it forms neodymium(III) oxide:[25]
- 4 Nd + 3 O2 → 2 Nd2O3
Neodymium is electropositive and reacts with water to produce neodymium(III) hydroxide and hydrogen. The reaction is slow in cold water and faster in hot water:[25]
- 2 Nd + 6 H2O → 2 Nd(OH)3 + 3 H2
It also dissolves in dilute sulfuric acid, releasing hydrogen and forming a lilac solution containing hydrated neodymium(III) ions.[25]
- 2 Nd(s) + 3 H2SO4(aq) → 2 Nd3+(aq) + 3 SO2−4(aq) + 3 H2(g)
In aqueous solution, water molecules coordinate to neodymium(III). A model with nine directly coordinated water molecules, [Nd(H2O)9]3+, agrees closely with spectroscopic measurements of the aqua ion.[26]
Compounds
Some neodymium compounds change their apparent color under different types of illumination.[27]
Neodymium sulfate, nitrate, and chloride (left to right) under fluorescent tube lighting
The compounds under compact fluorescent lighting
The compounds in daylight
| Compound | Formula | Crystal structure |
|---|---|---|
| Neodymium(III) oxide | Nd2O3 | Hexagonal and cubic forms[28] |
| Neodymium monoxide | NdO | Cubic, rock-salt type[29] |
| Monosulfide, monoselenide, and monotelluride | NdS, NdSe, NdTe | Cubic, rock-salt type[30] |
| Neodymium tetraboride | NdB4 | Tetragonal[31] |
| Neodymium hexaboride | NdB6 | Cubic[32] |
| Neodymium trihydride | NdH3 | Trigonal, tysonite type[33] |
Oxides
Neodymium(III) oxide, Nd2O3, also called neodymia, occurs in hexagonal and cubic crystal forms. Both react with atmospheric moisture and carbon dioxide, undergoing hydration and carbonation; these changes occur more rapidly in the cubic samples studied.[28] The oxide can also be prepared by the thermal decomposition of neodymium(III) oxalate. The decomposition proceeds through several stages, whose course depends on whether heating takes place in an oxidizing or inert atmosphere.[34]
Neodymium monoxide, NdO, has also been synthesized at high pressure and temperature. It adopts the rock-salt structure and is metastable. One preparation used a pressure of 5 GPa and a temperature of 1,473 K (1,200 °C). Its properties differ between bulk samples and thin films; films 45 nm thick have been reported to show ferromagnetic ordering below approximately 19 K.[29]
Chalcogenides
Neodymium forms compounds with sulfur, selenium, and tellurium, including the monochalcogenides NdS, NdSe, and NdTe. These are metallic compounds with the rock-salt structure. Neutron diffraction measurements show that all three develop antiferromagnetic order at low temperatures. Their magnetic structures are similar, although the direction of the ordered magnetic moments in the sulfide differs from those in the selenide and telluride.[30]
Neodymium telluride is stable at high temperatures, with a reported melting point of about 2,025 °C (3,677 °F). Its formation has been investigated as a way of binding neodymium produced in uranium–zirconium nuclear fuel, thereby limiting its availability to react with the fuel cladding.[35]
Halides
Neodymium reacts with fluorine, chlorine, bromine, and iodine to form the corresponding trihalides: NdF3, NdCl3, NdBr3, and NdI3. These reactions can be represented by the general equation below, where X denotes a halogen:[25]
- 2 Nd + 3 X2 → 2 NdX3
The fluoride and bromide are described as violet, the chloride as mauve, and the iodide as green.[25]
Neodymium(III) chloride can also be prepared in an anhydrous form by heating neodymium(III) oxide with ammonium chloride. The resulting chloride is sensitive to moisture.[36]
Lower halides include neodymium(II) chloride, NdCl2,[37] and neodymium(II) iodide, NdI2, which can be prepared by direct reaction of neodymium metal with iodine under controlled conditions.[23] It acts as a reducing agent: in tetrahydrofuran, it converts several alkyl and aryl halides into the corresponding hydrocarbons.[38]
Borides
Neodymium forms borides including the tetraboride, NdB4, and hexaboride, NdB6. Neodymium tetraboride has a tetragonal structure in which the boron atoms form an interconnected network and the neodymium atoms form layers of squares and triangles.[31] Large single crystals can be grown by the floating-zone method, in which a molten region is moved along a rod of the starting material.[39]
The tetraboride is a frustrated magnet, in which competing magnetic interactions give rise to several low-temperature phases. Its response to an applied magnetic field depends strongly on the field's direction relative to the crystal axes. At low temperatures, a field applied along the c axis produces a plateau in the magnetization at approximately one-fifth of its saturation value.[40]
Neodymium hexaboride
Neodymium hexaboride, NdB6, has a cubic structure consisting of an interconnected framework of boron octahedra with neodymium atoms in the spaces between them.[32] Like the tetraboride, it can be grown as large single crystals by the floating-zone method.[41] It becomes antiferromagnetic below a Néel temperature of approximately 8.6 K.[42]
Hydroxide and salts
Neodymium(III) sulfate
Neodymium(III) acetate
Neodymium(III) hydroxide
sulfat.JPG)
_acetate.jpg)
_hydroxide.jpg)
Neodymium(III) hydroxide, Nd(OH)3, is sparingly soluble in water but dissolves in hydrochloric acid.[43]
Other salts include neodymium(III) carbonate, Nd2(CO3)3, which has been studied in the hydrated form Nd2(CO3)3·8H2O,[44] and neodymium(III) sulfate, Nd2(SO4)3, whose octahydrate has been investigated by infrared spectroscopy.[45]
Neodymium(III) acetate, Nd(CH3COO)3, also forms a monohydrate. Heating this hydrate removes its water of crystallization; further heating of the anhydrous salt releases acetone and carbon dioxide and produces an oxycarbonate through intermediate compounds.[46]
Other inorganic compounds
Reaction of neodymium metal with hydrogen produces hydrides whose structures depend on their hydrogen content. The trihydride, NdH3, has a trigonal structure related to that of tysonite. Neutron diffraction studies of its deuterium analogue, NdD3, have identified deuterium atoms in both tetrahedral and approximately triangular sites within the metal framework. Hydrogen-deficient compositions can instead have a cubic metal sublattice.[33]
Neodymium nitride, NdN, has been studied as a magnetic semiconductor. Thin films grown by molecular beam epitaxy have shown an optical band gap of about 0.9 eV and ferromagnetic ordering below about 43 K. The magnetic moment is dominated by the orbital contribution, and the measured properties depend on factors including strain and nitrogen vacancies.[47]
Neodymium also forms binary compounds with other pnictogens, including the phosphide NdP, arsenide NdAs, and antimonide NdSb. These have the rock-salt structure and show antiferromagnetic ordering at low temperatures.[48] Its carbides include the tetragonal dicarbide, NdC2, and cubic sesquicarbide, Nd2C3.[49]
Organometallic compounds
Organoneodymium compounds contain bonds between neodymium and carbon. They include cyclopentadienyl complexes, in which neodymium binds to carbon rings, and compounds with σ-bonded alkyl or aryl groups. Some of these compounds have polymeric structures. The cyclopentadienyl compounds include structures analogous to those of lanthanum.[50] Studies of substituted cyclopentadienyl complexes have found that their neodymium–ligand bonding is predominantly electrostatic, with little covalent character.[51]
Neodymium complexes are studied as catalysts for polymerization, particularly for controlling the arrangement of repeating units in polymers made from dienes. Neodymium-based catalytic systems have also been developed for vinyl monomers and ε-caprolactone.[52]
Isotopes
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| Standard atomic weight Ar°(Nd) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Natural neodymium contains seven isotopes: 142Nd, 143Nd, 144Nd, 145Nd, 146Nd, 148Nd, and 150Nd. The most abundant is 142Nd, which accounts for approximately 27.2% of natural neodymium.[53] Five of these isotopes have no observed radioactive decay. Of those five, 143Nd, 145Nd, 146Nd, and 148Nd are predicted to undergo extremely slow alpha decay and are therefore described as observationally stable.[54]
The other two natural isotopes are primordial radionuclides, whose long half-lives have allowed them to survive since before the formation of Earth. Neodymium-144 undergoes alpha decay to 140Ce with a half-life of (2.29±0.16)×1015 years.[54] Neodymium-150 undergoes double beta decay to 150Sm; the NEMO-3 experiment measured a half-life of approximately 9.3×1018 years for the transition to the daughter's ground state.[55]
Apart from these two primordial radionuclides, the known radioisotopes are short-lived. The longest-lived of these is 147Nd, with a half-life of 10.98 days, followed by 140Nd at 3.37 days. Neutron-deficient isotopes generally decay by electron capture or positron emission to praseodymium, whereas neutron-rich isotopes generally undergo beta-minus decay to promethium. Neodymium also has numerous nuclear isomers, in which the nucleus occupies a relatively long-lived excited state. The longest-lived is 139mNd, with a half-life of 5.5 hours; other examples include 135mNd at 5.5 minutes and 133m1Nd at approximately 70 seconds.[56]
Neodymium isotope ratios are used in geochronology and geochemistry. The alpha decay of 147Sm to 143Nd, with a half-life of approximately 1.07×1011 years,[56] forms the basis of samarium–neodymium dating. Measurements of the 143Nd/144Nd ratio, together with samarium-to-neodymium ratios, are used to investigate the ages and origins of rocks and the evolution of Earth's crust and mantle.[57] Other samarium isotopes are predicted to produce neodymium through unobserved alpha decays, including the decay of 149Sm to 145Nd.[54]
Neodymium isotopes are also used as targets for producing other radionuclides. Neutron capture by 146Nd produces 147Nd, which undergoes beta-minus decay to 147Pm. Irradiation of enriched 146Nd targets has been investigated as a source of 147Pm for betavoltaic batteries, which convert energy from beta radiation into electricity.[58] Bombardment of natural neodymium with deuterons has produced promethium isotopes including 143Pm, 144Pm, 146Pm, and 149Pm.[59] Enriched 142Nd targets have been used with fluorine and neon ion beams to produce short-lived thulium and ytterbium isotopes, including 153Tm, 154Tm, 154Yb, and 155Yb.[60]
Several neodymium isotopes occur among the products of nuclear fission. Measurements of 148Nd in spent nuclear fuel are used to determine burnup, the extent to which the fuel has undergone fission. Measurements of other neodymium isotopes can provide additional estimates and reduce uncertainty.[61]
Neodymium-150 is studied in experiments on double beta decay. Its relatively high decay energy of about 3.37 MeV makes it a candidate for searches for neutrinoless double beta decay, a hypothetical process that would establish that the neutrino is its own antiparticle. Its observed two-neutrino decay, in which two electrons and two antineutrinos are emitted, has been measured for transitions to both the ground state and an excited state of 150Sm. These measurements help test nuclear models used to interpret searches for neutrinoless decay.[62]
History
The discovery of neodymium followed a series of investigations of cerite, a mineral examined by the Swedish mineralogist Axel Fredrik Cronstedt in 1751. Carl Wilhelm Scheele subsequently analysed the mineral without identifying a new element. In 1803, Jöns Jacob Berzelius and Wilhelm Hisinger identified cerium in cerite; Martin Heinrich Klaproth made the discovery independently at about the same time. Berzelius and Hisinger named the new element after Ceres. Their material was an oxide, known as ceria, rather than the isolated metal.[64]
During the late 1830s and early 1840s, Carl Gustaf Mosander's studies of cerium compounds led to the identification of lanthanum and a further component that he named didymium.[65] The name, derived from the Greek for 'twin', referred to didymium's close association with lanthanum.[66] Didymium was initially accepted as an element and appeared in Dmitri Mendeleev's 1869 periodic table.[65] However, its composition was questioned as further samples were studied. In 1882, Bohuslav Brauner reported that didymium obtained from different minerals varied in composition.[63]
In 1885, the Austrian chemist Carl Auer von Welsbach separated didymium into praseodymium and neodymium in Vienna.[63] He used repeated fractional crystallization of double ammonium nitrate salts, exploiting small differences in their solubility. The smaller fraction, which formed green salts, was named praseodymium, while the larger fraction was named neodymium.[65] Spectroscopic analysis distinguished the two components.[63] The name neodymium combines the Greek neos ('new') and didymos ('twin'). Although the element had been identified in its compounds, neodymium metal was not isolated in relatively pure form until 1925.[66]
Separation of the rare-earth elements continued to rely on laborious fractional crystallization methods into the twentieth century, before the development of ion exchange techniques in the 1940s.[67] In 1947, Frank Spedding and his colleagues reported the separation of neodymium and praseodymium using ion-exchange columns.[68] Subsequent improvements at Iowa State College, including the use of EDTA as a complexing agent, led to a pilot plant operating by 1953. These methods were scaled up to produce kilogram quantities of purified rare-earth salts and were adopted by commercial producers, increasing the availability of the separated elements for research and industrial use.[69]
Occurrence and production
Occurrence
Neodymium occurs naturally in minerals containing other rare-earth elements.[70] Its estimated abundance in the Earth's crust is about 41 mg/kg, comparable to that of lanthanum.[71] Although rare-earth elements are relatively widespread, deposits in which they are sufficiently concentrated for economic extraction are less common.[72]
Like the other lanthanides, neodymium has a strong affinity for oxygen and occurs in phosphate, carbonate and silicate minerals. The size of the Nd3+ ion is similar to those of the neighbouring light lanthanides, which allows these elements to occupy the same sites in mineral structures. Consequently, neodymium commonly accompanies lanthanum, cerium and praseodymium.[73]
The principal commercial sources include bastnäsite, a group of rare-earth fluorocarbonates, and monazite, a group of rare-earth phosphates. These minerals generally contain several rare-earth elements, rather than neodymium alone.[72] Minerals in which neodymium is the dominant rare-earth constituent include monazite-(Nd), (Nd,La,Ce)PO4,[74] and kozoite-(Nd), NdCO3(OH). The latter was first described from cavities and fissures in basalt in Saga Prefecture, Japan, where it forms pale pinkish-purple to white aggregates.[75]
Major light-rare-earth deposits are associated with carbonatites and related igneous and hydrothermal activity. Examples include Mountain Pass in California and Bayan Obo in Inner Mongolia. Weathering can further concentrate rare-earth minerals, as at Mount Weld in Western Australia. Monazite also accumulates in placer deposits, where erosion and sedimentary sorting concentrate dense minerals in river or coastal sands.[72]
Neodymium is also present in meteorites and the solar photosphere. A 2025 compilation estimated its Solar System abundance at approximately 0.88 atoms per million silicon atoms, adopting the abundance measured in CI chondrites.[76]
Production
Ore processing
Production begins with the concentration of rare-earth-bearing minerals. For hard-rock ores, crushing and grinding liberate mineral grains from the surrounding rock. Froth flotation, gravity separation, magnetic separation and electrostatic separation are used in different combinations according to the ore's mineralogy. These operations exploit differences in surface properties, density, magnetism or electrical conductivity to separate the valuable minerals from gangue. They produce a mineral concentrate containing a mixture of rare-earth elements.[77]
The concentrate is then chemically treated to bring the rare-earth elements into solution. One industrial method is the sulfuric acid bake and leach process: heating the concentrate with concentrated acid converts rare-earth minerals into sulfates, which can subsequently be dissolved by leaching with water. The acid requirement, heating conditions and efficiency of extraction depend on the minerals present, so the treatment is adapted to the particular feedstock.[78]
Ore composition also affects the treatment of impurities and residues. Monazite commonly contains thorium, whereas bastnäsite generally contains less. Processing must separate these radioactive constituents from the rare-earth products and manage the resulting residues; the quantities involved depend on the deposit and processing route.[78][72]
Separation and purification
Separating neodymium from the other rare-earth elements is difficult because their trivalent ions have similar chemical properties. Industrial separation principally uses solvent extraction, in which an aqueous solution is contacted with an organic liquid containing an extractant. The elements partition differently between the two liquids, allowing successive extraction and washing stages to enrich particular rare earths. The extracted metals are subsequently transferred back into an aqueous solution in a step known as stripping. Complete separation can require many stages arranged in mixer-settler systems.[79]
Depending on the intended product, a separation plant may recover neodymium individually or produce a mixed praseodymium–neodymium fraction for permanent-magnet manufacture. Ion exchange is also used to obtain smaller quantities of highly purified rare earths.[79] In this process, dissolved ions bind reversibly to charged sites on a solid resin. Differences in their interactions with the resin and the solutions passed through it allow them to be separated.[80]
Following separation, neodymium can be recovered from solution by precipitation as an oxalate. Heating the precipitate converts it into neodymium(III) oxide, Nd2O3, which serves as a starting material for production of the metal.[81]
Metal production
An industrial route to neodymium metal is electrolysis of its oxide dissolved in a molten mixture of neodymium(III) fluoride and lithium fluoride. Neodymium ions are reduced at the cathode, and the molten metal collects at the bottom of the cell. A graphite anode is consumed during the process, producing carbon monoxide and carbon dioxide. The preparation of the fluoride electrolyte and the electricity consumed during electrolysis contribute to the environmental impacts of metal production.[81]
The metal can also be prepared by reducing anhydrous neodymium halides with calcium. For neodymium(III) fluoride, the reaction produces neodymium metal and calcium fluoride:[70]
- 2 NdF3 + 3 Ca → 2 Nd + 3 CaF2
Supply
The production and refining of neodymium are closely associated with those of the other rare earths used in magnets. According to the International Energy Agency, China accounted for 60% of mined output and 91% of refined output of these elements in 2024. These figures cover neodymium, praseodymium, dysprosium and terbium together.[82]
Demand is supported by the use of permanent magnets in electric vehicles, wind turbines and industrial motors. In its 2026 assessment, the agency reported that demand for the four magnet rare earths had doubled since 2015 and projected a further increase of approximately one-third by 2030 under the policy settings used in the assessment.[82]
Recycling
Scrap from magnet manufacture and discarded neodymium–iron–boron magnets provide secondary sources of neodymium. These magnets typically contain approximately 31–32% rare-earth elements by mass, principally neodymium and praseodymium, with some grades also containing dysprosium or terbium. Recovering magnets from discarded products can require dismantling equipment and removing coatings, adhesives and other attached materials.[83]
Recycling routes either recover the rare-earth elements chemically or reuse the magnetic alloy. Hydrometallurgical methods dissolve the material and separate the rare earths from iron and other constituents before recovering rare-earth compounds. Direct recycling instead preserves the alloy for remelting or reprocessing into magnets. The appropriate route depends on the composition, oxidation and contamination of the scrap.[83]
One direct-recycling method uses hydrogen to break sintered magnets into a demagnetised, hydrogenated powder. The powder can be mechanically separated from components such as hard disk drives and cleaned to reduce contamination from coatings. It can then be blended and resintered into new magnets, remelted, or subjected to further processing. The properties obtainable from the recycled material depend on the feedstock and the treatment used.[84]
Applications
Magnets
Neodymium magnets (an alloy, Nd2Fe14B) are the strongest permanent 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 than samarium–cobalt magnets. However, they are not superior in every aspect, as neodymium-based magnets lose their magnetism at lower temperatures[85] and tend to corrode,[86] while samarium–cobalt magnets do not.[87]
Neodymium magnets appear in products such as microphones, professional loudspeakers, headphones, guitar and bass guitar pick-ups, and computer hard disks where low mass, small volume, or strong magnetic fields are required. Neodymium is used in the electric motors of hybrid and electric automobiles[88] and in the electricity generators of some designs of commercial wind turbines (only wind turbines with "permanent magnet" generators use neodymium).[89] For example, drive electric motors of each Toyota Prius require one kilogram (2.2 pounds) of neodymium per vehicle.[11] Permanent neodymium iron boride (Nd2Fe14B) magnets are often made with heavy rare earth elements like dysprosium and terbium as substituents to improve their performance in heated conditions, since the magnets lose performance rapidly above room temperature.[90] Neodymium magnets are used in medical devices such as MRI and treatments for chronic pain and wound healing.[91]
Glass
Neodymium glass (Nd:glass) is produced by the inclusion of neodymium oxide (Nd2O3) in the glass melt. 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 shades ranging from pure violet through wine-red and warm gray.[92]
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.[93] Current sources include glassmakers in the Czech Republic, the United States, and China.[94]
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, blue under white fluorescent lighting, and greenish under trichromatic lighting. In combination with gold or selenium, 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 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 needed adjustments.[95]
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.[17] 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.[96] Neodymium is also used to remove the green color caused by iron contaminants from glass.[97]
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.[98] During World War I, didymium mirrors were reportedly used to transmit Morse code across battlefields.[99] Similar to its use in glasses, neodymium salts are used as a colorant for enamels.[17]
Lasers
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:YAP (yttrium aluminium perovskite),[100] 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.[101]
The 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.[102] 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.[103] 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.[104]
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.[105]
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.[106]
Other
Other applications of neodymium include:
- Neodymium has an unusually large specific heat capacity at liquid-helium temperatures, so is useful in cryocoolers.[107][108]
- Neodymium acetate can be used as a standard contrasting agent in electron microscopy (a substitute for the radioactive and toxic uranyl acetate).[109]
- Probably because of similarities to Ca2+, Nd3+ has been reported[110] to promote plant growth. Rare-earth element compounds are frequently used in China as fertilizer.[111]
- Samarium–neodymium dating is useful for determining the age relationships of rocks[112] and meteorites.[113]
- Neodymium isotopes recorded in marine sediments are used to reconstruct changes in past ocean circulation.[114][115]
Biological role and precautions
| Hazards | |
|---|---|
| GHS labelling: | |
  | |
| Danger | |
| H228, H251, H315, H319 | |
| P210, P235, P240, P241, P302+P352, P305+P351+P338[116] | |
| NFPA 704 (fire diamond) | |
| Hazards | |
|---|---|
| GHS labelling: | |
| |
| Warning | |
| H315, H319, H335 | |
| P261, P305+P351+P338[118] | |
| NFPA 704 (fire diamond) | |
The early lanthanides, including neodymium, as well as lanthanum, cerium and praseodymium, have been found to be essential to some methanotrophic bacteria living in volcanic mudpots, such as Methylacidiphilum fumariolicum.[120][121] Neodymium is not otherwise known to have a biological role in any other organisms.[122]
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.[123] 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.[124]
Neodymium magnets have been tested for medical uses such as magnetic braces and bone repair, but biocompatibility issues have prevented widespread applications.[125] 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.[126]
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 an estimated 1,700 emergency room visits[127] and necessitated the recall of the Buckyballs line of toys, which were construction sets of small neodymium magnets.[127][128]
See also
Notes
- The thermal expansion is anisotropic: the parameters (at 20 °C) for each crystal axis are αa = 4.8×10−6/K, αc = 10.5×10−6/K, and αaverage = αV/3 = 6.7×10−6/K.[3]
