Neodymium


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 the +2, +3 and +4 oxidation states. It is generally regarded as having one of the most complex spectra of the elements. 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 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 1047 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. 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 strong magnetic fields are required. Larger neodymium magnets are used in electric motors with high power-to-weight ratios and generators.

Physical properties

Metallic neodymium has a bright, silvery metallic luster. Neodymium commonly exists in two allotropic forms, with a transformation from a double hexagonal to a body-centered cubic structure taking place at about 863 °C. Neodymium, like most of the lanthanides, is paramagnetic at room temperature. It becomes an antiferromagnet upon cooling below. Below this transition temperature it exhibits a set of complex magnetic phases that have long spin relaxation times and spin glass behavior. Neodymium is a rare-earth metal that was present in the classical mischmetal at a concentration of about 18%. To make neodymium magnets it is alloyed with iron, which is a ferromagnet.

Electron configuration

Neodymium is the fourth member of the lanthanide series. In the periodic table, it appears between the lanthanides praseodymium to its left and the radioactive element promethium to its right, and above the actinide uranium. Its 60 electrons are arranged in the configuration 4f46s2, of which the six 4f and 6s electrons are valence. 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 inert xenon 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.

Chemical properties

Neodymium has a melting point of and a boiling point of. Like other lanthanides, it usually has the oxidation state +3, but can also form in the +2 and +4 oxidation states, and even, in very rare conditions, +0. Neodymium metal quickly oxidizes at ambient conditions, forming an oxide layer like iron rust that can spall 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 neighbor praseodymium, it readily burns at about 150 °C to form neodymium oxide; the oxide then peels off, exposing the bulk metal to the further oxidation:
Neodymium is an electropositive element, and it reacts slowly with cold water, or quickly with hot water, to form neodymium hydroxide:
Neodymium metal reacts vigorously with all the stable halogens:
Neodymium dissolves readily in dilute sulfuric acid to form solutions that contain the lilac Nd ion. These exist as a 3+ complexes:

Compounds

Some of the most important neodymium compounds include:
  • halides: NdF3; NdCl2; NdCl3; NdBr3; NdI2; NdI3
  • oxides: neodymium oxide|
  • hydroxide: neodymium hydroxide|
  • carbonate: Nd23
  • sulfate: neodymium sulfate|
  • acetate: Nd3
  • neodymium magnets
Some neodymium compounds vary in color under different types of lighting.

Organoneodymium compounds

Organoneodymium compounds are compounds that have a neodymium–carbon bond. These compounds are similar to those of the other lanthanides, characterized by an inability to undergo π backbonding. They are thus mostly restricted to the mostly ionic cyclopentadienides and the σ-bonded simple alkyls and aryls, some of which may be polymeric.

Isotopes

Naturally occurring neodymium is composed of five stable isotopes—142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant —and two radioisotopes with extremely long half-lives, 144Nd and 150Nd. In all, 35 radioisotopes of neodymium have been detected as of 2022, with the most stable radioisotopes being the naturally occurring ones: 144Nd and 150Nd. All of the remaining radioactive 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 stable artificial isotope is 147Nd with a half-life of 10.98 days.
Neodymium also has 15 known metastable isotopes, with the most stable one being 139mNd, 135mNd and 133m1Nd. 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 praseodymium isotopes, and the primary products after 142Nd are promethium isotopes. 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. Additionally, some observationally stable isotopes of samarium are predicted to decay to isotopes of neodymium.
Neodymium isotopes are used in various scientific applications. 142Nd has been used for the production of short-lived isotopes of thulium and ytterbium. 146Nd has been suggested for the production of 147Pm, which is a source of radioactive power. Several neodymium isotopes have been used for the production of other promethium isotopes. The decay from 147Sm to the stable 143Nd allows for samarium–neodymium dating. 150Nd has also been used to study double beta decay.

History

In 1751, the Swedish mineralogist Axel Fredrik Cronstedt discovered a heavy mineral from the mine at Bastnäs, later named cerite. Thirty years later, fifteen-year-old Wilhelm Hisinger, a member of the family owning the mine, sent a sample to Carl Scheele, who did not find any new elements within. In 1803, after Hisinger had become an ironmaster, he returned to the mineral with Jöns Jacob Berzelius and isolated a new oxide, which they named ceria after the dwarf planet Ceres, which had been discovered two years earlier. Ceria was simultaneously and independently isolated in Germany by Martin Heinrich Klaproth. Between 1839 and 1843, ceria was shown to be a mixture of oxides by the Swedish surgeon and chemist Carl Gustaf Mosander, who lived in the same house as Berzelius; he separated out two other oxides, which he named lanthana and didymia. He partially decomposed a sample of cerium nitrate by roasting it in air and then treating the resulting oxide with dilute nitric acid. The metals that formed these oxides were thus named lanthanum and didymium. Didymium was later proven to not be a single element when it was split into two elements, praseodymium and neodymium, by Carl Auer von Welsbach in Vienna in 1885. Von Welsbach confirmed the separation by spectroscopic analysis, but the products were of relatively low purity. Pure neodymium was first isolated in 1925. The name neodymium is derived from the Greek words neos, new, and didymos, 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 neodymium was primarily obtained through an ion exchange process from monazite, a mineral rich in rare-earth elements. The metal is obtained through electrolysis of its halide salts. Currently, most neodymium is extracted from bastnäsite and purified by solvent extraction. Ion-exchange purification is used for the highest purities. 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.