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.[6] Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach, who also discovered praseodymium. It 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.[7] 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. However, this 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. Neodymium-doped glasses 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 experiments 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, a powerful permanent magnet.[8] These magnets are widely used in products like 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 electric motors with a high power-to-weight ratio (e.g., in hybrid cars) and generators (e.g., aircraft and wind turbine electric generators).[9]

Characteristics[edit]

Physical properties[edit]

Metallic neodymium has a bright, silvery metallic luster.[10] 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.[11] Neodymium, like most of the lanthanides, is paramagnetic at room temperature and becomes an antiferromagnet upon cooling to 20 K (−253.2 °C).[12] 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.[13]

Electron configuration[edit]

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 [Xe]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.[14]

Chemical properties[edit]

Neodymium has a melting point of 1,024 °C (1,875 °F) and a boiling point of 3,074 °C (5,565 °F). It, like other lanthanides, usually has the oxidation state +3, but it can also form in the +2 and +4 oxidation states, and even, in very rare conditions, +0.[15] Neodymium metal quickly oxidizes at ambient conditions,[11] 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(III) oxide; the oxide peels off, exposing the bulk metal to the further oxidation:[11]

4Nd + 3O2 → 2Nd2O3

Neodymium is a quite electropositive element, and it reacts slowly with cold water, or quickly with hot water, to form neodymium(III) hydroxide:

2Nd (s) + 6H2O (l) → 2Nd(OH)3 (aq) + 3H2 (g)

Neodymium metal reacts vigorously with all the stable halogens:[16]

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 dilute sulfuric acid to form solutions that contain the lilac Nd(III) ion. These exist as a [Nd(OH2)9]3+ complexes:[17]

2Nd (s) + 3H2SO4 (aq) → 2Nd3+ (aq) + 3SO2−4 (aq) + 3H2 (g)

Compounds[edit]

Main article: Neodymium compounds
Neodymium(III) sulfate
Neodymium acetate powder
Neodymium(III) hydroxide powder

Some of the most important neodymium compounds include:

Some neodymium compounds have colors that vary based on the type of lighting.[18]