Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal which tarnishes in air. Neodymium was discovered in 1885. It is present in significant quantities in the ore minerals monazite and bastnäsite. Neodymium is not found naturally in metallic form or unaccompanied by other lanthanides and it is usually refined for general use. Neodymium has several important applications: it is a constituent of neodymium magnets, which are widely used in motors, loudspeakers and numerous appliances. Neodymium is a popular additive in glass, giving it a characteristic reddish-purple color; this glass is used in lasers emitting infrared light with the wavelength of 1.054–1.062 micrometers. Neodymium is also used in Nd:YAG lasers to generate 1.064 micrometer light. This is one of the most significant solid-state lasers. Neodymium is a key component of an alloy used to make high-power lightweight magnets for electric motors of hybrid cars, and in generators for wind turbines.
Neodymium, a rare earth metal, was present in classical mischmetal to the extent of about 18%. The metal has a bright, silvery metallic luster; however, as one of the more reactive rare earth (lanthanide) metals, it quickly oxidizes in air. The oxide layer then falls off, which exposes the metal to further oxidation. Thus a centimeter-sized Nd sample completely oxidizes within a year.
Neodymium exists in two allotropic forms, with a transformation from a double hexagonal to a body-centered cubic structure taking place at 863 °C.
Neodymium metal tarnishes slowly in air and burns readily at 150 °C to form neodymium(III) oxide:
4 Nd + 3 O2 → 2 Nd2O3
Neodymium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form neodymium hydroxide:
2 Nd (s) + 6 H2O (l) → 2 Nd(OH)3 (aq) + 3 H2 (g)
Neodymium metal reacts with all the halogens:
2 Nd (s) + 3 F2 (g) → 2 NdF3 (s) [violet]
Neodymium dissolves readily in dilute sulfuric acid to form solutions containing the lilac Nd(III) ions, which exist as a [Nd(OH2)9]3+ complexes:
2 Nd (s) + 3 H2SO4 (aq) → 2 Nd3+ (aq) + 3 SO2−4 (aq) + 3 H2 (g)
Neodymium compounds include
* Halides: NdF3, NdCl3, NdBr3, NdI3
Naturally occurring neodymium is composed of 5 stable isotopes, 142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant (27.2% natural abundance), and 2 radioisotopes, 144Nd and 150Nd. In all, 31 radioisotopes of neodymium have been characterized up to now, with the most stable being naturally occurring isotopes 144Nd (alpha decay, a half-life (T½) of 2.29×1015 years) and 150Nd (double beta decay, T½ = 7×1018 years). All of the remaining radioactive isotopes have half-lives that are less than 11 days, and the majority of these have half-lives that are less than 70 seconds. This element also has 13 known meta states with the most stable being 139mNd (T½ = 5.5 hours), 135mNd (T½ = 5.5 minutes) and 133m1Nd (T½ ~ 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 glass 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 when the fractional crystallization technology had to be relied on.
Occurrence and production
Neodymium is never found in nature as the free element; rather, it occurs in ores such as monazite and bastnäsite that contain small amounts of all the rare earth metals. The main mining areas are China, United States, Brazil, India, Sri Lanka and Australia; and reserves of neodymium are estimated at about 8 million tonnes. Although it belongs to "rare earth metals," neodymium is not rare at all - its abundance in the Earth crust is about 38 mg/kg, which is the second among rare-earth elements after cerium. The world production of neodymium is about 7,000 tonnes per year. The bulk of current production is from China, whose government has recently imposed strategic materials controls on the element, raising some concerns in consuming countries.
Neodymium typically comprises 10 to 18% of the rare earth content of commercial orebodies of the light rare earth element (LREE) dominant minerals bastnasite and monazite. With neodymium being the most strongly colored trivalent lanthanide, that level of neodymium can occasionally dominate the coloration of rare earth minerals, when competing chromophores are absent, and provide a pink coloration. Outstanding examples of this include monazite crystals from the tin veins of Llallagua, Bolivia, ancylite from Mont Saint-Hilaire, Quebec, or lanthanite from the Saucon Valley of Pennsylvania. As with neodymium glass, such minerals change color under the differing lighting conditions. The absorption bands of neodymium interact with the visible mercury vapor emission spectrum, such that unfiltered shortwave UV light causes neodymium-containing minerals to reflect a distinct green color. This can be observed with monazite-containing sands or bastnasite-containing ore.
* Neodymium magnets are the strongest permanent magnets known - Nd2Fe14B. These magnets are cheaper, lighter, and stronger than samarium-cobalt magnets. 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-flux capacity, it is heavily used in the electric motors of hybrid automobiles and in the electricity generators of commercial wind turbine generators.
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 glass solid-state lasers are used in extremely high power (terawatt scale), high energy (megajoules) multiple beam systems for inertial confinement fusion (see last bulleted paragraph above). Nd:glass lasers are usually frequency tripled to the third harmonic at 351 nm in laser fusion devices.
Neodymium glass is becoming widely used in incandescent light bulbs, to provide a more "natural" light. It has been patented for use in automobile rear-view mirrors, to reduce the glare at night.
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.
Neodymium metal dust is a combustion and 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, a person lost part of his finger when two magnets he was using snapped together from 50 cm away. Another danger is when two such magnets snap together, the force of the collision can cause them to shatter, sending sharp pieces flying around, potentially causing serious injuries.
* Neodymium magnet (NIB or Nd2Fe14B)
1. ^ Gschneidner, K.A., and Eyring, L., Handbook on the Physics and Chemistry of Rare Earths, North Holland Publishing Co., Amsterdam, 1978.
* "The Industrial Chemistry of the Lanthanons, Yttrium, Thorium and Uranium", by R.J. Callow, Pergamon Press 1967.