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The rare-earth elements (REE), also called the rare-earth metals or rare earths or, in context, rare-earth oxides, and sometimes the lanthanides (although yttrium and scandium, which do not belong to this series, are usually included as rare earths), are a set of 17 nearly indistinguishable lustrous silvery-white soft heavy metals.
- Overview
- Discovery and history
rare-earth element, any member of the group of chemical elements consisting of three elements in Group 3 (scandium [Sc], yttrium [Y], and lanthanum [La]) and the first extended row of elements below the main body of the periodic table (cerium [Ce] through lutetium [Lu]). The elements cerium through lutetium are called the lanthanides, but many scientists also, though incorrectly, call those elements rare earths.
The rare earths are generally trivalent elements, but a few have other valences. Cerium, praseodymium, and terbium can be tetravalent; samarium, europium and ytterbium, on the other hand, can be divalent. Many introductory science books view the rare earths as being so chemically similar to one another that collectively they can be considered as one element. To a certain degree that is correct—about 25 percent of their uses are based on this close similarity—but the other 75 percent of rare-earth usage is based on the unique properties of the individual elements. Furthermore, a close examination of these elements reveals vast differences in their behaviours and properties; e.g., the melting point of lanthanum, the prototype element of the lanthanide series (918 °C, or 1,684 °F), is much lower than the melting point of lutetium, the last element in the series (1,663 °C, or 3,025 °F). This difference is much larger than that found in many groups of the periodic table; e.g., the melting points of copper, silver, and gold vary by only about 100 °C (180 °F).
The name rare earths itself is a misnomer. At the time of their discovery in the 18th century, they were found to be a component of complex oxides, which were called “earths” at that time. Furthermore, these minerals seemed to be scarce, and thus these newly discovered elements were named “rare earths.” Actually, these elements are quite abundant and exist in many workable deposits throughout the world. The 16 naturally occurring rare earths fall into the 50th percentile of elemental abundances. By the early 21st century, China had become the world’s largest producer of rare-earth elements. Australia, Brazil, India, Kazakhstan, Malaysia, Russia, South Africa, and the United States also extract and refine significant quantities of these materials.
Many people do not realize the enormous impact the rare-earth elements have on their daily lives, but it is almost impossible to avoid a piece of modern technology that does not contain any. Even a product as simple as a lighter flint contains rare-earth elements. Their pervasiveness is exemplified by the modern automobile, one of the biggest consumers of rare-earth products. Dozens of electric motors in a typical automobile, as well as the speakers of its sound system, use neodymium-iron-boron permanent magnets. Electrical sensors employ yttria-stabilized zirconia to measure and control the oxygen content of the fuel. The three-way catalytic converter relies on cerium oxides to reduce nitrogen oxides to nitrogen gas and oxidize carbon monoxide to carbon dioxide and unburned hydrocarbons to carbon dioxide and water in the exhaust products. Phosphors in optical displays contain yttrium, europium, and terbium oxides. The windshield, mirrors, and lenses are polished using cerium oxides. Even the gasoline or diesel fuel that propels the vehicle was refined using rare-earth cracking catalysts containing lanthanum, cerium, or mixed-rare-earth oxides. Hybrid automobiles are powered by a nickel–lanthanum metal hydride rechargeable battery and an electrical traction motor, with permanent magnets containing rare-earth elements. In addition, modern media and communication devices—cell phones, televisions, and computers—all employ rare earths as magnets for speakers and hard drives and phosphors for optical displays. The amounts of rare earths used are quite small (0.1–5 percent by weight, except for permanent magnets, which contain about 25 percent neodymium), but they are critical, and any of those devices would not work as well, or would be significantly heavier, if it were not for the rare earths.
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Although the rare earths have been around since the formation of Earth, their existence did not come to light until the late 18th century. In 1787 the Swedish army lieutenant Carl Axel Arrhenius discovered a unique black mineral in a small quarry in Ytterby (a small town near Stockholm). That mineral was a mixture of rare earths, and the first individual element to be isolated was cerium in 1803.
The history of the individual rare-earth elements is both complex and confused, mainly because of their chemical similarity. Many “newly discovered elements” were not one element but mixtures of as many as six different rare-earth elements. Furthermore, there were claims of discovery of a large number of other “elements,” which were supposed to be members of the rare-earth series but were not.
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The last naturally occurring rare-earth element (lutetium) was discovered in 1907, but research into the chemistry of these elements was difficult because no one knew how many true rare-earth elements existed. Fortunately, in 1913–14 the research of Danish physicist Niels Bohr and English physicist Henry Gwyn Jeffreys Moseley resolved this situation. Bohr’s theory of the hydrogen atom enabled theoreticians to show that only 14 lanthanides exist. Moseley’s experimental studies verified the existence of 13 of these elements and showed that the 14th lanthanide must be element 61 and lie between neodymium and samarium.
In the 1920s the search for element 61 was intense. In 1926 groups of scientists at the University of Florence, Italy, and at the University of Illinois claimed to have discovered element 61 and named the element florentium and illinium, respectively, but their claims could not be independently verified. The furor of these claims and counterclaims eventually died down by 1930. It was not until 1947, after the fission of uranium, that element 61 definitely was isolated and named promethium by scientists at the U.S. Atomic Energy Commission’s Oak Ridge National Laboratory in Tennessee. (More details about the discovery of the individual elements are found in the articles about those elements.)
The rare earth elements (REE) are a set of seventeen metallic elements. These include the fifteen lanthanides on the periodic table plus scandium and yttrium . Rare earth elements are an essential part of many high-tech devices.
Rare earth elements are a group of seventeen chemical elements that occur together in the periodic table (see image). The group consists of yttrium and the 15 lanthanide elements (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium).
1 de feb. de 2019 · The rare earths (REs) are a family of 17 elements that exhibit pronounced chemical similarities as a group, while individually expressing distinctive and varied electronic properties. These atomistic electronic properties are extraordinarily useful and motivate the application of REs in many technologies and devices.
- Thibault Cheisson, Eric J. Schelter
- 2019
1 de jul. de 2019 · Rare earth elements (REE) include the lanthanide series elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) plus Sc and Y. Currently these metals have become very critical to several modern technologies ranging from cell phones and televisions to LED light bulbs and wind turbines.
16 de ene. de 2023 · Chemistry. How rare earth elements’ hidden properties make modern technology possible. These 17 metals fine-tune light and generate powerful magnetic fields. In August, China finished...
