Rare-Earth Element


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rare-earth element

[′rer ‚ərth ′el·ə·mənt]
(chemistry)
The name given to any of the group of chemical elements with atomic numbers 58 to 71; the name is a misnomer since they are neither rare nor earths; examples are cerium, erbium, and gadolinium.

Rare-Earth Element

 

any one of a group of chemical elements belonging to a secondary subgroup of group III of Mendeleev’s periodic system. The elements are scandium (symbol Sc, atomic number [Z] = 21), yttrium (Y, Z = 39), lanthanum (La, Z = 57), and the lanthanides (14 elements wherein Z ranges from 58 to 71). Scandium, however, is not always classed as a rare-earth element.

In the free state, rare-earth elements are metals. The term “rare-earth” was assigned to these elements because they occur relatively rarely in the earth’s crust and because they form refractory oxides that are practically insoluble in water. Prior to and during the early 19th century, such oxides were called common earths. An important characteristic of rare-earth elements is their occurrence together in nature. For example, the mineral monazite, one of the primary sources of these elements, contains phosphates of Y, La, and other rare earths. All rare earths display similar chemical properties; their characteristic oxidation state is +3 (valence of three). In the Sc-Y-La series, the basic properties of oxides and hydroxides become more pronounced from Sc to La. For example, scandium hydroxide Sc(OH)3 is amphoteric, whereas lanthanum hydroxide La(OH)3 is a rather strong base.

Actinium (Z = 89) closely resembles the rare-earth elements in chemical properties, but it is generally regarded separately because of its radioactivity (lack of stable isotopes).

S. S. BERDONOSOV

References in periodicals archive ?
Indeed, rare-earth elements are "rare" only in the sense that they are distributed in small quantities and must be extracted from ores, a time-consuming process.
Many countries are now planning to develop their own or alternative sources of rare-earth elements, and to accelerate efforts to develop technologies that are free of them.
There are 30 rare-earth elements. The scientists are working with the following lanthanide oxides: lanthanum, cerium, praseodymium, neodymium, samarium and gadolinium.
"All soil contains some rare-earth elements, so you have to be able to detect the tracer you are using," says Zhang.
There are 30 rare-earth elements. The scientists are working with seven lanthanide oxides: lanthanum, which is used in carbon lighting applications and optical glass manufacturing; cerium, used as a catalyst in sell-cleaning ovens; praseodymium, commonly used in an alloy found in lighter flints and carbon electrodes for are lighting; neodymium, used for coloring glass and ceramics and for filtering infrared radiation; samarium, used in magnets, in alloys with cobalt, and in nuclear reactors: and gadolinium, which is also used in magnets.
The researchers say the fine-powder rare-earth elements are a more effective tool for tracking movement of eroding sediment than what's currently the best tracer: minuscule amounts of the radioactive element cesium ([.sup.137.Cs]) that originated from nuclear-bomb testing and spread across the landscape through the atmosphere.
Rare-earth elements are also key to 'green' technology: Energy-efficient light bulbs use europium and yttrium, while hybrid car batteries and wind-power turbines use neodymium.
Rare Element Resources Limited (Rare Element Resources) (TSX-V: RES), a publicly traded mineral resource company focused on gold and strategic metals such as the rare-earth elements, has acquired the Nuiklavik rare-earth-element (REE) prospect from Altius Resources Incorporated (Altius).
Specialists in the field had generallyexpected that these materials, which are ceramic compounds of copper oxide with rare-earth elements, would have the capacity to stand very high currents.
Rare Element Resources Ltd (TSX V: RES), a Canada-based mineral resource exploration company focused on gold and strategic metals like rare-earth elements, has announced a technical report for the Bear Lodge property, located in Wyoming, US.
These materials are compounds of copper,oxygen and rare-earth elements. They are granular, and the exact proportion of the different elements can vary from place to place.
The new materials reported at the meeting are copper oxides containing rare-earth elements. P.M.