|
Search over 100 encyclopedias and dictionaries: |
Research categories | Follow us on Twitter |
Research categories
View all topics in the newsView all reference sources at Encyclopedia.com |
|||
rare-earth metals
rare-earth metals in chemistry, group of metals including those of the lanthanide series and actinide series and usually yttrium , sometimes scandium and thorium , and rarely zirconium . Promethium, which is not found in nature, is not usually considered a rare-earth metal. The metals usually occur together in minerals as their oxides ( rare earths ) and are somewhat difficult to separate because of their chemical similarity. A subgroup of the rare-earth metals, consisting of those with atomic numbers between 57 and 63 and ytterbium, is often called the cerium metals. Misch metal is an alloy of the cerium metals often used in lighter flints, in alloys with other metals (especially magnesium ), and to remove residual gases in the manufacture of vacuum tubes. Individual metals may be isolated as their compounds by ion exchange methods, solvent extraction, or fractional crystallization, and chemically or electrolytically reduced to the pure metal. Uses are discussed in articles on individual elements.
|
|
|
Cite this article
"rare-earth metals." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. "rare-earth metals." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1E1-rarearmet.html "rare-earth metals." The Columbia Encyclopedia, 6th ed.. 2011. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-rarearmet.html |
|
rare earths
rare earths in chemistry, oxides of the rare-earth metals . They were once thought to be elements themselves. They are widely distributed in the earth's crust and are fairly abundant, although they were once thought to be very scarce. Generally, the name of an earth is formed from the name of its element by replacing -um with -a ; e.g., the earth of cerium is ceria. Mixed rare earths are used in glassmaking, ceramic glazes, glass-polishing abrasives, carbon arc-light electrode cores, and catalysts for petroleum refining. Individual purified rare earths have many uses, e.g., in laser, fiber-optic transmission amplifiers, and night-vision goggles. Important rare-earth minerals include bastnasite, cerite, euxenite, gadolinite, monazite, and samarskite. |
|
|
Cite this article
"rare earths." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. "rare earths." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1E1-rarearth.html "rare earths." The Columbia Encyclopedia, 6th ed.. 2011. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-rarearth.html |
|
rare-earth element
rare-earth element (REE, lanthanide) One of those elements with atomic numbers between 57 and 71, that have closely similar chemical properties. The ionic radius decreases with increasing atomic number, a phenomenon referred to as the lanthanide contraction. Rare-earth elements occur in minerals only in trace amounts, sometimes replacing Ca2+ in apatite and hornblende. They tend to become concentrated in the residual fluid of magmas, and in some pegmatites the REE cerium replaces the calcium in epidote to form the mineral allanite. Lunar rocks, apart from anorthosite, show considerable enrichment in most of the rare-earth elements relative to the REE cosmic abundance. See EUROPIUM ANOMALY.
|
|
|
Cite this article
AILSA ALLABY and MICHAEL ALLABY. "rare-earth element." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "rare-earth element." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O13-rareearthelement.html AILSA ALLABY and MICHAEL ALLABY. "rare-earth element." A Dictionary of Earth Sciences. 1999. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-rareearthelement.html |
|
rare earth
rare earth (also rare earth el·e·ment or rare earth met·al) • n. Chem. any of a group of chemically similar metallic elements comprising the lanthanide series and (usually) scandium and yttrium. They are not esp. rare, but they tend to occur together in nature and are difficult to separate from one another. |
|
|
Cite this article
"rare earth." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. "rare earth." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O999-rareearth.html "rare earth." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-rareearth.html |
|
rare earth
rare earth See lanthanide series
|
|
|
Cite this article
"rare earth." World Encyclopedia. 2005. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. "rare earth." World Encyclopedia. 2005. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O142-rareearth.html "rare earth." World Encyclopedia. 2005. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-rareearth.html |
|
Search over 100 encyclopedias and dictionaries:
HighBeam™ Research, Inc. © Copyright 2012. All rights reserved.
The Encyclopedia.com advertising network includes:
