rare-earth metals definition of rare-earth metals in the Free Online Encyclopedia.

rare-earth metals, in chemistry, group of metals including those of the lanthanide series lanthanide series, a series of metallic elements, included in the rare-earth metals , in Group 3 of the periodic table . Members of the series are often called lanthanides, although lanthanum (atomic number 57) is not always considered a member of the series.
..... Click the link for more information. and actinide series actinide series, a series of radioactive metallic elements in Group 3 of the periodic table . Members of the series are often called actinides, although actinium (at. no. 89) is not always considered a member of the series.
..... Click the link for more information. , usually yttrium yttrium (ĭt`rēəm) [for Ytterby, a town in Sweden], metallic chemical element; symbol Y; at. no. 39; at. wt. 88.9059; m.p.
..... Click the link for more information. , sometimes scandium scandium (skăn`dēəm), metallic chemical element; symbol Sc; at. no. 21; at. wt. 44.9559; m.p. 1,541°C;; b.p. 2,831°C;; sp.
..... Click the link for more information. and thorium thorium (thôr`ēəm) [from Thor], radioactive chemical element; symbol Th; at. no. 90; at. wt. 232.0381; m.p.
..... Click the link for more information. , and rarely zirconium zirconium (zərkō`nēəm), metallic chemical element; symbol Zr; at. no. 40; at. wt. 91.22; m.p. about 1,852°C;; b.p.
..... Click the link for more information. . 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 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.
..... Click the link for more information. ) 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 magnesium (măgnē`zēəm, –zhəm), metallic chemical element; symbol Mg; at. no. 12; at. wt. 24.305; m.p. about 648.
..... Click the link for more information. ), 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.

Bibliography

See F. H. Spedding and A. H. Daane, ed., The Rare Earths (1961, repr. 1971); E. C. Subbarao and W. E. Wallace, ed., Science and Technology of Rare Earth Metals (1980).