(prā´´zēōdĭm'ēӘm, –sēō–) [Gr., =green twin], metallic chemical element; symbol Pr; at. no. 59; at. wt. 140.90765; m.p. 931 degrees Celsius; b.p. 3,512 degrees Celsius; sp. gr. about 6.8; valence +3 or +4. Praseodymium is a soft, malleable, ductile, silver-yellow metal. It exhibits allotropy; the α-form (hexagonal crystalline structure) has the density given above, but the β-form (above 800 degrees Celsius, body-centered cubic crystalline structure) is less dense. Praseodymium is a rare-earth metal of the lanthanide series in Group 3 of the periodic table. When exposed to air it forms a green oxide that does not protect it from further oxidation. Although the pure metal may be prepared by reduction of the chloride, it has few commercial uses. A major use of the metal is in a pyrophoric alloy used in cigarette lighter flints, but it need not be purified for this application. Praseodymium compounds have many uses. The oxide is used in carbon electrodes for arc lighting. The salts are used to color enamels and glass. Didymium glass used in glassblower's goggles contains praseodymium; this glass absorbs the yellow sodium glare of light from the torch flame. The major commercial source of praseodymium is the rare-earth minerals monazite and bastnasite. Praseodymium was discovered in 1885 by C. A. Von Welsbach, who separated Mosander's “didymium” into two components, the earths neodymia and praseodymia.
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(nē´´ōdĭm'ēӘm), metallic chemical element; symbol Nd; at. no. 60; at. wt. 144.242; m.p. about 1,021 degrees Celsius; b.p. about 3,068 degrees Celsiu
(sӘmâr'ēӘm), metallic chemical element; symbol Sm; at. no. 62; at. wt. 150.36; m.p. 1,072 degrees Celsius; b.p. 1,791 degrees Celsius; sp. gr. 7.54
Metallic chemical element, chemical symbol Nd, atomic number 60. Silvery white in colour, it is a rare earth metal and one of the lanthanoid series