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| '''"Rare earth elements"''' and '''"rare earth metals"''' are ]s sometimes applied to a collection of 17 ]s in the ] |
'''"Rare earth elements"''' and '''"rare earth metals"''' are ]s sometimes applied to a collection of 17 ]s in the ], namely ], ], and the ]s. (The lanthanide ], which does not occur naturally on Earth, is not generally not considered a rare earth element.) | ||
| "Earth" is an obsolete term for ]. At the time of their discovery, earths of these elements were believed to be scare in abundance as minerals (rare). However, the term "rare earth" is now deprecated by ], as some of the elements are in fact relatively abundant in the Earth's crust (indeed, even the least abundant 'rare' earth element, ] is 200 times more abundant than gold). Ore deposits of the rare earths are however more difficult to mine and extract than those of other ], making them relatively expensive. | "Earth" is an obsolete term for ]. At the time of their discovery, earths of these elements were believed to be scare in abundance as minerals (rare). However, the term "rare earth" is now deprecated by ], as some of the elements are in fact relatively abundant in the Earth's crust (indeed, even the least abundant 'rare' earth element, ] is 200 times more abundant than gold). Ore deposits of the rare earths are however more difficult to mine and extract than those of other ], making them relatively expensive. | ||
| The elemental forms of rare earths are iron gray to silvery lustrous ]s that are typically soft, malleable, and ductile and usually reactive, especially at elevated temperatures or when finely divided. All rare earth elements dissolve in acid to form triply charged ions in solution, and +3 is the default oxidation state. | The elemental forms of rare earths are iron gray to silvery lustrous ]s that are typically soft, malleable, and ductile and usually reactive, especially at elevated temperatures or when finely divided. All rare earth elements dissolve in acid to form triply charged ions in solution, and +3 is the default oxidation state. | ||
Revision as of 22:26, 7 December 2005
"Rare earth elements" and "rare earth metals" are trivial names sometimes applied to a collection of 17 chemical elements in the Periodic Table, namely scandium, yttrium, and the lanthanides. (The lanthanide promethium, which does not occur naturally on Earth, is not generally not considered a rare earth element.)
"Earth" is an obsolete term for oxide. At the time of their discovery, earths of these elements were believed to be scare in abundance as minerals (rare). However, the term "rare earth" is now deprecated by IUPAC, as some of the elements are in fact relatively abundant in the Earth's crust (indeed, even the least abundant 'rare' earth element, lutetium is 200 times more abundant than gold). Ore deposits of the rare earths are however more difficult to mine and extract than those of other transition metals, making them relatively expensive.
The elemental forms of rare earths are iron gray to silvery lustrous metals that are typically soft, malleable, and ductile and usually reactive, especially at elevated temperatures or when finely divided. All rare earth elements dissolve in acid to form triply charged ions in solution, and +3 is the default oxidation state.
The rare earths' unique properties are used in a wide variety of applications. For example, their ions are widely used as dopants in active laser media such as Nd:YAG (neodymium-doped yttrium aluminum garnet) and Erbium-doped fiber amplifiers. Half-full f shells in these elements can be used to produce exceedingly strong permanent magnets, with Samarium-Cobalt holding the record for highest Curie temperature and Neodymium-Iron-Boron having the highest known permanent magnetization of any material.
The principal economic sources of rare earths are the minerals bastnasite, monazite, and loparite and the lateritic ion-adsorption clays. The moniker "rare earth" can be misleading – the elements range in crustal abundance from cerium, the 25th most abundant element of the 78 common elements in the Earth's crust at 60 parts per million (more common than lead), to thulium and lutetium, the least abundant rare-earth elements at about 0.5 parts per million.
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