Synopsis
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Terbium - (Ytterby, village in Sweden), Tb; at. wt. 158.92534(3);
at. no. 65; m.p. 1356 deg C; b.p. 3230 deg C; sp. gr. 8.230; valence 3,
4. Discovered by Mosander in 1843. Terbium is a member of the lanthanide
or "rare earth" group of elements. It is found in cerite, gadolinite, and
other minerals along with other rare earths. It is recovered commercially
from monazite in which it is present to the extent of 0.03%, from xenotime,
and from euxenite, a complex oxide containing 1% of more of terbia. Terbium
has been isolated only in recent years with the development of ion-exchange
techniques for separating the rare-earth elements. As with other rare earths,
it can be produced by reducing the anhydrous chloride or fluoride with
calcium metal in a tantalum crucible. Calcium and tantalum impurities can
be removed by vacuum remelting. Other methods of isolation are possible.
Terbium is reasonably stable in air. It is a silver-gray metal, and is
malleable, ductile, and soft enough to be cut with a knife. Two crystal
modifications exist, with a transformation temperature of 1289 deg C. Forty
one isotopes and isomers are recognized. The oxide is a chocolate or dark
maroon color. Sodium terbium borate is used as a laser material and emits
coherent light at 0.546 um. Terbium is used to dope calcium fluoride, calcium
tungstate, and strontium molybdate, used in solid-state devices. The oxide
has potential application as an activator for green phosphors used in color
TV tubes. It can be used with ZrO2 as a crystal stabilizer of fuel cells
which operate at elevated temperature. Few other uses have been found.
The element is priced at about $30/g (99.9%). Little is known of the toxicity
of terbium. It should be handled with care as with other lanthanide elements. |
