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   Tb

TERBIUM

(Ytterby a village in Sweden)

Tb at. wt. 158.9254
   at. no. 65
   m.p. 1360 ±4°C
   b.p. 3041°C 
   sp. gr. 8.234
   valence 3,4 

Terbium was discovered by Mosanderin 1543. Terbium is a member of the lanthanide or "rare earth" group of ele- ments. 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 % or 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 cru- cible. 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 silvery gray metal, and is malleable, ductile and soft enough to be cut with a knife. Two crystal modifications exist, with a transformation temperature of 1315°C. Nineteen isotopes with atomic masses ranging from 147 to 164 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 5460 Å. 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 T.V. 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 $3/gm. or $750/lb. Little is known of the toxicity of terbium. It should be handled with care, as with other lanthanide elements.

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