Chemical Properties
silvery-white chip or ingot, or grey powder
Physical properties
There are two allotropic (crystal forms) of terbium, both of which are dependent on itstemperature. The alpha ((α) form exists at room temperatures and up to temperatures of1,298°C, and the beta (β) form exists beyond these temperatures. Although terbium is a silverymetal that resembles aluminum and feels like lead, it is much heavier than either of thesetwo elements. It is placed in the yttrium subgroup (lanthanide series) of the rare-earths. It isalso resistant to corrosion.
Its melting point is 1,356.9°C, its boiling point is 3,230°C, and its density is 8.23g/cm3.
Isotopes
There are a total of 52 isotopes of terbium, and only one of these is stable (Tb-159). Terbium-59 makes up 100% of the element found in the Earth’s crust.
Origin of Name
Named for a village in Sweden.
Occurrence
Of all the 17 rare-earths in the lanthanide series, terbium is number 14 in abundance.Terbium can be separated from the minerals xenotime (YPO4) and euxenite, a mixture of thefollowing: (Y, Ca, Er, La, Ce, Y, Th)(Nb, Ta, Ti2O6). It is obtained in commercial amountfrom monazite sand by the ion-exchange process. Monazite may contain as much as 50%rare-earth elements, and about 0.03% of this is terbium.
Characteristics
Terbium is not found in great quantities on Earth. In fact, minerals where terbium is foundcontain about 0.03% terbium. Not much of the stable isotope is found as a free metal; rathermost of it is mixed with other rare-earths or are in compound forms.
Preparation
Terbium is recovered from the minerals, monazite, xenotime, and euxenite. The recovery processes are quite similar to those of other lanthanide elements (See individual lanthanide elements). The metal is separated from other rareearths by ion exchange methods, which are relatively easy and faster than fractional crystallization techniques.
Terbium metal is obtained from its anhydrous trifluoride, TbF3, or trichloride, TbCl3, by thermal reduction with calcium, carried out in a tantalum crucible. Terbium produced by such methods may contain traces of calcium and tantalum. High purity metal can be prepared by various methods such as vacuum remelting, distillation, amalgam formation, floating zone melting, and various chemical processes.
Hazard
The halogens (group VIIA) of terbium are strong irritants. Most of the compounds aretoxic and some are explosive. A vacuum or inert atmosphere must be maintained when workingwith the metal because of its strong oxidation properties.
Flammability and Explosibility
Flammable
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