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(Thule, the earliest name for Scandinavia) Discovered in 1879 by Cleve. Thulium occurs
in small quantities along with other rare earths in a number of minerals. It is obtained
commercially from monazite, which contains about 0.007% of the element. Thulium is the
least abundant of the rare earth elements, but with new sources recently discovered, it is
now considered to be about as rare as silver, gold, or cadmium. Ion-exchange and solvent
extraction techniques have recently permitted much easier separation of the rare earths,
with much lower costs. Only a few years ago, thulium metal was not obtainable at any cost;
in 1985 the oxide sold for $3400/kg. Thulium metal costs $50/g. Thulium can be isolated by
reduction of the oxide with lanthanum metal or by calcium reduction of a closed container.
The element is silver-gray, soft, malleable, and ductile, and can be cut with a knife.
Twenty five isotopes are known, with atomic masses ranging from 152 to 176. Natural
thulium, which is 100% 169Tm, is stable. Because of the relatively high price of the
metal, thulium has not yet found many practical applications. 169Tm bombarded in a nuclear
reactor can be used as a radiation source in portable X-ray equipment. 171Tm is
potentially useful as an energy source. Natural thulium also has possible use in ferrites
(ceramic magnetic materials) used in microwave equipment. As with other lanthanides,
thulium has a low-to-moderate acute toxic rating. It should be handled with care.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.
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