An Overview about the Chemical Element Thulium


Symbol: Tm

Atomic Number: 69

Atomic Mass: 168.9342 amu (atomic mass units)

Melting Point: 1545.0 C (1818.15 K, 2813.0 F)

Boiling Point: 1727.0 C (2000.15 K, 3140.6 F)

Number of Protons: 69

Number of Electrons: 69

Number of Neutrons: 100

Classification: Rare Earth Metal

Crystal Structure: Hexagonal

Density @ 293 K: 9.321 grams per cubic centimeter

Color: silver/gray

In 1879 Per Theodor Cleve, a Swedish chemist, used the methodologies as previously described by the chemist Carl Gustaf Mosander to look for undiscovered rare earth metals. Using these methods Mosander had already discovered the elements lanthanum, erbium and terbium. The methods involved looking at the impurities that were present in the oxides of known rare earth metals. Per Theodor Cleve started with a sample of erbium oxide and removed all the known constituents. He was left with two different colored substances a green one which he named thulia and a brown one he called holmia. These colored substances were the oxides of two new rare earth elements thulium and holmium. Thulium gets its name from the ancient name for Scandinavia – Thule.

Thulium is a rare earth element of the lanthanide or lanthanoid series. It is the least abundant of all the naturally occurring rare earth metals. The pure metal is soft and malleable, so soft in fact that is can be cut with a knife. It is rated low to moderately toxic and so should be handled with care.

There is one naturally occurring isotope of thulium. This isotope is thulium-169 and it is stable. Twenty five isotopes of thulium have been identified with half lives ranging from 3.5 microseconds to 128.6 days.

The main source for thulium is monazite sand. Monazite contains many of the rare earth elements including the radioactive thorium so care must be taken in processing this mineral. It is purified by ion exchange and solvent extraction the pure metal has only been available recently. As it is low in abundance the cost of thulium metal is higher that that of other naturally occurring rare earth metals. Owing to it’s only recently becoming available and its relatively high cost thulium has very few economic uses.

* Natural thulium could be used in ferrite ceramic magnets that are used in microwave technology.

* Can be used to dope fiber lasers

* The isotope thulium-169 can be bombarded with radiation in a nuclear reactor before being used as a radiation source for portable X-ray machines.