Thulium

Name: Thulium
Symbol: Tm
Atomic Number: 69
Mass fraction of the earth’s shell: 2 x 10 ^-5 ppm
Melting Point: 1545°C
Boiling Point: 1947 °C
Electrical Conductivity: 1,47 x 10⁶ A·V⁻¹·m⁻¹

HISTORY

Per Theodor Cleve

Thule, the mythical island at the edge of the world, was the eponym for the oxide that the Swede Per Theodor Cleve discovered in 1879 while investigating erbia earths. The discovery of holmium also goes back to this research. The isolation of pure thulium oxide did not succeed until 1911. Thirty-nine years later, in 1950, it was finally possible to prepare metallic thulium.

CHARACTERISTICS & EXTRACTION

The base, very soft heavy metal, shimmers silvery-white. It is stable in dry air but must be protected from moisture. Thulium is electropositive and a strong reducing agent. Humid air causes it to tarnish, and thulium dissolves in water.

Thulium removed from nuclear reactors serves as a source of X-ray radiation.

In nature, thulium is mostly found in combination with yttrium and the heavy lanthanides. Monazite sand is needed for its production. First, it is separated from the other rare earth metals by ion exchange. It is then obtained by metallothermic reduction of the trifluoride with calcium, magnesium, or potassium. The use of thulium is limited because there are only a manageable number of commercial applications. One of these is TV sets: here, thulium activates the phosphors on the screen surface

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