Thulium, Tm, Atomic number 69


Thulium is a chemical element with the element symbol Tm and atomic number 69. In the periodic table it is in the group of lanthanides and is thus also one of the rare earth metals.
Thulium (Named after Thule, the mythical island on the edge of the world) was 1879 by the Swedish chemist Per Teodor Cleve with holmium in Erbia (Erbium) discovered (see History of the holmium).
In nature, only in thulium compounds. Thuliumhaltige minerals are of low concentration :
Monazite (This,The,Th,Nd,And)PO4 (Tm content < 0,01%)
Gadolinit (Tm content is about 0,25%)


After an extensive separation of the other Thuliumbegleiter the oxide with lanthanum to thulium metal reduces. Subsequently, the thulium removed by sublimation.

Special features

The silver-gray metal of the rare earths is very soft, stretchable and malleable.
In dry air is very stable thulium, in moist air, it goes to gray. At higher temperatures, it burns, it reacts to Sesquioxid.Mit water with evolution of hydrogen to hydroxide. In mineral acids it dissolves with the formation of hydrogen on.
In its compounds it is the oxidation state +3 before, the Tm3 ions in water are pastel blue-green solutions.


Use in television sets (for activation of the phosphors on the screen surface) there are few commercial applications:
Acts of nuclear reactors outsourced 170Tm as X-ray source (Gamma emitters in the test material)
Thuliumdotiertes Yttriumtantalat oder Lanthanoxybromid (LaOBr) serves as a scintillator in the X-ray intensifying screens or fluorescent screens in the X-ray technique
Thuliumdotiertes calcium sulfate is used as a detector in personal dosimeters for measurement of low radiation doses
Thuliumkristalle can be used as an active medium in diode-pumped solid state lasers (Wavelength 2 μm) with an overall efficiency of up to 10 % at a maximum of 60 W light power can be used.
Thuliumdotiertes silica glass as the active medium in fiber lasers (Wavelength 2 μm) was measured with a differential efficiency of 53,2 % at a power > 1000 W operated.
Thulium and Thuliumverbindungen are of low toxicity. Thuliumstäube are fire- and potentially dangerous.

Name, Symbol

Atomic number

Thulium, Tm, 69
Series Lanthanides
group, Period, Block The, 6, f
Appearance silvery grua
CAS-Nummer 7440-30-4
Mass fraction of element 0,19 ppm
Atomic mass 168,93421 you
Atomradius 175 pm
Kovalenter Radius 190 pm
Elektronenkonf. [Car] 4f(13) 6s2
1. Ionization 596,7 KJ / mol
2. Ionization 1160 KJ / mol
3. Ionization 2285 KJ / mol
Physical State fixed
Crystal structure hexagonal
Density 9,318 g/cm3 (25 ° C)
Magnetism paramagnetisch (χm = 0,017)
Melting point 1818 K (1545 C)
Boiling point 2223 K (1950 C)
Molar Volume 19,1 * 10(-6)m(3)/mol
Heat of vaporization 250 KJ / mol
Schmelzwärme 16,8 KJ / mol
Electrical conductivity 1,477*10(6) A/(V * m)
Thermal conductivity 16,8 W /(m*K)
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