General information
Thulium is a chemical element with the element symbol Tm and the atomic number 69. In the periodic table it is in the group of lanthanides and thus also belongs to the metals of the rare earths.
Thulium (named after Thule, the mythical island on the edge of the world) 1879 was discovered by the Swedish chemist Per Teodor Cleve along with holmium in Erbia (Erbiumoxid) (see history of holmium).
In nature thulium occurs only in compounds. Thulium-containing minerals of low concentration are:
Monazite (Ce, La, Th, Nd, Y) PO4 (Tm content <0,01%)
Gadolinite (Tm content about 0,25%)
Recovery
After extensive separation of the other Thuliumbegleiter the oxide is reduced with lanthanum to metallic thulium. Subsequently, the thulium is sublimed.
Features
The silver-gray metal of the rare earths is very soft, easily stretchable and malleable.
In dry air, thulium is quite stable, in moist air it turns gray. At higher temperatures it burns to Sesquioxid.With water, it reacts with evolution of hydrogen to the hydroxide. In mineral acids, it dissolves to form hydrogen.
In its compounds it is present in the oxidation state + 3, the Tm3 + cations form pastel-bluish-green solutions in water.
Usage
Use in televisions (to activate the phosphors on the screen) has few commercial applications:
170Tm outsourced from nuclear reactors serves as X-ray source (gamma emitter in materials testing)
Thulium-doped yttrium tantalate or lanthanum oxybromide (LaOBr) serves as a scintillator in X-ray intensifying screens or X-ray screens
Thulium-doped calcium sulfate serves as a detector in personal dosimeters for the measurement of low radiation doses
Thulium crystals can be used as the active medium in diode-pumped solid-state lasers (wavelength 2 μm) with an overall efficiency of up to 10% at maximum 60 W light output.
Thulium-doped silica glass as an active medium in fiber lasers (wavelength 2 µm) was operated with a differential efficiency of 53,2% at a power> 1000 W.
Thulium and thulium compounds are low in toxicity. Thulium dusts are fire and explosive.
| General | |
| Name, symbol
ordinal |
Thulium, Tm, 69 |
| Series | lanthanides |
| Group, period, block | La, 6, f |
| Appearance | silvery grua |
| CAS number | 7440-30-4 |
| Mass fraction of the earth's envelope | 0,19 ppm |
| Atomic | |
| atomic mass | 168,93421 u |
| atomic radius | 175 pm |
| Covalent radius | 190 pm |
| Elektronenkonf. | [Xe] 4f (13) 6s2 |
| 1. ionization | 596,7 KJ / mol |
| 2. ionization | 1160 KJ / mol |
| 3. ionization | 2285 KJ / mol |
| Physically | |
| Physical state | fest |
| crystal structure | hexagonal |
| density | 9,318 g / cm3 (25 ° C) |
| magnetism | paramagnetic (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 |
| heat of fusion | 16,8 KJ / mol |
| Electric conductivity | 1,477 * 10 (6) A / (V * m) |
| thermal conductivity | 16,8 W / (m * K) |
