Terbium
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Terbium is a chemical element with the element symbol Tb and atomic number 65 in the periodic table it is in the group of lanthanides and also making it one of the metals of the rare earths. Terbium is named after the first locality, the pit Ytterby in Stockholm, named, as well as yttrium, ytterbium and erbium.
History
The discovery of the element terbium is very confusing and not understood. Generally you can see Carl Gustav Mosander as explorers, who examined the early 1840s the yttria discovered by Johan Gadolin. However, the supposedly pure terbium compound was a mixture of several lanthanides ( Bunsen ).
Pure terbium was prepared only with advent of ion exchange technology since 1945.
From the name of the Swedish pit Ytterby headed Mosander from the element name.
Occurrence
Terbium is found in nature only in compounds. Known terbiumhaltige minerals are:
- Cerit
- Monazite (Ce, Lath, Nd, Y) PO4 with a Tb content of max. 0.03 %, the principal ore of TB
- Gadolinit ( occurrence in Ytterby are exhausted )
- Euxenite (Y, Ca, Er, La, Ce, U, Th) (Nb, Ta , Ti) 2O6 with a Tb content of max. 1%
Production and representation
After an extensive separation of the other Terbiumbegleiter the oxide is reacted with hydrogen fluoride for terbium. Then is reduced with calcium to form calcium fluoride to the terbium. The removal of residual calcium residues and contaminants carried in an additional remelting in a vacuum.
Properties
The silver-gray rare earth metal is ductile and malleable. At temperatures above 1315 ° C, α - terbium ( hcp lattice ) transforms into β - terbium. In air terbium is relatively stable, it becomes covered with an oxide layer. In the flame, it burns to the brown terbium ( III, IV ) oxide ( Tb4O7 ). With water it reacts with evolution of hydrogen to hydroxide.
Use
Terbium is used to dope calcium fluoride, calcium tungstate and strontium molybdate for use in semiconductors ( solid-state devices). Together with zirconium ( IV) oxide, it serves to stabilize the structure in high temperature fuel cells. The oxide is added to the green phosphor in cathode ray tubes and fluorescent lamps. Natriumterbiumborat serves as a laser medium to produce coherent light having a wavelength of 546 nm (green).
Terbium-iron -cobalt or terbium - gadolinium - iron -cobalt alloys are used as a coating on rewritable magneto- optical (MO) discs. Terbium - dysprosium - containing alloys show a strong magnetostriction ( change in length by a magnetic field or magnetic pulses in length change). Such alloys are used in material testing.
In neodymium-iron -boron magnets, to increase the coercivity, that is, the demagnetization resistance is increased.
The transparent artificial crystal terbium gallium garnet Tb3Ga5O12 shows a strong Faraday effect and is therefore used for optical isolators
Safety
Terbium and Terbiumverbindungen are considered to be of low toxicity. The element has no biological importance for the human organism. Terbiummetallstäube, like almost all metal dust fire and explosion hazard.
Compounds
- Terbium (III, IV) oxide Tb4O7
- Terbium (III ) oxide Tb2O3
- Terbium ( IV) oxide TbO2
- Terbium (II ) fluoride TBF2
- Terbium (III ) fluoride TbF3
- Terbium (IV ) fluoride TbF4
- Terbium ( III) sulphate Tb2 (SO4) 3 · 8 H2O: colorless crystals which fluoresce under green excitation with short-wave UV radiation.
- Terbium gallium garnet Tb3Ga5O12