Tellurium dioxide
Crystal structure | |||||||||||||||||||
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__ Te 4+ __ O 2− | |||||||||||||||||||
Crystal system |
tetragonal (α-TeO 2 ) |
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Space group |
P 4 1 2 1 2 (No. 92) |
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Lattice parameters |
a = 480 pm |
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Coordination numbers |
Te [4], O [2] |
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General | |||||||||||||||||||
Surname | Tellurium dioxide | ||||||||||||||||||
other names |
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Ratio formula | TeO 2 | ||||||||||||||||||
Brief description |
colorless, tetragonal, octahedral crystals |
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External identifiers / databases | |||||||||||||||||||
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properties | |||||||||||||||||||
Molar mass | 159.61 g mol −1 | ||||||||||||||||||
Physical state |
firmly |
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density |
6.02 g cm −3 (20 ° C) |
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Melting point |
733 ° C |
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boiling point |
1245 ° C |
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solubility |
practically insoluble in water |
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Refractive index |
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safety instructions | |||||||||||||||||||
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As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C |
Tellurium dioxide is an inorganic chemical compound , more precisely an oxide of tellurium with the formula TeO 2 . It is the anhydride of the volatile telluric acid (H 2 TeO 3 ) and a colorless solid under normal conditions.
Occurrence
Tellurium dioxide exists in two modifications , both of which also occur naturally in the form of the minerals paratellurite (α-TeO 2 , tetragonal ) and tellurite (β-TeO 2 , orthorhombic ). These two modifications are structurally very closely related to each other and can usually be differentiated by their color, tellurite often has a yellow color while paratellurite is usually colorless.
Extraction and presentation
Tellurium dioxide is created from elemental tellurium by combustion in air in a blue flame:
Technically, TeO 2 is produced by reacting tellurium with concentrated nitric acid (HNO 3 ) at 400 ° C. Elemental tellurium is oxidized to Te (IV) oxide , while nitric acid is reduced to nitrogen oxides :
properties
Physical Properties
Tellurium dioxide (paratellurite) is a solid and crystallizes in the tetragonal crystal system in the space group P 4 1 2 1 2 (space group no. 92) with the lattice constants a = 480 and c = 761 pm . The compound turns into a red melt at 732.6 ° C. Above 1245 ° C, TeO 2 is a yellow gas.
Chemical properties
Tellurium dioxide dissolves very poorly in water with the formation of small amounts of telluric acid:
The equilibrium constant of the reaction is very small, the equilibrium is far to the left. The resulting telluric acid is weakly amphoteric and reacts with strong acids (e.g. hydrochloric acid HCl) to form tellurium (IV) salts :
Reactions with bases lead to the formation of hydrogen tellurate (IV) - (HTeO 3 - ) or tellurate (IV) ions (TeO 3 2− ):
use
Glasses made from tellurium dioxide have very high refractive indices and can therefore be used in optical waveguides as an alternative to SiO 2 glasses . TeO 2 crystals are also used as acousto-optical modulators (AOM).
safety instructions
Tellurium dioxide is considered to be harmful, especially through inhalation of TeO 2 particles and dust.
See also
Individual evidence
- ↑ a b Entry on tellurium oxides. In: Römpp Online . Georg Thieme Verlag, accessed on December 22, 2014.
- ↑ a b c d e Entry on tellurium dioxide in the GESTIS substance database of the IFA , accessed on January 28, 2018(JavaScript required) .
- ↑ alineason.com: tellurium dioxide , accessed on April 17, 2013.
- ^ Almaz Optics, Inc.
- ↑ G. Brauer (Ed.): Handbook of Preparative Inorganic Chemistry 2nd ed., Vol. 1, Academic Press 1963, pp. 447-9.