Tellurium dioxide

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Crystal structure
Structure of tellurium dioxide
__ Te 4+      __ O 2−
Crystal system

tetragonal (α-TeO 2 )

Space group

P 4 1 2 1 2 (No. 92)Template: room group / 92

Lattice parameters

a = 480 pm
c = 761 pm

Coordination numbers

Te [4], O [2]

General
Surname Tellurium dioxide
other names
  • Tellurium (IV) oxide
  • Tellurium oxide
  • Paratellurite (α-TeO 2 )
  • Tellurite (β-TeO 2 )
Ratio formula TeO 2
Brief description

colorless, tetragonal, octahedral crystals

External identifiers / databases
CAS number 7446-07-3
EC number 231-193-1
ECHA InfoCard 100.028.357
PubChem 62638
ChemSpider 56390
Wikidata Q425220
properties
Molar mass 159.61 g mol −1
Physical state

firmly

density

6.02 g cm −3 (20 ° C)

Melting point

733 ° C

boiling point

1245 ° C

solubility

practically insoluble in water

Refractive index
  • 2.260 at 630 nm
  • Depending on the wavelength and the optical axis between 2.19 and 2.5
safety instructions
GHS labeling of hazardous substances
no GHS pictograms
H and P phrases H: no H-phrases
P: no P-phrases
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

Zemannite crystals on paratellurite (α-TeO 2 )

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. Template: room group / 92

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

  1. a b Entry on tellurium oxides. In: Römpp Online . Georg Thieme Verlag, accessed on December 22, 2014.
  2. a b c d e Entry on tellurium dioxide in the GESTIS substance database of the IFA , accessed on January 28, 2018(JavaScript required) .
  3. alineason.com: tellurium dioxide , accessed on April 17, 2013.
  4. ^ Almaz Optics, Inc.
  5. G. Brauer (Ed.): Handbook of Preparative Inorganic Chemistry 2nd ed., Vol. 1, Academic Press 1963, pp. 447-9.