Tellurium dioxide

Tetragonal ( α - TeO 2 )

A = 480 pm c = 761 pm

Te, O

  • Tellurium ( IV) oxide
  • Tellurium
  • Paratellurite ( α - TeO 2 )
  • Tellurite ( β - TeO2 )

Colorless, tetragonal, oktaederähnliche crystals

Fixed

6.02 g · cm -3 ( 20 ° C)

733 ° C

1245 ° C

Practically insoluble in water

  • 2.260 at 630 nm
  • Depending on the wavelength and the optical axis from 2.19 to 2.5

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Tellurium dioxide is an inorganic chemical compound, more precisely, an oxide of tellurium with the formula TeO2. It is the anhydride of the unstable tellurous acid ( H2TeO3 ) and under normal conditions a colorless solid.

Occurrence

Tellurium dioxide exists in two modifications, both ( orthorhombic β - TeO2, ) also occur in nature in the form of minerals paratellurite ( α - TeO 2, tetragonal) and tellurite. These two modifications are structurally very closely related and can usually be distinguished by their color, tellurite often has a yellow color is colorless while paratellurite usually.

Production and representation

Tellurium dioxide is produced from elemental tellurium by combustion in air in a blue flame:

TeO2 is technically prepared by reacting tellurium with concentrated nitric acid (HNO3) at 400 ° C. In this case, elemental tellurium is oxidized to Te (IV ) oxide, while the 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 P41212 with lattice constants a = 480 and c = 761 pm. The link goes to a red melt at 732.6 ° C. Above 1245 ° C TeO2 is a yellow gas.

Chemical Properties

Tellurium dioxide dissolves very poorly in water to form low amounts of acid tellurous:

The equilibrium constant of the reaction is very small, the equilibrium lies far to the left. The produced tellurous acid is weakly amphoteric and reacted with strong acids (such as hydrochloric acid HCl) formation of tellurium (IV ) salts:

Reactions with bases lead to the formation of Hydrogentellurat (IV ) - ( HTeO3 ) or tellurate (IV ) ions ( TeO32 ):

Use

Glasses of tellurium dioxide have very high refractive indices and can therefore be used in optical fibers as an alternative to SiO2 glasses. TeO2 crystals are also used as acousto-optical modulators ( AOM).

Biological Significance

Tellurium has no biological significance

Safety

Tellurium dioxide is considered to be harmful, especially through inhalation of TeO2 - particles and dust.

Coordination number CAS registry number Zemannite Chemical equilibrium
764737
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