Tellurium dioxide

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Tellurium dioxide
TeO2powder.jpg
Cryst struct teo2.png
α-TeO2, paratellurite
Identifiers
CAS number 7446-07-3 YesY
PubChem 62638
ChemSpider 56390 YesY
UNII 397E9RKE83 YesY
Jmol-3D images Image 1
Properties
Molecular formula TeO2
Molar mass 159.60 g/mol
Appearance white solid
Density 5.670 g/cm3 (tetragonal)
6.04 g/cm3 (orthorhombic) [1]
Melting point 732 °C (1,350 °F; 1,005 K)
Boiling point 1,245 °C (2,273 °F; 1,518 K)
Solubility in water negligible
Solubility soluble in acid and alkali
Refractive index (nD) 2.24
Hazards
EU Index Not listed
Flash point Non-flammable
Related compounds
Other cations Sulfur dioxide
Selenium dioxide
Related tellurium oxides Tellurium trioxide
Tellurium monoxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Tellurium dioxide (TeO2) is a solid oxide of tellurium. It is encountered in two different forms, the yellow orthorhombic mineral tellurite, β-TeO2, and the synthetic, colourless tetragonal (paratellurite), α-TeO2.[2] Most of the information regarding reaction chemistry has been obtained in studies involving paratellurite, α-TeO2.[3]

Preparation[edit]

Paratellurite, α-TeO2, is produced by reacting tellurium with O2:[2]

Te + O2 → TeO2

An alternative preparation is to dehydrate tellurous acid, H2TeO3, or to thermally decompose basic tellurium nitrate,Te2O4.HNO3 above 400 °C.[2]

Physical properties[edit]

The speed of sound in Tellurium dioxide is 4250 m/s[citation needed].

Chemical properties[edit]

TeO2 is highly insoluble in water and soluble in concentrated sulfuric acid. (According to reference 4 Tellurium dioxide is soluble in water, p59. Tellurium trioxide is insoluble in water, p56). It is also incompatible with strong acids and strong oxidizing agents. It is an amphoteric substance and therefore can act both as an acid or as a base depending on the solution it is in.[4] It reacts with acids to make tellurium salts and bases to make tellurites. It can be oxidized to telluric acid or tellurates.

Structure[edit]

Paratellurite, α-TeO2, converts at high pressure into the β-, tellurite form.[5] Both the α-, (paratellurite) and β- (tellurite forms) contain four coordinate Te with the oxygen atoms at four of the corners of a trigonal bipyramid. In paratellurite all vertices are shared to give a rutile-like structure, where the O-Te-O bond angle are 140°. α-TeO2 In tellurite pairs of trigonal pyramidal, TeO4 units, sharing an edge, share vertices to then form a layer.[5] The shortest Te-Te distance in tellurite is 317 pm, compared to 374 pm in paratellurite.[5] Similar Te2O6 units are found in the mineral denningite.[5]

TeO
2
melts at 732.6 °C, forming a red liquid.[6]

Uses[edit]

It is used as an acousto-optic material.

Tellurium dioxide is also a conditional glass former, which means it will form a glass with small molar% additions of a second compound such as an oxide or halide. TeO2 glasses have high refractive indices and transmit into the mid-infrared part of the electromagnetic spectrum, therefore they are of technological interest for optical waveguides. Tellurite glasses have also been shown to exhibit Raman gain up to 30 times that of silica, useful in optical fibre amplification.[7]

Safety[edit]

TeO2 is a possible teratogen.[8]

Exposure to tellurium compounds produces a garlic-like odour on the breath, caused by the formation of ethyl telluride.[9]

References[edit]

  1. ^ Pradyot Patnaik (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 0-07-049439-8. 
  2. ^ a b c Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. p. 911. ISBN 0-08-022057-6. 
  3. ^ W.R.McWhinnie (1995) Tellurium - Inorganic chemistry Encyclopedia of Inorganic Chemistry Ed. R. Bruce King (1994) John Wiley & Sons ISBN 978-0-471-93620-6
  4. ^ K. W. Bagnall (1966). The Chemistry of Selenium, Tellurium and Polonium. London: Elsevier. pp. 59–60. ISBN 0-08-018855-9. 
  5. ^ a b c d Wells, A. F. (1984), Structural Inorganic Chemistry (5th ed.), Oxford: Clarendon Press, ISBN 0-19-855370-6 
  6. ^ Egon Wiberg; Nils Wiberg; Arnold Frederick Holleman (2001). Inorganic chemistry. Academic Press. pp. 592–593. ISBN 0-12-352651-5. 
  7. ^ Stegeman R, Jankovic L, Kim H, Rivero C, Stegeman G, Richardson K, Delfyett P, Guo Y, Schulte A, Cardinal T (2003). "Tellurite glasses with peak absolute Raman gain coefficients up to 30 times that of fused silica". Optics Letters 28 (13): 1126–8. doi:10.1364/OL.28.001126. PMID 12879929. 
  8. ^ Perez-D'Gregorio RE, Miller RK, Baggs RB (1988). "Maternal toxicity and teratogenicity of tellurium dioxide in the Wistar rat: relationship to pair-feeding". Reprod. Toxicol. 2 (1): 55–61. doi:10.1016/S0890-6238(88)80009-1. PMID 2980402. 
  9. ^ Atta-ur-Rahman (2008). Studies in Natural Products Chemistry, Volume 35. Elsevier. p. 905. ISBN 0-444-53181-5. 

External links[edit]