Germanium dioxide

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IUPACName = germanium dioxide
OtherNames = Germanium oxide, Germanium(IV) oxide, Germania, Germanic oxide (crystalline), Germanic acid, ACC10380, G-15
Section1 = Chembox Identifiers
CASNo = 1310-53-8
PubChem = 14796
SMILES = O= [Ge] =O
InChI = 1/GeO2/c2-1-3
Section2 = Chembox Properties
Formula = GeO₂
MolarMass = 104.61 g/mol
Appearance = white powder or colourless crystals
Density = 3.64 g/cm³
MeltingPt = 1115 °C
BoilingPt = 1200 °C
Solubility =5.2 g/l (25 °C)10.7 g/l (100 °C)
Section3 = Chembox Hazards
MainHazards =
FlashPt =
Autoignition =
RPhrases = R22

Germanium dioxide, also called germanium oxide and germania, is an inorganic compound, an oxide of germanium. Its chemical formula is GeO₂. Its other names are germanic acid, G-15, and ACC10380. It forms as a passivation layer on pure germanium in contact with atmospheric oxygen.

tructure

The forms of germanium dioxide to an extent parallel those of silicon dioxide, hexagonal GeO₂ has the same structure as β-quartz (coordination number of germanium 4), tetragonal GeO₂ (the mineral argutite) has the rutile like structure of stishovite,(coordination number of germanium 6) and amorphous GeO₂ is similar to fused silica. Greenwood&Earnshaw] It can be prepared both crystalline and amorphous. At very high pressures,amorphous (glassy) germanium dioxide forms changes coordination to 6 coordinate, when the pressure is reduced the structure reverts back to the 4 coordinate form. [Formation and Structure of a Dense Octahedral Glass, M. Guthrie, C. A. Tulk, C. J. Benmore, J. Xu, J. L. Yarger, D. D. Klug, J. S. Tse, H-k. Mao, R. J. Hemley, Physical Review Letters, 93, 115502, doi|10.1103/PhysRevLett.93.115502] At high pressure the rutile form converts to an orthorhombic CaCl₂ form [Structural evolution of rutile-type and CaCl₂-type germanium dioxide at high pressure, J. Haines, J. M.Léger, C.Chateau, A. S.Pereira, Physics and Chemistry of Minerals, 27, 8 ,(2000), 575-582,doi|10.1007/s002690000092]

Reactions

Heating germanium dioxide with powdered germanium at 1000 °C forms germanium monoxide (GeO).
The rutile form of germanium dioxide is more soluble than the hexagonal form and dissolves to form germanic acid, H₄GeO₄ which may be Ge(OH)₄.Egon Wiberg, Arnold Frederick Holleman, (2001) "Inorganic Chemistry", Elsevier ISBN 0123526515] GeO₂ is only slightly soluble in acid but dissolves more readily in alkali to give germanates.
It is not flammable. In contact with hydrochloric acid it releases volatile and corrosive germanium tetrachloride.

Uses

Germanium dioxide's refractive index (1.7) and optical dispersion properties make it useful as an optical material for wide-angle lenses and in optical microscope objective lenses. It is transparent in infrared.
A mixture of silicon dioxide and germanium dioxide ("silica-germania") is used as an optical material for optical fibers and optical waveguides.cite web| url =http://minerals.usgs.gov/minerals/pubs/commodity/germanium/220400.pdf | title = GERMANIUM| author = Robert D. Brown, Jr.| publisher = U.S. Geological Survey | year = 2000] Controlling the ratio of the elements allows precise control of refractive index. Silica-germania glasses have lower viscosity and higher refractive index than pure silica. Germania replaced titania as the silica dopant for silica fiber, eliminating the need for subsequent heat treatment, which made the fibers brittle. [ [http://www.sri.com/policy/csted/reports/sandt/techin2/chp3.html Chapter Iii: Optical Fiber For Communications ] ]

Germanium dioxide is also used as a catalyst in production of polyethylene terephthalate resin,cite journal | author = Thiele, Ulrich K. | year = 2001 | title = The Current Status of Catalysis and Catalyst Development for the Industrial Process of Poly(ethylene terephthalate) Polycondensation | journal = International Journal of Polymeric Materials | volume = 50 | issue = 3 | pages = 387 – 394 |doi = 10.1080/00914030108035115 ] and for production of other germanium compounds. It is used as a feedstock for production of some phosphors and semiconductor materials.In the manufacture of integrated circuits and transistors, germanium dioxide is a rather poor dielectric and is chemically unstable, which is one of the disadvantages of germanium in comparison with silicon.

Toxicity and medical

Germanium dioxide has low toxicity; in higher doses it is nephrotoxic. Germanium dioxide is used as a germanium supplement in some questionable dietary supplements and "miracle cures". [cite journal | author = Tao, S.H. and Bolger, P.M. | year = 1997 | month = June | title = Hazard Assessment of Germanium Supplements | journal = Regulatory Toxicology and Pharmacology | volume = 25 | issue = 3 | pages = 211–219 | doi = 10.1006/rtph.1997.1098 ] High doses of these resulted in several cases of germanium poisonings.

References