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| Names | |||
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| IUPAC name Germanium dioxide | |||
| Other names Germanium(IV) oxide Germania ACC10380 G-15 Neutral germanium oxide (1:2) Germanic oxide Salt of germanium | |||
| Identifiers | |||
3D model (JSmol) | |||
| ChemSpider |
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| ECHA InfoCard | 100.013.801 | ||
| RTECS number |
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| UNII | |||
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| Properties | |||
| GeO2 | |||
| Molar mass | 104.6388 g/mol | ||
| Appearance | White powder or colourless crystals | ||
| Density | 4.228 g/cm3 | ||
| Melting point | 1,115 °C (2,039 °F; 1,388 K) | ||
| 4.47 g/L (25 °C) 10.7 g/L (100 °C) | |||
| Solubility | Soluble inHF, insoluble in other acid. Soluble in strong alkaline conditions. | ||
| −34.3·10−6 cm3/mol | |||
Refractive index (nD) | 1.650 | ||
| Structure | |||
| Hexagonal | |||
| Hazards | |||
| NFPA 704 (fire diamond) | |||
| Flash point | Non-flammable | ||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) | 3700 mg/kg (rat, oral) | ||
| Related compounds | |||
Otheranions | Germanium disulfide Germanium diselenide | ||
Othercations | Carbon dioxide Silicon dioxide Tin dioxide Lead dioxide | ||
Related compounds | Germanium monoxide | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Germanium dioxide, also calledgermanium(IV) oxide,germania, andsalt of germanium,[1] is aninorganic compound with the chemical formulaGeO2. It is the main commercial source of germanium. It also forms as apassivation layer on pure germanium in contact with atmospheric oxygen.
The two predominant polymorphs of GeO2 are hexagonal and tetragonal. Hexagonal GeO2 has the same structure as α-quartz, with germanium havingcoordination number 4. Tetragonal GeO2 (the mineralargutite) has therutile-like structure seen instishovite. In this motif, germanium has the coordination number 6. An amorphous (glassy) form of GeO2 is similar tofused silica.[2]
Germanium dioxide can be prepared in bothcrystalline andamorphous forms. At ambient pressure the amorphous structure is formed by a network of GeO4 tetrahedra. At elevated pressure up to approximately 9 GPa the germanium averagecoordination number steadily increases from 4 to around 5 with a corresponding increase in the Ge–O bond distance.[3] At higher pressures, up to approximately 15 GPa, the germaniumcoordination number increases to 6, and the dense network structure is composed of GeO6 octahedra.[4] When the pressure is subsequently reduced, the structure reverts to the tetrahedral form.[3][4] At high pressure, the rutile form converts to an orthorhombic CaCl2 form.[5]
Heating germanium dioxide with powderedgermanium at 1000 °C formsgermanium monoxide (GeO).[2]
The hexagonal (d = 4.29 g/cm3) form of germanium dioxide is more soluble than the rutile (d = 6.27 g/cm3) form and dissolves to form germanic acid, H4GeO4, or Ge(OH)4.[6] GeO2 is only slightly soluble in acid but dissolves more readily in alkali to givegermanates.[6] The Germanic acid forms stable complexes with di- and polyfunctionalcarboxylic acids,poly-alcohols, ando-diphenols.[7]
In contact withhydrochloric acid, it releases the volatile and corrosivegermanium tetrachloride.
Therefractive index (1.7) andoptical dispersion properties of germanium dioxide make it useful as an optical material forwide-angle lenses, inoptical microscopeobjectivelenses, and for the core of fiber-optic lines. SeeOptical fiber for specifics on the manufacturing process. Both germanium and its glass oxide, GeO2, are transparent to theinfrared (IR) spectrum. The glass can be manufactured into IR windows and lenses, used fornight-vision technology in the military, luxury vehicles,[8] andthermographic cameras. GeO2 is preferred over other IR transparent glasses because it is mechanically strong and therefore preferred for rugged military usage.[9]
A mixture of silicon dioxide and germanium dioxide ("silica-germania") is used as an optical material foroptical fibers andoptical waveguides.[10] 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 replacedtitania as the silica dopant for silica fiber, eliminating the need for subsequent heat treatment, which made the fibers brittle.[11]
Germanium dioxide is used as a colorant in borosilicate glass, used in lampworking. When combined with copper oxide, it provides a more stable red. It gives the glass a very reactive/changeable color, "a wonderful rainbow effect" when combined with silver oxide, that can shift light amber to a somewhat reddish and even deep purple appearance. The color can vary based on flame chemistry of the flame used to melt the glass (whether it has more oxygen or whether it has more fuel) And also it can change colors depending on the temperature of the kiln used to anneal the glass.[12]
Germanium dioxide is also used as acatalyst in production ofpolyethylene terephthalate resin,[13] and for production of other germanium compounds. It is used as a feedstock for production of somephosphors andsemiconductor materials.
Germanium dioxide is used inalgaculture as an inhibitor of unwanteddiatom growth in algal cultures, since contamination with the comparatively fast-growing diatoms often inhibits the growth of or outcompetes the original algae strains. GeO2 is readily taken up by diatoms and leads to silicon being substituted by germanium in biochemical processes within the diatoms, causing a significant reduction of the diatoms' growth rate or even their complete elimination, with little effect on non-diatom algal species. For this application, the concentration of germanium dioxide typically used in the culture medium is between 1 and 10 mg/L, depending on the stage of the contamination and the species.[14]
Germanium dioxide has low toxicity, but it isnephrotoxic in higher doses.[citation needed]
Germanium dioxide is used as a germanium supplement in some questionabledietary supplements and "miracle cures".[15] High doses of these resulted in several cases of germanium poisonings.
