Germanium tetrachloride

Germanium tetrachloride is a colourless liquid used as an intermediate in the production of purified germanium metal. In recent years, GeCl₄ usage has increased substantially due to its use as a reagent for fiber optic production.

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Production

Most commercial production of germanium is from treating flue-dusts of zinc- and copper-ore smelters, although a significant source is also found in the ash from the combustion of certain types of coal called vitrain. Germanium tetrachloride is an intermediate for the purification of germanium metal or its oxide, GeO₂.^[1]

Germanium tetrachloride can be generated directly from GeO₂ by dissolution of the oxide in concentrated hydrchloric acid. The resulting mixture is fractionally distilled to purify and separate the germanium tetrachloride from other products and impurities.^[2] The GeCl₄ can be rehydrolyzed with deionized water to produce pure GeO₂, which is then reduced under hydrogen to produce germanium metal.^[1][2]

Production of GeO₂, however, is dependent on the oxidized form of germanium extracted from the ore. Copper-lead-sulfide and zinc-sulfide ores will produce GeS₂, which is subsequently oxidized to GeO₂ with an oxidizer such as sodium chlorate. Zinc-ores are roasted and sintered and can produce the GeO₂ directly. The oxide is then processed as discussed above.^[1]

Application

Germanium tetrachloride is used almost exclusively as an intermediate for several optical processes. GeCl₄ can be directly hydrolyzed to GeO₂, an oxide glass with several unique properties and applications, described below:

Fiber Optics

Most notable of GeO₂ is its high index of refraction and low optical dispersion, used for wide camera lens, microscopy, and for the core of fiber-optic lines.^[2] See Optical fiber for specifics on the manufacturing process. Overall, silicon tetrachloride, SiCl₄ and germanium tetrachloride, GeCl₄ are introduced with oxygen into a hollow glass preform, which is carefully heated to allow for oxidation of the reagents to their respective oxides and formation of a glass mixture. The GeO₂ has a high index of refraction, so by varying the flowrate of germanium tetrachloride the overall index of refraction of the optical fiber can be specifically controlled. The GeO₂ is about 4% by weight of the glass.^[1]

Infrared

Germanium and its glass oxide, GeO₂ are transparent to the infrared spectrum. The glass can be manufactured into IR windows and lenses, used for night-vision technology in the military and luxury vehicles.^[2] GeO₂ is preferred over other IR transparent glasses because it is mechanically strong and therefore preferred for rugged military usage.^[1]

Future

As of the year 2000, about 15% of United States consumption of germanium is used for infrared optics technology and 50% for fiber-optics. Over the past 20 years, infrared use has consistently decreased; fiber optic demand, however, is slowly increasing. There is discussion on the over-production of fiber-optic networks and that 30-50% of current lines are unused "dark" fiber, suggesting a future reduction in demand. Worldwide, demand is increasing dramatically as countries such as China are expanding fiber-optic based telecommunication throughout the country.^[1]

References

1. ^ ^{a b c d e f} "Germanium" Mineral Commodity Profile, U.S. Geological Survey, 2005.
2. ^ ^{a b c d} "The Elements" C.R. Hammond, David R. Lide, ed. CRC Handbook of Chemistry and Physics, Edition 85 (CRC Press, Boca Raton, FL) (2004)

See also

• Germanium
• Optical fiber
• Infrared