Germanium tetrachloride is a colourless, fuming liquid with a peculiar, acidic odour. It is used as an intermediate in the production of purified germanium metal. In recent years, GeCl<sub>4</sub> usage has increased substantially due to its use as a reagent for fiber optic 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, GeO<sub>2</sub>.
Germanium tetrachloride can be generated directly from GeO<sub>2</sub> (germanium dioxide) by dissolution of the oxide in concentrated hydrochloric acid.
The resulting mixture is fractionally distilled to purify and separate the germanium tetrachloride from other products and impurities. The GeCl<sub>4</sub> can be rehydrolysed with deionized water to produce pure GeO<sub>2</sub>, which is then reduced under hydrogen to produce germanium metal.
Production of GeO<sub>2</sub>, however, is dependent on the oxidized form of germanium extracted from the ore. Copper-lead-sulfide and zinc-sulfide ores will produce GeS<sub>2</sub>, which is subsequently oxidized to GeO<sub>2</sub> with an oxidizer such as sodium chlorate. Zinc-ores are roasted and sintered and can produce the GeO<sub>2</sub> directly. The oxide is then processed as discussed above.
The classic synthesis from chlorine and germanium metal at elevated temperatures is also possible. Additionally, a chlorine free activation of germanium has been developed, giving a less energy intensive and more environmentally friendly alternative synthesis for germanium precursors.
Germanium tetrachloride is used almost exclusively as an intermediate for several optical processes. GeCl<sub>4</sub> can be directly hydrolysed to GeO<sub>2</sub>, an oxide glass with several unique properties and applications, described below and in linked articles:
A notable derivative of GeCl<sub>4</sub> is germanium dioxide. In the manufacture of optical fibers, silicon tetrachloride, SiCl<sub>4</sub>, and germanium tetrachloride, GeCl<sub>4</sub>, 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 GeO<sub>2</sub> has a high index of refraction, so by varying the flow rate of germanium tetrachloride the overall index of refraction of the optical fiber can be specifically controlled. The GeO<sub>2</sub> is about 4% by weight of the glass.