Ge - Germanium
|Chemical Element||Germanium||Melting Point °C||938|
|Chemical Symbol||Ge||Boiling Point °C||2,830|
|Atomic Number||32||Density g/cm3||5.3|
Ultra-pure germanium is a silvery-white, brittle, semi-metal element that is found in Group 14 of the Periodic Table, and it is the 52nd most abundant element in the Earth’s crust. It is stable in air and water and is unaffected by acids, except HNO3 (Nitric Acid). Germanium is a relatively rare element and is never found in its pure form in nature. Germanium has unusual properties when exposed to different light: namely, it is opaque in visible light, but transparent in infrared light. This is not germanium’s only interesting property, as this element is a semi-conducting material. Germanium has many similar qualities to those of silicon, both physically and chemically. Mendeleyev predicted the existence of germanium and also said that it would have similar properties to silicon in his Periodic Table, therefore the discovery of this element was one that proved the power of his predictions. Germanium is one of four elements named after a country, in this case, Germany.
The discovery of germanium is credited to German chemist, Clemens Winkler, who discovered it in 1886, 15 years after its existence had been predicted by Mendeleyev. When writing his Periodic Table, he had left gaps for elements which he felt sure existed. The name “germanium” comes from the Latin Germania, the name for Germany. Winkler came across germanium when a colleague obtained a sample from a local mine. Once found, debates arose as to which missing element from Mendeleyev’s periodic table it might be. Mendeleyev thought it might be in the zinc/cadmium group, whilst Winkler thought it would belong to Group 5 and be a neighbour of anitomy. Both were in fact wrong, and as germanium’s properties were revealed, it became clear that it filled the gap between silicon and tin.
Due to germanium containing ores’ rarity, it is mainly recovered as a by-product from zinc and copper refining, and is also found in the flue dusts and ash of the combustion of certain coals for power generation. This process produces about 80mts per year, with the remainder coming from recycling (approx 30%) from the manufacture of optical devices, where at least 60% of the germanium used is recycled as scrap. The global production of germanium in 2009 was approximately 140 mts per year. According to USGS, the US produces about 4.6mt, China 100mt approx, Russia 5mt approx and other nations producing in total an extra 30mt. The US also holds reserves of about 450mt. In order to be utilised, germanium is mostly converted from germanium metal to germanium tetrachloride (GeCl4) or germanium dioxide (GeO2).
Germanium is mainly consumed in the form of germanium tetrachloride used in optical fibre production, infrared devices and substrates for electronic devices due to its properties as a semiconductor. Worldwide consumption of germanium is dominated by its use in fibre optics and infrared comprising 30% and 50% of the market respectively. Polymerisation catalyst production counts for 25% of germanium consumption, with electronics and solar electric applications at 15% and others (phosphors, metallurgy and chemotherapy at 5%). The US however differs slightly in its germanium consumption, as it uses no germanium for polymerisation catalysts and instead, 50% of the germanium consumed in the US is for infrared optics. Most germanium oxide is used in speciality glass in wide-angle camera lenses due to its high refractive index. Germanium substrates are used for applications requiring high levels of brightness and so are used in LEDs for LCD screens and vehicle headlights. Satellite applications also utilise germanium substrates over PV solar cells, which are said to convert sunlight into electricity to an efficiency of 41.6%.
The future of germanium looks bright, given its apparently leading efficiency in solar technology and the fact that metallic compounds containing CIGS (cadmium-indium-gallium-selenium) can be substituted by germanium, as it is often more reliable in many high-frequency electronics applications and more economical for some LED applications. Germanium can, however, be substituted by silicon in certain electronic applications, as it is less expensive, while titanium has the potential to substitute germanium as a polymerisation catalyst. The germanium metal market is higher than for germanium dioxide, though prices for both forms follow the same trend.