Ga - Gallium
|Chemical Element||Gallium||Melting Point °C||29.7646|
|Chemical Symbol||Ga||Boiling Point °C||2403|
|Atomic Number||31||Density g/cm3||Solid 5.9, Liquid 6.1|
Gallium is a silvery-white metal belonging to Group 13 of the Periodic Table. It is the 34th most abundant element within the Earth’s crust. Gallium is so soft that it can be cut with a knife and melts very close to room temperature, and therefore in hot countries over 30°C, mercury is not the only liquid metal. Gallium is stable in air and water, but it reacts and dissolves in acids and alkalis. As gallium has such a low melting temperature, if held, it will melt in the hand leaving a brown stain. Gallium’s most characteristic property is that it has the longest liquid range of all the elements, with a boiling point of 2403°C, meaning that it is in liquid form for 2373°C. Another interesting property of gallium is that it expands when frozen, similar to water.
In 1869, gallium was predicted by Dmitri Mendeleyev when he published his book of elements; Mendeleyev was able to predict its existence, position and its properties. Unaware of this previous prediction, Paul-Emile Lecoq de Bois-Baudran discovered gallium in Paris in the year1875. Whilst analysing the spectrum of some zinc he had obtained from a zinc ore, he noticed a new pale violet line at 416 nanometres. This line meant that there must be a new element present in the zinc. By November 1875, Bois-Baudran had already isolated gallium as a metal and had even purified it by electrolysis. On 6 December 1875, he presented a sample to the French Academy of Sciences and christened the element ‘gallium’ after the Latin name for his country, France.
Current world production of gallium is about 200 mt per year, with the main producing nations being China, Germany, Kazakhstan and Ukraine. Smaller producing nations include Hungary (Ajka), Japan, Russia and Slovakia. There are many countries also involved in the recycling and refining of gallium scrap, Japan being one of the leading nations in this area. Gallium is mainly recovered as a by-product of treating bauxite (the main source of aluminium). Several ores do contain gallium, but in such small quantities that they are not economically viable sources, especially as these are widely dispersed geographically. Coal can contain approximately 1.5% Ga, but there are no ores which are mined purely for gallium extraction.
Gallium consumption is centred on the superconductor industry. When alloyed with arsenic to produce gallium arsenide (GaAs), it can convert electricity to light. Due to such properties, it is used in LEDs, and has been found to produce less heat than silicon, rendering it suitable for use in supercomputers. Tiny amounts of tin and zinc can also be added to gallium arsenide in order to slightly modify and adjust levels of superconductivity. According to USGS, over 95% of the US gallium market is used as superconductors, 67% of which is used in integrated circuits, 31% in optoelectronics (laser diodes, LEDs, photo-detectors and solar cells), the final 2% is used in research and development, speciality alloys and other applications. Overall, about 98% of US gallium consumption was as GaAs and GaN in electronics components.
Today, gallium has received a great deal of publicity due to its use in CIGS solar cell technology, which is becoming increasingly efficient. MIT has also developed an integrated GaN and Si hybrid microchip, which is expected to be smaller, faster and more efficient than conventional chips, and has the potential to be brought to market in the near future.
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- Gray, Theodore. The Elements, A Visual Exploration of Every Known Atom in the Universe, Black Dog & Leventhal Publishers, Inc, NY, 2009
- Stwertka, Albert. A Guide to the Elements, 3rd Edition, Oxford University Press, 2012