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Gallium

Background

Gallium (Ga) was predicted and described by Mendeleev as ekaaluminum, and discovered spectroscopically by Lecoq de Boisbaudran in 1875. That same year Lecoq de Boisbaudran obtained the free metal by electrolysis of a solution of the hydroxide in KOH. Gallium can be found as a trace element in diaspore, sphalerite, germanite, bauxite and coal. Gallium exists in nature in about the same amount as lead, but it is widely dissipated and not found concentrated in any ore. It is mainly recovered from the smelter flue dust of zinc ores and as a by-product of copper smelting and aluminium production.

Along side mercury, caesium/cesium and rubidium, gallium is the only metal which can be liquid near room temperatures. It possesses one of the longest liquid ranges of any metal and a low vapour pressure even at elevated temperatures. Gallium has a strong tendency to supercool below its freezing point, making seeding necessary to initiate solidification.

High purity gallium exhibits a beautiful silvery white appearance (resembling mercury). Like glass, it exhibits a conchoidal fracture. Upon solidifying gallium expands 3.8% and hence should not be stored in glass containers. When it is made under certain conditions gallium exhibits superconductivity at –262°C (-440°F).

Pure gallium is resistant to mineral acids and dissolves with difficulty in caustic alkali. It forms numerous salts at different valences. In the molten state it attacks other metals.

Applications

Because of it wide liquid temperature range gallium finds uses for high-temperature thermometers. It is used as a wetting agent in tin-lead solders, which also decreases the solders susceptibility to oxidation.

Gallium is used as an electron carrier in silicon semiconductors. Gallium arsenide (GaAs) is used as a semiconductor and in rectifiers that operate at temperatures to 316°C (600°F). Gallium arsenide is capable of converting electricity directly into coherent light. It is also used in lenses in CO2 laser systems.

As an alloying agent to reduce the melting point of the alloy.

Magnesium gallate containing divalent impurities such as Mn2+ is finding use in commercial ultraviolet activated powders phosphors.

Gallium selenide (GaSe) and gallium triiodide (GaI3) are used on electronic applications.

Primary author: AZoM.com

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