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Gallium

Author: Robert Husted, Mollie Boorman

Atomic Number 31
Atomic Symbol Ga
CAS ID No. 7440-55-3
Atomic Weight 69.7200 amu
Electron Configuration [Ar] 3d10 4s2 4p1
Melting Point 29.9 C
Boiling Point 2205 C
Density 5.910 g/cm3
History

(L. Gallia: France; also from Latin, gallus, a translation of "Lecoq", a cock) Predicted and described by Mendeleev as ekaaluminum, and discovered spectroscopically by Lecoq de Boisbaudran in 1875, who in the same year obtained the free metal by electrolysis of a solution of the hydroxide in KOH.

Sources

Gallium is often found as a trace element in diaspore, sphalerite, germanite, bauxite, and coal. Some flue dusts from burning coal have been shown to contain as much 1.5 percent gallium.

Properties

It is one of four metals - mercury, cesium, and rubidium - which can be liquid near room temperature and, thus, can be used in high-temperature thermometers. It has one of the longest liquid ranges of any metal and has a low vapor pressure even at high temperatures.

There is a strong tendency for gallium to supercool below its freezing point. Therefore, seeding may be necessary to initiate solidification.

Ultra-pure gallium has a beautiful, silvery appearance, and the solid metal exhibits a conchoidal fracture similar to glass. The metal expands 3.1 percent on solidifying; therefore, it should not be stored in glass or metal containers, because they may break as the metal solidifies.

High-purity gallium is attacked only slowly by mineral acids.

Uses

Gallium wets glass or porcelain and forms a brilliant mirror when it is painted on glass. It is widely used in doping semiconductors and producing solid-state devices such as transistors.

Magnesium gallate containing divalent impurities, such as Mn+2, is finding use in commercial ultraviolet-activated powder phosphors. Gallium arsenide is capable of converting electricity directly into coherent light. Gallium readily alloys with most metals, and has been used as a component in low-melting alloys.

Handling

Its toxicity appears to be of a low order, but should be handled with care until more data is available.




Last Update: 2011-02-16