Gallium

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.[1]

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.[1]

Properties

General
Name : gallium
Symbol : Ga
Atomic Number : 31
Chemical Series : Post-transition Metal (Poor Metal)
Block, Period : 13, 4
Appearance : silvery white
Atomic Properties
Atomic Weight (amu) : 69.723
Covalent Radius (pm) : 126
Physical Properties
Matter : solid (diamagnetic)
Density (kg/) : 5904
Hardness : 1.5
Melting Point (K) : 302.9146
Boiling Point (K) : 2477
Evaporation Heat (kJ/mol) : 258.7
Fusion Heat (kJ/mol) : 5.59
Specific Heat (J/(kg*K) ) : 370
Miscellaneous
Electrical Conductivity (/m ohm) : 6.78
Thermal Conductivity (W/(m*K) ) : 40.6

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.[1]

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.[1]

Handling

Its toxicity appears to be of a low order, but should be handled with care until more data is available.[1]

Notes

[1] From Los Alamos National Laboratory's Chemistry Division Website