Gallium

Gallium is a chemical element in the periodic table that has the symbol Ga and atomic number 31. A rare, soft silvery metallic true metal, gallium is brittle at low temperatures but is liquid above room temperature and occurs in trace amounts in bauxite and zinc ores. Gallium arsenide is used as a semiconductor, most notably in light-emitting diodes (LEDs).

Table of contents

1 Notable Characteristics
2 Applications
3 History
4 Occurrence
5 External Links

Notable Characteristics

Very-pure gallium has a stunning silvery color and its solid metal fractures conchoidally like glass. Gallium metal expands 3.1 percent when it solidifys and therefore shouldn't be stored in either glass or metal containers. Gallium also corrodes most other metals by diffusing into their metal lattice.

Gallium is one of four metals (with cesium, mercury, and rubidium) which are liquid at near normal room temperature and can therefore be used in high-temperature thermometers. It is also notable for having one of the largest liquid ranges for a metal and for having a low vapor pressure at high temperatures.

This metal has a strong tendency supercool below its melting point thus necessitating seeding in order to solidify. High-purity gallium is attacked slowly by mineral acids. The melting point temperature is very low, T=30 �C, and the density is higher in the liquid state than in the crystalline state (like in the case of water; the opposite effect is normally found for metals).

Ga does not crystallize in any of the simple crystal structures. The stable phase under normal conditions is orthorhombic with 8 atoms in the conventional unit cell. Each atom has only one nearest neighbor (at a distance of 2.44 Å) and six other neighbors within additional 0.39 Å. Many stable and metastable phases are found as function of temperature and pressure.

The bonding between the nearest neighbors is found to be of covalent character, hence Ga₂ dimers is seen as the fundamental building block of the crystal. The compound, gallium arsenide can convert electricity directly into coherent light (this property is vital to light-emitting diodes).

Applications

Analog integrated circuits are the largest application for gallium, with optoelectronic devices (mostly laser diodes and light-emitting diodes) as the second largest end use. Other uses;

Since it wets glass or porcelain, gallium is used to create brilliant mirrors.
Used widely to dope semiconductors and produce solid-state devices like transistors.
Gallium readily alloys with most metals, and has been used as a component in low-melting alloys.

Magnesium gallate containing impurities (such as Mn⁺²), is beginning to be used in ultraviolet-activated phosphor powder.

History

Gallium (Latin Gallia meaning "France"; also gallus, meaning "cock") was discovered spectroscopically by Lecoq de Boisbaudran in 1875 by its characteristic spectrum (two violet lines) in an examination of a zinc blende from the Pyrenees. Before its discovery, most of its properties had been predicted and described by Dmitri Mendeleev (who called the hypothetical element eka-aluminum) on the basis of its position in his periodic table. Later in 1875, Boisbaudran obtained the free metal through the electrolysis hydroxide in K O H solution. He named the element after his native land of France and, in one of those multilingual puns so beloved of men of science of the early 19th century, after himself, as 'Lecoq' = the rooster, and Latin for rooster is "gallus".

Occurrence

This true metal is oftentimes found as a trace component in bauxite, coal, diaspore, germanite, and sphalerite. Some flue dusts from burning coal have been shown to contain as much 1.5 percent gallium.