Gallium
| Topics: |
Geology (main)
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Contents
Background
Gallium is a soft, silvery metallic element, with an atomic number of 31 and a symbol of Ga. The French chemist Paul-Emile Lecoq de Boisbaudran discovered gallium in 1875. Its existence was predicted in 1871 by a chemist named Mendeleev who said that gallium would be very much like aluminum in its physical properties, which proved to be quite accurate. In 1875, de Boisbaudran also isolated gallium by electrolysis of a solution of gallium hydroxide Ga(OH)3 in potassium hydroxide (KOH).
Gallium has some physical properties that are worth noting. Like water, gallium expands as it freezes which means it becomes less dense. Solid gallium has such a low melting temperature (85.6° F, 29.8° C) it will turn to liquid when held in the hand! It is a liquid over a wider range of temperatures than any other element. By contrast, the boiling point of gallium is unusually high (3999° F, 2204° C).
Studies have shown that gallium is not useful to living organisms, although gallium and gallium compounds do not appear to be toxic.
Name
| Previous Element: Zinc Next Element: Germanium |
| |
| Physical Properties | ||
|---|---|---|
| Color | silvery-blue | |
| Phase at Room Temp. | solid | |
| Density (g/cm3) | 5.904 | |
| Hardness (Mohs) | 1.5 | |
|
Melting Point (K) |
302.98 | |
|
Boiling Point (K) |
2676 | |
| Heat of Fusion (kJ/mol) | 5.59 | |
| Heat of Vaporization (kJ/mol) | 280 | |
| Heat of Atomization (kJ/mol) | 286 | |
| Thermal Conductivity (J/m sec K) | 48.3 | |
| Electrical Conductivity (1/mohm cm) | 57.471 | |
| Source | Bauxite (oxide) | |
| Atomic Properties | ||
| Electron Configuration | [Ar]3d104s24p1 | |
|
Number of Isotopes |
2 | |
| Electron Affinity (kJ/mol) | 30 | |
| First Ionization Energy (kJ/mol) | 578.8 | |
| Second Ionization Energy (kJ/mol) | 1978.9 | |
| Third Ionization Energy (kJ/mol) | 2963 | |
| Electronegativity | 1.81 | |
| Polarizability (Å3) | 8.1 | |
| Atomic Weight | 69.72 | |
| Atomic Volume (cm3/mol) | 11.8 | |
| Ionic Radius2- (pm) | --- | |
| Ionic Radius1- (pm) | --- | |
| Atomic Radius (pm) | 135 | |
| Ionic Radius1+ (pm) | --- | |
| Ionic Radius2+ (pm) | --- | |
| Ionic Radius3+ (pm) | 76 | |
| Common Oxidation Numbers | +3 | |
| Other Oxid. Numbers | +1, +2 | |
| Abundance | ||
| In Earth's Crust (mg/kg) | 1.9×101 | |
| In Earth's Ocean (mg/L) | 3×10-5 | |
| In Human Body (%) | near 0% | |
| Regulatory / Health | ||
| CAS Number | 7440-55-3 | |
| OSHA Permissible Exposure Limit (PEL) | No limits | |
| OSHA PEL Vacated 1989 | No limits | |
|
NIOSH Recommended Exposure Limit (REL) |
No limits | |
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Sources: |
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One theory says that the name gallium comes from the Latin word for France, Gallia. Another theory, however says that its discoverer, Paul-Emile Lecoq de Boisbaudran, may have taken the name from the Latin word gallum which means the cock, a reference to his own name (Lecoq).
Sources
Gallium does not easily combine with other elements or ions to form ore minerals. It is, however, found as a trace element in a number of minerals and ores, the most important of which is bauxite (aluminum ore). In fact, gallium is a by-product] of aluminum production. On average, there is 50 parts per million (ppm)of gallium in bauxite. Based on this average, known U.S. bauxite deposits could produce 15 million kilograms of gallium. Two million kilograms are in the Arkansas bauxite deposits alone. World bauxite resources are so large (estimated at 55 to 75 billion tons) that gallium could be retrieved from these ores for many years to come.
It is also found in zinc ore (sphalerite) and in coal. Some U.S. zinc deposits have 50 ppm gallium. Although zinc deposits are a secondary source after bauxite for gallium, they may be a significant source of gallium in the future.
Gallium is not produced from ore in the United States, but some is produced from scrap and impure metals. Consequently, nearly all gallium consumed in the U.S. is imported. Gallium imports are from France, the leading refiner of gallium metal, Russia, Canada, Kazakhstan, and other countries.
Uses
Gallium is used in a variety of highly specialized electrical applications. Gallium arsenide (GaAs) is able to change electricity directly into laser light. Such gallium arsenide products represent the majority of annual gallium consumption. These products are used for lasers, photo detectors, light-emitting diodes (LEDs), solar cells, and highly specialized integrated circuits, semi-conductors and transistors.
Gallium is important in some sophisticated physics experiments. The search for a particle known as a solar neutrino involves enormous amounts of gallium. Two such experiments used a total of 90 tons of gallium in the quest to detect these particles.
Because of its high boiling temperature, gallium is used to make thermometers designed to measure very high temperatures.
Gallium is also used in making mirrors.
Substitutes and Alternative Sources
Silicon can be used in place of GaAs in solar cell applications. Gallium arsenide circuits are very specialized and do not have a substitute. Though there is little chance of running short of gallium in the foreseeable future, alternative sources, such as zinc deposits, might one day become important as the more easily accessible sources are used up.
Further Reading
- Common Minerals and Their Uses, Mineral Information Institute.
- More than 170 Mineral Photographs, Mineral Information Institute.
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