Where Found (Encyclopedia of Global Resources)
Primary Uses (Encyclopedia of Global Resources)
Technical Definition (Encyclopedia of Global Resources)
Gallium (abbreviated Ga), atomic number 31, belongs to Group IIIA of the periodic table of the elements and resembles aluminum in its chemical and physical properties. It has two naturally occurring isotopes and an average atomic weight of 69.72. Pure gallium is a silvery-white, soft metal that takes on a bluish tinge when exposed to air. Its density is 5.9 grams per cubic centimeter; it has a melting point of 29.8° Celsius and a boiling point of 2,403° Celsius.
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Description, Distribution, and Forms (Encyclopedia of Global Resources)
Gallium is a rare but widely distributed element resembling aluminum. It occurs mostly as an oxide but may also occur as a sulfide. It is combined with antimony, arsenic, or phosphorus to create compounds useful in making semiconductors.
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History (Encyclopedia of Global Resources)
Gallium was discovered in 1875 by the French chemist Paul-Émile Lecoq de Boisbaudran. Although it was seen to have unusual properties, including a large difference between its melting and boiling points, it was of little practical use until the middle of the twentieth century.
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Obtaining Gallium (Encyclopedia of Global Resources)
Although gallium is found in concentrations of up to 1 percent in South African germanium ores, this ore has been exhausted to the point where recovery is no longer practical. Instead, it is obtained from worldwide aluminum ores and from zinc ores in Missouri, Oklahoma, and Kansas. These ores contain about 1 percent gallium as the same amount of the South African germanium ores.
Gallium is obtained as a by-product of aluminum production by chemically removing leftover aluminum from the liquid remaining after most of the aluminum is obtained from the ore. The gallium is then removed from the liquid by electrolysis. Gallium is obtained as a by-product of zinc production by treating the ore with sulfuric acid and neutralizing it to remove iron, aluminum, and gallium. This solution is treated with a base and neutralized to remove the aluminum and gallium. The mixture is next treated with hydrochloric acid to remove the gallium and some aluminum. It is then treated with ether to remove the gallium, treated with a base to remove traces of iron, and electrolyzed to recover the gallium.
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Uses of Gallium (Encyclopedia of Global Resources)
Gallium used for semiconductors must be very pure. Iron and organic impurities may be removed by treating the gallium with a base. Zinc and remaining iron may be removed by treating it with an acid. Other impurities may be removed by crystallizing the gallium.
In 1952, German chemists produced the first semiconductors using gallium compounds. Gallium antimonide, gallium arsenide, and gallium phosphide are the most useful for this purpose. These compounds are used in much the same way that silicon compounds and germanium compounds are used in electronic devices. In 2008, about 65 percent of gallium consumption in the United States was for integrated circuit manufacture.
Another and increasingly important use of gallium is in optoelectronic devices such as light-emitting diodes (LEDs), laser diodes, and solar cells for applications in consumer goods, aerospace medical equipment, industrial equipment, and telecommunications. Gallium phosphide and gallium indium arsenide can be used in these devices to convert nearly 41 percent of the light that strikes them into electricity. In 2008, U.S. consumption of gallium for such purposes comprised about 29 percent.
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Gallium (Chemical Elements)
In the late 1860s Russian chemist Dmitri Mendeleev (1834-1907) made one of the greatest discoveries in modern chemistry: the periodic law. The periodic law describes how chemical elements are related to each other. These elements are in the periodic table. This is a chart that lists all of the chemical elements and sorts them into groups based on similarities. Elements in vertical columns are similar to each other in many ways.
When Mendeleev first proposed the periodic law, he made a troubling discovery. There were a few empty spots in his table. For example, the box set aside for element number 31 was empty. No element had been found that belonged in that box.
Part of Mendeleev's genius was what he did next. He said that an "element number 31" did exist. Scientists simply had not found it yet. But Mendeleev described what the element would be like. He based his...
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