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Barium

Gist

Barium is a chemical element with the symbol Ba and atomic number 56. It is a soft, silvery-white alkaline earth metal that is highly reactive. Due to its reactivity, it is never found as a free element in nature. Barium is commonly used in diagnostic X-ray procedures (barium swallows and enemas) to visualize the gastrointestinal tract.

Summary

Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2; and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.

The most common minerals of barium are barite (barium sulfate, BaSO4) and witherite (barium carbonate, BaCO3). The name barium originates from the alchemical derivative "baryta" from Greek  (barys), meaning 'heavy'. Baric is the adjectival form of barium. Barium was identified as a new element in 1772, but not reduced to a metal until 1808 with the advent of electrolysis.

Barium has few industrial applications. Historically, it was used as a getter for vacuum tubes and in oxide form as the emissive coating on indirectly heated cathodes. It is a component of YBCO (high-temperature superconductors) and electroceramics, and is added to steel and cast iron to reduce the size of carbon grains within the microstructure. Barium compounds are added to fireworks to impart a green color. Barium sulfate is used as an insoluble additive to oil well drilling fluid. In a purer form it is used as X-ray radiocontrast agents for imaging the human gastrointestinal tract. Water-soluble barium compounds are poisonous and have been used as rodenticides.

Details

Barium (Ba), chemical element, one of the alkaline-earth metals of Group 2 (IIa) of the periodic table. The element is used in metallurgy, and its compounds are used in pyrotechnics, petroleum production, and radiology.

Element Properties

atomic number  :  56
atomic weight  :  137.327
melting point  :  727 °C (1,341 °F)
boiling point  :  1,805 °C (3,281 °F)
specific gravity:  3.51 (at 20 °C, or 68 °F)

Occurrence, properties, and uses

Barium, which is slightly harder than lead, has a silvery white luster when freshly cut. It readily oxidizes when exposed to air and must be protected from oxygen during storage. In nature it is always found combined with other elements. The Swedish chemist Carl Wilhelm Scheele discovered (1774) a new base (baryta, or barium oxide, BaO) as a minor constituent in pyrolusite, and from that base he prepared some crystals of barium sulfate, which he sent to Johan Gottlieb Gahn, the discoverer of manganese. A month later Gahn found that the mineral barite is also composed of barium sulfate, BaSO4. A particular crystalline form of barite found near Bologna, Italy, in the early 17th century, after being heated strongly with charcoal, glowed for a time after exposure to bright light. The phosphorescence of “Bologna stones” was so unusual that it attracted the attention of many scientists of the day, including Galileo. Only after the electric battery became available could Sir Humphry Davy finally isolate (1808) the element itself by electrolysis.

Barium minerals are dense (e.g., BaSO4, 4.5 grams per cubic centimetre; BaO, 5.7 grams per cubic centimeter), a property that was the source of many of their names and of the name of the element itself (from the Greek barys, “heavy”). Ironically, metallic barium is comparatively light, only 30 percent denser than aluminum. Its cosmic abundance is estimated as 3.7 atoms (on a scale where the abundance of silicon = {10}^{6}
atoms). Barium constitutes about 0.03 percent of Earth’s crust, chiefly as the minerals barite (also called barytes or heavy spar) and witherite. Between six and eight million tons of barite are mined every year, more than half of it in China. Lesser amounts are mined in India, the United States, and Morocco. Commercial production of barium depends upon the electrolysis of fused barium chloride, but the most effective method is the reduction of the oxide by heating with aluminum or silicon in a high vacuum. A mixture of barium monoxide and peroxide can also be used in the reduction. Only a few tons of barium are produced each year.

The metal is used as a getter in electron tubes to perfect the vacuum by combining with final traces of gases, as a deoxidizer in copper refining, and as a constituent in certain alloys. The alloy with nickel readily emits electrons when heated and is used for this reason in electron tubes and in spark plug electrodes. The detection of barium (atomic number 56) after uranium (atomic number 92) had been bombarded by neutrons was the clue that led to the recognition of nuclear fission in 1939.

Naturally occurring barium is a mixture of six stable isotopes: barium-138 (71.7 percent), barium-137 (11.2 percent), barium-136 (7.8 percent), barium-135 (6.6 percent), barium-134 (2.4 percent), and barium-132 (0.10 percent). Barium-130 (0.11 percent) is also naturally occurring but undergoes decay by double electron capture with an extremely long half-life (more than 4 × {10}^{21} years). More than 30 radioactive isotopes of barium are known, with mass numbers ranging from 114 to 153. The isotope with the longest half-life (barium-133, 10.5 years) is used as a gamma-ray reference source.

Additional Information:

Appearance

Barium is a soft, silvery metal that rapidly tarnishes in air and reacts with water.

Uses

Barium is not an extensively used element. Most is used in drilling fluids for oil and gas wells. It is also used in paint and in glassmaking.

All barium compounds are toxic; however, barium sulfate is insoluble and so can be safely swallowed. A suspension of barium sulfate is sometimes given to patients suffering from digestive disorders. This is a ‘barium meal’ or ‘barium enema’. Barium is a heavy element and scatters X-rays, so as it passes through the body the stomach and intestines can be distinguished on an X-ray.

Barium carbonate has been used in the past as a rat poison. Barium nitrate gives fireworks a green colour.

Biological role

Barium has no known biological role, although barium sulfate has been found in one particular type of algae. Barium is toxic, as are its water- or acid-soluble compounds.

Natural abundance

Barium occurs only in combination with other elements. The major ores are barite (barium sulfate) and witherite (barium carbonate). Barium metal can be prepared by electrolysis of molten barium chloride, or by heating barium oxide with aluminium powder.

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