Barium (pronEng|ˈbɛəriəm) is a
chemical element. It has the symbol Ba, and atomic number56. Barium is a soft silvery metallic alkaline earth metal. It is never found in nature in its pure form due to its reactivitywith air. Its oxide is historically known as barytabut it reacts with water and carbon dioxide and is not found as a mineral. The most common naturally occurring minerals are the very insoluble barium sulfate, BaSO4 ( barite), and barium carbonate, BaCO3 ( witherite). Benitoiteis a rare gem containing barium.
Barium is a
metallic element that is chemically similar to calciumand strontium, but more reactive. This metal oxidizes very easily when exposed to air and is highly reactive with water or alcohol, producing hydrogengas. Burning in airor oxygenproduces not just barium oxide(BaO) but also the peroxide. Simple compounds of this heavy element are notable for their high specific gravity. This is true of the most common barium-bearing mineral, its sulfate bariteBaSO4, also called 'heavy spar' due to the high density (4.5 g/cm³).
Barium has some medical and many industrial uses:
*Barium compounds, and especially barite (BaSO4), are extremely important to the petroleum industry. Barite is used in
drilling mud, a weighting agent in drilling new oil wells.
Barium sulfateis used as a radiocontrastagent for X-ray imaging of the digestive system (" barium meals" and " barium enemas").
Barium carbonateis a useful rat poisonand can also be used in making bricks. Unlike the sulfate, the carbonate dissolves in stomach acid, allowing it to be poisonous.
*An alloy with
nickelis used in spark plugwire.
Barium oxideis used in a coating for the electrodes of fluorescent lamps, which facilitates the release of electrons.
*The metal is a "
getter" in vacuum tubes, to remove the last traces of oxygen.
Barium carbonateis used in glassmaking. Being a heavy element, barium increases the refractive indexand luster of the glass.
Bariteis used extensively in rubberproduction.
Barium nitrateand chlorate give green colors in fireworks.
barium sulfidephosphoresces after exposure to the light.
Lithopone, a pigmentthat contains barium sulfateand zinc sulfide, is a permanent white that has good covering power, and does not darken in when exposed to sulfides.
Barium peroxidecan be used as a catalyst to start an aluminothermic reactionwhen welding rail tracks together. It can also be used in green tracer ammunition.
Barium titanatewas proposed in 2007 [http://www.technologyreview.com/Biztech/18086/] to be used in next generation battery technology for electric cars.
Barium fluorideis used for optics in infrared applications, since it is transparent from about 500nm to about 9000nm.
*Barium is a key element in
*An isotope of Barium, 133Ba, is routinely used as a standard source in the calibration of
gamma-raydetectors in nuclear physics studies.
Barium (Greek "bary", meaning "heavy") was first identified in 1774 by
Carl Scheeleand extracted in 1808 by Sir Humphry Davyin England. The oxide was at first called barote, by Guyton de Morveau, which was changed by Antoine Lavoisierto baryta, from which "barium" was derived to describe the metal.
Because barium quickly becomes oxidized in air, it is difficult to obtain this metal in its pure form. It is primarily found in and extracted from the
mineral baritewhich is crystallized barium sulfate. Because barite is so insoluble, it cannot be used directly for the preparation of other barium compounds. Instead, the ore is heated with carbon to reduce it to barium sulfide[Toxicological Profile for Barium and Barium Compounds. Agency for Toxic Substances and Disease Registry, CDC. 2007. [http://www.atsdr.cdc.gov/toxprofiles/tp24.pdf] ]
The barium sulfide is then hydrolyzed or reacted with acids to form other barium compounds such as the chloride, nitrate, and carbonate.
Barium is commercially produced through the
electrolysisof molten barium chloride(BaCl2)"Isolation" (* follow):
cathode) Ba2+* + 2e- → Ba:( anode) Cl-* → ½Cl2 (g) + e-
The most important compounds are barium peroxide, barium chloride, sulfate, carbonate, nitrate, and chlorate.
Naturally occurring barium is a mix of seven stable
isotopes. There are twenty-two isotopes known, but most of these are highly radioactiveand have half-lives in the several millisecond to several minute range. The only notable exceptions are 133Ba which has a half-life of 10.51 years, and 137mBa (2.55 minutes).
All water or acid
solublebarium compounds are extremely poisonous. At low doses, barium acts as a muscle stimulant, while higher doses affect the nervous system, causing cardiac irregularities, tremors, weakness, anxiety, dyspneaand paralysis. This may be due to its ability to block potassium ion channelswhich are critical to the proper function of the nervous system. Barium sulfatecan be taken orally because it is highly insoluble in water, and is eliminated completely from the digestive tract. Unlike other heavy metals, barium does not bioaccumulate. [ [http://www.epa.gov/region5/superfund/ecology/html/toxprofiles.htm#ba Toxicity Profiles, Ecological Risk Assessment | Region 5 Superfund | US EPA ] ] However, inhaled dust containing barium compounds can accumulate in the lungs, causing a benigncondition called baritosis. Oxidationoccurs very easily and, to remain pure, barium should be kept under a petroleum-based fluid (such as kerosene) or other suitable oxygen-free liquids that exclude air.
Barium acetate could lead to death in high doses.
Marie Robardspoisoned her father with the substance in Texas in 1993. She was tried and convicted in 1996.
* [http://www.webelements.com/webelements/elements/text/Ba/index.html WebElements.com – Barium]
* [http://elements.vanderkrogt.net/elem/ba.html Elementymology & Elements Multidict]
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