is a chemical element
. It has the symbol Ba
, and atomic number
56. Barium is a soft silvery metallic alkaline earth metal
. It is never found in nature in its pure form due to its reactivity
. Its oxide is historically known as baryta
but 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
), and barium carbonate
is a rare gem containing barium.
Barium is a metallic
element that is chemically similar to calcium
, but more reactive. This metal oxidizes
very easily when exposed to air and is highly reactive
, producing hydrogen
gas. Burning in air
produces 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 barite
, 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 sulfate is used as a radiocontrast agent for X-ray imaging of the digestive system ("barium meals" and "barium enemas").
- Barium carbonate is a useful rat poison and can also be used in making bricks. Unlike the sulfate, the carbonate dissolves in stomach acid, allowing it to be poisonous.
- An alloy with nickel is used in spark plug wire.
- Barium oxide is 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 carbonate is used in glassmaking. Being a heavy element, barium increases the refractive index and luster of the glass.
- Barite is used extensively in rubber production.
- Barium nitrate and chlorate give green colors in fireworks.
- Impure barium sulfide phosphoresces after exposure to the light.
- Lithopone, a pigment that contains barium sulfate and zinc sulfide, is a permanent white that has good covering power, and does not darken in when exposed to sulfides.
- Barium peroxide can be used as a catalyst to start an aluminothermic reaction when welding rail tracks together. It can also be used in green tracer ammunition.
- Barium titanate was proposed in 2007 to be used in next generation battery technology for electric cars.
- Barium fluoride is used for optics in infrared applications, since it is transparent from about 500nm to about 9000nm.
- Barium is a key element in YBCO superconductors.
- An isotope of Barium, 133Ba, is routinely used as a standard source in the calibration of gamma-ray detectors in nuclear physics studies.
Barium (Greek bary
, meaning "heavy") was first identified in 1774 by Carl Scheele
and extracted in 1808 by Sir Humphry Davy
. The oxide was at first called barote, by Guyton de Morveau
, which was changed by Antoine Lavoisier
to 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 barite
which 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
- BaSO4 + 2C → BaS + 2CO2
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 electrolysis of 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
, and chlorate
Naturally occurring barium is a mix of seven stable isotopes
. There are twenty-two isotopes known, but most of these are highly radioactive
and have half-lives
in the several millisecond to several minute range. The only notable exceptions are 133
Ba which has a half-life of 10.51 years, and 137m
Ba (2.55 minutes).
All water or acid soluble
barium 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
. This may be due to its ability to block potassium ion channels
which are critical to the proper function of the nervous system.
Barium sulfate can 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. However, inhaled dust containing barium compounds can accumulate in the lungs, causing a benign condition called baritosis.
Oxidation occurs 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 Robards poisoned her father with the substance in Texas in 1993. She was tried and convicted in 1996.