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 {{#invoke:Lang|lang}} (Template:Transliteration), 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.
CharacteristicsEdit
Physical propertiesEdit
Barium is a soft, silvery-white metal, with a slight golden shade when ultrapure.<ref name="Ullman2005">Template:Ullmann</ref>Template:Rp The silvery-white color of barium metal rapidly vanishes upon oxidation in air yielding a dark gray layer containing the oxide. Barium has a medium specific weight and high electrical conductivity. Because barium is difficult to purify, many of its properties have not been accurately determined.<ref name="Ullman2005" />Template:Rp
At room temperature and pressure, barium metal adopts a body-centered cubic structure, with a barium–barium distance of 503 picometers, expanding with heating at a rate of approximately 1.8Template:E/°C.<ref name="Ullman2005" />Template:Rp It is a soft metal with a Mohs hardness of 1.25.<ref name="Ullman2005" />Template:Rp Its melting temperature of Template:Convert<ref name="Lide2004">Template:Cite book</ref>Template:Rp is intermediate between those of the lighter strontium (Template:Convert)<ref name="Lide2004" />Template:Rp and heavier radium (Template:Convert);<ref name="Lide2004" />Template:Rp however, its boiling point of Template:Convert exceeds that of strontium (Template:Convert).<ref name="Lide2004" />Template:Rp The density (3.62 g/cm3)<ref name="Lide2004" />Template:Rp is again intermediate between those of strontium (2.36 g/cm3)<ref name="Lide2004" />Template:Rp and radium (≈5 g/cm3).<ref name="Lide2004" />Template:Rp
Chemical reactivityEdit
Barium is chemically similar to magnesium, calcium, and strontium, but more reactive. Its compounds are almost invariably found in the +2 oxidation state. As expected for a highly electropositive metal, barium's reaction with chalcogens is highly exothermic (release energy). Barium reacts with atmospheric oxygen in air at room temperature. For this reason, metallic barium is often stored under oil or in an inert atmosphere.<ref name="Ullman2005" />Template:Rp Reactions with other nonmetals, such as carbon, nitrogen, phosphorus, silicon, and hydrogen, proceed upon heating.<ref name="Ullman2005" />Template:Rp Reactions with water and alcohols are also exothermic and release hydrogen gas:<ref name="Ullman2005" />Template:Rp
- Ba + 2 ROH → Ba(OR)2 + H2↑ (R is an alkyl group or a hydrogen atom)
Barium reacts with ammonia to form the electride [Ba(NH3)6](e−)2, which near room temperature gives the amide Ba(NH2)2.<ref>Template:Greenwood&Earnshaw2nd</ref>
The metal is readily attacked by acids. Sulfuric acid is a notable exception because passivation stops the reaction by forming the insoluble barium sulfate on the surface.<ref>Template:Ullmann</ref> Barium combines with several other metals, including aluminium, zinc, lead, and tin, forming intermetallic phases and alloys.<ref>Template:Cite book</ref>
CompoundsEdit
| Template:Chem2 | Template:Chem2 | Template:Chem2 | Template:Chem2 | Template:Chem2 | Template:Chem2 | Template:Chem2 | Template:Chem2 | |
|---|---|---|---|---|---|---|---|---|
| Template:Chem2<ref name="Lide2004" />Template:Rp | 3.34 | 2.59 | 3.18 | 2.15 | 2.96 | 2.83 | 2.9 | 1.7 |
| Template:Chem2<ref name="Lide2004" />Template:Rp | 5.1 | 3.7 | 4.24 | 3.05 | 3.96 | 3.5 | 4.78 | 3.26 |
| Template:Chem2<ref name="Lide2004" />Template:Rp | 5.72 | 4.3 | 4.89 | 3.89 | 4.49 | 4.29 | 4.96 | 4.16 |
| Template:Chem2<ref name="Lide2004" />Template:Rp | 5.6 | 4.09 | 4.95 | 2.09 | 3.54 | 4.4 | 1.57 | — |
Barium salts are typically white when solid and colorless when dissolved.<ref>Template:Cite book</ref> They are denser than the strontium or calcium analogs, except for the halides (see table; zinc is given for comparison).
Barium hydroxide ("baryta") was known to alchemists, who produced it by heating barium carbonate. Unlike calcium hydroxide, it absorbs very little CO2 in aqueous solutions and is therefore insensitive to atmospheric fluctuations. This property is used in calibrating pH equipment.
Barium compounds burn with a green to pale green flame, which is an efficient test to detect a barium compound. The color results from spectral lines at 455.4, 493.4, 553.6, and 611.1 nm.<ref name="Ullman2005" />Template:Rp
Organobarium compounds are a growing field of knowledge: recently discovered are dialkylbariums and alkylhalobariums.<ref name="Ullman2005" />Template:Rp
IsotopesEdit
{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}}
Barium found in the Earth's crust is a mixture of seven primordial nuclides, barium-130, 132, and 134 through 138.<ref name="iso" /> Barium-130 undergoes very slow radioactive decay to xenon-130 by double beta plus decay, with a half-life of (0.5–2.7)×1021 years (about 1011 times the age of the universe). Its abundance is ≈0.1% that of natural barium.<ref name="iso">Template:CIAAW2003</ref> Theoretically, barium-132 can similarly undergo double beta decay to xenon-132; this decay has not been detected.Template:NUBASE2016 The radioactivity of these isotopes is so weak that they pose no danger to life.
Of the stable isotopes, barium-138 composes 71.7% of all barium; other isotopes have decreasing abundance with decreasing mass number.<ref name="iso" />
In total, barium has 40 known isotopes, ranging in mass between 114 and 153. The most stable artificial radioisotope is barium-133 with a half-life of approximately 10.51 years. Five other isotopes have half-lives longer than a day.Template:NUBASE2016 Barium also has 10 meta states, of which barium-133m1 is the most stable with a half-life of about 39 hours.Template:NUBASE2016
HistoryEdit
Alchemists in the early Middle Ages knew about some barium minerals. Smooth pebble-like stones of mineral baryte were found in volcanic rock near Bologna, Italy, and so were called "Bologna stones". Alchemists were attracted to them because after exposure to light they would glow for years.<ref name="history" /> The phosphorescent properties of baryte heated with organics were described by V. Casciorolus in 1602.<ref name="Ullman2005" />Template:Rp
Carl Scheele determined that baryte contained a new element in 1772, but could not isolate barium, only barium oxide. Johan Gottlieb Gahn also isolated barium oxide two years later in similar studies. Oxidized barium was at first called "barote" by Guyton de Morveau, a name that was changed by Antoine Lavoisier to baryte (in French) or baryta (in Latin). Also in the 18th century, English mineralogist William Withering noted a heavy mineral in the lead mines of Cumberland, now known to be witherite. Barium was first isolated by electrolysis of molten barium salts in 1808 by Sir Humphry Davy in England.<ref name="Davy-1808">Template:Cite journal</ref> Davy, by analogy with calcium, named "barium" after baryta, with the "-ium" ending signifying a metallic element.<ref name="history">Template:Cite book</ref> Robert Bunsen and Augustus Matthiessen obtained pure barium by electrolysis of a molten mixture of barium chloride and ammonium chloride.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
The production of pure oxygen in the Brin process was a large-scale application of barium peroxide in the 1880s, before it was replaced by electrolysis and fractional distillation of liquefied air in the early 1900s. In this process barium oxide reacts at Template:Convert with air to form barium peroxide, which decomposes above Template:Convert by releasing oxygen:<ref name="O2">Template:Cite journal</ref><ref>Template:Cite book</ref>
- 2 BaO + O2 ⇌ 2 BaO2
Barium sulfate was first applied as a radiocontrast agent in X-ray imaging of the digestive system in 1908.<ref>Template:Cite journal</ref>
Occurrence and productionEdit
The abundance of barium is 0.0425% in the Earth's crust and 13 μg/L in sea water. The primary commercial source of barium is baryte (also called barytes or heavy spar), a barium sulfate mineral.<ref name="Ullman2005" />Template:Rp with deposits in many parts of the world. Another commercial source, far less important than baryte, is witherite, barium carbonate. The main deposits are located in Britain, Romania, and the former USSR.<ref name="Ullman2005" />Template:Rp
Template:Multiple image The baryte reserves are estimated between 0.7 and 2 billion tonnes. The highest production, 8.3 million tonnes, was achieved in 1981, but only 7–8% was used for barium metal or compounds.<ref name="Ullman2005" />Template:Rp Baryte production has risen since the second half of the 1990s from 5.6 million tonnes in 1996 to 7.6 in 2005 and 7.8 in 2011. China accounts for more than 50% of this output, followed by India (14% in 2011), Morocco (8.3%), US (8.2%), Iran and Kazakhstan (2.6% each) and Turkey (2.5%).<ref>Miller, M. M. Barite. USGS.gov</ref>
The mined ore is washed, crushed, classified, and separated from quartz. If the quartz penetrates too deeply into the ore, or the iron, zinc, or lead content is abnormally high, then froth flotation is used. The product is a 98% pure baryte (by mass); the purity should be no less than 95%, with a minimal content of iron and silicon dioxide.<ref name="Ullman2005" />Template:Rp It is then reduced by carbon to barium sulfide:<ref name="Ullman2005" />Template:Rp
- BaSO4 + 2 C → BaS + 2 CO2
The water-soluble barium sulfide is the starting point for other compounds: treating BaS with oxygen produces the sulfate, with nitric acid the nitrate, with aqueous carbon dioxide the carbonate, and so on.<ref name="Ullman2005" />Template:Rp The nitrate can be thermally decomposed to yield the oxide.<ref name="Ullman2005" />Template:Rp Barium metal is produced by reduction with aluminium at Template:Convert. The intermetallic compound BaAl4 is produced first:<ref name="Ullman2005" />Template:Rp
- 3 BaO + 14 Al → 3 BaAl4 + Al2O3
BaAl4 is an intermediate reacted with barium oxide to produce the metal. Note that not all barium is reduced.<ref name="Ullman2005" />Template:Rp
- 8 BaO + BaAl4 → Ba↓ + 7 BaAl2O4
The remaining barium oxide reacts with the formed aluminium oxide:<ref name="Ullman2005" />Template:Rp
- BaO + Al2O3 → BaAl2O4
and the overall reaction is<ref name="Ullman2005" />Template:Rp
- 4 BaO + 2 Al → 3 Ba↓ + BaAl2O4
Barium vapor is condensed and packed into molds in an atmosphere of argon.<ref name="Ullman2005" />Template:Rp This method is used commercially, yielding ultrapure barium.<ref name="Ullman2005" />Template:Rp Commonly sold barium is about 99% pure, with main impurities being strontium and calcium (up to 0.8% and 0.25%) and other contaminants contributing less than 0.1%.<ref name="Ullman2005" />Template:Rp
A similar reaction with silicon at Template:Convert yields barium and barium metasilicate.<ref name="Ullman2005" />Template:Rp Electrolysis is not used because barium readily dissolves in molten halides and the product is rather impure.<ref name="Ullman2005" />Template:Rp
GemstoneEdit
The barium mineral, benitoite (barium titanium silicate), occurs as a very rare blue fluorescent gemstone, and is the official state gem of California.
Barium in seawaterEdit
Barium exists in seawater as the Ba2+ ion with an average oceanic concentration of 109 nmol/kg.<ref name="www.mbari.org">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Barium also exists in the ocean as BaSO4, or barite.<ref name="Griffith-2012">Template:Cite journal</ref> Barium has a nutrient-like profile<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> with a residence time of 10,000 years.<ref name="www.mbari.org" />
Barium shows a relatively consistent concentration in upper ocean seawater, excepting regions of high river inputs and regions with strong upwelling.<ref name="Hsieh-2017">Template:Cite journal</ref> There is little depletion of barium concentrations in the upper ocean for an ion with a nutrient-like profile, thus lateral mixing is important.<ref name="Hsieh-2017" /> Barium isotopic values show basin-scale balances instead of local or short-term processes.<ref name="Hsieh-2017" />
ApplicationsEdit
Metal and alloysEdit
Barium, as a metal or when alloyed with aluminium, is used to remove unwanted gases (gettering) from vacuum tubes, such as TV picture tubes.<ref name="Ullman2005" />Template:Rp Barium is suitable for this purpose because of its low vapor pressure and reactivity towards oxygen, nitrogen, carbon dioxide, and water; it can even partly remove noble gases by dissolving them in the crystal lattice. This application is gradually disappearing due to the rising popularity of the tubeless LCD, LED, and plasma sets.<ref name="Ullman2005" />Template:Rp
Other uses of elemental barium are minor and include an additive to silumin (aluminium–silicon alloys) that refines their structure, as well as<ref name="Ullman2005" />Template:Rp
- bearing alloys;
- lead–tin soldering alloys – to increase the creep resistance;
- alloy with nickel for spark plugs;
- additive to steel and cast iron as an inoculant;
- alloys with calcium, manganese, silicon, and aluminium as high-grade steel deoxidizers.
Barium sulfate and baryteEdit
Barium sulfate (the mineral baryte, BaSO4) is important to the petroleum industry as a drilling fluid in oil and gas wells.<ref name="Lide2004" />Template:Rp The precipitate of the compound (called "blanc fixe", from the French for "permanent white") is used in paints and varnishes; as a filler in ringing ink, plastics, and rubbers; as a paper coating pigment; and in nanoparticles, to improve physical properties of some polymers, such as epoxies.<ref name="Ullman2005" />Template:Rp
Barium sulfate has a low toxicity and relatively high density of ca. 4.5 g/cm3 (and thus opacity to X-rays). For this reason it is used as a radiocontrast agent in X-ray imaging of the digestive system ("barium meals" and "barium enemas").<ref name="Lide2004" />Template:Rp Lithopone, a pigment that contains barium sulfate and zinc sulfide, is a permanent white with good covering power that does not darken when exposed to sulfides.<ref>Template:Cite book</ref>
Other barium compoundsEdit
Other compounds of barium find only niche applications, limited by the toxicity of Ba2+ ions (see Template:Section link), which is not a problem for the insoluble BaSO4.
- Barium oxide coating on the electrodes of fluorescent lamps facilitates the release of electrons.
- By its great atomic density, barium carbonate increases the refractive index and luster of glass<ref name="Lide2004" />Template:Rp and reduces leaks of X-rays from CRT screens.<ref name="Ullman2005" />Template:Rp
- Barium, typically as barium nitrate imparts a yellow or "apple" green color to fireworks when no chlorine donors are present.<ref>Template:Cite book</ref>; emerald greens are generated using chlorine donors (barium chlorate acting as the donor and oxidizer in many formulas) to produce barium chloride in-situ.Template:Citation needed
- Barium peroxide is a catalyst in the aluminothermic reaction (thermite) for welding rail tracks. It is also a green flare in tracer ammunition and a bleaching agent.<ref>Template:Cite journal</ref>
- Barium titanate is a promising electroceramic.<ref>Template:Cite book</ref>
- Barium fluoride is used for optics in infrared applications because of its wide transparency range of 0.15–12 micrometers.<ref>{{#invoke:citation/CS1|citation
|CitationClass=web }}</ref>
- YBCO was the first high-temperature superconductor cooled by liquid nitrogen, with a transition temperature of Template:Convert greater than the boiling point of nitrogen (Template:Convert).<ref>Template:Cite journal</ref>
- Ferrite, a type of sintered ceramic composed of iron oxide (Fe2O3) and barium oxide (BaO), is both electrically nonconductive and ferrimagnetic, and can be temporarily or permanently magnetized.
PalaeoceanographyEdit
The lateral mixing of barium is caused by water mass mixing and ocean circulation.<ref name="Pyle-2018">Template:Cite journal</ref> Global ocean circulation reveals a strong correlation between dissolved barium and silicic acid.<ref name="Pyle-2018" /> The large-scale ocean circulation combined with remineralization of barium show a similar correlation between dissolved barium and ocean alkalinity.<ref name="Pyle-2018" />
Dissolved barium's correlation with silicic acid can be seen both vertically and spatially.<ref name="Bates-2017">Template:Cite journal</ref> Particulate barium shows a strong correlation with particulate organic carbon or POC.<ref name="Bates-2017" /> Barium is becoming more popular as a base for palaeoceanographic proxies.<ref name="Bates-2017" /> With both dissolved and particulate barium's links with silicic acid and POC, it can be used to determine historical variations in the biological pump, carbon cycle, and global climate.<ref name="Bates-2017" />
The barium particulate barite (BaSO4), as one of many proxies, can be used to provide a host of historical information on processes in different oceanic settings (water column, sediments, and hydrothermal sites).<ref name="Griffith-2012" /> In each setting there are differences in isotopic and elemental composition of the barite particulate.<ref name="Griffith-2012" /> Barite in the water column, known as marine or pelagic barite, reveals information on seawater chemistry variation over time.<ref name="Griffith-2012" /> Barite in sediments, known as diagenetic or cold seeps barite, gives information about sedimentary redox processes.<ref name="Griffith-2012" /> Barite formed via hydrothermal activity at hydrothermal vents, known as hydrothermal barite, reveals alterations in the condition of the earth's crust around those vents.<ref name="Griffith-2012" />
ToxicityEdit
Template:Chembox Soluble barium compounds have LD50 near 10 mg/kg (oral rats). Symptoms include "convulsions... paralysis of the peripheral nerve system ... severe inflammation of the gastrointestinal tract".<ref name="Ullman2005" />Template:Rp The insoluble sulfate is nontoxic and is not classified as a dangerous goods in transport regulations.<ref name="Ullman2005" />Template:Rp
Little is known about the long term effects of barium exposure.<ref>Template:Cite journal</ref> The US EPA considers it unlikely that barium is carcinogenic when consumed orally. Inhaled dust containing insoluble barium compounds can accumulate in the lungs, causing a benign condition called baritosis.<ref name="pmid1257935">Template:Cite journal</ref>
Barium carbonate has been used as a rodenticide.<ref name=clarkson> Template:Cite book</ref> Though considered obsolete, it may still be in use in some countries.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
See alsoEdit
- Han purple and Han blue – synthetic barium copper silicate pigments developed and used in ancient and imperial China
ReferencesEdit
External linksEdit
- Barium at The Periodic Table of Videos (University of Nottingham)
- Elementymology & Elements Multidict
- 3-D Holographic Display Using Strontium Barium Niobate
Template:Barium compounds Template:Periodic table (navbox) Template:Alkaline earth metals Template:Subject bar Template:Authority control Template:Good article