Barium
Barium | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Pronunciation | /ˈbɛəriəm/ | ||||||||||||||||||||||||||||||||||||||||||||||||||
Appearance | silvery gray; with a pale yellow tint[1] | ||||||||||||||||||||||||||||||||||||||||||||||||||
Standard atomic weight Ar°(Ba) | |||||||||||||||||||||||||||||||||||||||||||||||||||
Barium in the periodic table | |||||||||||||||||||||||||||||||||||||||||||||||||||
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kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||
Heat of vaporization | 142 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||
Molar heat capacity | 28.07 J/(mol·K) | ||||||||||||||||||||||||||||||||||||||||||||||||||
Vapor pressure
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Atomic properties | |||||||||||||||||||||||||||||||||||||||||||||||||||
Discovery | Carl Wilhelm Scheele (1772) | ||||||||||||||||||||||||||||||||||||||||||||||||||
First isolation | Humphry Davy (1808) | ||||||||||||||||||||||||||||||||||||||||||||||||||
Isotopes of barium | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Barium is a
The most common minerals of barium are
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.
Characteristics
Physical properties
Barium is a soft, silvery-white metal, with a slight golden shade when ultrapure.[8]: 2 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.[8]: 2
At room temperature and pressure, barium metal adopts a
Chemical reactivity
Barium is chemically similar to magnesium, calcium, and strontium, but even more reactive. It is usually found in the +2 oxidation state. Most exceptions are in a few rare and unstable molecular species that are only characterised in the gas phase such as BaF,
- Ba + 2 ROH → Ba(OR)2 + H2↑ (R is an alkyl group or a hydrogen atom)
Barium reacts with ammonia to form complexes such as Ba(NH3)6.[8]: 3
The metal is readily attacked by acids.
Compounds
O2− |
S2− |
F− |
Cl− |
SO2− 4 |
CO2− 3 |
O2− 2 |
H− | |
---|---|---|---|---|---|---|---|---|
Ca2+ [9]: 4–48–50 |
3.34 | 2.59 | 3.18 | 2.15 | 2.96 | 2.83 | 2.9 | 1.7 |
Sr2+ [9]: 4–86–88 |
5.1 | 3.7 | 4.24 | 3.05 | 3.96 | 3.5 | 4.78 | 3.26 |
Ba2+ [9]: 4–43–45 |
5.72 | 4.3 | 4.89 | 3.89 | 4.49 | 4.29 | 4.96 | 4.16 |
Zn2+ [9]: 4–95–96 |
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.[13] 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.
Volatile 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.[8]: 3
Organobarium compounds are a growing field of knowledge: recently discovered are dialkylbariums and alkylhalobariums.[8]: 3
Isotopes
Barium found in the Earth's crust is a mixture of seven
Of the stable isotopes, barium-138 composes 71.7% of all barium; other isotopes have decreasing abundance with decreasing mass number.[14]
In total, barium has 40 known isotopes, ranging in mass between 114 and 153. The most stable
History
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.[16] The phosphorescent properties of baryte heated with organics were described by V. Casciorolus in 1602.[8]: 5
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 500–600 °C (932–1,112 °F) with air to form barium peroxide, which decomposes above 700 °C (1,292 °F) by releasing oxygen:[20][21]
- 2 BaO + O2 ⇌ 2 BaO2
Barium sulfate was first applied as a
Occurrence and production
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.[8]: 5 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.[8]: 5
The baryte reserves are estimated between 0.7 and 2 billion tonnes. The maximum production, 8.3 million tonnes, was produced in 1981, but only 7–8% was used for barium metal or compounds.[8]: 5 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%), Turkey (2.5%), Iran and Kazakhstan (2.6% each).[23]
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.[8]: 7 It is then reduced by carbon to barium sulfide:[8]: 6
- 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.
- 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.[8]: 3
- 8 BaO + BaAl4 → Ba↓ + 7 BaAl2O4
The remaining barium oxide reacts with the formed aluminium oxide:[8]: 3
- BaO + Al2O3 → BaAl2O4
and the overall reaction is[8]: 3
- 4 BaO + 2 Al → 3 Ba↓ + BaAl2O4
Barium vapor is condensed and packed into molds in an atmosphere of argon.[8]: 3 This method is used commercially, yielding ultrapure barium.[8]: 3 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%.[8]: 4
A similar reaction with silicon at 1,200 °C (2,190 °F) yields barium and barium metasilicate.[8]: 3 Electrolysis is not used because barium readily dissolves in molten halides and the product is rather impure.[8]: 3
Gemstone
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 seawater
Barium exists in seawater as the Ba2+ ion with an average oceanic concentration of 109 nmol/kg.[24] Barium also exists in the ocean as BaSO4, or barite.[25] Barium has a nutrient-like profile[26] with a residence time of 10,000 years.[24]
Barium shows a relatively consistent concentration in upper ocean seawater, excepting regions of high river inputs and regions with strong upwelling.[27] There is little depletion of barium concentrations in the upper ocean for an ion with a nutrient-like profile, thus lateral mixing is important.[27] Barium isotopic values show basin-scale balances instead of local or short-term processes.[27]
Applications
Metal and alloys
Barium, as a metal or when alloyed with aluminium, is used to remove unwanted gases (gettering) from vacuum tubes, such as TV picture tubes.[8]: 4 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.[8]: 4
Other uses of elemental barium are minor and include an additive to
- 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 baryte
Barium sulfate (the mineral baryte, BaSO4) is important to the petroleum industry as a drilling fluid in oil and gas wells.[9]: 4–5 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.[8]: 9
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
Other barium compounds
Other compounds of barium find only niche applications, limited by the toxicity of Ba2+ ions (barium carbonate is a
- Barium oxide coating on the electrodes of fluorescent lamps facilitates the release of electrons.
- By its great atomic density, cathode ray tubes (CRT) TV sets.[8]: 12–13
- Barium, typically as barium nitrate imparts a yellow or "apple" green color to fireworks;[29] for brilliant green barium monochloride is used.
- 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.[30]
- electroceramic.[31]
- Barium fluoride is used for optics in infrared applications because of its wide transparency range of 0.15–12 micrometers.[32]
- YBCO was the first high-temperature superconductor cooled by liquid nitrogen, with a transition temperature of 93 K (−180.2 °C; −292.3 °F) greater than the boiling point of nitrogen (77 K or −196.2 °C or −321.1 °F).[33]
- ferrimagnetic, and can be temporarily or permanently magnetized.
Palaeoceanography
The lateral mixing of barium is caused by water mass mixing and ocean circulation.[34] Global ocean circulation reveals a strong correlation between dissolved barium and silicic acid.[34] The large-scale ocean circulation combined with remineralization of barium show a similar correlation between dissolved barium and ocean alkalinity.[34]
Dissolved barium's correlation with silicic acid can be seen both vertically and spatially.[35] Particulate barium shows a strong correlation with particulate organic carbon or POC.[35] Barium is becoming more popular to be used a base for palaeoceanographic proxies.[35] 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.[35]
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).[25] In each setting there are differences in isotopic and elemental composition of the barite particulate.[25] Barite in the water column, known as marine or pelagic barite, reveals information on seawater chemistry variation over time.[25] Barite in sediments, known as diagenetic or cold seeps barite, gives information about sedimentary redox processes.[25] 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.[25]
Toxicity
Hazards | |
---|---|
GHS labelling:[36] | |
Danger | |
H228, H260, H301, H314 | |
P210, P231+P232, P260, P280, P303+P361+P353, P304+P340+P310, P305+P351+P338 | |
NFPA 704 (fire diamond) |
Because of the high reactivity of the metal, toxicological data are available only for compounds.
Barium is not carcinogenic
To avoid a potentially vigorous chemical reaction, barium metal is kept in an argon atmosphere or under mineral oils. Contact with air is dangerous and may cause ignition. Moisture, friction, heat, sparks, flames, shocks, static electricity, and exposure to oxidizers and acids should be avoided. Anything that may contact with barium should be electrically grounded.[37]
See also
- Han purple and Han blue – synthetic barium copper silicate pigments developed and used in ancient and imperial China
References
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- ^ W. Xu and M. Lerner, "A New and Facile Route Using Electride Solutions To Intercalate Alkaline Earth Ions into Graphite" Chemistry of Materials 2018 30 (19), 6930-6935 https://DOI.org/10.1021/acs.chemmater.8b03421
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- ^ Miller, M. M. Barite. USGS.gov
- ^ a b "Barium". www.mbari.org. Retrieved 2020-11-24.
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- ^ "Graph". www.mbari.org. Retrieved 2020-11-24.
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- ^ "Crystran Ltd. Optical Component Materials". crystran.co.uk. Archived from the original on 2010-06-11. Retrieved 2010-12-29.
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- ^ S2CID 104170533.
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- ^ "Barium 237094". Sigma-Aldrich. 2021-10-28. Retrieved 2021-12-21.
- ^ a b c d e Barium. ESPI Metals. Retrieved 2012-06-11.
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- ^ "Toxicity Profiles, Ecological Risk Assessment". US EPA. Archived from the original on 2010-01-10. Retrieved 2012-06-16.
- ^ Moore, J. W. (1991). Inorganic Contaminants of Surface Waters, Research and Monitoring Priorities. New York: Springer-Verlag.
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External links
- Barium at The Periodic Table of Videos(University of Nottingham)
- Elementymology & Elements Multidict
- 3-D Holographic Display Using Strontium Barium Niobate