Barium
Barium is a chemical element with 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. Its hydroxide,
known in pre-modern history as baryta, does not occur as a mineral,
but can be prepared by heating barium carbonate.
The most common naturally occurring minerals of barium are barite
(barium sulfate, BaSO4) and witherite (barium carbonate, BaCO3), both
insoluble in water. The name barium originates from the alchemical
derivative "baryta", from Greek βαρύς (barys), meaning "heavy."
Baric is the adjectival form of barium.
Barium
Barium was identified as a new
element in 1774, but not reduced to a metal until 1808 with the advent
of electrolysis.
Barium
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
Barium compounds are added to fireworks to impart a
green color.
Barium sulfate
Barium sulfate is used as an insoluble additive to oil
well drilling fluid, as well as in a purer form, as X-ray
radiocontrast agents for imaging the human gastrointestinal tract. The
soluble barium ion and soluble compounds are poisonous, and have been
used as rodenticides.
Contents
1 Characteristics
1.1 Physical properties
1.2 Chemical reactivity
1.3 Compounds
1.4 Isotopes
2 History
3 Occurrence and production
3.1 Gemstone
4 Applications
4.1 Metal and alloys
4.2
Barium sulfate
Barium sulfate and barite
4.3 Other barium compounds
5 Toxicity
6 See also
7 References
8 External links
Characteristics[edit]
Physical properties[edit]
Oxidized barium
Barium
Barium is a soft, silvery-white metal, with a slight golden shade when
ultrapure.[5]:2 The silvery-white color of barium metal rapidly
vanishes upon oxidation in air yielding a dark gray oxide layer.
Barium
Barium has a medium specific weight and good electrical conductivity.
Ultrapure barium is very difficult to prepare, and therefore many
properties of barium have not been accurately measured yet.[5]:2
At room temperature and pressure, barium has a body-centered cubic
structure, with a barium–barium distance of 503 picometers,
expanding with heating at a rate of approximately
1.8×10−5/°C.[5]:2 It is a very soft metal with a
Mohs hardness
Mohs hardness of
1.25.[5]:2 Its melting temperature of 1,000 K (730 °C;
1,340 °F)[6]:4–43 is intermediate between those of the lighter
strontium (1,050 K or 780 °C or 1,430 °F)[6]:4–86
and heavier radium (973 K or 700 °C or
1,292 °F);[6]:4–78 however, its boiling point of 2,170 K
(1,900 °C; 3,450 °F) exceeds that of strontium
(1,655 K or 1,382 °C or 2,519 °F).[6]:4–86 The
density (3.62 g·cm−3)[6]:4–43 is again intermediate between
those of strontium (2.36 g·cm−3)[6]:4–86 and radium
(~5 g·cm−3).[6]:4–78
Chemical reactivity[edit]
Barium
Barium is chemically similar to magnesium, calcium, and strontium, but
even more reactive. It always exhibits the oxidation state of +2,
except in a few rare and unstable molecular species that are only
characterised in the gas phase such as BaF.[5]:2 Reactions with
chalcogens are highly exothermic (release energy); the reaction with
oxygen or air occurs at room temperature, and therefore barium is
stored under oil or in an inert atmosphere.[5]:2 Reactions with other
nonmetals, such as carbon, nitrogen, phosphorus, silicon, and
hydrogen, are generally exothermic and proceed upon heating.[5]:2–3
Reactions with water and alcohols are very exothermic and release
hydrogen gas:[5]:3
Ba + 2 ROH → Ba(OR)2 + H2↑ (R is an alkyl group or a hydrogen
atom)
Barium
Barium reacts with ammonia to form complexes such as Ba(NH3)6.[5]:3
The metal is readily attacked by most acids.
Sulfuric acid
Sulfuric acid is a
notable exception because passivation stops the reaction by forming
the insoluble barium sulfate on the surface.[7]
Barium
Barium combines with
several metals, including aluminium, zinc, lead, and tin, forming
intermetallic phases and alloys.[8]
Compounds[edit]
Selected alkaline earth and zinc salts densities, g·cm−3
O2−
S2−
F−
Cl−
SO2−
4
CO2−
3
O2−
2
H−
Ca2+[6]:4–48–50
3.34
2.59
3.18
2.15
2.96
2.83
2.9
1.7
Sr2+[6]:4–86–88
5.1
3.7
4.24
3.05
3.96
3.5
4.78
3.26
Ba2+[6]:4–43–45
5.72
4.3
4.89
3.89
4.49
4.29
4.96
4.16
Zn2+[6]:4–95–96
5.6
4.09
4.95
2.09
3.54
4.4
1.57
—
Barium
Barium salts are typically white when solid and colorless when
dissolved, and barium ions provide no specific coloring.[9] They are
denser than the strontium or calcium analogs, except for the halides
(see table; zinc is given for comparison).
Barium hydroxide
2monohydrate.tif/lossless-page1-440px-Ba(OH)2monohydrate.tif.png)
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.[5]:3
Organobarium compounds are a growing field of knowledge: recently
discovered are dialkylbariums and alkylhalobariums.[5]:3
Isotopes[edit]
Main article: Isotopes of barium
Barium
Barium found in the Earth's crust is a mixture of seven primordial
nuclides, barium-130, 132, and 134 through 138.[10] Barium-130
undergoes very slow radioactive decay to xenon-130 by double beta plus
decay, and barium-132 theoretically decays similarly to xenon-132,
with half-lives a thousand times greater than the age of the
Universe.[11] The abundance is ~0.1% that of natural barium.[10] 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, and
the lighter the isotope, the less abundant.[10]
In total, barium has about 50 known isotopes, ranging in mass between
114 and 153. The most stable metastable isotope is barium-133 with a
half-life of approximately 10.51 years. Five other isotopes have
half-lives longer than a day.[11]
Barium
Barium also has 10 meta states, out
of which barium-133m1 is the most stable with a half-life of about 39
hours.[11]
History[edit]
Sir Humphry Davy, who first isolated barium metal
Alchemists in the early Middle Ages knew about some barium minerals.
Smooth pebble-like stones of mineral barite were found in volcanic
rock near Bologna, Italy, and so were called "
Bologna
Bologna stones."
Alchemists were attracted to them because after exposure to light they
would glow for years.[12] The phosphorescent properties of barite
heated with organics were described by V. Casciorolus in 1602.[5]:5
Carl Scheele
Carl Scheele determined that barite contained a new element in 1774,
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
Antoine Lavoisier to baryta. Also in the 18th
century, English mineralogist
William Withering
William Withering noted a heavy mineral
in the lead mines of Cumberland, now known to be witherite.
Barium
Barium was
first isolated by electrolysis of molten barium salts in 1808 by Sir
Humphry Davy
Humphry Davy in England.[13] Davy, by analogy with calcium, named
"barium" after baryta, with the "-ium" ending signifying a metallic
element.[12]
Robert Bunsen
_(cropped).jpg/440px-Robert_Wilhelm_Bunsen_(HeidICON_53016)_(cropped).jpg)
Robert Bunsen and
Augustus Matthiessen obtained pure
barium by electrolysis of a molten mixture of barium chloride and
ammonium chloride.[14][15]
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:[16][17]
2 BaO + O2 ⇌ 2 BaO2
Barium sulfate
Barium sulfate was first applied as a radiocontrast agent in X-ray
imaging of the digestive system in 1908.[18]
Occurrence and production[edit]
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
barite (also called barytes or heavy spar), a barium sulfate
mineral.[5]:5 with deposits in many parts of the world. Another
commercial source, far less important than barite, is witherite, a
barium carbonate mineral. The main deposits are located in England,
Romania, and the former USSR.[5]:5
Barite, left to right: appearance, graph showing trends in production
over time, and the map showing shares of the most important producer
countries in 2010.
The barite 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.[5]:5 Barite
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
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).[19]
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 barite (by mass); the purity should be
no less than 95%, with a minimal content of iron and silicon
dioxide.[5]:7 It is then reduced by carbon to barium sulfide:[5]:6
BaSO4 + 2 C → BaS + 2 CO2↑
The water-soluble barium sulfide is the starting point for other
compounds: reacting BaS with oxygen produces the sulfate, with nitric
acid the nitrate, with carbon dioxide the carbonate, and so on.[5]:6
The nitrate can be thermally decomposed to yield the oxide.[5]:6
Barium
Barium metal is produced by reduction with aluminium at 1,100 °C
(2,010 °F). The intermetallic compound BaAl4 is produced
first:[5]:3
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.[5]:3
8 BaO + BaAl4 → Ba↑ + 7 BaAl2O4
The remaining barium oxide reacts with the formed aluminium
oxide:[5]:3
BaO + Al2O3 → BaAl2O4
and the overall reaction is[5]:3
4 BaO + 2 Al → 3 Ba↑ + BaAl2O4
Barium
Barium vapor is condensed and packed into molds in an atmosphere of
argon.[5]:3 This method is used commercially, yielding ultrapure
barium.[5]: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%.[5]:4
A similar reaction with silicon at 1,200 °C (2,190 °F)
yields barium and barium metasilicate.[5]:3
Electrolysis
Electrolysis is not used
because barium readily dissolves in molten halides and the product is
rather impure.[5]:3
Benitoite
Benitoite crystals on natrolite. The mineral is named for the San
Benito River in
San Benito County
San Benito County where it was first found.
Gemstone[edit]
The barium mineral, benitoite (barium titanium silicate), occurs as a
very rare blue fluorescent gemstone, and is the official state gem of
California.
Applications[edit]
Metal and alloys[edit]
Barium, as a metal or when alloyed with aluminium, is used to remove
unwanted gases (gettering) from vacuum tubes, such as TV picture
tubes.[5]:4
Barium
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 and
plasma sets.[5]:4
Other uses of elemental barium are minor and include an additive to
silumin (aluminium–silicon alloys) that refines their structure, as
well as[5]:4
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
Barium sulfate and barite[edit]
Amoebiasis
Amoebiasis as seen in radiograph of barium-filled colon
Barium sulfate
Barium sulfate (the mineral barite, BaSO4) is important to the
petroleum industry as a drilling fluid in oil and gas wells.[6]: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.[5]:9
Barium sulfate
Barium sulfate has a low toxicity and relatively high density of ca.
4.5 g·cm−3 (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").[6]:4–5 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.[20]
Other barium compounds[edit]
Green barium fireworks
Other compounds of barium find only niche applications, limited by the
toxicity of Ba2+ ions (barium carbonate is a rat poison), which is not
a problem for the insoluble BaSO4.
Barium oxide
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[6]:4–5 and reduces leaks of X-rays from
cathode ray tubes (CRT) TV sets.[5]:12–13
Barium, typically as barium nitrate imparts a yellow or "apple" green
color to fireworks;[21] for brilliant green barium monochloride is
used.
Barium peroxide
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.[22]
Barium titanate
Barium titanate is a promising electroceramic.[23]
Barium fluoride
Barium fluoride is used for optics in infrared applications because of
its wide transparency range of 0.15–12 micrometers.[24]
YBCO was the first high-temperature superconductor cooled by liquid
nitrogen, with a transition temperature of 93 K
(−180.2 °C; −292.3 °F) that exceeded the boiling point
of nitrogen (77 K or −196.2 °C or −321.1 °F).[25]
Ferrite, a type of sintered ceramic composed of
Iron
Iron
Oxide
Oxide (Fe2O3) and
barium oxide (BaO), is both electrically nonconductive and
ferrimagnetic, and can be temporarily or permanently magnetized.
Toxicity[edit]
Because of the high reactivity of the metal, toxicological data are
available only for compounds.[26] Water-soluble barium compounds are
poisonous. In low doses, barium ions act as a muscle stimulant, and
higher doses affect the nervous system, causing cardiac
irregularities, tremors, weakness, anxiety, shortness of breath, and
paralysis. This toxicity may be caused by Ba2+ blocking potassium ion
channels, which are critical to the proper function of the nervous
system.[27] Other organs damaged by water-soluble barium compounds
(i.e., barium ions) are the eyes, immune system, heart, respiratory
system, and skin[26] causing, for example, blindness and
sensitization.[26]
Barium
Barium is not carcinogenic[26] and it does not bioaccumulate.[28][29]
Inhaled dust containing insoluble barium compounds can accumulate in
the lungs, causing a benign condition called baritosis.[30] The
insoluble sulfate is nontoxic and is not classified as a dangerous
goods in transport regulations.[5]:9
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. Anyone who works with the metal should wear
pre-cleaned non-sparking shoes, flame-resistant rubber clothes, rubber
gloves, apron, goggles, and a gas mask. Smoking in the working area is
forbidden. Thorough washing is required after handling barium.[26]
See also[edit]
Han purple and Han blue
Han purple and Han blue – synthetic barium copper silicate pigments
developed and used in ancient and imperial China
References[edit]
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External links[edit]
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Ba(BO2)2
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Ba(ClO3)2
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