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22 décembre 2011 4 22 /12 /décembre /2011 02:23

Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (82 °F), which makes it one of only five elemental metals that are liquid at (or near) room temperature.Sony VAIO VPCEB17FX/G Battery

Caesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium. The metal is extremely reactive and pyrophoric, reacting with water even at ?116 °C (?177 °F). It is the least electronegative element that has stable isotopes, of which it has only one, caesium-133.Sony VAIO VPCEB17FX/L Battery

Caesium is mined mostly from pollucite, while the radioisotopes, especially caesium-137, a fission product, are extracted from waste produced by nuclear reactors.

Two German chemists, Robert Bunsen and Gustav Kirchhoff, discovered caesium in 1860 by the newly developed method of flame spectroscopy.Sony VAIO VPCEB17FX/P Battery

The first small-scale applications for caesium have been as a "getter" in vacuum tubes and in photoelectric cells. In 1967, a specific frequency from the emission spectrum of caesium-133 was chosen to be used in the definition of thesecond by the International System of Units. Since then, caesium has been widely used in atomic clocks.Sony VAIO VPCEB17FX/W Battery

Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids. It has a range of applications in the production of electricity, in electronics, and in chemistry. The radioactive isotope caesium-137 has ahalf-life of about 30 years and is used in medical applications, industrial gauges, and hydrology.Sony VAIO VPCEB190X Battery

Although the element is only mildly toxic, it is a hazardous material as a metal and its radioisotopes present a high health risk in case of radiation leaks.

Physical properties

Caesium is a very soft (it has the lowest Mohs hardness of all elements (0.2)), veryductile, silvery-white metal, which develops a silvery-gold hue in the presence of trace amounts of oxygen.Sony VAIO VPCEB19FX Battery

It has a melting point of 28.4 °C (83.1 °F), making it one of the few elemental metals which are liquid near room temperature. Mercury is the only elemental metal with a known melting point lower than caesium. In addition, the metal has a rather low boiling point, 641 °C (1,186 °F), the lowest of all metals other than mercury. Its compounds burn with a blue color.Sony VAIO VPCEB19GX Battery

Caesium forms alloys with the other alkali metals as well as with gold, and amalgams with mercury. At temperatures below 650 °C (1,202 °F), it alloys with cobalt, iron,molybdenum, nickel, platinum, tantalum or tungsten. It forms well-defined intermetallic compounds with antimony, gallium, indium and thorium, which are photosensitive.Sony VAIO VPCEB1AFX Battery

It mixes with the other alkali metals (except with lithium), and the alloy with a molardistribution of 41% caesium, 47% potassium, and 12% sodium has the lowest melting point of any known metal alloy, at ?78 °C (?108 °F). A few amalgams have been studied:CsHg2is black with a purple metallic lustre, while CsHg is golden-coloured, also with a metallic lustre.Sony VAIO VPCEB1AFX/B Battery

Chemical properties

Caesium metal is highly reactive and very pyrophoric. In addition to igniting spontaneously in air, it reacts explosively with water even at low temperatures, more so than other members of the first group of the periodic table. The reaction with solid water occurs at temperatures as low as ?116 °C (?177 °F).Sony VAIO VPCEB1AGX Battery

Because of its high reactivity, the metal is classified as a hazardous material. It is stored and shipped in dry saturated hydrocarbons such as mineral oil. Similarly, it must be handled under inert atmosphere such as argon. It can be stored in vacuum-sealed borosilicate glass ampoules. In quantities of more than about 100 grams (3.5 oz), caesium is shipped in hermetically sealed stainless steel containers.Sony VAIO VPCEB1AGX/BI Battery

The chemistry of caesium is similar to that of other alkali metals, but is more closely similar to that of rubidium, the element above caesium in the periodic table. Some small differences arise from the fact that it has a higher atomic mass and is moreelectropositive than other (non-radioactive) alkali metals. Caesium is the most electropositive stable chemical element.Sony VAIO VPCEB1BGX Battery

The caesium ion is also larger and less "hard" than those of the lighter alkali metals.

Compounds

The vast majority of caesium compounds contain the element as the cation Cs+, which binds ionicallyto a wide variety of anions. One noteworthy exception is provided by the caeside anion (Cs?). Other exceptions include the several suboxides (see section on oxides below).Sony VAIO VPCEB1BGX/BI Battery

Returning to more normal compounds, salts of Cs+ are almost invariably colorless unless the anion itself is colored. Many of the simple salts are hygroscopic, but less so than the corresponding salts of the lighter alkali metals. The acetate, carbonate, halides, oxide, nitrate, and sulfatesalts are water-soluble.Sony VAIO VPCEB1CGX Battery

Double salts are often less soluble, and the low solubility of caesium aluminium sulfate is exploited in the purification of Cs from its ores. The double salt with antimony (such as CsSbCl4), bismuth, cadmium, copper, iron, and lead are also poorly soluble. 

Caesium hydroxide (CsOH) is hygroscopic and a very strong base.Sony VAIO VPCEB1CGX/BI Battery

It rapidly etches the surface ofsemiconductors such as silicon. CsOH has been previously regarded by chemists as the "strongest base", reflecting the relatively weak attraction between the large Cs+ ion and OH–.;it is indeed the strongest Arrhenius base, but a number of compounds that cannot exist in aqueous solution, such as n-butyllithiumand sodium amide,are more basic.Sony VAIO VPCEB1DGX Battery

A stoichiometric mixture of caesium and gold will react to form caesium auride.

Complexes

Like all metal cations, Cs+ forms complexes with Lewis bases in solution. Because of its large size, Cs+ usually adopts coordination numbers greater than six-coordination, which is typical for the lighter alkali metal cations.Sony VAIO VPCEB1DGX/BI Battery

This trend is already apparent by the 8-coordination in CsCl, vs the halite motif adopted by the other alkali metal chlorides. Its high coordination number and softness (tendency to form covalent bonds) are the basis of the separation of Cs+ from other cations, as is practiced in the remediation of nuclear wastes, where 137Cs+ is separated from large amounts of non-radioactive K+.Sony VAIO VPCEB1EGX Battery

Halides

Caesium chloride (CsCl) crystallizes in the simple cubic crystal system. Also called the "caesium chloride structure", this structural motif is composed of aprimitive cubic lattice with a two-atom basis, each with an eightfold coordination; the chloride atoms lie upon the lattice points at the edges of the cube, while the caesium atoms lie in the holes in the center of the cubes.Sony VAIO VPCEB1EGX/BI Battery

This structure is shared with CsBr and CsI, and many other compounds that do not contain Cs. In contrast, most other alkaline halides adopt the sodium chloride (NaCl) structure.[16] The CsCl structure is preferred because Cs+ has an ionic radius of 174 pm andCl?181 pm.Sony VAIO VPCEB1FGX Battery

Oxides

More so than the other alkali metals, caesium forms numerous binary compounds with oxygen. When caesium burns in air, the superoxide CsO2 is the main product. The "normal" caesium oxide (Cs2O) forms yellow-orange hexagonal crystals, and is the only oxide of the anti-CdCl2 type.Sony VAIO VPCEB1FGX/BI Battery

It vaporizes at 250 °C (482 °F), and decomposes to caesium metal and the peroxide Cs2O2 at temperatures above 400 °C (752 °F).[25] Aside from the superoxide and the ozonide CsO3, several brightly colored suboxides have also been studied. These include Cs7O, Cs4O, Cs11O3, Cs3O (dark-green ), CsO, Cs3O2,[30] as well as Cs7O2.Sony VAIO VPCEB1GGX Battery

The latter may be heated under vacuum to generate Cs2O.[24] Binary compounds with sulfur,selenium, and tellurium also exist.

Caesium has a total of 39 known isotopes that range in their mass number (i.e. number of nucleons in its nucleus) from 112 to 151.Sony VAIO VPCEB1GGX/BI Battery

Several of these are synthesized from lighter elements by the slow neutron capture process (S-process) inside old stars, as well as inside supernova explosions (R-process). However, the onlystable isotope is 133Cs, which has 78 neutrons. Although it has a large nuclear spin (7/2+), nuclear magnetic resonance studies can be done with this isotope at a resonating frequency of 11.7 MHz.Sony VAIO VPCEB1HGX Battery

while 137Cs and 134Cs have half-lives of 30 and 2 years, respectively. 137Cs decomposes to a short-lived 137mBa by beta decay, and then to non-radioactive barium, while 134Cs transforms into 134Ba directly. The isotopes with mass numbers of 129, 131, 132 and 136, have half-times between a day and two weeks, while most of the other isotopes have half-lives from a few seconds to fractions of a second.Sony VAIO VPCEB1HGX/BI Battery

There are at least 21 metastable nuclear isomers. Other than 134mCs (with a half-life of just under 3 hours), all are very unstable and decay with half-lives of a few minutes or less.

The isotope 135Cs is one of the long-lived fission products of uranium which form in nuclear reactors.Sony VAIO VPCEB1JFX Battery

However, itsfission product yield is reduced in most reactors because its predecessor, 135Xe, is an extremely potent neutron poison and transmutes frequently to stable 136Xe before it can decay to 135Cs.

Because of its beta decay (to 137mBa), 137Cs is a strong emitter of gamma radiation.Sony VAIO VPCEB1JFX/B Battery

Its half-life makes it the principalmedium-lived fission product along with 90Sr—both are responsible for radioactivity of spent nuclear fuel after several years of cooling up to several hundred years after use. For example 137Cs together with 90Sr currently generate the largest source of radioactivity generated in the area around the Chernobyl disaster.Sony VAIO VPCEB1JFX/G Battery

It is not feasible to dispose of 137Cs through neutron capture (due to the low capture rate) and as a result it must be allowed to decay.

Almost all caesium produced from nuclear fission comes from beta decay of originally more neutron-rich fission products, passing through various isotopes of iodineand of xenon.Sony VAIO VPCEB1JFX/L Battery

Because iodine and xenon are volatile and can diffuse through nuclear fuel or air, radioactive caesium is often created far from the original site of fission.[46] With the commencement of nuclear weapons testing around 1945, 137Cs was released into the atmosphere and then returned to the surface of the earth as a component of radioactive fallout.Sony VAIO VPCEB1JFX/P Battery

Occurrence

Caesium is a relatively rare element as it is estimated to average approximately 3 parts per million in the Earth's crust. This makes it the 45th most abundant of all elements and the 36th of all the metals.Sony VAIO VPCEB1JFX/W Battery

Nevertheless, it is more abundant than such elements as antimony, cadmium, tin and tungsten, and two orders of magnitude more abundant than mercury or silver, but 30 times less abundant than rubidium—with which it is so closely chemically associated.

Due to its large ionic radius, caesium is one of the "incompatible elements."Sony VAIO VPCEB1KGX Battery

During magma crystallization, caesium is concentrated in the liquid phase and crystallizes last. Therefore the largest deposits of caesium are zone pegmatite ore bodies formed by this enrichment process. Because caesium does not substitute for potassium as readily as does rubidium, the alkali evaporite minerals sylvite (KCl) and carnallite (KMgCl3·6H2O) may contain only 0.002% caesium.Sony VAIO VPCEB1KGX/B Battery

Consequently, Cs is found in few minerals. Percent amounts of caesium may be found in beryl (Be3Al2(SiO3)6) and avogadrite ((K,Cs)BF4), up to 15 wt% Cs2O in the closely related mineral pezzottaite (Cs(Be2Li)Al2Si6O18), up to 8.4 wt% Cs2O in the rare mineral londonite ((Cs,K)Al4Be4(B,Be)12O28), and less in the more widespreadrhodizite.Sony VAIO VPCEB1KGX/W Battery

The only economically important source mineral for caesium is pollucite Cs(AlSi2O6), which is found in a few places around the world in zoned pegmatites, and is associated with the more commercially important lithium minerals lepidolite and petalite. Within the pegmatites, the large grain size and the strong separation of the minerals create high-grade ore for mining.Sony VAIO VPCEB1LFX Battery

One of the world's most significant and richest sources of the metal is the Tanco mine at Bernic Lake in Manitoba, Canada. The deposits there are estimated to contain 350,000 metric tons of pollucite ore, which represents more than two-thirds of the world's reserve base.Sony VAIO VPCEB1LFX/BI Battery

Although the stoichiometric content of caesium in pollucite is 42.6%, pure pollucite samples from this deposit contain only about 34% caesium, while the average content is 24 wt%. Commercial pollucite contains over 19% caesium. The Bikita pegmatite deposit in Zimbabwe is mined for its petalite but it also contains a significant amount of pollucite.Sony VAIO VPCEB1LFX/WI Battery

Notable amounts of pollucite are also mined in the Karibib Desert, Namibia.[50] At the present rate of world mine production of 5 to 10 metric tons per year, reserves will last for thousands of years.

Production

The mining of pollucite ore is a selective process and is conducted on a small scale in comparison with most metal mining operations.Sony VAIO VPCEB1MFX Battery

The ore is crushed, hand-sorted, but not usually concentrated, and then ground. Caesium is then extracted from pollucite mainly by three methods: acid digestion, alkaline decomposition, and direct reduction.

In the acid digestion, the silicate pollucite rock is dissolved with strong acids such as hydrochloric (HCl), sulfuric (H2SO4), hydrobromic (HBr), or hydrofluoric(HF).Sony VAIO VPCEB1MFX/BI Battery

With hydrochloric acid, a mixture of soluble chlorides is produced, and the insoluble chloride double salts of caesium are precipitated as caesium antimony chloride (Cs4SbCl7), caesium iodine chloride (Cs2ICl), or caesium hexachlorocerate (Cs2(CeCl6)). After separation, the pure precipitated double salt is decomposed, and pure CsCl is obtained after evaporating the water.Sony VAIO VPCEB1NFX Battery

The method using sulfuric acid yields the insoluble double salt directly as caesium alum (CsAl(SO4)2·12H2O). The aluminium sulfate in it is converted to the insoluble aluminium oxide by roasting the alum with carbon, and the resulting product is leached with water to yield a Cs2SO4 solution.Sony VAIO VPCEB1NFX/B Battery

The roasting of pollucite with calcium carbonate and calcium chloride yields insoluble calcium silicates and soluble caesium chloride. Leaching with water or diluteammonia (NH4OH) yields then a dilute chloride (CsCl) solution. This solution can be evaporated to produce caesium chloride or transformed into caesium alum or caesium carbonate.Sony VAIO VPCEB1NFX/L Battery

Albeit not commercially feasible, direct reduction of the ore with potassium, sodium or calcium in vacuum can produce caesium metal directly.

Most of the mined caesium (as salts) is directly converted into caesium formate (HCOO?Cs+) for applications such as oil drilling.Sony VAIO VPCEB1NFX/P Battery

To supply the developing market,Cabot Corporation built a production plant in 1997 at the Tanco Mine near Bernic Lake in Manitoba, Canada, with a capacity of 12,000 barrels (1,900 m3) per year of caesium formate solution.[53] The primary smaller-scale commercial compounds of caesium are caesium chloride and its nitrate.Sony VAIO VPCEB1NFX/W Battery

Alternatively, caesium metal may be obtained from the purified compounds derived from the ore. Caesium chloride, and the other caesium halides as well, can be reduced at 700 to 800 °C (1,292 to 1,472 °F) with calcium or barium, followed by distillation of the caesium metal.Sony VAIO VPCEB1PFX Battery

In the same way, the aluminate, carbonate, or hydroxide may be reduced by magnesium.[7] The metal can also be isolated by electrolysis of fused caesium cyanide (CsCN). Exceptionally pure and gas-free caesium can be made by the thermal decomposition at 390 °C (734 °F) of caesium azide CsN3, which is produced from aqueous caesium sulfate and barium azide.Sony VAIO VPCEB1PFX/B Battery

In vacuum applications, caesium dichromate can be reacted with zirconium forming pure caesium metal without other gaseous products.

Cs2Cr2O7 + 2 Zr ? 2 Cs + 2 ZrO2+ Cr2O3

The price of 99.8% pure caesium (metal basis) in 2009 was about US$10 per gram ($280 per ounce), but its compounds are significantly cheaper.Sony VAIO VPCEB1QGX Battery

In 1860, Robert Bunsen and Gustav Kirchhoff discovered caesium in the mineral water from Dürkheim, Germany. Due to the bright blue lines in its emission spectrum, they chose a name derived from the Latin word caesius, meaning sky-blue. Caesium was the first element to be discovered spectroscopically, only one year after the invention of the spectroscope by Bunsen and Kirchhoff.Sony VAIO VPCEB1QGX/BI Battery

To obtain a pure sample of caesium, 44,000 litres (9,700 imp gal; 12,000 US gal) of mineral water had to be evaporated to yield 240 kilograms (530 lb) of concentrated salt solution. The alkaline earth metals were precipitated either as sulfates or oxalates, leaving the alkali metal in the solution.Sony VAIO VPCEB1RGX Battery

After conversion to the nitrates and extraction with ethanol, a sodium-free mixture was obtained. From this mixture, the lithium was precipitated by ammonium carbonate. Potassium, rubidium and caesium form insoluble salts with chloroplatinic acid, but these salts show a slight difference in solubility in hot water.Sony VAIO VPCEB1RGX/BI Battery

Therefore, the less-soluble caesium and rubidium hexachloroplatinate ((Cs,Rb)2PtCl6) could be obtained by fractional crystallization. After reduction of the hexachloroplatinate with hydrogen, caesium and rubidium could be separated by the difference in solubility of their carbonates in alcohol.Sony VAIO VPCEB20 Battery

The process yielded 9.2 grams (0.32 oz) of rubidium chloride and 7.3 grams (0.26 oz) of caesium chloride from the initial 44,000 liters of mineral water.

The two scientists used the caesium chloride thus obtained to estimate the atomic weight of the new element at 123.35 (compared to the currently accepted one of 132.9).Sony VAIO VPCEC20 Battery

They tried to generate elemental caesium by electrolysis of molten caesium chloride, but instead of a metal, they obtained a blue homogenous substance which "neither under the naked eye nor under the microscope" showed the slightest trace of metallic substance;" as a result, they assigned it as a subchloride (Cs2Cl).Sony VAIO VPCEE20 Battery

In reality, the product was probably a colloidal mixture of the metal and caesium chloride.[58] The electrolysis of the aqueous solution of chloride with a mercury anode produced a caesium amalgam which readily decomposed under the aqueous conditions.Sony VAIO VPCEF20 Battery

The pure metal was eventually isolated by the German chemist Carl Setterberg while working on his doctorate with Kekulé and Bunsen. In 1882 he produced caesium metal by electrolyzing caesium cyanide, and thus avoiding the problems with the chloride.Sony VAIO VPCF112FX/B Battery

Historically, the most important use for caesium has been in research and development, primarily in chemical and electrical fields. Very few applications existed for caesium until the 1920s when it became used in radio vacuum tubes. It had two functions: as a getter it removed excess oxygen after manufacture, and as a coating on the heated cathode, it increased its electrical conductivity.Sony VAIO VPCF115FG/B Battery

Caesium did not become recognized as a high-performance industrial metal until the 1950s. Applications of non-radioactive caesium included photoelectric cells, photomultiplier tubes, optical components of infrared spectrophotometers, catalysts for several organic reactions, crystals for scintillation counters, and in magnetohydrodynamic power generators.Sony VAIO VPCF116FGBI Battery

Since 1967, the International System of Measurements has based its unit of time, the second, on the properties of caesium. The International System of Units (SI) defines the second as 9,192,631,770 cycles of the radiation, which corresponds to the transition between two hyperfine energy levels of the ground state of the caesium-133 atom.Sony VAIO VPCF117FJ/W Battery

The 13th General Conference on Weights and Measures of 1967 defined a second as: "the duration of 9,192,631,770 cycles of microwave light absorbed or emitted by the hyperfine transition of caesium-133 atoms in their ground state undisturbed by external fields".Sony VAIO VPCF117HG/BI Battery

Petroleum exploration

The largest current end-use of non-radioactive caesium is in caesium formate-based drilling fluids for the extractive oil industry. Aqueous solutions of caesium formate (HCOO–Cs+)—made by reacting caesium hydroxide with formic acid—were developed in the mid-1990s for use as oil well drilling and completion fluids.Sony VAIO VPCF118FJ/W Battery

The function of caesium formate as a drilling fluid is to lubricate drill bits, to bring rock cuttings to the surface, and to maintain pressure on the formation during drilling of the well. As completion fluid, which assists the emplacement of control hardware after drilling but prior to production, the function of caesium formate is to maintain the pressure.Sony VAIO VPCF119FC Battery

The high density of the caesium formate brine (up to 2.3 g·cm?3, or 19.2 pounds per gallon), coupled with the relatively benign nature of most caesium compounds, reduces the requirement for toxic high-density suspended solids in the drilling fluid—a significant technological, engineering and environmental advantage.Sony VAIO VPCF119FC/BI Battery

Unlike the components of many other heavy liquids, caesium formate is relatively environment-friendly.The caesium formate brine can be blended with potassium and sodium formates to decrease the density of the fluids down to that of water (1.0 g·cm?3, or 8.3 pounds per gallon).Sony VAIO VPCF119FJ/BI Battery

Furthermore, it is biodegradable and reclaimable, and may be recycled, which is important in view of its high cost (about $4,000 per barrel in 2001). Alkali formates are safe to handle and do not damage the producing formation or downhole metals as their corrosive alternative, high-density brines (such as zinc bromide ZnBr2 solutions),sometimes do; they also require less cleanup and disposal costs.Sony VAIO VPCF11AFJ Battery

Atomic clocks

Caesium-based atomic clocks observe electromagnetic transitions in the hyperfine structure of caesium-133 atoms and use it as a reference point. The first accurate caesium clock was built by Louis Essen in 1955 at the National Physical Laboratory in the UK.Sony VAIO VPCF11AGJ Battery

Since then, they have been improved repeatedly over the past half-century, and form the basis for standards-compliant time and frequency measurements. These clocks measure frequency with an error of 2 to 3 parts in 1014, which would correspond to a time measurement accuracy of 2 nanoseconds per day, or one second in 1.4 million years.Sony VAIO VPCF11AHJ Battery

The latest versions are accurate to better than 1 part in 1015, which means they would be off by about 2 seconds since the extinction of the dinosaurs 65 million years ago,[7] and has been regarded as "the most accurate realization of a unit that mankind has yet achieved.Sony VAIO VPCF11JFX/B Battery

Caesium clocks are also used in networks that oversee the timing of cell phone transmissions and the information flow on the Internet.

Electric power and electronics

Caesium vapor thermionic generators are low-power devices that convert heat energy to electrical energy.Sony VAIO VPCF11M1E Battery

In the two-electrodevacuum tube converter, it neutralizes the space charge that builds up near the cathode, and in doing so, it enhances the current flow.

Caesium is also important for its photoemissive properties by which light energy is converted to electron flow.Sony VAIO VPCF11M1E/H Battery

It is used inphotoelectric cells because caesium-based cathodes such as the intermetallic compound K2CsSb have low threshold voltage for emission of electrons.[67] The range of photoemissive devices using caesium include optical character recognition devices,photomultiplier tubes, and video camera tubes.Sony VAIO VPCF11MFX/B Battery

Nevertheless, germanium, rubidium, selenium, silicon, tellurium, and several other elements can substitute caesium in photosensitive materials.

Caesium iodide (CsI), bromide (CsBr) and caesium fluoride (CsF) crystals are employed for scintillators in scintillation counterswidely used in mineral exploration and particle physics research as they are well suited for the detection of gamma and x-rayradiation.Sony VAIO VPCF11S1E Battery

Caesium, being a heavy element, provides good stopping power contributing to better detectivity. Caesium compounds may also provide a faster response (CsF) and be less hygroscopic (CsI).

Caesium vapor is used in many common magnetometers.[70] The element is also used as an internal standard in spectrophotometry.Sony VAIO VPCF11S1E/B Battery

Like other alkali metals, caesium has a great affinity for oxygen and is used as a "getter" in vacuum tubes.[72] Other uses of the metal include high-energy lasers,vapor glow lamps, and vapor rectifiers.[7]

Centrifugation fluids

Because of their high density, solutions of caesium chloride (CsCl), sulfate (Cs2SO4), and trifluoroacetate (Cs(O2CCF3)) are commonly used in molecular biology for density gradient ultracentrifugation.Sony VAIO VPCF11Z1E Battery

This technology is primarily applied to the isolation of viral particles, sub-cellular organelles and fractions, andnucleic acids from biological samples.[74]

Chemical and medical use

Relatively few chemical applications exist for caesium.Sony VAIO VPCF11Z1E/BI Battery

Doping with caesium compounds is used to enhance the effectiveness of several metal-ion catalysts used in the production of chemicals, such as acrylic acid, anthraquinone, ethylene oxide, methanol,phthalic anhydride, styrene, methyl methacrylate monomers, and various olefins. Sony VAIO VPCF11ZHJ Battery

It is also used in the catalytic conversion ofsulfur dioxide into sulfur trioxide in the production of sulfuric acid.

Caesium fluoride enjoys niche use in organic chemistry as a base, or as an anhydrous source of fluoride ion. Caesium salts sometimes replace potassium or sodium salts in organic synthesis, such as cyclization, esterification, and polymerization.Sony VAIO VPCF127HGBI Battery

Nuclear and isotope applications

Caesium-137 is a very common radioisotope used as a gamma-emitter in industrial applications. Its advantages include a half-life of roughly 30 years, its availability from the nuclear fuel cycle, and having 137Ba as stable end product. The high water solubility is a disadvantage which makes it incompatible with irradiation of food and medical supplies.Sony VAIO VPCF137HG/BI Battery

It has been used in agriculture, cancer treatment, and the sterilization of food, sewage sludge, and surgical equipment. Radioactive isotopes of caesium in radiation devices were used in the medical field to treat certain types of cancer, but emergence of better alternatives and the use of water-soluble caesium chloride in the sources, which could create wide-ranging contamination, gradually put some of these caesium sources out of use.Sony VAIO VPC-P111KX/B Battery

Caesium-137 has been employed in a variety of industrial measurement gauges, including moisture, density, leveling, and thickness gauges. It has also been used in well logging devices for measuring the electron density of the rock formations, which is analogous to the bulk density of the formations.Sony VAIO VPC-P111KX/D Battery

Isotope 137 has also been used in hydrologic studies analogous to those using tritium. It is a daughter product of nuclear fission reactions. With the commencement of nuclear testing around 1945, and continuing through the mid-1980s, caesium-137 was released into the atmosphere where it is absorbed readily into solution.Sony VAIO VPC-P111KX/G Battery

Known year-to-year variation within that period allows correlation with soil and sediment layers. Caesium-134, and to a lesser extent caesium-135, have also been used in hydrology as a measure of caesium output by the nuclear power industry. While they are less prevalent than either caesium-133 or caesium-137, these isotopes have the advantage of being produced solely from anthropogenic sources.Sony VAIO VPC-P111KX/P Battery

Other uses

Caesium and mercury were used as a propellant in early ion engines designed for spacecraft propulsion on very long interplanetary or extraplanetary missions. The ionization method was to strip the outer electron from the propellant upon contact with a tungsten electrode that had voltage applied.Sony VAIO VPC-P111KX/W Battery

Concerns about the corrosive action of caesium on spacecraft components have pushed development in the direction of use of inert gas propellants such as xenon; this is easier to handle in ground-based tests and has less potential to interfere with the spacecraft. Eventually, xenon was used in the experimental spacecraft Deep Space 1 launched in 1998.Sony VAIO VPC-P112KX/B Battery

Nevertheless, field emission electric propulsion thrusters which use a simple system of accelerating liquid metal ions such as of caesium to create thrust have been built.

Caesium nitrate is used as an oxidizer and pyrotechnic colorant to burn silicon in infrared flares such as the LUU-19 flare, because it emits much of its light in the near infrared spectrum.Sony VAIO VPC-P112KX/D Battery

Caesium has been used to reduce the radar signature of exhaust plumes in the SR-71 Blackbird military aircraft.Caesium, along with rubidium, has been added as a carbonate to glass because it reduces electrical conductivity and improves stability and durability offiber optics and night vision devices.Sony VAIO VPC-P112KX/G Battery

Caesium fluoride or caesium aluminium fluoride are used in fluxes formulated for the brazing of aluminium alloys that contain magnesium.

Prognostications

Magnetohydrodynamic (MHD) power-generating systems were researched but failed to gain widespread acceptance.Sony VAIO VPC-P112KX/P Battery

Caesium metal has also been considered as the working fluid in high-temperature Rankine cycle turboelectric generators. Caesium salts have been evaluated as antishock reagents to be used following the administration of arsenical drugs. Because of their effect on heart rhythms, however, they are less likely to be used than potassium or rubidium salts. They have also been used to treat epilepsy.Sony VAIO VPC-P112KX/W Battery

Health and safety hazards

The portion of the total radiation dose (in air) contributed by each isotope versus time after the Chernobyl disaster depicting caesium-137 becoming the largest source of radiation about 200 days after the accident.Sony VAIO VPCP113KX/B Battery

Caesium compounds are rarely encountered by most people, but most caesium compounds are mildly toxic because of chemical similarity of caesium to potassium. Exposure to large amounts of caesium compounds can causehyperirritability and spasms, but as such amounts would not ordinarily be encountered in natural sources, caesium is not a major chemical environmental pollutant.Sony VAIO VPC-P113KX/B Battery

The median lethal dose (LD50) value for caesium chloride in mice is 2.3 g per kilogram, which is comparable to the LD50 values of potassium chloride and sodium chloride.

Caesium metal is one of the most reactive elements and is highly explosive when it comes in contact with water.Sony VAIO VPCP113KX/D Battery

The hydrogen gas produced by the reaction is heated by the thermal energy released at the same time, causing ignition and a violent explosion. This can occur with other alkali metals, but caesium is so potent that this explosive reaction can even be triggered by cold water.Sony VAIO VPC-P113KX/D Battery

The metal is highly pyrophoric, and ignites spontaneously in air to form caesium hydroxide and various oxides. Caesium hydroxide is a very strong base, and can rapidly corrode glass.

The isotopes 134 and 137 (present in the biosphere in small amounts from radiation leaks) represent a radioactivity burden which varies depending on location.Sony VAIO VPCP113KX/G Battery

Radiocaesium does not accumulate in the body as effectively as many other fission products (such as radioiodine and radiostrontium). As with other alkali metals, radiocaesium washes out of the body relatively quickly in sweat and urine. However, radiocaesium follows potassium and tends to accumulate in plant tissues, including fruits and vegetables.Sony VAIO VPC-P113KX/G Battery

It is also well-documented that mushrooms from contaminated forests accumulate radiocaesium (caesium-137) in their fungalsporocarps. Accumulation of caesium-137 in lakes has been a high concern after the Chernobyl disaster. Experiments with dogs showed that a single dose of 3.8 millicuries (140 MBq, 4.1 ?g of caesium-137) per kilogram is lethal within three weeks;Sony VAIO VPCP113KX/P Battery

smaller amounts may cause infertility and cancer. TheInternational Atomic Energy Agency and other sources have warned that radioactive materials, such as caesium-137, could be used in radiological dispersion devices, or "dirty bombs".

Barium is a chemical element with the symbol Ba and atomic number 56.Sony VAIO VPC-P113KX/P Battery

It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivitywith air. Its oxide is historically known as baryta but it reacts with water and carbon dioxide and is not found as a mineral.Sony VAIO VPCP113KX/W Battery

The most common naturally occurring minerals are the very insoluble barium sulfate, BaSO4 (barite), and barium carbonate, BaCO3(witherite). Barium's name originates from Greek barys (?????), meaning "heavy", describing the high density of some common barium-containing ores.Sony VAIO VPC-P113KX/W Battery

Barium has few industrial applications, but the metal has been historically used to scavenge air in vacuum tubes. Barium compounds impart a green color to flames and have been used in fireworks. Barium sulfate is used for its density, insolubility, and X-ray opacity.Sony VAIO VPC-P114KX/B Battery

It is used as an insoluble heavy mud-like paste when drilling oil wells, and in purer form, as an X-ray radiocontrast agent for imaging the human gastrointestinal tract. Soluble barium compounds are poisonous due to release of the soluble barium ion, and have been used as rodenticides.Sony VAIO VPC-P114KX/D Battery

New uses for barium continue to be sought. It is a component of some "high temperature" YBCO superconductors, and electroceramics.

Physical properties

Barium is a soft, silvery white alkali earth metal, which quickly oxidizes in air.It crystallizes in body centered cubic lattices. It burns with a green to pale green flame, resulting from emission at 524.2 and 513.7 nm.Sony VAIO VPC-P114KX/G Battery

Its simple compounds are notable for their relatively high (for an alkaline earth element) specific gravity. This high density is true of the most common barium-bearing mineral, barite (BaSO4), also called 'heavy spar' due to the high density (4.5 g/cm³).

Chemical properties

Barium, as for other alkali earth (group II) metals, is highly reducing.Sony VAIO VPC-P114KX/P Battery

It reacts exothermically with oxygen at room temperature to form barium oxide and peroxide. Because of its sensitivity to air, samples are generally stored under protective oils. The reaction is violent if barium is powdered. The metal is readily attacked in most acids, with the notable exception of sulfuric acid, as passivation stops the reaction by forming the insoluble barium sulfate.Sony VAIO VPC-P114KX/W Battery

It also reacts violently with water according to the reaction:

Ba + 2 H2O ? Ba(OH)2 + H2?

Barium combines with several metals, including aluminium, zinc, lead and tin, forming intermetallic phases and alloys.Sony VAIO VPCP115JC Battery

Naturally occurring barium is a mix of seven stable isotopes, the most abundant being 138Ba (71.7 %). 22 isotopes are known, but most of these are highly radioactive and have half-lives in the several millisecond to several day range. The only notable exceptions are 133Ba which has a half-life of 10.51 years, and 137mBa (2.55 minutes).Sony VAIO VPCP115JC/B Battery

133Ba is a standard calibrant for gamma-ray detectors in nuclear physics studies.

Occurrence

The abundance of barium is 0.0425 % in the Earth's crust and 13 µg/L in sea water. It occurs in the minerals barite (as the sulfate) and witherite (as the carbonate).Sony VAIO VPCP115JC/D Battery

Although witherite deposits were mined from the 17th century till 1969[4] in northern England, for example in the Settlingstones Mine near Newbrough,[5] today nearly all barium is mined as barite.

Large deposits of barite are found in China, Germany, India, Morocco, and in the United States.[6] A rare gem containing barium is known, called benitoite.Sony VAIO VPCP115JC/G Battery

Production

Because barium quickly oxidizes in air, it is difficult to obtain the free metal and it is never found free in nature. The metal is primarily found in, and extracted from, barite. Because barite is so insoluble, it cannot be used directly for the preparation of other barium compounds, or barium metal.Sony VAIO VPCP115JC/P Battery

Instead, the ore is heated with carbon to reduce it tobarium sulfide:

BaSO4 + 2 C ? BaS + 2 CO2

The barium sulfide is then hydrolyzed or treated with acids to form other barium compounds, such as the chloride, nitrate, and carbonate.Sony VAIO VPCP115JC/W Battery

Barium is commercially produced through the electrolysis of molten barium chloride (BaCl2):

(cathode) Ba2+ + 2 e?? Ba

(anode) 2 Cl– ? Cl2 + 2 e?
Barium metal is also obtained by the reduction of barium oxide with finely divided aluminium at temperatures between 1100 and 1200 °C:Sony VAIO VPCP115KG Battery

4 BaO + 2 Al ? BaO·Al2O3 + 3 Ba

The barium vapor is cooled and condensed to give the solid metal, which can be cast into rods or extruded into wires. Being a flammable solid, it is packaged under argon in steel containers or plastic bags.

Compounds

Ba2+ is the dominant oxidation state throughout the chemistry of barium.Sony VAIO VPCP116KG Battery

Its properties generally resemble those of other alkaline earth ions such as strontium and calcium. All halides, pseudohalides and chalcogenides are known, usually as colourless solids. The sulfate is famously insoluble. BaO forms a peroxide when heated in air. The oxide is basic and reacts with acids to give salts. Barium reduces oxides, chlorides and sulfides of less active metals.Sony VAIO VPC-P116KX/B Battery

For example:

Ba + CdO ? BaO + Cd

Ba + ZnCl2 ? BaCl2 + Zn

3 Ba + Al2S3 ? 3 BaS + 2 Al

At elevated temperatures, barium combines with nitrogen and hydrogen to produce the nitride Ba3N2 and hydride BaH2, respectively. When heated with nitrogen and carbon, it forms the cyanide:Sony VAIO VPC-P116KX/D Battery

Ba + N2 + 2 C ? Ba(CN)2

Barium's name originates from Greek ????? barys, meaning "heavy", describing the density of some common barium-containing ores. Alchemists in the early Middle Ages knew about some barium minerals. Smooth pebble-like stones of mineral barite found in Bologna, Italy were known as "Bologna stones".Sony VAIO VPC-P116KX/G Battery

Witches and alchemists were attracted to them because after exposure to light they would glow for years.

Carl Scheele identified barite as containing 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, byGuyton de Morveau, a name which was changed by Antoine Lavoisier to baryta.Sony VAIO VPC-P116KX/P Battery

Also in the 18th century, English mineralogistWilliam 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. Davy, by analogy with calcium named "barium" after baryta, with the "-ium" ending signifying a metallic element.Sony VAIO VPC-P116KX/W Battery

Robert Bunsen and Augustus Matthiessen yie

lded pure barium by electrolysis of a molten mixture of barium chloride and ammonium chloride.

The production of pure oxygen in the Brin process was a large scale application of barium peroxide before electrolysis and fractionally distill liquefied air became the dominant ways to produce oxygen. Sony VAIO VPCP118JC Battery

In this process the barium oxide reacts at 500–600°C with air to form barium peroxide which decomposes at above 700°C by releasing oxygen.

2 BaO + O2 ? 2 BaO2

Applications

The dominating application of elemental barium is as a scavenger or "getter" removing the last traces of oxygen and other gases in electronic vacuum tubes such as television cathode ray tubes.Sony VAIO VPCP118JC/B Battery

An alloy of barium with nickel is commonly used in automobile ignitions.

Applications of barium sulfate

Barium sulfate (the mineral barite, BaSO4) is important to the petroleum industry, for example, as drilling mud, a weighting agent in drilling new oil wells.Sony VAIO VPCP118JC/P Battery

It is also a filler in a variety of products such as rubber. Taking advantage of its opacity to X-rays, the sulfate is used as a radiocontrast agent for X-ray imaging of the digestive system ("barium meals" and "barium enemas").[6] Lithopone, a pigment that contains barium sulfate and zinc sulfide, is a permanent white that has good covering power, and does not darken when exposed to sulfides.Sony VAIO VPCP118JC/W Battery

Applications of other barium compounds

Aside from the sulfate, other compounds of barium find only niche applications. Applications are limited by the toxicity of Ba2+ions (Barium carbonate is a rat poison), which is not a problem for the insoluble BaSO4.Sony VAIO VPC-P118KX/B Battery

  • Barium oxide is used in a coating for the electrodes of fluorescent lamps, which facilitates the release of electrons.
  • Barium carbonate is also used in glassmaking. Being a heavy element, barium increases the refractive index and luster of the glass.Sony VAIO VPC-P118KX/D Battery
  • Barium, commonly as barium nitrate, is used to give green colors in fireworks. The species responsible for the brilliant green is barium monochloride; in the absence of a source of chlorine a yellow or "apple" green is produced instead.
  • 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 and as a bleaching agent.Sony VAIO VPC-P118KX/G Battery
  • Barium titanate is a promising electroceramic.
  • Barium fluoride is used for optics in infrared applications, since it is transparent from about 0.15 to 12 micrometres.

Precautions

Soluble barium compounds are poisonous.Sony VAIO VPC-P118KX/P Battery

At low doses, barium acts as a muscle stimulant, whereas higher doses affect the nervous system, causing cardiac irregularities, tremors, weakness, anxiety, dyspnea and paralysis. This may be due to its ability to block potassium ion channels which are critical to the proper function of the nervous system.Sony VAIO VPC-P118KX/W Battery

However, individual responses to barium salts vary widely, with some being able to handle barium nitrate casually without problems, and others becoming ill from working with it in small quantities. For example, barium acetate was used by Marie Robards to poison her father in 1993.Sony VAIO VPCP119JC Battery


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