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:CsHg2 is 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 yielded 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
Non-toxicity of barium sulfate
Because it is highly insoluble in water as well as stomach acids, barium sulfate can be taken orally. It is eliminated completely from the digestive tract. Unlike other heavy metals, barium does not bioaccumulate. However, inhaled dust containing barium compounds can accumulate in the lungs, causing a benign condition called baritosis.Sony VAIO VPCP119JC/BI Battery
Lanthanum is a chemical element with the symbol La and atomic number 57. Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and other rare earth elements.Sony VAIO VPCP11S1E/B Battery
Lanthanum is a malleable, ductile, and soft metal that oxidizes rapidly when exposed to air. It is produced from the minerals monazite andbastnäsite using a complex multistage extraction process. Lanthanum compounds have numerous applications as catalysts, additives in glass, carbon lighting for studio lighting and projection,Sony VAIO VPC-P11S1E/B Battery
ignition elements in lighters and torches, electron cathodes, scintillators, and others. Lanthanum carbonate (La2(CO3)3) was approved as a medication against renal failure.
Physical properties
Lanthanum is a soft, malleable, silvery white metal which has hexagonal crystal structure at room temperature.Sony VAIO VPCP11S1E/D Battery
At 310 °C, lanthanum changes to a face-centered cubic structure, and at 865 °C into a body-centered cubic structure. Lanthanum easily is oxidized (a centimeter-sized sample will completely oxidize within a year) and is therefore used as in elemental form only for research purposes.Sony VAIO VPC-P11S1E/D Battery
For example, single La atoms have been isolated by implanting them intofullerene molecules.[4] If carbon nanotubes are filled with those lanthanum-encapsulated fullerenes and annealed, metallic nanochains of lanthanum are produced inside carbon nanotubes.Sony VAIO VPCP11S1E/G Battery
Chemical properties
Lanthanum exhibits two oxidation states, +3 and +2, the former being much more stable. For example, LaH3 is more stable than LaH2.Lanthanum burns readily at 150 °C to form lanthanum(III) oxide:
4 La + 3 O2 ? 2 La2O3
However, when exposed to moist air at room temperature, lanthanum oxide forms a hydrated oxide with a large volume increase.Sony VAIO VPC-P11S1E/G Battery
Lanthanum is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form lanthanum hydroxide:
2 La (s) + 6 H2O (l) ? 2 La(OH)3 (aq) + 3 H2 (g)
Lanthanum metal reacts with all the halogens. The reaction is vigorous if conducted at above 200 °C:Sony VAIO VPCP11S1E/P Battery
2 La (s) + 3 F2 (g) ? 2 LaF3 (s)
2 La (s) + 3 Cl2 (g) ? 2 LaCl3 (s)
2 La (s) + 3 Br2 (g) ? 2 LaBr3 (s)
2 La (s) + 3 I2 (g) ? 2 LaI3 (s)
Lanthanum dissolves readily in dilute sulfuric acid to form solutions containing the La(III) ions, which exist as [La(OH2)9]3+ complexes:Sony VAIO VPCP11S1E/W Battery
2 La(s) + 3 H2SO4 (aq) ? 2 La3+(aq) + 3 SO2?
4 (aq) + 3 H2 (g)
Lanthanum combines with nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon and arsenic at elevated temperatures, forming binary compounds.Sony VAIO VPC-P11S1E/W Battery
Naturally occurring lanthanum is composed of one stable (139La) and one radioactive (138La) isotope, with the stable isotope, 139La, being the most abundant (99.91% natural abundance). 38 radioisotopes have been characterized with the most stable being 138La with a half-life of 1.05×1011 years, and 137La with a half-life of 60,000 years.Sony VAIO VPCP11Z9E/B Battery
Most of the remaining radioactive isotopes have half-lives that are less than 24 hours, and the majority of these have half-lives less than 1 minute. This element also has three meta states.
The isotopes of lanthanum range in atomic weight from 117 u (117La) to 155 u (155La).Sony VAIO VPCS111FM/S Battery
The word lanthanum comes from the Greek ??????? [lanthan?] = to lie hidden. Lanthanum was discovered in 1839 bySwedish chemist Carl Gustav Mosander, when he partially decomposed a sample of cerium nitrate by heating and treating the resulting salt with dilute nitric acid.Sony VAIO VPCS115EC Battery
From the resulting solution, he isolated a new rare earth he called lantana. Lanthanum was isolated in relatively pure form in 1923.
Lanthanum is the most strongly basic of all the trivalent lanthanides, and this property is what allowed Mosander to isolate and purify the salts of this element.Sony VAIO VPCS115FG Battery
Basicity separation as operated commercially involved the fractional precipitation of the weaker bases (such as didymium) from nitrate solution by the addition of magnesium oxide or dilute ammonia gas. Purified lanthanum remained in solution. (The basicity methods were only suitable for lanthanum purification; didymium could not be efficiently further separated in this manner.)Sony VAIO VPCS117GG Battery
The alternative technique of fractional crystallization was invented by Dmitri Mendeleev, in the form of the double ammonium nitrate tetrahydrate, which he used to separate the less-soluble lanthanum from the more-soluble didymium in the 1870s. This system was used commercially in lanthanum purification until the development of practical solvent extraction methods that started in the late 1950s.Sony VAIO VPCS117GGB Battery
(A detailed process using the double ammonium nitrates to provide 99.99% pure lanthanum, neodymium concentrates and praseodymium concentrates is presented in Callow 1967, at a time when the process was just becoming obsolete.) As operated for lanthanum purification, the double ammonium nitrates were recrystallized from water.Sony VAIO VPCS118EC Battery
When later adapted by Carl Auer von Welsbach for the splitting of didymium, nitric acid was used as a solvent to lower the solubility of the system. Lanthanum is relatively easy to purify, since it has only one adjacent lanthanide, cerium, which itself is very readily removed due to its potential tetravalency.Sony VAIO VPCS119FJ/B Battery
The fractional crystallization purification of lanthanum as the double ammonium nitrate was sufficiently rapid and efficient, that lanthanum purified in this manner was not expensive. The Lindsay Chemical Division of American Potash and Chemical Corporation, for a while the largest producer of rare earths in the world,Sony VAIO VPCS119GC Battery
in a price list dated October 1, 1958 priced 99.9% lanthanum ammonium nitrate (oxide content of 29%) at $3.15 per pound, or $1.93 per pound in 50-pound quantities. The corresponding oxide (slightly purer at 99.99%) was priced at $11.70 or $7.15 per pound for the two quantity ranges. The price for their purest grade of oxide (99.997%) was $21.60 and $13.20, respectively.Sony VAIO VPCS11AFJ Battery
Occurrence
Although lanthanum belongs to the element group called rare earth metals, it is not rare at all. Lanthanum is available in relatively large quantities (32 ppm in Earth’s crust). "Rare earths" got their name because they were indeed rare as compared to the "common" earths such as lime or magnesia, and historically only a few deposits were known.Sony VAIO VPCS11AGJ Battery
Monazite (Ce, La, Th, Nd, Y)PO4, and bastnäsite (Ce, La, Y)CO3F, are the principal ores in which lanthanum occurs, in percentages of up to 25 to 38 percent of the total lanthanide content. In general, there is more lanthanum in bastnäsite than in monazite. Until 1949, bastnäsite was a rare and obscure mineral, not even remotely contemplated as a potential commercial source for lanthanides.Sony VAIO VPCS11AHJ Battery
In that year, the large deposit at the Mountain Pass rare earth mine in California was discovered. This discovery alerted geologists to the existence of a new class of rare earth deposit, the rare-earth bearingcarbonatite, other examples of which soon surfaced, particularly in Africa and China.Sony VAIO VPCS11AVJ Battery
Production
Lanthanum is most commonly obtained from monazite and bastnäsite. The mineral mixtures are crushed and ground. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths.Sony VAIO VPCS11J7E/B Battery
The acidic filtrates are partially neutralized with sodium hydroxide to pH 3-4. Thorium precipitates out of solution as hydroxide and is removed. After that, the solution is treated with ammonium oxalate to convert rare earths to their insoluble oxalates. The oxalates are converted to oxides by annealing.Sony VAIO VPCS11M1E/W Battery
The oxides are dissolved in nitric acid that excludes one of the main components, cerium, whose oxide is insoluble in HNO3. Lanthanum is separated as a double salt with ammonium nitrate by crystallization. This salt is relatively less soluble than other rare earth double salts and therefore stays in the residue.Sony VAIO VPCS11V9E Battery
The most efficient separation routine for lanthanum salt from the rare-earth salt solution is, however, ion exchange. In this process, rare-earth ions are adsorbed onto suitable ion-exchange resin by exchange with hydrogen, ammonium or cupric ions present in the resin.Sony VAIO VPCS11V9E/B Battery
The rare earth ions are then selectively washed out by a suitable complexing agent, such as ammonium citrate or nitrilotriacetate. Lanthanum can also be separated from a solution of rare earth nitrates by liquid-liquid extraction with a suitable organic liquid, such as tributyl phosphalate.Sony VAIO VPCS11X9E/B Battery
Currently, the most widely used extractant for the purification of lanthanum and the other lanthanides is the 2-ethylhexyl ester of 2-ethylhexylphosphonic acid; this has better handling characteristics than the previously used bis-2-ethylhexyl phosphate.
Lanthanum metal is obtained from its oxide by heating it with ammonium chloride or fluoride and hydrofluoric acid at 300-400 °C to produce the chloride or fluoride:Sony VAIO VPCS123FGB Battery
La2O3 + 6 NH4Cl ? 2 LaCl3 + 6 NH3 + 3 H2O
This is followed by reduction with alkali or alkaline earth metals in vacuum or argon atmosphere:
LaCl3 + 3 Li ? La + 3 LiCl
Also, pure lanthanum can be produced by electrolysis of molten mixture of anhydrous LaCl3 and NaCl or KCl at elevated temperatures.Sony VAIO VPCS125EC Battery
Applications
The first historical application of lanthanum was in gas lantern mantles. Carl Auer von Welsbach used a mixture of 60% magnesium oxide, 20% lanthanum oxide and 20% yttrium oxide which he called Actinophor, and patented in 1885.Sony VAIO VPCS128EC Battery
The original mantles gave a green-tinted light and were not very successful, and his first company, which established a factory in Atzgersdorf in 1887, failed in 1889.
Modern uses of lanthanum include:Sony VAIO VPCS129GC Battery
- One material used for anodic material of nickel-metal hydride batteries is La(Ni3.6Mn0.4Al0.3Co0.7. Due to high cost to extract the other lanthanides a mischmetal with more than 50% of lanthanum is used instead of pure lanthanum. The compound is an intermetalliccomponent of the AB5 type.Sony VAIO VPCS12C7E/B Battery
As most hybrid cars use nickel-metal hydride batteries, massive quantities of lanthanum are required for the production of hybrid automobiles. A typical hybrid automobile battery for aToyota Prius requires 10 to 15 kg (22-33 lb) of lanthanum. As engineers push the technology to increase fuel mileage, twice that amount of lanthanum could be required per vehicle.Sony VAIO VPCS12L9E/B Battery
- Hydrogen sponge alloys can contain lanthanum. These alloys are capable of storing up to 400 times their own volume of hydrogen gas in a reversible adsorption process. Heat energy is released every time they do so; therefore these alloys have possibilities in energy conservation systems.Sony VAIO VPCS12V9E/B Battery
- Mischmetal, a pyrophoric alloy used in lighter flints, contains 25% to 45% lanthanum.
- Lanthanum oxide and the boride are used in electronic vacuum tubes as hot cathode materials with strong emissivity ofelectrons. Crystals of LaB6 are used in high brightness, extended life, thermionic electron emission sources for electron microscopes and Hall effect thrusters.Sony VAIO VPCW111XX/P Battery
- Lanthanum fluoride (LaF3) is an essential component of a heavy fluoride glass named ZBLAN. This glass has superior transmittance in the infrared range and is therefore used for fiber-optical communication systems.
- Cerium doped lanthanum bromide and lanthanum chloride are the recent inorganic scintillators which have a combination of high light yield, best energy resolution and fast response.Sony VAIO VPCW111XX/PC Battery
- Their high yield converts into superior energy resolution; moreover, the light output is very stable and quite high over a very wide range of temperatures, making it particularly attractive for high temperature applications. These scintillators are already widely used commercially in detectors of neutrons or gamma rays.Sony VAIO VPCW111XX/T Battery
- Carbon arc lamps use a mixture of rare earth elements to improve the light quality. This applications, especially by themotion picture industry for studio lighting and projection, consumed about 25% of the rare-earth compounds produced until the phase out of Carbon arc lamps.Sony VAIO VPCW111XX/W Battery
- Lanthanum(III) oxide (La2O3) improves the alkali resistance of glass, and is used in making special optical glasses, such as infrared-absorbing glass, as well as camera and telescope lenses, because of the high refractive index and low dispersion of rare-earth glasses.Sony VAIO VPCW111XXP Battery
- Lanthanum oxide is also used as a grain growth additive during the liquid phase sintering of silicon nitride and zirconium diboride.
- Small amounts of lanthanum added to steel improves its malleability, resistance to impact and ductility. Whereas addition of lanthanum to molybdenum decreases its hardness and sensitivity to temperature variations.Sony VAIO VPCW111XXT Battery
- Small amounts of lanthanum are present in many pool products to remove the phosphates that feed algae.[19]
- Lanthanum oxide additive to tungsten is used in gas tungsten arc welding electrodes, as a substitute for radioactive thorium.Sony VAIO VPCW111XXW Battery
- Various compounds of lanthanum and other rare-earth elements (oxides, chlorides, etc.) are components of various catalysis, such as petroleum crackingcatalysts.
- Lanthanum-barium radiometric dating is used to estimate age of rocks and ores, though the technique has limited popularity.Sony VAIO VPCW115XG Battery
- Lanthanum carbonate was approved as a medication (Fosrenol, Shire Pharmaceuticals) to absorb excess phosphate in cases of end-stage renal failure.
- Lanthanum fluoride is used in phosphor lamp coatings. Mixed with europium fluoride, it is also applied in the crystal membrane of fluoride ion-selective electrodes.Sony VAIO VPCW115XGP Battery
- Like horseradish peroxidase, lanthanum is used as an electron-dense tracer in molecular biology.
Biological role
Lanthanum has no known biological role. The element is very poorly absorbed after oral administration and when injected its elimination is very slow. Lanthanum carbonate was approved as a medication named Fosrenol to absorb excess phosphate in cases of end-stage renal failure.Sony VAIO VPCW115XW/P Battery
While lanthanum has pharmacological effects on several receptors and ion channels, its specificity for the GABA receptor is unique among divalent cations. Lanthanum acts at the same modulatory site on the GABA receptor as zinc- a known negative allosteric modulator.Sony VAIO VPCW115XW/T Battery
The Lanthanum cation La3+ is a positive allosteric modulator at native and recombinant GABA receptors, increasing open channel time and decreasing desensitization in a subunit configuration dependent manner.
Precautions
Lanthanum has a low to moderate level of toxicity and should be handled with care. In animals, the injection of lanthanum solutions produces hyperglycaemia, low blood pressure, degeneration of the spleen and hepatic alterations.Sony VAIO VPCW115XW/W Battery
The application in carbon arc light led to the exposure of people to rare earth element oxides and fluorides, sometimes led to pneumoconiosis.
Cerium /?s??ri?m/ is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air.Sony VAIO VPCW117XC/P Battery
Cerium was named after the dwarf planet Ceres (itself named for the Roman goddess of agriculture). Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is found in a number of minerals, the most important being monazite and bastnasite.Sony VAIO VPCW117XC/T Battery
Commercial applications of cerium are numerous. They include catalysts, additives to fuel to reduce emissions and to glass and enamels to change their color. Cerium oxideis an important component of glass polishing powders and phosphors used in screens and fluorescent lamps.Sony VAIO VPCW117XC/W Battery
Physical properties
Cerium is a silvery metal, belonging to the lanthanide group. It resembles iron in color and luster, but is soft, and both malleable and ductile. Cerium has the third-longest liquid range of any element: 2648 C° (795 °C to 3443 °C) or 4766 F° (1463 °F to 6229 °F). (Neptunium and Thorium have the longer liquid ranges.)Sony VAIO VPCW119XJ Battery
Cerium is especially interesting because of its variable electronic structure. The energy of the inner 4f level is nearly the same as that of the outer or valence electrons, and only small energy is required to change the relative occupancy of these electronic levels. This gives rise to dual valency states.Sony VAIO VPCW119XJ/P Battery
For example, a volume change of about 10% occurs when cerium is subjected to high pressures or low temperatures. It appears that the valence changes from about 3 to 4 when it is cooled or compressed. The low temperature behavior of cerium is complex. Four allotropic modifications are thought to exist: cerium at room temperature and at atmospheric pressure is known as ? cerium.Sony VAIO VPCW119XJ/W Battery
Upon cooling to –16 °C, ? cerium changes to ? cerium. The remaining ? cerium starts to change to ? cerium when cooled to –172 °C, and the transformation is complete at –269 °C. ? Cerium has a density of 8.16; ? cerium exists above 726 °C. At atmospheric pressure, liquid cerium is more dense than its solid form at the melting point.Sony VAIO VPCW11AXJ Battery
Chemical properties
Cerium metal tarnishes slowly in air and burns readily at 150 °C to form cerium(IV) oxide:
Ce + O2 ? CeO2
Cerium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form cerium hydroxide:Sony VAIO VPCW11S1E/P Battery
2 Ce (s) + 6 H2O (l) ? 2 Ce(OH)3 (aq) + 3 H2 (g)
Cerium metal reacts with all the halogens:
2 Ce (s) + 3 F2 (g) ? 2 CeF3 (s) [white]
2 Ce (s) + 3 Cl2 (g) ? 2 CeCl3 (s) [white]
2 Ce (s) + 3 Br2 (g) ? 2 CeBr3 (s) [white]
2 Ce (s) + 3 I2 (g) ? 2 CeI3 (s) [yellow]
Cerium dissolves readily in dilute sulfuric acid to form solutions containing the colorless Ce(III) ions, which exist as a [Ce(OH2)9]3+ complexes:Sony VAIO VPCW11S1E/T Battery
2 Ce (s) + 3 H2SO4 (aq) ? 2 Ce3+ (aq) + 3 SO2?4 (aq) + 3 H2 (g)
Compounds
Cerium(IV) (ceric) salts are orange red or yellowish, whereas cerium(III) (cerous) salts are usually white or colorless. Both oxidation states absorb ultraviolet light strongly.Sony VAIO VPCW11S1E/W Battery
Cerium(III) can be used to make glasses that are colorless, yet absorb ultraviolet light almost completely. Cerium can be readily detected in rare earth mixtures by a very sensitive qualitative test: addition of ammonia and hydrogen peroxide to an aqueous solution of lanthanides produces a characteristic dark brown color if cerium is present.Sony VAIO VPCW121AX Battery
Cerium exhibits three oxidation states, +2, +3 and +4. The +2 state is rare and is observed in CeH2, CeI2 and CeS. The most common compound of cerium is cerium(IV) oxide (CeO2), which is used as "Jeweller's rouge" as well as in the walls of some self-cleaning ovens.Sony VAIO VPCW126AG Battery
Two common oxidizing agents used in titrations are ammonium cerium(IV) sulfate (ceric ammonium sulfate, (NH4)2Ce(SO4)3) and ammonium cerium(IV) nitrate (ceric ammonium nitrate or CAN, (NH4)2Ce(NO3)6). Cerium also forms a chloride, CeCl3 or cerium(III) chloride, used to facilitate reactions at carbonyl groupsin organic chemistry.Sony VAIO VPCW127JC/P Battery
Other compounds include cerium(III) carbonate (Ce2(CO3)3), cerium(III) fluoride (CeF3), cerium(III) oxide (Ce2O3), as well as cerium(IV) sulfate (ceric sulfate, Ce(SO4)2) and cerium(III) triflate (Ce(OSO2CF3)3).
The two oxidation states of cerium differ enormously in basicity: cerium(III) is a strong base, comparable to the other trivalent lanthanides, but cerium(IV) is weak.Sony VAIO VPCW127JC/T Battery
This difference has always allowed cerium to be by far the most readily isolated and purified of all the lanthanides, otherwise a notoriously difficult group of elements to separate. A wide range of procedures have been devised over the years to exploit the difference. Among the better ones:Sony VAIO VPCW127JC/W Battery
- Leaching the mixed hydroxides with dilute nitric acid: the trivalent lanthanides dissolve in cerium-free condition, and tetravalent cerium remains in the insoluble residue as a concentrate to be further purified by other means. A variation on this uses hydrochloric acid and the calcined oxides from bastnasite, but the separation is less sharp.Sony VAIO VPCW127JC/WZ Battery
- Precipitating cerium from a nitrate or chloride solution using potassium permanganate and sodium carbonate in a 1:4 molar ratio.
- Boiling rare-earth nitrate solutions with potassium bromate and marble chips.Sony VAIO VPCW12AAJ Battery
Formerly used commercially was a method whereby a solution of cerium(IV) in nitric acid would be added to dilute sulfuric acid. This caused cerium(IV) to largely precipitate as a basic salt, leaving trivalent lanthanide in solution. However, the finely divided precipitate was difficult to filter from the highly corrosive medium.Sony VAIO VPCW12AKJ Battery
Using the classical methods of rare-earth separation, there was a considerable advantage to a strategy of removing cerium from the mixture at the beginning. Cerium typically comprised 45% of the cerite or monazite rare earths, and removing it early greatly reduced the bulk of what needed to be further processed (or the cost of reagents to be associated with such processing).Sony VAIO VPCW12AVJ Battery
However, not all cerium purification methods relied on basicity. Ceric ammonium nitrate [ammonium hexanitratocerate(IV)] crystallization from nitric acid was one purification method. Cerium(IV) nitrate (hexanitratoceric acid) was more readily extractable into certain solvents (e.g. tri-n-butyl phosphate) than the trivalent lanthanides.Sony VAIO VPCW12S1E/P Battery
However, modern practice in China seems to be to do purification of cerium by counter-current solvent extraction, in its trivalent form, just like the other lanthanides.
Cerium(IV) is a strong oxidant under acidic conditions, but stable under alkaline conditions, when it is cerium(III) that becomes a strong reductant, easily oxidized by atmospheric oxygen (O2).Sony VAIO VPCW12S1E/T Battery
This ease of oxidation under alkaline conditions leads to the occasional geochemical parting of the ways between cerium and the trivalent light lanthanides under supergeneweathering conditions, leading variously to the "negative cerium anomaly" or to the formation of the mineral cerianite.Sony VAIO VPCW12S1E/W Battery
Air-oxidation of alkaline cerium(III) is the most economical way to get to cerium(IV), which can then be handled in acid solution.
Naturally occurring cerium is composed of 4 stable isotopes; 136
Ce, 138
Ce, 140
Ce, and 142
Ce, with 140
Ce being the most abundant (88.48% natural abundance).Sony VAIO VPCW213AG/L Battery
136
Ce and 142
Ce are predicted to be double beta active but no signs of activity were ever observed (for 142
Ce, the lower limit on half-life is 5×1016 yr). 26 radioisotopes have been characterized, with the most long-lived being 144
Ce with a half-life of 284.893 days, 139
Ce with a half-life of 137.640 days, and 141
Ce with a half-life of 32.501 days.Sony VAIO VPCW213AG/P Battery
All of the remaining radioactive isotopes have half-lives that are less than 4 days and the majority of these have half-lives that are less than10 minutes. This element also has 2 meta states.
The known isotopes of cerium range in atomic weight from 123 u (123Ce) to 152 u (152Ce).Sony VAIO VPCW213AG/T Battery
144
Ce is a high-yield product of nuclear fission; the ORNL Fission Product Pilot Plant separated substantial quantities of 144
Ce from reactor waste, and it was used in the Aircraft Nuclear Propulsion and SNAP programs.Sony VAIO VPCW213AG/W Battery
Cerium was discovered in Bastnäs in Sweden by Jöns Jakob Berzelius and Wilhelm Hisinger, and independently in Germany by Martin Heinrich Klaproth, both in 1803. Cerium was named by Berzelius after the dwarf planet Ceres, discovered two years earlier (1801). As originally isolated, cerium was in the form of its oxide, and was named ceria, a term that is still used.Sony VAIO VPCW215AG/L Battery
The metal itself was too electropositive to be isolated by then-current smelting technology, a characteristic of rare earth metals in general. After the development of electrochemistry by Humphry Davy five years later, the earths soon yielded the metals they contained.Sony VAIO VPCW217JC Battery
Ceria, as isolated in 1803, contained all of the lanthanides present in the cerite ore from Bastnäs, Sweden, and thus only contained about 45% of what is now known to be pure ceria. It was not until Carl Gustaf Mosander succeeded in removing lanthana and "didymia" in the late 1830s, that ceria was obtained pure.Sony VAIO VPCW217JC/L Battery
Wilhelm Hisinger was a wealthy mine owner and amateur scientist, and sponsor of Berzelius. He owned or controlled the mine at Bastnäs, and had been trying for years to find out the composition of the abundant heavy gangue rock (the "Tungstein of Bastnäs"), now known as cerite, that he had in his mine.Sony VAIO VPCW217JC/P Battery
Mosander and his family lived for many years in the same house as Berzelius, and Mosander was undoubtedly persuaded by Berzelius to investigate ceria further.
When the rare earths were first discovered, since they were strong bases like the oxides of calcium or magnesium, they were thought to be divalent.Sony VAIO VPCW217JC/T Battery
Thus, "ceric" cerium was thought to be trivalent, and the oxidation state ratio was therefore thought to be 1.5. Berzelius was annoyed to keep on getting the correct ratio 1.33. He was after all one of the finest analytical chemists in Europe.
In the late 1950s, the Lindsay Chemical Division of American Potash and Chemical Corporation of West Chicago,Sony VAIO VPCW217JC/W Battery
Illinois, then the largest producer of rare earths in the world, was offering cerium compounds in two purity ranges, "commercial" at 94-97% purity, and "purified", at a reported 99.9+% purity. In their October 1, 1958 price list, one-pound quantities of the oxides were priced at $3.30 or $8.10 respectively for the two purities;Sony VAIO VPCW218JC Battery
the per-pound price for 50-pound quantities were respectively $1.95 or $4.95 for the two grades. Cerium salts were proportionately cheaper, reflecting their lower net content of oxide.
Occurrence
Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight.Sony VAIO VPCW218JC/L Battery
It is found in a number of minerals including allanite (also known as orthite)—(Ca,Ce,La,Y)2(Al,Fe)3(SiO4)3(OH), monazite (Ce,La,Th,Nd,Y)PO4,bastnasite (Ce,La,Y)CO3F, hydroxylbastnasite (Ce,La,Nd)CO3(OH,F), rhabdophane (Ce,La,Nd)PO4-H2O, zircon (ZrSiO4), and synchysiteCa(Ce,La,Nd,Y)(CO3)2F.Sony VAIO VPCW218JC/P Battery
Monazite and bastnasite are presently the two most important sources of cerium. Large deposits of monazite,allanite, and bastnasite will supply cerium, thorium, and other rare-earth metals for many years to come.
Production
The mineral mixtures are crushed, ground and treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths.Sony VAIO VPCW218JC/T Battery
The acidic filtrates are partially neutralized with sodium hydroxide to pH 3–4. Thorium precipitates out of solution as hydroxide and is removed. After that the solution is treated with ammonium oxalate to convert rare earths in to their insoluble oxalates. The oxalates are converted to oxides by annealing.Sony VAIO VPCW218JC/W Battery
The oxides are dissolved in nitric acid that excludes one of the main components, cerium, whose salts are insoluble in HNO3. Metallic cerium is prepared by metallothermic reduction techniques, such as by reducing cerium fluoride or chloride with calcium, or by electrolysis of molten cerous chloride or other cerous halides. The metallothermic technique is used to produce high-purity cerium.Sony VAIO VPCW219AJ/L Battery
Applications
A major technological application for Cerium(III) oxide is a catalytic converter for the reduction of CO emissions in the exhaust gases from motor vehicles. In particular, cerium oxide is added into Diesel fuels. Another important use of the cerium oxide is a hydrocarbon catalyst in self cleaning ovens, incorporated into oven walls and as a petroleum cracking catalyst in petroleum refining.Sony VAIO VPCW219AJ/P Battery
Cerium(IV) oxide is considered one of the most efficient agents for precision polishing of optical components. Cerium compounds are also used in the manufacture ofglass, both as a component and as a decolorizer. For example, cerium(IV) oxide in combination with titanium(IV) oxide gives a golden yellow color to glass;Sony VAIO VPCW219AJ/W Battery
it also allows for selective absorption of ultraviolet light in glass. Cerium oxide has high refractive index and is added to enamel to make it more opaque.
Cerium(IV) oxide is used in incandescent gas mantles, such as the Welsbach mantle, where it was combined with thorium, lanthanum, magnesium or yttrium oxides.Sony VAIO VPCW21AAJ Battery
Doped with other rare earth oxides, it has been investigated as a solid electrolyte in intermediate temperature solid oxide fuel cells: The cerium(IV) oxide-cerium(III) oxide cycle or CeO2/Ce2O3 cycle is a two step thermochemical process based on cerium(IV) oxide and cerium(III) oxide for hydrogen production.Sony VAIO VPCW21AKJ Battery
The photostability of pigments can be enhanced by addition of cerium. It provides pigments with light fastness and prevents clear polymers from darkening in sunlight. Television glass plates are subject to electron bombardment, which tends to darken them by creation of F-center color centers.Sony VAIO VPCW21AVJ Battery
This effect is suppressed by addition of cerium oxide. Cerium is also an essential component of phosphors used in TV screens and fluorescent lamps.
A traditional use of cerium was in the pyrophoric mischmetal alloy used for light flints. Because of the high affinity of cerium to sulfur and oxygen, it is used in various aluminium alloys, and iron alloys.Sony VAIO VPCY115FGS Battery
In steels, cerium degasifies and can help reduce sulfides and oxides, and it is a precipitation hardening agent instainless steel. Adding cerium to cast irons opposes graphitization and produces a malleable iron. Addition of 3–4% of cerium to magnesium alloys, along with 0.2 to 0.6% zirconium, helps refine the grain and give sound casting of complex shapes. It also adds heat resistance to magnesium castings.Sony VAIO VPCY115FX/BI Battery
Cerium alloys are used in permanent magnets and in tungsten electrodes for gas tungsten arc welding. Cerium is used in carbon-arc lighting, especially in the motion picture industry. Cerium oxalate is an anti-emetic drug. Cerium(IV) sulfate is used extensively as a volumetric oxidizing agent in quantitative analysis.Sony VAIO VPCY115FXBI Battery
Ceric ammonium nitrate is a useful one-electron oxidant in organic chemistry, used to oxidatively etch electronic components, and as a primary standard for quantitative analysis.
Precautions
Cerium, like all rare-earth metals, is of low to moderate toxicity. Cerium is a strong reducing agent and ignites spontaneously in air at 65 to 80 °C. Fumes from cerium fires are toxic.Sony VAIO VPCY118EC Battery
Water should not be used to stop cerium fires, as cerium reacts with water to produce hydrogen gas. Workers exposed to cerium have experienced itching, sensitivity to heat, and skin lesions. Animals injected with large doses of cerium have died due to cardiovascular collapse.Sony VAIO VPCY118GX/BI Battery
Cerium(IV) oxide is a powerful oxidizing agent at high temperatures and will react with combustible organic materials. While cerium is not radioactive, the impure commercial grade may contain traces of thorium, which is radioactive. Cerium serves no known biological function.Sony VAIO VPCY119FJ/S Battery,Sony VAIO VPCY11AFJ Battery,Sony VAIO VPCY11AGJ Battery,Sony VAIO VPCY11AHJ Battery,Sony VAIO VPCY11AVJ Battery,Sony VAIO VPCY11M1E/S Battery,Sony VAIO VPCY11S1E Battery
No comments:
Post a Comment