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22 décembre 2011 4 22 /12 /décembre /2011 02:29

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, CeCl3or 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

  1. 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
  1. Precipitating cerium from a nitrate or chloride solution using potassium permanganate and sodium carbonate in a 1:4 molar ratio.
  2. 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

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