Metallic cerium is prepared by reduction techniques, such as
by reducing cerous fluoride with calcium, or by electrolysis of molten cerous
chloride or other cerous halides.
Cerium is an iron-grey lustrous metal. It is malleable, and oxidises very readily at room temperature, especially in moist air. Except for europium, cerium is the most reactive of the rare-earth metals. It slowly decomposes in cold water, and rapidly in hot water. Alkali solutions and dilute and concentrated acids attack the metal rapidly. The pure metal may ignite when scratched with a knife. It reacts with all of the halides (F, Cl, Br, I)
It is the most abundant of the rare earth metals and is found in minerals including allanite, monazite, cerite, and bastnaesite. There are large deposits found in India, Brazil and the USA.
•Name: Cerium
•Symbol: Ce
•Atomic number: 58
•Atomic weight: 140.116 (1) [see note g]
•Standard state: solid at 298 K
•CAS Registry ID: 7440-45-1
•Group in periodic table:
•Group name: Lanthanoid
•Period in periodic table: 6 (lanthanoid)
•Block in periodic table: f-block
•Color: silvery white
•Classification: Metallic
Historical information
Cerium was discovered by Wilhelm von Hisinger, Jöns Jacob Berzelius, Martin Klaproth at 1803 in Sweden, and independently by Maratin Klparothe, Germany. Cerium was named by Berzelius after the dwarf planet Ceres, discovered two years earlier (1801) Ceres, which was itself named for the Roman goddess of agriculture. It was isolated from a mineral from an iron mine at Bastnas.
Physical properties
•Melting point: 1068 [or 795 °C (1463 °F)] K
•Boiling point: 3633 [or 3360 °C (6080 °F)] K
•Density of solid: 6689 kg m-3
Orbital properties
•Ground state electron configuration: [Xe].4f1.5d1.6s2
•Shell structure: 2.8.18.19.9.2
•Term symbol: 1G4
Isolation
Cerium metal is available commercially so it is not normally necessary to make it in the laboratory, which is just as well as it is difficult to isolate as the pure metal. This is largely because of the way it is found in nature. The lanthanoids are found in nature in a number of minerals. The most important are xenotime, monazite, and bastnaesite. The first two are orthophosphate minerals LnPO4 (Ln deonotes a mixture of all the lanthanoids except promethium which is vanishingly rare) and the third is a fluoride carbonate LnCO3F. Lanthanoids with even atomic numbers are more common. The most comon lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and ytrrium which makes handling difficult since thorium and its decomposition products are radioactive.
For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Initially, the metals are extracted as salts from the ores by extraction with sulphuric acid (H2SO4), hydrochloric acid (HCl), and sodium hydroxide (NaOH). The ceric ion, Ce(IV) is more easily hydrolysed than the lanthanide (III) ions and therefore precipitates as a salt upon treatment with an oxidizing agent such as KMnO4.
Pure cerium is available through the electrolysis of a mixture of molten CeCl3 and NaCl (or CaCl2) in a graphite cell which acts as cathode using graphite as anode. The other product is chlorine gas.
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. 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. Cerium is not toxic when consumed orally, but animals injected with large doses of cerium have died due to cardiovascular collapse. Cerium is more dangerous to aquatic organisms, on account of being damaging to cell membranes. 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 weakly radioactive.
Biological Role:
Cerium can act similar to calcium in organisms, so accumulates in bones in small amounts. Cerium is also found in small amounts in tobacco plants, barley, and the wood of beech trees. However, very little cerium accumulates in the food chain. Human blood contains 0.001 ppm, human bones contain 3 ppm, and human tissue contains 0.3 ppm of cerium. There is a total of 40 milligrams of cerium in a typical 70-kilogram human. Humans typically consume less than a milligram per day of cerium. Cerium serves no known biological function, but cerium salts can stimulate metabolism.
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.
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 of glass, 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; it also allows for selective absorption of ultraviolet light in glass. Cerium oxide has a 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. 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.
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. This effect is suppressed by addition of cerium oxide. Cerium is also an essential component of phosphors used in TV screens and fluorescent lamps. Cerium sulfide forms a red pigment that stays stable of to 350 °C. The pigment is a nontoxic alternative to cadmium sulfide pigments.
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. In steels, cerium degasifies and can help reduce sulfides and oxides, and it is a precipitation hardening agent in stainless 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. Cerium metal is sometimes added to aluminum to improve aluminum's corrosion resistance.
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. 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.
Cerium is an iron-grey lustrous metal. It is malleable, and oxidises very readily at room temperature, especially in moist air. Except for europium, cerium is the most reactive of the rare-earth metals. It slowly decomposes in cold water, and rapidly in hot water. Alkali solutions and dilute and concentrated acids attack the metal rapidly. The pure metal may ignite when scratched with a knife. It reacts with all of the halides (F, Cl, Br, I)
It is the most abundant of the rare earth metals and is found in minerals including allanite, monazite, cerite, and bastnaesite. There are large deposits found in India, Brazil and the USA.
•Name: Cerium
•Symbol: Ce
•Atomic number: 58
•Atomic weight: 140.116 (1) [see note g]
•Standard state: solid at 298 K
•CAS Registry ID: 7440-45-1
•Group in periodic table:
•Group name: Lanthanoid
•Period in periodic table: 6 (lanthanoid)
•Block in periodic table: f-block
•Color: silvery white
•Classification: Metallic
Historical information
Cerium was discovered by Wilhelm von Hisinger, Jöns Jacob Berzelius, Martin Klaproth at 1803 in Sweden, and independently by Maratin Klparothe, Germany. Cerium was named by Berzelius after the dwarf planet Ceres, discovered two years earlier (1801) Ceres, which was itself named for the Roman goddess of agriculture. It was isolated from a mineral from an iron mine at Bastnas.
Physical properties
•Melting point: 1068 [or 795 °C (1463 °F)] K
•Boiling point: 3633 [or 3360 °C (6080 °F)] K
•Density of solid: 6689 kg m-3
Orbital properties
•Ground state electron configuration: [Xe].4f1.5d1.6s2
•Shell structure: 2.8.18.19.9.2
•Term symbol: 1G4
Isolation
Cerium metal is available commercially so it is not normally necessary to make it in the laboratory, which is just as well as it is difficult to isolate as the pure metal. This is largely because of the way it is found in nature. The lanthanoids are found in nature in a number of minerals. The most important are xenotime, monazite, and bastnaesite. The first two are orthophosphate minerals LnPO4 (Ln deonotes a mixture of all the lanthanoids except promethium which is vanishingly rare) and the third is a fluoride carbonate LnCO3F. Lanthanoids with even atomic numbers are more common. The most comon lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and ytrrium which makes handling difficult since thorium and its decomposition products are radioactive.
For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Initially, the metals are extracted as salts from the ores by extraction with sulphuric acid (H2SO4), hydrochloric acid (HCl), and sodium hydroxide (NaOH). The ceric ion, Ce(IV) is more easily hydrolysed than the lanthanide (III) ions and therefore precipitates as a salt upon treatment with an oxidizing agent such as KMnO4.
Pure cerium is available through the electrolysis of a mixture of molten CeCl3 and NaCl (or CaCl2) in a graphite cell which acts as cathode using graphite as anode. The other product is chlorine gas.
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. 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. Cerium is not toxic when consumed orally, but animals injected with large doses of cerium have died due to cardiovascular collapse. Cerium is more dangerous to aquatic organisms, on account of being damaging to cell membranes. 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 weakly radioactive.
Biological Role:
Cerium can act similar to calcium in organisms, so accumulates in bones in small amounts. Cerium is also found in small amounts in tobacco plants, barley, and the wood of beech trees. However, very little cerium accumulates in the food chain. Human blood contains 0.001 ppm, human bones contain 3 ppm, and human tissue contains 0.3 ppm of cerium. There is a total of 40 milligrams of cerium in a typical 70-kilogram human. Humans typically consume less than a milligram per day of cerium. Cerium serves no known biological function, but cerium salts can stimulate metabolism.
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.
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 of glass, 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; it also allows for selective absorption of ultraviolet light in glass. Cerium oxide has a 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. 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.
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. This effect is suppressed by addition of cerium oxide. Cerium is also an essential component of phosphors used in TV screens and fluorescent lamps. Cerium sulfide forms a red pigment that stays stable of to 350 °C. The pigment is a nontoxic alternative to cadmium sulfide pigments.
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. In steels, cerium degasifies and can help reduce sulfides and oxides, and it is a precipitation hardening agent in stainless 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. Cerium metal is sometimes added to aluminum to improve aluminum's corrosion resistance.
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. 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.
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