Cerium

Cerium is a chemical element with symbol Ce and atomic number 58. Cerium is a soft, ductile and silvery-white metal that tarnishes when exposed to air, and it is soft enough to be cut with a knife. Cerium is the second element in the lanthanide series, and while it often shows the +3 oxidation state characteristic of the series, it also exceptionally has a stable +4 state that does not oxidize water. It is also considered one of the rare-earth elements. Cerium has no biological role and is not very toxic.

Despite always occurring in combination with the other rare-earth elements in minerals such as those of the monazite and bastnäsite groups, cerium is easy to extract from its ores, as it can be distinguished among the lanthanides by its unique ability to be oxidized to the +4 state. It is the most common of the lanthanides, followed by neodymium, lanthanum, and praseodymium. It is the 26th-most abundant element, making up 66 ppm of the Earth's crust, half as much as chlorine and five times as much as lead.

Cerium was the first of the lanthanides to be discovered, in Bastnäs, Sweden by Jöns Jakob Berzelius and Wilhelm Hisinger in 1803, and independently by Martin Heinrich Klaproth in Germany in the same year. In 1839 Carl Gustaf Mosander became the first to isolate the metal. Today, cerium and its compounds have a variety of uses: for example, cerium(IV) oxide is used to polish glass and is an important part of catalytic converters. Cerium metal is used in ferrocerium lighters for its pyrophoric properties. Cerium-doped YAG phosphor is used in blue light-emitting diodes to produce white light.

Cerium,  58Ce
Cerium2
Cerium
Pronunciation/ˈsɪəriəm/ (SEER-ee-əm)
Appearancesilvery white
Standard atomic weight Ar, std(Ce)140.116(1)[1]
Cerium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Ce

Th
lanthanumceriumpraseodymium
Atomic number (Z)58
Groupgroup n/a
Periodperiod 6
Blockf-block
Element category  lanthanide
Electron configuration[Xe] 4f1 5d1 6s2[2]
Electrons per shell
2, 8, 18, 19, 9, 2
Physical properties
Phase at STPsolid
Melting point1068 K ​(795 °C, ​1463 °F)
Boiling point3716 K ​(3443 °C, ​6229 °F)
Density (near r.t.)6.770 g/cm3
when liquid (at m.p.)6.55 g/cm3
Heat of fusion5.46 kJ/mol
Heat of vaporization398 kJ/mol
Molar heat capacity26.94 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1992 2194 2442 2754 3159 3705
Atomic properties
Oxidation states+1, +2, +3, +4 (a mildly basic oxide)
ElectronegativityPauling scale: 1.12
Ionization energies
  • 1st: 534.4 kJ/mol
  • 2nd: 1050 kJ/mol
  • 3rd: 1949 kJ/mol
  • (more)
Atomic radiusempirical: 181.8 pm
Covalent radius204±9 pm
Color lines in a spectral range
Spectral lines of cerium
Other properties
Natural occurrenceprimordial
Crystal structuredouble hexagonal close-packed (dhcp)
Double hexagonal close packed crystal structure for cerium

β-Ce
Crystal structureface-centered cubic (fcc)
Face-centered cubic crystal structure for cerium

γ-Ce
Speed of sound thin rod2100 m/s (at 20 °C)
Thermal expansionγ, poly: 6.3 µm/(m·K) (at r.t.)
Thermal conductivity11.3 W/(m·K)
Electrical resistivityβ, poly: 828 nΩ·m (at r.t.)
Magnetic orderingparamagnetic[3]
Magnetic susceptibility(β) +2450.0·10−6 cm3/mol (293 K)[4]
Young's modulusγ form: 33.6 GPa
Shear modulusγ form: 13.5 GPa
Bulk modulusγ form: 21.5 GPa
Poisson ratioγ form: 0.24
Mohs hardness2.5
Vickers hardness210–470 MPa
Brinell hardness186–412 MPa
CAS Number7440-45-1
History
Namingafter dwarf planet Ceres, itself named after Roman deity of agriculture Ceres
DiscoveryMartin Heinrich Klaproth, Jöns Jakob Berzelius, Wilhelm Hisinger (1803)
First isolationCarl Gustaf Mosander (1838)
Main isotopes of cerium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
134Ce syn 3.16 d ε 134La
136Ce 0.186% stable
138Ce 0.251% stable
139Ce syn 137.640 d ε 139La
140Ce 88.449% stable
141Ce syn 32.501 d β 141Pr
142Ce 11.114% stable
143Ce syn 33.039 d β 143Pr
144Ce syn 284.893 d β 144Pr

Characteristics

Physical

Cerium is the second element of the lanthanide series. In the periodic table, it appears between the lanthanides lanthanum to its left and praseodymium to its right, and above the actinide thorium. It is a ductile metal with a hardness similar to that of silver.[6] Its 58 electrons are arranged in the configuration [Xe]4f15d16s2, of which the four outer electrons are valence electrons. Immediately after lanthanum, the 4f orbitals suddenly contract and are lowered in energy to the point that they participate readily in chemical reactions; however, this effect is not yet strong enough at cerium and thus the 5d subshell is still occupied.[7] Most lanthanides can use only three electrons as valence electrons, as afterwards the remaining 4f electrons are too strongly bound: cerium is an exception because of the stability of the empty f-shell in Ce4+ and the fact that it comes very early in the lanthanide series, where the nuclear charge is still low enough until neodymium to allow the removal of the fourth valence electron by chemical means.[8]

Cerium phase diagram
Phase diagram of cerium

Four allotropic forms of cerium are known to exist at standard pressure, and are given the common labels of α to δ:[9]

  • The high-temperature form, δ-cerium, has a bcc (body-centred cubic) crystal structure and exists above 726 °C.
  • The stable form below 726 °C to approximately room temperature is γ-cerium, with an fcc (face-centred cubic) crystal structure.
  • The dhcp (double hexagonal close-packed) form β-cerium is the equilibrium structure approximately from room temperature to −150 °C.
  • The fcc form α-cerium is stable below about −150 °C; it has a density of 8.16 g/cm3.
  • Other solid phases occurring only at high pressures are shown on the phase diagram.
  • Both γ and β forms are quite stable at room temperature, although the equilibrium transformation temperature is estimated at around 75 °C.[9]

Cerium has a variable electronic structure. The energy of the 4f electron is nearly the same as that of the outer 5d and 6s electrons that are delocalized in the metallic state, and only a small amount of energy is required to change the relative occupancy of these electronic levels. This gives rise to dual valence states. 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.[10]

At lower temperatures the behavior of cerium is complicated by the slow rates of transformation. Transformation temperatures are subject to substantial hysteresis and values quoted here are approximate. Upon cooling below −15 °C, γ-cerium starts to change to β-cerium, but the transformation involves a volume increase and, as more β forms, the internal stresses build up and suppress further transformation.[9] Cooling below approximately −160 °C will start formation of α-cerium but this is only from remaining γ-cerium. β-cerium does not significantly transform to α-cerium except in the presence of stress or deformation.[9] At atmospheric pressure, liquid cerium is more dense than its solid form at the melting point.[6][11][12]

Isotopes

Naturally occurring cerium is made up of four isotopes: 136Ce (0.19%), 138Ce (0.25%), 140Ce (88.4%), and 142Ce (11.1%). All four are observationally stable, though the light isotopes 136Ce and 138Ce are theoretically expected to undergo inverse double beta decay to isotopes of barium, and the heaviest isotope 142Ce is expected to undergo double beta decay to 142Nd or alpha decay to 138Ba. Additionally, 140Ce would release energy upon spontaneous fission. None of these decay modes have yet been observed, though the double beta decay of 136Ce, 138Ce, and 142Ce has been experimentally searched for. The current experimental limits for their half-lives are:[13]

136Ce: >3.8×1016 y
138Ce: >1.5×1014 y
142Ce: >5×1016 y

All other cerium isotopes are synthetic and radioactive. The most stable of them are 144Ce with a half-life of 284.9 days, 139Ce with a half-life of 137.6 days, 143Ce with a half-life of 33.04 days, and 141Ce with a half-life of 32.5 days. All other radioactive cerium isotopes have half-lives under four days, and most of them have half-lives under ten minutes.[13] The isotopes between 140Ce and 144Ce inclusive occur as fission products of uranium.[13] The primary decay mode of the isotopes lighter than 140Ce is inverse beta decay or electron capture to isotopes of lanthanum, while that of the heavier isotopes is beta decay to isotopes of praseodymium.[13]

The great rarity of the proton-rich 136Ce and 138Ce is explained by the fact that they cannot be made in the most common processes of stellar nucleosynthesis for elements beyond iron, the s-process (slow neutron capture) and the r-process (rapid neutron capture). This is so because they are bypassed by the reaction flow of the s-process, and the r-process nuclides are blocked from decaying to them by more neutron-rich stable nuclides. Such nuclei are called p-nuclei, and their origin is not yet well understood: some speculated mechanisms for their formation include proton capture as well as photodisintegration.[14] 140Ce is the most common isotope of cerium, as it can be produced in both the s- and r-processes, while 142Ce can only be produced in the r-process. Another reason for the abundance of 140Ce is that it is a magic nucleus, having a closed neutron shell (it has 82 neutrons), and hence it has a very low cross-section towards further neutron capture. Although its proton number of 58 is not magic, it is granted additional stability, as its eight additional protons past the magic number 50 enter and complete the 1 g7/2 proton orbital.[14] The abundances of the cerium isotopes may differ very slightly in natural sources, because 138Ce and 140Ce are the daughters of the long-lived primordial radionuclides 138La and 144Nd, respectively.[13]

Chemistry

Cerium tarnishes in air, forming a spalling oxide layer like iron rust; a centimeter-sized sample of cerium metal corrodes completely in about a year.[15] It burns readily at 150 °C to form the pale-yellow cerium(IV) oxide, also known as ceria:[16]

Ce + O2 → CeO2

This may be reduced to cerium(III) oxide with hydrogen gas.[17] Cerium metal is highly pyrophoric, meaning that when it is ground or scratched, the resulting shavings catch fire.[18] This reactivity conforms to periodic trends, since cerium is one of the first and hence one of the largest lanthanides.[19] Cerium(IV) oxide has the fluorite structure, similarly to the dioxides of praseodymium and terbium. Many nonstoichiometric chalcogenides are also known, along with the trivalent Ce2Z3 (Z = S, Se, Te). The monochalcogenides CeZ conduct electricity and would better be formulated as Ce3+Z2−e. While CeZ2 are known, they are polychalcogenides with cerium(III): cerium(IV) chalcogenides remain unknown.[17]

Cerium(IV) oxide
Cerium(IV) oxide

Cerium is a highly electropositive metal and reacts with water. The reaction is slow with cold water but speeds up with increasing temperature, producing cerium(III) hydroxide and hydrogen gas:[16]

2 Ce (s) + 6 H2O (l) → 2 Ce(OH)3 (aq) + 3 H2 (g)

Cerium metal reacts with all the halogens to give trihalides:[16]

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]

Reaction with excess fluorine produces the stable white tetrafluoride CeF4; the other tetrahalides are not known. Of the dihalides, only the bronze diiodide CeI2 is known; like the diiodides of lanthanum, praseodymium, and gadolinium, this is a cerium(III) electride compound.[20] True cerium(II) compounds are restricted to a few unusual organocerium complexes.[21][22]

Cerium dissolves readily in dilute sulfuric acid to form solutions containing the colorless Ce3+ ions, which exist as a [Ce(H2O)9]3+ complexes:[16]

2 Ce (s) + 3 H2SO4 (aq) → 2 Ce3+ (aq) + 3 SO2−
4
(aq) + 3 H2 (g)

The solubility of cerium is much higher in methanesulfonic acid.[23] Cerium(III) and terbium(III) have ultraviolet absorption bands of relatively high intensity compared with the other lanthanides, as their configurations (one electron more than an empty or half-filled f-subshell respectively) make it easier for the extra f electron to undergo f→d transitions instead of the forbidden f→f transitions of the other lanthanides.[24] Cerium(III) sulfate is one of the few salts whose solubility in water decreases with rising temperature.[25]

Ceric ammonium nitrate
Ceric ammonium nitrate

Cerium(IV) aqueous solutions may be prepared by reacting cerium(III) solutions with the strong oxidising agents peroxodisulfate or bismuthate. The value of E(Ce4+/Ce3+) varies widely depending on conditions due to the relative ease of complexation and hydrolysis with various anions, though +1.72 V is a usually representative value; that for E(Ce3+/Ce) is −2.34 V. Cerium is the only lanthanide which has important aqueous and coordination chemistry in the +4 oxidation state.[26] Due to ligand-to-metal charge transfer, aqueous cerium(IV) ions are orange-yellow.[27] Aqueous cerium(IV) is metastable in water[28] and is a strong oxidising agent that oxidizes hydrochloric acid to give chlorine gas.[26] For example, ceric ammonium nitrate is a common oxidising agent in organic chemistry, releasing organic ligands from metal carbonyls.[29] In the Belousov–Zhabotinsky reaction, cerium oscillates between the +4 and +3 oxidation states to catalyse the reaction.[30] Cerium(IV) salts, especially cerium(IV) sulfate, are often used as standard reagents for volumetric analysis in cerimetric titrations.[31]

The nitrate complex [Ce(NO3)6]2− is the most common cerium complex encountered when using cerium(IV) is an oxidising agent: it and its cerium(III) analogue [Ce(NO3)6]3− have 12-coordinate icosahedral molecular geometry, while [Ce(NO3)5]2− has 10-coordinate bicapped dodecadeltahedral molecular geometry. Cerium nitrates also form 4:3 and 1:1 complexes with 18-crown-6 (the ratio referring to that between cerium and the crown ether). Halogen-containing complex ions such as CeF4−
8
, CeF2−
6
, and the orange CeCl2−
6
are also known.[26] Organocerium chemistry is similar to that of the other lanthanides, being primarily that of the cyclopentadienyl and cyclooctatetraenyl compounds. The cerium(III) cyclooctatetraenyl compound has the uranocene structure.[32]

Cerium(IV)

Despite the common name of cerium(IV) compounds, the Japanese spectroscopist Akio Kotani wrote "there is no genuine example of cerium(IV)". The reason for this can be seen in the structure of ceria itself, which always contains some octahedral vacancies where oxygen atoms would be expected to go and could be better considered a non-stoichiometric compound with chemical formula CeO2−x. Furthermore, each cerium atom in ceria does not lose all four of its valence electrons, but retains a partial hold on the last one, resulting in an oxidation state between +3 and +4.[33][34] Even supposedly purely tetravalent compounds such as CeRh3, CeCo5, or ceria itself have X-ray photoemission and X-ray absorption spectra more characteristic of intermediate-valence compounds.[35] The 4f electron in cerocene, Ce(C8H8)2, is poised ambiguously between being localized and delocalized and this compound is also considered intermediate-valent.[34]

History

Ceres - RC3 - Haulani Crater (22381131691)
The dwarf planet Ceres, after which cerium is named

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.[36] Cerium was named by Berzelius after the dwarf planet Ceres, discovered two years earlier.[36][37] The dwarf planet itself is named after the Roman goddess of agriculture, grain crops, fertility and motherly relationships, Ceres.[36]

Cerium was originally isolated in the form of its oxide, which was named ceria, a term that is still used. 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. 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. Wilhelm Hisinger was a wealthy mine-owner and amateur scientist, and sponsor of Berzelius. He owned and controlled the mine at Bastnäs, and had been trying for years to find out the composition of the abundant heavy gangue rock (the "Tungsten of Bastnäs", which despite its name contained no tungsten), now known as cerite, that he had in his mine.[37] 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.[38]

Occurrence and production

Cerium is the most abundant of all the lanthanides, making up 66 ppm of the Earth's crust; this value is just behind that of copper (68 ppm), and cerium is even more abundant than common metals such as lead (13 ppm) and tin (2.1 ppm). Thus, despite its position as one of the so-called rare-earth metals, cerium is actually not rare at all.[39] Cerium content in the soil varies between 2 and 150 ppm, with an average of 50 ppm; seawater contains 1.5 parts per trillion of cerium.[37] Cerium occurs in various minerals, but the most important commercial sources are the minerals of the monazite and bastnäsite groups, where it makes up about half of the lanthanide content. Monazite-(Ce) is the most common representative of the monazites, with "-Ce" being the Levinson suffix informing on the dominance of the particular REE element representative.[40][41][42]). Also the cerium-dominant bastnäsite-(Ce) is the most important of the bastnäsites.[43][44] Cerium is the easiest lanthanide to extract from its minerals because it is the only one that can reach a stable +4 oxidation state in aqueous solution.[45] Because of the decreased solubility of cerium in the +4 oxidation state, cerium is sometimes depleted from rocks relative to the other rare-earth elements and is incorporated into zircon, since Ce4+ and Zr4+ have the same charge and similar ionic radii.[46] In extreme cases, cerium(IV) can form its own minerals separated from the other rare-earth elements, such as cerianite (correctly named cerianite-(Ce)[47][48][49]), (Ce,Th)O2.[50][51][52]

Bastnaesite crystal structure
Crystal structure of bastnäsite-(Ce). Color code: carbon, C, blue-gray; fluorine, F, green; cerium, Ce, white; oxygen, O, red.

Bastnäsite, LnIIICO3F, is usually lacking in thorium and the heavy lanthanides beyond samarium and europium, and hence the extraction of cerium from it is quite direct. First, the bastnäsite is purified, using dilute hydrochloric acid to remove calcium carbonate impurities. The ore is then roasted in the air to oxidize it to the lanthanide oxides: while most of the lanthanides will be oxidized to the sesquioxides Ln2O3, cerium will be oxidized to the dioxide CeO2. This is insoluble in water and can be leached out with 0.5 M hydrochloric acid, leaving the other lanthanides behind.[45]

The procedure for monazite, (Ln,Th)PO4, which usually contains all the rare earths, as well as thorium, is more involved. 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. 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. The oxides are dissolved in nitric acid, but cerium oxide is insoluble in HNO3 and hence precipitates out.[12] Care must be taken when handling some of the residues as they contain 228Ra, the daughter of 232Th, which is a strong gamma emitter.[45]

Applications

Auer von Welsbach
Carl Auer von Welsbach, who discovered many applications of cerium

The first use of cerium was in gas mantles, invented by the Austrian chemist Carl Auer von Welsbach. In 1885, he had previously experimented with mixtures of magnesium, lanthanum, and yttrium oxides, but these gave green-tinted light and were unsuccessful.[53] Six years later, he discovered that pure thorium oxide produced a much better, though blue, light, and that mixing it with cerium dioxide resulted in a bright white light.[54] Additionally, cerium dioxide also acts as a catalyst for the combustion of thorium oxide. This resulted in great commercial success for von Welsbach and his invention, and created great demand for thorium; its production resulted in a large amount of lanthanides being simultaneously extracted as by-products.[55] Applications were soon found for them, especially in the pyrophoric alloy known as "mischmetall" composed of 50% cerium, 25% lanthanum, and the remainder being the other lanthanides, that is used widely for lighter flints.[55] Usually, iron is also added to form an alloy known as ferrocerium, also invented by von Welsbach.[56] Due to the chemical similarities of the lanthanides, chemical separation is not usually required for their applications, such as the mixing of mischmetall into steel to improve its strength and workability, or as catalysts for the cracking of petroleum.[45] This property of cerium saved the life of writer Primo Levi at the Auschwitz concentration camp, when he found a supply of ferrocerium alloy and bartered it for food.[57]

Ceria is the most widely used compound of cerium. The main application of ceria is as a polishing compound, for example in chemical-mechanical planarization (CMP). In this application, ceria has replaced other metal oxides for the production of high-quality optical surfaces.[56] Major automotive applications for the lower sesquioxide are as a catalytic converter for the oxidation of CO and NOx emissions in the exhaust gases from motor vehicles,[58][59] Ceria has also been used as a substitute for its radioactive congener thoria, for example in the manufacture of electrodes used in gas tungsten arc welding, where ceria as an alloying element improves arc stability and ease of starting while decreasing burn-off.[60] Cerium(IV) sulfate is used as an oxidising agent in quantitative analysis. Cerium(IV) in methanesulfonic acid solutions is applied in industrial scale electrosynthesis as a recyclable oxidant.[61] Ceric ammonium nitrate is used as an oxidant in organic chemistry and in etching electronic components, and as a primary standard for quantitative analysis.[6][62]

The photostability of pigments can be enhanced by the 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.[63][64] Cerium sulfide forms a red pigment that stays stable up to 350 °C. The pigment is a nontoxic alternative to cadmium sulfide pigments.[37]

Cerium is used as alloying element in aluminum to create castable eutectic alloys, Al-Ce alloys with 6–16 wt.% Ce, to which Mg and/or Si can be further added; these alloys have excellent high temperature strength.[65]

Biological role and precautions

Cerium
Hazards
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Danger
H228, H302, H312, H332, H315, H319, H335
P210, P261, P280, P301, P312, P330, P305, P351, P338, P370, P378[66]
NFPA 704
Flammability code 0: Will not burn. E.g., waterHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
2
0

Cerium has no known biological role in humans, but is not very toxic either; it does not accumulate in the food chain to any appreciable extent. Because it often occurs together with calcium in phosphate minerals, and bones are primarily calcium phosphate, cerium can accumulate in bones in small amounts that are not considered dangerous. Cerium, like the other lanthanides, is known to affect human metabolism, lowering cholesterol levels, blood pressure, appetite, and risk of blood coagulation. Cerium nitrate is an effective topical antimicrobial treatment for third-degree burns,[37][67] although large doses can lead to cerium poisoning and methemoglobinemia.[68] The early lanthanides act as essential cofactors for the methanol dehydrogenase of the methanotrophic bacterium Methylacidiphilum fumariolicum SolV, for which lanthanum, cerium, praseodymium, and neodymium alone are about equally effective.[69]

Like all rare-earth metals, cerium is of low to moderate toxicity. A strong reducing agent, it 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 eaten, but animals injected with large doses of cerium have died due to cardiovascular collapse.[37] Cerium is more dangerous to aquatic organisms, on account of being damaging to cell membranes, but this is not an important risk because it is not very soluble in water.[37]

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Bibliography

Ceric ammonium nitrate

Ceric ammonium nitrate (CAN) is the inorganic compound with the formula (NH4)2Ce(NO3)6. This orange-red, water-soluble cerium salt is a specialised oxidizing agent in organic synthesis and a standard oxidant in quantitative analysis.

Cerium(III) bromide

Cerium(III) bromide is an inorganic compound with the formula CeBr3. This white hygroscopic solid is of interest as a component of scintillation counters.

Cerium(III) chloride

Cerium(III) chloride (CeCl3), also known as cerous chloride or cerium trichloride, is a compound of cerium and chlorine. It is a white hygroscopic solid; it rapidly absorbs water on exposure to moist air to form a hydrate, which appears to be of variable composition, though the heptahydrate CeCl3·7H2O is known. It is highly soluble in water, and (when anhydrous) it is soluble in ethanol and acetone.

Cerium(III) fluoride

Cerium(III) fluoride (or cerium trifluoride), CeF3, is an ionic compound of the rare earth metal cerium and fluorine.

It appears as a mineral in the form of fluocerite-(Ce).

Cerium(III) oxide

Cerium(III) oxide, also known as cerium oxide, cerium trioxide, cerium sesquioxide, cerous oxide or dicerium trioxide, is an oxide of the rare-earth metal cerium. It has chemical formula Ce2O3 and is gold-yellow in color.

Cerium(III) sulfate

Cerium(III) sulfate, also called cerous sulfate, is an inorganic compound with the formula Ce2(SO4)3. It is one of the few salts whose solubility in water decreases with rising temperature.

Cerium(IV) oxide

Cerium(IV) oxide, also known as ceric oxide, ceric dioxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare-earth metal cerium. It is a pale yellow-white powder with the chemical formula CeO2. It is an important commercial product and an intermediate in the purification of the element from the ores. The distinctive property of this material is its reversible conversion to a nonstoichiometric oxide.

Cerium(IV) sulfate

Cerium(IV) sulfate, also called ceric sulfate, is an inorganic compound. It exists as the anhydrous salt Ce(SO4)2 as well as a few hydrated forms: Ce(SO4)2(H2O)x, with x equal to 4, 8, or 12. These salts are yellow to yellow/orange solids that are moderately soluble in water and dilute acids. Its neutral solutions slowly decompose, depositing the light yellow oxide CeO2. Solutions of ceric sulfate have a strong yellow color. The tetrahydrate loses water when heated to 180-200 °C.

It is insoluble in glacial acetic acid and pure (96%) ethanol.

It was historically produced by direct reaction of fine, calcined cerium (IV) oxide and concentrated sulfuric acid, yielding the tetrahydrate.

Cerium nitrate

Cerium nitrate refers to a family of nitrates of cerium in the three or four oxidation state. Often these compounds contain water, hydroxide, or hydronium ions in addition to cerium and nitrate. Double nitrates of cerium also exist.

Cerium oxalate

Cerium(III) oxalate (cerous oxalate) is the inorganic cerium salt of oxalic acid. It is a white crystalline solid with the chemical formula of Ce2(C2O4)3. It could be obtained by the reaction of oxalic acid with cerium(III) chloride.

Ferrocerium

Ferrocerium is a synthetic pyrophoric alloy that produces hot sparks that can reach temperatures of 3,000 °C (5,430 °F) when rapidly oxidized by the process of striking. This property allows it to have many commercial applications, such as the ignition source for lighters (where it is often known by the misleading name "flint"), strikers for gas welding and cutting torches, deoxidization in metallurgy, and ferrocerium rods (also called ferro rods, flint-spark-lighters and wrongly "flint-and-steel" as this is the name of a different type of lighter using a section of high carbon steel and a natural flint). Due to ferrocerium's ability to ignite in adverse conditions, rods of ferrocerium are commonly used as an emergency combustion device in survival kits.Ferrocerium was invented in 1903 by the Austrian chemist Carl Auer von Welsbach. It takes its name from its two primary components: iron (from Latin: ferrum), and the rare-earth element cerium. The pyrophoric effect is dependent on the brittleness of the alloy and its low autoignition temperature.

Isotopes of cerium

Naturally occurring cerium (58Ce) is composed of 4 stable isotopes: 136Ce, 138Ce, 140Ce, and 142Ce, with 140Ce being the most abundant (88.48% natural abundance) and the only one theoretically stable; 136Ce, 138Ce, and 142Ce are predicted to undergo double beta decay but this process has never been observed. There are 35 radioisotopes that have been characterized, with the most stable being 144Ce, with a half-life of 284.893 days; 139Ce, with a half-life of 137.640 days and 141Ce, with a half-life of 32.501 days. 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 than 10 minutes. This element also has 10 meta states.

The isotopes of cerium range in atomic weight from 119 u (119Ce) to 157 u (157Ce).

Lanthanide

The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare earth elements.

The informal chemical symbol Ln is used in general discussions of lanthanide chemistry to refer to any lanthanide. All but one of the lanthanides are f-block elements, corresponding to the filling of the 4f electron shell; depending on the source, either lanthanum or lutetium is considered a d-block element, but is included due to its chemical similarities with the other 14. All lanthanide elements form trivalent cations, Ln3+, whose chemistry is largely determined by the ionic radius, which decreases steadily from lanthanum to lutetium.

They are called lanthanides because the elements in the series are chemically similar to lanthanum. Both lanthanum and lutetium have been labeled as group 3 elements, because they have a single valence electron in the 5d shell. However, both elements are often included in discussions of the chemistry of lanthanide elements. Lanthanum is the more often omitted of the two, because its placement as a group 3 element is somewhat more common in texts and for semantic reasons: since "lanthanide" means "like lanthanum", it has been argued that lanthanum cannot logically be a lanthanide, but IUPAC acknowledges its inclusion based on common usage.In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table, with placeholders or else a selected single element of each series (either lanthanum and actinium, or lutetium and lawrencium) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively. This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows (periods).

Lanthanum

Lanthanum is a chemical element with symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. It is also sometimes considered the first element of the 6th-period transition metals, which would put it in group 3, although lutetium is sometimes placed in this position instead. Lanthanum is traditionally counted among the rare earth elements. The usual oxidation state is +3. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.

Lanthanum usually occurs together with cerium and the other rare earth elements. Lanthanum was first found by the Swedish chemist Carl Gustav Mosander in 1839 as an impurity in cerium nitrate – hence the name lanthanum, from the Ancient Greek λανθάνειν (lanthanein), meaning "to lie hidden". Although it is classified as a rare earth element, lanthanum is the 28th most abundant element in the Earth's crust, almost three times as abundant as lead. In minerals such as monazite and bastnäsite, lanthanum composes about a quarter of the lanthanide content. It is extracted from those minerals by a process of such complexity that pure lanthanum metal was not isolated until 1923.

Lanthanum compounds have numerous applications as catalysts, additives in glass, carbon arc lamps for studio lights and projectors, ignition elements in lighters and torches, electron cathodes, scintillators, GTAW electrodes, and other things. Lanthanum carbonate is used as a phosphate binder in cases of renal failure. It is also an element in the 6th period and in the 3rd group.

Organocerium chemistry

Organocerium compounds are chemical compounds that contain one or more chemical bond between carbon and cerium. Organocerium chemistry is the corresponding science exploring properties, structure and reactivity of these compounds. In general, organocerium compounds are not isolable, and are rather studied in solution via their reactions with other species. There are notable exceptions, such as the Cp*3Ce(III) complex shown at right, but they are relatively rare. Complexes involving cerium of various oxidation states are known: though lanthanides are most stable in the +3 state, complexes of cerium(IV) have been reported. These latter compounds have found less widespread use due to their oxidizing nature, and the majority of literature regarding organometallic cerium complexes involves the +3 oxidation state. In particular, organocerium compounds have been developed extensively as non-basic carbon nucleophiles in organic synthesis. Because cerium is relatively non-toxic, they serve as an "environmentally friendly" alternative to other organometallic reagents. Several reviews detailing these applications have been published.

Praseodymium

Praseodymium is a chemical element with symbol Pr and atomic number 59. It is the third member of the lanthanide series and is traditionally considered to be one of the rare-earth metals. Praseodymium is a soft, silvery, malleable and ductile metal, valued for its magnetic, electrical, chemical, and optical properties. It is too reactive to be found in native form, and pure praseodymium metal slowly develops a green oxide coating when exposed to air.

Praseodymium always occurs naturally together with the other rare-earth metals. It is the fourth most common rare-earth element, making up 9.1 parts per million of the Earth's crust, an abundance similar to that of boron. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare-earth oxide residue he called didymium from a residue he called "lanthana", in turn separated from cerium salts. In 1885, the Austrian chemist Baron Carl Auer von Welsbach separated didymium into two elements that gave salts of different colours, which he named praseodymium and neodymium. The name praseodymium comes from the Greek prasinos (πράσινος), meaning "green", and didymos (δίδυμος), "twin".

Like most rare-earth elements, praseodymium most readily forms the +3 oxidation state, which is the only stable state in aqueous solution, although the +4 oxidation state is known in some solid compounds and, uniquely among the lanthanides, the +5 oxidation state is attainable in matrix-isolation conditions. Aqueous praseodymium ions are yellowish-green, and similarly praseodymium results in various shades of yellow-green when incorporated into glasses. Many of praseodymium's industrial uses involve its ability to filter yellow light from light sources.

Rare-earth element

A rare-earth element (REE) or rare-earth metal (REM), as defined by IUPAC, is one of a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides, as well as scandium and yttrium. Scandium and yttrium are considered rare-earth elements because they tend to occur in the same ore deposits as the lanthanides and exhibit similar chemical properties. Rarely, a broader definition that includes actinides may be used, since the actinides share some mineralogical, chemical, and physical (especially electron shell configuration) characteristics.The 17 rare-earth elements are cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y).

Despite their name, rare-earth elements are – with the exception of the radioactive promethium – relatively plentiful in Earth's crust, with cerium being the 25th most abundant element at 68 parts per million, more abundant than copper. However, because of their geochemical properties, rare-earth elements are typically dispersed and not often found concentrated in rare-earth minerals; as a result economically exploitable ore deposits are less common. The first rare-earth mineral discovered (1787) was gadolinite, a mineral composed of cerium, yttrium, iron, silicon, and other elements. This mineral was extracted from a mine in the village of Ytterby in Sweden; four of the rare-earth elements bear names derived from this single location.

Yttrium aluminium garnet

Yttrium aluminium garnet (YAG, Y3Al5O12) is a synthetic crystalline material of the garnet group. It is also one of three phases of the yttrium-aluminium composite, the other two being yttrium aluminium monoclinic (YAM, Y4Al2O9) and yttrium aluminium perovskite (YAP, YAlO3).YAG, like garnet and sapphire, has no uses as a laser medium when pure. However, after being doped with an appropriate ion, YAG is commonly used as a host material in various solid-state lasers. Rare earth elements such as neodymium and erbium can be doped into YAG as active laser ions, yielding Nd:YAG and Er:YAG lasers, respectively. Cerium-doped YAG (Ce:YAG) is used as a phosphor in cathode ray tubes and white light-emitting diodes, and as a scintillator.

Zinc–cerium battery

Zinc–cerium batteries are a type of redox flow battery first developed by Plurion Inc. (UK) during the 2000s. In this rechargeable battery, both negative zinc and positive cerium electrolytes are circulated though an electrochemical flow reactor during the operation and stored in two separated reservoirs. Negative and positive electrolyte compartments in the electrochemical reactor are separated by a cation-exchange membrane, usually Nafion (DuPont). The Ce(III)/Ce(IV) and Zn(II)/Zn redox reactions take place at the positive and negative electrodes, respectively. Since zinc is electroplated during charge at the negative electrode this system is classified as a hybrid flow battery. Unlike in zinc–bromine and zinc–chlorine redox flow batteries, no condensation device is needed to dissolve halogen gases. The reagents used in the zinc-cerium system are considerably less expensive than those used in the vanadium flow battery.

Due to the high standard electrode potentials of both zinc and cerium redox reactions in aqueous media, the open-circuit cell voltage is as high as 2.43 V. Among the other proposed rechargeable aqueous flow battery systems, this system has the largest cell voltage and its power density per electrode area is second only to H2-Br2 flow battery. Methanesulfonic acid is used as supporting electrolyte, as it allows high concentrations of both zinc and cerium; the solubility of the corresponding methanesulfonates is 2.1 M for Zn, 2.4 M for Ce(III) and up to 1.0 M for Ce(IV). Methanesulfonic acid is particularly well suited for industrial electrochemical applications and is considered to be a green alternative to other support electrolytes.The Zn-Ce flow battery is still in early stages of development. The main technological challenge is the control of the inefficiency and self discharge (Zn corrosion via hydrogen evolution) at the negative electrode. In commercial terms, the need for expensive Pt-Ti electrodes increases the capital cost of the system in comparison to other RFBs.

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