Cerium is a
chemical element
A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...
with the
symbol Ce and
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
58. Cerium is a
soft,
ductile
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
, and silvery-white
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
that tarnishes when exposed to air. Cerium is the second element in the
lanthanide series, and while it often shows the +3
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
characteristic of the series, it also has a stable +4 state that does not oxidize water. It is also considered one of the
rare-earth element
The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides ( yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silv ...
s. Cerium has no known biological role in humans but is not particularly toxic, except with intense or continued exposure.
Despite always occurring in combination with the other rare-earth elements in minerals such as those of the
monazite
Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the ceriu ...
and
bastnäsite
The mineral bastnäsite (or bastnaesite) is one of a family of three carbonate-fluoride minerals, which includes bastnäsite-( Ce) with a formula of (Ce, La)CO3F, bastnäsite-( La) with a formula of (La, Ce)CO3F, and bastnäsite-( Y) with a formul ...
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 in aqueous solution. It is the most common of the lanthanides, followed by
neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishe ...
,
lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lant ...
, and
praseodymium
Praseodymium is a chemical element with the symbol Pr and the atomic number 59. It is the third member of the lanthanide series and is considered to be one of the rare-earth metals. It is a soft, silvery, malleable and ductile metal, valued for i ...
. It is the 25th-most
abundant element, making up 66
ppm of the Earth's crust, half as much as
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
and five times as much as
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
.
Cerium was the first of the lanthanides to be discovered, in
Bastnäs, Sweden, by
Jöns Jakob Berzelius
Jöns is a Swedish given name and a surname.
Notable people with the given name include:
* Jöns Jacob Berzelius (1779–1848), Swedish chemist
* Jöns Budde (1435–1495), Franciscan friar from the Brigittine monastery in NaantaliVallis Grati ...
and
Wilhelm Hisinger
Wilhelm Hisinger (23 December 1766 – 28 June 1852) was a Swedish physicist and chemist who in 1807, working in coordination with Jöns Jakob Berzelius, noted that in electrolysis any given substance always went to the same pole, and that substan ...
in 1803, and independently by
Martin Heinrich Klaproth
Martin Heinrich Klaproth (1 December 1743 – 1 January 1817) was a German chemist. He trained and worked for much of his life as an apothecary, moving in later life to the university. His shop became the second-largest apothecary in Berlin, and ...
in Germany in the same year. In 1839
Carl Gustaf Mosander
Carl Gustaf Mosander (10 September 1797 – 15 October 1858) was a Swedish chemist. He discovered the rare earth elements lanthanum, erbium and terbium.
Early life and education
Born in Kalmar, Mosander attended school there until he moved ...
became the first to isolate the metal. Today, cerium and its compounds have a variety of uses: for example,
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 produc ...
is used to polish glass and is an important part of
catalytic converter
A catalytic converter is an vehicle emissions control, exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalysis, catalyzing a redox chemic ...
s. Cerium metal is used in
ferrocerium
Ferrocerium (also known in Europe as Auermetall) is a synthetic pyrophoric alloy of mischmetal (cerium, lanthanum, neodymium, other trace lanthanides and some iron – about 95% lanthanides and 5% iron) hardened by blending in oxides o ...
lighters for its
pyrophoric
A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolit ...
properties. Cerium-doped
YAG phosphor is used in conjunction with blue
light-emitting diode
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (co ...
s to produce white light in most commercial white LED light sources.
Characteristics
Physical
Cerium is the second element of the
lanthanide series. In the periodic table, it appears between the lanthanides
lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lant ...
to its left and
praseodymium
Praseodymium is a chemical element with the symbol Pr and the atomic number 59. It is the third member of the lanthanide series and is considered to be one of the rare-earth metals. It is a soft, silvery, malleable and ductile metal, valued for i ...
to its right, and above the
actinide
The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The info ...
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
. It is a
ductile
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
metal with a hardness similar to that of
silver
Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
.
Its 58 electrons are arranged in the
configuration ef
15d
16s
2, of which the four outer electrons are
valence electron
In chemistry and physics, a valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed. In a single covalent bond, a shared pair form ...
s.
[Greenwood and Earnshaw, pp. 1232–5] The 4f, 5d, and 6s energy levels are very close to each other, and the transfer of one electron to the 5d shell is due to strong interelectronic repulsion in the compact 4f shell. This effect is overwhelmed when the atom is positively ionised; thus Ce
2+ on its own has instead the regular configuration
ef
2, although in some solid solutions it may be
ef
15d
1. 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 Ce
4+ and the fact that it comes very early in the lanthanide series, where the nuclear charge is still low enough until
neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishe ...
to allow the removal of the fourth valence electron by chemical means.
Cerium has a variable
electronic structure
In quantum chemistry, electronic structure is the state of motion of electrons in an electrostatic field created by stationary nuclei. The term encompasses both the wave functions of the electrons and the energies associated with them. Electr ...
. 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.
Chemical properties of the element
With ''E''
⦵ of −2.34 V for the Ce
3+/Ce) couple, cerium metal is a good reductant.
[Greenwood and Earnshaw, pp. 1244–8] Logically, it tarnishes in air, forming a
passivating oxide layer like
iron
Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
rust. A centimeter-sized sample of cerium metal corrodes completely in about a year. More dramatically, metallic cerium can be highly
pyrophoric
A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolit ...
:Ce + O
2 → CeO
2
Being highly electropositive, cerium reacts with water. The reaction is slow with cold water but speeds up with increasing temperature, producing cerium(III) hydroxide and hydrogen gas:
:2 Ce + 6 H
2O → 2 Ce(OH)
3 + 3 H
2
Allotropes
![Cerium phase diagram](https://upload.wikimedia.org/wikipedia/commons/6/64/Cerium_phase_diagram.jpg)
Four
allotropic
Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element: th ...
forms of cerium are known to exist at standard pressure, and are given the common labels of α to δ:
* The high-temperature form, δ-cerium, has a bcc (
body-centered cubic
In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.
There are three main varieties of ...
) crystal structure and exists above 726 °C.
* The stable form below 726 °C to approximately room temperature is γ-cerium, with an fcc (
face-centered cubic
In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.
There are three main varieties of ...
) crystal structure.
* The DHCP (double
hexagonal close-packed
In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement (or lattice). Carl Friedrich Gauss proved that the highest average density – that is, the greatest fraction of space occu ...
) 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/cm
3.
* 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 75 °C.
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.
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.
At atmospheric pressure, liquid cerium is more dense than its solid form at the melting
point.
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
Stable nuclides are nuclides that are not radioactive and so (unlike radionuclides) do not spontaneously undergo radioactive decay. When such nuclides are referred to in relation to specific elements, they are usually termed stable isotopes.
Th ...
, though the light isotopes
136Ce and
138Ce are theoretically expected to undergo inverse
double beta decay
In nuclear physics, double beta decay is a type of radioactive decay in which two neutrons are simultaneously transformed into two protons, or vice versa, inside an atomic nucleus. As in single beta decay, this process allows the atom to move clos ...
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 have been experimentally searched for. The current experimental limits for their half-lives are:
:
136Ce: >3.8×10
16 y
:
138Ce: >5.7×10
16 y
:
142Ce: >5.0×10
16 y
All other cerium isotopes are
synthetic and
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...
. The most stable of them are
144Ce with a half-life of 284.9 days,
139Ce with a half-life of 137.6 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. The isotopes between
140Ce and
144Ce inclusive occur as
fission products of
uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
. The primary decay mode of the isotopes lighter than
140Ce is
inverse beta decay
Inverse beta decay, commonly abbreviated to IBD, is a nuclear reaction involving an electron antineutrino scattering off a proton, creating a positron and a neutron. This process is commonly used in the detection of electron antineutrinos in ...
or
electron capture
Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Thi ...
to
isotopes of lanthanum, while that of the heavier isotopes is
beta decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
to
isotopes of praseodymium. Some
isotopes of neodymium
Naturally occurring neodymium (60Nd) is composed of 5 stable isotopes, 142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant (27.2% natural abundance), and 2 long-lived radioisotopes, 144Nd and 150Nd. In all, 33 radioisotopes o ...
can
alpha decay
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an at ...
or are predicted to decay to isotopes of cerium.
The 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
Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, ...
) 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
p-nuclei (''p'' stands for proton-rich) are certain proton-rich, naturally occurring isotopes of some elements between selenium and mercury inclusive which cannot be produced in either the s- or the r-process.
Definition
The classical, gro ...
, and their origin is not yet well understood: some speculated mechanisms for their formation include
proton capture
Proton capture is a nuclear reaction in which an atomic nucleus and one or more protons collide and merge to form a heavier nucleus.
Since protons have positive electric charge, they are repelled electrostatically by the positively charged nucl ...
as well as
photodisintegration
Photodisintegration (also called phototransmutation, or a photonuclear reaction) is a nuclear process in which an atomic nucleus absorbs a high-energy gamma ray, enters an excited state, and immediately decays by emitting a subatomic particle. The ...
.
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
Cross section may refer to:
* Cross section (geometry)
** Cross-sectional views in architecture & engineering 3D
*Cross section (geology)
* Cross section (electronics)
* Radar cross section, measure of detectability
* Cross section (physics)
**Abs ...
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 1g
7/2 proton orbital.
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 radionuclide
In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the ...
s
138La and
144Nd, respectively.
Compounds
Cerium exists in two main oxidation states, Ce(III) and Ce(IV). This pair of adjacent oxidation states dominates several aspects of the chemistry of this element. Cerium(IV) aqueous solutions may be prepared by reacting cerium(III) solutions with the strong oxidizing agents
peroxodisulfate
The peroxydisulfate ion, , is an oxyanion, the anion of peroxydisulfuric acid. It is commonly referred to as persulfate, but this term also refers to the peroxomonosulfate ion, . It is also called ''peroxodisulfate''. Approximately 500,000 tons o ...
or
bismuthate Bismuthate is an ion. Its chemical formula is BiO3−. It has bismuth in its +5 oxidation state.
It is a very strong oxidizing agent. It reacts with hot water to make bismuth(III) oxide and oxygen. It also reacts with acids. Sodium bismuthate is t ...
. The value of ''E''
⦵(Ce
4+/Ce
3+) varies widely depending on conditions due to the relative ease of complexation and hydrolysis with various anions, although +1.72 V is representative. Cerium is the only lanthanide which has important aqueous and coordination chemistry in the +4 oxidation state.
Halides
Cerium forms all four trihaldies CeX
3 (X = F, Cl, Br, I) usually by reaction of the oxides with the hydrogen halides. The anhydrous halides are pale-colored, paramagnetic, hygroscopic solids. Upon hydration, the trihalides convert to complexes containing aquo complexes
2O)8-9">e(H2O)8-9sup>3+. Unlike most lanthanides, Ce forms a tetrafluoride, a white solid. It also forms a bronze-colored diiodide, which has metallic properties.
[Greenwood and Earnshaw, pp. 1240–2]
Aside from the binary halide phases, a number of anionic halide complexes are known. Fluoride gives the Ce(IV) derivatives and . Chloride gives the orange .
Oxides and chalcogenides
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 produc ...
("ceria") has the
fluorite
Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon.
The Mohs sca ...
structure, similarly to the dioxides of praseodymium and
terbium
Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable, and ductile. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with w ...
. Ceria is a
nonstoichiometric compound
In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); mos ...
, meaning that the real formula is CeO
2−x, where x is about 0.2. Thus, the material is not perfectly described as Ce(IV). Ceria reduces to
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 and is gold-yellow in color.
Applications Engine and exha ...
with hydrogen gas.
Many
nonstoichiometric chalcogen
The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioac ...
ides are also known, along with the trivalent Ce
2Z
3 (Z =
S,
Se,
Te). The monochalcogenides CeZ conduct electricity and would better be formulated as Ce
3+Z
2−e
−. While CeZ
2 are known, they are polychalcogenides with cerium(III): cerium(IV) derivatives of S, Se, and Te are unknown.
[Greenwood and Earnshaw, pp. 1238–9]
Cerium(IV) complexes
![Cerium(IV) oxide](https://upload.wikimedia.org/wikipedia/commons/e/e8/Cerium%28IV%29_oxide.jpg)
The compound
ceric ammonium nitrate
Ceric ammonium nitrate (CAN) is the inorganic compound with the formula . This orange-red, water-soluble cerium salt is a specialised oxidizing agent in organic synthesis and a standard oxidant in quantitative analysis.
Preparation, properties, ...
("CAN") is the most common cerium compound encountered in the laboratory. The six nitrate ligands bind as
bidentate ligands. The complex is 12-coordinate, a high coordination number which emphasizes the large size of the Ce
4+ ion. CAN is popular oxidant in
organic synthesis, both as a stoichiometric reagent and as a catalyst. It is inexpensive, easily handled. It operates by one-electron redox. Cerium nitrates also form 4:3 and 1:1 complexes with
18-crown-6
18-Crown-6 is an organic compound with the formula 2H4Osub>6 and the IUPAC name of 1,4,7,10,13,16-hexaoxacyclooctadecane. It is a white, hygroscopic crystalline solid with a low melting point. Like other crown ethers, 18-crown-6 functions as a ...
(the ratio referring to that between cerium and the
crown ether
In organic chemistry, crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups (). The most common crown ethers are cyclic oligomers of ethylene oxide, the repeating unit being ethyleneoxy, i.e., . Impo ...
).
Classically CAN] is a primary standard for quantitative analysis.
Cerium(IV) salts, especially
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 th ...
, are often used as standard reagents for
volumetric analysis
Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the ''titrant' ...
in
cerimetric titrations.
![Ceric ammonium nitrate](https://upload.wikimedia.org/wikipedia/commons/a/af/Ceric_ammonium_nitrate.jpg)
Due to
ligand-to-metal charge transfer, aqueous cerium(IV) ions are orange-yellow.
Aqueous cerium(IV) is metastable in water and is a strong oxidizing agent that oxidizes
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
to give
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
gas.
In the
Belousov–Zhabotinsky reaction
A Belousov–Zhabotinsky reaction, or BZ reaction, is one of a class of reactions that serve as a classical example of non-equilibrium thermodynamics, resulting in the establishment of a nonlinear chemical oscillator. The only common element in ...
, cerium oscillates between the +4 and +3 oxidation states to catalyze the reaction.
Organocerium compounds
Organocerium chemistry is similar to that of the other
lanthanides
The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and ytt ...
, often involving complexes of
cyclopentadienyl and
cyclooctatetraenyl
1,3,5,7-Cyclooctatetraene (COT) is an unsaturated derivative of cyclooctane, with the formula C8H8. It is also known as nnulene. This polyunsaturated hydrocarbon is a colorless to light yellow flammable liquid at room temperature. Because of ...
ligands.
Cerocene (Ce(C
8H
8)
2) adopts the
uranocene
Uranocene, U(C8H8)2, is an organouranium compound composed of a uranium atom sandwiched between two cyclooctatetraenide rings. It was one of the first organoactinide compounds to be synthesized. It is a green air-sensitive solid that dissolves in ...
molecular structure.
[Greenwood and Earnshaw, pp. 1248–9] The 4f electron in cerocene, , is poised ambiguously between being localized and delocalized and this compound is considered intermediate-valent.
Alkyl
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloa ...
,
alkynyl
\ce
\ce
Acetylene
\ce
\ce
\ce
Propyne
\ce
\ce
\ce
\ce
1-Butyne
In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and ...
, and
alkenyl
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, a ...
organocerium derivatives are prepared from the
transmetallation Transmetalation (alt. spelling: transmetallation) is a type of organometallic reaction that involves the transfer of ligands from one metal to another. It has the general form:
:M1–R + M2–R′ → M1–R′ + M2–R
where R and R′ can be, but ...
of the respective
organolithium
In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom ...
or
Grignard reagents, and are more
nucleophilic
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...
but less basic than their precursors.
History
![Jöns Jacob Berzelius x Johan Way](https://upload.wikimedia.org/wikipedia/commons/d/d1/J%C3%B6ns_Jacob_Berzelius_x_Johan_Way.jpg)
Cerium was discovered in
Bastnäs in Sweden by
Jöns Jakob Berzelius
Jöns is a Swedish given name and a surname.
Notable people with the given name include:
* Jöns Jacob Berzelius (1779–1848), Swedish chemist
* Jöns Budde (1435–1495), Franciscan friar from the Brigittine monastery in NaantaliVallis Grati ...
and
Wilhelm Hisinger
Wilhelm Hisinger (23 December 1766 – 28 June 1852) was a Swedish physicist and chemist who in 1807, working in coordination with Jöns Jakob Berzelius, noted that in electrolysis any given substance always went to the same pole, and that substan ...
, and independently in Germany by
Martin Heinrich Klaproth
Martin Heinrich Klaproth (1 December 1743 – 1 January 1817) was a German chemist. He trained and worked for much of his life as an apothecary, moving in later life to the university. His shop became the second-largest apothecary in Berlin, and ...
, both in 1803.
Cerium was
named by Berzelius after the asteroid
Ceres
Ceres most commonly refers to:
* Ceres (dwarf planet), the largest asteroid
* Ceres (mythology), the Roman goddess of agriculture
Ceres may also refer to:
Places
Brazil
* Ceres, Goiás, Brazil
* Ceres Microregion, in north-central Goiás ...
, discovered two years earlier.
The asteroid is itself named after the Roman goddess
Ceres
Ceres most commonly refers to:
* Ceres (dwarf planet), the largest asteroid
* Ceres (mythology), the Roman goddess of agriculture
Ceres may also refer to:
Places
Brazil
* Ceres, Goiás, Brazil
* Ceres Microregion, in north-central Goiás ...
, goddess of agriculture, grain crops, fertility and motherly relationships.
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
Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outco ...
by
Humphry Davy
Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for t ...
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
Carl Gustaf Mosander (10 September 1797 – 15 October 1858) was a Swedish chemist. He discovered the rare earth elements lanthanum, erbium and terbium.
Early life and education
Born in Kalmar, Mosander attended school there until he moved ...
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
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
), now known as cerite, that he had in his mine.
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.
The element played a role in the
Manhattan Project
The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
, where cerium compounds were investigated in the
Berkeley
Berkeley most often refers to:
*Berkeley, California, a city in the United States
**University of California, Berkeley, a public university in Berkeley, California
* George Berkeley (1685–1753), Anglo-Irish philosopher
Berkeley may also refer ...
site as materials for
crucible
A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. While crucibles were historically usually made from clay, they can be made from any material that withstands te ...
s for
uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
and
plutonium
Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
casting.
For this reason,
new methods for the preparation and casting of cerium were developed within the scope of the
Ames
Ames may refer to:
Places United States
* Ames, Arkansas, a place in Arkansas
* Ames, Colorado
* Ames, Illinois
* Ames, Indiana
* Ames, Iowa, the most populous city bearing this name
* Ames, Kansas
* Ames, Nebraska
* Ames, New York
* Ames, Ok ...
daughter project (now the
Ames Laboratory
Ames National Laboratory, formerly Ames Laboratory, is a United States Department of Energy national laboratory located in Ames, Iowa, and affiliated with Iowa State University. It is a top-level national laboratory for research on national sec ...
).
Production of extremely pure cerium in Ames commenced in mid-1944 and continued until August 1945.
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
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
(68 ppm), and cerium is even more abundant than common metals such as
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
(13 ppm) and
tin
Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal.
Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...
(2.1 ppm). Thus, despite its position as one of the so-called
rare-earth metal
The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous sil ...
s, cerium is actually not rare at all.
[Greenwood and Earnshaw, p. 1294] 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.
Cerium occurs in various minerals, but the most important commercial sources are the minerals of the
monazite
Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the ceriu ...
and
bastnäsite
The mineral bastnäsite (or bastnaesite) is one of a family of three carbonate-fluoride minerals, which includes bastnäsite-( Ce) with a formula of (Ce, La)CO3F, bastnäsite-( La) with a formula of (La, Ce)CO3F, and bastnäsite-( Y) with a formul ...
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.
Also the cerium-dominant bastnäsite-(Ce) is the most important of the bastnäsites.
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.
[Greenwood and Earnshaw, pp. 1229–1232] 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
Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...
, since Ce
4+ and
Zr4+ have the same charge and similar ionic radii. In extreme cases, cerium(IV) can form its own minerals separated from the other rare-earth elements, such as
cerianite (correctly named cerianite-(Ce)
).
![Bastnaesite crystal structure](https://upload.wikimedia.org/wikipedia/commons/0/0d/Bastnaesite_crystal_structure.png)
Bastnäsite, Ln
IIICO
3F, is usually lacking in
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
and the heavy lanthanides beyond
samarium
Samarium is a chemical element with symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of samar ...
and
europium, and hence the extraction of cerium from it is quite direct. First, the bastnäsite is purified, using dilute
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
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 Ln
2O
3, cerium will be oxidized to the dioxide CeO
2. This is insoluble in water and can be leached out with 0.5 M hydrochloric acid, leaving the other lanthanides behind.
The procedure for
monazite
Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the ceriu ...
, , 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
The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...
to convert rare earths to their insoluble
oxalate
Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl ...
s. The oxalates are converted to oxides by annealing. The oxides are dissolved in nitric acid, but cerium oxide is insoluble in HNO
3 and hence precipitates out.
Care must be taken when handling some of the residues as they contain
228Ra, the daughter of
232Th, which is a strong gamma emitter.
Applications
![Auer von Welsbach](https://upload.wikimedia.org/wikipedia/commons/f/f7/Auer_von_Welsbach.jpg)
Cerium has two main applications, both of which use CeO
2. The industrial application of ceria is for polishing, especially
chemical-mechanical planarization (CMP). In its other main application, CeO
2 is used to decolorize glass. It functions by converting green-tinted ferrous impurities to nearly colorless ferric oxides.
Sensors
Other
automotive applications for the lower sesquioxide are as a
catalytic converter
A catalytic converter is an vehicle emissions control, exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalysis, catalyzing a redox chemic ...
for the oxidation of CO and
NO''x'' emissions in the exhaust gases from motor vehicles, 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
Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode are protected from oxidation or other atm ...
, where ceria as an alloying element improves arc stability and ease of starting while decreasing burn-off.
Gas mantles and pyrophoric alloys
The first use of cerium was in
gas mantle
A Coleman white gas lantern mantle glowing at full brightness
An incandescent gas mantle, gas mantle or Welsbach mantle is a device for generating incandescent bright white light when heated by a flame. The name refers to its original heat sou ...
s, invented by Austrian chemist
Carl Auer von Welsbach
Carl Auer von Welsbach (1 September 1858 – 4 August 1929), who received the Austrian noble title of Freiherr Auer von Welsbach in 1901, was an Austrian scientist and inventor, who separated didymium into the elements neodymium and praseo ...
. In 1885, he had previously experimented with mixtures of
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
, lanthanum, and yttrium oxides, but these gave green-tinted light and were unsuccessful. Six years later, he discovered that pure
thorium oxide
Thorium dioxide (ThO2), also called thorium(IV) oxide, is a crystalline solid, often white or yellow in colour. Also known as thoria, it is produced mainly as a by-product of lanthanide and uranium production. Thorianite is the name of the minera ...
produced a much better, though blue, light, and that mixing it with cerium dioxide resulted in a bright white light. Cerium dioxide also acts as a catalyst for the combustion of thorium oxide.
This resulted in 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.
[Greenwood and Earnshaw, p. 1228] Applications were soon found for them, especially in the pyrophoric alloy known as "
mischmetal
Mischmetal (from german: Mischmetall – "mixed metal") is an alloy of rare-earth elements. It is also called cerium mischmetal, or rare-earth mischmetal. A typical composition includes approximately 55% cerium, 25% lanthanum, and 15 ...
" composed of 50% cerium, 25% lanthanum, and the remainder being the other lanthanides, that is used widely for lighter flints.
Usually iron is added to form the alloy
ferrocerium
Ferrocerium (also known in Europe as Auermetall) is a synthetic pyrophoric alloy of mischmetal (cerium, lanthanum, neodymium, other trace lanthanides and some iron – about 95% lanthanides and 5% iron) hardened by blending in oxides o ...
, also invented by von Welsbach. Due to the chemical similarities of the lanthanides, chemical separation is not usually required for their applications, such as the addition of mischmetal to steel as an inclusion modifier to improve mechanical properties, or as catalysts for the cracking of petroleum.
This property of cerium saved the life of writer
Primo Levi
Primo Michele Levi (; 31 July 1919 – 11 April 1987) was an Italian chemist, partisan, writer, and Jewish Holocaust survivor. He was the author of several books, collections of short stories, essays, poems and one novel. His best-known works ...
at the
Auschwitz concentration camp, when he found a supply of ferrocerium alloy and bartered it for food.
Pigments and phosphors
The photostability of
pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
s can be enhanced by the addition of cerium, as it provides pigments with
lightfastness
Lightfastness is a property of a colourant such as dye or pigment that describes its resistance to fading when exposed to light. Dyes and pigments are used for example for dyeing of fabrics, plastics or other materials and manufacturing paints or ...
and prevents clear polymers from darkening in sunlight.
An example of a cerium compound used on its own as an
inorganic pigment is the vivid red
cerium(III) sulfide
Cerium(III) sulfide, also known as cerium sesquisulfide, is an inorganic compound with the formula Ce2S3. It is the sulfide salt of Cerium#Chemistry, cerium(III) and exists as three Polymorphism (materials science), polymorphs with different cryst ...
(cerium sulfide red), which stays chemically inert up to very high temperatures. The pigment is a safer alternative to lightfast but toxic
cadmium selenide-based pigments.
The addition of cerium oxide to older
cathode-ray tube television glass plates was beneficial, as it suppresses the darkening effect from the creation of
F-center
An F center or Farbe center (from the original German ''Farbzentrum'', where ''Farbe'' means ''color'' and ''zentrum'' means center) is a type of crystallographic defect in which an anionic vacancy in a crystal lattice is occupied by one or more un ...
defects due to the continuous electron bombardment during operation.
Cerium is also an essential component as a
dopant
A dopant, also called a doping agent, is a trace of impurity element that is introduced into a chemical material to alter its original electrical or optical properties. The amount of dopant necessary to cause changes is typically very low. When ...
for
phosphors used in CRT TV screens, fluorescent lamps, and later
white light-emitting diodes.
[Cerium dioxide](_blank)
. nanopartikel.info (2011-02-02) The most commonly used example is
cerium(III)-doped yttrium aluminium garnet (Ce:YAG) which emits green to yellow-green light (550–530 nm) and also behaves as a
scintillator.
Other alloys and refractories
Cerium salts, such as the sulfides
Ce2S3 and Ce
3S
4, were considered during the
Manhattan Project
The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
as advanced
refractory materials
In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...
for the construction of crucibles which could withstand the high temperatures and strongly
reducing conditions when casting plutonium metal.
Despite desirable properties, these sulfides were never widely adopted due to practical issues with their synthesis.
Cerium is used as alloying element in aluminum to create castable eutectic
aluminum alloys with 6–16 wt.% Ce, to which Mg and/or Si can be further added. These Al-Ce alloys have excellent high temperature strength and are suitable for automotive applications ''e.g.'' in
cylinder head
In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders and forms the roof of the combustion chamber.
In sidevalve engines, the head is a simple sheet of metal; whereas in more modern ...
s. Other alloys of cerium include Pu-Ce and Pu-Ce-Co
plutonium alloys, which have been used as
nuclear fuel.
Biological role and precautions
The early lanthanides have been found to be essential to some
methanotrophic
Methanotrophs (sometimes called methanophiles) are prokaryotes that metabolize methane as their source of carbon and chemical energy. They are bacteria or archaea, can grow aerobically or anaerobically, and require single-carbon compounds to s ...
bacteria living in
volcanic mudpots, such as ''
Methylacidiphilum fumariolicum'': lanthanum, cerium, praseodymium, and neodymium are about equally effective. Cerium is otherwise not known to have biological role in any other organisms, 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
The term calcium phosphate refers to a family of materials and minerals containing calcium ions (Ca2+) together with inorganic phosphate anions. Some so-called calcium phosphates contain oxide and hydroxide as well. Calcium phosphates are whi ...
, 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
Cerium nitrate refers to a family of nitrates of cerium in the +3 or +4 oxidation state. Often these compounds contain water, hydroxide, or hydronium ions in addition to cerium and nitrate. Double nitrates of cerium also exist.
Cerium(III) nitrat ...
is an effective topical antimicrobial treatment for
third-degree burn
A burn is an injury to skin, or other tissues, caused by heat, cold, electricity, chemicals, friction, or ultraviolet radiation (like sunburn). Most burns are due to heat from hot liquids (called scalding), solids, or fire. Burns occur mai ...
s,
although large doses can lead to cerium poisoning and
methemoglobinemia. The early lanthanides act as essential cofactors for the methanol dehydrogenase of the
methanotrophic
Methanotrophs (sometimes called methanophiles) are prokaryotes that metabolize methane as their source of carbon and chemical energy. They are bacteria or archaea, can grow aerobically or anaerobically, and require single-carbon compounds to s ...
bacterium ''
Methylacidiphilum fumariolicum'' SolV, for which lanthanum, cerium, praseodymium, and neodymium alone are about equally effective.
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.
Cerium is more dangerous to aquatic organisms, on account of being damaging to cell membranes; this is an important risk because it is not very soluble in water, thus causing contamination of the environment .
References
Bibliography
*
{{Authority control
Chemical elements
Chemical elements with double hexagonal close-packed structure
Lanthanides
Reducing agents