Cer Chemische Eigenschaften,Einsatz,Produktion Methoden
R-S?tze Betriebsanweisung:
R22:Gesundheitssch?dlich beim Verschlucken.
R23:Giftig beim Einatmen.
R36/38:Reizt die Augen und die Haut.
R36/37/38:Reizt die Augen, die Atmungsorgane und die Haut.
R20/21/22:Gesundheitssch?dlich beim Einatmen,Verschlucken und Berührung mit der Haut.
R11:Leichtentzündlich.
S-S?tze Betriebsanweisung:
S26:Bei Berührung mit den Augen sofort gründlich mit Wasser abspülen und Arzt konsultieren.
S36:DE: Bei der Arbeit geeignete Schutzkleidung tragen.
S36/37/39:Bei der Arbeit geeignete Schutzkleidung,Schutzhandschuhe und Schutzbrille/Gesichtsschutz tragen.
S16:Von Zündquellen fernhalten - Nicht rauchen.
Beschreibung
Cerium is a rare earth metal and the most abundant member of
the lanthanide series discovered by Jons J. Berzelius and W. von
Hisinger in 1803 in Sweden. Berzelius and Hisinger discovered
the new element in a rare reddish-brown mineral now known
as cerite, a cerium–lanthanide silicate. Although they could not
isolate the pure metal, they found that cerium had two
oxidation states: trivalent state (Ce3+, cerous, usually orangered)
and the tetravalent state (Ce4+, ceric, usually colorless).
Cerium is the only material known to have a solid-state critical
point.
Chemische Eigenschaften
Elemental cerium has a face-centered cubic crystal structure at 25 °C. Cerium is the most abundant element of the rare-earth group and is 28th in ranking of the naturally occurring elements in the earth’s crust. The element is a silver-gray metal which oxidizes readily at room temperature, particularly in moist air, to form the oxide CeO2, which is of a pale yellowish-green color. Above 300 °C, the element may ignite and burn with a bright red glow. Of the nineteen isotopes of cerium, only four occur in nature,
136Ce,
138Ce,
140Ce, and
142Ce. The thermal neutron-absorption cross section of the element is low. The element has a low toxicity rating.
Physikalische Eigenschaften
Cerium is a grayish/iron-colored, very reactive metallic element that is attacked by bothacids and alkalies. Pure cerium will ignite if scratched with a knife, but it can be combinedsafely with many other elements and materials. It is relatively soft and both malleable andductile.
Its melting point is 798°C, its boiling point is 3,443°C, and its density is 6.770g/cm
3.
Isotopes
There are 44 isotopes of cerium, four of which are considered stable. Ce-140accounts for most of the cerium (88.450%) found in the Earth’s crust, and Ce-138makes up just 0.251% of the element in the crust. There are two isotopes with half-liveslong enough to be considered stable: Ce-136 (0.185%), with a half-life of 0.7×10
+14years, and Ce-142 (11.14%), with a half-life of 5×10
+16 years. All the other isotopes areradioactive with half-lives ranging from 150 nanoseconds to 137.641 days. All are madeartificially.
Origin of Name
Named for the asteroid Ceres, which was discovered two years before
the element.
Occurrence
Cerium is the 25th most abundant element on Earth. It is also the most abundant rareearthmetal in the lanthanide series. Its major ores are monazite and bastnasite. Cerium isfound in the Earth’s crust in 46 ppm, which is about 0.0046% of the Earth’s crust. Ceriumis mixed with other elements in its ores, making it difficult to find, isolate, and identify. Itsexistence was unknown until about 1803.
Monazite sands contain most of the rare-earths. The sands of the beaches of Florida andparts of California contain monazite. Monazite is also found in South Africa, India, andBrazil. Bastnasite is found in southern California and New Mexico.
Charakteristisch
As a pure metal, cerium is unstable and will decompose rapidly in moist air. It also decomposesin hot water to form hydrogen. Its oxide compounds and halides are stable and have anumber of uses.
Cerium is separated from other rare-earth elements by an ion-exchange process in whichit reacts with fluoride. This compound is then reduced with calcium metal (3Ca +2CeF
3 →2Ce + 3CaF
3). Cerium can also be produced by the electrolysis of molten cerium salts. Themetal ion collects at the cathode, and the chlorine or fluorine gases of the salt compound atthe anode.
Verwenden
The compound cerium oxide (either Ce
2O
3 or CeO
2) is used to coat the inside of ovensbecause it was discovered that food cannot stick to oven walls that are coated with ceriumoxide. Cerium compounds are used as electrodes in high-intensity lamps and film projectorsused by the motion picture industry. Cerium is also used in the manufacturing andpolishing of high-refraction lenses for cameras and telescopes and in the manufacture ofincandescent lantern mantles. It additionally acts as a chemical reagent, a misch metal, anda chemical catalyst. Cerium halides are an important component of the textile and photographicindustries, as an additive to other metals, and in automobile catalytic converters.Cerium is also used as an alloy to make special steel for jet engines, solid-state instruments,and rocket propellants.
Definition
Symbol Ce. A silvery metallicelement belonging to the lanthanoids;a.n. 58; r.a.m. 140.12; r.d.6.77 (20°C); m.p. 799°C; b.p. 3426°C.It occurs in allanite, bastnasite,cerite, and monazite. Four isotopesoccur naturally: cerium–136, –138,–140, and –142; fifteen radioisotopeshave been identified. Cerium is usedin mischmetal, a rare-earth metalcontaining 25% cerium, for use inlighter flints. The oxide is used inthe glass industry. It was discoveredby Martin Klaproth (1743–1817) in1803.
Vorbereitung Methode
Cerium is obtained from its ores by chemical processing and separation. The process involves separation of cerium from other rare-earth metals present in the ore. The ore is crushed, ground, and treated with acid. The extract solution is buffered to pH 3-4 and the element is precipitated selectively as Ce
4+ salt. Cerium also may be separated from other metals by an ionexchange process.
Also, the metal may be obtained by high temperature reduction of cerium(III) chloride with calcium:
2CeCl
3 + 3Ca → 2Ce + 3CaCl
2
Allgemeine Beschreibung
Cerium is a gray colored, ductile solid. This form of cerium is slabs, ingots or rods. When heated to high temperatures CERIUM will burn readily and may be difficult to extinguish. CERIUM is used to make signaling devices.
Air & Water Reaktionen
Finely divided metal powder is pyrophoric [Bretherick 1979 p. 170-171]. CERIUM will react vigorously if exposed to water or moist air and will generate flammable and/or toxic fumes.
Reaktivit?t anzeigen
CERIUM is a strong reducing agent. Resembles aluminum in its chemical properties. [Lewis]. Reactivity is enhanced by a state of high physical subdivision, as in TURNINGS OR GRITTY POWDER. Attacked by dilute and concentrated mineral acids and alkalis with the generation of flammable gases. Readily oxidized by moist air at room temperature. Reacts with zinc with explosively violence. Gives very exothermic reactions with antimony or bismuth. Reacts violently with phosphorus at 400-500°C [Mellor 8, Supp. 3:347 1971].
Hazard
Most of the compounds of cerium are toxic if ingested or if the fumes are inhaled. Ceriumwill ignite when heated.
Health Hazard
Oxides from metallic fires are a severe health hazard. Inhalation or contact with substance or decomposition products may cause severe injury or death. Fire may produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may cause pollution.
Brandgefahr
May react violently or explosively on contact with water. Some are transported in flammable liquids. May be ignited by friction, heat, sparks or flames. Some of these materials will burn with intense heat. Dusts or fumes may form explosive mixtures in air. Containers may explode when heated. May re-ignite after fire is extinguished.
Industrielle Verwendung
A chemical element, cerium (Ce) is the mostabundant metallic element of the rare earthgroup in the periodic table. Cerium occursmixed with other rare earths in many minerals,particularly monazite and blastnasite, and isfound among the products of the fission of uranium,thorium, plutonium.
Ceric oxide, CeO2, is the oxide usuallyobtained when cerium salts of volatile acids areheated. CeO2 is an almost white powder that isinsoluble in most acids, although it can be dissolvedin H2SO4 or other acids when a reducingagent is present. The metal is an iron-gray colorand it oxidizes readily in air, forming a graycrust of oxide. Misch metal, an alloy of cerium,is used in the manufacture of lighter flints.Cerium has the interesting property that, at verylow temperatures or when subjected to highpressures, it exhibits a face-centered cubicform, which is diamagnetic and 18% denserthan the common form.
Sicherheitsprofil
Cerium resembles
aluminum in its pharmacological action as
well as in its chemical properties. The
insoluble salts such as the oxalates are stated
to be nontoxic even in large doses. It is used
to prevent vomiting in pregnancy. The
average dose is from 0.05 to 0.5 g.
The effect on the central nervous system
of the rare-earth metals following inhalation
may preclude welding operations with these
materials to any large extent. Cerium is
stated to produce polycythemia but is
useless in the treatment of anemia owing to
its toxic effects. The salts of cerium increase
the blood coagulation rate. See also RARE EARTHS. A strong reducing agent.
Moderate fire hazard; ignites spontaneously
in air at 150-180'. Moderate explosion
hazard in the form of dust when exposed to
flame. The metal or its alloys spark with
friction. Many alloys are pyrophoric in air.
See also IRON DUST. Explosive reaction
with zinc. Very exothermic reaction with
antimony or bismuth. Ignites when heated
in atmospheres of CO2 + N2, Cl2, or Br2.
Violent reaction when heated with
phosphorus (4OO℃), silicon (1400℃).
Environmental Fate
Cerium resembles aluminum in its biologic and chemical
properties. Cerium and cerium compounds have low to
moderate toxicity unless the associated anions are toxic.
Intratracheally administered nanoparticles tend to accumulate
in liver and cause damage there.
Cer Upstream-Materialien And Downstream Produkte
Upstream-Materialien
Downstream Produkte
