Praseodym Chemische Eigenschaften,Einsatz,Produktion Methoden
R-S?tze Betriebsanweisung:
R17:Selbstentzündlich an der Luft. Spontaneously flammable in air.
R11:Leichtentzündlich.
S-S?tze Betriebsanweisung:
S17:Von brennbaren Stoffen fernhalten.
S7/9:Beh?lter dicht geschlossen an einem gut gelüfteten Ort aufbewahren.
S33:Ma?nahmen gegen elektrostatische Aufladungen treffen.
S16:Von Zündquellen fernhalten - Nicht rauchen.
Chemische Eigenschaften
grey powder
Physikalische Eigenschaften
Praseodymium is a silvery-white, soft metal that is easily formed into various shapes. Whenthe pure metal is exposed to the air, a green oxide coating forms on its surface. To preventoxidation, praseodymium is usually kept in oil in a covered container.
Its melting point is 931°C, its boiling point is 3,520°C, and its density is 6.77g/cm
3.
Isotopes
There are 45 isotopes of praseodymium. All are artificially produced and radioactivewith half-lives ranging from several hundred nanoseconds to 23.6 days. Only oneis stable (Pa-141), and it makes up 100% of the praseodymium found in the Earth’scrust.
Origin of Name
The name is derived from two Greek words, prasios and didymos,
which together mean “green twins.”
Occurrence
Praseodymium is the 41st most abundant element on Earth and is found in the ores of monazite,cerite, bastnasite, and allanite along with other rare-earths. Praseodymium is also the stableisotope resulting from the process of fission of some other heavy elements, such as uranium.
Praseodymium is mainly found in monazite sands and bastnasite ores. The monazite sandscontain all of the rare-earths and are found in river sand in India and Brazil as well as inFlorida beach sand. A large deposit of bastnasite exists in California.
Praseodymium is separated from its ore and other rare-earths by a process called ionexchange, which exchanges one type of ion for another.
History
In 1879, Lecoq de Boisbaudran isolated
a new earth, samaria, from didymia obtained from the
mineral samarskite. Six years later, in 1885, von Welsbach separated
didymia into two others, praseodymia and neodymia,
which gave salts of different colors. As with other rare earths,
compounds of these elements in solution have distinctive
sharp spectral absorption bands or lines, some of which are
only a few Angstroms wide. Praseodymium occurs along with
other rare-earth elements in a variety of minerals. Monazite
and bastnasite are the two principal commercial sources of
the rare-earth metals. Ion-exchange and solvent extraction
techniques have led to much easier isolation of the rare earths
and the cost has dropped greatly. Thirty-seven isotopes and
isomers are now recognized. Praseodymium can be prepared
by several methods, such as by calcium reduction of the anhydrous
chloride or fluoride. Misch metal, used in making
cigarette lighters, contains about 5% praseodymium metal.
Praseodymium is soft, silvery, malleable, and ductile. It was
prepared in relatively pure form in 1931. It is somewhat more
resistant to corrosion in air than europium, lanthanum, cerium,
or neodymium, but it does develop a green oxide coating
that splits off when exposed to air. As with other rare-earth
metals it should be kept under a light mineral oil or sealed
in plastic. The rare-earth oxides, including Pr2O3, are among
the most refractory substances known. Along with other rare
earths, it is widely used as a core material for carbon arcs used
by the motion picture industry for studio lighting and projection.
Salts of praseodymium are used to color glasses and
enamels; when mixed with certain other materials, praseodymium
produces an intense and unusually clean yellow color in glass. Didymium glass, of which praseodymium is a component,
is a colorant for welder’s goggles. The metal (99.9% pure)
is priced at about $4/g.
Charakteristisch
As a metal, Pr is hygroscopic (adsorbs water) and tarnishes in the atmosphere. It will reactwith water to liberate hydrogen. It is soluble in acids and forms greenish salts, along with someother rare-earths. It is used to fabricate the electrodes for high-intensity lights.
Verwenden
Praseodymium salts, ingredient of mischmetal,
core material for carbon arcs, colorant in glazes and
glasses, catalyst, phosphors, lasers.
synthetische
Praesodymium may be recovered from its minerals monazite and bastanasite. The didymia extract of rare earth minerals is a mixture of praesodymia and neodymia, primarily oxides of praesodymium and neodymium. Several methods are known for isolation of rare earths. These are applicable to all rare earths including praesodymium. They include solvent extractions,ionexchange, and fractional crystallization. While the first two methods form easy and rapid separation of rare earth metals, fractional crystallization is more tedious. Extractions and separations of rare earths have been discussed in detail earlier (see Neodymium and Cerium).
Praesodymium metal can be obtained from its anhydrous halides by reduction with calcium. The metal also may be prepared by electrolysis of fused praesodymium chloride at elevated temperatures (about 1,000°C).Alternatively, an eutectic mixture of praesodymium chloride, potassium chloride, and sodium chloride may be electrolyzed. In such electrolysis graphite is the anode and tungsten the cathode.
Definition
A soft ductile malleable silvery element of
the lanthanoid series of metals. It occurs in
association with other lanthanoids.
Praseodymium is used in several alloys, as
a catalyst, and in enamel and yellow glass
for eye protection.
Symbol: Pr; m.p. 931°C; b.p. 3512°C;
r.d. 6.773 (20°C); p.n. 59; r.a.m. 140.91.
Hazard
If praseodymium gets wet or is submerged in water, the hydrogen released may explode. Itmust be kept dry and protected from the atmosphere.
Praseodym Upstream-Materialien And Downstream Produkte
Upstream-Materialien
Downstream Produkte
