Europium

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47.8 %

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52.2 %

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Risk

Europium is a chemical element with the element symbol Eu and atomic number 63 in the periodic table it is in the group of lanthanides and also making it one of the metals of the rare earths. Only europium and americium are after a continent named items.

As with the other lanthanides europium is a silvery heavy metal. The properties of europium not follow the lanthanide contraction. Due to its electronic configuration, the element has a significantly lower density and a lower melting point and boiling point than the adjacent elements. It is the most chemically reactive of the rare earth. After the first references to the element by William Crookes and Paul Émile Lecoq de Boisbaudran 1896 Eugène- Anatole Demarcay could first prove the element spectroscopy and then insulate.

Europium has a high technical importance in phosphors, as used for example in CRT monitors, which were formerly used for computer monitors and televisions, in fluorescent lamps and plasma screens. Both the red and the blue phosphor in these screens and bulbs are substances that are doped with europium and thus exhibit fluorescence in the corresponding spectral region.

• 8.1 oxygen compounds
• 8.2 Further europium

History

The first evidence for the later mentioned element europium found 1885 William Crookes. In the analysis of the fluorescence spectra of samarium yttrium mixtures he was able to measure signals of a unusual orange spectral line was stronger in mixtures of the elements than the pure materials. He called this may suggest an unknown element spectral line " abnormal line," the hypothetical element S.delta. Another discovery on the way to the unknown element made ​​1892 Paul Émile Lecoq de Boisbaudran when he next to the abnormal line Crookes also discovered three previously unknown blue spectral lines in the spark spectrum of samarium. 1896 postulated Eugène- Anatole Demarcay based on ultraviolet spectra, the existence of a previously unknown element between samarium and gadolinium, which he realized in 1900 that this element must be equal to the presumed Crookes and Boisbaudran. 1901 Demarcay succeeded in isolating this by fractional crystallization of the samarium / europium magnesium nitrate double salts. He named the element after the continent of Europe europium. In analogy to europium named Glenn T. Seaborg, Ralph A. James and Leon O. Morgan 1948, the year-on system exploiting dividend directly under the europium actinide also to a continent americium.

The first important technical application of the element was the production of doped europium yttrium vanadate. This discovered in 1964 by Albert K. Levine and Frank C. Palilla red phosphor soon played an important role in the development of color television. For this application, then the first mine was greatly expanded for the extraction of rare earths, which has been operated since 1954 in the Mountain Pass, California.

Occurrence

Europium is a rare element on Earth, the incidence in the continental crust is about 2 ppm.

Europium is present as a minor component in various lanthanide minerals, minerals having europium as a main component are not known. The element is included in both Ceriterden as monazite and bastnaesite and in ytterbium earths such as xenotime, the proportion of europium is generally between 0.1 and 0.2 %. The most important for the extraction of europium occurrence was until 1985 the Bastnäsiterz in Mountain Pass, California, after winning Chinese mines - especially the Bayan Obo ore deposit in - very important.

In some igneous rocks, the concentration of europium is higher or lower than would be expected from the particular with chondrites as a standard relative frequency ratio of the rare earth metals. This phenomenon is referred to as Europiumanomalie and based on the fact that under reducing conditions in magma Eu3 to Eu2 can be reduced. This has a larger ionic radius than trivalent europium and is therefore easily incorporated into certain minerals, such as in place of strontium or calcium in K-feldspar and plagioclase, which thus have a positive Europiumanomalie. These minerals crystallized from the melt magma and thereby separated while trivalent europium remains dissolved in the residual melt. For installation in mafic rocks such as pyroxene and olivine instead of iron, magnesium and calcium, the Eu2 ion, however, is too large and there is a negative Europiumanomalie. Except by crystallization of plagioclase may result in a Europiumanomalie also during melting of rocks. Since the partition coefficient between crystal and melt is about 10 -fold greater than for the other rare earth elements during partial melting of a plagioclase - rich rock little europium is released into the melt and resolidification results when a rock with negative Europiumanomalie. The Europiumanomalie is an indicator of the degree of fractionation of an igneous rock.

A pronounced Europiumanomalie was found in lunar rocks, the plagioclase - rich rocks of the lunar highlands, a positive (increased Europiumgehalte ), the basaltic rocks found in craters and Maria have a negative Europiumanomalie. This allows us to draw conclusions about the geological history of the Moon. It is assumed that the Highlanders with their anorthosites differentiated before about 4.6 to 4.4 billion years ago from the moon coat and this thus consists of europium -depleted olivine - pyroxene rocks. The younger basalts in the Maria, which consist of basaltic partial melting of this mantle, which is why are so poor in europium.

Production and representation

Due to the similarity to the accompanying metals and the low concentration in the ore, the separation of the other lanthanides is difficult to simultaneously but technically particularly important because of the use of the element. After digestion of the raw materials such as monazite or Bastnäsit with sulfuric acid or sodium hydroxide to separate different ways are possible. In addition to the ion exchange, especially a method is used which is based on liquid-liquid extraction, and the reduction of Eu3 to Eu 2 . Here, the cerium is in bastnasite as a starting material is initially separated in the form of cerium ( IV) oxide, and the remaining rare earth elements dissolved in hydrochloric acid. Then be separated from the other rare earth metals with a mixture of DEHPA ( di (2- ethylhexyl) phosphoric acid) and kerosene in liquid -liquid extraction, europium, gadolinium, and samarium. The separation of these three elements of the reduction of the europium to Eu2 and precipitated as a sparingly soluble europium ( II) -sulfate, whereas the other ions in solution.

Europium metal may be obtained by reaction of europium (III ) oxide, lanthanum or mischmetal. This reaction is carried out in vacuo, distilled from europium and can be separated from other metals and impurities:

2010, about 600 tons of europium were produced and consumed 500 tons ( in each case as europium oxide ). Due to the increasing demand for europium is to be feared that in the medium term, demand exceeds supply and there will be a shortage. Therefore, it is working on an expansion of Europiumproduktion, in particular by opening more mines as the Mount Weld in Australia and a reopening of the Mountain Pass mine. Due to the high demand for europium, the price of the item has risen sharply. He in 2002 was still at 240 U.S. dollars per kilogram, he rose in 2011 to up to $ 1,830 per kilogram ( both 99 % purity).

Properties

Physical Properties

Europium is like the other lanthanides a silvery soft heavy metal. It has to 5.245 g/cm3, an unusually low density, which is significantly lower than that of the adjacent lanthanides such as samarium or gadolinium and less than that of lanthanum. The same applies also for the relatively low melting point of 826 ° C and the boiling point of 1527 ° C ( gadolinium: melting point 1312 ° C, boiling point 3250 ° C). These values ​​are contrary to the otherwise applicable lanthanide and are caused by the electron configuration [ Xe] 4f7 6s2 of europium. Through the half-filled f shell only the two valence electrons ( 6s2 ) are available for metallic bonds available; therefore there is less binding ability and to a much larger metal atom radius. A comparable result can also be observed in ytterbium. In this element, stand by a completely filled f shell also only two valence electrons for metallic bonds available.

Europium crystallizes under normal conditions in a body-centered cubic lattice with the lattice parameters a = 455 pm. In addition to this structure, two other modifications known high pressure. The order of modification with increasing pressure when the ytterbium as not corresponding to that of the other lanthanides. So neither a Europiummodifikation in double - hexagonal structure is still known in samarium structure. The first phase transition in the metal takes place at 12.5 GPa, above this pressure crystallized europium in a hexagonal closest- structure with the lattice parameters a = 241 pm and c = 545 pm. Above 18 GPa was similar structure found with Eu III further, the hexagonal closest packing of spheres.

At high pressures of at least 34 GPa, the electronic configuration of europium in the metal changes from two - to trivalent. This also allows a superconductivity of the element, which occurs at a pressure of about 80 GPa and a temperature of about 1.8K.

Europium ions incorporated into suitable host lattice, exhibit a pronounced fluorescence. The emitted wavelength is dependent on the oxidation state. Eu3 fluorescence largely independent of the host lattice 613-618 nm which corresponds to an intense red color. The maximum of the emission of Eu2 is, however, strongly dependent on the host lattice and is, for example barium with 447 nm in the blue, with strontium ( SrAl2O4: Eu2 ) with 520 nm in the green spectral range.

Chemical Properties

Europium is a typical base metal and reacts with most non-metals. It is the most reactive of the lanthanides and reacts rapidly with oxygen. It is heated to about 180 ° C, spontaneously ignites in the air and burns to europium ( III) oxide.

With the halogens fluorine, chlorine, bromine and iodine reacts with the europium trihalides. In the reaction with hydrogen to form non-stoichiometric Hydridphasen, the hydrogen enters the gaps of the spherical packing of the metal.

Europium dissolves in water slowly in acids rapidly to form hydrogen and the colorless Eu3 - Iones. This also colorless Eu2 ion can be obtained by electrolytic reduction at the cathode in aqueous solution. It is the only divalent lanthanide ion, which is stable in aqueous solution. Europium dissolves in ammonia, as the case of alkali metals, forming a blue solution, present in the solvated electrons.

Isotopes

There are a total of 38 known isotopes and another 13 Kernisomere of europium between 130Eu and 167Eu. Of these, one, 153Eu, stable, another, 151Eu, has long been considered stable; Notes were in 2007 but found out that it decays with a half -life of at least 1.7 trillion years as alpha emitters. These two isotopes are found in nature, where 153Eu with a share of 52.2 % to the natural isotopic composition is the more frequent, the proportion of 151Eu is therefore 47.8 %.

Several Europiumisotope as 152Eu, 154Eu and 155Eu occur during nuclear fission of uranium and plutonium. This 155Eu with a share of about 0.03 % of the total amount of fission products the most common Europiumisotop among the fission products. It was demonstrated three years after the contamination by the Castle Bravo nuclear test, among others, in the Rongelap Atoll.

Use

Europium is used primarily as a dopant for the production of phosphors that are needed such as in CRT screens, which were earlier used primarily for computer monitors and televisions as well as for aircraft instruments, and are used in compact fluorescent lamps. Phosphors are used with both two-and trivalent europium for different colors. For red phosphors especially europium -doped yttrium oxide ( Y2O3: Eu3 ) were also used to yttrium or as the first major red phosphor yttrium: Eu3 used. And barium ( BaMgAl11O17: Eu2 , BAM): Eu2 ( Eu2 , Strontiumchloroapatit SCAP Sr5 (PO4) 3Cl ) is usually as a blue phosphor in compounds such as Strontiumchlorophosphat used. Plasma displays require phosphors, which convert the light emitted from the rare gas plasma VUV radiation into visible light. For this purpose, europium-doped phosphors are used for both the blue and red spectrum - blue light BAM, for red (Y, Gd) BO3: Eu3 .

In high-pressure mercury lamps, such as those used in street lighting, europiumdotiertes yttrium is deposited on the glass so that the light appears white and natural.

In euro banknotes europium fluorescence is used against counterfeiting. It can also be utilized in fluorescence spectroscopy. To europium is bound, for example, in a suitable complex which reacts preferentially at the desired location, such as with a particular protein and accumulates there.

Europium can be used due to its neutron absorption in control rods for nuclear reactors. Europium control rods were tested, among others, in various Soviet experimental reactors such as BOR -60 and BN -600.

Biological significance and toxicity

Europium is found only in minimal amounts in the body and has no biological significance. Also by plant roots, the element can not be recorded.

Soluble europium compounds are mildly toxic; as a LD50 value of 550 mg / kg for intraperitoneal and 5000 mg / kg for oral administration in mice was measured for europium ( III) chloride. There was no chronic toxicity are detected, possibly linked to the low uptake of europium in the intestine and the rapid conversion of soluble to insoluble europium europium oxide under basic conditions. Insoluble europium compounds are considered to be largely non-toxic, as determined in a study of europium ( III ) hydroxide nanoparticles in mice.

In europium ( III ) hydroxide nanoparticles ( but not in amorphous europium ( III ) hydroxide ) is a pro- angiogenic effect was found, they promote in vitro cell proliferation of endothelial cells in vivo in chicken eggs increased formation was observed of small blood vessels. One possible mechanism for this observation is the formation of reactive oxygen species, and the activation of MAP kinases through these nanoparticles.

Compounds

These are compounds in the oxidation states 2 and 3 known, and exist as with all lanthanides while the trivalent stage, the more stable, but which is also divalent unusually stable, and therefore a variety of Eu ( II) compounds. The ionic radii differ depending on the oxidation state, with Eu2 ions greater than Eu3 ions. With the coordination number six, they amount to 131 pm for Eu2 and 108.7 pm for Eu3 . The effective ionic radius (which as a reference with a 140 pm to 14 pm larger O2 - ion used ) thus amounts to 117 pm and 94.7 pm for coordination number six. In higher coordination numbers, the ionic radii are larger, so it is eight 139 pm for Eu2 in the coordination number.

Oxygen compounds

Europium (III ) oxide, Eu2O3, is the technically most important europium compound and serves as a starting material for producing other europium and as a dopant for fluorescent dyes, such as Y2O3: Eu3 , which is a very intense red fluorescence with a europium ( III) oxide content of about 10% shows. It crystallizes as the other lanthanide oxides in the cubic lanthanide - C structure.

Europium (II) -oxide, EuO, is a purple - black solid with a ferromagnetic Curie temperature of 70 K, which is crystallized in a sodium chloride structure. It can be obtained by reduction of europium ( III ) oxide and europium oxide is the only divalent lanthanides, which is stable under normal conditions. Besides these two oxides is also the mixed-valent europium oxide (II, III ) oxide, Eu3O4, known.

More europium

Similar properties as EuO also have the Eu - chalcogenides (ie sulfides, selenides and tellurides - ) and their disordered alloys. EU1 xSrxS for example, for x = 0, a ferromagnet, which is for spinning into an insulating glass, which, inter alia, is particularly suitable because of its non-metallic behavior for computer simulations.

The halogens fluorine, chlorine, bromine and iodine, reacts to europium trihalides. These decompose on heating to give the dihalides and elemental halogens.

Europium forming metal-organic compounds. Unlike the other lanthanides no cyclopentadienyl compound of trivalent europium, however, can be synthesized. Although it is known a connection, which additionally contains one molecule of tetrahydrofuran molecules in addition to three cyclopentadienyl, this is, however, strongly bound to the europium and can not be removed by heating or under vacuum, since the compound decomposes before. However, the Europiumdicyclopentadienyl (Cp) 2eu (II) and other known derivatives are stable. From bivalent europium and alkynyl europium compounds are known.

An overview of europium compounds offers the category: europium.