Europium, Eu, ordinal 63

General information about europium

Europium is a chemical element with the element symbol Eu and the atomic number 63. In the periodic table it is in the group of lanthanides and thus also belongs to the metals of the rare earths. Europium is next to americium the only named after a continent element. Americum, is an artificial one. radioactive transuran of actinides, which is irrelevant to our metal considerations.

Paul Emile Lecoq de Boisbaudran discovered 1890 in a samarium-gadolinium concentrate unknown spectral lines. The discovery of the element is awarded to Eugene Anatole Demarcay, who suspected 1896 in the just discovered samarium another element. 1901 succeeded him in the separation of europium.

Metallic europium was not produced until years later. Europium only occurs in compounds. It is contained in many minerals; it was detected in the spectrum of the sun and some stars. The minerals monazite and bastnasite are technically important. Recently, indications have been found that an isotope of europium is an alphastraler. The lower limit for the half-life is given as 1,7 trillion years.

History of Europium

The first reference to the element later called europium was found by William Crookes in 1885. When examining the fluorescence spectra of samarium-yttrium mixtures, he was able to measure signals of an unusual orange-colored spectral line that was stronger in mixtures of the elements than in the pure substances. He called this spectral line, which points to an unknown element, "anomalous line", the hypothetical element Sδ. Another discovery on the way to the unknown element was made in 1892 by Paul Émile Lecoq de Boisbaudran, when he discovered three previously unknown blue spectral lines in the spark spectrum of Samarium in addition to the abnormal Crookes line. In 1896, Eugène-Anatole Demarçay postulated the existence of a previously unknown element between samarium and gadolinium based on ultraviolet spectra, and in 1900 he realized that this element must be the same as that of Crookes and Boisbaudran. In 1901 Demarçay succeeded in isolating this by fractional crystallization of the samarium / europium magnesium nitrate double salts. He named the element Europium after the continent of Europe. In 1948, in analogy to europium, Glenn T. Seaborg, Ralph A. James and Leon O. Morgan named the actinoid, which is located directly below europium in the periodic table, also after a continent americium.

 

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

Extraction of europium

Starting from monazite or bastnaesite, the separation of the rare earths via ion exchange, solvent extraction or electrochemical deposition takes place. In a final process step, the high-purity europium oxide is reduced with metal lanthanum to the metal and sublimated.

Features

Europium is one of the most reactive rare earth metals. In air, the shiny silvery metal starts immediately. At temperatures above 150 ° C it ignites and burns with red flame to the sesquioxide Eu2O3. In water, it reacts with evolution of hydrogen to the hydroxide. With a density of 5,244 g / cm3 Europium is the lightest heavy metal, the next-ever lighter titanium (4,507 g / cm3) is already one of the light metals.

While 153Eu is stable, evidence was found in 2007 that 151Eu is an alpha emitter. The lower limit for the half-life is given as 1,7 trillion years. Europium and europium compounds are to be regarded as toxic. Metal dusts are flammable and explosive.

 

 

 

 

Occurrence of europium

Europium is a rare element on earth, its abundance in the continental crust is around 2 ppm.

Europium occurs as a minor component in various lanthanide minerals, minerals with europium as the main component are unknown. The element is contained in cerite earths such as monazite and bastnesite as well as in ytter earths such as xenotime, the proportion of europium is usually between 0,1 and 0,2%. The most important deposit for the extraction of europium was the Bastnasite ore in Mountain Pass, California until 1985, after which Chinese mines - especially the ore deposit in Bayan Obo - gained great importance.

In some igneous rocks, the concentration of europium is higher or lower than would be expected from the relative abundance ratio of rare earth metals determined using chondrites as a standard. This phenomenon is known as the europium anomaly and is based on the fact that Eu3 + can be reduced to Eu2 + under reducing conditions in magma. This has a larger ionic radius than trivalent europium and is therefore easily incorporated into certain minerals, for example instead of strontium or calcium in potassium feldspar and plagioclase, which therefore have a positive europium anomaly. These minerals crystallize from the magma melt and are thereby separated, while trivalent europium remains dissolved in the residual melt. In contrast, the Eu2 + ion is too large for installation in mafic rocks such as pyroxene and olivine instead of iron, magnesium and calcium and a negative europium anomaly occurs. In addition to the crystallization of plagioclase, a europium anomaly can also arise when rocks are melted. Since the distribution coefficient between crystal and melt is about 10 times greater than for the other rare earth elements, only a small amount of europium is released into the melt when a rock rich in plagioclase is partially melted, and a rock with a negative europium anomaly results when it solidifies. The europium anomaly is an indicator of the degree of fractionation of igneous rock.

A pronounced europium anomaly was found in lunar rocks, with the plagioclase-rich rocks of the lunar highlands showing a positive (increased europium content), the basalt rocks found in craters and Maria a negative europium anomaly. This allows conclusions to be drawn about the geological history of the moon. It is assumed that the highlands with their anorthosites differentiated from the lunar mantle around 4,6–4,4 billion years ago and that this therefore consists of europium-depleted olivine-pyroxene rocks. The younger basalts in the Maria, which consist of basaltic partial melts of this mantle, are therefore so poor in europium.

 

Extraction and preparation of europium

Due to the similarity to the accompanying metals and the low concentration in the ores, the separation from the other lanthanoids is difficult, but at the same time it is technically particularly important because of the use of the element. After digestion of the starting materials such as monazite or bastnäsite with sulfuric acid or sodium hydroxide solution, various ways of separation are possible. In addition to the ion exchange, a process is mainly used that is based on liquid-liquid extraction and the reduction of Eu3 + to Eu2 +. In the case of bastnäsite as the starting material, the cerium is first separated in the form of cerium (IV) oxide and the remaining rare earths are dissolved in hydrochloric acid. Then with the help of a mixture of DEHPA (di (2-ethylhexyl) phosphoric acid) and kerosene in liquid-liquid extraction, europium, gadolinium and samarium are separated from the other rare earth metals. These three elements are separated by reducing the europium to Eu2 + and precipitating it as poorly soluble europium (II) sulfate, while the other ions remain in solution.

Metallic europium can be obtained by reacting europium (III) oxide with lanthanum or mischmetal. If this reaction is carried out in a vacuum, europium is distilled off and can thus be separated from other metals and impurities.

In 2010 around 600 tons of europium were produced and 500 tons were consumed (each calculated as europium oxide). Due to the increasing demand for europium, however, it is to be feared that in the medium term demand will exceed supply and that there will be a shortage. We are therefore working on expanding europium production, in particular by opening additional mines such as the one in Mount Weld, Australia, and reopening the Mountain Pass mine. Due to the high demand for europium, the price of the element has also risen sharply. In 2002 it was still at 240 US dollars per kilogram, in 2011 it rose to 1830 dollars per kilogram (99% purity in each case).

 

Physical properties of europium

Like the other lanthanides, europium is a silvery, soft heavy metal. It has an unusually low density of 5,245 g / cm3, which is significantly lower than that of the neighboring lanthanides such as samarium or gadolinium and lower than that of lanthanum. The same applies to the relatively low melting point of 826 ° C and the boiling point of 1440 ° C (gadolinium: melting point 1312 ° C, boiling point 3000 ° C). These values ​​oppose the otherwise applicable lanthanide contraction and are caused by the electron configuration of europium. Due to the half-filled f-shell, only the two valence electrons are available for metallic bonds; therefore, there are lower binding forces and a significantly larger metal atom radius. The same can be observed for ytterbium. With this element, due to the completely filled f-shell, only two valence electrons are available for metallic bonds.

Europium crystallizes under normal conditions in a body-centered cubic lattice with the lattice parameter a = 455 pm. In addition to this structure, two other high-pressure modifications are known. As with ytterbium, the sequence of modifications with increasing pressure does not correspond to that of the other lanthanoids. Neither a europium modification in a double-hexagonal structure nor in a samarium structure is known. The first phase transition in the metal takes place at 12,5 GPa, above this pressure europium crystallizes in a hexagonal, densest structure with the lattice parameters a = 241 pm and c = 545 pm. Above 18 GPa, Eu-III was found to be another structure similar to the hexagonal closest packing of spheres.

At high pressures of at least 34 GPa, the electron configuration of the europium in the metal changes from bivalent to trivalent. This also enables a superconductivity of the element, which occurs at a pressure of about 80 GPa and a temperature of about 1,8K.

Europium ions built into suitable host lattices show pronounced fluorescence. The emitted wavelength depends on the oxidation level. Eu3 + fluoresces largely independently of the host lattice between 613 and 618 nm, which corresponds to an intense red color. The maximum of the emission of Eu2 +, on the other hand, is more dependent on the host lattice and is, for example, 447 nm in the blue spectral range for barium magnesium aluminate, and in the green spectral range for strontium aluminate (SrAl2O4: Eu2 +) at 520 nm.

 

Chemical properties of europium

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

Europium also reacts with the halogens fluorine, chlorine, bromine and iodine to form trihalides. In the reaction with hydrogen, non-stoichiometric hydride phases are formed, with the hydrogen entering the gaps in the spherical packing of the metal.

Europium dissolves slowly in water and rapidly in acids with the formation of hydrogen and the colorless Eu3 + ion. The likewise colorless Eu2 + ion can be obtained by electrolytic reduction on cathodes in an aqueous solution. It is the only divalent lanthanide ion that is stable in aqueous solution. Europium dissolves in ammonia, forming a blue solution, as with alkali metals, in which there are solvated electrons.

In addition to Sm3 +, Tb3 + and Dy3 +, the Eu3 + cation belongs to the lanthanide cations which, in a suitable complex, can emit light in the visible range when certain wavelengths are absorbed. The trivalent europium cation is colorless in an aqueous solution, but if organic ligands are coordinated with an extensive π-electron system, the antenna effect ensures that the luminescent properties of the central particle increase sharply. The π-electrons of the ligand conduct the absorbed energy of the incident light (approx. 355 nm) to the 5d-electrons of the Eu3 +, whereby these get into the 4f-orbital and when falling back light in the visible range (at approx. 610 nm) emit.

 

Isotopes of Europium

A total of 38 isotopes and a further 13 core isomers of europium between 130Eu and 167Eu are known. Of these, one, 153Eu, is stable, another, 151Eu, has long been considered stable; In 2007, however, indications were found that it decays as an alpha emitter with a half-life of at least 1,7 trillion years. These two isotopes occur naturally, with 153Eu being the more common with a share of 52,2% of the natural isotopic composition, the share of 151Eu is accordingly 47,8%.

Several europium isotopes such as 152Eu, 154Eu and 155Eu are formed during nuclear fission of uranium and plutonium. With a share of about 155% of the total amount of fission products, 0,03Eu is the most common europium isotope among the fission products. It could be detected in the Rongelap Atoll three years after the contamination by the Castle Bravo nuclear weapons test.

 

Use of europium

Europium is mainly used as a dopant for the production of phosphors, which are used, for example, in cathode ray tube screens, which were previously mainly used for computer screens and televisions, as well as for aircraft instruments, and in compact fluorescent lamps. Phosphors with both bivalent and trivalent europium are used for different colors. For red phosphors, yttrium oxide doped with europium (Y2O3: Eu3 +) is mainly used; yttrium oxysulfide or, as the first important red phosphor, yttrium vanadate: Eu3 + were also used in the past. Eu2 + is mostly used as a blue phosphor in compounds such as strontium chlorophosphate (Sr5 (PO4) 3Cl: Eu2 +, strontium chloroapatite SCAP) and barium magnesium aluminate (BaMgAl11O17: Eu2 +, BAM).

Plasma picture screens require phosphors that convert the VUV radiation emitted by the noble gas plasma into visible light. For this purpose, europium-doped phosphors are used for both the blue and red spectrum - BAM for blue light, BO3: Eu3 + for red (Y, Gd).

In high-pressure mercury lamps, such as those used in street lighting, europium-doped yttrium vanadate is applied to the glass so that the light appears white and more natural.

Due to its neutron absorption, europium can be used in control rods for nuclear reactors. Control rods containing europium were tested in various Soviet test reactors such as BOR-60 and BN-600.

As EuropiumHexaBorid, it is also offered as a coating for the production of oxide cathodes for glow emission.

Europium fluorescence is used to prevent counterfeiting of euro banknotes.

This property can also be used in fluorescence spectroscopy. For this purpose, the europium is bound in a suitable complex, for example, which reacts preferentially at the desired location, for example with a certain protein, and accumulates there.

Biological significance and toxicity of europium

Europium occurs only in minimal amounts in the body and has no biological significance. The element cannot be absorbed by plant roots either.

Soluble europium compounds are slightly toxic; an LD50 value of 550 mg / kg for intraperitoneal and 5000 mg / kg for oral administration to mice was determined for europium (III) chloride. No chronic toxicity could be determined, which may be related to the low uptake of europium in the intestine and the rapid conversion of soluble europium chloride to insoluble europium oxide under basic conditions. Insoluble europium compounds are largely non-toxic, as was determined in a study with europium (III) hydroxide nanoparticles in mice.

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

 

Connections from europium

Compounds in the oxidation states +2 and +3 are known, whereby, as with all lanthanides, although the trivalent state is the more stable, the divalent state is also unusually stable and therefore a large number of Eu (II) compounds exist. The ionic radii differ depending on the oxidation state, with Eu2 + ions being larger than Eu3 + ions. With the coordination number six they are 131 pm for Eu2 + and 108,7 pm for Eu3 +. The effective ion radius (which uses an O140 ion which is 14 pm larger by 2 pm as a reference) is accordingly 117 pm or 94,7 pm for the coordination number six. The ionic radii are larger in higher coordination numbers; for Eu2 + in the coordination number eight it is 139 pm.

 

Oxygen compounds of europium

Europium (III) oxide, Eu2O3, is the technically most important europium compound and serves as a starting material for the production of other europium compounds and as a dopant for fluorescent dyes such as Y2O3: Eu3 +, which has a particularly intense red fluorescence with a europium (III) oxide content of around 10% shows. Like the other lanthanoid oxides, it crystallizes in the cubic lanthanoid C structure.

Europium (II) oxide, EuO, is a purple-black ferromagnetic solid with a Curie temperature of 70 K that crystallizes in a sodium chloride structure. It can be obtained by reducing europium (III) oxide with europium and is the only divalent oxide of the lanthanoids that is stable under normal conditions. In addition to these two oxides, the mixed-valence oxide europium (II, III) oxide, Eu3O4, is also known.

 

Other europium compounds

Eu chalcogenides (i.e. sulfides, selenides and tellurides) and their disordered alloys have similar properties to EuO. Eu1-xSrxS is e.g. B. for x = 0 a ferromagnet, which for x≅0.5x becomes an insulating spin glass, which is particularly suitable for computer simulations because of its non-metallic behavior.

Europium reacts with the halogens fluorine, chlorine, bromine and iodine to form the trihalides. These decompose when heated to the dihalides and elemental halogens.

Europium (III) chromate can also be created in an equimolar solution of europium (III) acetate and chromium (VI) oxide.

Europium forms organometallic compounds. In contrast to the other lanthanides, however, no cyclopentadienyl compound of trivalent europium can be synthesized. A compound is known that contains three molecules of cyclopentadienyl and one molecule of tetrahydrofuran, but this is strongly bound to the europium and cannot be removed by heating or in a vacuum, since the compound decomposes beforehand. In contrast, europium dicyclopentadienyl (Cp) 2Eu (II) and other known derivatives are stable. Alkynyl europium compounds of the divalent europium are also known.

 

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Usage

1. Europium (III) -doped yttrium oxide sulfide Y2O2S: Eu3 + forms the red phosphor (luminophore) in color picture tubes.
2. Europium (II) doped barium fluorobromide BaFBr: Eu2 + is used for photostimulated luminescence (PSL)
3. Eu3 + doped solids usually show a red luminescence, Eu2 + can emit depending on the host lattice in the entire optical spectral range (UV to red).
4. Doping element in phosphors for light sources such as high-pressure mercury lamps and energy-saving lamps.
5. Doping material in scintillation crystals (as activator).
6. Organic compounds as shift reagent in NMR spectroscopy.
7. Europium-tetracycline complexes in fluorescence spectroscopy for the detection of hydrogen peroxide
8. TRFIA = time-resolved fluoroimmunoassay. Eu3 + ions fluoresce only briefly in water. Therefore, one uses chelating agents, which build around the Eu3 + ions around a hydrophobic environment. This leads to a longer duration of fluorescence. This makes it possible to distinguish it from all other, shorter-lived fluorescences that can occur in organic mixtures.

 

Europium prices

Prices for Europium -> prices for rare earths

 

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