europium

samarium ← europium → gadolinium

-↑Eu↓

Am

Appearance

silvery white, but rarely seen without oxide

discoloration

General properties

Name, symbol,

number

europium, Eu, 63

Pronunciation /jʊˈroʊpiəm/

yoo-ROH-pee-əm

Element category lanthanide

Group, period,

block

n/a, 6, f

Standard atomic

weight

151.964

Electron

configuration[Xe] 4f7 6s2

Electrons per shell 2, 8, 18, 25, 8, 2

(Image)

Physical properties

Phase solid

Density (near r.t.) 5.264 g·cm−3

EuropiumFrom Wikipedia, the free encyclopedia

Europium ( /jʊˈroʊpiəm/ ew-ROH-pee-əm) is achemical element with the symbol Eu andatomic number 63. It is named after thecontinent of Europe. It is a moderately hardsilvery metal which readily oxidizes in air andwater. Being a typical member of thelanthanide series, europium usually assumesthe oxidation state +3, but the oxidation state+2 is also common: all europium compoundswith oxidation state +2 are slightly reducing.Europium has no significant biological role andis relatively non-toxic compared to other heavymetals. Most applications of europium exploitthe phosphorescence of europium compounds.

Contents

1 Characteristics1.1 Physical properties1.2 Chemical properties

1.2.1 Eu(II) vs.Eu(III)

1.3 Isotopes1.3.1 Europium as anuclear fissionproduct

1.4 Occurrence

2 Production3 Compounds

3.1 Halides3.2 Chalcogenides andpnictides

4 History5 Applications6 Precautions7 See also8 References9 External links

Characteristics

Periodic table

63Eu

Europium - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Europium

1 of 13 Saturday 26 November 2011 07:26 PM

Liquid density at

m.p.5.13 g·cm−3

Melting point 1099 K, 826 °C,

1519 °F

Boiling point 1802 K, 1529 °C,

2784 °F

Heat of fusion 9.21 kJ·mol−1

Heat of

vaporization176 kJ·mol−1

Molar heat capacity 27.66 J·mol−1·K−1

Vapor pressure

P (Pa) 1 10 100 1 k 10 k 100 k

at T (K) 863 957 1072 1234 1452 1796

Atomic properties

Oxidation states 3, 2 (mildly basic

oxide)

Electronegativity ? 1.2 (Pauling scale)

Ionization energies 1st: 547.1 kJ·mol−1

2nd: 1085 kJ·mol−1

3rd: 2404 kJ·mol−1

Atomic radius 180 pm

Covalent radius 198±6 pm

Miscellanea

Crystal structure body-centered cubic

Magnetic ordering paramagnetic[1]

Electrical resistivity (r.t.) (poly) 0.900

µΩ·m

Thermal

conductivityest. 13.9 W·m−1·K−1

Thermal expansion (r.t.) (poly)

35.0 µm/(m·K)

Young's modulus 18.2 GPa

Shear modulus 7.9 GPa

Bulk modulus 8.3 GPa

Poisson ratio 0.152

Vickers hardness 167 MPa

About 300 g of dendriticsublimated 99.998% pureeuropium handled in a glovebox

Oxidized europium, coatedwith yellow europium(II)carbonate

Physical properties

Europium is aductile metalwith a hardnesssimilar to that oflead. Itcrystallizes in abody-centeredcubic lattice.[2]

Some propertiesof europium arestronglyinfluenced by itshalf-filledelectron shell.Europium hasthe secondlowest meltingpoint and thelowest density ofalllanthanides.[2]

Europiumbecomes asuperconductorwhen it is cooledbelow 1.8 K andcompressed to

above 80 GPa. This is because europium isdivalent in the metallic state,[3] and isconverted into the trivalent state by the appliedpressure. In the divalent state, the strong localmagnetic moment (J = 7/2) suppresses thesuperconductivity, which is induced byeliminating this local moment (J = 0 in Eu3+).[4]

Chemical properties

Europium is the most reactive rare earthelement. It rapidly oxidizes in air, so that bulkoxidation of a centimeter-sized sample occurswithin several days.[5] Its reactivity with wateris comparable to that of calcium, and thereaction is

2 Eu + 6 H2O → 2 Eu(OH)3 + 3 H2



CAS registry

number

7440-53-1

Most stable isotopes

Main article: Isotopes of europium

iso NA half-life DM DE(MeV)

DP

150Eu syn 36.9 y ε 2.261 150Sm

151Eu 47.8% 5×1018

y

α 147Pm

152Eu syn 13.516 y ε 1.874 152Sm

β− 1.819 152Gd

153Eu 52.2% 153Eu is stable with 90

neutrons

Because of the high reactivity, samples of solideuropium rarely have the shiny appearance ofthe fresh metal, even when coated with aprotective layer of mineral oil. Europiumignites in air at 150 to 180 °C to formeuropium(III) oxide:

4 Eu + 3 O2 → 2 Eu2O3

Europium dissolves readily in dilute sulfuricacid to form pale pink solutions of the hydratedEu(III), which exist as a nonahydrate:[6]

2 Eu + 3 H2SO4 + 18 H2O → 2 [Eu(OH2)9]3+

+ 3 SO2−4 + 3 H2

Eu(II) vs. Eu(III)

Although usually trivalent, europium readilyforms divalent compounds. This behavior isunusual to most lanthanides, which almost exclusively form compounds with anoxidation state of +3. The +2 state has an electron configuration 4f7 because thehalf-filled f-shell gives more stability. In terms of size and coordination number,europium(II) and barium(II) are similar. For example, the sulfates of both barium andeuropium(II) are also highly insoluble in water.[7] Divalent europium is a mild reducingagent, oxidizing in air to form Eu(III) compounds. In anaerobic, and particularlygeothermal conditions, the divalent form is sufficiently stable that it tends to beincorporated into minerals of calcium and the other alkaline earths. This ion-exchangeprocess is the basis of the "negative europium anomaly", the low europium content inmany lanthanide minerals such as monazite, relative to the chondritic abundance.Bastnäsite tends to show less of a negative europium anomaly than does monazite, andhence is the major source of europium today. The development of easy methods toseparate europium from the other trivalent lanthanides made europium accessible evenwhen present in low concentration, as it usually is.

Isotopes

Main article: Isotopes of europium

Naturally occurring europium is composed of 2 isotopes, 151Eu and 153Eu, with 153Eubeing the most abundant (52.2% natural abundance). While 153Eu is stable, 151Eu was

recently found to be unstable to alpha decay with half-life of 5+11−3 ×1018 years,[8] giving

about 1 alpha decay per two minutes in every kilogram of natural europium. This valueis in reasonable agreement with theoretical predictions. Besides the naturalradioisotope 151Eu, 35 artificial radioisotopes have been characterized, the most stablebeing 150Eu with a half-life of 36.9 years, 152Eu with a half-life of 13.516 years, and154Eu with a half-life of 8.593 years. All the remaining radioactive isotopes have



Isotope 151Eu 152Eu 153Eu 154Eu 155Eu

Yield ~10 low 1580 >2.5 330

Barns 5900 12800 312 1340 3950

Thermal neutron capture crosssections

Prop:Unit:

t½

aYield

%Q *keV

βγ*

155Eu 4.76 .0803 252 βγ85Kr 10.76 .2180 687 βγ

113mCd 14.1 .0008 316 β90Sr 28.9 4.505 2826 β

137Cs 30.23 6.337 1176 βγ121mSn 43.9 .00005 390 βγ151Sm 90 .5314 77 β

Medium-livedfission products

half-lives shorter than 4.7612 years, and the majority of these have half-lives shorterthan 12.2 seconds. This element also has 8 meta states, with the most stable being150mEu (T½=12.8 hours), 152m1Eu (T½=9.3116 hours) and 152m2Eu (T½=96 minutes).[9]

The primary decay mode for isotopes lighter than 153Eu is electron capture, and theprimary mode for heavier isotopes is beta minus decay. The primary decay productsbefore 153Eu are isotopes of samarium (Sm) and the primary products after are isotopesof gadolinium (Gd).[9]

Europium as a nuclear fission product

Europium isproducedby nuclearfission, butthe fissionproductyields ofeuropiumisotopes arelow nearthe top ofthe massrange forfissionproducts.

Like other lanthanides, many isotopes, especially isotopes with odd mass numbers andneutron-poor isotopes like 152Eu, have high cross sections for neutron capture, oftenhigh enough to be neutron poisons.

151Eu is the beta decay product of samarium-151, but since this has a long decayhalf-life and short mean time to neutron absorption, most 151Sm instead winds up as152Sm.

152Eu (half-life 13.516 years) and 154Eu (half-life 8.593 years) cannot be beta decayproducts because 152Sm and 154Sm are non-radioactive, but 154Eu is the only long-lived"shielded" nuclide, other than 134Cs, to have a fission yield of more than 2.5 parts permillion fissions.[10] A larger amount of 154Eu is produced by neutron activation of asignificant portion of the non-radioactive153Eu; however, much of this is furtherconverted to 155Eu.

155Eu (half-life 4.7612 years) has a fission yield of 330 parts per million (ppm) foruranium-235 and thermal neutrons; most of it is transmuted to non-radioactive andnonabsorptive gadolinium-156 by the end of fuel burnup.

Overall, europium is overshadowed by caesium-137 and strontium-90 as a radiation



Monazite

hazard, and by samarium and others as a neutron poison.[11][12][13][14][15][16][17]

Occurrence

Europium is not found in nature as a free element. Manyminerals contain europium, with the most importantsources being bastnäsite, monazite, xenotime andloparite.[18]

Depletion or enrichment of europium in minerals relativeto other rare earth elements is known as the europiumanomaly.[19] Europium is commonly included in traceelement studies in geochemistry and petrology tounderstand the processes that form igneous rocks (rocksthat cooled from magma or lava). The nature of theeuropium anomaly found helps reconstruct therelationships within a suite of igneous rocks.

Divalent europium (Eu2+) in small amounts is the activator of the bright bluefluorescence of some samples of the mineral fluorite (CaF2). The reduction from Eu3+ to

Eu2+ is induced by irradiation with energetic particles.[20] The most outstandingexamples of this originated around Weardale and adjacent parts of northern England; itwas the fluorite found here that fluorescence was named after, although it was not untilmuch later that europium was determined to be the cause.

Production

Europium is associated with the other rare earth elements and is therefore minedtogether with them. Separation of the rare earth elements is a step in the laterprocessing. Rare earth elements are found in the minerals bastnäsite, loparite,xenotime, and monazite in mineable quantities. The first two are orthophosphateminerals LnPO4 (Ln denotes a mixture of all the lanthanides except promethium), andthe third is a fluorocarbonate LnCO3F. Monazite also contains thorium and yttrium,which complicates handling because thorium and its decay products are radioactive. Forthe extraction from the ore and the isolation of individual lanthanides, several methodshave been developed. The choice of method is based on the concentration andcomposition of the ore and on the distribution of the individual lanthanides in theresulting concentrate. Roasting the ore and subsequent acidic and basic leaching is usedmostly to produce a concentrate of lanthanides. If cerium is the dominant lanthanide,then it is converted from cerium(III) to cerium(IV) and then precipitated. Furtherseparation by solvent extractions or ion exchange chromatography yields a fractionwhich is enriched in europium. This fraction is reduced with zinc, zinc/amalgam,electrolysis or other methods converting the europium(III) to europium(II). Europium(II)reacts in a way similar to that of alkaline earth metals and therefore it can beprecipitated as carbonate or is co-precipitated with barium sulfate.[21] Europium metalis available through the electrolysis of a mixture of molten EuCl3 and NaCl (or CaCl2) ina graphite cell, which serves as cathode, using graphite as anode. The other product ischlorine gas.[18][21][22][23][24]



Europium sulfate,Eu2(SO4)3

Europium sulfatefluorescing red underultraviolet light

A few large deposits produce or produced a significant amount of the world production.The Bayan Obo iron ore deposit contains significant amounts of bastnäsite and monaziteand is, with an estimated 36 million tonnes of rare earth element oxides, the largestknown deposit.[25][26][27] The mining operations at the Bayan Obo deposit made Chinathe largest supplier of rare earth elements in the 1990s. Only 0.2% of the rare earthelement content is europium. The second large source for rare earth elements between1965 and its closure in the late 1990s was the Mountain Pass rare earth mine. Thebastnäsite mined there is especially rich in the light rare earth elements (La-Gd, Sc, andY) and contains only 0.1% of europium. Another large source for rare earth elements isthe loparite found on the Kola peninsula. It contains besides niobium, tantalum andtitanium up to 30% rare earth elements and is the largest source for these elements inRussia.[18][28]

Compounds

See also: Category:Europium compounds

Halides

Europium metal reacts with all the halogens:

2 Eu + 3 X2 → 2 EuX3 (X = F, Cl, Br, I)

This route gives white europium(III) fluoride (EuF3), yelloweuropium(III) chloride (EuCl3), gray europium(III) bromide(EuBr3), and colorless europium(III) iodide (EuI3).Europium also forms the corresponding dihalides:yellow-green europium(II) fluoride (EuF2), colorlesseuropium(II) chloride (EuCl2), colorless europium(II)

bromide (EuBr2), and green europium(II) iodide (EuI2).[2]

Chalcogenides and pnictides

Europium forms stable compounds with all of thechalcogenides, but the heavier chalcogenides stabilize thelower oxidation state. Three oxides are known: europium(II)oxide (EuO), europium(III) oxide (Eu2O3), and the mixedoxide (Eu3O4). Otherwise, the main chalcogenides areeuropium(II) sulfide (EuS), europium(II) selenide (EuSe)and europium(II) telluride (EuTe): all three of these areblack solids. EuS is prepared by sulfiding the oxide attemperatures sufficiently high to decompose the Eu2O3:[29]

Eu2O3 + 3 H2S → 2 EuS + 3 H2O + S

The main nitride is europium(III) nitride (EuN).

History



Although europium is present in most of the minerals containing the other rareelements, due to the difficulties in separating the elements it was not until the late1800s that the element was isolated. William Crookes observed the phosphorescentspectra of the rare elements and observed spectral lines later associated toeuropium.[30] Europium was first found by Paul Émile Lecoq de Boisbaudran in 1890,who obtained basic fractions from samarium-gadolinium concentrates which hadspectral lines not accounted for by samarium or gadolinium. However, the discovery ofeuropium is generally credited to French chemist Eugène-Anatole Demarçay, whosuspected samples of the recently discovered element samarium were contaminatedwith an unknown element in 1896 and who was able to isolate it in 1901; he then namedit europium.[31][32]

When the europium-doped yttrium orthovanadate red phosphor was discovered in theearly 1960s, and understood to be about to cause a revolution in the color televisionindustry, there was a scramble for the limited supply of europium on hand among themonazite processors,[33] as the typical europium content in monazite is about 0.05%.However, the Molycorp bastnäsite deposit at the Mountain Pass rare earth mine,California, whose lanthanides had an unusually high europium content of 0.1%, wasabout to come on-line and provide sufficient europium to sustain the industry. Prior toeuropium, the color-TV red phosphor was very weak, and the other phosphor colors hadto be muted, to maintain color balance. With the brilliant red europium phosphor, it wasno longer necessary to mute the other colors, and a much brighter color TV picture wasthe result.[33] Europium has continued in use in the TV industry ever since, and, ofcourse, also in computer monitors. Californian bastnäsite now faces stiff competitionfrom Bayan Obo, China, with an even "richer" europium content of 0.2%.

Frank Spedding, celebrated for his development of the ion-exchange technology thatrevolutionized the rare earth industry in the mid-1950s once related the story of how[34]

he was lecturing on the rare earths in the 1930s when an elderly gentleman approachedhim with an offer of a gift of several pounds of europium oxide. This was an unheard-ofquantity at the time, and Spedding did not take the man seriously. However, a packageduly arrived in the mail, containing several pounds of genuine europium oxide. Theelderly gentleman had turned out to be Herbert Newby McCoy who had developed afamous method of europium purification involving redox chemistry.[23][35]

Following the lighter neptunium, plutonium, and heavier curium, americium was thefourth transuranium element to be discovered. At the time of the discovery of americiumin 1944, the periodic table had been restructured by Glenn T. Seaborg to its presentlayout, containing the actinide row below the lanthanide one. This led to americiumbeing located right below its twin lanthanide element europium; it was thus by analogynamed after another continent, America: "The name americium (after the Americas) andthe symbol Am are suggested for the element on the basis of its position as the sixthmember of the actinide rare-earth series, analogous to europium, Eu, of the lanthanideseries."[36][37][38]

Applications

Relative to most other elements, commercial applications for europium are few and



Europium is one of theelements used to make thered color in CRT televisions.

rather specialized. Almost invariably, they exploit itsphosphorescence, either in the +2 or +3 oxidation state.

It is a dopant in some types of glass in lasers and otheroptoelectronic devices. Europium oxide (Eu2O3) is widelyused as a red phosphor in television sets and fluorescentlamps, and as an activator for yttrium-based phosphors.[39][40] Color TV screens contain between 0.5 and 1 g ofeuropium.[41] Whereas trivalent europium gives redphosphors, the luminescence of divalent europiumdepends on the host lattice, but tends to be on the blueside. The two classes of europium-based phosphor (redand blue), combined with the yellow/green terbiumphosphors give "white" light, the color temperature ofwhich can be varied by altering the proportion or specificcomposition of the individual phosphors. This phosphorsystem is typically encountered in the helical fluorescent

light bulbs. Combining the same three classes is one way to make trichromatic systemsin TV and computer screens.[39] Europium is also used in the manufacture of fluorescentglass. One of the more common persistent after-glow phosphors besides copper dopedzinc sulfide is europium doped strontium aluminate.[42] Europium fluorescence is usedto interrogate biomolecular interactions in drug-discovery screens. It is also used in theanti-counterfeiting phosphors in Euro banknotes.[43][44]

An application that has almost fallen out of use with the introduction of affordablesuperconducting magnets is the use of europium complexes, such as Eu(fod)3, as shiftreagents in NMR spectroscopy. Chiral shift reagents, such as Eu(hfc)3 are still used to

determine enantiomeric purity.[45][46][47][48][49]

Precautions

There are no clear indications that europium is particularly toxic compared to otherheavy metals. Europium chloride nitrate and oxide have been tested for toxicity:europium chloride shows an acute intraperitoneal LD50 toxicity of 550 mg/kg and theacute oral LD50 toxicity is 5000 mg/kg. Europium nitrate shows a slightly higherintraperitoneal LD50 toxicity of 320 mg/kg, while the oral toxicity is above 5000 mg/kg.[50][51] The metal dust presents a fire and explosion hazard.[52]

See also

Europium anomaly

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External links

It's Elemental – Europium (http://education.jlab.org/itselemental/ele063.html)

Retrieved from "http://en.wikipedia.org/w/index.php?title=Europium&oldid=461199955"Categories: Chemical elements Lanthanides Europium Neutron poisons

Reducing agents

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