A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics

More documents

Recommendations

Info

PHOSPHATESThe LnPO 4 compounds can be prepared [2], for example, by :• precipitation from aqueous solution,e.g. La 3+ + H 3 PO 4 => LaPO 4 .½H 2 O• reaction of phosphoric acid, or ammonium phosphates,with Ln salts such as the oxide or carbonate.The exothermic reactions should be controlled by slurrying the oxide orsalt in water. The more complex phosphates, e.g. metaphosphates, can bemade by the solid state reaction of the lanthanide salt and a phosphatesource mixed in appropriate ratios.In common with all Ln minerals, Monazite and Xenotime, in theirnaturally occurring forms, contain a "natural ratio" of many of the Lnelements, as well as other cations, and are not to be envisaged as purecompounds of any individual lanthanide. Monazite contains mainly lightlanthanides whereas Xenotime is a source for Yttrium and heavy Ln's.The monazite and xenotime structures have exceptional thermalstabilities and, probably, single-phase behavior up totheir melting points[3] and indeed this, combined with a limited chemicalreactivity, accounts for the difficulty of processing phosphate ores. (Lnphosphates have been suggested as hosts for the long-term storage ofradio-active waste.)The more complex phosphates on heating decompose to theorthophosphate, e.g. :LnPO4melting points°CMonazite-typeLa 2072Ce 2045Pr 1938Nd 1975Sm 1916Xenotime-typeY 1995Er 1896• La 5 PO 14 => La(PO 3 ) 3 => LaPO 4The doped lanthanum salt, (La,Ce,Tb)PO 4 , is now widely used as the preferredgreen-emitting phosphor for energy-efficient fluorescent lighting[4]. Ln phosphates have also beenproposed as scintillators and laser hosts.[2] Syntheses of Rare-Earth Orthophosphates, Y.Hikichi et al., Bull.Chem.Soc.Jpn., 1978, 51(12), 3645[3] Melting Temperatures of Monazite and Xenotime, Y. Hikichi and Ts. Nomura, J.Am. Ceram. Soc., 1987,70(10), C-252[4] Phosphors based on Rare-Earths, a New Era in Fluorescent Lighting, B.M.J.Smets, Mat. Chem. Phys.,1987, 16, 28329
PRASEODYMIUMIn most compounds this element is trivalent likeLanthanum and, in chemical behavior, Pr(III) compoundsclosely resemble the analogous La(III) derivatives. Most Pr 3+salts are pale green due to strong absorption bands in theblue from 440 to 490 nm.[1] (Similar color and bands areseen in a glass matrix when Pr 3+ is present.[2])Most praseodymium salts when calcined in airproduce, not a sesquioxide, Ln 2 O 3 , but a black materialwhose composition is best expressed as Pr 6 O 11 . Thetetra-valent state of Pr is of just sufficient stability to formpreferentially this oxide with mixed Pr valencies, chargetransfer behavior and thereby an enhanced stability. (ThePr-O phase diagram is complex and several oxides, forminga homologous series, Pr n O 2n-2 , are known[3], each with adefect fluorite structure.) The Pr(IV) ion is only stable in afew solid compounds, all oxide and fluoride based. A palegreen Pr 2 O 3 oxide can be made under strongly reducingconditions but it is not stable in air.Praseodymiurn forms ≈4 % of the lanthanide contentof bastnasite but all that proportion is not recovered as aseparated pure-Pr material because there is currentlyinsufficient commercial demand. The element will be presentMetallic Radius 183 pmin a small amount in almost all mixed-light-Ln derivatives, see Lanthanum Concentrate.The most popular yellow ceramic pigment is a Pr-doped zircon[4] that is "cleaner" and"brighter" than alternatives probably due to the Pr-pigment having an optimum reflectance at ≈560nm. In the preparation a "mineralizer", usually a metal halide MX, must be present to ensurecomplete reaction. Presumably the vapor phasePrElementAtomic Number 59Atomic Weight 140.91Electron[Xe]4f 4 6s 2configurationValency 3 (4)Ionic radius for 8- 113 pmcoordinationMagnetic moment 3.60 µBmetalCrystal Structure DhcpMelting Point 931 °CBoiling Point 3520 °CDensity6.77 g/cm3[1] Analysis of Rare Earth Mixtures by a Recording Spectrophotometer, D.C.Stewart and D.Kato, Anal.Chem.,1958,30,164[2] Absorption Spectra of Praseodymium in Glass, A-Singh and P.Nath, Glass Ceram.Bull., 1983, 30, 6[3] The Binary Rare Earth Oxides, L.Eyring, in "Handbook on the <strong>Physics</strong> and Chemistry of Rare Earths", ed.K.A.Gschneidner and L.Eyring, publ. North-Holland, 1979, Vol.3, p.337[4] Formation of Praseodymium-Doped Zircon Colors in Presence of Halides, R.A.Eppler, Ind.Eng.Chem.Prod.Res.Dev., 1971, 10(3), 352 : Zirconia-based Colors for Ceramic Glazes, R.A-Eppler, Cer.Bull.,1977, 56(2), 21330
Page 2 and 3: ALANTHANIDELANTHOLOGYPart II, M - Z
Page 6 and 7: Compounds of the perovskite, ABO 3
Page 8 and 9: METALSThe lanthanides, when prepare
Page 10: METALSMetallo-thermic oxide-reducti
Page 13 and 14: MONAZITEMonazite, a light-lanthanid
Page 15 and 16: NEODYMIUMNeodymium is the third mos
Page 18 and 19: [2] Preparation, Phase Equilibria,
Page 20 and 21: NOMENCLATURE58 - 71; the term is in
Page 22 and 23: OXALATESAddition of oxalic acid, or
Page 24 and 25: OXIDESCalcination in air for the th
Page 26 and 27: OXIDESFurthermore oxides with Ln IV
Page 28 and 29: OXYCHLORIDESThermal decomposition o
Page 30 and 31: OXYSULFIDESAll the elements of the
Page 32 and 33: PEROVSKITESA very wide range of mat
Page 36 and 37: PRASEODYMIUMtransport of Pr happens
Page 38 and 39: RESOURCESFor significant resources
Page 40 and 41: RESOURCESSignificant new resources
Page 42 and 43: SAMARIUMSamarium metal is made dire
Page 44 and 45: SILICATESWithin the binary Ln 2 O 3
Page 46 and 47: SOLVENT EXTRACTIONSome text books s
Page 48 and 49: SULFATESLanthanide sulfates can be
Page 50 and 51: SULFIDESThe thermochernistry of CeS
Page 52 and 53: THULIUMThulium, the rarest of the "
Page 54 and 55: TITANATES, TITANIUM DIOXIDELanthani
Page 56 and 57: YTTERBIUMIn broad chemical behavior
Page 58 and 59: YTTRIUMCompoundIdealFormulaFormula
Page 60 and 61: YTTRIUM OXIDEThe very stable oxide,
Page 62 and 63: YTTRIUM OXIDEThe widespread introdu

A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?