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THE PHYSICAL METALLURGY OF THE RARE EARTH METALS

THE PHYSICAL METALLURGY OF THE RARE EARTH METALS. Karl A. Gschneidner, Jr. Department of Materials Science and Engineering Iowa State University Ames, Iowa 50011-2300,USA. Res Metallica Katholieke Universiteit Leuven, Belgium May 23, 2012. I OWA S TATE U NIVERSITY

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THE PHYSICAL METALLURGY OF THE RARE EARTH METALS

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  1. THE PHYSICAL METALLURGY OF THE RARE EARTH METALS Karl A. Gschneidner, Jr. Department of Materials Science and Engineering Iowa State University Ames, Iowa 50011-2300,USA Res Metallica KatholiekeUniversiteit Leuven, Belgium May 23, 2012 IOWA STATE UNIVERSITY OF SCIENCE AND TECHNOLOGY

  2. AS A CONSUMER – I The automobile is the largest rare earth containing product you will purchase (or contains a product derived by using rare earths) GAS OR DIESEL POWERED AUTOMOBILE PRODUCTS Electric motors (~35 in an average car) [Nd,Pr,Dy] Speakers for sound system [Nd,Pr,Dy] Sensors to measure and control oxygen content in fuel [Y] 3-way catalytic converter [Ce] Optical displays – phosphors [Y,Eu,Tb] Ni-metal-hydride battery [Hybrid Vehicles] [La,MM] Electric traction motor [Hybrid Vehicles] [Nd,Dy] DERIVED PRODUCTS Gasoline – FCC cracking catalysts [La,Ce, mixed REO] Windshield, mirrors – polishing [Ce]

  3. AS A CONSUMER – II The automobile is the largest rare earth containing product you will purchase (or contains a product derived by using rare earths) ALL ELECTRICAL VEHICLE (a trade-off) ADD Traction Motors [Nd,Pr,Dy] TOSS 3-way Catalytic converter [Ce] Oxygen sensors [Y]

  4. AMES LABORATORY - I How Did Rare Earths Get to Ames? Spedding – Assoc. Prof. of Chemistry, Iowa State College – 1937 spectrascopist, but had to separate and purify his REs First Atomic Reactor – Stagg Field, Univ. Chicago needed 6 tons uranium metal developed a new and better way to make U Aug.-Nov. 1942 delivered 2 tons U Delivered 1,000 tons U for other reactors by Dec. 1945 Delivered 300 tons Th after World War II Ames Laboratory became an Atomic Energy Commission laboratory May 17, 1947.

  5. AMES LABORATORY - II Discovered and developed ion exchange chromatography separate and purify REs up to 99.9999% pure first time scientists had high purity REs in reasonable quantities available to study applications soon followed, e.g. Eu for color TV Analytical Chemistry developed new analytical techniques four different methods – in 1940s-1950s ICP-MS – inductively coupled plasma-mass spectrometry (1970-80s) Process Metallurgy high purity metals >99.8 atomic % pure with respect to all elements (routine) special – 99.99 atomic % pure 15 tons Y metal (nuclear aircraft) lanthothermic process – preparation: Sm, Eu, Tm, Yb Basic Research chemistry, metallurgy, materials science, condensed matter physics Interdisciplinary Research magnetism X-ray crystallography

  6. PERIODIC TABLE Group Period 1 18 1 1 H 2 2 He 13 14 15 16 17 2 3 Li 4 Be 10 Ne 5 B 6 C 7 N 8 O 9 F 3 13 Al 14 Si 15 P 16 S 3 4 5 6 7 8 9 10 11 12 11 Na 12 Mg 17 Cl 18 Ar 4 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 5 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 6 55 Cs 56 Ba 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 57 La 7 58 Ce 87 Fr 88 Ra 59 Pr 60 Nd 61 Pm LANTHANIDES 62 Sm 63 Eu 64 Gd 65 Tb 66 Dy 67 Ho 68 Er 69 Tm 70 Yb 71 Lu RARE EARTHS (R): Sc, Y, + Lanthanides (Ln)

  7. ELECTRONS DO IT ALL Four kinds of electrons s – fast moving electrons; weak bonds (high electrical conductivity in copper) p – moderately fast moving electrons; form strong bonds d – slow moving electrons; form very strong bonds highest melting metal - 3380°C second highest boiling point - 5725°C f – do not move, sit by the nucleus; little if any bonding lower melting point no effect on boiling point tungsten lanthanides

  8. LOCATION OF ELECTRONS IN AN ATOM N = nucleus Outer electrons: valence electrons – bonding conduction electrons – conduct electricity, heat lanthanides – 6s and 5d; Y – 5s,4d; Sc – 4s,3d Inner electrons: core electrons – s p d f where the 4f electrons reside

  9. ELECTRON WAVE FUNCTIONS OF AN ISOLATED GADOLINIUM ATOM

  10. SHAPES OF THE 4f CHARGE DENSITIES In the absence of crystal field Crystal field – due to the electric charges on other atoms in a solid and their locations in the unit cell oblate (red shading) prolate (green shading spherical (blue shading) (f) Eu2+J = O M = O Gd3+ M7/2; Lu3+

  11. ELECTRONIC STRUCTURES OF THE RARE EARTH GROUND STATES Configuration found in many text books and handbooks Generally not important to most scientists – who work with solid or liquid materials Important in chemical thermodynamic cycles if the R(g) state is involved

  12. ELECTRONIC STRUCTURES OF THE RARE EARTH IONS

  13. ELECTRONIC STRUCTURES OF THE RARE EARTH STANDARD STATES T = 298 K, P = 1 atm Standard state starting point for thermodynamic calculations, e.g. free energy formation of a RXn compound For most rare earth elements it is the trivalent state, for Eu and Yb it is the divalent state

  14. USES THAT DEPEND UPON VALENCE AND SIZE Mixed rare earths Petroleum cracking catalyst (also La, Ce) Mischmetal lighter flints alloy additive Individual rare earth elements Nickel-metal(La)-hydride batteries Alloying agent (La, Ce, Nd, Y)

  15. USES THAT DEPEND ON 4f ELECTRONS Permanent Magnets (purity not a problem  95%R) Nd, Pr, Sm, Dy Phosphors (very sensitive to impurities,  99.999%R; i.e. 5 nines) Eu (red, blue) Tb (green) fluorescent lamps optical displays (TV, etc.) Fiber optics (very sensitive to impurities,  99.999%R; i.e. 5 nines) Er

  16. USES THAT DEPEND ON THE ABSENCE OF ELECTRONIC TRANSITIONS IN UV, OPTICAL AND IR WAVE LENGTHS High Purities Required  99.999%R Optical lenses La, Gd, Lu Phosphor hosts Y, Gd Artificial gem stones Y ___________________________ Y3+ and La3+ - no 4f electrons Gd3+ lowest transition in the very short ultraviolet region Lu3+ completely filled 4f level, all 4f electrons paired up

  17. USES THAT DEPEND UPON VALENCE CHANGES Moderately Pure R Required > 98% pure) Ce3+ Ce4+ 4f1  4f0 Automotive 3-way emission catalysts UV light absorption Polishing compounds

  18. ABUNDANCES OF NATURALLY OCCURRING ELEMENTS IN THE LITHOSPHERE

  19. SELECTED RARE EARTH MINERALS

  20. RARE EARTH CONTENT IN SELECTED MINERALS

  21. PROCESSING AND SEPARATION - I Greatly Depends Upon Source Only Mined for Rare Earths Lights Bastnasite Monazite Heavies Ionic Clays (laterite) Xenotime Co-mined for Rare Earths Separate non-REs from REs then process for REs

  22. PROCESSING AND SEPARATION - II Ores (1  8% REO)  Mineral (15  80% REO)  Concentrate (~70% REO)  use as mixed rare earth  Individual RE Available purities: 90  99.999% – What do you need? That’s what you buy.

  23. SCHEMATIC OF SEPARATING TWO RARE EARTHS BY FRACTIONAL CRYSTALLIZATION Original solution Redissolve and crystallize Evaporate some H2O Sol. Liq. liquid solid Redissolve and crystallize Evaporate some H2O Sol. Liq. Combine liquid liquid solid solid Sol. Combine Combine Liq. La3+Pr3+Nd3+Sm3+

  24. SEPARATION OF RARE EARTH ELEMENTS Chemically very similar To get a given rare earth element No specific chemical can pull out a desired RE Must separate all of the elements before it in the series Exceptions Ce – make use of its dual valence (3+/4+) oxidize it to 4+ state and separate by precipitation this reduces the amount of rare earth to be separated by ~50% Eu – make use of its dual valence (2+/3+) carry out extraction process to remove La, Nd, Pr this increases the amount of Eu in the solution of the remaining REs reduce it to 2+ and precipitate EuSO4

  25. STABILITY CONSTANTS OF COMPLEXING AGENTS DTPA EDTA HEDTA The slope is more important than the magnitude.

  26. THE SPECIAL CASE OF YTTRIUM Change complexingagents Use DTPA or HEDTA Moves Y into the lights and separates Y from the heavies Then use EDTA To separate Y from the lights DTPA EDTA HEDTA

  27. PROBLEM: SEPARATION SEQUENCE Mountain Pass, California Mountain Pass, California To get to Eu, Tb and Dy need to remove ~99% other RE Remove Ce by oxidation process, cuts problem in half Bokan Mountain, Alaska To get to Eu, Tb and Dy and Y need to remove ~52% of the lighter REs, below Eu. Remove Ce by oxidation process, cut problem in half After getting Eu Y, can stop separation process and save Ho and Er Still no simple solution to get the critical elements Y <0.1 Bokan Mountain, Alaska Y 27

  28. ELECTROLYTIC PREPARATION OF RARE EARTH METALS For R with melting point less than 1050°C (La, Ce, Pr, Nd, MM) COMMENT: oxide solubility in the flux is small; control of amount oxide is critical and difficult to do; some NdF3 may be reduced to Nd + F2(g) when Nd2O3 is consumed. Electrolytic Cell + ¾ ¾ ¾ ¾ ¾ ® 4Nd 3O2 2 Nd2O3 (g) NdF3-LiF Flux 10,000 Amps ° 1100 C + some F2(g)

  29. CALCIOTHERMIC PREPARATION OF RARE EARTH METALS For R with melting point greater than 1050°C (R = Sc, Y, Gd Er, Lu) Ta OR CaF2 Gd

  30. LANTHANOTHERMIC PREPARATION OF Sm, Eu, Tm, Yb La* + R2O3 R + La2O3 Dy distillate *Could also use Ce and MM (some Nd impurity) instead of La

  31. SUBLIMATION/DISTILLATION OF RARE EARTH METALS To improve the metal purity R + i  Rg(i remains in residue) R  rare earth metal i  impurities (O, C, N, Ta, Mo) heat

  32. CLOSE-PACKED CRYSTAL STRUCTURES OF THE RARE EARTH METALS A A C B c c c A A A b b b C a a a hcp: Sc, Y, Sm, Gd, Tb,Dy, Ho, Er, Tm, Yb, Lu C B A [111] C B A B A C A dhcp: La, Ce, Pr, Nd, Pm B B A A fcc: La, Ce, Yb Sm-type: Sm Eu is body-centered cubic (not shown)

  33. METALLIC RADIUS OF THE RARE EARTH METALS

  34. THE MELTING AND TRANSFORMATION TEMPERATURES OF THE RARE EARTH METALS

  35. THE BOILING POINTS OF THE RARE EARTH METALS

  36. OXIDES Normal Oxides – Sesquioxide R2O3 Among the most stable oxides Other Valence State Oxides Tetravalent or partially tetravalent CeO2all 4+ Pr6O11 4PrO2 + Pr2O3 Tb4O7 2TbO2 + Tb2O3 Divalent or partially divalent EuO 2+ Eu3O4EuO + Eu2O3 Notable CeO2 (with Ce2O3) automotive 3 way emission catalyst EuO – ferromagnetic semiconductor

  37. THE FREE ENERGY OF FORMATION AT 298 K OF THE R2O3 PHASE Eu2O3 and Yb2O3 are Anomalous

  38. RARE EARTH HYDRIDES - I Metals readily react with hydrogen to form RH2 and RH3 Exceptions: Sc, Eu and Yb only form RH2 Structures RH2 CaF2 type structure (fluoride) RH3 fluorite – La, Ce, Pr, Nd hexagonal HoH3-type – Y, Sm, Gd-Tm, Lu RH2Eu, Yb: Orthorhombic, isostructural with alkaline earth MH2 Reactive in air RHx + O2 R2O3 + H2O RH3 semiconductors: R3+ + 3H-

  39. RARE EARTH HYDRIDES - II Semiconductors x < 2.7 metallic conduction x > 2.8 semiconductor at x  2.8 metal to semiconductor transition Switchable Mirrors thin films of RHx x  3 x < 2.9 films reflect light (mirrors) x = 3.0 films are transparent

  40. RARE EARTH HALIDES - IX = F, Cl, Br and I RX3 normal phase X = F – stable in air; insoluble in H2O and acids X = Cl, Br, I – hygroscopic RX4 only R = Ce, Pr and Tb RX2 R = Sm, Eu, Yb reported “RX2” – not true RX2 phases, stabilized by interstitial elements (H, C) RF3 or RCl3 start material for making R metals RF3 – component of heavy metal fluoride glasses ZrF4-BaF2-LaF3-AlF3 fiber optic glasses

  41. RARE EARTH HALIDES - II Fluoride Melting Points Halide Melting and Boiling Points

  42. PHOSPHORS, LASERS Critically depend on the 4f electrons Sharp transitions Each lanthanide (Ln) is unique Must be 99.99+ pure Y, La, Lu are hosts (no unpaired 4f electrons; also must be pure) 0.5 to 10% Ln in hosts V G R B 4f electron energy levels in the absence of a crystal field

  43. MAGNETIC PROPERTIES - I Curie temperature  TC ferromagnetic below TC spins aligned parallel to one another     paramagnetic above TC spins randomly orientated Neél temperature  TN antiferromagnetic below TN spins aligned antiparallel to one another    paramagnetic above TN spins randomly orientated Sometimes above TN – paramagnetic below TN – antiferromagnetic changes to ferromagnetic (Tc)

  44. MAGNETIC PROPERTIES - II Quantum Numbers for Trivalent Lanthanides SPIN S ½n (n = 1,2 . . .7), where n is the number of unpaired 4f electrons ORBITAL L li = 3,2,1,0,-1,-2,-3; L = li TOTALJ J = L ± S - for less than half filled (Ce Eu) + for more than half filled (Tb  Yb) for Gd: L = 0 and J = S = 7/2 DIVALENT LANTHANIDES Eu2+ 4f7 same as Gd3+ Yb2+ 4f14 same as Lu3+

  45. MAGNETIC PROPERTIES - III Magnetic Strength Effective Magnetic Moment, peff Paramagnetic region: peff=g[J(J+1)]½ Ferromagnetic region at T  0K: peff = gJ The larger peff the stronger the magnet Gyromagnetic Ratio, g

  46. MAGNETIC PROPERTIES - IV Magnetic Ordering Temperatures DeGennes Factor: (g-1)2J(J+1)

  47. MAGNETIC PROPERTIES - V Magnetic Entropy: SM = Rln(2J+1) Important in magnetic refrigeration, the larger the entropy change the larger the cooling power

  48. PERMANENT MAGNET COMPOUNDS Saturation Magnetic Moments = S3d JR For 3d = Co in RCo5+x

  49. INTERESTING INTERMETALLIC COMPOUNDS Terfenol D (Tb0.3Dy0.7)Fe1.9 Giant magnetostrictive material LaNi5Hy Nickel-metal-hydride battery LaB6 Electron gun for electron microscopes Giant Magnetocaloric Effect Materials Gd5(Si2Ge2) La(Fe1-xSix)13 Magnetic Refrigeration/Heating

  50. TOXICITY Low Can be safely handled with ordinary care Organically complexed ions are more toxic than solids or inorganic solutions Dust and vapors should not be inhaled – true for most chemicals Solutions splashed into eyes should be washed out – true for most chemicals Splinters of metal should be removed – true for most metals

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