High Purity Rare Earth Metals Preparation 2011 Materials Preparation Center A US Department of Energy Specialized Research Center High Purity Rare Earth Metals Preparation Trevor M. Riedemann Manager, MPC Rare Earth Materials Section 122 Metals Development Building Ames Laboratory Ames, IA 50011-3020 Phone: 515-294-1366 Fax: 515-294-8727 E-mail: riedemann@ameslab.gov

Acknowledgements The Materials Preparation Center (MPC) is a U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences & Engineering specialized research center located at the Ames Laboratory. MPC operations are primarily funded by the Materials Discovery, Design, & Synthesis team's Synthesis & Processing Science core research activity. Thomas A. Lograsso Division Director Division of Materials Science & Engineering 124 Metals Development Building Ames, IA 50011-3020 Phone: 515-294-8425 Fax: 515-294-8727 E-mail: lograsso@ameslab.gov Lawrence L. Jones Director, MPC 121 Metals Development Building Ames Laboratory Ames, IA 50011-3020 Phone: 515-294-5236 Fax: 515-294-8727 E-mail: jonesll@ameslab.gov

Acknowledgements The Rare Earths, F.H Spedding & A.H. Daane, eds. (1961) John Wiley & Sons. Chapter 6 – Preparation of the Rare Earth Fluorides, O.N. Carlson & F.A. Schmidt Chapter 8 – Metallothermic Preparation of Rare Earth Metals, A.H. Daane Beaudry, B.J. & P.E. Palmer, (1974) “The use of inert atmospheres in the preparation and handling of high purity rare earth metals” Haschke, J.M, and H.A. Eich, eds. Proceedings of the 11th Rare Earth Research Conference (CONF-741002, Part 2, NTIS, Springfield, Virginia 22151) pp 612-620 Handbook on the Physics and Chemistry of Rare Earths, Vol 1 – Metals, (1978) K.A.Gschneidner, Jr. & L.R. Eyring, eds. Chapter 2 – Preparation and Basic Properties of the Rare Earth metals, B.J. Beaudry & K.A. Gschneidner A Lanthanide Lanthology, Part I & II, B.T. Kilbourn (1993) Molycorp. Inc.

The Rare Earths - A very Brief History 1794 J. Gadolin first reports their existence 1804 M.H. Klaproth isolated ceria 1827 Preparation of first REM (Ce) … 1931 Preparation of “reasonably pure” metal by electrolysis 1937 Pure enough to determine crystal structures 1947 Separation adjacent RE by ion exchange. 1950’s Spedding and Daane – developed “Ames Process” 1787 – 1987 Two Hundred Years of Rare Earths Rare Earth Information Center IS-RIC 10 Institute for Physical Research and Technology Iowa State University K.A. Gschneidner Jr & J. Capellen, ed.

The Rare Earths - Etymology Z Symbol Name Etymology 21 Sc Scandium Latin Scandia (Scandinavia) Y Yttrium Ytterby, Sweden, where the first ore was discovered. 57 La Lanthanum Greek "lanthanein", meaning to be hidden. 58 Ce Cerium For the dwarf planet Ceres. 59 Pr Praseodymium Greek "prasios” leek-green, &"didymos", meaning twin. 60 Nd Neodymium Greek "neos” new, and "didymos", meaning twin. 61 Pm Promethium Titan Prometheus, who brought fire to mortals. 62 Sm Samarium Vasili Samarsky-Bykhovets, who discovered samarskite. 63 Eu Europium For the continent of Europe. 64 Gd Gadolinium Johan Gadolin (1760–1852), to honor his study of REE. 65 Tb Terbium Ytterby, Sweden. 66 Dy Dysprosium Greek "dysprositos", meaning hard to get. 67 Ho Holmium Stockholm (in Latin, "Holmia”) 68 Er Erbium Ytterby, Sweden. 69 Tm Thulium For the mythological northern land of Thule. 70 Yb Ytterbium Ytterby, Sweden. 71 Lu Lutetium Lutetia, the city which later became Paris. 1787 – 1987 Two Hundred Years of Rare Earths Rare Earth Information Center IS-RIC 10 Institute for Physical Research and Technology Iowa State University K.A. Gschneidner Jr & J. Capellen, ed.

The Rare Earths - Abundance US Geological Survey Fact Sheet 087-02 Rare Earth Elements – Critical Resources for High Technology Gordon B. Haxel, James B. Hedrick, and Greta J. Orris

High Purity Oxide Prices La2O3 CeO2 Pr6O11 Nd2O3 Sm2O3 Eu2O3 Gd2O3 Tb4O7 Dy2O3 Ho2O3 Er2O3 Tm2O3 Yb2O3 Lu2O3 III / IV Dy output and consumption are approximately an order of magnitude lower than Nd. In 2000, Dy was in great demand, as its use in NdFeB alloys increased significantly and some hoarding and speculating took place in the second half of that year. Demand grew faster than actual output, reaching a virtual balance in 2000 but diverged again in 2001. Dy prices went through the roof in 2000 only to come crushing down in the second half of 2001, as shown in Figure 2. At the end of 2003, the supply/demand spread started to close again, which was reflected in prices rising sharply in the third quarter of 2003 and continuing strong. As indicated in Figure 5, with the limited availability of Dy, it does not take much of an increase in demand to trigger an imbalance, particularly since Dy is used in magnetic alloys and electronic ceramic chips, both of which are growing strongly again. We expect the Dy tightness to continue. (d) Terbium Tb has a similar functionality as Dy in magnetic alloys and certain producers favour Tb over Dy. Still, not a lot of Tb is used in magnetic alloys and for good reasons. Two things should be apparent when one examines Figure 6. First, the availability of Tb is about two orders of magnitude lower than Nd and, second, Tb consumption has traditionally been in much closer balance with output than most rare earths. UPDATE ON THE GLOBAL RARE EARTH INDUSTRY: Prospect for Magnetic Rare Earth Materials 2004 China Magnet Symposium Global Markets and Business Opportunities May 17-21, 2004, Xi’an, China Constantine E. Karayannopoulos

High Purity Oxide Prices La2O3 CeO2 Pr6O11 Nd2O3 Sm2O3 Eu2O3 Gd2O3 Tb4O7 Dy2O3 Ho2O3 Er2O3 Tm2O3 Yb2O3 Lu2O3 III / IV 2004 2007 2008 2009 11/2010 La 99% US$/kg 1.60 3.10 7.75 6.25 61.00 Ce 99% US$/kg 1.57 2.50 4.35 4.50 49.00 Pr 99% US$/kg 7.44 28.00 27.00 14.00 72.00 Nd 99% US$/kg 5.64 29.00 27.00 14.00 77.00 Eu 99% US$/kg 292.00 300.00 475.00 450.00 630.00 Tb 99% US$/kg 341.00 555.00 650.00 350.00 605.00 Dy 99% US$/kg 31.00 85.00 110.00 100.00 295.00 Dy output and consumption are approximately an order of magnitude lower than Nd. In 2000, Dy was in great demand, as its use in NdFeB alloys increased significantly and some hoarding and speculating took place in the second half of that year. Demand grew faster than actual output, reaching a virtual balance in 2000 but diverged again in 2001. Dy prices went through the roof in 2000 only to come crushing down in the second half of 2001, as shown in Figure 2. At the end of 2003, the supply/demand spread started to close again, which was reflected in prices rising sharply in the third quarter of 2003 and continuing strong. As indicated in Figure 5, with the limited availability of Dy, it does not take much of an increase in demand to trigger an imbalance, particularly since Dy is used in magnetic alloys and electronic ceramic chips, both of which are growing strongly again. We expect the Dy tightness to continue. (d) Terbium Tb has a similar functionality as Dy in magnetic alloys and certain producers favour Tb over Dy. Still, not a lot of Tb is used in magnetic alloys and for good reasons. Two things should be apparent when one examines Figure 6. First, the availability of Tb is about two orders of magnitude lower than Nd and, second, Tb consumption has traditionally been in much closer balance with output than most rare earths. Source: Metal Pages

The Rare Earths - Physical Properties

The Rare Earths - Ames Process High purity oxides from Ion-Exchange (2) Preparation of anhydrous RE-fluorides (3) Metallothermic reduction by Ca metal (4) Metallothermic reduction by La metal R2O3 + 6HF  2RF3 + 3H2O 3Ca + 2RF3  2R + 3CaF2 R2O3 + 2La  La2O3 + 2R

? Ames Process = High purity Impurity Sources: Oxygen: Incomplete oxide conversion Calcium reductant Atmosphere (handling and processing) N, C, & H: Adsorbed on oxide/fluoride Tantalum Crucible Atmosphere Ca & F: Reductant and incomplete reduction (10% excess Ca is used in Rx) Insufficient vacuum casting Fe, Co, Ni & Cu: Tantalum Crucible Impurities in oxide & HF Contamination of oxide during handling Cross Contamination in Processing Line Foundry vs Chip Fab

How Pure? Ames Commercial 99.996 99.99 99.99 99.96 99.9 99.2 150 175 555 660 3105 2100 N/T 99.996 99.99 99.99 99.96 99.9 99.2

Anlaysis of three commercial Tb samples and MPC Tb (ppm at). Source A Source D MPC Impurity Ingot Distilled Distilled Distilled H 7400 6800 22200 945 C n.a. n.a. n.a. 132 N 810 8000 1070 91 O 10900 28800 34400 665 Fe 156 117 60 14 La 200 120 35 1 Ta 5000 9 0 11 Total mag. RE 68 86 112 17 at% pure <97.5 <95.6 <94.2 <99.81 Semiquantitative MS for 25 elements (H,N and O by vacuum fusion) High purity Rare Earth Metals – Do We Need Them? Proc. of the first Symposium Rare Metals Forum, Extra-High Purification Technology and New Functional Materials Creation of Rare Earth Metals, Society of Non-Traditional Technology, Tokyo, Japan (1989) pp 13-29 K.A. Gschneidner, Jr.

Why do we need High Purity Metals? Impurities affect the basic properties of pure metals (and alloys) Lattice parameters Crystal structure Melting point Hardness Strength Resistivity Susceptibility Grain growth Magnetic domain wall motion Stoichiometry of alloy is shifted Second phase can form and change the properties. Crystal Growth Oxygen as impurity in crystal growth of intermetallics, D. Souptel, W. Lo¨ ser, W. Gruner, G. Behr, Journal of Crystal Growth 307 (2007) 410–420 Impurities may mask the INTRINSIC behavior of the pure metal or alloy material

Why do we need High Purity Metals? V. K. Pecharsky and K. A. Gschneidner, Jr. Giant Magnetocaloric Effect in Gd5Si2Ge2 Physical Review Letters 78 (1997) No. 23 T. Zhang , et. Al (Sichuan University) The structure and magnetocaloric effect of rapidly quenched Gd5Si2Ge2 alloy with low-purity gadolinium Materials Letters 61 (2007) 440–443 K. A. Gschneidner, Jr., et al. Method of Making Active Magentic Refrigerant, Colossal Magnetostriction and Giant Magentoresistive Materials Based on Gd-Si-Ge Alloys US Patent: 6,589,366 B1 (2003) -ΔSm (J/kg K) Impurities are suppressing a structural transition from orthorhombic to monoclinic Gd5Si2Ge2 alloy was prepared by arc-melt method in an argon atmosphere with low-purity commercial Gd (99 wt.%), high-purity Si and Ge (purities both better than 99.99 wt.%). The typical impurities of the commercial grade Gd are (wt.%):O: 1500 ppm,C: 200 ppm, Fe: 300 ppm, Ca: 300 ppm, Mg: 300 ppm, Si: 100 ppm, Al: 100 ppm. Gd5Si2Ge2: 0 – 5 T Temperature (K)

Why do we need High Purity Metals? Y. Matsumoto, et al. Quantum Criticality Without Tuning in the Mixed Valence Compound  -YbAlB4. Science, 2011; 331 (6015) S. Nakatsuji, et al. Superconductivity and quantum criticality in the heavy-fermion system –YbAlB4 Nature Physics 4, 603 - 607 (2008) Robin T. Macaluso, et. al Crystal Structure and Physical Properties of Polymorphs of LnAlB4 (Ln = Yb, Lu) Chem. Mater., 2007, 19 (8), pp 1918–1922 An exotic new superconductor based on the element ytterbium displays unusual properties that could change how scientists understand and create materials for superconductors and electronics. Beta-YbAlB4, can reach a quantum critical, without being subject to massive changes in pressure, magnetic fields, or chemical impurities.

High Purity Oxides Inputs: Oxides GARBAGE IN = GARBAGE OUT Y2O3 La2O3 CeO2 Pr6O11 Nd2O3 Sm2O3 Eu2O3 Gd2O3 Tb4O7 Dy2O3 Ho2O3 Er2O3 Tm2O3 Yb2O3 Lu2O3 III / IV GARBAGE IN = GARBAGE OUT Praseodymium Oxide Pr6O11 99.999% pure <10 ppm REM

Inputs: Calcium Reductant Triple Distilled commercial Ca has ~2000 – 5000 ppm oxygen

Distilled under He pp to remove oxygen 6 Days 900 g/run Ce 1900g Ca Lu 505g Ca Oxygen content is lowered <10 ppm Glove box protected Ca readily picks up O from H2O >1000 ppm from air in 5 minutes The effect of handing the Ca in air results in a 30-fold increase in O content in Cerium metal (BJB)

X X X X X X Inputs: Tantalum 10” x 14” x 0.030” = $1081.00 Alumina Magnesia Quartz Zirconia Graphite Iron X X X X X

Inputs: Tantalum Element R05200 R05400 C 0.010 0.010 O 0.015 0.03 ASTM B708 – 05 R05200, unalloyed tantalum, electron-beam furnace or vacuum-arc melt, or both ASTM B708 – 05 R05400, unalloyed tantalum, powder-metallurgy consolidation Element R05200 R05400 C 0.010 0.010 O 0.015 0.03 N 0.010 0.010 H 0.0015 0.0015 Fe 0.010 0.010 Mo 0.020 0.010 Nb 0.100 0.010 Ni 0.010 0.010 Si 0.005 0.010 Ti 0.010 0.010 W 0.05 0.010 Cleanest Ta: Pickled Annealed 2000ºC degassed

Nasty Stuff Inputs: Hydrofluoric Acid (HF) Purity range from 99% to 99.99% Parameter Level † HF 99.95 wt% H2SO4 100 wt ppm SO2 50 wt ppm H2O 200 wt ppm As 25 wt ppm Hydrofluosilicic 0.05 mol %* †Honeywell Specifications *Handbook of Compressed Gasses, 4th ed. (1999) H2SiF6 IDLH = 30 ppm, (Immediately Dangerous to Life and heath, for comparison Cyanide Gas has an IDLH of 50 ppm) LC50 = 1,276 ppm (Lethal Concentration 50, half of exposed group dies, tests conducted on rats, dogs, and monkeys) OSHA Permissible Exposure Limit (PEL) = 3 ppm 8 hours Short Term Exposure Limit (STEL) = 6 ppm 15 min. Deaths have been reported from as little as 2.5% body surface area (BSA) burns from concentrated acid. The palm of your hand is approximately 1% BSA. Nasty Stuff Not a lot of impurities to worry about…but…..

1 2 3 4 The Rare Earths - Physical Properties Vapor Pressure at Melting Point Tm 73.4 mm Hg Ce 3.6(10)-12 mm Hg

Ames Process – Flow Diagram 1 4 2 3

Ames Process – Flow Diagram Sm, Eu, Tm and Yb Low Boiling Points Reduction by Lanthanum from Oxide Easily purified by Sublimation Sm, Eu, Tm and Yb can be melted in Ta crucibles without Ta contamination Tm is very difficult to arc melt due to ~74mm vapor pressure at its melting point

Ames Process – Procedure Sm, Eu, Tm and Yb Dry Oxide Removes H2O and CO2 Machine lanthanum chips Mix oxide and La chips (in dry box) Pack in crucible (in dry box) Load into induction furnace Heat under vacuum. Hold for 8 hours Perform a low temp sublimation. Strip Ta from sublimate mass Europium is extruded.

Ames Process

Sublimed Ytterbium Metal

Ames Process – Flow Diagram La, Ce, Nd and Pr Low Melting but high Boiling Points Volatile impurities (Ca & F) can be quantitatively removed by vacuum casting without loss of metal Ta solubility at M.P. is low therefore Ta dissolved during vacuum casting can be removed by precipitation.

Ames Process – Procedure La, Ce, Nd and Pr Dry Oxide LT/HT Fluorination of oxide Heat mixture of Ca & REF3 Cool, remove slag Total of three reductions in same crucible Vacuum cast at high temperature Cool to just above melting point. Hold to precipitate tantalum Decant or “pour” RE into thin wall crucible Machine off crucible Arc cast into ingots

Ames Process: Low Temp Fluorination

Ames Process Reduction Step

Ames Process Post Reduction

Ames Process Pour/Decant Step

Ames Process – Flow Diagram Sc, Dy, Ho and Er High Melting and low to intermediate Boiling Points. To remove F impurity thru vacuum casting, must loose up to 30% of metal Easily purified with respect to O, N, C, Ta and other non-volatile impurities by sublimation.

Ames Process – Procedure Sc, Dy, Ho and Er Dry oxide LT Fluorination of oxide Heat mixture of Ca & REF3 Cool, remove slag Total of three reductions in same crucible Excluding Sc Vacuum cast Metal loss occurs Sublimate to purify Machine off crucible Arc cast into ingots

Ames Process Reduction Step

Dysprosium metal (as Reduced)

Ames Process Sublimation Step

Ames Process – Flow Diagram Y, Gd, Tb and Lu High Melting and High Boiling Points. Volatile impurities (Ca & F) can be removed by vacuum casting without significant loss of metal Ta solubility at MP is high, but can be removed by distillation. Slow distillations will reduce O, N, C slightly

Erosion of Ta by Refluxing During Distillation Scandium At MP ~ 3.2 at.% Ta (11.8 wt%) Cerium, At MP ~ 0.10 at% Ta

Ames Process – Flow Diagram Hey! What about me! So why don’t we “top” Sc, Dy, Ho, and Er? The common interstitial impurities O, N, and C that form stable compounds are left behind during sublimation. This not is the case for Y, Gd, Tb, & Lu distillation. ScF3 powder will absorb sufficient moisture in approximately 2 days to cause a violent reaction with the Ca reductant when heated.

High Purity Fluorides YF3 Praseodymium Fluoride PrF3 “Topped” LaF3 CeF3 PrF3 NdF3 SmF3 EuF3 GdF3 TbF3 DyF3 HoF3 ErF3 TmF3 YbF3 LuF3 Praseodymium Fluoride PrF3 “Topped”

High Purity Fluorides R2O3 + 6NH4HF2  2RF3 + 3NH3 + 3H2O Commercial: R2O3 + 6NH4HF2  2RF3 + 3NH3 + 3H2O 450ºC 1000 to 5000 ppm residual O Also a source of N impurity Ames LT: R2O3 + 6HF(anhydrous) + Ar  2RF3 + 3H2O + Ar 650ºC 10 to 1000 ppm residual O Pt lined furnace eliminated source of transition metal impurities. RF3 + HF(anhydrous)  RF3 + H2O Ames HT “Topped”: <10 ppm residual O Some reduction of transition metals La – Nd, Gd, Tb, Lu M.P.

High Purity Fluorides RF3 + HF(anhydrous)  RF3 + (H2O, other trace) M.P. RF3 + HF(anhydrous)  RF3 + (H2O, other trace) Metal T Al Si Cr Fe Ni Cu La - 20 60 9.5 66 15 2.9 Yes 0.5 3 0.1 15 1.0 0.5 Ce - 4.0 30 1.1 40 10 5.1 Yes 0.5 <9 0.6 10 6.6 2.6 Tb - 2 10 1 19 4 3.6 Yes 0.5 <0.2 0.3 18 3 5.0 Beaudry, B.J. & P.E. Palmer

Oxygen content in AT PPM of selected REM prepared from various grades of fluorides and calcium. La Ce Pr Nd Gd Tb Lu Y (1) 7800 5020 7000 9000 12770 27500 (2) 3040 2900 2500 2700 (3) 3040 3070 (4) 204 260 254 480 735 745 1145 2170 (5) 304 130 260 307 245 440 430 145 (1) Typical commercial purity (2) Fluoride prepared by NH4HF2 and reduced with purified calcium (3) Topped fluoride, purified calcium, handled in air (4) Low-temp fluoride, purified calcium, handled in glove box (5) Topped fluoride, purified calcium, handled in glove box Beaudry, B.J. & P.E. Palmer

Ames Process = High Purity Start with pure inputs Keep them pure Semper Fidelis