Novel process of rare-earth free magnet and thermochemical route for fabrication of permanent magnet

Transcription

1 Korea Magnetic Society Pyeongchang, Korea, Dec. 7, 2013 Novel process of rare-earth free magnet and thermochemical route for fabrication of permanent magnet Chul-Jin Choi Korea Institute of Materials Science, 797 Changwondaero, Changwon, Kyungnam, Korea

2 Scope Powder processing of Mn-Al based materials for rare earth free magnets Spray drying and reduction /diffusion route for Nd-Fe-B permanent magnet Summary

3 Alloy Design and Powder processing of Mn-Al based materials for rare earth free magnets

4 Price [$/kg] Mn-Al Magnetic Alloy Advantages μ 0 M r (T) μ 0 H c (T) (BH) max (KJ/m 3 ) Ferrite Alnico MnAl SmCo NdFeB Tb Ta Eu Dy CoSmNd Ni Cu La Al Pb ZnMn C Fe Metal

5 How to produce the ferromagnetic Mn-Al alloy wt.% Mn τ phase is usually produced by 1. Rapid quenching of theεphase followed by isothermal annealing between Cooling the εphase at a rate of 10 /min Al at.% Mn Mn Phase diagram of MnAl Until now Methods Warm-extruded Magnetron sputtering Melt spinning Mechanical milling Water-atomization This study Methods Plasma-arc discharge Gas-atomization Morphology Bulk Thin films Micro-powder Micro-powder Micro-powder Morphology Nano-powder Micro-powder

6 Temperature / C Manufacturing of MnAl alloy and estimation of (BH) max for MnAl-soft shell nanomagnet Objectives: Manufacturing of ε-phase Mn 54 Al 46 powder; Optimization of processing parameters to obtain τ-phase Mn 54 Al 46 powder (theoretical limit: 144 emu/g); Calculation of (BH) max for core-shell nanomagnet with Skomski s equation Liquid Phase transformation of MnAl alloy ε ε τ γ ε c quenching γ 2 τ Atomic Percent Manganese ß 2. Annealing a b No change in the volume: V = 27.16A 3 Orthorhombic (ε ) structure Tetragonal (τ) structure a b c 3.006A a = b = 2.77A, c = 3.54 A a:c = 1:1.28 6

7 Magnetic moment and total energy versus c/a ratio forτ-mnal Magnetic moment [ B ] Relative Total Energy [Ryd] μ B (161 emu/g) c/a 0.00 MAE of mev ( J/m 3 ) 38 koe of magnetocrystalline anisotropy field Estimated (BH) max MGOe for τ-phase Mn 50 Al 50 (B r = 0.7 B s )

8 (BH) max (MGOe) Thickness (nm) Theoretical (BM) max τ-mnal core/shell nanomagnet K Soft magnet τ-mnal δ s D h B r of soft magnet [T] 1.3 T 1.6 T 1.9 T 2.2 T [5] 10 Thickness and diameter s, D h = 50 nm s, D h = 70 nm s, D h = 100 nm s, D h = 250 nm Fraction of hard magnetic phase (f h ) 12.3 MGOe for single phase MnAl 2 0.3kT c 4Ka nm, Experiment al 15 nm δ s 2 x domain wall width of hard phase particle [4] [1] Q. Zeng, I. Baker, J. B. Cui, and Z. C. Yan, J. Magn. Magn. Mater. 308, 214 (2007). [2] N. I. Vlasova, G. S. Kandaurova, YA. S. Shur and N. N. Bykhanova, Phys. Met. Metall. 51, 1 (1981). [3] Y. Zhang, and D. G. Ivey, Mat. Sci. Eng. B, 140, 15 (2007). [4] E. F. Kneller and R. Hawig, IEEE Trans. Mag., 27, 3588 (1991). [5] G. F. Korznikova, Journal of Microscopy, 239, 239 (2010).

9 (BH) max (MGOe) Development trend of permanent magnets K Nd-Fe-B Core (MnAl) shell (soft 1.9 T) KS NKS MK Alnico OP 2-17:Sm-Co 1-5:Sm-Co Pt-Co year Pt-Fe SmFeN MnBi FeCrCo MnAlC Sr- or Ba-Ferrite *S. Sugimoto, J. Phys. D: Appl. Phys., 44, (2011).

10 Plasma Arc Discharge process valve gas circulation circulation fan anode cooling jacket cathode plasma arc collector scrapper vacuum out - Synthesis of Metal/Ceramic nanoparticles - Continuous production - High-purity and Non-agglomeration - Surface stability of nanoparticles sample auto feeding system Ar H 2 collect jar

11 Mn-Al Nano powder by Plasma Arc Discharge TEM micrograph ε-τ phase transition

12 Magnetization Magnetic Property of Mn-Al Nano powder 400 o C 500 o C 600 o C Magnetic properties of the MnAl system alloys prepared by different methods Methods Morphology Magnetic Properties H c (koe) Warm-extruded Bulk 3.02 Magnetron sputtering Thin films 3.0 Melt spinning Micro-powder 1.6 Mechanical milling Micro-powder 4.8 Plasma arc discharge Nanoparticles H(Oe) The Highest Coercivity

13 Gas Atomized Mn-Al Materials To produce ferromagnetic MnAl powders by gas-atomization Gas atomization Condition: Mn-30 wt.%al ingots; At nitrogen atmosphere; sieve S:25-38 m M: m B: m Annealing HT: at o C for 20 min Ball milling process P2 P1 τ-phase : S size, HT at 650 o C for 20 min Ball milling : 5-26 h Further annealing: at 280 o C for 20 min ε-phase : S sized powder, ball milled for 5-26 h HT: at 650 o C for 20 min

14 Phase change with ball milling P1 Good P2 Bad XRD patterns of the gas-atomized Mn-Al alloy powders treated by different two p rocesses: (a) P1; (b)p2.

15 Gas atomized Mn-Al Powder SEM images of gas-atomized Mn-Al powders with different particle size: (a) μm (b) μm (c) μm. 1.4 m 4 m

16 Phase and Magnetic property change with Annealing XRD patterns of Mn-Al powders annealed for 20 min At (a) 500, (b) 550, (c) 600, (d) 650, and (e) 700 o C.

17 Phase change and Magnetic property change Particle size with milling Magnetic Property Annealing Effect 5 h 10 h 20 h 26 h D~ 4.0 m SEM images of powders treated by P1 process Dependence of M r and H c of the powders on the ball milling time.

18 Comparison of Magnetic Property Theoretical Experimental Theoretical Mn 50 Al 50] Magnetic moment MAE (BH) max 2.37 μ B (161emu/g) mev ( J/m 3 ) MGOe Experimental Mn 54 Al 46 Magnetic moment (BH) max Curie temperature 1.44 μ B (98.3 emu/g) 4.7 MGOe 388 ºC

19 Thermochemical Route - Spray Drying and Reduction/Diffusion process - for permanent magnet

20 Application of process Ore of RE Extraction from RE ore MRI electronic device motor HDD RE Chloride Nd extraction from Ore Direct application of Rare-chloride or oxide Recycling of Nd from wastes Cost effective production of Nd-permanent magnet with novel process combined spray drying and R/D

21 Outline of process Spray drying/ Reduction-diffusion - Relatively cheap Nd-salt of Nd-oxide as starting material - Applicable to direct use of extracted Nd from ores and recycling of Nd from wastes Cost-effective / Fine magnetic powders 1μm μm - Preparation of fine magnetic powders under μm size - Reduction of defects from milling process NdCl 3 6H 2 O FeCl 3 6H 2 O H 3 BO 3 Mixed salt solution Spray drying Reduction/diffusion Nd-Fe-B powders packing/alignment/forming Magnetization Nd-permanent magnet

22 Design of process NdCl 3 6H 2 O FeCl 3 6H 2 O H 3 BO 3 Spray - drying Desalting Milling H 2 Reduction Ca Reduction Washing Nd 2 Fe 14 B Particles

23 Schematic diagram of spray dryer Precursor (20 ml /min ) Air in (250 ) Chamber Rotary Atomizer (15000rpm) Air out (120 ) Cyclone Collector

24 SEM micrographs of the powders (a) Spray-dried precursors (b) Desalted at 750 (c) Milling for 40h & H 2 -reducing at 1000 (d) Ca-reducing at 1000 & washing

25 Effects of temperature on debinding process a b c d Debinding for 2 hours at (a) 500 o C; (b) 750 o C; (c) 900 o C; (d) 1000 o C.

26 Weight (%) endo DTA ( o C/mg) exo TG-DTA for debinding process 100 NdOCl o C 15.48% (2.922mg) Fe 2 O % (1.649mg) Fe 2 O 3.Nd 2 O o C o C 506 o C 558 o C 14.13% (2.669mg) % (0.821mg) % (0.7011mg) Temperature ( o C) TG-DTA curves for spray-dried precursor in air at 10 o C/min of heating rate.

27 Intensity (arb. units) Effects of temperature on debinding process FeNdO 3 Fe 2 O 3 NdOCl FeB (d) Fe 2 O 3, Fe 2 O 3, Nd 2 O 3, FeB (c) Fe 2 O 3, NdOCl, Fe 2 O 3 Nd 2 O 3 (b) Fe 2 O 3, NdOCl, Fe 2 O 3 Nd 2 O 3 (a) Fe 2 O 3, NdOCl XRD patterns of the powders debinded at (a) 500 o C; (b) 750 o C; (c) 900 o C; (d) 1000 o C.

28 Weight (%) DTA ( o C/mg) endo exo TG-DTA for Ca-reduction process o C Ca melting 1075 o C 1131 o C Nd reduction and 1107 Rreation o C o C Temperature ( o C) TG-DTA curves for the mixture of Ca and H 2 -reduced powder in flowing Ar at 10 o C/min of heating rate.

29 Intensity (arb. unit) Phase evolution in the processes Nd 2 Fe 14 B (e) Washed CaO (D) (d) Ca reducing -Fe (c) (C) H 2 reducing Fe 2 O 3 NdOCl (b) Desalting (750 o C) (a) Precursor (spray-dried) XRD patterns of the products in all steps of (a) Spray drying; (b) Desalted at 750 in air; (c) H 2 -reducing at 800 ; (d) Ca-reducing at 1000 in flowing Ar; (e) washing.

30 TEM photograph of Nd 2 Fe 14 B particle 20nm

31 BH max (MGOe) Washing and magnetic properties washing conditon Weight ratio of Ca/powder = 0.40 De-ionized water washing, 1~3 hrs under sonication Increase of washing time oxidation of powders Increase of washing time effective removal of impurities R/D DIW-1hr DIW-2hrs DIW-3hrs [DIW; De-Ionized water Washing] Ca/powder (wt. ratio) condition H c (kg) M r (emu/g) M s (emu/g) Ca total (wt. %) 0.40 After R/D After washing for 1 hr After washing for 2 hrs After washing for 3 hrs

32 Summary The magnetic property of Mn-Al alloy was calculated, it showed 12.3 MGO for single phase and 60 MGO for core-shell nanomagnet. Mn-Al nanoparticles were successfully prepared by plasma arc discharge and gas atomization processes and the nanopowders exhibited very high coercivity, compared to other processes. The fully tau phase of Mn-Al powders were synthesized by gas atomization, and (BH)max was 4.7 MGO. To increase the magnetic properties, the fabrication of nanocomposite is in investigation. The ultrafine grained Nd-Fe-B magnetic powders were successfully fabricated by the thermochemical route including spray drying and reduction/diffusion process. The magnetic property of powder show 10 MGO of (BH)max after washing. The enhancement of magnetic property and application to magnet is under study.

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34 Prediction of magnetic property by simulation c c c a a a a = 4.287, c = a = 4.461, c = a = 4.566, c = Mn-Bi (LTP) structure (Vol. 97 Å 3 ] Mn-Bi-Co structure (Vol. 103 Å 3 ] Mn-Bi-Co-Fe structure (Vol. 107 Å 3 ] Table I. Comparison of calculated magnetic data for conventional Mn-Bi, new Mn-Bi-Co hard magnet, and Mn-Bi-Co-Fe soft magnet. Magnet Volume (Å 3 ) Magnetic Moment (μ B /u.c.) Magnetization (emu/cc) MAE (mev/u.c.) K (anisotropy constant) (10 6 J/m 3 ) T c (K) Mn-Bi (UA) (0.87 Tesla) Mn-Bi-Co (UA) (1.04 Tesla) Mn-Bi-Co-Fe (UA) (1.51 Tesla)

35 (BH) max [MGOe] Thickness [nm] (BH) max [MGOe] Thickness [nm] Computer simulation of Magnetic property Mn Phase transformation of MnAl alloy : ε ε τ Al c c a b a a K Soft magnet τ-mnal δ s D h B r of soft magnet [T] 1.3 T 1.6 T 1.9 T 2.2 T 2.5 T Thickness and diameter s, D h = 10 nm s, D h = 25 nm s, D h = 50 nm s, D h = 70 nm s, D h = 100 nm s, D h = 250 nm K MGOe for 0 1 pure MnAl Fraction of hard magnetic phase (f h ) 2 0.3kT c 4Ka nm, Experimental 15nm[5] M h = 1 T K h = 1.5 MJ/m 3 K s = MJ/m 3 δ s 2 x domain wall width of hard phase particle [4] 12.3 MGOe for pure MnAl Fraction of hard magnetic phase (f h ) 2 0.3kT c 4Ka nm, Experimental 15 nm