EP4066963A1 - Procédé de formation d'un matériau de départ pour produire des aimants permanents aux terres rares à partir de matériaux recyclés et matériau de départ correspondant - Google Patents
Procédé de formation d'un matériau de départ pour produire des aimants permanents aux terres rares à partir de matériaux recyclés et matériau de départ correspondant Download PDFInfo
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- EP4066963A1 EP4066963A1 EP21165521.2A EP21165521A EP4066963A1 EP 4066963 A1 EP4066963 A1 EP 4066963A1 EP 21165521 A EP21165521 A EP 21165521A EP 4066963 A1 EP4066963 A1 EP 4066963A1
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- C—CHEMISTRY; METALLURGY
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
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- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
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- H01F1/0572—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes with a protective layer
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- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
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- H01F1/0578—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together bonded together
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- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- H—ELECTRICITY
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- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
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- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
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- H01F1/053—Alloys characterised by their composition containing rare earth metals
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- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
- H01F1/0573—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes obtained by reduction or by hydrogen decrepitation or embrittlement
Definitions
- the present invention relates to a method for reprocessing of recycled Nd 2 Fe 14 B grains from bulk sintered Nd-Fe-B magnets and/or magnet scraps, to form a starting material for novel high-performance permanent magnets with better corrosion resistance via conventional and novel sintering routes.
- the invention also relates to the structure of the starting material.
- the present invention addresses both challenges simultaneously, reducing dependency on newly mined REE CRMs, while delivering novel starting material for novel permanent magnets with improved corrosion behaviour and an increased energy product at the same time, thus surpassing substantially the existing belief that Nd-Fe-B type material has come to its technical limits with respect to energy density.
- the improvement of the PMs performance measured as the energy density product BH max (a figure of merit for permanent magnets); has improved significantly during time and todays strongest PMs like Nd-Fe-B (Nd 14 Fe 80 B 6 ) reach as high as 450 kJ/m 3 .
- the addition of Gd is known to improve the temperature coefficient of the coercivity.
- Nd-Fe-B Cu and Al are added to Nd-Fe-B to improve sintering of the magnet alloy, while Nb is added for refining of the magnetic grains.
- Ga is added as it improves the intrinsic coercivity and the hot workability of the alloy and Co is added to increase the Curie temperature of Nd-Fe-B PMs.
- Nd-Fe-B PM typically contains about 31-32 wt. % of the total rare-earth elements (REEs) concentration in the PM mainly Nd + Pr plus a few minor, heavy rare-earth elements (HREEs) such as Dy, Tb, and Gd [2], that exceeds the stochiometric composition Nd 2 Fe 14 B that contains 26,7 wt. % Nd, 73,2 wt. % Fe and 0.1 wt.
- REEs total rare-earth elements
- HREEs heavy rare-earth elements
- the non-magnetic Nd-rich phase plays a major role in the production of REE PMs with good magnetic properties: in a liquid-phase sintering process that is taken into an advantage in conventional Nd-Fe-B PMs processing, it wets the surface of the Nd 2 Fe 14 B matrix grains, aiding to enhanced diffusion of atoms to promote densification, smoothing grain boundaries to limit the deleterious effects of local demagnetising fields at sharp edges, and providing a thin, smooth, defect-free grain boundary layer in order to magnetically insulate the RE 2 Fe 14 B crystallites and provide a barrier to demagnetisation of neighbouring grains [3].
- the Nd-Fe-B ternary-based sintered magnet cannot be used due to the thermal degradation of coercivity.
- Dy, Tb are added in small amounts (few % wt.) on the surface of the already sintered Nd-Fe-B magnets, where they are diffused along the grain boundaries towards magnet interior substituting a part of Nd in the Nd 2 Fe 14 B phase forming the so-called core shell structure of the Dy, Nd 2 Fe 14 B surrounding the Nd 2 Fe 14 B phase.
- CN104959618A discloses a core-shell structure Nd-Fe-B magnetic powder high in electrical resistivity and magnetic performance and application.
- the Strip Cast and Hydrogen decrepitated Nd-Fe-B powders are subjected to NH 3 gas (50-300 ml/min) at elevated temperatures 300-400°C in between 5 and 30 min. Afterwards the powders are cooled down to room temperature.
- a core shell microstructure of the Nd 2 Fe 14 B matrix phase was developed, where the shell was a nitrided Nd 2 Fe 14 B phase.
- Such NH 3 modified materials exhibited enhanced properties with regards to electrical resistivity and corrosion performance, however the magnetic properties degraded upon nitriding.
- CN110853854 A describes a method to increase the anisotropy of main hard magnetic phase Nd 2 Fe 14 B phase in Nd-Fe-B permanent magnets, via diffusion of PrHoFe alloy and ZrCu alloy that is applied on the hydrogen crushed particles.
- US2006022175 A and US2006191601 A describe the formation of a fluorine-containing layer on the surface of the ferromagnetic (Nd-Fe-B) powder by using a solution containing at least one kind of alkaline earth element or rare-earth element, and fluorine.
- US2014291296 A discloses a method of producing nanoparticles by spark erosion and 1) coating the surface of the nanoparticles with smaller nanoparticles; or 2) forming an oxidized coating on the surface of the nanoparticles to produce core-shell surface oxidized nanoparticles.
- Implementations of the disclosed technology can produce permanent magnets that include Nd-Fe-B magnets further enhanced by addition of more expensive rare earth elements, e.g., such as Dy.
- the disclosed spark erosion techniques can produce both Nd-Fe-B magnet alloy nanoparticles (e.g., less than 100 nm, and in some examples, less than 50 nm) and Dy or Dy-containing alloy nanoparticles of comparably or smaller size that are substantially free of surface oxide.
- single Nd 2 Fe 14 B grains of end-of-life Nd 2 Fe 14 B magnets and/or magnet scraps are provided.
- the single grains are preferably obtained from the end-of-life Nd 2 Fe 14 B magnets and/or magnet scraps by extracting the single grains via hydrogen or electrochemistry assisted methods, in particular by using selective electrochemical etching or hydrogen decrepitation.
- the provided single grains are then coated with a single layer or with a layer sequence of one or several grain boundary materials such that said single layer or layer sequence is covering each individual grain.
- the grain boundary material of said single layer or of the lowermost layer of said layer sequence is selected from one or several metals or metal compounds or alloys.
- the coated grains can then be condensed to bulk Nd-Fe-B permanent magnets, optionally via subsequent thermal treatments.
- the coating of the grains is preferably performed with one or several of the following methods: chemical vapor deposition (CVD), physical vapor deposition (PVD), electroplating, electroless plating, electrophoretic deposition, powder blending, spray coating and sol-gel, the latter with the help of a solvent, which evaporates after the sol-gel coating procedure at room temperature or slightly elevated temperatures.
- CVD chemical vapor deposition
- PVD physical vapor deposition
- electroplating electroless plating
- electrophoretic deposition electrophoretic deposition
- powder blending blending
- spray coating sol-gel
- the grain boundary material(s) in addition to the metals and alloys of lowermost layer, i.e. in other layers of the layer sequence, or as a closer specification of the metals and alloys of the single layer or lowermost layer may comprise any of the following components:
- the grain boundary material of the single layer and of the lowermost or second layer (covering said lowermost layer) of the layer sequence is preferably selected from metals, metal compounds or alloys which are rare earth free or low in rare earth content. With this measure, we aim to reduce the total rare earth content of the PMs below the current ⁇ 32 wt.%. In the Nd-Fe-B PMs having GBs with low REE content we aim at total rare earth content of the PMs of preferably 29 wt.% and below. For the Nd-Fe-B PMs with GBs, not containing the REEs, we aim to total rare earth content of the PMs to equal the stoichiometry of Nd 2 Fe 14 B phase that equals to 26.7 wt. % of the REEs. Some, examples of appropriate metals or alloys for the grain boundary material are Nd-Cu, or Cu, Al-Cu-Zn or only Zn or Sn.
- the grain boundary material of said single layer or of at least one layer of said layer sequence is selected to have a lower melting point than the hard-magnetic Nd 2 Fe 14 B phase and doesn't react with that phase. This enables the condensing of the coated grains to permanent magnets using thermal treatments without the need of any further binding material.
- the single grains for the proposed method are preferably obtained via selective electrochemical etching or hydrogen decrepitation.
- the selective electrochemical etching is performed by anodically oxidizing the Nd 2 Fe 14 B magnets and/or magnet scraps using a non-aqueous liquid electrolyte.
- the Nd 2 Fe 14 B grains in said Nd 2 Fe 14 B magnets and/or magnet scraps released.
- the released Nd 2 Fe 14 B grains are collected magnetically during and/or after said anodic oxidation.
- the non-aqueous liquid electrolyte is formed of a transition metal-based salt in a non-aqueous bath.
- the hydrogen decrepitation is performed by treating the Nd 2 Fe 14 B magnets and/or magnet scraps with hydrogen gas.
- the hydrogen decrepitation releases a friable, demagnetised, hydrogenated powder from said Nd 2 Fe 14 B magnets and/or magnet scraps.
- the powder contains an interstitial hydride of Nd 2 Fe 14 BHx (particles of 10 microns) and smaller particles ( ⁇ 1 micron) from the grain-boundary phase (NdH 2.7 ) of the magnets and/or magnet scraps.
- the starting material according to the present invention is the result of the proposed method.
- the starting material comprises single Nd 2 Fe 14 B grains of end-of-life Nd 2 Fe 14 B magnets and/or magnet scraps, which grains are coated with a single layer or with a layer sequence of one or several grain boundary materials such that said single layer or layer sequence is covering each individual grain.
- the grain boundary material of the single layer or of the layers of the layer sequence is selected according to one or several embodiments of the above method.
- novel bulk permanent magnets with increased properties and better corrosion resistance can be formed from end-of life Nd-Fe-B magnets and/or magnet scraps using different kinds of densification methods.
- the Nd-rich grain boundary can be exchanged with a novel grain boundary phase (based on a low amount of REEs or based on compositions that don't contain any REEs) that is not prone to corrosion.
- the amount of the HREEs elements like Dy can be finetuned to the ultimate concentration, that increases the coercivity (Hc i ) leaving the remanence (B r ) unaffected, that leads to an increased energy product (BH max ).
- the present invention suggests a new approach to increase the performance of Nd-Fe-B based permanent magnets: Single-crystal Nd 2 Fe 14 B particles recycled from end-of-life magnets are coated in nanometer- to micrometer thicknesses with grain boundary materials that are preferably either completely RE-free or much lower in RE-content than currently known grain boundary phases, before producing the magnet.
- grain boundary materials that are preferably either completely RE-free or much lower in RE-content than currently known grain boundary phases, before producing the magnet.
- This allows much more efficient use of scarce heavy-REE materials like Dy or Tb, and also the introduction of completely new grain boundary phase materials in single-layer or multi-layer configurations, consisting of e.g. metals, alloys, polymers, ceramics or glasses (and combinations thereof), enabling to improve coercivity and remanence of the material at the same time.
- single-crystal Nd 2 Fe 14 B matrix grains can be recovered by recycling of sintered magnets, grain smoothing processes have already happened during primary production, giving a new degree of freedom to use other materials as grain boundary phase to insulate the grains, and to tailor the magnetic properties during remanufacturing.
- the SEE procedure is based on the electrochemical anodic etching of sintered Nd-Fe-B magnets in a non-aqueous dimethylformamide/FeCl 2 bath. Selective recovery of Nd 2 Fe 14 B grains is realized with application of current densities ⁇ 10 mA cm -2 .
- the etching priority of phases (metallic Nd > intergranular NdFe 4 B 4 > matrix Nd 2 Fe 14 B) results in granular decomposition of the magnet, as shown in Figure 1 (right).
- the Nd 2 Fe 14 B grains are then separated from the nonmagnetic grain-boundary phase (mainly consisting of Nd 2 O 3 , Dy 2 O 3 and NdB 4 ).
- the removed Nd 2 Fe 14 B grains are preferably coated depending on the material
- Figure 2 shows the concept of the invention in comparison to coating of the magnetic particles via state-of-the-art methods.
- State of the art approaches Fig. 2a and Fig. 2b show conventional sintering and annealing (a) and grain boundary diffusion of sintered magnets (b).
- Nd 2 Fe 14 B grains 1 with Nd-rich phase are mixed with Dy-rich particles 2 and then sintered and annealed to form the dense magnets. This results in corresponding Nd, Dy-rich grain boundaries 3.
- Dy, Tb elements 4 are added in small amounts on the surface of already sintered Nd-Fe-B magnets, where they are diffused along the Nd, Dy-rich grain boundaries 3 towards magnet interior substituting a part of Nd in the Nd 2 Fe 14 B phase and forming a Nd, Dy, Tb -rich grain boundary 5.
- the present invention is presented in scheme (c) by way of example - grain boundary engineering of recycled magnet powder. On the left side the recycled single crystalline powder particles 6 are presented that are coated in this example with metal elements (Element A, layer 7), e.g. lanthanoide elements and/or their alloys, and alloys (Element B, layer 8) with or without the lanthanoide elements.
- the binding for forming the dense magnets from the coated grains is done either via the grain material (A, B) of the lowermost two layers or via glasses or ceramics C or polymers D of one or several further layers.
- the coated single Nd 2 Fe 14 B grains 6 are then bonded by means of heat, pressure, evaporation of a solvent or a combination thereof to form a dense magnet.
- the single grains 6 are separated by each other, as shown in Fig. 2c , by the coating 9 formed of the grain material of the lowermost two layers (A, B or AB) and by a coating 10 formed in this example by the ceramics C or polymers D.
- this further coating 10 may be formed of all involved materials or material combinations A, B, C, D.
- Fig 2 shows a comparison of the HC-BR-diagrams of the magnets achieved with the different methods, wherein the solid line refers to the method of Fig. 2a , the dashed line to the method of Fig. 2b and the dotted line to the method of Fig. 2c .
- the rare earth recycled magnet starting material produced by the method of the invention can be used for forming dense magnets.
- the magnets are densified by liquefaction and subsequent hardening of at least one of the layers of the grain boundary phase. This can be achieved by all materials that are liquid at temperatures below the melting point of the Nd 2 Fe 14 B hard-magnetic phase: metals with respective melting points, polymers, but also glue, resin, or amorphous materials with respective melting points like some glasses.
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