Magnetic materials and the production of magnetic materials

Abstract

Methods for the production of rare earth magnetic materials including magnetic crystals of Nd2F14B and the magnetic materials produced thereby. The methods lead to the formation of magnetic materials having a high concentration of Nd2F14B crystals. The method comprises steps of: admixing a neodymium borate powder, iron powder and calcium hydride to form a precursor powder; compacting the precursor powder to form a compacted precursor powder body; and heating the compacted precursor powder body to form a consolidated powder body.

Description

MAGNETIC MATERIALS AND THE PRODUCTION OF MAGNETIC MATERIALSFIELD

[0001] The present disclosure relates to the field of magnetic materials, and in particular to rare earth magnetic materials and methods for their production.SUMMARY

[0002] The present disclosure is directed to methods for the production of magnetic materials comprising magnetic crystals of Nd2Fei4B. In certain embodiments, the methods are capable of the production of magnetic materials having a high concentration of Nd2Fei4B magnetic crystals.

[0003] In one embodiment, a method for the production of a rare earth magnetic material of the form Nd2Fei4B is disclosed. The method includes the steps of admixing a neodymium borate powder (NdBO3), iron (Fe) powder and calcium hydride to form a precursor powder. The precursor powder is compacted under a compaction pressure to form a compacted precursor powder body. The compacted precursor powder body is then heated to a reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a consolidated powder body comprising a rare earth magnetic powder comprising Nd2Fei4B crystals, NdFe4B4 crystals and calcium oxide.

[0004] In another embodiment, a method for the refinement of a magnetic powder comprising Nd2Fei4B magnetic crystals and NdFe4B4 crystals is disclosed. The method includes the step of admixing a magnetic powder comprising Nd2Fei4B magnetic crystals and NdFe4B4 crystals with iron metal powder and neodymium metal powder to form a powder blend. The powder blend is compacted to form a compacted powder blend body, and the compacted powder blend body is heated to a reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a consolidated powder body comprising a rare earth magnetic powder comprising Nd2Fei4B crystals and NdFe4B4 crystals. The consolidated powder body is milled to form a refined magnetic powder, wherein the refined magnetic powder comprises a higher mass ratio of Nd2Fei4B crystals to NdFe4B4 than the magnetic powder.

[0005] In another embodiment, a method for the refinement ot a magnetic powder comprising Nd2Fei4B magnetic crystals and NdFe4B4 crystals is disclosed. According to this embodiment, a magnetic powder comprising Nd2Fei4B magnetic crystals and NdFe4B4 crystals is admixed with iron metal powder, neodymium metal powder, neodymium oxide powder and calcium hydride powder to form a powder blend. The powder blend is compacted to form a compacted powder blend body which is heated to a reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a consolidated powder body including Nd2Fei4B crystals, NdFe4B4 crystals and calcium oxide. The consolidated powder body is milled to form a calcium- containing magnetic powder and the calcium oxide is separated from the calcium- containing rare earth magnetic powder to form a refined rare earth magnetic powder. The refined rare earth magnetic powder includes a higher mass ratio of Nd2Fei4B crystals to NdFe4B4 than the magnetic powder.

[0006] In yet another embodiment, a method for the production of a rare earth magnetic material of the form Nd2Fei4B is disclosed. The method includes the steps of admixing a neodymium borate powder (NdBOs), iron (Fe) powder, neodymium metal, neodymium oxide and calcium hydride to form a precursor powder. The precursor powder is compacted under a compaction pressure to form a compacted precursor powder body and the compacted precursor powder body is heated to a reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a consolidated powder body comprising a rare earth magnetic powder comprising Nd2Fei4B crystals and calcium oxide.

[0007] These and other embodiments, characterizations and implementations of the present disclosure, including the attached claims, will be apparent to one of skill in the art.DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a flowsheet illustrating a method for the production of a rare earth magnetic material comprising crystals of Nd2Fei4B and NdFe4B4.

[0009] FIG. 2 is a flowsheet illustrating a method for the production of a refined rare earth magnetic material comprising crystals of Nd2Fei4B.

[0010] FIG. 3 is a flowsheet illustrating a method for the production of a refined rare earth magnetic material comprising crystals of Nd2Fei4B.

[0011] FIG. 4 is a flowsheet illustrating a method for the production of a rare earth magnetic material comprising crystals of Nd2Fei4B.DESCRIPTION OF THE EMBODIMENTS

[0012] The present disclosure is directed to the production of rare earth magnetic materials, particularly rare earth magnetic materials of the form RexMeyBz, where Re is a rare earth metal and Me is selected from iron (Fe), cobalt (Co) and combinations thereof. As used herein, the term magnetic material may refer to a material in a variety of forms, such as a free-flowing powder (e.g., a powder batch), a consolidated powder body or a bulk magnetic body, e.g., a sintered magnetic body.

[0013] The rare earth metal(s) Re may be selected from any rare earth metal, i.e., scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and combinations thereof. In one particular implementation, Re is selected from the group consisting of neodymium (Nd), praseodymium (Pr), dysprosium (Dy) and combinations thereof. The non-rare earth metal(s) Me may be selected from iron, cobalt and combinations thereof. For simplicity, the following description and the claims refer to the production of a Nd2Fei4B magnetic material. However, as will be apparent, the rare earth may also comprise other rare earth metals such as Pr and / or Dy, and cobalt may substitute for a portion of the iron, e.g., in the magnetic phase (Nd,Pr,Dy)2(Fe,Co)i4B.

[0014] The disclosed methods are particularly suitable for the production of a magnetic material, e.g., a magnetic powder, comprising a high concentration of Nd2Fei4B magnetic crystals, e.g., tetragonal crystals of Nd2Fei4B.

[0015] In one embodiment, a method is disclosed for the production of a Nd2Fei4B magnetic material from rare earth borates (ReBOs), e.g., from NdBOs. In this embodiment, the neodymium borate is the source of both the rare earth element and the boron in the Nd2Fei4B magnetic phase. The general chemical equation may be written as:NdBOs + CaH2 + Fe - NcbFeuB + NdFe4B4 + CaU (1 )

[0016] One embodiment of a method for producing a Nd2Fei4B magnetic material from rare earth borates and iron metal is illustrated in FIG. 1. The method includes admixing (e.g., combining, blending) rare earth borate powders, non-rare earth metal powders such as iron and calcium hydride powder (CaH2) to form a precursor powder that may be subsequently processed to form the magnetic material. Additionally, small concentrations of other metal powders may be added to the precursor powder, such as copper (Cu), aluminum (I), gallium (Ga) and niobium (Nb). Typically, the total concentration of these other metals will be not greater than about 1 wt.%. Table I illustrates one example of a batch for input to the admixing step.Table I

[0017] The components that form the precursor powder, e.g., the rare earth borates, iron and calcium hydride, may have a relatively small mean average particle size (d50) to facilitate the desired reactions. In one characterization, the component powders will have a mean average particle size of not greater than about 20 pm, such as not greater thanabout 15 pm, such as not greater than about 12 pm or even not greater than about 1U pm. Typically, the mean average particle size of the component powders will be at least about 1 pm, such as at least about 2 pm.

[0018] The mixed precursor powder is then compacted under a compaction pressure to form a compacted precursor powder body. In one characterization, the precursor powder is compacted to form the compacted precursor body at a compaction pressure of at least about 15 MPa, such as at least about 18 MPa, such at least about 24 MPa. Typically, the compaction pressure will not exceed about 35 MPa. In one refinement, the compaction pressure is at least about 24 MPa and is not greater than about 30 MPa. The compacted precursor body may take a variety of forms, such as blocks, disks, pellets and the like.

[0019] After compaction, the compacted precursor body is sintered, e.g., to react the components, to form a consolidated powder body predominately comprising the rare earth magnetic crystals Nd2Fei4B along with NdFe4B4 and CaO. See Equation (1 ). In one characterization, the compacted precursor body is heated to a reaction temperature of at least about 850°C, such as at least about 880°C, such as at least about 890°C. In one refinement, the reaction temperature does not exceed about 910°C. Maintaining the reaction temperature below about 910°C will inhibit the formation of non-magnetic iron species such as y-Fe. In one particular refinement, the reaction temperature is about 900°C.

[0020] The reaction may also be carried out under a reaction pressure, and in one characterization is carried out under a reaction pressure that is greater than atmospheric pressure, i.e., a reaction pressure that is greater than about 0.1 MPa. In one refinement, the reaction pressure is at least about 0.3 MPa, such as at least about 0.4 MPa, such as at least about 0.5 MPa.

[0021] To facilitate the reaction to form the Nd2Fei4B magnetic material from the neodymium borate powder, the reaction atmosphere may be a reducing atmosphere. For example, the reaction atmosphere may be a vacuum atmosphere. In one characterization, the reaction atmosphere is a hydrogen-comprising atmosphere. For example, the hydrogen-comprising atmosphere may comprise at least about 4%hydrogen, such as at least about 12% hydrogen. Preferably, the reaction atmosphere contains substantially no oxygen, e.g., not greater than about 0.1 % oxygen.

[0022] The consolidated powder body from the sintering step may be characterized as being friable, e.g., subject to being crushed without significant milling energy being applied. In this regard, the method may further include the step of milling the consolidated powder body to form a free-flowing powder mixture comprising Nd2Fei4B powder, NdFe4B4 powder and CaO powder. For example, the consolidated powder body may be milled in a jet mill having an inert atmosphere, e.g., a nitrogen (N2) atmosphere. In one implementation, the milling may break up powder agglomerates to form a free-flowing powder mixture having a mean average particle size of not greater than about 15 pm, such as not greater than about 12 pm, such as not greater than about 10 pm or even not greater than about 8 pm. The free-flowing powder mixture will typically have a mean average particle size of at least about 2 pm. In one particular characterization, the free- flowing powder mixture will have a mean average particle size of at least about 2 pm and not greater than about 8 pm.

[0023] Thereafter, the calcium oxide may be separated from the remainder of the magnetic powder, e.g., from the Nd2Fei4B and NdFe4B4 phases, to form a free-flowing rare earth magnetic powder that is substantially free of calcium. Known methods for the separation of the calcium oxide may be utilized, such as selective separation using cyclosizers or selective digestion from which calcium oxide is recovered. The calcium may advantageously be recovered and recycled at the backend of the process utilizing an electrolysis method.

[0024] After calcium oxide separation, the calcium-free powder will predominately comprise, e.g., will consist essentially of, the Nd2Fei4B tetragonal magnetic phase and the NdFe4B4 non-magnetic phase. The rare earth magnetic powder will have little to no metal oxide phases, e.g., little to no neodymium oxide phases such as Nd2Os and NdO. Further, the rare earth magnetic powder may have substantially no iron, substantially no carbon, and substantially no nitrogen. An exemplary composition of the rare earth magnetic powder after calcium separation is illustrated in Table II.Table II

[0025] If desired, the concentration of iron that is admixed with the rare earth borate powder and calcium hydride may be adjusted, e.g., may be increased, to provide small quantities of free iron, e.g., a-Fe, in the rare earth magnetic powder.

[0026] In one characterization, the free-flowing rare earth magnetic powder may comprise at least about 85 wt.% Nd2Fei4B magnetic crystals, such as at least about 88 wt.% Nd2Fei4B magnetic crystals. In another characterization, the free-flowing rare earth magnetic powder may comprise not greater than about 12 wt.% NdFe4B4 magnetic crystals, such as not greater than about 10 wt.% NdFe4B4 magnetic crystals. In another characterization, the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals in the free- flowing rare earth magnetic powder is at least about 8:1 , such as at least about 9:1 .

[0027] As is noted above, the Nd2Fei4B phase will include praseodymium and dysprosium substituting for a portion of the neodymium, and cobalt substituting for a small portion of the iron. See Table I. Thus, the magnetic phases may include Nd2(Fe,Co)i4B magnetic crystals, Pr2(Fe,Co)i4B magnetic crystals, Dy2(Fe,Co)i4B magnetic crystals and / or (Nd,Pr,Dy)2(Fe,Co)i4B magnetic crystals.

[0028] The free-flowing magnetic powder may be characterized as having a mean average particle size of not greater than about 12 pm, such as not greater than about 10 pm, such as not greater than about 8 pm or even not greater than about 6 pm. In one particular characterization, the free-flowing powder mixture will have a mean average particle size of at least about 2 pm and not greater than about 5 pm.

[0029] This free flowing magnetic powder is useful for the production of bulk magnets, e.g., by compacting and sintering the magnetic powder at temperatures on the order of 1080°C to 1120°C to form blocks, disks, pellets and the like.

[0030] It may be desirable to further refine this magnetic powder, e.g., to reduce the concentration of the non-magnetic NdFe4B4 phase in the powder. In one embodiment, a method is disclosed for the formation of a magnetic material, e.g., a free-flowing rare earth magnetic powder, that comprises a very high concentration of Nd2Fei4B magnetic crystals and a low concentration of non-magnetic phases such as NdFe4B4. The method may be applied to rare earth magnetic materials formed from rare earth borates and iron, e.g., as disclosed above, or may be applied to similar magnetic material compositions formed by other methods.

[0031] FIG. 2 illustrates a method according to this embodiment for the refinement of a magnetic material. As used herein, refinement means converting the residual nonmagnetic NdFe4B4 phase to the magnetic Nd2Fei4B phase. The NdFe4B4 phase is the source of boron required to produce additional Nd2Fei4B tetragonal magnetic crystals. However, NdFe4B4 does not contain sufficient neodymium and iron to form Nd2Fei4B, hence additional neodymium and iron are admixed with the NdFe4B4. The amount of neodymium and iron required are approximately equal to the amount that was added to produce the dual phase powder Nd2Fei4B / NdFe4B4 powder.

[0032] As illustrated in FIG. 2, the method includes admixing (e.g., combining, blending) the rare earth magnetic powder with neodymium powder and iron powder to form a powder mixture. In one characterization, the amount of iron powder added to the magnetic powder may be approximately equal to the concentration of iron in the Nd2Fei4B and NdFe4B4 phases. For example, if the magnetic powder is produced in accordance with FIG. 1 as described above, the amount of iron added to the magnetic powder may be approximately equal to the amount of iron that is combined and reacted with the rare earth borates. The amount of neodymium metal powder added to the magnetic powder may be approximately one-half of the amount of iron powder added, for example.

[0033] Subsequently, compaction of this powder mixture is carried out to form a compacted powder body. In one characterization, the powder mixture is compacted to form the compacted powder body at a compaction pressure of at least about 15 MPa, such as at least about 18 MPa, such at least about 24 MPa. Typically, the compaction pressure will not exceed about 35 MPa. In one refinement, the compaction pressure isat least about 24 MPa and is not greater than about 30 MPa. I he compacted powder body may take a variety of forms, such as blocks, disks, pellets and the like.

[0034] Thereafter, the compacted powder body is sintered (e.g., heated, reacted) to react the components, particularly to react the NdFe4B4 phase with the neodymium metal and the iron metal. The NdFe4B4 phase is converted to Nd2Fei4B in accordance with the following reaction:NdFe4B4 + 7Nd + 52Fe 4Nd2Fei4B (3)

[0035] Notably, the neodymium metal and the iron metal do not react with the Nd2Fei4B magnetic phase and the reaction advantageously increases the concentration of the Nd2Fei4B magnetic phase while reducing the concentration of the NdFe4B4 nonmagnetic phase.

[0036] In one characterization, this sintering step comprises heating to a temperature of about 800°C, e.g., from about 750°C to about 850°C. The sintering may also be carried out under a reaction pressure, and in one characterization is carried out under a reaction pressure that is greater than atmospheric pressure, i.e., a reaction pressure that is greater than about 0.1 MPa. In one refinement, the reaction pressure is at least about 0.3 MPa, such as at least about 0.4 MPa, such as at least about 0.5 MPa.

[0037] To facilitate the reaction to form the Nd2Fei4B magnetic phase, the reaction atmosphere may be a reducing atmosphere. For example, the reaction atmosphere may be a vacuum atmosphere. In one characterization, the reaction atmosphere is a hydrogen-comprising atmosphere. In one implementation, the hydrogen-comprising atmosphere comprises at least about 4% hydrogen, such as at least about 12% hydrogen. Preferably, the reaction atmosphere contains substantially no oxygen, e.g., not greater than about 0.1 % oxygen. The sintering may be carried out for a period of time to maximize the reaction to form the Nd2Fei4B magnetic phase, and in one implementation the sintering is carried out for at least about 1.5 hours, such as from about 2 hours to about 3 hours.

[0038] After sintering, the magnetic material, i.e., the sintered body, may have the composition shown in Table III.Table III

[0039] As can be seen by comparing Table II to Table III, the concentration of NdFe4B4 rare earth is reduced and the concentration of the Nd2Fei4B magnetic phase is increased. In one characterization, the refined magnetic powder comprises at least about 92 wt.% Nd2Fei4B magnetic crystals, such as at least about 95 wt.% Nd2Fei4B magnetic crystals, such as at least about 98 wt.% Nd2Fei4B magnetic crystals. In another characterization, the refined magnetic powder comprises not greater than about 8 wt.% NdFe4B4 crystals, such as not greater than about 5 wt.% NdFe4B4 crystals, such as not greater than about 2 wt.% NdFe4B crystals. In yet another characterization, the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals in the refined magnetic powder is at least about 20:1 , such as at least about 25:1 .

[0040] While this magnetic material offers many advantages due to the very high concentration of the Nd2Fei4B magnetic phase, the bulk sintered body may be difficult to machine into desirable shapes due to the lack of “soft” material phases, e.g., rare earth oxides, within the body.

[0041] In another embodiment, as illustrated in FIG. 3, a refining method is disclosed that may advantageously increase the concentration of these soft phases to enhance the machinability of the sintered body, enabling the sintered body to be machined using common, commercially available machining equipment.

[0042] Referring to FIG. 3, the magnetic powder to be refined may be similar to the magnetic powder that is refined according to the foregoing embodiment as illustrated in FIG. 2. That is, the magnetic powder may include the Nd2Fei4B magnetic phase,moderate concentrations of the NdFe4B4 non-magnetic phase, and an a-he phase, bee Table II. The method of this embodiment may be applied to magnetic materials formed from rare earth borates as disclosed above (FIG. 1 ), or may be applied to similar magnetic material compositions formed by other methods.

[0043] According to this embodiment, the magnetic powder is mixed (e.g., combined, blended) with neodymium metal, neodymium oxide, iron powder and calcium hydride to form a powder mixture. In one characterization, the amount of iron powder added to the magnetic powder may be approximately equal to the concentration of iron in the Nd2Fei4B and NdFe4B4 phases. For example, if the magnetic powder is produced in accordance with FIG. 1 as described above, the amount of iron added to the magnetic powder may be approximately equal to the amount of iron that is combined with the rare earth borates. The amount of neodymium metal powder and neodymium oxide powder added to the magnetic powder may be approximately one-half of the amount of iron powder added, for example. In one implementation, the weight ratio of neodymium metal to neodymium oxide that is added to the magnetic powder is from about 8:1 to about 10:1. The concentrations and ratios of neodymium metal and neodymium oxide may be adjusted to obtain different levels of machinability in the final sintered magnet.

[0044] The components that form the powder mixture may have a small average particle size to facilitate the desired reactions. In one characterization, the component powders will have a mean average particle size (d50) of not greater than about 20 pm, such as not greater than about 15 pm, such as not greater than about 12 pm or even not greater than about 10 pm. Typically, the mean average particle size of the component powders will be at least about 1 pm, such as at least about 2 pm.

[0045] The powder mixture is then compacted under a compaction pressure to form a compacted powder body. In one characterization, the powder mixture is compacted to form the compacted powder body at a compaction pressure of at least about 15 MPa, such as at least about 20 MPa, such at least about 24 MPa. Typically, the compaction pressure will not exceed about 35 MPa. In one refinement, the compaction pressure is at least about 24 MPa and is not greater than about 30 MPa. The compacted powder body may take a variety of forms, such as blocks, disks, pellets and the like.

[0046] Thereafter, the compacted powder body is sintered (e.g., heated, reacted) to react the components, particularly to react the NdFe4B4 phase with the neodymium metal and the iron metal. The addition of Nd2O3and Nd metal in the presence of calcium may convert substantially all of the NdFe4B4 to Nd2Fei4B:3NdFe4B4+ 13Nd + 4Nd2O3+ 12Ca + 156Fe 12Nd2Fei4B + 12CaO (4)

[0047] In one characterization, this sintering step comprises heating to a temperature of about 800°C, e.g., from about 750°C to about 850°C. The sintering may also be carried out under a reaction pressure, and in one characterization is carried out under a reaction pressure that is greater than atmospheric pressure, i.e., a reaction pressure that is greater than about 0.1 MPa. In one refinement, the reaction pressure is at least about 0.3 MPa, such as at least about 0.4 MPa, such as at least about 0.5 MPa.

[0048] To facilitate the reaction to form the Nd2Fei4B magnetic phase, the reaction atmosphere may be a reducing atmosphere. For example, the reaction atmosphere may be a vacuum atmosphere. In one characterization, the reaction atmosphere is a hydrogen-comprising atmosphere. In one implementation, the hydrogen-com prising atmosphere comprises at least about 4% hydrogen, such as at least about 12% hydrogen. Preferably, the reaction atmosphere contains substantially no oxygen, e.g., not greater than about 0.1 % oxygen. The sintering may be carried out for a period of time to maximize the reaction to form the Nd2Fei4B magnetic phase, and in one implementation the sintering is carried out for at least about 1.5 hours, such as from about 2 hours to about 3 hours.

[0049] The foregoing reaction conditions are conducive to the formation of a magnetic material that predominately comprises Nd2Fei4B magnetic crystals and very small concentrations of non-magnetic phases. Further, the magnetic material will comprise a sufficient concentration of soft phases to enhance the machinability of sintered magnetic blocks formed from the magnetic powder. An exemplary composition of the magnetic powder is shown in Table IV.Table IV

[0050] The consolidated powder body from the sintering step may be characterized as being friable, e.g., subject to being crushed without significant milling energy being applied. In this regard, the method may further include the step of milling the consolidated powder body to form a free-flowing powder mixture comprising Nd2Fei4B powder and calcium oxide powder. Thereafter, the calcium oxide may be separated from the remainder of the magnetic powder, e.g., from the Nd2Fei4B powder, to form a free-flowing rare earth magnetic powder that is substantially free of calcium. Known methods for the separation of the calcium oxide may be utilized, such as selective separation using cyclosizers or selective digestion from which calcium oxide is recovered. The calcium may advantageously be recovered and recycled at the backend of the process utilizing an electrolysis method.

[0051] Yet another embodiment of a method for the production of a magnetic material is illustrated in FIG. 4. In this embodiment, the method for the production of a magnetic material from rare earth borates and iron metal illustrated in FIG. 1 is advantageously combined with the method for refining the magnetic powder illustrated in FIG. 3 in an “intensive” reaction, e.g., in a single reaction step. Referring to FIG. 4, the method includes admixing (e.g., combining, blending) rare earth borate powders, neodymium powder, neodymium oxide powder, iron powder and calcium hydride powder (CaH2) to form a precursor powder that may be subsequently processed to form the magnetic material.

[0052] Additionally, small concentrations of other metal powders may be added to the precursor powder, such as copper (Cu), aluminum (I), gallium (Ga) and niobium (Nb).Typically, the total concentration of these other metals will be not greater than about 1 wt.%. Table V illustrates one example of a batch for input to the admixing step.Table V

[0053] The components that form the precursor powder, e.g., the rare earth borates, neodymium metal, neodymium oxide, iron and calcium hydride, may have a relatively small mean average particle size (d50) to facilitate the desired reactions. In one characterization, the component powders will have a mean average particle size of not greater than about 20 pm, such as not greater than about 15 pm, such as not greater than about 12 pm or even not greater than about 10 pm. Typically, the mean average particle size of the component powders will be at least about 1 pm, such as at least about 2 pm.

[0054] The mixed precursor powder is then compacted under a compaction pressure to form a compacted precursor powder body. In one characterization, the precursorpowder is compacted to form the compacted precursor body at a compaction pressure ot at least about 15 MPa, such as at least about 18 MPa, such at least about 24 MPa. Typically, the compaction pressure will not exceed about 35 MPa. In one refinement, the compaction pressure is at least about 24 MPa and is not greater than about 30 MPa. The compacted precursor body may take a variety of forms, such as blocks, disks, pellets and the like.

[0055] After compaction, the compacted precursor body is sintered, e.g., to react the components, to form a consolidated powder body predominately comprising the rare earth magnetic crystals Nd2Fei4B and CaO. In one characterization, the compacted precursor body is heated to a reaction temperature of at least about 840°C, such as at least about 880°C, such as at least about 890°C. In one refinement, the reaction temperature does not exceed about 910°C. Maintaining the reaction temperature below about 910°C will inhibit the formation of non-magnetic iron species such as y-Fe. In one particular refinement, the reaction temperature is about 900°C.

[0056] The reaction may also be carried out under a reaction pressure, and in one characterization is carried out under a reaction pressure that is greater than atmospheric pressure, i.e., a reaction pressure that is greater than about 0.1 MPa. In one refinement, the reaction pressure is at least about 0.3 MPa, such as at least about 0.4 MPa, such as at least about 0.5 MPa.

[0057] To facilitate the reaction to form the Nd2Fei4B magnetic material from the neodymium borate powder, the reaction atmosphere may be a reducing atmosphere. For example, the reaction atmosphere may be a vacuum atmosphere. In one characterization, the reaction atmosphere is a hydrogen-comprising atmosphere. For example, the hydrogen-comprising atmosphere may comprise at least about 4% hydrogen, such as at least about 12% hydrogen. Preferably, the reaction atmosphere contains substantially no oxygen, e.g., not greater than about 0.1 % oxygen.

[0058] The consolidated powder body from the sintering step may be characterized as being friable, e.g., subject to being crushed without significant milling energy being applied. In this regard, the method may further include the step of milling the consolidated powder body to form a free-flowing powder mixture comprising Nd2Fei4B powder andCaO powder. For example, the consolidated powder body may be milled in a jet mill having an inert atmosphere, e.g., a nitrogen (N2) atmosphere. In one implementation, the milling may break up powder agglomerates to form a free-flowing powder mixture having a mean average particle size of not greater than about 15 pm, such as not greater than about 12 pm, such as not greater than about 10 pm or even not greater than about 8 pm. In one particular characterization, the free-flowing powder mixture will have a mean average particle size of at least about 2 pm and not greater than about 8 pm.

[0059] Thereafter, the calcium oxide may be separated from the remainder of the magnetic powder, e.g., from the Nd2Fei4B powder, to form a free-flowing rare earth magnetic powder that is substantially free of calcium. Known methods for the separation of the calcium oxide may be utilized, such as selective separation using cyclosizers or selective digestion from which calcium oxide is recovered. The calcium may advantageously be recovered and recycled at the back end of the process utilizing an electrolysis method.

[0060] After calcium oxide removal, the calcium-free powder will comprise, e.g., will consist essentially of, the Nd2Fei4B tetragonal magnetic phase, free neodymium and neodymium oxide. An exemplary composition of the magnetic powder after calcium separation is illustrated in Table VI.Table VI

[0061] The magnetic powder may be characterized as having a mean average particle size of not greater than about 12 pm, such as not greater than about 10 pm, such as notgreater than about 8 m or even not greater than about 6 pm. In one particular characterization, the free-flowing powder mixture will have a mean average particle size of at least about 2 pm and not greater than about 5 pm.

[0062] This magnetic powder is useful for the production of bulk magnets, e.g., by compacting and sintering the magnetic powder at temperatures on the order of 1080°C to 1120°C to form blocks, disks, pellets and the like.

[0063] As will be appreciated by those of skill in the art, the free-flowing magnetic powders disclosed above may be compacted, sintered and magnetized to form a rare earth magnet body, e.g., as a block, a disk or any other desirable shape. The rare earth magnet body may have the same compositional characteristics as the foregoing compositional characteristics of the free-flowing magnetic powder. That is, the sintering and magnetization of the powder will not substantially alter the compositional characteristics of the magnetic material.

[0064] While various embodiments of rare earth magnetic materials and methods for the production of rare earth magnetic materials have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure.

Claims

What is Claimed Is:1 . A method for the production of a rare earth magnetic material of the form Nd2Fei4B, comprising the steps of: admixing a neodymium borate powder (NdBOs), iron (Fe) powder and calcium hydride to form a precursor powder; compacting the precursor powder under a compaction pressure to form a compacted precursor powder body; heating the compacted precursor powder body to a reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a consolidated powder body comprising a rare earth magnetic powder comprising Nd2Fei4B crystals, NdFe4B4 crystals and calcium oxide.

2. The method recited in Claim 1 , wherein the compaction pressure is at least about 20 MPa.

3. The method recited in any one of Claims 1 or 2, wherein the reaction temperature is at least about 850°C.

4. The method recited in any one of Claims 1 to 3, wherein the reaction temperature is at least about 880°C.

5. The method recited in any one of Claims 1 to 4, wherein the reaction temperature is not greater than about 910°C.

6. The method recited in any one of Claims 1 to 5, wherein the reaction pressure is at least about 3 bar (0.3 MPa).

7. The method recited in any one of Claims 1 to 6, wherein the reaction pressure is at least about 4 bar (0.4 MPa).

8. The method recited in any one of Claims 1 to 17, wherein the reaction atmosphere is a hydrogen-comprising atmosphere.

9. The method recited in Claim 8, wherein the hydrogen-comprising atmosphere comprises at least about 4% hydrogen.

10. The method recited in Claim 9, wherein the hydrogen-com prising atmosphere comprises at least about 12% hydrogen.11 . The method recited in any one of Claims 1 to 10, further comprising the step of milling the consolidated powder body to form a free-flowing powder mixture.

12. The method recited in Claim 11 , further comprising the step of separating the calcium oxide from the free-flowing powder mixture to form a free-flowing rare earth magnetic powder that is substantially free of calcium.

13. The method recited in Claim 12, wherein the free-flowing rare earth magnetic powder comprises at least about 85 wt.% Nd2Fei4B magnetic crystals.

14. The method recited in Claim 13, wherein the free-flowing rare earth magnetic powder comprises at least about 88 wt.% Nd2Fei4B magnetic crystals.

15. The method recited in any one of Claims 12 to 14, wherein the free-flowing rare earth magnetic powder comprises not greater than about 12 wt.% NdFe4B4 nonmagnetic crystals.

16. The method recited in Claim 15, wherein the free-flowing rare earth magnetic powder comprises not greater than about 10 wt.% NdFe4B4 magnetic crystals.

17. The method recited in any one of Claims 15 to 19, wherein the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals in the free-flowing rare earth magnetic powder is at least about 8:1.

18. The method recited in Claim 17, wherein the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals in the free-flowing rare earth magnetic powder is at least about 9:1 .

19. The method recited in any one of Claims 12 to 18, wherein the free-flowing magnetic powder comprises substantially no iron.

20. The method recited in any one of Claims 12 to 19, wherein the free-flowing magnetic powder comprises substantially no metal oxides.21 . The method recited in any one of Claims 12 to 20, wherein the free-flowing magnetic powder comprises substantially no carbon.

22. The method recited in any one of Claims 12 to 21 , wherein the tree-flowing magnetic powder comprises substantially no nitrogen.

23. The method recited in any one of Claims 1 to 22, wherein the neodymium borate powder and iron powder have a mean average particle size of not greater than about 12 pm.

24. The method recited in Claim 26, wherein the neodymium borate powder and iron powder have a mean average particle size of at least about 2 pm.

25. A method for the refinement of a magnetic powder comprising Nd2Fei4B magnetic crystals and NdFe4B4 crystals, comprising the steps of: admixing a magnetic powder comprising Nd2Fei4B magnetic crystals and NdFe4B4 crystals with iron metal powder and neodymium metal powder to form a powder blend; compacting the powder blend to form a compacted powder blend body; heating the compacted powder blend body to a reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a consolidated powder body comprising a rare earth magnetic powder comprising Nd2Fei4B crystals and NdFe4B4 crystals; milling the consolidated powder body to form a refined magnetic powder, wherein the refined magnetic powder comprises a higher mass ratio of Nd2Fei4B crystals to NdFe4B4 than the magnetic powder.

26. The method recited in Claim 25, wherein the compaction pressure is at least about 20 MPa.

27. The method recited in any one of Claims 25 to 26, wherein the reaction temperature is at least about 750°C.

28. The method recited in any one of Claims 25 to 27, wherein the reaction temperature is at least about 780°C.

29. The method recited in any one of Claims 25 to 28, wherein the reaction temperature is not greater than about 850°C.

30. The method recited in any one of Claims 25 to 20, wherein the reaction pressure is at least about 4 bar (0.4 MPa).

31. The method recited in any one of Claims 25 to 30, wherein the reaction pressure is at least about 5 bar (0.5 MPa).

32. The method recited in any one of Claims 25 to 31 , wherein the reaction atmosphere is a hydrogen-comprising atmosphere.

33. The method recited in Claim 32, wherein the hydrogen-comprising atmosphere comprises at least about 4% hydrogen.

34. The method recited in Claim 33, wherein the hydrogen-comprising atmosphere comprises at least about 12% hydrogen.

35. The method recited in any one of Claims 25 to 34, wherein the refined magnetic powder comprises at least about 92 wt.% Nd2Fei4B magnetic crystals.

36. The method recited in Claim 35, wherein the refined magnetic powder comprises at least about 95 wt.% Nd2Fei4B magnetic crystals.

37. The method recited in Claim 36, wherein the refined magnetic powder comprises at least about 98 wt.% Nd2Fei4B magnetic crystals.

38. The method recited in any one of Claims 25 to 37, wherein the refined magnetic powder comprises not greater than about 8 wt.% NdFe4B4 crystals.

39. The method recited in Claim 38, wherein the refined magnetic powder comprises not greater than about 5 wt.% NdFe4B4 crystals.

40. The method recited in Claim 39, wherein the refined magnetic powder comprises not greater than about 2 wt.% NdFe4B4 crystals.

41. The method recited in any one of Claims 25 to 40, wherein the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals in the refined magnetic powder is at least about 20:1.

42. The method recited in Claim 41 , wherein the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals in the refined magnetic powder is at least about 25:1.

43. The method recited in any one of Claims 25 to 42, wherein the refined magnetic powder comprises substantially no iron.

44. The method recited in any one of Claims 25 to 43, wherein the refined magnetic powder comprises substantially no metal oxides.

45. The method recited in any one of Claims 25 to 44, wherein the refined magnetic powder comprises substantially no carbon.

46. The method recited in any one of Claims 25 to 45, wherein the refined magnetic powder comprises substantially no nitrogen.

47. The method recited in any one of Claims 25 to 46, wherein the refined magnetic powder has a mean average particle size of not greater than about 10 pm.

48. The method recited in Claim 47, wherein the refined magnetic powder has a mean average particle size of at least about 2 pm.

49. A magnetic powder, wherein the magnetic powder comprises Nd2Fei4B magnetic crystals and NdFe4B4 crystals is formed by a method recited in any one of Claims 25 to 49.

50. A method for the refinement of a magnetic powder comprising Nd2Fei4B magnetic crystals and NdFe4B4 crystals, comprising the steps of: admixing a magnetic powder comprising Nd2Fei4B magnetic crystals and NdFe4B4 crystals with iron metal powder, neodymium metal powder, neodymium oxide powder and calcium hydride powder to form a powder blend; compacting the powder blend to form a compacted powder blend body; heating the compacted powder blend body to a reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a consolidated powder body comprising Nd2Fei4B crystals, NdFe4B4 crystals and calcium oxide; milling the consolidated powder body to form a calcium-containing magnetic powder; andseparating the calcium oxide from the calcium-contaming rare earth magnetic powder to form a refined rare earth magnetic powder, wherein the refined rare earth magnetic powder comprises a higher mass ratio of Nd2Fei4B crystals to NdFe4B4 than the magnetic powder.51 . The method recited in Claim 50, wherein the compaction pressure is at least about 20 MPa.

52. The method recited in any one of Claims 50 or 51 , wherein the reaction temperature is at least about 750°C.

53. The method recited in any one of Claims 50 to 52, wherein the reaction temperature is at least about 780°C.

54. The method recited in any one of Claims 50 to 53, wherein the reaction temperature is not greater than about 850°C.

55. The method recited in any one of Claims 50 to 54, wherein the reaction pressure is at least about 4 bar (0.4 MPa).

56. The method recited in any one of Claims 50 to 55, wherein the reaction pressure is at least about 5 bar (0.5 MPa).

57. The method recited in any one of Claims 50 to 56, wherein the reaction atmosphere is a hydrogen-comprising atmosphere.

58. The method recited in Claim 57, wherein the hydrogen-comprising atmosphere comprises at least about 4% hydrogen.

59. The method recited in Claim 58, wherein the hydrogen-comprising atmosphere comprises at least about 12% hydrogen.

60. The method recited in any one of Claims 50 to 59, wherein the refined magnetic powder comprises at least about 92 wt.% Nd2Fei4B magnetic crystals.

61. The method recited in Claim 60, wherein the refined magnetic powder comprises at least about 95 wt.% Nd2Fei4B magnetic crystals.

62. The method recited in Claim 61 , wherein the refined magnetic powder comprises at least about 98 wt.% Nd2Fei4B magnetic crystals.

63. The method recited in any one of Claims 50 to 62, wherein the refined magnetic powder comprises not greater than about 8 wt.% NdFe4B4 crystals.

64. The method recited in Claim 63, wherein the refined magnetic powder comprises not greater than about 5 wt.% NdFe4B4 crystals.

65. The method recited in Claim 64, wherein the refined magnetic powder comprises not greater than about 2 wt.% NdFe4B4 crystals.

66. The method recited in any one of Claims 50 to 65, wherein the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals in the refined magnetic powder is at least about 20:1.

67. The method recited in Claim 66, wherein the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals in the refined magnetic powder is at least about 25:1.

68. The method recited in any one of Claims 50 to 67, wherein the refined magnetic powder comprises substantially no iron.

69. The method recited in any one of Claims 50 to 68, wherein the refined magnetic powder comprises substantially no metal oxides.

70. The method recited in any one of Claims 50 to 69, wherein the refined magnetic powder comprises substantially no carbon.

71. The method recited in any one of Claims 50 to 70, wherein the refined magnetic powder comprises substantially no nitrogen.

72. The method recited in any one of Claims 50 to 71 , wherein the refined magnetic powder has a mean average particle size of not greater than about 10 pm.

73. The method recited in Claim 72, wherein the refined magnetic powder has a mean average particle size of at least about 2 pm.

74. A magnetic powder, wherein the magnetic powder comprising Nd2Fei4B magnetic crystals and NdFe4B4 crystals is formed by a method recited in any one of Claims 50 to 73.

75. A method for the production of a rare earth magnetic material of the form Nd2Fei4B, comprising the steps of: admixing a neodymium borate powder (NdBOs), iron (Fe) powder, neodymium metal, neodymium oxide and calcium hydride to form a precursor powder; compacting the precursor powder under a compaction pressure to form a compacted precursor powder body; heating the compacted precursor powder body to a reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a consolidated powder body comprising a rare earth magnetic powder comprising Nd2Fei4B crystals and calcium oxide.

76. The method recited in Claim 75, wherein the compaction pressure is at least about 20 MPa.

77. The method recited in any one of Claims 75 or 76, wherein the reaction temperature is at least about 850°C.

78. The method recited in any one of Claims 75 to 77, wherein the reaction temperature is at least about 880°C.

79. The method recited in any one of Claims 75 to 78, wherein the reaction temperature is not greater than about 910°C.

80. The method recited in any one of Claims 75 to 79, wherein the reaction pressure is at least about 4 bar (0.4 MPa).

81. The method recited in any one of Claims 75 to 80, wherein the reaction pressure is at least about 5 bar (0.5 MPa).

82. The method recited in any one of Claims 75 to 81 , wherein the reaction atmosphere is a hydrogen-comprising atmosphere.

83. The method recited in Claim 82, wherein the hydrogen-comprising atmosphere comprises at least about 4% hydrogen.

84. The method recited in Claim 83, wherein the hydrogen-com prising atmosphere comprises at least about 12% hydrogen.

85. The method recited in any one of Claims 75 to 84, further comprising the step of milling the consolidated powder body to form a free-flowing powder mixture.

86. The method recited in Claim 85, further comprising the step of separating the calcium oxide from the free-flowing powder mixture to form a free-flowing rare earth magnetic powder that is substantially free of calcium.

87. The method recited in Claim 86, wherein the free-flowing rare earth magnetic powder comprises at least about 94 wt.% Nd2Fei4B magnetic crystals.

88. The method recited in Claim 87, wherein the free-flowing rare earth magnetic powder comprises at least about 96 wt.% Nd2Fei4B magnetic crystals.

89. The method recited in any one of Claims 86 to 88, wherein the free-flowing rare earth magnetic powder comprises not greater than about 0.5 wt.% NdFe4B4 magnetic crystals.

90. The method recited in Claim 89, wherein the free-flowing rare earth magnetic powder comprises not greater than about 0.3 wt.% NdFe4B4 magnetic crystals.91 . The method recited in any one of Claims 89 or 90, wherein the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals is at least about 20:1 .

92. The method recited in Claim 91 , wherein the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals is at least about 25:1.

93. The method recited in any one of Claims 86 to 92, wherein the free-flowing magnetic powder comprises substantially no iron.

94. The method recited in any one of Claims 86 to 93, wherein the free-flowing magnetic powder comprises substantially no carbon.

95. The method recited in any one of Claims 86 to 94, wherein the free-flowing magnetic powder comprises substantially no nitrogen.

96. The method recited in any one of Claims 75 to 95, wherein the rare earth borate powder and iron powder have a mean average particle size of not greater than about 10 pm.

97. The method recited in Claim 96, wherein the rare earth borate powder and iron powder have a mean average particle size of at least about 2 pm.

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