Rare earth materials and the production of rare earth materials

Abstract

Rare earth material and methods for the production of rare earth materials, wherein the method for the production of a rare earth magnetic material of the form ReFeB comprises the steps of: combining a rare earth borate powder (ReBOg). iron powder and calcium hydride to form a precursor powder; compacting the precursor powder under a compaction pressure; and heating the compacted precursor powder body, the method for the production of a rare earth magnetic material of the form ReFeB comprises the steps of: combining a rare earth boride powder (ReB) and iron powder to form a precursor powder; compacting the precursor powder; and heating the compacted precursor powder body, and the method for the production of a rare earth nitride material (ReN) comprises the steps of: combining a rare earth borate powder (ReBOg) with calcium hydride to form a precursor powder; introducing nitrogen into the precursor powder; compacting the nitrogen-rich precursor powder; and heating the compacted precursor powder block..

Description

RARE EARTH MATERIALS AND THE PRODUCTION OF RARE EARTH MATERIALSFIELD

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

[0002] In a first embodiment, A method for the production of a rare earth magnetic material of the form ReFeB is disclosed, where Re is a rare earth metal. The method includes the steps of combining a rare earth borate powder (ReBOs), iron 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 Re2Fei4B crystals and calcium oxide.

[0003] The foregoing method is subject to a number of refinements, characterizations and implementations, which may be applied to the foregoing method individually or in any combination.

[0004] In one refinement, Re is selected from the group consisting of Nd, Pr, Dy and combinations thereof. In a further refinement, Re comprises Nd.

[0005] In another refinement, the precursor powder further comprises at least one base metal powder selected from the group consisting of cobalt, copper and combinations thereof. In a further refinement, the compacted powder body further comprises at least one base metal selected from the group consisting of cobalt, copper and combinations thereof.

[0006] In another refinement, the compaction pressure is at least about 20 MPa.

[0007] In another refinement, the reaction temperature is at least about 850°C, such as at least about 880°C. In a further refinement, the reaction temperature is notgreater than about 910°C. In another refinement, the reaction pressure is at least about 4 bar (0.4 MPa), such as at least about 5 bar (0.5 MPa).

[0008] In another refinement, the reaction atmosphere is a hydrogen-com prising atmosphere. In a further refinement, the hydrogen-comprising atmosphere comprises at least about 4% hydrogen, such as at least about 12% hydrogen.

[0009] In another refinement, the rare earth borate powder and the iron powder that are combined with the calcium hydride are produced by a method comprising the steps of combining a rare earth borate powder with iron oxalate powder and heating the combined rare earth borate and iron oxalate powder to a reduction temperature that is sufficient to reduce the iron oxalate powder to iron powder. In a further refinement, reduction temperature is at least about 700°C.

[0010] In another refinement, the method further comprises the step of milling the consolidated powder body to form a free-flowing powder mixture. In a further refinement, the method also includes the step of separating the calcium oxide from the free-flowing powder mixture to form a free-flowing rare earth magnetic powder. In yet a further refinement, the step of separating the calcium oxide from the free-flowing powder mixture comprises washing the free-flowing magnetic powder with a dilute hydrochloric acid (HCI) solution.

[0011] In one characterization, the free-flowing magnetic powder comprises Nd2Fei4B magnetic crystals. In another characterization, the free-flowing magnetic powder comprises at least about 60 wt.% Nd2Fei4B magnetic crystals, such as at least about 70 wt.% Nd2Fei4B magnetic crystals, such as at least about 75 wt.% Nd2Fei4B magnetic crystals. In another characterization, the free-flowing magnetic powder further comprises NdFe4B4 crystals. In one characterization, the free-flowing magnetic powder comprises not greater than about 15 wt.% NdFe4B4 crystals. In another characterization, the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals is at least about 50:3. In another characterization, the free-flowing magnetic powder comprises a-iron, and in a particular characterization comprises not greater than about 4 wt.% a- iron. In another characterization, the free-flowing magnetic powder further comprises Pr2Fei4B magnetic crystals. In yet another characterization, the free-flowing magnetic powder further comprises Dy2Fei4B magnetic crystals.

[0012] In another embodiment, a method for the production of a rare earth magnetic material of the form ReFeB is disclosed, where Re is a rare earth metal. The method comprises the steps of combining a rare earth boride powder (ReB) and iron powder to form a precursor powder, compacting the precursor powder under a compaction pressure to form a compacted precursor powder body and 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 Re2Fei4B crystals.

[0013] The foregoing method is subject to a number of refinements, characterizations and implementations, which may be applied to the foregoing method individually or in any combination.

[0014] In one refinement, Re is selected from the group consisting of Nd, Pr, Dy and combinations thereof. In one particular refinement, Re comprises Nd.

[0015] In another refinement, the precursor powder further comprises at least one base metal selected from the group consisting of cobalt, copper and combinations thereof. In a further refinement, the compacted powder body further comprises at least one base metal selected from the group consisting of cobalt, copper and combinations thereof.

[0016] In another refinement, the compaction pressure is at least about 20 MPa. In another refinement, the reaction temperature is at least about 850°C, such as at least about 880°C. In another refinement, the reaction temperature is not greater than about 910°C.

[0017] In another refinement, the reaction pressure is at least about 4 bar (0.4 MPa), such as at least about 5 bar (0.5 MPa). In another refinement, the reaction atmosphere is a hydrogen-comprising atmosphere. In a further refinement, the hydrogen-comprising atmosphere comprises at least about 12% hydrogen.

[0018] In one characterization, the compacted powder body comprises substantially no calcium.

[0019] In a further refinement, the method also includes the step of milling the consolidated powder body to form a free-flowing magnetic powder.

[0020] In one characterization, the free-flowing magnetic powder comprises Nd2Fei4B magnetic crystals. In a further characterization, the free-flowing magnetic powder comprises at least about 60 wt.% Nd2Fei4B magnetic crystals, such as at least about 70 wt.% Nd2Fei4B magnetic crystals, such as at least about 75 wt.% Nd2Fei4B magnetic crystals.

[0021] In another characterization, the free-flowing magnetic powder further comprises NdFe4B4 crystals. In yet another characterization, the free-flowing magnetic powder comprises not greater than about 15 wt.% NdFe4B4 crystals. In yet another characterization, the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals is at least about 50:3. In another characterization, the free-flowing magnetic powder further comprises a-iron, such as not greater than about 4 wt.% a-iron.

[0022] In another characterization, the free-flowing magnetic powder further comprises Pr2Fei4B magnetic crystals. In another characterization, the free-flowing magnetic powder further comprises Dy2Fei4B magnetic crystals.

[0023] In another embodiment, a sintered rare earth magnetic body is disclosed. The sintered rare earth magnetic body comprises at least about 75 wt.% Re2Fei4B magnetic crystals and not greater than about 11 wt.% ReFe4B4 crystals, wherein Re is selected from the group consisting of Nd, Pr, Dy and combinations thereof.

[0024] The foregoing sintered rare earth magnetic body is subject to a number of refinements, characterizations and implementations, which may characterize the foregoing sintered rare earth magnetic body individually or in any combination.

[0025] In one characterization, the sintered rare earth magnetic body magnetic body comprises at least about 78 wt.% Re2Fei4B magnetic crystals, such as at least about 80 wt.% Re2Fei4B magnetic crystals. In another characterization, the sintered rare earth magnetic body magnetic body comprises not greater than about 8 wt.% ReFe4B4 crystals. In yet another characterization, the sintered rare earth magnetic body magnetic body comprises not greater than about 1 wt.% (Nd,Pr,Dy)2Fei4B crystals.

[0026] In another characterization, the sintered rare earth magnetic body magnetic body comprises not greater than about 4 wt.% a-iron, such as not greater than about 2 wt.% a-iron.

[0027] In another characterization, the sintered rare earth magnetic body has a magnetic coercivity of at least about 0.85T. In yet another characterization, the sintered rare earth magnetic body has a magnetic remanence of at least about 0.75T.

[0028] In another embodiment, a method for the production of a rare earth nitride material (ReN, where Re is a rare earth metal) is disclosed. The method includes the steps of combining a rare earth borate powder (ReBOs) with calcium hydride to form a precursor powder, introducing nitrogen into the precursor powder to form a nitrogen- rich precursor powder, compacting the nitrogen-rich precursor powder to form a compacted precursor powder block, and heating the compacted precursor powder block to a reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a rare earth nitride material (ReN).

[0029] The foregoing method for the production of a rare earth nitride material is subject to a number of refinements, characterizations and implementations, which may be applied to the foregoing method individually or in any combination.

[0030] In one refinement, Re is selected from the group consisting of Nd, Pr, La, Y, Sc, Sm and combinations thereof.

[0031] In another refinement, the step of introducing nitrogen into the precursor powder comprises heating the precursor powder in a nitrogen-containing atmosphere. In a further refinement, the nitrogen-containing atmosphere comprises at least about 98% nitrogen.

[0032] In another refinement, the step of heating the precursor powder in a nitrogen-containing atmosphere comprises heating the precursor powder under a pressure of at least about 4 bar (0.4 MPa). In another refinement, the step of heating the precursor powder in a nitrogen-containing atmosphere comprises heating the precursor powder to a temperature of at least about 200°C.

[0033] In yet another refinement, the step of compacting the powder mixture comprises compacting the nitrogen-rich precursor powder at a pressure of at least about 20 MPa. In another refinement, the step of heating the compacted precursor powder block comprises heating the compacted precursor powder block to a temperature of at least about 850°C. In a further refinement, the step of heating the compacted precursor powder block comprises heating the compacted precursorpowder block under a pressure of at least about 4 bar (0.4 MPa). In another refinement, the step of heating the compacted precursor powder block comprises heating the compacted precursor powder block under a hydrogen-comprising atmosphere.

[0034] In one characterization, the rare earth nitride material comprises calcium oxide. In another characterization, the rare earth nitride material comprises residual nitrogen-rich borate. In one refinement, the method further comprises the step of separating the calcium oxide and / or the residual nitrogen-rich borate from the rare earth nitride. In one particular refinement, the method includes the step of separating the calcium oxide and / or the residual nitrogen-rich borate by contacting the rare earth nitride material with a dilute hydrochloric acid solution.

[0035] These and other embodiments of the present disclosure will be apparent from the following description.DESCRIPTION

[0036] The present disclosure is directed to the production of rare earth materials and rare earth materials having desirable properties for a variety of applications.

[0037] In one embodiment, the present disclosure is directed to a method for the production of a rare earth magnetic material of the form RexFeyBz from rare earth borate powder (ReBOs).NdBOs + Ca + Fe -> Re2Fei4B + NdFe4B4 + CaO

[0038] The method is particularly suitable for the production of a magnetic material comprising a substantial concentration of Re2Fei4B magnetic crystals, e.g., tetragonal crystals of Re2Fei4B. As used herein, Re can be any rare earth element. In a particular characterization, Re is selected from the group consisting of neodymium (Nd), praseodymium (Pr), dysprosium (Dy) and combinations thereof. Thus, in this characterization, the magnetic crystals may include Nd2Fei4B magnetic crystals, Pr2Fei4B magnetic crystals and Dy2Fei4B magnetic crystals, including combinations of these magnetic crystals. In one refinement, the magnetic material may predominantly comprise Nd2Fei4B. As used herein, the term magnetic material may refer to a material in a variety of forms, such as a consolidated powder body, a free- flowing powder (e.g., a powder batch) or a sintered magnetic body.

[0039] According to this embodiment, the method includes combining a rare earth borate powder (ReBOs), iron powder (Fe) and calcium hydride (CaFh) to form a precursor powder. The precursor powder is compacted under a compaction pressure to form a compacted precursor powder body. Thereafter, the compacted precursor powder body is heated to reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a consolidated powder body comprising rare earth magnetic powder crystals Re2Fei4B and calcium oxide (CaO). As is discussed below, the CaO may be separated from the rare earth magnetic powder crystals.

[0040] The precursor powder may also include other metals, including base metals. For example, the precursor powder may include base metals such as cobalt, copper and combinations thereof. As a result, the compacted powder body and the consolidated powder body will also include cobalt, copper and combinations thereof. Typically, such additional metals will be present in low concentrations such as at least not greater than 1 wt.%.

[0041] 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 20 MPa, or at least about 24 MPa. Typically, the compaction pressure will not need to 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.

[0042] After compaction, the compacted precursor body is reacted to form a consolidated powder body comprising the rare earth magnetic crystals Nd2Fei4B. 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. Keeping the reaction temperature below 910°C will deter the formation of nonmagnetic iron species such as y-Fe. In one particular refinement, the reaction temperature is about 900°C.

[0043] The reaction is also carried out under a reaction pressure, and in one characterization is carried out under a reaction pressure that is greater thanatmospheric pressure, i.e., 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.

[0044] To facilitate the reaction to form the Re2Fei4B magnetic material from the rare earth borate powder (ReBOs), 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 refinement, 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.

[0045] The foregoing reaction conditions are conducive to the formation of a magnetic material that predominately comprises Re2Fei4B and comprises very small concentrations of non-magnetic phases.

[0046] The rare earth borate powder (ReBOs) and the iron powder supplied to the compaction step with the calcium hydride may be procured by the manufacturer, e.g., from a third-party. However, there are self-ignition risks with the storage of fine particle size iron. In one implementation of the foregoing method the rare earth borate powder and the iron powder are produced by a method that includes the steps of combining a rare earth borate powder with iron oxalate powder (FeC2O4) and heating the combined rare earth borate and iron oxalate powder to a reduction temperature that is sufficient to reduce the iron oxalate powder to iron powder.

[0047] Because the formed iron powder will be diluted with the rare earth borate powder, the risk of self-ignition of the iron powder will be diminished even though the formed iron particles may have a very small mean particle size of not greater than about 10 pm, such as not greater than about 8 pm or even not greater than about 6 pm. In one implementation, the reduction temperature is at least about 700°C. It will be appreciated that if small amounts of base metals such as copper (Cu) and cobalt (Co) are desired in the final magnetic powder, they may be introduced with the iron oxalate, e.g., in the form of copper oxalate (CUC2O4) or cobalt oxalate (COC2O4).

[0048] The consolidated powder body 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 Re2Fei4B powder and calcium oxide powder. Thereafter, the calcium oxide may be separated from the remainder of the powder, e.g., from the Re2Fei4B powder, to form a free-flowing rare earth magnetic powder that is substantially free of calcium. In one characterization, the separation of the calcium oxide from the free-flowing powder mixture includes washing the free- flowing magnetic powder with an aqueous solution, such as a dilute hydrochloric acid (HCI) solution that will soluble the calcium oxide without substantially degrading the remaining components of the free-flowing.

[0049] The magnetic material, e.g., the free flowing rare earth magnetic powder, may advantageously have a high concentration of the Re2Fei4B magnetic phase, e.g., Nd2Fei4B tetragonal magnetic crystals and a relatively low concentration of nonmagnetic phases. For example, the magnetic material may be substantially free of the non-magnetic phases Fe2B and FeNds. Further, the magnetic material may be substantially free of oxide phases such as Nd20s, NdO and NdFeO. The magnetic material may comprise little to no free neodymium, praseodymium or dysprosium.

[0050] In one characterization, the free-flowing magnetic powder comprises at least about 60 wt.% Nd2Fei4B magnetic crystals, such as at least about 70 wt.% Nd2Fei4B magnetic crystals, such as at least about 75 wt.% Nd2Fei4B magnetic crystals or even at least about 80 wt.% Nd2Fei4B magnetic crystals. In another characterization, the free-flowing magnetic powder further comprises a relatively low concentration of NdFe4B4 crystals. In one refinement, the free-flowing magnetic powder comprises not greater than about 15 wt.% NdFe4B4 crystals, such as not greater than about 11 wt.% NdFe4B4 crystals. In yet another characterization, the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals is at least about 50:3.

[0051] The free-flowing magnetic powder may also comprise a-iron, and in one characterization the free-flowing magnetic powder comprises not greater than about 4 wt.% a-iron, a magnetic allotrope of iron. In one characterization, the free-flowing magnetic powder comprises substantially no y-iron, which is a non-magnetic allotrope of iron.

[0052] As is discussed above, the free-flowing magnetic powder may also include a combination of Re2Fei4B magnetic crystals. For example, the Nd2Fei4B magnetic powder may also include Pr2Fei4B magnetic crystals and / or Dy2Fei4B magnetic crystals. In one characterization, the magnetic powder comprises very low concentrations of mixed phase Re2Fei4B crystals in which Nd atoms are substituted by other rare earth atoms, e.g., (Nd,Pr,Dy)2Fei4B, exist in the free flowing magnetic powder.

[0053] As will be appreciated by those of skill in the art, the free-flowing magnetic powder 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. It is often desirable to machine the rare earth magnet body to a desired shape. In this regard, the Re2Fei4B magnetic phase has a high hardness and may be difficult to machine if the concentration of Re2Fei4B is too high. In this regard, relatively low concentrations of some of the foregoing “soft” phases, such as a-iron, may be desirable in the rare earth magnetic body to facilitate the machining of the body.

[0054] In a further embodiment, another method for the production of a rare earth magnetic material of the form ReFeB from rare earth boride powder (ReB) is disclosed.ReB + Fe = Re2Fei4B + ReFe4B4

[0055] In this embodiment, the rare earth magnetic material is formed directly from rare earth boride powder (ReB). The method includes the steps of combining a rare earth boride powder (ReB) and iron powder to form a precursor powder. The precursor powder is compacted under a compaction pressure to form a compacted precursor powder body. Subsequently, 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 Re2Fei4B crystals. As with the embodiment disclosed above, this method is particularly suitable for the production of a magnetic material comprising a substantial concentration of Re2Fei4B magnetic crystals, e.g., tetragonal crystals of Re2Fei4B. In a particularcharacterization, Re is selected from the group consisting of neodymium (Nd), praseodymium (Pr), dysprosium (Dy) and combinations thereof. Thus, the magnetic crystals may include Nd2Fei4B magnetic crystals, Pr2Fei4B magnetic crystals and Dy2Fei4B magnetic crystals, including combinations of these magnetic crystals. In one refinement, the magnetic material may predominantly comprise Nd2Fei4B. As used herein, the term magnetic material may refer to a material in a variety of forms, such as a consolidated powder body, a free-flowing powder (e.g., a powder batch) or a sintered magnetic body.

[0056] In one characterization, the precursor powder includes at least one base metal selected from the group consisting of cobalt, copper and combinations thereof. As a result, the compacted powder body further comprises at least one base metal selected from the group consisting of cobalt, copper and combinations thereof.

[0057] In one characterization, the precursor powder is compacted to form the compacted precursor powder body at a compaction pressure of at least about 15 MPa, such as at least about 20 MPa, or at least about 24 MPa. Typically, the compaction pressure will not need to 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 powder body may take a variety of forms, such as blocks, disks, pellets and the like.

[0058] After compaction, the compacted precursor powder body is reacted to form a consolidated powder body comprising the rare earth magnetic crystals, e.g., Nd2Fei4B. In one characterization, the compacted precursor powder 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. Keeping the reaction temperature below 910°C will deter the formation of non-magnetic iron species such as y-Fe. In one particular refinement, the reaction temperature is about 900°C.

[0059] The reaction is also 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., 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 asat least about 0.5 MPa. The reaction atmosphere may be a hydrogen-com prising atmosphere.

[0060] To facilitate the reaction to form the Re2Fei4B magnetic material from the ReB powder and iron 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. In one refinement, 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.

[0061] One advantage of forming Re2Fei4B magnetic materials from ReB and Fe powders is that a reductant such as calcium is not required. That is, the compacted powder body comprises substantially no calcium and preferably is free from calcium. This advantageously eliminates the need to wash the powder in an aqueous solution to remove the calcium.

[0062] The consolidated powder body 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.

[0063] The magnetic material, e.g., the free flowing rare earth magnetic powder, may advantageously have a high concentration of the Re2Fei4B magnetic phase, e.g., Nd2Fei4B tetragonal magnetic crystals and a relatively low concentration of nonmagnetic phases. For example, the magnetic material may be substantially free of the non-magnetic phases Fe2B and FeNds. Further, the magnetic material may be substantially free of oxide phases such as Nd20s, NdO and NdFeO. The magnetic material may comprise little to no free neodymium, praseodymium or dysprosium.

[0064] In one characterization, the free-flowing rare earth magnetic powder comprises at least about 60 wt.% Nd2Fei4B magnetic crystals, such as at least about 70 wt.% Nd2Fei4B magnetic crystals, such as at least about 75 wt.% Nd2Fei4B magnetic crystals or even at least about 80 wt.% Nd2Fei4B magnetic crystals. In another characterization, the free-flowing rare earth magnetic powder further comprises a relatively low concentration of NdFe4B4 crystals. In one refinement, thefree-flowing rare earth magnetic powder comprises not greater than about 15 wt.% NdFe4B4 crystals, such as not greater than about 11 wt.% NdFe4B4 crystals. In yet another characterization, the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals is at least about 50:3.

[0065] The free-flowing rare earth magnetic powder may also comprise a-iron, and in one characterization the free-flowing magnetic powder comprises not greater than about 4 wt.% a-iron, a magnetic allotrope of iron. In one characterization, the free- flowing magnetic powder comprises substantially no y-iron, which is a non-magnetic allotrope of iron.

[0066] As is discussed above, the free-flowing rare earth magnetic powder may also include a combination of Re2Fei4B magnetic crystals. For example, the Nd2Fei4B magnetic powder may also include Pr2Fei4B magnetic crystals and / or Dy2Fei4B magnetic crystals. In one characterization, the rare earth magnetic powder comprises very low concentrations of mixed phase Re2Fei4B crystals in which Nd atoms are substituted by other rare earth atoms, e.g., (Nd,Pr,Dy)2Fei4B, exist in the free flowing magnetic powder.

[0067] As will be appreciated by those of skill in the art, the free-flowing magnetic rare earth powder 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. It is often desirable to machine the rare earth magnet body to a desired shape. In this regard, the Re2Fei4B magnetic phase has a high hardness and may be difficult to machine if the concentration of Re2Fei4B is too high. In this regard, relatively low concentrations of some of the foregoing “soft” phases, such as a-iron, may be desirable in the rare earth magnetic body to facilitate the machining of the body.

[0068] Other modifications to the foregoing method for producing Re2Fei4B magnetic material from rare earth borides and iron powder are contemplated. For example, other rare earth borides such as NdB4, NdBs and / or NdBe could be used inthe precursor powder to substitute for some or all of the NdB. However, it is believed that the use of NdB reduces the formation of the NdFe4B4 phase in the final powder.

[0069] Another embodiment of the present disclosure is directed to sintered rare earth magnetic bodies.

[0070] The sintered rare earth magnetic bodies may be fabricated, for example, by compacting, sintering and magnetizing the free-slowing rare earth magnetic powders produced according to the foregoing embodiments.

[0071] In one characterization, a sintered rare earth magnetic body comprises at least about 75 wt.% Re2Fei4B magnetic crystals and not greater than about 11 wt.% ReFe4B4 crystals, where Re is selected from the group consisting of Nd, Pr, Dy and combinations thereof. For example, the sintered rare earth magnetic body may comprise at least about 78 wt.% Re2Fei4B magnetic crystals, such as at least about 80 wt.% Re2Fei4B magnetic crystals. In another characterization, the sintered magnetic body comprises not greater than about 8 wt.% ReFe4B4 crystals, such as not greater than about 8 wt.% ReFe4B4 crystals.

[0072] The hard magnetic material Re2Fei4B constitutes the largest magnetic portion in the sintered magnetic body, as is disclosed above. The soft phases of the sintered magnetic body comprise the tetrahedral magnetic crystals of ReFe4B4, e.g., not greater than about 9 wt. % of the sintered magnetic body, such as not greater than about 7 wt.% of the of the sintered magnetic body. The soft phases of the sintered magnetic body may also include traces of non-magnetic materials such as NdO, Nd2Os or NdFeO, which may comprise not greater than about 0.1 wt.% of the sintered magnetic body.

[0073] In another characterization, the sintered rare earth magnetic body comprises not greater than about 4 wt.% a-iron, such as not greater than about 2 wt.% a-iron.

[0074] The sintered rare earth magnetic body may also be characterized as having a magnetic coercivity of at least about 0.85T (Tesla). The sintered rare earth magnetic body may also be characterized as having a magnetic remanence of at least about 0.75T.

[0075] Another embodiment of the present disclosure is directed to a method for the production of a rare earth nitride material (ReN). This method may utilize the reaction:

[0076] The method includes the steps of combining a rare earth borate powder (ReBOs) with calcium hydride to form a precursor powder. Nitrogen is introduced into the precursor powder to form a nitrogen-rich precursor powder. The nitrogen-rich precursor powder is compacted to form a compacted precursor powder body, which is heated to a reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a rare earth nitride material (ReN).

[0077] In one characterization, the rare earth metal Re is selected from the group consisting of Nd, Pr, La, Y, Sc, Sm and combinations thereof.

[0078] In another characterization, the step of introducing nitrogen into the precursor powder comprises heating the precursor powder in a nitrogen-containing atmosphere, e.g., in a nitrogen atmosphere comprising at least about 98% nitrogen. The heating of the precursor powder in the nitrogen-containing atmosphere may be carried out at an elevated temperature, such as at least about 180°C, such as at least about 200°C. The introduction of nitrogen may also be carried out under an elevated pressure, e.g., above atmospheric pressure, and in one characterization is carried out under a pressure that is at least about 0.3 MPa, such as at least about 0.4 MPa, such as at least about 0.5 MPa.

[0079] The reaction temperature may be at least about 850°C, such as at least about 880°C or even at least about 900°C.

[0080] The compaction pressure may be at least about 15 MPa, such as at least about 20 MPa, or at least about 24 MPa. Typically, the compaction pressure will not need to 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 powder body may take a variety of forms, such as blocks, disks, pellets and the like.

[0081] The reaction atmosphere may be a reducing atmosphere. For example, the reaction atmosphere may be a vacuum atmosphere. In one characterization, thereaction atmosphere is a hydrogen-comprising atmosphere. In one refinement, 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.

[0082] The rare earth nitride material comprises calcium oxide and residual nitrogen-rich borate as is shown above. In this regard, the method may include separating the calcium oxide and / or the residual nitrogen-rich borate from the rare earth nitride. In one characterization, the calcium oxide and / or the residual nitrogen- rich borate is separated by contacting the rare earth nitride material with a dilute hydrochloric acid solution to selectively solubilize the calcium oxide and / or the residual nitrogen-rich borate.

[0083] While various embodiments of rare earth materials and methods for the production of rare earth 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, 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 ReFeB, comprising the steps of: combining a rare earth borate powder (ReBOs), iron 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 Re2Fei4B crystals and calcium oxide.

2. The method recited in Claim 1 , wherein Re is selected from the group consisting of Nd, Pr, Dy and combinations thereof.

3. The method recited in Claim 2, wherein Re comprises Nd.

4. The method recited in any one of Claims 1 to 3, wherein the precursor powder further comprises at least one base metal powder selected from the group consisting of cobalt, copper and combinations thereof.

5. The method recited in Claim 4, wherein the compacted powder body further comprises at least one base metal selected from the group consisting of cobalt, copper and combinations thereof.

6. The method recited in any one of Claims 1 to 5, wherein the compaction pressure is at least about 20 MPa.

7. The method recited in any one of Claims 1 to 6, wherein the reaction temperature is at least about 850°C.

8. The method recited in any one of Claims 1 to 7, wherein the step of reaction temperature is at least about 880°C.

9. The method recited in any one of Claims 1 to 8, wherein the reaction temperature is not greater than about 910°C.

10. The method recited in any one of Claims 1 to 9, wherein the reaction pressure is at least about 4 bar (0.4 MPa).

11. The method recited in any one of Claims 1 to 10, wherein the reaction pressure is at least about 5 bar (0.5 MPa).

12. The method recited in any one of Claims 1 to 21 , wherein the reaction atmosphere is a hydrogen-comprising atmosphere.

13. The method recited in Claim 12, wherein the hydrogen-comprising atmosphere comprises at least about 4% hydrogen.

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

15. The method recited in any one of Claims 1 to 14, wherein the rare earth borate powder and the iron powder that are combined with the calcium hydride are produced by a method comprising the steps of: combining a rare earth borate powder with iron oxalate powder; and heating the combined rare earth borate and iron oxalate powder to a reduction temperature that is sufficient to reduce the iron oxalate powder to iron powder.

16. The method recited in Claim 15, wherein the reduction temperature is at least about 700°C.

17. The method recited in any one of Claims 1 to 16, further comprising the step of milling the consolidated powder body to form a free-flowing powder mixture.

18. The method recited in Claim 16, further comprising the step of separating the calcium oxide from the free-flowing powder mixture to form a free-flowing rare earth magnetic powder.

19. The method recited in Claim 18, wherein the step of separating the calcium oxide from the free-flowing powder mixture comprises washing the free- flowing magnetic powder with a dilute hydrochloric acid (HCI) solution.

20. The method recited in any one of Claims 1 to 19, wherein the free-flowing magnetic powder comprises Nd2Fei4B magnetic crystals.

21. The method recited in Claim 20, wherein the free-flowing magnetic powder comprises at least about 60 wt.% Nd2Fei4B magnetic crystals.

22. The method recited in Claim 20, wherein the free-flowing magnetic powder comprises at least about 70 wt.% Nd2Fei4B magnetic crystals.

23. The method recited in Claim 20, wherein the free-flowing magnetic powder comprises at least about 75 wt.% Nd2Fei4B magnetic crystals.

24. The method recited in any one of Claims 20 to 23, wherein the free- flowing magnetic powder further comprises NdFe4B4 crystals.

25. The method recited in Claim 24, wherein the free-flowing magnetic powder comprises not greater than about 15 wt.% NdFe4B4 crystals.

26. The method recited in any one of Claims 24 or 25, wherein the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals is at least about 50:3.

27. The method recited in any one of Claims 20 to 26, wherein the free- flowing magnetic powder comprises a-iron.

28. The method recited in Claim 27, wherein the free-flowing magnetic powder comprises not greater than about 4 wt.% a-iron.

29. The method recited in any one of Claims 20 to 28, wherein the free- flowing magnetic powder further comprises Pr2Fei4B magnetic crystals.

30. The method recited in any one of Claims 20 to 29, wherein the free- flowing magnetic powder further comprises Dy2Fei4B magnetic crystals.31 . A method for the production of a rare earth magnetic material of the form ReFeB, comprising the steps of: combining a rare earth boride powder (ReB) and iron powder 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 thatare sufficient to form a consolidated powder body comprising Re2Fei4B crystals.

32. The method recited in Claim 31 , wherein Re is selected from the group consisting of Nd, Pr, Dy and combinations thereof.

33. The method recited in Claim 32, wherein Re comprises Nd.

34. The method recited in any one of Claims 31 to 33, wherein the precursor powder further comprises at least one base metal selected from the group consisting of cobalt, copper and combinations thereof.

35. The method recited in Claim 34, wherein the compacted powder body further comprises at least one base metal selected from the group consisting of cobalt, copper and combinations thereof.

36. The method recited in any one of Claims 31 to 35, wherein the compaction pressure is at least about 20 MPa.

37. The method recited in any one of Claims 31 to 36, wherein the reaction temperature is at least about 850°C.

38. The method recited in any one of Claims 31 to 37, wherein the reaction temperature is at least about 880°C.

39. The method recited in any one of Claims 31 to 38, wherein the reaction temperature is not greater than about 910°C.

40. The method recited in any one of Claims 31 to 39, wherein the reaction pressure is at least about 4 bar (0.4 MPa).41 . The method recited in any one of Claims 31 to 40, wherein the reaction pressure is at least about 5 bar (0.5 MPa).

42. The method recited in any one of Claims 31 to 41 , wherein the reaction atmosphere is a hydrogen-comprising atmosphere.

43. The method recited in Claim 42, wherein the hydrogen-comprising atmosphere comprises at least about 12% hydrogen.

44. The method recited in any one of Claims 31 to 43, wherein the compacted powder body comprises substantially no calcium.

45. The method recited in any one of Claims 31 to 34, further comprising the step of milling the consolidated powder body to form a free-flowing magnetic powder.

46. The method recited in any one of Claims 31 to 45, wherein the free- flowing magnetic powder comprises Nd2Fei4B magnetic crystals.

47. The method recited in Claim 46, wherein the free-flowing magnetic powder comprises at least about 60 wt.% Nd2Fei4B magnetic crystals.

48. The method recited in Claim 46, wherein the free-flowing magnetic powder comprises at least about 70 wt.% Nd2Fei4B magnetic crystals.

49. The method recited in Claim 46, wherein the free-flowing magnetic powder comprises at least about 75 wt.% Nd2Fei4B magnetic crystals.

50. The method recited in any one of Claims 46 to 49, wherein the free- flowing magnetic powder further comprises NdFe4B4 crystals.

51. The method recited in Claim 50, wherein the free-flowing magnetic powder comprises not greater than about 15 wt.% NdFe4B4 crystals.

52. The method recited in any one of Claims 50 to 51 , wherein the mass ratio of Nd2Fei4B crystals to NdFe4B4 crystals is at least about 50:3.

53. The method recited in any one of Claims 45 to 52, wherein the free- flowing magnetic powder further comprises a-iron.

54. The method recited in Claim 53, wherein the free-flowing magnetic powder comprises not greater than about 4 wt.% a-iron.

55. The method recited in any one of Claims 45 to 54, wherein the free- flowing magnetic powder further comprises Pr2Fei4B magnetic crystals.

56. The method recited in any one of Claims 45 to 56, wherein the free- flowing magnetic powder further comprises Dy2Fei4B magnetic crystals.

57. A method for the production of a rare earth nitride material (ReN), comprising the steps of: combining a rare earth borate powder (ReBOs) with calcium hydride to form a precursor powder;introducing nitrogen into the precursor powder to form a nitrogen-rich precursor powder; compacting the nitrogen-rich precursor powder to form a compacted precursor powder block; and heating the compacted precursor powder block to a reaction temperature, under a reaction pressure and under a reaction atmosphere that are sufficient to form a rare earth nitride material (ReN).

58. The method recited in Claim 57, wherein Re is selected from the group consisting of Nd, Pr, La, Y, Sc, Sm and combinations thereof.

59. The method recited in any one of Claims 57 or 58, wherein the step of introducing nitrogen into the precursor powder comprises heating the precursor powder in a nitrogen-containing atmosphere.

60. The method recited in Claim 59, wherein the nitrogen containing atmosphere comprises at least about 98% nitrogen.61 . The method recited in any one of Claims 59 to 60, wherein the step of heating the precursor powder in a nitrogen-containing atmosphere comprises heating the precursor powder under a pressure of at least about 4 bar (0.4 MPa).

62. The method recited in any one of Claims 59 to 61 , wherein the step of heating the precursor powder in a nitrogen-containing atmosphere comprises heating the precursor powder to a temperature of at least about 200°C.

63. The method recited in any one of Claims 57 to 62, wherein the step of compacting the powder mixture comprises compacting the nitrogen-rich precursor powder at a pressure of at least about 20 MPa.

64. The method recited in any one of Claims 57 to 63, wherein the step of heating the compacted precursor powder block comprises heating the compacted precursor powder block to a temperature of at least about 850°C.

65. The method recited in any one of Claims 57 to 64, wherein the step of heating the compacted precursor powder block comprises heating the compacted precursor powder block under a pressure of at least about 4 bar (0.4 MPa).

66. The method recited in any one of Claims 57 to 65 wherein the step of heating the compacted precursor powder block comprises heating the compacted precursor powder block under a hydrogen-comprising atmosphere.

67. The method recited in any one of Claims 57 to 66, wherein the rare earth nitride material comprises calcium oxide.

68. The method recited in Claim 67, wherein the rare earth nitride material comprises residual nitrogen-rich borate.

69. The method recited in any one of Claims 67 or 68, further comprising the step of separating the calcium oxide and / or the residual nitrogen-rich borate from the rare earth nitride.

70. The method recited in Claim 69, wherein the step of separating the calcium oxide and / or the residual nitrogen-rich borate comprises contacting the rare earth nitride material with a dilute hydrochloric acid solution.71 . A sintered rare earth magnetic body, comprising: at least about 75 wt.% Re2Fei4B magnetic crystals; and not greater than about 11 wt.% ReFe4B4 crystals, wherein Re is selected from the group consisting of Nd, Pr, Dy and combinations thereof.

72. The sintered rare earth magnetic body recited in Claim 71 , wherein the sintered rare earth magnetic body comprises at least about 78 wt.% Re2Fei4B magnetic crystals.

73. The sintered rare earth magnetic body recited in Claim 72, wherein the sintered rare earth magnetic body comprises at least about 80 wt.% Re2Fei4B magnetic crystals.

74. The sintered rare earth magnetic body recited in any one of Claims 71 to 73, wherein the sintered rare earth magnetic body comprises not greater than about 8 wt.% ReFe4B4 crystals.

75. The sintered rare earth magnetic body recited in any one of Claims 71 to 74, wherein the sintered rare earth magnetic body comprises not greater than about1 wt.% (Nd,Pr,Dy)2Fei4B crystals.

76. The sintered rare earth magnetic body recited in any one of Claims 71 to 75, wherein the sintered rare earth magnetic body comprises not greater than about 4 wt.% a-iron.

77. The sintered rare earth magnetic body recited in any one of Claims 71 to 76, wherein the sintered rare earth magnetic body comprises not greater than about2 wt.% a-iron.

78. The sintered rare earth magnetic body recited in any one of Claims 71 to 77, wherein the sintered rare earth magnetic body has a magnetic coercivity of at least about 0.85T.

79. The sintered rare earth magnetic body recited in any one of Claims 71 to 78, wherein the sintered rare earth magnetic body has a magnetic remanence of at least about 0.75T.