Rare earth magnetic materials and the production of rare earth magnetic materials

Abstract

Sintered rare earth magnetic bodies and methods for the production of a sintered rare earth magnetic body. The sintered rare earth magnetic body may comprise a high concentration of magnetic crystals such as Re2Co17 magnetic crystals, where Re is a rare earth metal selected from Sm and Nd.

Description

PCT Patent ApplicationAttorney Ref. 51370-00038RARE EARTH MAGNETIC MATERIALS AND THE PRODUCTION OF RARE EARTH MAGNETIC MATERIALSFIELD

[0001] The present disclosure relates to the field of rare earth magnetic materials, and in particular to binary rare earth magnetic materials such as S1T12C017 and Nd2Fei7.SUMMARY

[0002] In one embodiment, a method for the production of a rare earth magnetic material of the form Re2Coi7 (where Re is a rare earth metal) is disclosed. The metho includes the steps of preparing a rare earth oxide powder comprising a rare earth oxide powder (Re2Os), cobalt powder (Co) and calcium hydride (CaH2), compacting the rare earth oxide powder under a compaction pressure to form a compacted rare earth oxide powder body, and heating the compacted rare earth oxide 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 Re2Coi7 and calcium oxide powder CaO.

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

[0004] In one refinement, Re is selected from the group consisting of samarium (Sm) and neodymium (Nd). In a further refinement, Re is samarium (Sm).

[0005] In another refinement, the rare earth oxide powder (Re2Os) and cobalt powder (Co) are formed by combining a rare earth oxalate powder (Re2(C2CM)3 and cobalt oxalate (COC2O4) to form an oxalate precursor powder and heating the oxalate precursor powder to a conversion temperature, under a conversion pressure and under a conversion atmosphere to form a rare earth oxide powder comprising rare earth oxide powder (Re2Os) and cobalt powder (Co). In a further refinement, the conversion temperature is at least about 800°C. In yet a further refinement, the conversion temperature is not greater than about 900°C. In yet another refinement, the conversion pressure is at least about 2 bar. In a further refinement, the conversion pressure is not greater than about 5.5 bar.PCT Patent ApplicationAttorney Ref. 51370-00038

[0006] In another refinement, the conversion atmosphere is a hydrogen-comprising atmosphere. In a further refinement, the hydrogen-comprising atmosphere comprises at least about 4% hydrogen. In yet a further refinement, the hydrogen-comprising atmosphere comprises at least about 12% hydrogen.

[0007] In another refinement, the compaction pressure is at least about 20 MPa. In a further 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. 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 yet another refinement, the reaction atmosphere is a hydrogencomprising 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 method also includes the step of milling the consolidated powder body to form a free-flowing powder comprising Re2Coi7 powder and calcium oxide powder (CaO). In a further refinement, the method includes the step of separating the calcium oxide from the free-flowing powder to form a free- flowing rare earth magnetic powder comprising Re2Coi7. For example, the step of separating the calcium oxide from the free-flowing powder mixture may include washing the free-flowing powder mixture with dilute hydrochloric acid.

[0010] In one characterization, the free-flowing rare earth magnetic powder comprises S1T12C017 magnetic crystals. In one particular characterization, the free- free-flowing rare earth magnetic powder comprises at least about 80 wt.% S1T12C017 magnetic crystals.

[0011] In another embodiment, a sintered rare earth magnetic body is disclosed. The sintered rare earth magnetic body includes at least about 90 wt.% Re2Coi7 magnetic crystals, wherein Re is selected from the group consisting of Sm and Nd and wherein the sintered rare earth magnetic body has at least one of: (i) a magnetic coercivity of at least about 0.25 Tesla, or (ii) a magnetic remanence of at least about 0.79 Tesla.DESCRIPTIONPCT Patent ApplicationAttorney Ref. 51370-00038

[0012] In one embodiment of the present disclosure, a method for the production of a rare earth magnetic material of the form Re2Coi7 from a rare earth oxide is disclosed.

[0013] The method may include preparing a rare earth oxide powder comprising a rare earth oxide powder (Re2Os), cobalt powder (Co) and calcium hydride (CaFte). The rare earth oxide is compacted under a compaction pressure to form a compacted rare earth oxide powder body. The compacted rare earth oxide 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 )Re2Coi7) and calcium oxide powder (CaO).

[0014] In one characterization, Re is selected from the group consisting of samarium (Sm) and neodymium (Nd). In one refinement, Re is samarium (Sm).

[0015] In another characterization, the rare earth oxide powder (Re2Os) and cobalt powder (Co) are formed from the metal oxalates in the presence of a reductant such a hydrogen.Re2(C2O4)3+ COC2O4 + H2 -> Re2Os + Co

[0016] Thus, the rare earth oxalate powder, e.g., (Srri2(C2O4)3 and cobalt oxalate (COC2O4) react to form a precursor powder comprising Re2Os and Co. Other metals such as iron and copper can be formed from their oxalates in a similar manner.

[0017] In one characterization, reacting the oxalate powders includes heating the oxalate precursor powders to a conversion temperature, under a conversion pressure and under a conversion atmosphere to form a mixture of the rare earth oxide powder (Re2Os) and the cobalt powder (Co). In one refinement, the conversion temperature is at least about 800°C. In another refinement, the conversion temperature is not greater than about 900°C. In another refinement, the conversion pressure is at least about 2 bar. In yet another refinement, the conversion pressure is not greater than about 5.5 bar.PCT Patent ApplicationAttorney Ref. 51370-00038

[0018] In another refinement, the conversion atmosphere is a hydrogen-comprising atmosphere. For example, the hydrogen-comprising atmosphere may include at least about 4% hydrogen, such as at least about 12% hydrogen.

[0019] In one characterization, the rare earth oxide powder is compacted to form the compacted rare earth oxide 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 rare earth oxide powder body may take a variety of forms, such as blocks, disks, pellets and the like.

[0020] After compaction, the compacted rare earth oxide precursor body is reacted in the presence of calcium hydride to form a consolidated powder body comprising the rare earth magnetic material Re2Coi7. In one characterization, the compacted rare earth oxide 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.

[0021] 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 as at least about 0.5 MPa.

[0022] 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.

[0023] The method may also include the step of milling the consolidated powder body to form a free-flowing powder mixture comprising Re2Coi7 magnetic powder and calcium oxide powder (CaO). In this regard, the calcium oxide may be separated from the free-flowing powder to form a free-flowing rare earth magnetic powder comprisingPCT Patent ApplicationAttorney Ref. 51370-00038Re2Coi7. In one characterization, the separation of the calcium oxide from the free- flowing powder includes washing the free-flowing 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.

[0024] As a result, the free-flowing rare earth magnetic powder comprises C02C017 magnetic crystals. In an alternative characterization, the magnetic powder comprises Nd2Coi7. For example, the free-free-flowing rare earth magnetic powder may comprise at least about 80 wt.% Re2Coi7 magnetic crystals, such as at least about 85 wt.% and even at least about 90 wt.% Re2Coi7 magnetic crystals.

[0025] 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.

[0026] Thus, in another embodiment of the present disclosure, a sintered rare earth magnetic body is disclosed comprising at least about 80 wt.% Re2Coi7 magnetic crystals, where Re is selected from the group consisting of Sm and Nd. Advantageously, the sintered rare earth magnetic body may have at least one of: (i) a magnetic coercivity of at least about 0.25 Tesla, or (ii) a magnetic remanence of at least about 0.79 Tesla.

[0027] FIG. 1 illustrates a method for the production of a rare earth magnetic material of the form Re2Coi7 according to the present disclosure.

[0028] While various embodiments of a rare earth magnetic material and methods for the production of a rare earth magnetic material 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

PCT Patent ApplicationAttorney Ref. 51370-00038What is Claimed is:1 . A method for the production of a rare earth magnetic material of the form Re2Coi7, comprising the steps of: preparing a rare earth oxide powder comprising a rare earth oxide powder (Re2O3), cobalt powder (Co) and calcium hydride (CaH2); compacting the rare earth oxide powder under a compaction pressure to form a compacted rare earth oxide powder body; and heating the compacted rare earth oxide 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 Re2Coi7 and calcium oxide powder CaO.

2. The method recited in Claim 1 , wherein Re is selected from the group consisting of samarium (Sm) and neodymium (Nd).

3. The method recited in Claim 2, wherein Re is samarium (Sm).

4. The method recited in any one of Claims A1 to A3, wherein the rare earth oxide powder (Re2Os) and cobalt powder (Co) are formed by a method comprising the steps of: combining a rare earth oxalate powder (Re2(C2O4)3 and cobalt oxalate (COC2O4) to form an oxalate precursor powder; heating the oxalate precursor powder to a conversion temperature, under a conversion pressure and under a conversion atmosphere to form a rare earth oxide powder comprising rare earth oxide powder (Re2Os) and cobalt powder (Co).

5. The method recited in Claim 4, wherein the conversion temperature is at least about 800°C and not greater than about 900°C.

6. The method recited in any one of Claims 4 or 5, wherein the conversion pressure is at least about 2 bar and is not greater than about 5.5 bar.

7. The method recited in any one of Claims 4 to 6, wherein the conversion atmosphere is a hydrogen-comprising atmosphere.PCT Patent ApplicationAttorney Ref. 51370-000388. The method recited in Claim 7, wherein the hydrogen-comprising atmosphere comprises at least about 4% hydrogen.

9. The method recited in Claim 7, wherein the hydrogen-comprising atmosphere comprises at least about 12% hydrogen.

10. The method recited in any one of Claims 1 to 9, wherein the compaction pressure is at least about 20 MPa.

11. The method recited in any one of Claims 1 to 10, wherein the reaction temperature is at least about 850°C.

12. The method recited in any one of Claims 1 to 11 , wherein the reaction temperature is at least about 880°C.

13. The method recited in any one of Claims 1 to 12, wherein the reaction temperature is not greater than about 910°C.

14. The method recited in any one of Claims 1 to 13, wherein the reaction pressure is at least about 4 bar (0.4 MPa).

15. The method recited in any one of Claims 1 to 14, wherein the reaction pressure is at least about 5 bar (0.5 MPa).

16. The method recited in any one of Claims 1 to 15, wherein the reaction atmosphere is a hydrogen-comprising atmosphere.

17. The method recited in Claim 16, wherein the hydrogen-comprising atmosphere comprises at least about 4% hydrogen.

18. The method recited in Claim 16, wherein the hydrogen-comprising atmosphere comprises at least about 12% hydrogen.

19. The method recited in any one of Claims 1 to 18, further comprising the step of milling the consolidated powder body to form a free-flowing powder comprising Re2Coi7 powder and calcium oxide powder (CaO).

20. The method recited in Claim 19, further comprising the step of separating the calcium oxide from the free-flowing powder to form a free-flowing rare earth magnetic powder comprising Re2Coi7.PCT Patent ApplicationAttorney Ref. 51370-0003821. 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 powder mixture with a dilute hydrochloric acid.

22. The method recited in any one of Claims 1 to 21 , wherein the free-flowing rare earth magnetic powder comprises Srri2Coi7 magnetic crystals.

23. The method recited in Claim 22, wherein the free-flowing rare earth magnetic powder comprises at least about 80 wt.% Srri2Coi7 magnetic crystals.

24. A sintered rare earth magnetic body, comprising: at least about 90 wt.% Re2Coi7 magnetic crystals; wherein Re is selected from the group consisting of Sm and Nd, and wherein the sintered rare earth magnetic body has at least one of: (i) a magnetic coercivity of at least about 0.25 Tesla, or (ii) a magnetic remanence of at least about 0.79 Tesla.

25. The sintered rare earth magnetic body recited in Claim 24, wherein the sintered rare earth magnetic body has a magnetic coercivity of at least about 0.25 Tesla.

26. The sintered rare earth magnetic body recited in any one of Claims 24 or 25, wherein the sintered rare earth magnetic body has a magnetic remanence of at least about 0.79 Tesla.

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