Metallization of metal oxides to form rare earth metals

Abstract

Methods for the production of free-flowing rare earth metal powders are disclosed. The methods include the metallization of rare earth metal oxides.

Description

PCT Patent ApplicationAttorney Ref. 51370-00041METALLIZATION OF METAL OXIDES TO FORM RARE EARTH METALSCROSS-REFERENCE TO RELATED APPLCATIONS

[0001] This application claims the priority benefit of US Provisional Patent Application No. 63 / 689,275, filed on August 30, 2025, which is incorporated herein by reference in its entirety.FIELD

[0002] The present disclosure relates to the field of metals and metal alloys, particularly to rare earth metals and metal alloys that are useful for the production of magnetic materials.SUMMARY

[0003] In one embodiment, a method for the production of a free-flowing rare earth powder is disclosed. The method includes the steps of admixing a rare earth oxide powder (RexOy), where Re is a rare earth element) with a first portion of calcium hydride (CaH2) powder to form an initial admixed precursor powder; compacting the initial admixed precursor powder under a first compaction pressure to form an initial compacted precursor powder body; heating the initial compacted precursor powder body to a first reaction temperature and under a first reaction pressure that are sufficient to form an intermediate consolidated powder body comprising a rare earth metal and unreacted rare earth oxide; milling the intermediate consolidated powder body to form a milled intermediate powder; admixing a second portion of calcium hydride powder with the milled intermediate powder to form an intermediate admixed precursor powder; compacting the intermediate admixed precursor powder under a second compaction pressure to form an intermediate compacted precursor powder body; heating the intermediate compacted precursor powder body to a second reaction temperature and under a second reaction pressure to form a rare earth consolidated powder body; and milling the rare earth consolidated powder body to form a free-flowing rare earth powder, wherein at least about 95% of the rare earth element from the rare earth oxide powder is converted to the rare earth metal in the free-flowing rare earth powder.PCT Patent Application Attorney Ref. 51370-00041

[0004] The foregoing method is subject to a number of characterizations and refinements that may be implemented individually or in any combination.

[0005] In one characterization, the step of admixing the earth oxide powder with the first portion of calcium hydride powder comprises admixing the powders in a substantially stoichiometric ratio. In another characterization, the first compaction pressure is at least about 20 MPa. In yet another characterization, the first compaction pressure is not greater than about 30 MPa. In one characterization, the first reaction temperature is at least about 810°C. In another characterization, the first reaction temperature is not greater than about 910°C.

[0006] In one characterization, the first reaction pressure is a vacuum. In another characterization, the initial compacted precursor powder body is maintained at the first reaction temperature for a period of time of at least about 2 hours and not greater than about 4 hours.

[0007] In one characterization, at least about 65% of the rare earth element from the rare earth oxide powder is converted to the rare earth metal in the milled intermediate powder.

[0008] In one characterization, the step of admixing the second portion of calcium hydride powder with the milled intermediate powder comprises admixing the powders in a ratio of CaH2 to the rare earth oxide in a concentration of CaH2 to the rare earth oxide in a concentration of CaH2 to the rare earth oxide that is above the stoichiometric ratio. In one refinement, the ratio of CaH2 to the rare earth oxide in the milled intermediate admixed precursor powder mixture is at least about 10% above the stoichiometric ratio.

[0009] In another characterization, the second compaction pressure is at least about 20 MPa. In another characterization, the second compaction pressure is not greater than about 30 MPa.

[0010] In another characterization, the second reaction temperature is at least about 800°C. In yet another characterization, the second reaction temperature is not greater than about 910°C. In another characterization, the intermediate compacted precursor powder body is maintained at the second reaction temperature for a period of time of atPCT Patent ApplicationAttorney Ref. 51370-00041 least about 1 .5 hours. In a further characterization, the intermediate compacted precursor powder body is maintained at the second reaction temperature for a period of time of not greater than about 2.5 hours.

[0011] In another characterization, at least about 98% of the rare earth element from the rare earth oxide powder is converted to the rare earth metal in the free-flowing rare earth powder. In one refinement, at least about 99% of the rare earth element from the rare earth oxide powder is converted to the rare earth metal in the free-flowing rare earth powder.

[0012] In another characterization, the first and second portions of calcium hydride powder comprise calcium hydride particulates having a mean average particle size (d50) of at least about 5 pm. In yet another characterization, the first and second portions of calcium hydride powder comprise calcium hydride particulates having a mean average particle size (d50) of not greater than about 15 pm.

[0013] In another characterization, the method further includes the step of separating calcium compounds from the milled intermediate powder. In yet another characterization, the method further includes the step of separating calcium compounds from the free- flowing rare earth powder.

[0014] In another characterization, the rare earth oxide is of the form Re2Os. In one refinement, Re is selected from the group consisting of Nd, Pr, Dy and Tb.

[0015] In another characterization, a non-rare earth metal powder is added to at least one of: (i) the step of admixing the rare earth oxide powder with the first portion of calcium hydride powder; and (ii) admixing a second portion of calcium hydride powder with the milled intermediate powder. In one refinement, the non-rare earth metal powder is added to the step of adm ixing the rare earth oxide powder with the first portion of calcium hydride powder. In another refinement, the non-rare earth metal powder is added to the step of admixing a second portion of calcium hydride powder with the milled intermediate powder mixture. In yet another refinement, the non-rare earth metal powder is selected from the group consisting of iron, nickel, cobalt and copper, and in one particular refinement, the non-rare earth metal powder comprises iron. Within the scope of this refinement, the rare earth element may be selected from the group consisting of Nd, Pr and Dy and the free-PCT Patent Application Attorney Ref. 51370-00041 flowing rare earth powder comprises a metal alloy selected from the group consisting of a NdFe, a PrFe alloy and a DyFe alloy. In another refinement, the non-rare earth metal powder comprises cobalt. In yet another refinement, the rare earth element comprises samarium and wherein the free-flowing rare earth powder comprises a SmCo alloy.

[0016] These and other embodiments, characterizations and refinements of the present disclosure will be apparent from the following description.DESCRIPTION

[0017] The present disclosure is directed to the production of metal powders. In one embodiment, the metal powders may comprise rare earth metal powders, including rare earth metal alloys, e.g., rare earth master alloys, that include at least one rare earth element and one non-rare earth element. In another embodiment, the metal powders may comprise metal alloys of two or more non-rare earth elements.

[0018] In the first embodiment, the rare earth metal (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), terbium (Tb) and combinations thereof. For the production of rare earth metal alloys, the non-rare earth metals (Me) may be selected from iron, cobalt, copper, nickel, aluminum and combinations thereof. Some examples of such rare earth metal alloys include, but are not limited to, NdFe, DyFe, NbFe, TbFe, LaCo, GdCo, YCu, DyCu, LaNi, ScAI and SmAI.

[0019] The methods disclosed in this first embodiment include the metallization, e.g., the reduction, of a rare earth oxide (Re2Oa) powder with an alkaline earth metal hydride such as calcium hydride (CaFh) powder. This metallization of the rare earth oxide powder may be carried out solely with the rare earth oxide powder to form the rare earth metal powder or may be carried out in the presence of a non-rare earth metal powder to form a metal alloy of the metals. Broadly stated, the method includes the admixing of alkaline earth metal hydride powder with the rare earth oxide powder, compacting the powder mixture and heating the compacted powder mixture to reduce the rare earth oxide withPCT Patent Application Attorney Ref. 51370-00041 the alkaline earth metal hydride. This cycle may be repeated to metallize substantially all of the rare earth oxide with the alkaline earth metal hydride.

[0020] In certain implementations, the method includes metallization of the rare earth oxide powder in the presence of a calcium hydride in at least two cycles to ensure substantially complete metallization of the rare earth oxide powder. During the heating steps in the presence of calcium hydride, the following reaction occurs at the reaction temperatures:Re?O3 + CaH? — > Re + CaO + H2f (1 )

[0021] While not wishing to be bound by any theory, it is believed that this reaction is not carried to completion in one step due to inhomogeneous mixing of the rare earth oxide powder and the calcium hydride powder in the initial compacted powder body. As a result, a subsequent step of admixing the partially reacted powder with additional calcium hydride, compacting and heating are desirable to react substantially all of the unreacted rare earth oxide.

[0022] In one implementation, the method includes the step of admixing a rare earth oxide powder, e.g., RexOy, where Re is a rare earth element, with calcium hydride (CaH2) powder, e.g., a first portion of calcium hydride powder, to form an initial admixed precursor powder. These powders may be mixed in a substantially stoichiometric ratio, i.e. , where the molar ratio of calcium to oxygen is at least about 0.95:1 and is not greater than about 1 .05: 1 . For example, 100 grams of Nd20s would require about 37.5 grams of CaH2 for a Ca:O molar ratio of about 1 :1. In one characterization, the molar ratio of Ca:O is at least about 0.9:1. In another characterization, the molar ratio of Ca:O is not greater than about 1.1 :1. To facilitate the reaction, the calcium hydride powder may have a fine mean average (d50) particle size. In one characterization, the calcium hydride powder has a mean average particle size of not greater than about 25 pm, such as not greater than about 20 pm, such as not greater than about 15 pm. In another characterization, the mean average particle size of the calcium hydride is at least about 3 pm, such as at least about 5 pm.

[0023] The initial admixed precursor powder comprising the rare earth oxide powder and the calcium hydride powder is then compacted under a compaction pressure, e.g., aPCT Patent Application Attorney Ref. 51370-00041 first compaction pressure, to form an initial compacted precursor powder body. The compaction may be carried out in a uniaxial press, for example, and the compacted precursor powder body may have any useful shape such as a block or disk. The compaction pressure is selected such that the compacted precursor powder body may be handled, e.g., to be placed in a reactor, with minimal loss of powder from the compacted body. In one characterization, the compaction pressure is at least about 15 MPa, such as at least about 20 MPa. In another characterization, the compaction pressure is not greater than about 35 MPa, such as not greater than about 30 MPa.

[0024] After compaction, the initial compacted precursor powder body is then heated, e.g., sintered, at a reaction temperature, e g., a first reaction temperature, and under a reaction pressure, e.g., a first reaction pressure, that are sufficient to react the rare earth oxide with the calcium hydride (see Equation 1 ) to form an intermediate consolidated powder body comprising the rare earth metal. In one characterization, the first reaction temperature is at least about 790°C, such as at least about 800°C, such as at least about 810°C. In another characterization, the first reaction temperature is not greater than about 920°C, such as not greater than about 910°C, such a not greater than about 900°C.

[0025] In another characterization, the reaction pressure is very low and in in one implementation the reaction pressure may be a substantial vacuum, i.e., where the reaction pressure is not greater than about 100 Pa, such as not greater than about 60 Pa, such as not greater than about 50 Pa. While not wishing to be bound by any theory, it is believed that heating in a substantial vacuum will reduce or prevent the undesirable formation of metal hydrides, e.g., of rare earth metal hydrides. In one implementation, the initial compacted precursor powder body may be heated at the reduced pressure for at least about 2 hours and not greater than about 4 hours.

[0026] The intermediate consolidated powder body will comprise the rare earth metal and will also comprise some unreacted rare earth oxide. That is, the reaction to form the rare earth metal will typically not be complete after one cycle of compacting and heating the powders. In one characterization, at least about 60% of the rare earth element from the initial rare earth oxide powder is converted to the rare earth metal in intermediate consolidated powder body. In another characterization, at least about 65% of the rarePCT Patent Application Attorney Ref. 51370-00041 earth element from the initial rare earth oxide powder is converted to the rare earth metal in intermediate consolidated powder body

[0027] This intermediate consolidated powder body may then be milled to dissociate the consolidated powder body into a powder, e.g., a free-flowing milled intermediate powder comprising the rare earth metal and the rare earth oxide. This free-flowing powder may then be admixed with additional calcium hydride powder, e.g., a second portion of calcium hydride powder, to form an intermediate admixed precursor powder comprising the rare earth metal powder, the rare earth oxide powder and the calcium hydride powder. In one implementation, these powders may be mixed in a ratio that is above stoichiometric with respect to calcium, i.e., where the molar ratio of calcium to oxygen is at least about 1.1 :1. For example, 35 grams of Nd20s in the free-flowing milled intermediate powder would require about 14.4 grams of CaH2 for a Ca:O molar ratio of about 1.1 :1. In one characterization, the molar ratio of Ca:O is at least about 1.2:1. In another characterization, the molar ratio of Ca:O is not greater than about 1.5:1. As with the initial metallization cycle, the second portion of calcium hydride powder may have a fine mean average particle size. In one characterization, the calcium hydride powder has a mean average particle size of not greater than about 25 pm, such as not greater than about 20 pm, such as not greater than about 15 pm. In another characterization, the mean average particle size of the calcium hydride is at least about 3 pm, such as at least about 5 pm.

[0028] This intermediate admixed precursor powder is then compacted, e.g., under a second compaction pressure to form an intermediate compacted precursor powder body. This second compaction step may be carried out in a manner similar to the first compaction step, e.g., the compaction pressure may be at least about 15 MPa, such as at least about 20 MPa, and may be not greater than about 35 MPa, such as not greater than about 30 MPa.

[0029] This intermediate compacted precursor powder body is then heated, e.g., sintered, at a second reaction temperature and under a second reaction pressure to form a rare earth consolidated powder body wherein a substantial portion of the previously unreacted rare earth oxide is converted to the rare earth metal. The second reactionPCT Patent Application Attorney Ref. 51370-00041 temperature and pressure may be similar to the first heating step, e.g., the first reaction temperature may be at least about 780°C, such as at least about 800°C, such as at least about 820°C, and may be not greater than about 920°C, such as not greater than about 910°C, such a not greater than about 900°C. The reaction pressure may also be very low and in in one implementation the reaction pressure may be a substantial vacuum, i.e. , where the reaction pressure is not greater than about 100 Pa, such as not greater than about 60 Pa, such as not greater than about 50 Pa. In one implementation, the intermediate compacted precursor powder body may be heated at the reduced pressure for at least about 1 .5 hours and not greater than about 2.5 hours.

[0030] In either of the heating steps described above, the consolidated powder bodies may be cooled from the reaction temperature under conditions that inhibit or prevent the formation of oxide phases as the material cools. For example, the consolidated bodies may be cooled under a substantial vacuum to inhibit the formation of metal oxides or metal nitrides.

[0031] The resulting, the rare earth consolidated powder body will include a high proportion of the rare earth metal. In one characterization, at least about 95% of the rare earth element from the initial rare earth oxide powder will be converted to the rare earth metal in the rare earth consolidated powder body. In another characterization, at least about 98% of the rare earth element from the initial rare earth oxide powder will be converted to the rare earth metal in the rare earth consolidated powder body, such as at least about 99% or even at least about 99.5%.

[0032] This rare earth consolidated powder body may then be milled to form a free- flowing rare earth powder, e.g., a free-flowing rare earth powder wherein at least about 95% of the rare earth element from the initial rare earth oxide powder will be converted to the rare earth metal.

[0033] As is apparent from Equation (1 ), calcium compounds such as calcium oxide (CaO) are formed as a by-product of the reaction of the rare earth oxide with calcium hydride. This calcium oxide can be separated from the other reaction products during processing. For example, calcium oxide can be removed from the milled intermediatePCT Patent Application Attorney Ref. 51370-00041 powder before admixing additional calcium hydride and may also be removed from the free-flowing rare earth powder.

[0034] As is noted above, the rare earth oxide may be of the form Re2O3. In one characterization, Re is selected from the group consisting of Nd, Pr, Dy, Tb and mixtures thereof. Thus, the method is particularly adapted for the formation of fine metal powders of rare earth elements such as Nd, Pr, Dy and Tb.

[0035] As is noted above, the method may also be utilized to form metal alloys of a rare earth metal and a non-rare earth metal (Me) such as a base metal. In this implementation, at least one non-rare earth metal powder is added to at least one of: (i) the step of admixing the rare earth oxide powder with the first portion of calcium hydride powder, and / or (ii) the step of admixing a second portion of calcium hydride powder with the milled intermediate powder. In one characterization, the non-rare earth metal is selected from the group consisting of iron (Fe), nickel (Ni), cobalt (Co) and copper (Cu). These non-rare earth metals may be admixed with the rare earth oxide and the calcium hydride in a suitable ratio of Me to Re to form the desired metal alloy.

[0036] In one example, the non-rare earth metal powder comprises iron. In one implementation, the rare earth element is selected from the group consisting of Nd, Pr and Dy, wherein the free-flowing rare earth powder comprises a metal alloy selected from the group consisting of a NdFe, a PrFe alloy and a DyFe alloy. In another example, the non-rare earth metal powder comprises cobalt. In one implementation, the rare earth element comprises samarium, wherein the free-flowing rare earth powder comprises a SmCo alloy.

[0037] Non-limiting examples of such metal alloys and their applications are illustrated in Table I.Table IPCT Patent ApplicationAttorney Ref. 51370-00041Prophetic Example

[0038] FIG. 1 is a flowsheet illustrating the production of neodymium metal powder from neodymium oxide (Nd2O3). The Nd2O3rare earth oxide powder is admixed 102 with a first portion of calcium hydride powder in a stoichiometric ratio of Ca:O to form an initial admixed precursor powder having a fine particle size.

[0039] The admixed precursor powder is then compacted 104 in a uniaxial press at a pressure of about 25 MPa to form an initial compacted precursor powder body. Thereafter, this initial compacted precursor powder body is heated 106 to about 850°C under a substantial vacuum for about 4 hours and is cooled under the vacuum to form an intermediate consolidated powder body comprising Nd metal and unreacted Nd2O3. This intermediate consolidated powder body is milled 108 in a ball mill to form a milled intermediate powder and calcium oxide is separated from the milled intermediate powder by gravity separation.

[0040] A second portion of calcium hydride powder is then admixed 110 with the milled intermediate powder to form an intermediate admixed precursor powder, where the stoichiometric ratio of Ca:O in the intermediate admixed precursor powder is about 1.2:1. Thereafter, the intermediate admixed precursor powder is compacted 112 under a second compaction pressure of about 25 MPa to form an intermediate compacted precursorPCT Patent Application Attorney Ref. 51370-00041 powder body. This body is heated 114 to about 850°C under a substantial vacuum for about 2 hours and is cooled under the vacuum to form an intermediate consolidated powder body comprising Nd metal and little to no Nd2Os. After milling 116 in a ball mill, calcium oxide is separated from the free-flowing rare earth powder. The resulting free- flowing rare earth powder comprises at least about 99% neodymium having a fine average particle size.

[0041] While various embodiments of free-flowing rare earth metal powders and methods for the production of rare earth metal powders have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. Such modifications and adaptations are within the spirit and scope of the present disclosure.

Claims

PCT Patent ApplicationAttorney Ref. 51370-00041What is Claimed Is:1 . A method for the production of a free-flowing rare earth powder, comprising the steps of: admixing a rare earth oxide powder (RexOy), where Re is a rare earth element) with a first portion of calcium hydride (CaH2) powder to form an initial admixed precursor powder; compacting the initial admixed precursor powder under a first compaction pressure to form an initial compacted precursor powder body; heating the initial compacted precursor powder body to a first reaction temperature and under a first reaction pressure that are sufficient to form an intermediate consolidated powder body comprising a rare earth metal and unreacted rare earth oxide; milling the intermediate consolidated powder body to form a milled intermediate powder; admixing a second portion of calcium hydride powder with the milled intermediate powder to form an intermediate admixed precursor powder; compacting the intermediate admixed precursor powder under a second compaction pressure to form an intermediate compacted precursor powder body; heating the intermediate compacted precursor powder body to a second reaction temperature and under a second reaction pressure to form a rare earth consolidated powder body; and milling the rare earth consolidated powder body to form a free-flowing rare earth powder, wherein at least about 95% of the rare earth element from the rare earth oxide powder is converted to the rare earth metal in the free-flowing rare earth powder.PCT Patent Application Attorney Ref. 51370-000412. The method recited in Claim 1 , wherein the step of admixing the earth oxide powder with the first portion of calcium hydride powder comprises admixing the powders in a substantially stoichiometric ratio.

3. The method recited in any one of Claims 1 to 2, wherein the first compaction pressure is at least about 20 MPa and is not greater than about 30 MPa.

4. The method recited in any one of Claims 1 to 3, wherein the first reaction temperature is at least about 810°C.

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

6. The method recited in any one of Claims 1 to 5, wherein the first reaction pressure is a vacuum.

7. The method recited in any one of Claims 1 to 6, wherein the initial compacted precursor powder body is maintained at the first reaction temperature for a period of time of at least about 2 hours and not greater than about 4 hours.

8. The method recited in any one of Claims 1 to 7, wherein at least about 65% of the rare earth element from the rare earth oxide powder is converted to the rare earth metal in the milled intermediate powder.

9. The method recited in any one of Claims 1 to 8, wherein the step of admixing the second portion of calcium hydride powder with the milled intermediate powder comprises admixing the powders in a ratio of CaH to the rare earth oxide in a concentration of CaH2 to the rare earth oxide in a concentration of CaH2 to the rare earth oxide that is above the stoichiometric ratio.

10. The method recited in Claim 9, wherein the ratio of CaH2 to the rare earth oxide in the milled intermediate admixed precursor powder mixture is at least about 10% above the stoichiometric ratio.

11. The method recited in any one of Claims 1 to 10, wherein the second compaction pressure is at least about 20 MPa and is not greater than about 30 MPa.PCT Patent Application Attorney Ref. 51370-0004112. The method recited in any one of Claims 1 to 11 , wherein the second reaction temperature is at least about 800°C.

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

14. The method recited in any one of Claims 1 to 13, wherein the intermediate compacted precursor powder body is maintained at the second reaction temperature for a period of time of at least about 1 .5 hours and not greater than about 2.5 hours.

15. The method recited in any one of Claims 1 to 14, wherein at least about 98% of the rare earth element from the rare earth oxide powder is converted to the rare earth metal in the free-flowing rare earth powder.

16. The method recited in Claim 15, wherein at least about 99% of the rare earth element from the rare earth oxide powder is converted to the rare earth metal in the free-flowing rare earth powder.

17. The method recited in any one of Claims 1 to 16, wherein the first and second portions of calcium hydride powder comprise calcium hydride particulates having a mean average particle size (d50) of at least about 5 pm and not greater than about 15 pm.

18. The method recited in any one of Claims 1 to 17, further comprising the step of separating calcium compounds from the milled intermediate powder.

19. The method recited in any one of Claims 1 to 18, further comprising the step of separating calcium compounds from the free-flowing rare earth powder.

20. The method recited in any one of Claims 1 to 19, wherein the rare earth oxide is of the form Re2O3.

21. The method recited in Claim 20, wherein Re is selected from the group consisting of Nd, Pr, Dy and Tb.

22. The method recited in any one of Claims 1 to 21 , wherein a non-rare earth metal powder is added to at least one of: (i) the step of admixing the rare earth oxidePCT Patent Application Attorney Ref. 51370-00041 powder with the first portion of calcium hydride powder; and (ii) admixing a second portion of calcium hydride powder with the milled intermediate powder.

23. The method recited in Claim 22, wherein the non-rare earth metal powder is added to the step of admixing the rare earth oxide powder with the first portion of calcium hydride powder.

24. The method recited in Claim 22, wherein the non-rare earth metal powder is added to the step of admixing a second portion of calcium hydride powder with the milled intermediate powder mixture.

25. The method recited in Claim 22, wherein the non-rare earth metal powder is selected from the group consisting of iron, nickel, cobalt and copper.

24. The method recited in Claim 23, wherein the non-rare earth metal powder comprises iron.

25. The method recited in Claim 24, wherein the rare earth element is selected from the group consisting of Nd, Pr and Dy and wherein the free-flowing rare earth powder comprises a metal alloy selected from the group consisting of a NdFe, a PrFe alloy and a DyFe alloy.

26. The method recited in Claim 23, wherein the non-rare earth metal powder comprises cobalt.

27. The method recited in Claim 26, wherein the rare earth element comprises samarium and wherein the free-flowing rare earth powder comprises a SmCo alloy.

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