Method for the production of rare earth magentic materials from metal salts

Abstract

This disclosure relates to magnetic powders, precursors for magnetic powders, and methods for the fabrication of the powders and precursor powders. The method comprises the steps of: combining a rare earth metal salt with a base metal powder and calcium hydride to form a magnetic powder precursor; compacting the magnetic powder precursor to form a compacted magnetic precursor body; heating the compacted magnetic precursor body to a reaction temperature and under an inert gas or a vacuum to reduce the rare earth metal salt to a rare earth metal and form an intermediate product comprising calcium hydroxide and a magnetic powder; and separating the calcium hydroxide from the intermediate product to form a fine rare earth magnetic powder.

Description

METHOD FOR THE PRODUCTION OF RARE EARTH MAGENTIC MATERIALS FROM METAL SALTSFIELD

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

[0002] In a first embodiment, a method for the production of a fine rare earth magnetic powder selected from ReFeB and SmCo is disclosed. The method includes the steps of combining a rare earth metal salt of the form ReBOs or Sm2(C2O4)3 with a base metal powder and calcium hydrides to form a magnetic powder precursor and compacting the magnetic powder precursor to form a compacted magnetic precursor body. The compacted magnetic precursor body is heated to a reaction temperature and under an inert gas or a vacuum to reduce the rare earth metal salt to a rare earth metal and form an intermediate product comprising a magnetic powder selected from ReFeB and SmCo and calcium hydroxide. The calcium hydroxide may then be separated from the intermediate product to form the fine rare earth magnetic powder.

[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, the fine rare earth magnetic powder comprises ReFeB. In one implementation, the rare earth metal salt comprises ReBOs. In another implementation, Re is selected from the group consisting of Nd, Pr and Dy.

[0005] In another refinement, the fine rare earth magnetic powder comprises SmCo. In one implementation, the rare earth metal salt comprises S i2(C2O4)3.

[0006] In another refinement, the reaction temperature is at least about 900°C. In yet another refinement, the reduced reaction pressure is a vacuum.

[0007] In another refinement, the fine rare earth magnetic powder has a mean average particle size of not greater than about 12 pm. In one implementation, the fine rare earth magnetic powder has a mean average particle size of not greater than about 9 pm.

[0008] In a second embodiment, a method for the formation of rare earth borate powder is disclosed. The method includes the steps of combining a rare earth oxalate powder with aqueous boric acid (HBO3) to form a precursor solution, and heating the precursor solution to a reaction temperature that is sufficient to form a rare earth borate powder and an oxalic acid by-product. The rare earth borate powder may then be separated from the oxalic acid.

[0009] The foregoing method of the second embodiment is subject to a number of refinements, characterizations and implementations, which may be applied to the foregoing method individually or in any combination.

[0010] In one refinement, the rare earth is selected from the group consisting of Nd, Pr and Dy. In one implementation, the rare earth is Nd.

[0011] In another refinement, the rare earth oxalate powder is of the form Re2(C2O4)3.

[0012] In another refinement, the reaction temperature is at least about 70°C. In one implementation, the reaction temperature is at least about 75°C.

[0013] In another refinement, the oxalic acid is recovered. In one implementation, the recovered oxalic acid is reacted with a rare earth metal compound to form a rare earth oxalate.

[0014] In another refinement, the rare earth oxalate powder has a mean average particle size of at least about 100 pm. In one implementation, the rare earth borate powder has a mean average particle size of not greater than about 12 pm.

[0015] In a third embodiment, a method for the production of a rare earth magnetic powder precursor is disclosed. The method includes the steps of combining a rare earth metal salt with at least a first base metal oxalate powder to form a first precursor powder, and heating the first precursor powder at a reaction temperature and under an elevated reaction pressure and in the presence of hydrogen to form the rare earth magnetic powder precursor comprising a metallic base metal powder and a rare earth borate powder.

[0016] The foregoing method of the third embodiment is subject to a number of refinements, characterizations and implementations, which may be applied to the foregoing method individually or in any combination.

[0017] In one refinement, the rare earth metal salt comprises a rare earth metal oxalate and wherein the first precursor powder further comprises boric acid.

[0018] In another refinement, the rare earth metal salt comprises a rare earth borate.

[0019] In another refinement, the base metal salt comprises a base metal oxalate.

[0020] In another refinement, the rare earth metal is selected from Nd, Pr and Dy. In one implementation, the rare earth metal comprises Nd.

[0021] In another refinement, the base metal is selected from Fe, Cu and Co. In one implementation, the base metal comprises Fe.

[0022] In another refinement, the reaction temperature is at least about 800°C. In one implementation, the reaction temperature is not greater than about 950°C.

[0023] In another refinement, the reaction pressure is at least about 2 bar. In one implementation, the reaction pressure is not greater than about 5.5 bar.

[0024] In another refinement, the reaction gas comprises at least about 10% hydrogen.

[0025] In another refinement, the base metal salt has a mean average particle size of at least about 100 pm. In one implementation, the base metal powder has a mean average particle size of not greater than about 12 pm.

[0026] In a fourth embodiment, a method for the production of a rare earth magnetic powder of the form SmCo is disclosed. The method includes the steps of combining samarium oxalate powder with cobalt oxalate powder to form a first precursor powder and heating the first precursor powder at a reaction temperature under an elevated reaction pressure and in the presence of a reducing gas comprising hydrogen to form the rare earth magnetic powder precursor. The rare earth magnetic powder precursor comprising samarium oxide powder and metallic cobalt powder is combined with calcium hydride to form a magnetic powder precursor and the magnetic powder precursor is compacted toform a compacted magnetic precursor body. The compacted magnetic precursor body is heated to reduce the samarium oxide and form an intermediate magnetic precursor comprising SmCo magnetic powder and calcium hydroxide. The calcium hydroxide may then be separated from the SmCo magnetic powder.

[0027] In a fifth embodiment, a magnetic powder of the form NdFeB is disclosed, wherein the magnetic powder comprises at least about 80 wt.% Nd2Fei4B.

[0028] The foregoing magnetic powder of the fifth embodiment is subject to a number of refinements, characterizations and implementations, which may be implemented individually or in any combination.

[0029] In one refinement, the magnetic powder comprises at least about 85 wt.% Nd2Fei4B. In one characterization, the magnetic powder comprises not greater than about 10 wt.% NdFe4B4. In another characterization, the magnetic powder comprises not greater than about 6 wt.% NdFe4B4.

[0030] In another refinement, the magnetic powder further comprises free iron.

[0031] In yet another refinement, the magnetic powder has a mean average particle size of not greater than about 12 pm. In one characterization, the magnetic powder has a mean average particle size of not greater than about 10 pm. In another characterization, the magnetic powder has a mean average particle size of not greater than about 8 pm.

[0032] In a sixth embodiment, a rare earth magnetic powder of the form NdFeB or SmCo is disclosed. The magnetic powder has a mean average particle size of not greater than about 20 pm and comprises not greater than about 0.12 wt.% carbon, not greater than about 0.05 wt.% nitrogen, and not greater than about 0.18 wt.% oxygen.

[0033] These and other embodiments of the present disclosure will be apparent from the following description.DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is a flowsheet illustrating a method for the production of a NdFeB magnetic powder according to an embodiment.

[0035] FIG. 2 is a flowsheet illustrating a method for the production of rare earth borate powder according to an embodiment.

[0036] FIG. 3 is a flowsheet illustrating a method for the production of a rare earth NdFeB magnetic precursor powder according to an embodiment.

[0037] FIG. 4 is a flowsheet illustrating a method for the production of a rare earth SmCo magnetic powder according to an embodiment.

[0038] FIG. 5 is a flowsheet illustrating a method for the production of a NdFeB magnetic powder according to an embodiment.DESCRIPTION

[0039] The present disclosure is directed to the production of rare earth magnetic powders and precursor powders, particularly powders of the form ReFeB (where Re is a rare earth metal) and SmCo. As used herein, the nomenclature ReFeB refers to rare earth magnets including, but not limited to, crystals of a magnetic composition including the rare earth, iron and boron, such as Re2Fei4B, ReFe4B4, and the like. Similarly, the nomenclature SmCo refers to a magnetic material including, but not limited to, crystals of a SmCo composition such as SmCos and Sm2Coi7. The present disclosure is particularly directed to the formation of fine magnetic powders of these magnetic materials that are formed from metal salts. This is in contrast to the formation of the magnetic materials in bulk, e.g. , in the form of a metal ingot, and subsequent strip casting and pulverizing of the magnetic material to form a powder. The conversion of metal salts to the powdered magnetic material offers many advantages as compared to such known processes. In this regard, the present disclosure is also directed to the production of intermediate products, e.g., precursors to the magnetic materials that include metal salts.

[0040] In one embodiment, a method for the production of a rare earth magnetic powder is disclosed, wherein the rare earth magnetic powder is selected from ReFeB and SmCo. FIG. 1 illustrates an exemplary flowsheet of this method for the production of Nd2Fei4B magnetic powder. In the case of ReFeB, Re may be selected from any rare earth metal. In one characterization, the rare earth metal is selected from the groupconsisting of neodymium (Nd), praseodymium (Pr), dysprosium (Dy) and combinations thereof. In one particular characterization the rare earth comprises Nd. For example, the magnetic powder may comprise a high concentration of magnetic Nd2Fei4B crystals. In the case of SmCo, the magnetic powder may comprise a high concentration of magnetic Sm2Coi7 crystals.

[0041] The method may include the step of combining (e.g., mixing) a rare earth metal salt of the form ReBOs (i.e. , a rare earth borate) or Srri2(C2O4)3 (i.e., samarium oxalate) with a base metal and CaH2 (calcium hydride) to form a magnetic powder precursor. The magnetic powder precursor may then be compacted to form a compacted magnetic precursor body. This precursor body may then be heated, e.g., in a reactor, to a reaction temperature and under a sub-atmospheric reaction pressure in the presence of hydrogen. The heating is carried out under conditions to reduce the rare earth metal salt to a rare earth metal and form an intermediate magnetic precursor comprising a magnetic powder selected from ReFeB and SmCo, the base metal and calcium hydroxide. The calcium hydroxide may be separated from the intermediate magnetic precursor to form the fine rare earth magnetic powder.

[0042] As used herein, the term metal salts refers to ionic compounds of a metal cation and an anion such as oxalate metal salts, borate metal salts, hydroxide metal salts, and the like. As used herein, metal salts do not include metal oxide compounds such as rare earth oxides. In certain embodiments and refinements disclosed herein, the metal salts include one or more of metal borates and metal oxalates, e.g., rare earth borates and rare earth oxalates.

[0043] When the desired fine rare earth magnetic powder is ReFeB, the rare earth metal salt may comprise a rare earth borate ReBOa. For example, Re may be selected from the group consisting of Nd, Pr, Dy and combinations thereof. In one particular characterization, the rare earth metal Re comprises Nd, e.g., where the rare earth metal salt comprises NdBOs.

[0044] When the desired fine rare earth magnetic powder is SmCo, the rare earth metal salt comprises samarium oxalate, e.g., Sm2(C2O4)3.

[0045] The magnetic powder precursor also includes a base metal. As used herein, the term base metal includes iron, cobalt, copper, lead, nickel, zinc, aluminum, tin, tungsten, molybdenum, tantalum, bismuth, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium and thallium. Base metals do not include rare earth metals and precious metals. In certain embodiments and refinements disclosed herein, the base metal(s) may be selected from iron, cobalt and copper as these are the most relevant base metals for use in rare earth magnetic materials. Further, the magnetic powder precursor may include more than one base metal, e.g., at least two base metals or at least three base metals.

[0046] The rare earth metal salts, e.g., borate salts and / or oxalate salts, may have a mean average particle size of not greater than about 250 pm, such as not greater than about 200 pm, such as not greater than about 175 pm. It is an advantage of this method that the average particle size of the metal salts does not have to be low in order to create magnetic powders having a very fine particle size. Although there is no particular lower limit for the mean average particle size of the rare earth metal salts, generally the rare earth metal salts will have a mean average particle size of at least about 50 pm. As used herein, the mean average particle size is determined by laser scattering in wet mode. One example of a particle size analyzer for carrying out such a measurement is the Horiba Partica LA-960V2 analyzer available from Horiba Instruments Incorporated, Irvine, CA, USA.

[0047] The base metal powder that is combined with the rare earth metal salt may have a relatively small particle size. For example, the base metal may have a mean average particle size of not greater than about 20 pm, such as not greater than about 15 pm or even not greater than about 10 pm. Base metal powders having a mean average particle size of not greater than about 3 pm are generally not desirable as they may be difficult to process due to the small size. Nonetheless, methods for producing fine base metal powders in-situ with the rare earth metal salt are disclosed below.

[0048] The calcium hydride may also be supplied as a powder and the mean average particle size of the calcium hydride is not believed to be highly relevant to the presentmethod. In one characterization, the calcium hydride may have an average particle size of at least about 50 pm and not greater than about 300 pm.

[0049] As noted above, the magnetic powder precursor is compacted to form a compacted magnetic precursor body, to facilitate the reaction of the components to form the fine rare earth magnetic powder. The magnetic powder precursor may be compacted under a wide range of pressures. In one example, the magnetic powder precursor may be compacted, e.g., in a uniaxial press, at a pressure of at least about 15 MPa and not greater than about 40 MPa, such as at least about 20 MPa and not greater than about 30 MPa.

[0050] After compaction, the compacted magnetic precursor body is subjected to reaction conditions that are sufficient to reduce the rare earth metal salt to the rare earth metal in the presence of the base metal, and form calcium hydroxide and hydrogen gas. For example, the compacted magnetic precursor body may be heated to a reaction temperature of at least about 850°C, such as at least about 875°C, such as at least about 900°C. Typically, it will not be necessary to heat the compacted magnetic precursor body to a temperature of greater than about 1050°C, such as not greater than about 1010°C. The heating may take place, e.g., in a reactor, under an inert gas such as nitrogen or argon, or may take place under a vacuum, e.g., a reduced pressure. The reaction is carried out until substantially all of the rare earth metal salt has been reduced to the rare earth metal. Although reaction times may vary, in one example the compacted magnetic precursor body is held at the reaction temperature for at least about 6 hours and not greater than about 8 hours.

[0051] The resulting product is a compacted body of an intermediate magnetic precursor that includes the magnetic powder and calcium hydroxide. A fine rare earth magnetic powder is then formed by removing the calcium hydroxide from the intermediate magnetic precursor. The calcium hydroxide may be removed using water, e.g., deionized water, which may be slightly acidified, to dissolve the calcium hydroxide in one or more steps. Prior to removing the calcium hydroxide, the frangible compacted body may be milled to break up any loose agglomerate of magnetic particles to form the fine magnetic powder.

[0052] The resulting fine magnetic powder may be characterized in several ways. For example, the fine magnetic powder may be characterized as having a small particle size. In one characterization, the fine magnetic 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 or even not greater than about 12 pm or not greater than about 9 pm. However, powders having too fine of a size may be difficult to handle, and in one characterization the fine magnetic powder has a mean average particle size of at least about 0.5 pm such as at least about 1 pm.

[0053] In another embodiment, a method for the formation of rare earth borate powder, e.g., ReBOs metal salt, is disclosed. See FIG. 2. The method utilizes a double displacement metathesis reaction to form the solid rare earth borate powder:H3BO3 + Re2(C2O4)3— ReBOs + H2C2O4

[0054] In one implementation, the method for the formation of rare earth borate powder may be utilized with the foregoing method for the manufacture of a fine rare earth magnetic powder, e.g., the formation of ReFeB using ReBOs as the source of the rare earth metal Re. The method for the formation of rare earth borate powder includes the steps of combining a rare earth oxalate powder, e.g., Re2(C2O4)3, with aqueous boric acid (H3BO3) to form a precursor solution. The precursor solution is heated to a reaction temperature that is sufficient to form the rare earth borate powder and an oxalic acid byproduct. The rare earth borate powder may then be separated from the oxalic acid and dried to form a dry rare earth borate powder.

[0055] In one characterization, the rare earth (Re) is selected from the group consisting of Nd, Pr, Dy and combinations thereof. In one particular refinement, the rare earth is Nd.

[0056] The reaction temperature for the formation of the rare earth borate may be, for example, at least about 60°C, such as at least about 65°C, such as at least about 70°C or even at least about 75°C. Generally, the reaction temperature need not exceed 100°C, such as not greater than about 95°C, such as not greater than about 90°C. In one particular implementation, the reaction temperature is about 80°C.

[0057] Advantageously, the oxalic acid that is formed as a by-product may be recovered, e.g., may be stored for sale or later use. In one characterization, the oxalic acid is recycled for the formation of additional rare earth oxalate powder for feed to the process. For example, the oxalic acid may be reacted with a rare earth metal compound to form the rare earth oxalate. In one particular implementation, the rare earth metal compound is a rare earth chloride, e.g., NdCb. In this manner, it is possible to recover and recycle 100% of the oxalic acid, e.g., in a closed loop.

[0058] The rare earth oxalate powder may have a mean average particle size of not greater than about 250 pm, such as not greater than about 200 pm, such as not greater than about 175 pm. It is an advantage of this method that the average particle size of the rare earth oxalate powder does not have to be low in order to form rare earth borate powders having a fine particle size. Although there is no particular lower limit for the mean average particle size of the rare earth metal salts, generally the rare earth metal salts will have a mean average particle size of at least about 50 pm, such as at least about 100 pm.

[0059] The produced rare earth borate powder may be characterized as having a relatively small mean average particle size. In one characterization, the rare earth borate 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 or even not greater than about 12 pm or not greater than about 9 pm. However, powders having too fine of a size may be difficult to handle, and in one characterization the rare earth borate powder has a mean average particle size of at least about 1 pm.

[0060] In another embodiment, a method for the production of a rare earth magnetic powder precursor is disclosed. For example, the rare earth magnetic powder precursor may include one or more metallic base metal powders and a rare earth borate powder, which may subsequently be converted to a fine rare earth magnetic powder comprising ReFeB crystals. See FIG. 5.

[0061] The method for the production of the powder precursor may include the steps of combining a rare earth metal salt with at least a first base metal oxalate powder to form a first precursor powder. The first precursor powder is heated at a reaction temperatureand under an elevated reaction pressure and in the presence of hydrogen to form the rare earth magnetic powder precursor, e.g., comprising a metallic base metal powder and a rare earth borate powder.

[0062] In one characterization, the rare earth metal salt is a rare earth borate salt. For example, the rare earth borate salt may be produced by the method disclosed above and exemplified by the flowsheet illustrated in FIG. 2. In another characterization, the rare earth metal salt comprises a rare earth metal oxalate salt. In this characterization, the first precursor powder further comprises boric acid, e.g., boric acid powder, that is combined with the rare earth metal salt and the base metal oxalate powder. See FIG. 3. In either implementation, the rare earth may be selected from Nd, Pr, Dy and combinations thereof, and in one particular implementation the rare earth is Nd.

[0063] In another characterization, the base metal is selected from Fe, Cu, Co and combinations thereof, and in one particular characterization the base metal comprises Fe.

[0064] The reaction temperature is sufficient to convert substantially all of the base metal salts to the base metal in the presence of the rare earth borate. In one characterization, the reaction temperature is at least about 800°C, such as at least about 825°C or at least about 850°C. Typically, the reaction temperature need not exceed about 975°C, such as not greater than about 950°C or not greater than about 900°C. The reaction may be carried out under an elevated pressure, e.g., above about one bar in a pressurized reactor. In one characterization, the reaction pressure is at least about 1.5 bar, such as at least about 2 bar. Typically, the reaction pressure need not exceed about 6 bar, such as not greater than about 5.5 bar. The reaction gas may comprise hydrogen, such as at least about 10% hydrogen, to facilitate reduction of the base metal salt and the formation of base metal powder having a fine size and a high purity.

[0065] For example, the mean average particle size of the base metal powder in the rare earth magnetic powder precursor may be not greater than about 20 pm, such as not greater than about 15 pm or even not greater than about 10 pm. In contrast, the rare earth metal salt e.g., base metal oxalate salt, may have a mean average particle size of not greater than about 250 pm, such as not greater than about 200 pm, such as notgreater than about 175 pm. Although there is no particular lower limit for the mean average particle size of the base metal salts, generally the base metal salts will have a mean average particle size of at least about 50 pm, such as at least about 100 pm.

[0066] In another embodiment, a method for the production of a rare earth magnetic powder of the form NdFeB is disclosed. The method includes the steps of combining a neodymium oxalate powder with aqueous boric acid to form a precursor solution, heating the precursor solution to a reaction temperature that is sufficient to form a neodymium borate powder and an oxalic acid by-product, and separating the neodymium borate powder from the oxalic acid. See FIG. 2, where Re = Nd.

[0067] The method further includes combining the neodymium borate powder with iron oxalate powder to form a first precursor powder, heating the first precursor powder at a reaction temperature under an elevated reaction pressure and in the presence of a reducing gas comprising hydrogen to form the rare earth magnetic powder precursor comprising metallic iron powder and neodymium borate powder.

[0068] The rare earth magnetic powder precursor comprising metallic iron powder and neodymium borate powder is then combined, e.g., mixed, with calcium hydride (CaH2) to form a magnetic powder precursor, e.g., in the form of a free-flowing powder. The magnetic powder precursor is then compacted to form a compacted magnetic precursor body. The precursor body is then heated to reduce the neodymium borate and form an intermediate magnetic precursor comprising NdFeB magnetic powder and calcium hydroxide. The calcium hydroxide may then be separated from the NdFeB magnetic powder.

[0069] The foregoing method may advantageously form a fine NdFeB magnetic powder having highly desirable characteristics. On one characterization, the NdFeB magnetic powder may include at least about 60 wt.% Nd2Fei4B, e.g., tetrahedral crystals of Nd2Fei4B, such as at least about 70 wt.% Nd2Fei4B, at least about 80 wt.% Nd2Fei4B, or even at least about 80 wt.% Nd2Fei4B. Further, the NdFeB magnetic powder may comprise NdFe4B4, and in one characterization the NdFeB magnetic powder comprises not greater than about 10 wt.% NdFe4B4. While Nd2Fei4B may be the majority phase inthe magnetic powder, it is believed that the presence of a relatively low concentration of NdFe4B4 may improve certain characteristics of a magnet formed from the powder.

[0070] In another embodiment, a method for the production of a rare earth magnetic powder of the form SmCo is disclosed. The method includes the steps of combining samarium oxalate powder with cobalt oxalate powder to form a first precursor powder. The first precursor powder is heated to a reaction temperature under an elevated reaction pressure and in the presence of a reducing gas comprising hydrogen to form the rare earth magnetic powder precursor comprising samarium oxide powder and metallic cobalt powder. This rare earth magnetic powder precursor is then combined, e.g., mixed, with calcium hydride to form a magnetic powder precursor. The magnetic powder precursor is then compacted to form a compacted magnetic precursor body, which is subsequently heated to reduce the samarium oxide and form an intermediate magnetic precursor comprising SmCo magnetic powder and calcium hydroxide. The calcium hydroxide may then be separated from the SmCo magnetic powder.

[0071] The present disclosure is also directed to magnetic materials, e.g., magnetic powders, having unique properties. In one embodiment, a magnetic powder of the form NdFeB comprises at least about 80 wt.% Nd2Fei4B, e.g., tetrahedral crystals of Nd2Fei4B, such as at least about 85 wt.% Nd2Fei4B, or even at least about 85 wt.% Nd2Fei4B. The NdFeB magnetic powder may also include NdFe4B4, which may be advantageous for enhancing certain magnetic properties of bulk products formed from the magnetic powder. For example, the magnetic powder may include not greater than about 10 wt.% NdFe4B4, such as not greater than about 6 wt.% NdFe4B4. In another characterization, the magnetic powder may include at least about 2 wt.% NdFe4B4, such as at least about 4 wt.% NdFe4B4.

[0072] In another characterization, the magnetic powder may further include free iron, e.g., an iron phase. It is believed that low concentrations of iron in the bulk products formed from the magnetic powder may enhance the machinability of the bulk products. It will be appreciated that the magnetic powder may also include small concentrations of other base metals, such as copper and cobalt.

[0073] The magnetic powder, e.g., NdFeB or SmCo, may also be characterized as being a fine metal powder, e.g., having a relatively small mean average particle size. In one characterization, the fine magnetic 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 or even not greater than about 12 pm or not greater than about 9 pm. However, powders having too fine of a size may be difficult to handle, and in one characterization the fine magnetic powder has a mean average particle size of at least about 0.5 pm such as at least about 1 pm. The powders may be free-flowing and may have very good compaction properties.

[0074] The rare earth magnetic powder may also have a high purity. For example, the magnetic powder may be characterized as including little to no carbon, little to no nitrogen and little to no oxygen. Bulk products, e.g., permanent magnets, manufactured by sintering and magnetizing the magnetic powder may have advantageous magnetic properties such as high magnetic coercivity and high magnetic flux density.

[0075] While various embodiments of rare earth magnetic materials and methods for producing magnetic materials and their precursors 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 fine rare earth magnetic powder selected from ReFeB and SmCo, comprising the steps of: combining a rare earth metal salt of the form ReBOs or Srri2(C2O4)3 with a base metal powder and calcium hydride to form a magnetic powder precursor; compacting the magnetic powder precursor to form a compacted magnetic precursor body; heating the compacted magnetic precursor body to a reaction temperature and under an inert gas or a vacuum to reduce the rare earth metal salt to a rare earth metal and form an intermediate product comprising calcium hydroxide and a magnetic powder selected from ReFeB and SmCo; and separating the calcium hydroxide from the intermediate product to form the fine rare earth magnetic powder.

2. The method recited in Claim 1 , wherein the fine rare earth magnetic powder comprises ReFeB.

3. The method recited in Claim 2, wherein the rare earth metal salt comprises ReBOs.

4. The method recited in Claim 3, wherein Re is selected from the group consisting of Nd, Pr and Dy.

5. The method recited in Claim 1 , wherein the fine rare earth magnetic powder comprises SmCo.

6. The method recited in Claim 5, wherein the rare earth metal salt comprises Sm2(C2O4)3.

7. The method recited in any one of Claims 1 to 6, wherein the reaction temperature is at least about 900°C.

8. The method recited in any one of Claims 1 to 7, wherein the reduced reaction pressure is a vacuum.

9. The method recited in any one of Claims 1 to 8, wherein the fine rare earth magnetic powder has a mean average particle size of not greater than about 12 pm.

10. The method recited in Claim 9, wherein the fine rare earth magnetic powder has a mean average particle size of not greater than about 9 pm.

11. A method for the formation of rare earth borate powder, comprising the steps of: combining a rare earth oxalate powder with aqueous boric acid to form a precursor solution; heating the precursor solution to a reaction temperature that is sufficient to form a rare earth borate powder and an oxalic acid by-product; and separating the rare earth borate powder from the oxalic acid.

12. The method recited in Claim 11 , wherein the rare earth is selected from the group consisting of Nd, Pr and Dy.

13. The method recited in Claim 12, wherein the rare earth is Nd.

14. The method recited in any one of Claims 11 to 13, wherein the rare earth oxalate powder is of the form Re2(C2C>4)3.

15. The method recited in any one of Claims 11 to 14, wherein the reaction temperature is at least about 70°C.

16. The method recited in Claim 15, wherein the reaction temperature is at least about 75°C.

17. The method recited in any one of Claims 11 to 16, wherein the oxalic acid is recovered.

18. The method recited in Claim 17, wherein the recovered oxalic acid is reacted with a rare earth metal compound to form a rare earth oxalate.

19. The method recited in any one of Claims 11 to 18, wherein the rare earth oxalate powder has a mean average particle size of at least about 100 pm.

20. The method recited in any one of Claims 11 to 19, wherein the rare earth borate powder has a mean average particle size of not greater than about 12 pm.

21. A method for the production of a rare earth magnetic powder precursor, comprising the steps of: combining a rare earth metal salt with at least a first base metal oxalate powder to form a first precursor powder; and heating the first precursor powder at a reaction temperature and under an elevated reaction pressure and in the presence of hydrogen to form the rare earth magnetic powder precursor comprising a metallic base metal powder and a rare earth borate powder.

22. The method recited in Claim 21 , wherein the rare earth metal salt comprises a rare earth metal oxalate and wherein the first precursor powder further comprises boric acid.

23. The method recited in Claim 21 , wherein the rare earth metal salt comprises a rare earth borate.

24. The method recited in any one of Claims 21 to 23, wherein the base metal salt comprises a base metal oxalate.

25. The method recited in any one of Claims 21 to 24, wherein the rare earth metal is selected from Nd, Pr and Dy.

26. The method recited in Claim 25, wherein the rare earth metal comprises Nd.

27. The method recited in any one of Claims 21 to 26, wherein the base metal is selected from Fe, Cu and Co.

28. The method recited in Claim 27, wherein the base metal comprises Fe.

29. The method recited in any one of Claims 21 to 28, wherein the reaction temperature is at least about 800°C.

30. The method recited in Claim 29, wherein the reaction temperature is not greater than about 950°C.

31. The method recited in any one of Claims 21 to 30, wherein the reaction pressure is at least about 2 bar.

32. The method recited in Claim 31 , wherein the reaction pressure is not greater than about 5.5 bar.

33. The method recited in any one of Claims 21 to 32, wherein the reaction gas comprises at least about 10% hydrogen.

34. The method recited in any one of Claims 21 to 33, wherein the base metal salt has a mean average particle size of at least about 100 pm.

35. The method recited in Claim 34, wherein the base metal powder has a mean average particle size of not greater than about 12 pm.

36. A method for the production of a rare earth magnetic powder of the form SmCo, comprising the steps of: combining samarium oxalate powder with cobalt oxalate powder to form a first precursor powder; heating the first precursor powder at a reaction temperature under an elevated reaction pressure and in the presence of a reducing gas comprising hydrogen to form the rare earth magnetic powder precursor comprising samarium oxide powder and metallic cobalt powder; combining a rare earth magnetic powder precursor with calcium hydride to form a magnetic powder precursor; compacting the magnetic powder precursor to form a compacted magnetic precursor body; heating the compacted magnetic precursor body to reduce the samarium oxide and form an intermediate magnetic precursor comprising SmCo magnetic powder and calcium hydroxide; and separating the calcium hydroxide from the SmCo magnetic powder.

37. A magnetic powder of the form NdFeB, wherein the magnetic powder comprises at least about 80 wt.% Nd2Fei B.

38. The magnetic powder recited in Claim 37, wherein the magnetic powder comprises at least about 85 wt.% Nd2Fei4B.

39. The magnetic powder recited in any one of Claims 37 to 38, wherein the magnetic powder comprises not greater than about 10 wt.% NdFe4B4.

40. The magnetic powder recited in Claim 39, wherein the magnetic powder comprises not greater than about 6 wt.% NdFe4B4.41 . The magnetic powder recited in any one of Claims 37 to 40, wherein the magnetic powder further comprises free iron.

42. The magnetic powder recited in any one of Claims 37 to 41 , wherein the magnetic powder has a mean average particle size of not greater than about 12 pm.

43. The magnetic powder recited in Claim 42, wherein the magnetic powder has a mean average particle size of not greater than about 10 pm.

44. The magnetic powder recited in Claim 43, wherein the magnetic powder has a mean average particle size of not greater than about 8 pm.

45. A rare earth magnetic powder of the form NdFeB or SmCo wherein the magnetic powder has a mean average particle size of not greater than about 20 pm, and wherein the magnetic powder comprises: not greater than about 0.12 wt.% carbon; not greater than about 0.05 wt.% nitrogen; and not greater than about 0.18 wt.% oxygen.

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