Process for producing rare earth magnetic materials from metal salts
By using a combined heating reduction method with metal salts, base metals, and calcium hydride, the problem of controlling the particle size and purity of rare earth magnetic material powders has been solved, producing fine powders suitable for high-performance magnetic materials and improving the machinability and magnetic properties of the materials.
Patent Information
- Application Number
- CN202480082566.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-11-01
- Filing Date
- 2024-11-01
- Publication Date
- 2026-08-25
AI Technical Summary
Existing technologies struggle to efficiently produce rare earth magnetic material powders with fine particle size and high purity, especially ReFeB and SmCo powders. Furthermore, traditional methods suffer from difficulties in particle size control and low purity.
A magnetic powder precursor is formed by combining metal salts with base metals and calcium hydride. After pressing, the rare earth metal is reduced by heating under inert gas or vacuum. Then, calcium hydroxide is separated to form rare earth magnetic fine powder, and the particle size and purity are controlled.
This technology enables the production of rare earth magnetic material powders with fine particle size and high purity, making them suitable for the production of high-performance magnetic materials and improving the machinability and magnetic properties of these materials.
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Figure CN122641903A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of rare earth magnetic materials and methods for producing rare earth magnetic materials. Summary of the Invention
[0002] In a first embodiment, a method for producing rare-earth magnetic fine powders selected from ReFeB and SmCo is disclosed. The method includes the following steps: combining a rare-earth metal salt in the form of ReBO3 or Sm2(C2O4)3 with a base metal powder and calcium hydride to form a magnetic powder precursor, and pressing the magnetic powder precursor to form a pressed magnetic precursor body. The pressed magnetic precursor body is heated to a reaction temperature and, under an inert gas or vacuum, the rare-earth metal salt is reduced to a rare-earth metal to form an intermediate product comprising magnetic powder selected from ReFeB and SmCo and calcium hydroxide. The calcium hydroxide can then be separated from the intermediate product to form the rare-earth magnetic fine powder.
[0003] The aforementioned method has undergone numerous refinements, characterizations, and implementations, and can be applied individually or in any combination thereof.
[0004] In one embodiment, the rare earth magnetic fine powder comprises ReFeB. In another embodiment, the rare earth metal salt comprises ReBO3. In yet another embodiment, Re is selected from Nd, Pr, and Dy.
[0005] In another improvement, the rare earth magnetic fine powder comprises SmCo. In one embodiment, the rare earth metal salt comprises Sm2(C2O4)3.
[0006] In another improvement, the reaction temperature is at least about 900°C. In yet another improvement, the reduced reaction pressure is a vacuum.
[0007] In another improvement, the mean average particle size of the rare earth magnetic fine powder is no greater than about 12 μm. In one embodiment, the rare earth magnetic fine powder has a mean average particle size of no greater than about 9 μm.
[0008] In a second embodiment, a method for forming rare earth borate powder is disclosed. The method includes the following steps: combining rare earth oxalate powder with aqueous boric acid (HBO3) to form a precursor solution, and heating the precursor solution to a reaction temperature sufficient to form the rare earth borate powder and oxalic acid byproduct. The rare earth borate powder can then be separated from the oxalic acid.
[0009] The aforementioned method of the second embodiment has undergone many improvements, characterizations and implementations, and can be applied to the aforementioned method alone or in any combination.
[0010] In one improvement, the rare earth element is selected from Nd, Pr, and Dy. In one implementation, the rare earth element is Nd.
[0011] In another improvement, the rare earth oxalate powder is in the form of Re2(C2O4)3.
[0012] In another improvement, the reaction temperature is at least about 70°C. In one embodiment, the reaction temperature is at least about 75°C.
[0013] In another improvement, oxalic acid is collected. In one implementation, the collected oxalic acid is reacted with a rare earth metal compound to form rare earth oxalates.
[0014] In another improvement, the average particle size of the rare earth oxalate powder is at least about 100 μm. In one embodiment, the rare earth borate powder has an average particle size of no more than about 12 μm.
[0015] In a third embodiment, a method for producing 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 elevated reaction pressure in the presence of hydrogen to form a rare-earth magnetic powder precursor comprising a metallic base metal powder and a rare-earth borate powder.
[0016] The aforementioned method of the third embodiment has undergone many improvements, characterizations and implementations, and can be applied to the aforementioned method alone or in any combination.
[0017] In one improvement, the rare earth metal salt comprises a rare earth metal oxalate, and wherein the first precursor powder further comprises boric acid.
[0018] In another improvement, rare earth metal salts include rare earth borates.
[0019] In another improvement, the base metal salt comprises a base metal oxalate.
[0020] In another improvement, the rare earth metal is selected from Nd, Pr, and Dy. In one embodiment, the rare earth metal comprises Nd.
[0021] In another improvement, the base metal is selected from Fe, Cu, and Co. In one embodiment, the base metal comprises Fe.
[0022] In another improvement, the reaction temperature is at least about 800°C. In one embodiment, the reaction temperature is no greater than about 950°C.
[0023] In another improvement, the reaction pressure is at least about 2 bar. In one implementation, the reaction pressure is no greater than about 5.5 bar.
[0024] In another improvement, the reaction gas contains at least about 10% hydrogen.
[0025] In another improvement, the base metal salt has an average particle size of at least about 100 μm. In one embodiment, the base metal powder has an average particle size of no more than about 12 μm.
[0026] In a fourth embodiment, a method for producing rare-earth magnetic powder in the form of SmCo is disclosed. The method includes the following steps: combining samarium oxalate powder with cobalt oxalate powder to form a first precursor powder; and heating the first precursor powder at a reaction temperature and elevated reaction pressure in the presence of a reducing gas containing hydrogen to form a rare-earth magnetic powder precursor. The rare-earth magnetic powder precursor containing samarium oxide powder and metallic cobalt powder is combined with calcium hydride to form a magnetic powder precursor, and the magnetic powder precursor is pressed to form a pressed magnetic precursor body. The pressed magnetic precursor body is heated to reduce samarium oxide and form an intermediate magnetic precursor containing SmCo magnetic powder and calcium hydroxide. The calcium hydroxide can then be separated from the SmCo magnetic powder.
[0027] In the fifth embodiment, a magnetic powder in the form of NdFeB is disclosed, wherein the magnetic powder contains at least about 80% by weight of Nd2Fe. 14 B.
[0028] The aforementioned magnetic powder of the fifth embodiment has undergone many improvements, characterizations and implementations, which can be implemented alone or in any combination.
[0029] In one improvement, the magnetic powder contains at least about 85% by weight of Nd2Fe. 14 B. In one characterization, the magnetic powder contains no more than about 10% by weight of NdFe4B4. In another characterization, the magnetic powder contains no more than about 6% by weight of NdFe4B4.
[0030] In another improvement, the magnetic powder further contains free iron.
[0031] In another improvement, the average particle size of the magnetic powder is no greater than about 12 μm. In one characterization, the average particle size of the magnetic powder is no greater than about 10 μm. In another characterization, the average particle size of the magnetic powder is no greater than about 8 μm.
[0032] In the sixth embodiment, rare earth magnetic powders in the form of NdFeB or SmCo are disclosed. The magnetic powders have an average particle size of not more than about 20 μm and contain not more than about 0.12% by weight of carbon, not more than about 0.05% by weight of nitrogen, and not more than about 0.18% by weight of oxygen.
[0033] These and other embodiments of this disclosure will become clear from the following description. Attached Figure Description
[0034] Figure 1 This is a flowchart illustrating a method for producing NdFeB magnetic powder according to one embodiment.
[0035] Figure 2 This is a flowchart illustrating a method for producing rare earth borate powder according to one embodiment.
[0036] Figure 3 This is a flowchart illustrating a method for producing rare earth NdFeB magnetic precursor powder according to one embodiment.
[0037] Figure 4 This is a flowchart illustrating a method for producing rare earth SmCo magnetic powder according to one embodiment.
[0038] Figure 5 This is a flowchart illustrating a method for producing NdFeB magnetic powder according to one embodiment. Detailed Implementation
[0039] This disclosure relates to the production of rare-earth magnetic powders and precursor powders, particularly powders in the form of ReFeB (where Re is a rare-earth metal) and SmCo. As used herein, the term ReFeB refers to a rare-earth magnet, including but not limited to crystals comprising magnetic compositions of rare earth elements, iron, and boron, such as Re₂Fe. 14 B, ReFe4B4, etc. Similarly, the term SmCo refers to magnetic materials, including but not limited to, SmCo compositions (e.g., SmCo5 and Sm2Co). 17 This disclosure relates in particular to the formation of fine magnetic powders of these magnetic materials formed from metal salts. This contrasts with the formation of magnetic materials in bulk (e.g., in the form of metal ingots) followed by strip casting and pulverization to form powder. The conversion of metal salts into powdered magnetic materials offers numerous advantages compared to such known processes. In this respect, this disclosure also relates to the production of intermediate products, such as precursors of magnetic materials comprising metal salts.
[0040] In one embodiment, a method for producing rare earth magnetic powder is disclosed, wherein the rare earth magnetic powder is selected from ReFeB and SmCo. Figure 1 This is shown as a method for producing Nd2Fe 14An exemplary flowchart of the method for producing magnetic powder B. In the case of ReFeB, Re can be selected from any rare earth metal. In one characterization, the rare earth metal is selected from neodymium (Nd), praseodymium (Pr), dysprosium (Dy), and combinations thereof. In a particular characterization, the rare earth element contains Nd. For example, the magnetic powder can contain a high concentration of magnetic Nd₂Fe. 14 B crystals. In the case of SmCo, the magnetic powder can contain a high concentration of magnetic Sm2Co. 17 Crystal.
[0041] This method may include the step of combining (e.g., mixing) a rare earth metal salt in the form of ReBO3 (i.e., rare earth borate) or Sm2(C2O4)3 (i.e., samarium oxalate) with a base metal and CaH2 (calcium hydride) to form a magnetic powder precursor. The magnetic powder precursor can then be pressed to form a pressed magnetic precursor body. This precursor body can then be heated, for example, in a reactor to a reaction temperature and at a reaction pressure below atmospheric pressure in the presence of hydrogen. Heating is carried out under conditions that reduce the rare earth metal salt to a rare earth metal and form an intermediate magnetic precursor comprising magnetic powder selected from ReFeB and SmCo, a base metal, and calcium hydroxide. The calcium hydroxide can be separated from the intermediate magnetic precursor to form a rare earth magnetic fine powder.
[0042] As used herein, the term metal salt refers to an ionic compound of metal cations and anions, such as oxalate metal salts, borate metal salts, hydroxide metal salts, etc. As used herein, metal salts do not include metal oxide compounds, such as rare earth oxides. In some embodiments and improvements disclosed herein, metal salts include one or more of metal borates and metal oxalates, such as rare earth borates and rare earth oxalates.
[0043] When the desired rare-earth magnetic fine powder is ReFeB, the rare-earth metal salt may comprise the rare-earth borate ReBO3. For example, Re may be selected from Nd, Pr, Dy, and combinations thereof. In a particular characterization, the rare-earth metal Re comprises Nd, for example, where the rare-earth metal salt comprises NdBO3.
[0044] When the desired rare earth magnetic fine powder is SmCo, the rare earth metal salt contains samarium oxalate, such as Sm2(C2O4)3.
[0045] Magnetic powder precursors also include base metals. 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 some embodiments and improvements disclosed herein, the base metal may be selected from iron, cobalt, and copper, as these are the most relevant base metals for rare earth magnetic materials. Furthermore, magnetic powder precursors may include more than one base metal, for example, at least two or at least three base metals.
[0046] Rare earth metal salts (e.g., borates and / or oxalates) can have a mean average particle size of no more than about 250 μm, for example, no more than about 200 μm, or even no more than about 175 μm. An advantage of this method is that the average particle size of the metal salt does not need to be low in order to produce magnetic powders with very fine particle sizes. Although there is no particular lower limit to the mean average particle size of rare earth metal salts, it is typically at least about 50 μm. As used herein, the mean average particle size is determined by laser scattering in wet mode. An example of a particle size analyzer used for performing such measurements is the Horiba Partica LA-960V2 analyzer, available from Horiba Instruments Incorporated, Irvine, CA, USA.
[0047] The base metal powder combined with rare earth metal salts can have a relatively small particle size. For example, the base metal can have an average particle size of no more than about 20 μm, such as no more than about 15 μm or even no more than about 10 μm. Base metal powders with an average particle size of no more than about 3 μm are generally undesirable because they may be difficult to process due to their small size. Nevertheless, a method for producing fine base metal powders in situ using rare earth metal salts is disclosed below.
[0048] Calcium hydride can also be supplied as a powder, and the average particle size of calcium hydride is not considered highly correlated with this method. In one characterization, calcium hydride may have an average particle size of at least about 50 μm and no greater than about 300 μm.
[0049] As described above, the magnetic powder precursor is pressed to form a pressed magnetic precursor body to promote the reaction of the components to form rare-earth magnetic fine powder. The magnetic powder precursor can be pressed under a wide range of pressures. In one example, the magnetic powder precursor can be pressed, for example, in a uniaxial press at a pressure of at least about 15 MPa and no more than about 40 MPa, such as at least about 20 MPa and no more than about 30 MPa.
[0050] Following pressing, the pressed magnetic precursor body is subjected to reaction conditions sufficient to reduce the rare earth metal salt to the rare earth metal in the presence of a base metal, forming calcium hydroxide and hydrogen. For example, the pressed magnetic precursor body can be heated to a reaction temperature of at least about 850°C, such as at least about 875°C, or at least about 900°C. Typically, it is not necessary to heat the pressed magnetic precursor body to a temperature greater than about 1050°C, such as no greater than about 1010°C. Heating can be carried out, for example, in a reactor under an inert gas such as nitrogen or argon, or under a vacuum, such as under reduced pressure. The reaction continues until substantially all of the rare earth metal salt has been reduced to the rare earth metal. Although the reaction time can vary, in one example, the pressed magnetic precursor body is held at the reaction temperature for at least about 6 hours and no more than about 8 hours.
[0051] The resulting product is a pressed body comprising an intermediate magnetic precursor of magnetic powder and calcium hydroxide. Rare-earth magnetic fine powder is then formed by removing the calcium hydroxide from the intermediate magnetic precursor. The calcium hydroxide can be removed using water (e.g., deionized water) in one or more steps, the water being slightly acidified to dissolve the calcium hydroxide. Prior to removing the calcium hydroxide, the brittle pressed body can be ground to break up any loose agglomerates of the magnetic particles to form the magnetic fine powder.
[0052] The resulting fine magnetic powder can be characterized in several ways. For example, the fine magnetic powder can be characterized by having a small particle size. In one characterization, the average particle size of the fine magnetic powder is no greater than about 25 μm, for example, no greater than about 20 μm, for example, no greater than about 15 μm, or even no greater than about 12 μm or no greater than about 9 μm. However, powders with too fine a size may be difficult to handle, and in one characterization, the average particle size of the fine magnetic powder is at least about 0.5 μm, for example, at least about 1 μm.
[0053] In another embodiment, a method for forming rare earth borate powder (e.g., ReBO3 metal salt) is disclosed. See also Figure 2 This method utilizes a double-substitution metathesis reaction to form solid rare-earth borate powder:
[0054]
[0055] In one embodiment, the method for forming rare earth borate powder can be used in conjunction with the aforementioned method for manufacturing rare earth magnetic fine powders, for example, using ReBO3 as the source of the rare earth metal Re to form ReFeB. The method for forming rare earth borate powder includes the step of combining a rare earth oxalate powder, such as Re2(C2O4)3, with hydrated boric acid (H3BO3) to form a precursor solution. The precursor solution is heated to a reaction temperature sufficient to form the rare earth borate powder and the oxalic acid byproduct. The rare earth borate powder can then be separated from the oxalic acid and dried to form dry rare earth borate powder.
[0056] In one characterization, rare earth elements (Re) are selected from Nd, Pr, Dy, and combinations thereof. In a specific improvement, the rare earth element is Nd.
[0057] The reaction temperature for forming rare earth borates can be, for example, at least about 60°C, at least about 65°C, at least about 70°C, or even at least about 75°C. Typically, the reaction temperature does not need to exceed 100°C, for example, not greater than about 95°C, for example, not greater than about 90°C. In one particular embodiment, the reaction temperature is about 80°C.
[0058] Advantageously, oxalic acid formed as a byproduct can be collected, for example, stored for sale or later use. In one characterization, oxalic acid is recycled to form additional rare earth oxalate powder for feeding into the process. For example, oxalic acid can react with a rare earth metal compound to form rare earth oxalates. In a particular embodiment, the rare earth metal compound is a rare earth chloride, such as NdCl3. In this way, 100% of the oxalic acid can be collected and recycled, for example, in a closed loop.
[0059] The average particle size of the rare earth oxalate powder can be no greater than about 250 μm, for example, no greater than about 200 μm, or for example, no greater than about 175 μm. An advantage of this method is that the average particle size of the rare earth oxalate powder does not need to be low in order to form rare earth borate powder with a fine particle size. Although there is no particular lower limit to the average particle size of rare earth metal salts, typically the average particle size of rare earth metal salts will be at least about 50 μm, for example, at least about 100 μm.
[0060] The produced rare earth borate powder can be characterized as having a relatively small average particle size. In one characterization, the rare earth borate powder has an average particle size of no more than about 25 μm, for example, no more than about 20 μm, for example, no more than about 15 μm, or even no more than about 12 μm or no more than about 9 μm. However, powders with too fine a size may be difficult to process, and in one characterization, the rare earth borate powder has an average particle size of at least about 1 μm.
[0061] In another embodiment, a method for producing rare-earth magnetic powder precursors is disclosed. For example, the rare-earth magnetic powder precursors may comprise one or more metallic base metal powders and rare-earth borate powders, which can subsequently be converted into rare-earth magnetic fine powders containing ReFeB crystals. See also Figure 5 .
[0062] A method for producing the powder precursor may include the step 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 temperature and elevated reaction pressure in the presence of hydrogen to form a rare earth magnetic powder precursor, for example, comprising a metallic base metal powder and a rare earth borate powder.
[0063] In one characterization, rare earth metal salts are rare earth borates. For example, rare earth borates can be produced by the methods disclosed above, and through... Figure 2 The flowchart shown is an example. In another characterization, the rare earth metal salt comprises a rare earth metal oxalate. In this characterization, the first precursor powder further comprises boric acid, such as boric acid powder, which is combined with the rare earth metal salt and the base metal oxalate powder. See also Figure 3 In any implementation, the rare earth element may be selected from Nd, Pr, Dy, and combinations thereof, and in a particular implementation, the rare earth element is Nd.
[0064] In another characterization, the base metal is selected from Fe, Cu, Co and combinations thereof, and in a particular characterization, the base metal contains Fe.
[0065] The reaction temperature is sufficient to convert substantially all base metal salts to base metals in the presence of rare earth borates. In one characterization, the reaction temperature is at least about 800°C, for example at least about 825°C or at least about 850°C. Typically, the reaction temperature does not need to exceed about 975°C, for example, not greater than about 950°C or not greater than about 900°C. The reaction can be carried out in a pressurized reactor at elevated pressure (e.g., above about 1 bar). In one characterization, the reaction pressure is at least about 1.5 bar, for example, at least about 2 bar. Typically, the reaction pressure does not need to exceed about 6 bar, for example, not greater than about 5.5 bar. The reaction gas may contain hydrogen, for example, at least about 10% hydrogen, to promote the reduction of the base metal salt and the formation of base metal powder with fine size and high purity.
[0066] For example, the average particle size of the base metal powder in a rare earth magnetic powder precursor may be no greater than about 20 μm, for example, no greater than about 15 μm or even no greater than about 10 μm. Conversely, rare earth metal salts (e.g., base metal oxalates) may have an average particle size no greater than about 250 μm, for example, no greater than about 200 μm, for example, no greater than about 175 μm. Although there is no particular lower limit to the average particle size of the base metal salt, it is generally expected to be at least about 50 μm, for example, at least about 100 μm.
[0067] In another embodiment, a method for producing rare-earth magnetic powder in the form of NdFeB is disclosed. The method includes the steps of: combining neodymium oxalate powder with aqueous boric acid to form a precursor solution; heating the precursor solution to a reaction temperature sufficient to form neodymium borate powder and oxalic acid byproducts; and separating the neodymium borate powder from the oxalic acid. See also Figure 2 , where Re=Nd.
[0068] The method further includes combining neodymium borate powder with iron oxalate powder to form a first precursor powder, heating the first precursor powder at a reaction temperature under elevated reaction pressure and in the presence of a reducing gas containing hydrogen to form a rare earth magnetic powder precursor comprising metallic iron powder and neodymium borate powder.
[0069] 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, for example, a free-flowing powder. The magnetic powder precursor is then pressed to form a pressed magnetic precursor body. The precursor body is then heated to reduce neodymium borate and form an intermediate magnetic precursor comprising NdFeB magnetic powder and calcium hydroxide. The calcium hydroxide can then be separated from the NdFeB magnetic powder.
[0070] The aforementioned method can advantageously form NdFeB magnetic fine powder with highly desirable properties. According to one characterization, the NdFeB magnetic powder may comprise at least about 60% by weight of Nd₂Fe. 14 B, for example, Nd2Fe 14 Tetrahedral crystals of bo, such as at least about 70% by weight of Nd₂Fe. 14 B. At least approximately 80% by weight of Nd2Fe 14 B, or even at least about 80% by weight of Nd2Fe 14 B. Furthermore, NdFeB magnetic powder may contain NdFe4B4, and in one characterization, the NdFeB magnetic powder contained no more than about 10% by weight of NdFe4B4. Although Nd2Fe 14B can be the major phase in magnetic powder, but it is believed that the presence of relatively low concentrations of NdFe4B4 can improve certain properties of magnets formed from powder.
[0071] In another embodiment, a method for producing rare-earth magnetic powder in the form of SmCo is disclosed. The method includes the step 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 elevated reaction pressure and in the presence of a reducing gas containing hydrogen to form a 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 pressed to form a pressed magnetic precursor body, which is subsequently heated to reduce samarium oxide and form an intermediate magnetic precursor comprising SmCo magnetic powder and calcium hydroxide. The calcium hydroxide can then be separated from the SmCo magnetic powder.
[0072] This disclosure also relates to magnetic materials with unique properties, such as magnetic powders. In one embodiment, the magnetic powder in the form of NdFeB contains at least about 80% by weight of Nd2Fe. 14 B, for example, Nd2Fe 14 Tetrahedral crystals of bo, such as at least about 85% by weight of Nd₂Fe. 14 B, or even at least about 85% by weight of Nd2Fe 14 B. The NdFeB magnetic powder may also include NdFe4B4, which can beneficially enhance certain magnetic properties of the bulk product formed from the magnetic powder. For example, the magnetic powder may include no more than about 10% by weight of NdFe4B4, such as no more than about 6% by weight of NdFe4B4. In another characterization, the magnetic powder may include at least about 2% by weight of NdFe4B4, such as at least about 4% by weight of NdFe4B4.
[0073] In another characterization, the magnetic powder may further include free iron, such as an iron phase. It is believed that a low concentration of iron in the bulk product formed from the magnetic powder can enhance the machinability of the bulk product. It should be understood that the magnetic powder may also include small concentrations of other base metals, such as copper and cobalt.
[0074] Magnetic powders, such as NdFeB or SmCo, can also be characterized as fine metallic powders, for example, having a relatively small average particle size. In one characterization, the average particle size of the magnetic fine powder is no greater than about 25 μm, for example, no greater than about 20 μm, for example, no greater than about 15 μm, or even no greater than about 12 μm or no greater than about 9 μm. However, powders with too fine a size may be difficult to handle, and in one characterization, the average particle size of the magnetic fine powder is at least about 0.5 μm, for example, at least about 1 μm. The powder can be free-flowing and can have very good pressing properties.
[0075] Rare earth magnetic powders can also have high purity. For example, magnetic powders can be characterized as containing very little to no carbon, very little to no nitrogen, and very little to no oxygen. Bulk products, such as permanent magnets, made by sintering and magnetizing the magnetic powders can have advantageous magnetic properties such as high magnetic coercivity and high magnetic flux density.
[0076] While various embodiments of rare-earth magnetic materials and methods for producing magnetic materials and their precursors have been described in detail, it is clear that modifications and adjustments to those embodiments will occur to those skilled in the art. However, it should be explicitly understood that such modifications and adjustments are within the spirit and scope of this disclosure.
Claims
1. A method for producing rare earth magnetic fine powders selected from ReFeB and SmCo, comprising the following steps: Rare earth metal salts in the form of ReBO3 or Sm2(C2O4)3 are combined with base metal powders and calcium hydride to form magnetic powder precursors. The magnetic powder precursor is pressed to form a pressed magnetic precursor body; The pressed magnetic precursor body is heated to the reaction temperature and under inert gas or vacuum to reduce the rare earth metal salt to a rare earth metal and form an intermediate product containing calcium hydroxide and magnetic powder selected from ReFeB and SmCo. and The calcium hydroxide is separated from the intermediate product to form a rare earth magnetic fine powder.
2. The method according to claim 1, wherein the rare earth magnetic fine powder comprises ReFeB.
3. The method according to claim 2, wherein the rare earth metal salt comprises ReBO3.
4. The method according to claim 3, wherein Re is selected from Nd, Pr and Dy.
5. The method according to claim 1, wherein the rare earth magnetic fine powder comprises SmCo.
6. The method according to claim 5, wherein the rare earth metal salt comprises Sm2(C2O4)3.
7. The method according to any one of claims 1-6, wherein the reaction temperature is at least about 900°C.
8. The method according to any one of claims 1-7, wherein the reduced reaction pressure is a vacuum.
9. The method according to any one of claims 1-8, wherein the rare earth magnetic fine powder has an average particle size of not more than about 12 μm.
10. The method according to claim 9, wherein the rare earth magnetic fine powder has an average particle size of not more than about 9 μm.
11. A method for forming rare earth borate powder, comprising the following steps: Rare earth oxalate powder was combined with aqueous boric acid to form a precursor solution; The precursor solution was heated to a reaction temperature sufficient to form rare earth borate powder and oxalic acid byproducts; and The rare earth borate powder is separated from the oxalic acid.
12. The method of claim 11, wherein the rare earth element is selected from Nd, Pr, and Dy.
13. The method of claim 12, wherein the rare earth element is Nd.
14. The method according to any one of claims 11-13, wherein the rare earth oxalate powder has the form of Re2(C2O4)3.
15. The method according to any one of claims 11-14, wherein the reaction temperature is at least about 70°C.
16. The method of claim 15, wherein the reaction temperature is at least about 75°C.
17. The method according to any one of claims 11-16, wherein the oxalic acid is collected.
18. The method of claim 17, wherein the collected oxalic acid reacts with a rare earth metal compound to form a rare earth oxalate.
19. The method according to any one of claims 11-18, wherein the rare earth oxalate powder has an average particle size of at least about 100 μm.
20. The method according to any one of claims 11-19, wherein the rare earth borate powder has an average particle size of not more than about 12 μm.
21. A method for producing rare earth magnetic powder precursors, comprising the following steps: A rare earth metal salt is combined with at least a first basic metal oxalate powder to form a first precursor powder; and The first precursor powder is heated at a reaction temperature and elevated reaction pressure in the presence of hydrogen to form a rare earth magnetic powder precursor comprising a metallic base metal powder and a rare earth borate powder.
22. The method of 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 of claim 21, wherein the rare earth metal salt comprises a rare earth borate.
24. The method according to any one of claims 21-23, wherein the base metal salt comprises a base metal oxalate.
25. The method according to any one of claims 21-24, wherein the rare earth metal is selected from Nd, Pr and Dy.
26. The method of claim 25, wherein the rare earth metal comprises Nd.
27. The method according to any one of claims 21-26, wherein the base metal is selected from Fe, Cu and Co.
28. The method of claim 27, wherein the base metal comprises Fe.
29. The method according to any one of claims 21-28, wherein the reaction temperature is at least about 800°C.
30. The method according to claim 29, wherein the reaction temperature is not greater than about 950°C.
31. The method according to any one of claims 21-30, wherein the reaction pressure is at least about 2 bar.
32. The method of claim 31, wherein the reaction pressure is not greater than about 5.5 bar.
33. The method according to any one of claims 21-32, wherein the reactant gas comprises at least about 10% hydrogen.
34. The method according to any one of claims 21-33, wherein the base metal salt has an average particle size of at least about 100 μm.
35. The method of claim 34, wherein the base metal powder has an average particle size of not more than about 12 μm.
36. A method for producing rare earth magnetic powder in the form of SmCo, comprising the following steps: Samarium oxalate powder and cobalt oxalate powder are combined to form a first precursor powder; The first precursor powder is heated at a reaction temperature and elevated reaction pressure in the presence of a reducing gas containing hydrogen to form a rare earth magnetic powder precursor containing samarium oxide powder and metallic cobalt powder. Rare earth magnetic powder precursors are combined with calcium hydride to form magnetic powder precursors; The magnetic powder precursor is pressed to form a pressed magnetic precursor body; Heating the pressed magnetic precursor bulk to reduce the samarium oxide and form an intermediate magnetic precursor comprising SmCo magnetic powder and calcium hydroxide; and The calcium hydroxide is separated from the SmCo magnetic powder.
37. Magnetic powder in the form of NdFeB, wherein the magnetic powder comprises at least about 80% by weight of Nd2Fe 14 B.
38. The magnetic powder of claim 37, wherein the magnetic powder comprises at least about 85% by weight Nd₂Fe. 14 B.
39. The magnetic powder according to any one of claims 37-38, wherein the magnetic powder contains no more than about 10% by weight of NdFe4B4.
40. The magnetic powder of claim 39, wherein the magnetic powder comprises no more than about 6% by weight of NdFe4B4.
41. The magnetic powder according to any one of claims 37-40, wherein the magnetic powder further comprises free iron.
42. The magnetic powder according to any one of claims 37-41, wherein the magnetic powder has an average particle size of not more than about 12 μm.
43. The magnetic powder according to claim 42, wherein the magnetic powder has an average particle size of not more than about 10 μm.
44. The magnetic powder according to claim 43, wherein the magnetic powder has an average particle size of not more than about 8 μm.
45. Rare earth magnetic powder in the form of NdFeB or SmCo, wherein the magnetic powder has an average particle size of not more than about 20 μm, and wherein the magnetic powder comprises: No more than approximately 0.12% by weight of carbon; Nitrogen not exceeding approximately 0.05% by weight; and Oxygen not more than about 0.18% by weight.