Preparation method of a rare earth anisotropic bonded magnetic powder

Abstract

A method for preparing a rare earth anisotropic bonded magnetic powder, comprises the following steps: (1) preparing raw powder with RTBH as the main component, wherein, R is Nd or Pr/Nd, and T is a transition metal containing Fe; (2) adding La hydride or Ce hydride and copper powder to the raw powder to form a mixture; (3) subjecting the mixture to atmosphere diffusion heat treatment to give the rare earth anisotropic bonded magnetic powder.

Claims

1. A preparation method of a rare earth anisotropic bonded magnetic powder, wherein the method comprises: (1) Preparing a raw powder with RTBH as a main component; wherein R is Nd or Pr/Nd, and T is any combination of transition metals and at least containing Fe; (2) Adding La hydride or Ce hydride and copper powder to the raw powder to make a mixture; wherein the La hydride or Ce hydride is added at a ratio of higher than 3.5 wt % and lower than 5.0 wt %, based on a weight of the raw powder; and the copper powder is added at a ratio of 25-100 wt %, based on a weight of the La hydride or Ce hydride; (3) Subjecting the mixture to atmosphere diffusion heat treatment to obtain the rare earth anisotropic bonded magnetic powder, the raw powder with RTBH as the main component is prepared by a HDDR method, which include the following steps: a. Hydrogen absorption and disproportionation stage: putting an RTBH alloy in a rotating gas-solid reaction furnace, heating up to 760-860? C. under a hydrogen pressure of 0-0.1 MPa, and then maintaining the hydrogen pressure at 20-100 kPa for 1 h-4 h to complete the hydrogen absorption and disproportionation stage; b. Slow dehydrogenation and repolymerization stage: after the completion of the hydrogen absorption and disproportionation stage, keeping the temperature in the furnace at 800-900? C., adjusting the hydrogen pressure in the furnace to 1-10 kPa, and maintaining the hydrogen pressure for 10-60 minutes to complete the slow dehydrogenation and repolymerization stage; c. Complete dehydrogenation stage: after the completion of the slow dehydrogenation and repolymerization stage, vacuum-pumping to a hydrogen pressure below 1 Pa to complete the complete dehydrogenation stage; d. Cooling stage: after the completion of the complete dehydrogenation stage, cooling down to room temperature to give the raw powder with RTBH as a main component.

2. The preparation method according to claim 1, wherein in step (1), the raw powder has an average particle size D50 of 80-120 ?m.

3. The preparation method according to claim 1, wherein in step (1), a content of R is ?28.9 wt %, based on a weight of the raw powder.

4. The preparation method of claim 1, wherein in step (2), the copper powder has an average particle size D50 of less than 10 ?m.

5. The preparation method according to claim 1 in step (3), the atmosphere diffusion heat treatment includes a hydrogen-containing atmosphere heat treatment or a vacuum heat treatment.

6. The preparation method according to claim 5, wherein the hydrogen-containing atmosphere heat treatment is carried out under conditions including: a hydrogen pressure of ?1 kPa, an annealing temperature of 700-900? C., and an annealing time of 20-180 min.

7. The preparation method according to claim 5, wherein the vacuum heat treatment is carried out under conditions including: vacuum degree ?5 Pa, annealing temperature of 700-900? C., annealing time of 20-180 min.

8. The preparation method according to any one of claim 1 in step (3), the rare earth anisotropic bonded magnetic powder has an average particle size D50 of 80-120 ?m.

9. The preparation method according to claim 1, wherein in step (3), crystal grains of the rare earth anisotropic bonded magnetic powder include a grain boundary phase and an R.sub.2T.sub.14B magnetic phase.

10. The preparation method according to claim 9, wherein a ratio of a Cu content in the grain boundary phase to a Cu content in the R.sub.2T.sub.14B magnetic phase is greater than 5.

11. The preparation method according to claim 9, wherein a ratio of a Cu content in the grain boundary phase to a Cu content in the R.sub.2T.sub.14B magnetic phase is greater than 10.

12. The preparation method according to claim 2, wherein in step (3), the atmosphere diffusion heat treatment includes a hydrogen-containing atmosphere heat treatment.

13. The preparation method according to claim 3, wherein in step (3), the atmosphere diffusion heat treatment includes a hydrogen-containing atmosphere heat treatment.

14. The preparation method according to claim 4, wherein in step (3), the atmosphere diffusion heat treatment includes a hydrogen-containing atmosphere heat treatment.

15. The preparation method according to claim 2, wherein in step (3), crystal grains of the rare earth anisotropic bonded magnetic powder include a grain boundary phase and an R.sub.2T.sub.14B magnetic phase.

16. The preparation method according to claim 3, wherein in step (3), crystal grains of the rare earth anisotropic bonded magnetic powder include a grain boundary phase and an R.sub.2T.sub.14B magnetic phase.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a low-magnification structure chart of the raw powder with RTBH as the main component obtained in Example 1;

(2) FIG. 2 is a high-magnification structure chart of the raw powder with RTBH as the main component obtained in Example 1;

(3) FIG. 3 is a low-magnification structure chart of the rare earth anisotropic bonded magnetic powder obtained in Example 4;

(4) FIG. 4 is a high-magnification structure chart of the rare earth anisotropic bonded magnetic powder obtained in Example 4.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) In order to make the objectives, technical solutions, and advantages of the present invention clearer, the invention is further illustrated in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the invention. In addition, in the following section, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concept of the present invention.

(6) The invention provides a preparation method of a rare earth anisotropic bonded magnetic powder, comprising the following steps: (1) Preparing a raw powder with RTBH as the main component; wherein R is Nd or Pr/Nd, and T is a transition metal containing Fe; (2) Adding La/Ce hydride and copper powder to the raw powder to make a mixture; (3) Subjecting the mixture to atmosphere diffusion heat treatment to give the rare earth anisotropic bonded magnetic powder.

(7) In the invention, the raw powder with RTBH as the main component is prepared by the HDDR method, which may include the following steps: a. Hydrogen absorption and disproportionation stage: putting the RTBH alloy in a rotating gas-solid reaction furnace, heating up to 760-860? C. under a hydrogen pressure of 0-0.1 MPa, and then maintaining the hydrogen pressure at 20-100 kPa for 1 h-4 h to complete the treatment of hydrogen absorption and disproportionation stage; b. Slow dehydrogenation and repolymerization stage: after the completion of the hydrogen absorption and disproportionation stage, keeping the temperature in the furnace at 800-900? C., adjusting the hydrogen pressure in the furnace to 1-10 kPa, and keeping the pressure for 10-60 minutes to complete the treatment of slow dehydrogenation and repolymerization stage; c. Complete dehydrogenation stage: after the completion of the slow dehydrogenation and repolymerization stage, quickly vacuum-pumping to a hydrogen pressure below 1 Pa to complete the complete dehydrogenation stage; d. Cooling stage: after the completion of the complete dehydrogenation stage, cooling down to room temperature to give the raw powder with RTBH as the main component.

(8) In step (1) of the invention, based on the weight of the raw powder, the content of R is 28.9 wt %, and the grain boundary phase can be evenly distributed along the grain boundary and surround the main phase grains, so that adjacent grains are magnetically separated, which can effectively play a role in demagnetization exchange coupling. Preferably, the content of R is 26.68-28.9 wt %, for example, the content of R may be 28.9 wt %, 28.5 wt %, 28.0 wt %, 27.5 wt %, 27 wt %, 26.68 wt %, and any numerical value in the range defined by any two numerical values among these point values.

(9) In step (1) of the invention, the raw powder has an average particle size D50 of 80-120 ?m.

(10) In the invention, La/Ce hydride is used as the grain boundary diffusion elements. During the heat treatment in step (3), La/Ce elements will enter the grain boundary phase.

(11) In step (2) of the invention, based on the weight of the raw powder, the La/Ce hydride is added at a ratio not higher than 5 wt %, preferably 0.5-5 wt %, for example, the ratio may be 0.5 wt %, 1.0 wt %, 1.5 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 3.5 wt %, 4.0 wt %, 4.5 wt %, 5.0 wt %, and any numerical value in the range defined by any two numerical values among these point values.

(12) In the invention, the copper powder is mainly used to lower the melting point of the La/Ce hydride, thereby effectively reducing the temperature that is required to melt the grain boundary phase during the heat treatment process.

(13) In step (2) of the invention, the copper powder is added at a ratio of 25-100 wt %, based on the weight of the La/Ce hydride.

(14) In step (2) of the invention, the copper powder has an average particle size D50 of less than 10 ?m, which is beneficial to the better diffusion of the copper powder into the grain boundary phase.

(15) In the invention, during the atmosphere diffusion heat treatment process, the grain boundary phase that has been melted into liquid is the diffusion channel, which is beneficial to the diffusion of La and Ce high-abundance rare earth elements and copper element from the surface of the raw powder with RTBH as the main component to the inside of the raw powder and then entry into the grain boundary phase. The above process increases the width of the grain boundary phase, and also effectively reduces the magnetism of the grain boundary phase and enhances the decoupling effect, thereby increasing the coercivity of the raw powder with RTBH as the main component.

(16) In step (3) of the invention, in a preferred embodiment, the atmosphere diffusion heat treatment includes hydrogen-containing atmosphere heat treatment or vacuum heat treatment.

(17) Preferably, the hydrogen-containing atmosphere heat treatment is carried out under conditions including: hydrogen pressure ?1 kPa, annealing temperature of 700-900? C., and annealing time of 20-180 min.

(18) Preferably, the vacuum heat treatment is carried out under conditions including: vacuum degree ?5 Pa, annealing temperature of 700-900? C., annealing time of 20-180 min.

(19) In step (3) of the invention, the rare earth anisotropic bonded magnetic powder has an average particle size D50 of 80-120 ?m.

(20) In step (3) of the invention, the crystal grains of the rare earth anisotropic bonded magnetic powder include grain boundary phase and R.sub.2T.sub.14B magnetic phase.

(21) Preferably, in the rare earth anisotropic bonded magnetic powder, the ratio of the La/Ce content in the grain boundary phase to the La/Ce content in the R.sub.2T.sub.14B magnetic phase is greater than 5. At this time, La/Ce elements are mainly concentrated in the grain boundary phase and the content in the R.sub.2T.sub.14B magnetic phase is relatively low, which can effectively increase the width of the grain boundary phase, reduce the magnetism of the grain boundary phase, and increase the coercivity without causing significant reduction of remanence.

(22) Preferably, in the rare earth anisotropic bonded magnetic powder, the ratio of the Cu content in the grain boundary phase to the Cu content in the R.sub.2T.sub.14B magnetic phase is greater than 10. At this time, the Cu element is mainly concentrated in the grain boundary phase and the content in the R.sub.2T.sub.14B in the magnetic phase is relatively low, which can effectively increase the width of the grain boundary phase, reduce the magnetism of the grain boundary phase, and increase the coercivity without causing significant reduction of remanence.

(23) The invention will be described in detail below through the examples. In the following examples,

(24) The parameters of the particle size distribution are measured in a PSA-laser particle size analyzer;

(25) The coercivity parameters are measured in a magnetic performance measuring instrument;

(26) The maximum magnetic energy product is measured in a magnetic performance measuring instrument;

(27) The remanence is measured in a magnetism measuring instrument.

(28) Unless otherwise specified, the raw materials used are all commercially available products.

Example 1

(29) The raw powder with NdFeBH as the main component was prepared by the HDDR method, comprising the following steps: (1) Hydrogen absorption and disproportionation stage: the NdFeBH alloy was put in a rotating gas-solid reaction furnace, and heated up to 800? C. under a hydrogen pressure of 0.1 MPa, and then the hydrogen pressure was maintained at 50 kPa for 2 h to complete the treatment of hydrogen absorption and disproportionation stage; (2) Slow dehydrogenation and repolymerization stage: after the completion of the hydrogen absorption and disproportionation stage, the temperature in the furnace was kept at 800? C. and the hydrogen pressure in the furnace was adjusted to 5 kPa; and then the temperature and pressure was maintained for 30 minutes to complete the treatment of slow dehydrogenation and repolymerization stage; (3) Complete dehydrogenation stage: after the completion of the slow dehydrogenation and repolymerization stage, the furnace was quickly vacuum-pumped to a hydrogen pressure below 1 Pa to complete the complete dehydrogenation stage; (4) Cooling stage: after the completion of the complete dehydrogenation stage, the furnace was cooled down to room temperature to give the raw powder with NdFeBH as the main component. The low-magnification structure chart and the high-magnification structure chart of the obtained raw powder are shown in FIG. 1 and FIG. 2, respectively. In FIG. 1, the main body is equiaxed Nd.sub.2Fe.sub.14B crystal grains, and the white phase distributed between the crystal grains is the grain boundary phase. FIG. 2 is a high-resolution image taken by a transmission electron microscope, the two distinct areas in the figure are two adjacent Nd.sub.2Fe.sub.14B crystal grains, and the adjacent area is the grain boundary phase with a thickness of 2 nm.

Example 2

(30) The raw powder with PrNdFeBH as the main component was prepared by the HDDR method, comprising the following steps: (1) Hydrogen absorption and disproportionation stage: the NdFeBH alloy was put in a rotating gas-solid reaction furnace, and heated up to 760? C. under a hydrogen pressure of 0.05 MPa, and then the hydrogen pressure was maintained at 30 kPa for 4 h to complete the treatment of hydrogen absorption and disproportionation stage; (2) Slow dehydrogenation and repolymerization stage: after the completion of the hydrogen absorption and disproportionation stage, the temperature in the furnace was kept at 900? C. and the hydrogen pressure in the furnace was adjusted to 3 kPa; and then the temperature and pressure was maintained for 60 minutes to complete the treatment of slow dehydrogenation and repolymerization stage; (3) Complete dehydrogenation stage: after the completion of the slow dehydrogenation and repolymerization stage, the furnace was quickly vacuum-pumped to a hydrogen pressure below 1 Pa to complete the complete dehydrogenation stage; (4) Cooling stage: after the completion of the complete dehydrogenation stage, the furnace was cooled down to room temperature to give the raw powder with PrNdFeBH as the main component.

Example 3

(31) A rare earth anisotropic bonded magnetic powder was prepared by a method comprising the following steps: (1) To the raw powder obtained in Example 1 with NdFeBH as the main component, 0.5 wt % La/Ce hydride and 0.125 wt % copper powder were added to make a mixture; (2) The mixture was subjected to hydrogen-containing atmosphere heat treatment to obtain the rare earth anisotropic bonded magnetic powder; wherein during the hydrogen-containing atmosphere heat treatment process, the hydrogen pressure was 0.6 kPa, the annealing temperature was 700? C., and the annealing time was 20 min.

Example 4

(32) A rare earth anisotropic bonded magnetic powder was prepared by a method comprising the following steps: (1) To the raw powder obtained in Example 2 with PrNdFeBH as the main component, 5.0 wt % La/Ce hydride and 1.25 wt % copper powder were added to make a mixture; (2) The mixture was subjected to vacuum heat treatment to obtain the rare earth anisotropic bonded magnetic powder; wherein, during the vacuum heat treatment process, the vacuum degree was maintained at 5 Pa, the annealing temperature was 700? C., and the annealing time was 180 min. The low-magnification structure chart and the high-magnification structure chart of the obtained raw powder are shown in FIG. 3 and FIG. 4, respectively. In FIG. 3, the main body is equiaxed Nd.sub.2Fe.sub.14B crystal grains, and the white phase distributed between the crystal grains is the grain boundary phase. FIG. 4 is a high-resolution image taken by a transmission electron microscope, the two distinct areas in the figure are two adjacent Nd.sub.2Fe.sub.14B crystal grains, and the adjacent area is the grain boundary phase with a thickness of about 5 nm.

Example 5

(33) A rare earth anisotropic bonded magnetic powder was prepared by a method comprising the following steps: (1) To the raw powder obtained in Example 2 with NdFeBH as the main component, 3.0 wt % La/Ce hydride and 3.0 wt % copper powder were added to make a mixture; (2) The mixture was subjected to hydrogen-containing atmosphere heat treatment to obtain the rare earth anisotropic bonded magnetic powder; wherein during the hydrogen-containing atmosphere heat treatment process, the hydrogen pressure was 0.5 kPa, the annealing temperature was 800? C., and the annealing time was 60 min.

Example 6

(34) A rare earth anisotropic bonded magnetic powder was prepared according to the method of Example 4, except that 5 wt % La/Ce hydride and 1.25 wt % copper powder were added to make a mixture.

Example 7

(35) A rare earth anisotropic bonded magnetic powder was prepared according to the method of Example 4, except that 5.0 wt % La/Ce hydride and 5.0 wt % copper powder were added to make a mixture.

Example 8

(36) A rare earth anisotropic bonded magnetic powder was prepared according to the method of Example 4, except that 4.0 wt % La/Ce hydride and 2.0 wt % copper powder were added to make a mixture.

Comparative Example 1

(37) A rare earth anisotropic bonded magnetic powder was prepared according to the method of Example 1 by using a rare earth alloy with identical chemical composition with the rare earth anisotropic bonded magnetic powder prepared in Example 3.

Comparative Example 2

(38) A rare earth anisotropic bonded magnetic powder was prepared according to the method of Example 1 by using a rare earth alloy with identical chemical composition with the rare earth anisotropic bonded magnetic powder prepared in Example 4.

Comparative Example 3

(39) A rare earth anisotropic bonded magnetic powder was prepared according to the method of Example 1 by using a rare earth alloy with identical chemical composition with the rare earth anisotropic bonded magnetic powder prepared in Example 5.

Test Example

(40) The average particle size D50, coercivity, maximum magnetic energy product and remanence of the raw powders obtained in Examples 1-2 with RTBH as the main component were tested respectively. The test results are shown in Table 1. The average particle size D50, coercivity, maximum energy product and remanence of the rare earth anisotropic bonded magnetic powders obtained in Examples 3-8 and Comparative Examples 1-3 were tested respectively. The test results are shown in Table 1. The testing process required the orientation of the magnetic powder in a magnetic field, and the magnetic field for the orientation was not less than 30 kOe to ensure that the orientation was complete. At that time, the easy magnetization direction of the magnetic powder was arranged parallel along the direction of the external field.

(41) TABLE-US-00001 TABLE 1 Average Maximum particle size magnetic Example D50 Coercivity energy product Remanence No. (?m) (kOe) (MGOe) (kGs) Example 1 80 13.0 39.5 13.0 Example 2 80 13.1 39.0 12.9 Example 3 80 13.5 38.3 12.8 Example 4 80 15.0 36.7 12.5 Example 5 80 14.5 37.3 12.6 Example 6 80 14.6 37.9 12.7 Example 7 80 15.8 36.0 12.4 Example 8 80 14.5 37.0 12.6 Comparative 80 13.0 35.7 12.3 Example 1 Comparative 80 13.5 34.7 12.1 Example 2 Comparative 80 13.2 35.3 12.2 Example 3

(42) From the results in Table 1, it can be seen that the Examples of the invention added La/Ce hydride and Cu powder on the basis of the raw powder of the anisotropic magnetic powder prepared by the HDDR method, and performed heat treatment, which effectively improved the coercivity of the magnetic powder without causing significant reduction of the remanence. Thus, the Examples of the invention obtained magnetic powders with high remanence, coercivity and maximum magnetic energy product. As compared with Comparative Examples 1-3, with the same chemical composition, the magnetic powders prepared by the methods of Examples 3-8 of the invention had higher magnetic performance, with significant effect.

(43) In summary, the invention aims to protect a preparation method of a rare earth anisotropic bonded magnetic powder that can improve coercivity and reduce cost.

(44) It should be understood that the foregoing specific embodiments of the invention are only used to exemplarily illustrate or explain the principle of the invention, and do not constitute a limitation to the invention. Therefore, any modifications, equivalent substitutions, improvements, and the like made without departing from the spirit and scope of the invention should be included in the protection scope of the invention. In addition, the appended claims of the invention are intended to cover all changes and modifications that fall within the scope and boundary of the appended claims, or equivalent forms of such scope and boundary.