Anisotropic complex sintered magnet comprising MnBi and atmospheric sintering process for preparing the same

Abstract

The present invention relates to an anisotropic complex sintered magnet including MnBi with magnetic characteristics enhanced and an atmospheric sintering method for preparing the same. The anisotropic complex sintered magnet including MnBi according to the present invention may implement excellent magnetic characteristics, and thus may replace rare earth bond magnets in the related art, and a continuous process is enabled because the magnet is prepared by an atmospheric sintering method, and a sintering method used in the permanent magnet process in the related art is used as it is, so that the anisotropic complex sintered magnet is economical.

Claims

1. An atmospheric sintering method for preparing an anisotropic complex sintered magnet comprising MnBi, the method comprising: (a) preparing a non-magnetic phase MnBi-based ribbon by a rapidly solidification process (RSP); (b) subjecting the non-magnetic phase MnBi-based ribbon to a heat treatment to convert the non-magnetic phase MnBi-based ribbon into a magnetic phase MnBi-based ribbon; (c) pulverizing the magnetic phase MnBi-based ribbon to prepare MnBi hard magnetic phase powders; (d) mixing the MnBi hard magnetic phase powders with rare earth hard magnetic phase powders in the presence of a lubricant into a mixture; (e) molding the mixture in a magnetic field by applying an external magnetic field and a pressure into a molded product; and (f) subjecting the molded product to an atmospheric sintering process, wherein the non-magnetic phase MnBi-based ribbon prepared in (a) has an average crystal grain size of 50 to 100 nm, and wherein the rapidly solidification process in the step (a) is performed with a wheel speed of 60 to 70 m/s.

2. The method of claim 1, wherein the lubricant is selected from the group consisting of ethyl butyrate, methyl caprylate, ethyl laurate, and stearates.

3. The method of claim 1, wherein the pressure applied in (e) is 300 to 1,000 Mpa.

4. The method of claim 1, wherein the atmospheric sintering process is performed in an atmospheric sintering furnace at a temperature of 200 to 500 C. for 1 minute to 5 hours.

5. The method of claim 1, wherein the heat treatment of (b) is performed at a temperature of 280 to 340 C.

6. The method of claim 1, wherein the MnBi hard magnetic phase powders have an average size of 0.5 to 5 m, and the rare earth hard magnetic phase powders have an average size of 1 to 5 m.

7. The method of claim 1, wherein during the process of pulverizing the magnetic phase MnBi-based ribbon in (c), a dispersing agent selected from the group consisting of oleic acid (C.sub.18H.sub.34O.sub.2), oleyl amine (C.sub.18H.sub.37N), polyvinylpyrrolidone, and polysorbate is used.

8. The method of claim 1, wherein the non-magnetic phase MnBi-based ribbon prepared in (a) comprises a non-magnetic phase in an amount of 90% or more.

9. The method of claim 1, wherein in (d), a maximal amount of the rare earth hard magnetic phase powders that is mixed with the MnBi hard magnetic phase powders is 30 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a schematic view of a process of preparing a complex sintered magnet of an MnBi hard magnetic phase powder/a rare earth hard magnetic phase powder according to an exemplary embodiment;

(2) FIG. 2 illustrates a distribution analysis of MnBi and SmFeN by a scanning electron microscope (SEM) in the MnBi/SmFeN (30 wt %) complex sintered magnet;

(3) FIG. 3 illustrates the residual flux density (Br) and maximum magnetic energy product [(BH)max] of the MnBi/SmFeN (30 wt %) complex sintered magnet according to the atmospheric sintering temperature (sintering time 6 minutes);

(4) FIG. 4 illustrates the density and maximum magnetic energy product [(BH)max] of the MnBi/SmFeN (30 wt %) complex sintered magnet according to the atmospheric sintering temperature (sintering time 6 minutes); and

(5) FIG. 5 illustrates the result of an X-ray photoelectron spectroscopy (XPS) of the MnBi/SmFeN (30 wt %) normal sintered magnet.

MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS

(6) Hereinafter, the present invention will be described in more detail through the Examples. These Examples are provided only for more specifically describing the present invention, and it will be obvious to a person with ordinary skill in the art to which the present invention pertains that the scope of the present invention is not limited by these Examples.

Example

Preparation of Anisotropic Complex Sintered Magnet Including MnBi

(7) In accordance with the schematic view illustrated in FIG. 1, an anisotropic complex sintered magnet was prepared, and specifically, an MnBi ribbon was prepared by first setting the wheel speed in a rapidly solidification process (RSP) of preparing the MnBi ribbon to 60 to 70 m/s to form MnBi, Bi phases with a crystal size of 50 to 100 nm.

(8) The non-magnetic phase MnBi-based ribbon prepared may comprise non-magnetic phase in an amount of 90% or more, preferably 99% or more. If non-magnetic phase MnBi-based ribbon comprises 90% or more of non-magnetic phase, it is possible to inhibit rapid grain growth in the heat treatment for forming an MnBi low temperature phase (LTP), and to have uniform MnBi LTP.

(9) As the next step, a low temperature heat treatment was performed at a temperature of 280 C. under the vacuum and inert gas atmosphere conditions in order to impart magnetic properties to the prepared non-magnetic phase MnBi ribbon, a heat treatment was performed for 24 hours to induce diffusion of Mn included in the non-magnetic phase MnBi ribbon and form a magnetic phase MnBi-based ribbon, and through this, an MnBi-based magnetic body was prepared.

(10) As a next step, a complex process was performed using the ball milling, and the pulverization process was performed for about 5 hours, the ratio of the magnetic phase powder, balls, a solvent, and a dispersing agent was about 1:20:6:0.12 (by mass), and the balls were set to 3 to 5.

(11) Subsequently, the SmFeN hard magnetic body powder (30 wt %) was maximally mixed with the magnetic powder (70 wt %) prepared by the ball milling under methyl caprylate without being pulverized, a magnetic field molding was performed under the magnetic field of about 1.6 T while an external pressure of 700 Mpa was applied thereto, and then atmospheric sintering was performed at various temperatures belonging to 260 C. to 480 C. under normal pressure for 6 minutes to prepare a sintered magnet.

(12) The cross-sectional state of the complex sintered magnet thus prepared was observed by a scanning electron microscope (SEM), and is illustrated in FIG. 2. In FIG. 2, it could be confirmed that a rare earth-free MnBi hard magnetic phase and a rare earth SmFeN hard magnetic phase were uniformly distributed.

(13) Detection of Carbon Reside at Interface Between Particles of Anisotropic Complex Sintered Magnet

(14) The X-ray photoelectron spectroscopy (XPS) result of the MnBi/SmFeN (30 wt %) normal sintered magnet prepared above are illustrated in FIG. 5. Referring to FIG. 5, it can be confirmed that the content of carbon residue (C1s) was 37.8 at %, and the carbon residue was detected at a thickness of 10 nm from the surface.

(15) Magnetic Characteristics and Density of Anisotropic Complex Sintered Magnet According to Atmospheric Sintering Temperature

(16) The intrinsic coercive force (HCi), residual flux density (Br), induced coercive force (HCB), density, and maximum magnetic energy product [(BH)max] of the MnBi/SmFeN (30 wt %) normal sintered magnet are shown, and the magnetic characteristics were measured at normal temperature (25 C.) using a vibrating sample magnetometer (VSM, Lake Shore #7300 USA, maximum 25 kOe), and the values are shown in the following Table and FIGS. 3 and 4.

(17) TABLE-US-00001 TABLE 1 Atmospheric sinteringtemperature HCl Br HCB Density (BH)max ( C.) (kOe) (kG) (kG) (g/cm3) (MGOe) 260 9.18 7.20 6.29 7.43 11.98 300 8.84 7.47 6.51 7.65 12.87 320 8.78 7.53 6.53 7.67 13.06 340 8.61 7.53 6.56 7.71 13.09 360 8.22 7.54 6.54 7.75 13.12 380 8.17 7.73 6.63 7.78 13.77 400 7.80 7.84 6.56 7.77 14.09 420 7.33 7.85 6.56 7.78 14.18 440 5.49 8.03 5.11 7.86 14.68 460 4.99 8.02 4.71 7.88 14.39 480 4.80 8.00 4.53 7.91 14.20

(18) Referring to Table 1 ad FIG. 3, when prepared by the atmospheric sintering process at 440 C. for 6 minutes, the anisotropic complex sintered magnet of MnBi/SmFeN (30 wt %) anisotropic complex sintered magnet of the present invention exhibited a maximum magnetic energy product [(BH)max]measured value of 14.68 MGOe at 25 C. This is a result showing that a continuous process was enabled because a rapid sintering process using the hot press and the like was not used, and a high-performance complex sintered magnet may be prepared using a sintering method used in the permanent magnet process in the related art as it is. FIG. 4 is a result showing that as the atmospheric sintering temperature is increased, the intrinsic coercive force is decreased and the density is increased, an increase in density is a result that as the heat treatment temperature is increased, the size of crystal grains is increased to improve the densification of the sintered body, and a decrease in intrinsic coercive force is a result that due to the growth of crystal grains, the domain wall is increased.