MANUFACTURING METHOD OF Sm-Fe-N SYSTEM MAGNETIC SUBSTANCE

Abstract

To provide a manufacturing method of a Sm-Fe-N system magnetic substance of which a magnetic characteristic is improved.SOLUTION: A manufacturing method of a Sm-Fe-N system magnetic substance contains: a step (a step 1) of performing a diffusion heat treatment under a specific temperature while mixing a powder of a Sm-Fe system alloy powder with a powder of a Sm-R-M alloy (R is an absence or one ore more elements selected from a group of Nd, Pr, Ce, La, Gd, Tb, Dy, and Ho, and M is one or more element selected from a group of Zn, Ga, Al, and Cu), and forming a particle having a core part and a shell part that coats the core part and of which a Sm concentration is higher than the core part; and a step (a step 2) of nitriding the powder to be formed in the step 1.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an Sm-Fe-N-based magnetic material.

Background Art

[0002] In recent years, Nd-Fe-B-based magnetic materials and Sm-Fe-N-based magnetic materials have been studied as high-performance magnetic materials. For example, Patent Document 1 discloses a method for manufacturing an Sm-Fe-N-based magnetic material by reducing an oxide containing Sm, Fe, La, and W and nitriding the reduced product.

[0003] Regarding Sm-Fe-N-based magnetic materials, in order to address future resource risks of Sm, partial substitution of Sm with Ce or La has been studied. However, in such Sm-Fe-N-based magnetic materials, the magnetic properties deteriorate. Therefore, it has also been studied to improve the magnetic properties by forming the magnetic material into a core-shell structure and concentrating Sm in the shell portion. As a method for forming the magnetic material into a core-shell structure, Patent Document 2 discloses a method for manufacturing an Nd-Fe-B-based magnetic material having a core-shell structure.

[0004] However, in Sm-Fe-N-based magnetic materials, at the heat treatment temperature during core-shell formation, the Sm-Fe-N phase decomposes, generating α-Fe that has an adverse effect on the magnetic properties, and the magnetic properties may deteriorate.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, in the conventional method for manufacturing Sm-Fe-N-based magnetic materials, the magnetic properties of the obtained magnetic materials may deteriorate. Therefore, an object of the present invention is to provide a method for manufacturing an Sm-Fe-N-based magnetic material with improved magnetic properties.

Means for Solving the Problems

[0007] The present inventors have found that by nitriding after core-shell coating of Sm-Fe alloy particles, it is possible to suppress the deterioration of the magnetic properties of Sm-Fe-N-based magnetic materials, and thus completed the present invention.

[0008] That is, the gist of the present invention is as follows. (1) A method for manufacturing an Sm-Fe-N-based magnetic material, comprising: Powder of Sm-Fe-based alloy particles in which part of Sm is substituted with La and / or Ce, and part of Fe may be substituted with Co and / or Ni, and Powder of an Sm-R-M alloy (R is an element selected from the group consisting of Nd, Pr, Ce, La, Gd, Tb, Dy, and Ho, or does not exist, and M is an element selected from the group consisting of Zn, Ga, Al, and Cu.) are While mixing, diffusion heat treatment is performed at a temperature equal to or higher than the melting point of the Sm-R-M alloy and lower than the melting point of the Sm-Fe-based alloy to diffuse at least Sm contained in the Sm-R-M alloy into the surface layer portion of the Sm-Fe-based alloy particles, forming particles having a core portion and a shell portion covering the core portion and having a higher Sm concentration than the core portion (Step 1); A step of nitriding the particles formed in Step 1 at 400°C to 500°C (Step 2); A method comprising the above. (2) The method according to (1) above, wherein the Sm-Fe-based alloy is an Sm-Ce-Fe alloy. (3) The method according to (1) or (2) above, wherein the Sm-R-M alloy is an Sm-Cu alloy, and the diffusion heat treatment temperature in Step 1 is 600°C to 650°C.

Advantages of the Invention

[0009] The present invention makes it possible to provide a method for manufacturing an Sm-Fe-N-based magnetic material with improved magnetic properties.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0012] The present invention relates to a method for manufacturing an Sm-Fe-N-based magnetic material. In the Sm-Fe-N-based magnetic material of the present invention, part of Sm is substituted with La and / or Ce, and part of Fe may be substituted with Co and / or Ni. When part of Sm is substituted with La and / or Ce, the magnetic properties usually deteriorate. However, the magnetic material of the present invention has a core-shell structure, and since the Sm concentration in the shell part is higher than that in the core part, a decrease in magnetic properties can be suppressed.

[0013] The method for manufacturing an Sm-Fe-N-based magnetic material of the present invention includes a step of diffusion heat treatment (Step 1) at a temperature equal to or higher than the melting point of the Sm-R-M alloy and lower than the melting point of the Sm-Fe-based alloy while mixing a powder of an Sm-Fe-based alloy particle (hereinafter, also referred to as a precursor) and a powder of an Sm-R-M alloy (hereinafter, also referred to as a modifier. R and M are as defined below), and a step of nitriding the particles formed in Step 1 at 400°C to 500°C (Step 2).

[0014] In the manufacturing method of the present invention, the Sm-Fe-based alloy particles are used as a precursor of the obtained Sm-Fe-N-based magnetic material. In the Sm-Fe-based alloy, a part of Sm may be substituted with La and / or Ce, and a part of Fe may be substituted with Co and / or Ni. In one embodiment, the Sm-Fe-based alloy is a Sm-La-Fe alloy composed of Sm, La, and Fe, or a Sm-Ce-Fe alloy composed of Sm, Ce, and Fe.

[0015] In one embodiment, the Sm-Fe-based alloy has, in atomic ratio, the formula (1): (Sm (1-x-y) La x Ce y )2(Fe (1-p-q) Co p Ni q ) 17 (where 0.1 ≦ x + y < 1 and 0 ≦ p + q ≦ 0.10). When the composition of the alloy is represented by atomic percent (at%), the composition in atomic percent can be appropriately converted into the composition in atomic ratio. At this time, in formula (1), the total of Fe, Co, and Ni is obtained so that the total of Sm, La, and Ce becomes 2. However, the value of the total of Fe, Co, and Ni shall be the value rounded to the first decimal place. For example, the Sm 5.38 Ce 5.38 Fe 89.24 (at%) is, in atomic ratio, (Sm 0.5 Ce 0.5 )2Fe 17 and is represented as.

[0016] In one embodiment, in formula (1), x is 0, p is 0, and q is 0, that is, the Sm-Fe-based alloy represented by formula (1) is a Sm-Ce-Fe alloy composed of Sm, Ce, and Fe. In another embodiment, in formula (1), 0.1 ≦ x + y ≦ 0.5.

[0017] The powder of Sm-Fe alloy particles can be prepared, for example, by preparing this alloy, performing a homogenization heat treatment at 800°C to 1200°C, and pulverizing it into powder form. The average particle size of the powder of Sm-Fe alloy particles is usually 32 μm or less. The average particle size of Sm-Fe alloy particles can be measured, for example, by dry sieving, calculation by the cutting method from an optical microscope image, etc.

[0018] In the manufacturing method of the present invention, the Sm-R-M alloy is used as a modifying material for modifying the surface layer portion of the Sm-Fe alloy particles. In the Sm-R-M alloy, R is either absent or one or more elements selected from the group consisting of Nd, Pr, Ce, La, Gd, Tb, Dy, and Ho, and M is one or more elements selected from the group consisting of Zn, Ga, Al, and Cu. In the present invention, the melting point of the Sm-R-M alloy is lower than the melting point of the Sm-Fe alloy.

[0019] In one embodiment, the Sm-R-M alloy is a Sm-M alloy in which R is absent.

[0020] In the Sm-R-M alloy, M is one or more elements selected from the group consisting of Zn, Ga, Al, and Cu, preferably Ga, Al, and Cu, and more preferably Cu.

[0021] In a preferred embodiment, the Sm-R-M alloy is a Sm-Cu alloy.

[0022] In one embodiment, the Sm-R-M alloy has an atomic ratio represented by the formula (2): (Sm (1-a) R a ) (1-b) -M b (wherein R is one or more elements selected from the group consisting of Nd, Pr, Ce, La, Gd, Tb, Dy, and Ho, M is one or more elements selected from the group consisting of Zn, Ga, Al, and Cu, and 0 ≦ a ≦ 0.1 and 0.1 ≦ b ≦ 0.4).)

[0023] In one embodiment, in formula (2), a is 0 and M is Cu. That is, the Sm-R-M alloy represented by formula (2) is a Sm-Cu alloy composed of Sm and Cu.

[0024] The average particle diameter of the powder of the Sm-R-M alloy is usually 32 μm or less. The average particle diameter of the powder of the Sm-R-M alloy can be measured in the same manner as the powder of the Sm-Fe-based alloy particles described above.

[0025] In step 1 of the manufacturing method of the present invention, the powder of the Sm-Fe-based alloy particles and the powder of the Sm-R-M alloy are subjected to diffusion heat treatment at a temperature equal to or higher than the melting point of the Sm-R-M alloy and lower than the melting point of the Sm-Fe-based alloy while being mixed. In the present invention, step 1 is also called a grain boundary diffusion step. In step 1, by performing diffusion heat treatment while mixing at a temperature within this range, the entire surface of the solid-phase Sm-Fe-based alloy particles comes into contact with the molten liquid-phase Sm-R-M alloy. By the diffusion heat treatment, at least Sm contained in the Sm-R-M alloy diffuses into the surface layer portion of the Sm-Fe-based alloy particles, and particles having a core portion and a shell portion that covers the core portion and has a higher Sm concentration than the core portion are formed. When R is present in the Sm-R-M alloy, R also usually diffuses into the surface layer portion of the Sm-Fe-based alloy particles by the diffusion heat treatment. Therefore, in one embodiment, by the diffusion heat treatment, Sm and R (when present) contained in the Sm-R-M alloy diffuse into the surface layer portion of the Sm-Fe-based alloy particles, and a shell portion having a higher concentration of Sm and R (when present) than the core portion is formed.

[0026] In step 1, the powder of the Sm-R-M alloy is usually used in an amount of 1 wt% to 20 wt% with respect to the powder of the Sm-Fe-based alloy particles.

[0027] In Process 1, the temperature of the diffusion heat treatment is a temperature that is equal to or higher than the melting point of the Sm-R-M alloy and lower than the melting point of the Sm-Fe-based alloy. The diffusion heat treatment temperature is preferably a temperature that is +10°C or higher, +20°C or higher, +30°C or higher, or +40°C or higher than the melting point of the Sm-R-M alloy. A person skilled in the art can appropriately set the diffusion heat treatment temperature according to the melting point of the materials used. The diffusion heat treatment temperature is usually 450°C to 800°C, and preferably 500°C to 700°C. In one embodiment, when the Sm-R-M alloy is a Sm-Cu alloy, the diffusion heat treatment temperature is preferably 600°C to 650°C.

[0028] In Process 1, the time of the diffusion heat treatment may be appropriately set according to the diffusion heat treatment temperature, but it is usually 0.5 hours to 5 hours.

[0029] In Process 1, for example, using a device equipped with a stirring mechanism and a heat source, the diffusion heat treatment can be carried out while mixing the powder of Sm-Fe-based alloy particles and the Sm-R-M alloy powder. Such a device is not particularly limited, and examples include a rotary kiln furnace, a stirred heating furnace, etc. In addition, in Process 1, the powder of Sm-Fe-based alloy particles and the Sm-R-M alloy powder may be separately charged into the device, or a mixed powder of these may be charged into the device and the diffusion heat treatment may be carried out while mixing. In one embodiment, when a rotary kiln furnace is used in Process 1, the rotation speed (number of rotations) is usually 0.2 rpm or higher and usually 50 rpm or lower.

[0030] In the particles formed in Process 1, the Sm concentration in the shell part is higher than the Sm concentration in the core part. The ratio of the Sm concentration in the shell part to the Sm concentration in the core part (Sm concentration in the shell part / Sm concentration in the core part) is an atomic ratio and may be greater than 1, preferably 1.1 or higher, and more preferably 1.2 or higher.

[0031] In step 2 of the manufacturing method of the present invention, the particles formed in step 1 are nitrided at 400°C to 500°C. Nitridation can be achieved by heating the particles formed in step 1 at a temperature within this range under a nitrogen atmosphere. By nitriding the core-shell structured particles obtained in step 1 at a specific temperature, decomposition of the nitride can be suppressed, and generation of α-Fe that adversely affects magnetic properties can be suppressed. In step 2, the nitridation treatment time is usually 4 hours to 20 hours.

[0032] The Sm-Fe-N-based magnetic material obtained by the manufacturing method of the present invention (hereinafter, also referred to as the magnetic material of the present invention) is particles having a core-shell structure, which has a core part and a shell part covering the core part.

[0033] The core part in the magnetic material of the present invention has an atomic composition corresponding to the nitride of the Sm-Fe-based alloy particles used as a precursor. The diameter (maximum diameter) of the core part is usually 1 μm to 30 μm. The diameter of the core part can be measured by SEM-EDX.

[0034] The shell part in the magnetic material of the present invention has an atomic composition corresponding to the nitride of the shell part in the particles formed in step 1. The thickness of the shell part is usually 0.02 μm to 1 μm. The presence or absence of the shell part and the thickness of the shell part in the magnetic material can be confirmed by SEM-EDX.

[0035] The magnetic material of the present invention has a higher Sm concentration in the shell part than in the core part and has excellent magnetic properties. The ratio of the Sm concentration of the shell part to that of the core part is as described above for the particles formed in step 1.

[0036] In the magnetic material of the present invention, the generation of α-Fe that adversely affects magnetic properties is suppressed. When Sm-Fe-based alloy particles are nitrided to obtain an Sm-Fe-N-based magnetic material and this is subjected to diffusion heat treatment at a predetermined temperature to form a core-shell structure, the nitride decomposes and α-Fe is generated at the interface between the core part and the shell part. On the other hand, in the production method of the present invention, since the Sm-Fe-based alloy particles are nitrided after being formed into a core-shell structure, the decomposition of the nitride does not occur, and the generation of α-Fe can be suppressed. In the magnetic material of the present invention, α-Fe does not exist, or even if it exists, the amount is extremely small. The presence or absence and the amount of α-Fe can be confirmed by measuring the presence or absence and the size of the peak corresponding to α-Fe by XRD.

[0037] The magnetic material of the present invention may have a part consisting of Sm or a part containing Sm (for example, an Sm-R-M part) derived from the Sm-R-M alloy of the modifier on the surface of the shell part. These parts are usually formed on a part of the surface of the shell part.

[0038] Despite the fact that a part of Sm in the magnetic material of the present invention is substituted with La and / or Ce, it has excellent magnetic properties. The magnetic material of the present invention has, for example, an anisotropy magnetic field Ha of 10.5 or more.

Examples

[0039] Hereinafter, the present invention will be described more specifically using examples. However, the technical scope of the present invention is not limited to these examples.

[0040] First, Sm 5.38 Ce 5.38 Fe 89.24 (at%) alloy prepared by high-frequency melting was homogenized at 1100 °C for 24 hours. Then, it was pulverized to 20 μm or less with a cutter mill to produce a precursor powder. All these steps were carried out under an inert atmosphere of Ar.

[0041] Comparative Example 1 The precursor powder was nitrided in a nitrogen atmosphere at 475 °C for 16 hours.

[0042] Comparative Example 2 The powder of the precursor was nitrided at 475 °C for 16 hours in a nitrogen atmosphere. The nitrided powder of the precursor was mixed with 10 wt% of Sm7Cu3 alloy (modifying material) powder with respect to this powder, and then heat treatment was carried out at 650 °C for 1 hour in a rotary kiln furnace.

[0043] Comparative Example 3 The powder of the precursor was mixed with 10 wt% of Sm7Cu3 alloy powder with respect to this powder, and then heat treatment was carried out at 550 °C for 1 hour in a rotary kiln furnace. The obtained powder was further nitrided at 475 °C for 16 hours in a nitrogen atmosphere.

[0044] Example 1 It was prepared in the same manner as Comparative Example 3 except that the heat treatment temperature was changed from 550 °C to 650 °C.

[0045] Example 2 It was prepared in the same manner as Comparative Example 3 except that the heat treatment temperature was changed from 550 °C to 600 °C.

[0046] For the obtained powders of Example 1, 2 and Comparative Examples 1 to 3, magnetic property evaluation was carried out by PPMS-VSM, microstructure observation was carried out by SEM-EDX, and crystal structure analysis was carried out by XRD. The obtained results are shown in Table 1. In Table 1, the composition of the core part and the presence or absence of the shell structure were confirmed by line analysis by SEM-EDX, and the presence or absence of α-Fe was confirmed by XRD. Figure 1 shows the results of line analysis by SEM-EDX near the particle interface of Example 1, and Figure 2 shows the results of line analysis by SEM-EDX near the particle interface of Comparative Example 2. Further, Figure 3 shows a schematic diagram of the manufacturing processes of Example 1 and Comparative Examples 1 and 2. In Figure 3, the composition of the shell part was confirmed by line analysis by SEM-EDX.

[0047]

Table 1

[0048] As shown in Table 1, the anisotropy magnetic field Ha of Comparative Example 2, which was nitrided first, was significantly lower than that of Comparative Example 1, which was not core-shell formed. On the other hand, Examples 1 and 2, which were nitrided after core-shell formation, had an improved anisotropy magnetic field Ha than Comparative Example 1. It is difficult to measure the anisotropy magnetic field Ha of only the shell part, but since the anisotropy magnetic field Ha of the core-shell formation is considered to be the average value of the core part and the shell part, it is presumed that the shell part has a significantly higher anisotropy magnetic field Ha than the core part. Furthermore, in Comparative Example 3, in which the diffusion heat treatment temperature was 550°C, no improvement in the anisotropy magnetic field Ha was confirmed.

[0049] The reason why the anisotropy field Ha of Comparative Example 2 was significantly decreased is considered to be due to the influence of Fe-rich components (α-Fe) precipitated when the nitrides were decomposed, as shown in Figs. 2 and 3. For Comparative Example 2, the presence of α-Fe was also confirmed by XRD analysis. In Comparative Example 3, the melting point of the Sm7Cu3 alloy was near 600°C, and the Sm7Cu3 alloy did not become liquid at 550°C, so it is considered that diffusion of Sm into the precursor did not occur. On the other hand, in Examples 1 and 2, in which the diffusion heat treatment temperatures were 650°C and 600°C, respectively, the Sm7Cu3 alloy became liquid, and diffusion of Sm into the precursor occurred, so that a shell portion richer in Sm than the core portion was formed near the surface layer of the particle, as shown in Figs. 1 and 3. Since the anisotropy field of the Sm-rich shell portion was higher than that of the core portion, it is considered that the average anisotropy field Ha of the entire particle was also high in Examples 1 and 2.

Claims

1. A method for manufacturing an Sm—Fe—N-based magnetic material, comprising: a powder of Sm—Fe-based alloy particles, wherein a part of Sm is substituted with La and / or Ce, and a part of Fe may be substituted with Co and / or Ni; and a powder of an Sm—R—M alloy (R is absent or is one or more elements selected from the group consisting of Nd, Pr, Ce, La, Gd, Tb, Dy, and Ho; M is one or more elements selected from the group consisting of Zn, Ga, Al, and Cu)), while mixing, performing diffusion heat treatment at a temperature equal to or higher than the melting point of the Sm—R—M alloy and lower than the melting point of the Sm—Fe-based alloy to diffuse at least Sm contained in the Sm—R—M alloy into the surface layer portion of the Sm—Fe-based alloy particles, thereby forming particles having a core portion and a shell portion covering the core portion and having a higher Sm concentration than the core portion (Step 1); nitriding the particles formed in Step 1 at 400° C. to 500° C. (Step 2); and a method comprising the above steps.

2. The method according to claim 1, wherein the Sm—Fe-based alloy is an Sm—Ce—Fe alloy.

3. The method according to claim 1 or 2, wherein the Sm—R—M alloy is an Sm—Cu alloy, and the diffusion heat treatment temperature in Step 1 is 600° C. to 650° C.

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