JP2011216732A - Permanent magnet and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a permanent magnet and a method for manufacturing the same, capable of improving the efficiency of operations in a manufacturing step and performing orientation at minute torque in a molding step.SOLUTION: A slurry 42 is prepared by doping, to fine particles of a pulverized neodymium magnet, an organic solvent containing an organic metal compound represented by M-(OR)(wherein M is V, Mo, Zr, Ta, Ti, W or Nb, R is one from among 2-6C alkyl groups and may be a straight chain or a branched chain, and x is an arbitrary integer), and after that, a magnetic field is applied to the slurry 42 injected into a cavity 54 by a molding machine 50, and a pressure is applied to the slurry in this state, and then, the organic solvent is evaporated, thereby obtaining a molded product. Subsequently, the molded product is subjected to temporary baking processing in hydrogen and baked at 800-1,180°C, thereby a permanent magnet is manufactured.

Description

  The present invention relates to a permanent magnet and a method for manufacturing the permanent magnet.

In recent years, permanent magnet motors used in hybrid cars, hard disk drives, and the like have been required to be smaller, lighter, higher in output, and more efficient. Further, in order to realize a reduction in size and weight, an increase in output, and an increase in efficiency in the permanent magnet motor, further improvement in magnetic characteristics is required for the permanent magnet embedded in the permanent magnet motor. Permanent magnets include ferrite magnets, Sm—Co magnets, Nd—Fe—B magnets, Sm ₂ Fe ₁₇ N _x magnets, etc. Nd—Fe—B magnets with particularly high residual magnetic flux density. Used as a permanent magnet for a permanent magnet motor.

  Here, as a manufacturing method of the permanent magnet, a powder sintering method is generally used. Here, in the powder sintering method, first, raw materials are coarsely pulverized, and magnet powder is manufactured by fine pulverization by a jet mill (dry pulverization). Thereafter, the magnet powder is put into a mold and press-molded into a desired shape while applying a magnetic field from the outside. And it manufactures by sintering the solid magnet powder shape | molded by the desired shape at predetermined temperature (for example, 800 to 1150 degreeC in the case of a Nd-Fe-B type magnet).

Japanese Patent No. 3298219 (pages 4 and 5)

  On the other hand, Nd-based magnets such as Nd—Fe—B have a problem that the heat-resistant temperature is low. Therefore, when an Nd magnet is used for a permanent magnet motor, the residual magnetic flux density of the magnet gradually decreases when the motor is continuously driven. Therefore, when using an Nd magnet for a permanent magnet motor, in order to improve the heat resistance of the Nd magnet, Dy (dysprosium) or Tb (terbium) having high magnetic anisotropy is added, and the coercive force of the magnet is added. It is intended to further improve the above.

  On the other hand, it is conceivable to improve the coercive force of the magnet without using Dy or Tb. For example, it is known that the magnetic performance of a permanent magnet is basically improved by reducing the crystal grain size of the sintered body because the magnetic properties of the magnet are derived by the single domain fine particle theory. . Here, in order to reduce the crystal grain size of the sintered body, it is necessary to reduce the grain size of the magnet raw material before sintering.

  However, magnet particles finely pulverized to have a small particle size have a problem that handling is difficult because the bulk specific gravity is very small. Therefore, there has been a problem that the working efficiency deteriorates when the magnet powder is molded and oriented after pulverization. Further, the magnet particles finely pulverized to have a small particle size have a problem that it is difficult to align with a small torque.

  The present invention has been made in order to solve the above-described problems in the prior art, and is formed by adding a solvent to the pulverized magnet powder to form a slurry, and forming the slurry while applying a magnetic field to the slurry. By forming a body, even magnetic particles finely pulverized to a fine particle size can be handled easily, and it is possible to improve the work efficiency in the manufacturing process, and in the molding process, An object of the present invention is to provide a permanent magnet capable of performing orientation by torque and capable of improving magnetic performance, and a method of manufacturing the permanent magnet.

  In order to achieve the object, a permanent magnet according to claim 1 of the present application includes a step of pulverizing a magnet raw material into magnet powder, a step of adding a solvent to the pulverized magnet powder, and generating a slurry. On the other hand, it is manufactured by the process of forming a molded object by shape | molding in the state which applied the magnetic field, and the process of sintering the said molded object.

  The permanent magnet according to claim 2 is the permanent magnet according to claim 1, wherein in the step of forming the formed body, the slurry is applied in a state in which a magnetic field is applied to a cavity for forming the formed body. Is injected into the cavity.

  The permanent magnet according to claim 3 is the permanent magnet according to claim 1, wherein in the step of forming the formed body, the slurry is injected into the cavity for forming the formed body, and then the cavity is formed with respect to the cavity. And applying a magnetic field.

The permanent magnet according to claim 4 is the permanent magnet according to any one of claims 1 to 3, wherein the solvent is represented by the following structural formula M- (OR) _x (where M is V, Mo). , Zr, Ta, Ti, W or Nb, R is any alkyl group having 2 to 6 carbon atoms, which may be linear or branched, and x is an arbitrary integer. It is an organic solvent containing a metal compound.

The permanent magnet according to claim 5 is the permanent magnet according to any one of claims 1 to 4, wherein the magnet powder is magnet powder containing magnet powder having a single domain particle diameter. To do.
The single domain particle diameter is a particle diameter of a single domain particle (a particle composed of a small region in which no domain wall exists in the thermal demagnetized state and only one magnetization direction exists), for example, 0.2 μm to The particle size is 1.2 μm.

  The method for producing a permanent magnet according to claim 6 includes a step of pulverizing a magnet raw material into magnet powder, a step of adding a solvent to the pulverized magnet powder to generate a slurry, and a magnetic field with respect to the slurry. It has the process of forming a molded object by shape | molding in the state which applied, and the process of sintering the said molded object, It is characterized by the above-mentioned.

  A method for manufacturing a permanent magnet according to claim 7 is the method for manufacturing a permanent magnet according to claim 6, wherein in the step of forming the molded body, a magnetic field is applied to the cavity for forming the molded body. The slurry is injected into the cavity in an applied state.

  A method for manufacturing a permanent magnet according to claim 8 is the method for manufacturing a permanent magnet according to claim 6, wherein in the step of forming the molded body, the slurry is injected into a cavity for forming the molded body. Then, a magnetic field is applied to the cavity.

The method for producing a permanent magnet according to claim 9 is the method for producing a permanent magnet according to any one of claims 5 to 8, wherein the solvent is represented by the following structural formula M- (OR) _x (wherein , M is V, Mo, Zr, Ta, Ti, W or Nb, R is any one of alkyl groups having 2 to 6 carbon atoms, and may be linear or branched, and x is an arbitrary integer. .) Is an organic solvent containing an organometallic compound.

Furthermore, the manufacturing method of the permanent magnet which concerns on Claim 10 is a manufacturing method of the permanent magnet in any one of Claim 5 thru | or 9. WHEREIN: The said magnet powder contains the magnet powder of a single domain particle diameter. It is characterized by being.
The single domain particle diameter is a particle diameter of a single domain particle (a particle composed of a small region in which no domain wall exists in the thermal demagnetized state and only one magnetization direction exists), for example, 0.2 μm to The particle size is 1.2 μm.

  According to the permanent magnet of claim 1, having the above-described configuration, a slurry is formed by adding a solvent to the pulverized magnet powder, and a molded body is formed by molding in a state where a magnetic field is applied to the slurry. Therefore, even magnet particles finely pulverized to a fine particle diameter can be handled easily, and the working efficiency in the manufacturing process can be increased. Further, in the molding process, it is possible to orient the magnet particles with a small torque, and it is possible to improve the magnetic performance.

  Further, according to the permanent magnet of the second aspect, in the step of forming the molded body, the slurry is injected into the cavity with the magnetic field applied to the cavity for forming the molded body. It becomes possible to orient the magnet particles in the slurry and improve the magnetic performance.

  According to the third aspect of the present invention, in the step of forming the molded body, the slurry is injected into the cavity for forming the molded body, and then the magnetic field is applied to the cavity. It becomes possible to orient the magnet particles inside, and to improve the magnetic performance.

Moreover, according to the permanent magnet of claim 4, M- (OR) _x (wherein M is V, Mo, Zr, Ta, Ti, W, or Nb as a solvent used when the slurry is generated). , R is any of an alkyl group having 2 to 6 carbon atoms, and may be linear or branched. X is an arbitrary integer.) Since an organic solvent containing an organometallic compound represented by It becomes possible to make the metal V, Mo, Zr, Ta, Ti, W, or Nb unevenly distributed at the grain boundaries of the magnet after sintering. As a result, V, Mo, Zr, Ta, Ti, W or Nb unevenly distributed at the grain boundaries suppresses the grain growth of magnet particles during sintering, and exchange interaction between crystal grains after sintering. By dividing, it is possible to prevent the magnetization reversal of each crystal grain and improve the magnetic performance.

  According to the permanent magnet of the fifth aspect, each of the crystal grains constituting the permanent magnet can have a single domain structure. As a result, the magnetic performance of the permanent magnet can be greatly improved. In addition, even magnetic particles finely pulverized to a single magnetic domain particle diameter can be easily handled, and work efficiency in the manufacturing process can be increased.

  Further, according to the method for producing a permanent magnet according to claim 6, a solvent is added to the pulverized magnet powder to produce a slurry, and the molded product is molded by applying a magnetic field to the slurry. Since they are formed, even magnetic particles finely pulverized to a fine particle diameter can be handled easily, and the working efficiency in the manufacturing process can be increased. Further, in the molding process, it is possible to orient the magnet particles with a minute torque, and it is possible to increase the working efficiency.

  Further, according to the method of manufacturing a permanent magnet according to claim 7, in the step of forming the molded body, the slurry is injected into the cavity in a state where a magnetic field is applied to the cavity for forming the molded body. It becomes possible to orient the magnetic particles in the slurry with a small torque, and it is possible to improve the magnetic performance.

  Further, according to the method of manufacturing a permanent magnet according to claim 8, since the magnetic field is applied to the cavity after the slurry is injected into the cavity for forming the molded body in the step of forming the molded body, It becomes possible to orient the magnet particles in the slurry by torque, and to improve the magnetic performance.

Moreover, according to the method for producing a permanent magnet according to claim 9, M- (OR) _x (wherein M is V, Mo, Zr, Ta, Ti, W or Nb, R is any alkyl group having 2 to 6 carbon atoms, and may be linear or branched. X is an arbitrary integer.) It becomes possible to produce a magnet in which V, Mo, Zr, Ta, Ti, W or Nb, which are high melting point metals, are unevenly distributed at grain boundaries after sintering. As a result, V, Mo, Zr, Ta, Ti, W or Nb unevenly distributed at the grain boundaries suppresses the grain growth of magnet particles during sintering, and exchange interaction between crystal grains after sintering. By dividing, it is possible to prevent the magnetization reversal of each crystal grain and improve the magnetic performance.

  Furthermore, according to the method for manufacturing a permanent magnet of the tenth aspect, it is possible to manufacture a permanent magnet in which each crystal grain has a single domain structure. As a result, it is possible to greatly improve the magnetic performance of the manufactured permanent magnet. In addition, even magnetic particles finely pulverized to a single magnetic domain particle diameter can be easily handled, and work efficiency in the manufacturing process can be increased.

1 is an overall view showing a permanent magnet according to the present invention. It is the schematic diagram which expanded and showed the vicinity of the grain boundary of the permanent magnet which concerns on this invention. It is the schematic diagram which showed the magnetic domain structure of the ferromagnetic material. It is the schematic diagram which expanded and showed the vicinity of the grain boundary of the permanent magnet which concerns on this invention. It is explanatory drawing which showed the manufacturing process in the manufacturing method of the permanent magnet which concerns on this invention. It is the figure which showed the SEM photograph after sintering of the permanent magnet of Example 1, and the elemental analysis result of the main phase. It is the figure which showed the SEM photograph after sintering of the permanent magnet of Example 1, and the elemental analysis result of the grain boundary phase. It is the figure which showed the carbon content in the permanent magnet of the permanent magnet of Examples 1, 2 and Comparative Examples 1-3. It is the figure which each showed the external appearance image after sintering of the permanent magnet of Example 1, and the SEM photograph of outer periphery vicinity. It is the figure which each showed the external appearance image after sintering of the permanent magnet of the comparative example 4, and the SEM photograph of outer periphery vicinity. It is the figure which showed the carbon content in the several permanent magnet manufactured by changing the conditions of calcination temperature about the permanent magnet of Example 1 and Comparative Examples 5 and 6. FIG.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of a permanent magnet and a method for producing a permanent magnet according to the present invention will be described in detail with reference to the drawings.

[Configuration of permanent magnet]
First, the configuration of the permanent magnet 1 according to the present invention will be described. FIG. 1 is an overall view showing a permanent magnet 1 according to the present invention. 1 has a cylindrical shape, the shape of the permanent magnet 1 varies depending on the shape of the cavity used for molding.
As the permanent magnet 1 according to the present invention, for example, an Nd—Fe—B magnet is used. Moreover, Nb (niobium), V (vanadium), Mo (molybdenum), Zr (zirconium) for increasing the coercive force of the permanent magnet 1 are formed at the interfaces (grain boundaries) of the crystal grains forming the permanent magnet 1. Ta (tantalum), Ti (titanium) or W (tungsten) is unevenly distributed. The content of each component is Nd: 25 to 37 wt%, Nb, V, Mo, Zr, Ta, Ti, W (hereinafter referred to as Nb or the like): 0.01 to 5 wt%, B: 1 to 2 wt%, Fe (electrolytic iron): 60 to 75 wt%. Further, in order to improve the magnetic characteristics, a small amount of other elements such as Co, Cu, Al and Si may be included.

  Specifically, in the permanent magnet 1 according to the present invention, a part of Nd is made of a refractory metal in the surface portion (outer shell) of the crystal grains of the Nd crystal particles 35 constituting the permanent magnet 1 as shown in FIG. By generating a layer 36 (hereinafter referred to as a refractory metal layer 36) substituted with some Nb or the like, Nb or the like is unevenly distributed with respect to the grain boundaries of the Nd crystal particles 35. FIG. 2 is an enlarged view showing the Nd crystal particles 35 constituting the permanent magnet 1. The refractory metal layer 36 is preferably nonmagnetic.

Here, in the present invention, substitution of Nb or the like is performed by adding an organometallic compound containing Nb or the like before forming a pulverized magnet powder as described later. Specifically, when sintering a magnet powder to which an organometallic compound containing Nb or the like is added, Nb or the like in the organometallic compound uniformly adhered to the particle surface of the Nd magnet particles by wet dispersion is an Nd crystal. Replacement is performed by diffusing and penetrating into the crystal growth region of the particles 35 to form a refractory metal layer 36 shown in FIG. The Nd crystal particles 35 are made of, for example, an Nd ₂ Fe ₁₄ B intermetallic compound, and the refractory metal layer 36 is made of, for example, an NbFeB intermetallic compound.

In the present invention, M- (OR) _x (wherein, M is V, Mo, Zr, Ta, Ti, W, or Nb, and R is an alkyl group having 2 to 6 carbon atoms, as described later) Any of which may be linear or branched. X is an arbitrary integer.) An organic metal compound containing Nb or the like (for example, niobium ethoxide, niobium propoxide, vanadium propoxide, etc.) Add to solvent and mix with magnet powder in wet state. Thereby, an organometallic compound containing Nb or the like can be dispersed in an organic solvent, and the organometallic compound containing Nb or the like can be uniformly attached to the particle surface of the Nd magnet particle.

Here, the above M- (OR) _x (wherein M is V, Mo, Zr, Ta, Ti, W or Nb, R is any one of alkyl groups having 2 to 6 carbon atoms, However, x is an arbitrary integer.) An organometallic compound satisfying the structural formula is a metal alkoxide. The metal alkoxide is represented by a general formula M (OR) _n (M: metal element, R: organic group, n: valence of metal or metalloid). In addition, as the metal or semimetal forming the metal alkoxide, W, Mo, V, Nb, Ta, Ti, Zr, Ir, Fe, Co, Ni, Cu, Zn, Cd, Al, Ga, In, Ge, Sb, Y, lanthanide, etc. are mentioned. However, in the present invention, a refractory metal is particularly used. Furthermore, it is preferable to use V, Mo, Zr, Ta, Ti, W or Nb among refractory metals in order to prevent mutual diffusion with the main phase of the magnet during sintering as will be described later.

  The type of alkoxide is not particularly limited, and examples thereof include methoxide, ethoxide, propoxide, isopropoxide, butoxide, alkoxide having 4 or more carbon atoms, and the like. However, in the present invention, those having a low molecular weight are used for the purpose of suppressing residual coal by low-temperature decomposition as described later. Further, since methoxide having 1 carbon is easily decomposed and difficult to handle, it is particularly preferable to use ethoxide, methoxide, isopropoxide, propoxide, butoxide, etc., which are alkoxides having 2 to 6 carbon atoms.

Further, if the molded body formed by compacting is fired under appropriate firing conditions, Nb or the like can be prevented from diffusing and penetrating into the crystal particles 35 (solid solution). Thereby, in this invention, even if Nb etc. are added, Nb etc. can be unevenly distributed only to a grain boundary after sintering. As a result, as a whole crystal grain (that is, as a whole sintered magnet), the core Nd ₂ Fe ₁₄ B intermetallic compound phase occupies a high volume ratio. Thereby, the fall of the residual magnetic flux density (magnetic flux density when the intensity of an external magnetic field is set to 0) of the magnet can be suppressed.

  In general, if the sintered Nd crystal particles 35 are in a dense state, it is considered that exchange interaction propagates between the Nd crystal particles 35. As a result, when a magnetic field is applied from the outside, the magnetization reversal of each crystal particle easily occurs, and even if each sintered crystal particle can have a single domain structure, the coercive force decreases. However, in the present invention, the exchange interaction between the Nd crystal particles 35 is divided by the nonmagnetic refractory metal layer 36 coated on the surface of the Nd crystal particles 35, and each crystal even when an external magnetic field is applied. Prevents magnetization reversal of particles.

  The refractory metal layer 36 coated on the surface of the Nd crystal particles 35 also functions as a means for suppressing so-called grain growth in which the average particle diameter of the Nd crystal particles 35 increases during sintering of the permanent magnet 1. . Hereinafter, a mechanism for suppressing grain growth of the permanent magnet 1 by the refractory metal layer 36 will be described with reference to FIG. FIG. 3 is a schematic diagram showing a magnetic domain structure of a ferromagnetic material.

  In general, a grain boundary, which is a discontinuous boundary surface left between a crystal and another crystal, has excessive energy, and therefore, grain boundary movement that attempts to reduce energy occurs at a high temperature. Therefore, when the magnet raw material is sintered at a high temperature (for example, 800 ° C. to 1150 ° C. for Nd—Fe—B magnets), the small crystal particles shrink and disappear, and the average particle size of the remaining crystal particles increases. So-called grain growth occurs.

Here, in the present invention, M- (OR) _x (wherein M is V, Mo, Zr, Ta, Ti, W, or Nb, and R is any one of alkyl groups having 2 to 6 carbon atoms). 3 may be linear or branched. X is an arbitrary integer.) By adding an organometallic compound represented by the following formula, Nb or the like, which is a refractory metal, is unevenly distributed at the interface of the magnet particles as shown in FIG. It becomes. And this unevenly distributed refractory metal prevents the movement of grain boundaries generated at high temperatures, and can suppress grain growth.

  Further, the particle diameter D of the Nd crystal particles 35 is desirably about 0.3 μm. Further, if the thickness d of the refractory metal layer 36 is about 2 nm, the grain growth of the Nd crystal particles 35 during the sintering can be suppressed, and the exchange interaction between the Nd crystal particles 35 after the sintering can be interrupted. can do. However, if the thickness d of the refractory metal layer 36 is too large, the content of non-magnetic components that do not exhibit magnetism increases, and the residual magnetic flux density decreases.

  The configuration in which the refractory metal is unevenly distributed with respect to the grain boundaries of the Nd crystal particles 35 is a configuration in which grains 37 made of a refractory metal are scattered with respect to the grain boundaries of the Nd crystal particles 35 as shown in FIG. It is also good. Even in the configuration shown in FIG. 4, it is possible to obtain the same effect (suppression of grain growth and disruption of exchange interaction). Note that how the refractory metal is unevenly distributed with respect to the grain boundaries of the Nd crystal particles 35 can be confirmed by, for example, SEM, TEM, or a three-dimensional atom probe method.

Further, the refractory metal layer 36 does not have to be a layer composed of only an Nb compound, a V compound, a Mo compound, a Zr compound, a Ta compound, a Ti compound, or a W compound (hereinafter referred to as a compound such as Nb). It may be a layer composed of a mixture of a compound and an Nd compound. In that case, a layer made of a mixture of a compound such as Nb and the Nd compound is formed by adding the Nd compound. As a result, liquid phase sintering during the sintering of the Nd magnet powder can be promoted. The Nd compound to be added includes NdH ₂ , neodymium acetate hydrate, neodymium (III) acetylacetonate trihydrate, neodymium (III) 2-ethylhexanoate, neodymium (III) hexafluoroacetylacetonate Hydrates, neodymium isopropoxide, neodynium (III) phosphate n hydrate, neodymium trifluoroacetylacetonate, neodymium trifluoromethanesulfonate, and the like are desirable.

[Permanent magnet manufacturing method]
Next, a method for manufacturing the permanent magnet 1 according to the present invention will be described with reference to FIG. FIG. 5 is an explanatory view showing a manufacturing process in the method for manufacturing the permanent magnet 1 according to the present invention.

  First, an ingot made of a predetermined fraction of Nd—Fe—B (for example, Nd: 26.7 wt%, Fe (electrolytic iron): 72.3 wt%, B: 1.0 wt%) is manufactured. Thereafter, the ingot is roughly pulverized to a size of about 200 μm by a stamp mill or a crusher. Alternatively, the ingot is melted, flakes are produced by strip casting, and coarsely pulverized by hydrogen crushing.

  Subsequently, the coarsely pulverized magnet powder is either (a) in an atmosphere made of an inert gas such as nitrogen gas, Ar gas, or He gas having substantially 0% oxygen content, or (b) having an oxygen content of 0.0001. An average particle diameter of a single domain particle diameter (for example, 0.2 μm to 1.2 μm) by pulverizing with a jet mill 41 in an atmosphere made of inert gas such as nitrogen gas, Ar gas, and He gas of about 0.5% A fine powder having The oxygen concentration of substantially 0% is not limited to the case where the oxygen concentration is completely 0%, but may contain oxygen in such an amount that a very small amount of oxide film is formed on the surface of the fine powder. Means good. Moreover, the fine powder should just have the magnet particle of a single domain particle diameter as a main component, and magnet particles other than a single domain particle diameter may be contained.

On the other hand, an organometallic compound solution (organic solvent) to be added to the fine powder finely pulverized by the jet mill 41 is prepared. Here, an organometallic compound containing Nb or the like is added in advance to the organometallic compound solution and dissolved. The organometallic compound to be dissolved is M- (OR) _x (wherein M is V, Mo, Zr, Ta, Ti, W, or Nb, and R is any one of alkyl groups having 2 to 6 carbon atoms). And an organic metal compound (for example, niobium ethoxide, niobium propoxide, vanadium propoxide, etc.) corresponding to x is an arbitrary integer. The amount of the organometallic compound containing Nb or the like to be dissolved is not particularly limited, but the content of Nb or the like with respect to the magnet after sintering is 0.001 wt% to 10 wt%, preferably 0.01 wt% to 5 wt%. An amount is preferred.

  Subsequently, the organometallic compound solution is added to the fine powder classified by the jet mill 41. Thereby, the slurry 42 in which the fine powder of the magnet raw material and the organometallic compound solution are mixed is generated. The addition of the organometallic compound solution is performed in an atmosphere made of an inert gas such as nitrogen gas, Ar gas, or He gas.

  Thereafter, the generated slurry 42 is injected into the cavity 54 formed in the molding apparatus 50. As shown in FIG. 5, the molding apparatus 50 includes a cylindrical mold 51, a lower punch 52 that slides up and down with respect to the mold 51, and an upper punch 53 that also slides up and down with respect to the mold 51. And a space surrounded by them constitutes the cavity 54. In addition, a pair of magnetic field generating coils 55 and 56 are disposed in the molding apparatus 50 at the upper and lower positions of the cavity 54, and the lines of magnetic force are applied to the slurry 42 filled in the cavity 54. The applied magnetic field is, for example, 1 MA / m.

When compacting, the magnetic field is applied to the cavity 54 by the magnetic field generating coils 55 and 56 before the slurry 42 is injected into the cavity 54. In this state, first, the slurry 42 is injected into the cavity 54 with a magnetic field applied to the cavity 54. Thereafter, the lower punch 52 and the upper punch 53 are driven, and pressure is applied in the direction of the arrow 61 to the slurry 42 filled in the cavity 54 to form the slurry. Thereby, a pulse magnetic field is applied to the slurry 42 filled in the cavity 54 simultaneously with the pressurization by the magnetic field generating coils 55 and 56 in the direction of the arrow 62 parallel to the pressurization direction. As a result, the magnetic field is oriented in a desired direction. The direction in which the magnetic field is oriented needs to be determined in consideration of the magnetic field direction required for the permanent magnet 1 formed from the slurry 42.
And in the manufacturing method of the permanent magnet 1 which concerns on this invention, since it shape | molds with the shaping | molding apparatus 50 in the state which applied the magnetic field with respect to the magnet powder made into slurry form by adding a solvent as mentioned above, it is single domain particle diameter Even magnet particles finely pulverized to a fine particle size (particle size: 0.2 μm to 1.2 μm) are easy to handle, and work efficiency in the manufacturing process can be increased. . Further, in the molding process, it is possible to orient the magnet particles with a small torque, and it is possible to improve the magnetic performance.

  In the molding step, a magnetic field may be applied to the slurry 42 in the cavity 54 by the magnetic field generating coils 55 and 56 after the slurry 42 is injected into the cavity 54. Even in such a configuration, it is possible to apply a pulsed magnetic field to the slurry 42 filled in the cavity 54 simultaneously with pressurization by the magnetic field generating coils 55 and 56 in the direction of the arrow 62 parallel to the pressurization direction. . Further, the magnetic field generating coils 55 and 56 may be arranged so that the application direction is perpendicular to the pressing direction.

  Next, the organic powder is volatilized by drying the magnet powder compacted in a wet state by the molding apparatus 50 by vacuum drying or the like, and the compact 71 is obtained. Thereafter, a calcination treatment in hydrogen is performed by holding at 200 ° C. to 900 ° C., more preferably 400 ° C. to 900 ° C. (eg 600 ° C.) for several hours (eg 5 hours) in a hydrogen atmosphere. The amount of hydrogen supplied during calcination is 5 L / min. In the calcination treatment in hydrogen, so-called decarbonization is performed in which the organometallic compound is thermally decomposed to reduce the amount of carbon in the calcined body. Further, the calcination treatment in hydrogen is performed under the condition that the carbon content in the calcined body is 1000 ppm or less, more preferably 500 ppm or less. Accordingly, the entire permanent magnet 1 can be densely sintered by the subsequent sintering process, and the residual magnetic flux density and coercive force are not reduced.

Then, the sintering process which sinters the molded object 71 calcined by the calcination process in hydrogen is performed. In the sintering process, the temperature is raised to about 800 ° C. to 1180 ° C. at a predetermined rate of temperature rise and held for about 2 hours. During this time, vacuum firing is performed, but the degree of vacuum is preferably 10 ⁻⁴ Torr or less. Thereafter, it is cooled and heat-treated again at 600 ° C. for 2 hours. And the permanent magnet 1 is manufactured as a result of sintering.

Below, the Example of this invention is described, comparing with Comparative Examples 1-6.
Example 1
The alloy composition of the neodymium magnet powder of Example 1 is Nd / Fe / B = 26.7 / 72.3 / 1.0 in wt%. In addition, an organic solvent containing 5 wt% of the organometallic compound niobium propoxide was added as a solvent to the pulverized neodymium magnet powder. The calcination treatment was performed by holding at 600 ° C. for 5 hours in a hydrogen atmosphere. The supply amount of hydrogen during calcination is 5 L / min. The other steps are the same as those described in the above [Permanent magnet manufacturing method].

(Example 2)
The organometallic compound contained in the organic solvent to be added was niobium ethoxide. Other conditions are the same as in the first embodiment.

(Comparative Example 1)
The organometallic compound contained in the organic solvent to be added was vanadium oleate. Other conditions are the same as in the first embodiment.

(Comparative Example 2)
The organometallic compound contained in the organic solvent to be added was dysprosium acetylacetonate. Other conditions are the same as in the first embodiment.

(Comparative Example 3)
The organometallic compound contained in the organic solvent to be added was zinc stearate. Other conditions are the same as in the first embodiment.

(Comparative Example 4)
The alloy composition of the neodymium magnet powder of Comparative Example 1 is wt%, and Nd / Fe / B = 26.7 / 72.3 / 1.0 as in Example 1. However, it manufactured without performing the process regarding the calcination process in hydrogen. Other conditions are the same as in the first embodiment.

(Comparative Example 5)
The alloy composition of the neodymium magnet powder of Comparative Example 2 is wt% and Nd / Fe / B = 26.7 / 72.3 / 1.0 as in Example 1. However, the calcination treatment was performed in a He atmosphere instead of a hydrogen atmosphere. Other conditions are the same as in the first embodiment.

(Comparative Example 6)
The alloy composition of the neodymium magnet powder of Comparative Example 3 is wt%, and Nd / Fe / B = 26.7 / 72.3 / 1.0 as in Example 1. However, the calcination treatment was performed in a vacuum atmosphere instead of a hydrogen atmosphere. Other conditions are the same as in the first embodiment.

(Examination of elemental analysis results in permanent magnets of examples)
FIG. 6 is a view showing an SEM photograph after sintering of the permanent magnet of Example 1 and the result of elemental analysis of the main phase. FIG. 7 is a view showing an SEM photograph after sintering of the permanent magnet of Example 1 and the elemental analysis results of the grain boundary phase.
As shown in FIG. 6, in the permanent magnet of Example 1, Nb is not detected from the main phase. Further, as shown in FIG. 7, Nb is detected from the grain boundary phase. That is, in the permanent magnet of Example 1, Nb does not diffuse from the grain boundary phase to the main phase, and the phase of the NbFeB intermetallic compound in which part of Nd is substituted with Nb in the grain boundary phase is the main phase particle. It can be seen that it is generated on the surface. That is, in Example 1, it turns out that Nb can be unevenly distributed in the grain boundary of a magnet. Further, since Nb does not dissolve in the main phase during sintering, grain growth can be suppressed by solid phase sintering.

(Comparison study of examples and comparative examples based on the type of organometallic compound)
FIG. 8 is a diagram showing the remaining carbon amount [wt%] in the permanent magnets of Examples 1 and 2 and Comparative Examples 1 to 3, respectively.
Moreover, as shown in FIG. 8, it turns out that Example 1 and Example 2 can reduce the carbon amount which remains in a magnet particle more compared with Comparative Examples 1-3. In particular, in Example 1 and Example 2, the amount of carbon remaining in the magnet particles can be 500 ppm or less.

That is, M- (OR) _x (wherein M is V, Mo, Zr, Ta, Ti, W or Nb, R is any alkyl group having 2 to 6 carbon atoms, and even straight chain Branches may be used. X is an arbitrary integer.) When an organic solvent containing an organometallic compound represented by (2) is added, the magnet particles are compared with the case where an organic solvent containing another organometallic compound is added. It can be seen that the carbon content can be greatly reduced. That is, the metal organic compound contained in the organic solvent to be added is M- (OR) _x (wherein M is V, Mo, Zr, Ta, Ti, W or Nb, and R is a carbon number of 2 to 6). Any one of alkyl groups, which may be linear or branched. X is an arbitrary integer.), So that decarbonization can be easily performed in a calcination treatment in hydrogen. As a result, it is possible to prevent dense sintering of the entire magnet and a decrease in coercive force.

(Comparison study of examples and comparative examples based on the presence or absence of calcination treatment in hydrogen)
9 and 10 show an appearance image after sintering of the permanent magnets of Example 1 and Comparative Example 4 and SEM photographs near the outer periphery, respectively.
Comparing the appearance images, in Example 1, the whole magnet was densely sintered, but in Comparative Example 4, the outer periphery was densely sintered although the central portion was densely sintered. Not. As a result, in Comparative Example 4, a crack occurred in the central portion due to the difference in volume shrinkage rate during sintering between the central portion and the outer peripheral portion.

Further, when the SEM photographs of Example 1 and Comparative Example 4 are compared, Example 1 basically sintered from the main phase (Nd ₂ Fe ₁₄ B) 91 of the neodymium magnet and the grain boundary phase 92 that looks like white spots. Whereas the later permanent magnet is formed, in Comparative Example 4, a large number of voids 93 are formed between the main phase 91 and the grain boundary phase 92. Here, the voids 93 are caused by carbide remaining during sintering. That is, since the reactivity between Nd and C is very high, if a C-containing material in the organometallic compound remains at a high temperature in the sintering process, carbide is formed. As a result, voids 93 are generated by the formed carbide. And when such a space | gap 93 arises, the magnetic performance of a permanent magnet will fall remarkably. Further, even when no voids are generated, αFe is precipitated in the main phase of the sintered magnet by the formed carbide, and there is a problem that the magnetic properties are greatly deteriorated.

  On the other hand, in Example 1 in which the calcination treatment in hydrogen is performed, the organometallic compound is thermally decomposed by the calcination treatment, and the contained carbon can be burned out beforehand (the amount of carbon is reduced). In addition, by setting the temperature at the time of calcination to 200 ° C. to 900 ° C., more preferably 400 ° C. to 900 ° C., the carbon contained can be burned out more than necessary, and the carbon remaining in the magnet after sintering The amount can be 1000 ppm or less, more preferably 500 ppm or less. And if carbon content is 1000 ppm or less, More preferably, it is 500 ppm or less, In Example 1, a carbide | carbonized_material will hardly be formed by a sintering process, and there is no possibility that the space | gap like the comparative example 4 may arise. As a result, as shown in FIG. 9, the entire permanent magnet 1 can be densely sintered by the sintering process, and the magnetic performance of the permanent magnet does not deteriorate. Further, αFe is not precipitated in the main phase of the magnet after sintering, and the magnet characteristics are not greatly deteriorated. In addition, only Nb or the like that contributes to an improvement in coercive force can be selectively unevenly distributed in the main phase grain boundary. In the present invention, from the viewpoint of suppressing residual carbon by low-temperature decomposition as described above, an organometallic compound to be added preferably has a low molecular weight (consisting of an alkyl group having 2 to 6 carbon atoms). .

(Comparison study of examples and comparative examples based on conditions of calcination in hydrogen)
FIG. 11 is a graph showing the carbon amount [wt%] in a plurality of permanent magnets manufactured by changing the calcination temperature conditions for the permanent magnets of Example 1 and Comparative Examples 5 and 6. FIG. 11 shows the result of maintaining the supply amounts of hydrogen and helium during calcination at 1 L / min for 3 hours.
As shown in FIG. 11, it can be seen that the amount of carbon in the magnet particles can be greatly reduced when calcined in a hydrogen atmosphere as compared with calcining in a He atmosphere or a vacuum atmosphere. Further, from FIG. 11, if the calcining temperature at the time of calcining the magnet powder in a hydrogen atmosphere is increased, the amount of carbon is greatly reduced. You can see that it is possible.

As described above, in the permanent magnet 1 and the method for manufacturing the permanent magnet 1 according to the present embodiment, a solvent is added to the pulverized magnet powder to generate the slurry 42, which is then injected into the cavity 54 in the molding apparatus 50. The slurry 42 is molded by applying pressure in a state where a magnetic field is applied, and then the organic solvent is volatilized to obtain a molded body, so that the particle size of the single magnetic domain (particle diameter 0.2 μm to 1.2 μm) is obtained. Even magnet particles finely pulverized to a very small particle size can be handled easily, and the work efficiency in the manufacturing process can be increased. Further, in the molding process, it is possible to orient the magnet particles with a small torque, and it is possible to improve the magnetic performance.
The solvent to be added is M- (OR) _x (wherein M is V, Mo, Zr, Ta, Ti, W, or Nb, and R is any one of alkyl groups having 2 to 6 carbon atoms). , Which may be linear or branched. X is an arbitrary integer.), And is an organic solvent containing an organometallic compound represented by V, Mo, Zr, Ta, Ti, W or Nb which is a refractory metal. Can be unevenly distributed at the grain boundaries of the magnet after sintering. As a result, V, Mo, Zr, Ta, Ti, W or Nb unevenly distributed at the grain boundaries suppresses the grain growth of magnet particles during sintering, and exchange interaction between crystal grains after sintering. By dividing, it is possible to prevent the magnetization reversal of each crystal grain and improve the magnetic performance.
In addition, a magnet to which an organic solvent containing an organometallic compound is added is calcined in a hydrogen atmosphere before sintering, so that the organometallic compound is thermally decomposed and the carbon contained in the magnet particles is previously burned out (carbon amount) Can be reduced), and carbide is hardly formed in the sintering process. As a result, it is possible to sinter the entire magnet densely without generating voids between the main phase and the grain boundary phase of the sintered magnet, and to prevent the coercive force from being lowered. . Further, αFe is not precipitated in the main phase of the magnet after sintering, and the magnet characteristics are not greatly deteriorated.
Furthermore, since the step of calcining the molded body is performed by holding the molded body for a predetermined time in a temperature range of 200 ° C. to 900 ° C., more preferably 400 ° C. to 900 ° C., the carbon contained in the magnet particles is contained. It can be burned out more than necessary.
As a result, the amount of carbon remaining in the magnet after sintering is 1000 ppm or less, more preferably 500 ppm or less, so that no voids are formed between the main phase of the magnet and the grain boundary phase, and the entire magnet is made dense. It becomes possible to set it as the sintered state, and it can prevent that a residual magnetic flux density falls.

In addition, this invention is not limited to the said Example, Of course, various improvement and deformation | transformation are possible within the range which does not deviate from the summary of this invention.
Moreover, the pulverization conditions, kneading conditions, sintering conditions, etc. of the magnet powder are not limited to the conditions described in the above examples.

Moreover, in the said Example, as a solvent added to magnet powder, M- (OR) _x (In formula, M is V, Mo, Zr, Ta, Ti, W, or Nb, R is C2-C6. An organic solvent containing an organometallic compound represented by the formula (1), wherein x is an arbitrary integer, but no organometallic compound is added. May be used. Further, other solvents may be used as long as they have low reactivity. For example, rust preventive oil or the like can be used.

  In the above embodiment, the slurry 42 is injected into the cavity 54 and applied with a magnetic field for orientation. However, the present invention is not limited to the cavity 54 and can be used for free boundary conditions. It becomes possible.

1 Permanent Magnet 35 Nd Crystal Particle 36 High Melting Point Metal Layer 37 High Melting Point Metal Grain 91 Main Phase 92 Grain Boundary Phase 93 Void

Claims (10)

Crushing magnet raw material into magnet powder;
Adding a solvent to the pulverized magnet powder to produce a slurry;
Forming a molded body by molding in a state where a magnetic field is applied to the slurry;
A permanent magnet manufactured by the step of sintering the molded body.   2. The permanent magnet according to claim 1, wherein in the step of forming the molded body, the slurry is injected into the cavity in a state where a magnetic field is applied to the cavity for forming the molded body.   The permanent magnet according to claim 1, wherein in the step of forming the molded body, a magnetic field is applied to the cavity after the slurry is injected into the cavity for forming the molded body. The solvent has the following structural formula M- (OR) _x
(In the formula, M is V, Mo, Zr, Ta, Ti, W, or Nb, R is any one of alkyl groups having 2 to 6 carbon atoms, and may be linear or branched. (It is an integer.)
The permanent magnet according to claim 1, wherein the permanent magnet is an organic solvent containing an organometallic compound represented by the formula:   The permanent magnet according to any one of claims 1 to 4, wherein the magnet powder is magnet powder containing magnet powder having a single magnetic domain particle diameter. Crushing magnet raw material into magnet powder;
Adding a solvent to the pulverized magnet powder to produce a slurry;
Forming a molded body by molding in a state where a magnetic field is applied to the slurry;
And a step of sintering the molded body.   The manufacturing method of the permanent magnet according to claim 6, wherein in the step of forming the molded body, the slurry is injected into the cavity in a state where a magnetic field is applied to the cavity for forming the molded body. Method.   The method for producing a permanent magnet according to claim 6, wherein, in the step of forming the molded body, a magnetic field is applied to the cavity after injecting the slurry into the cavity for forming the molded body. . The solvent has the following structural formula M- (OR) _x
(In the formula, M is V, Mo, Zr, Ta, Ti, W, or Nb, R is any one of alkyl groups having 2 to 6 carbon atoms, and may be linear or branched. (It is an integer.)
The method for producing a permanent magnet according to claim 5, wherein the organic solvent contains an organometallic compound represented by the formula:   The method of manufacturing a permanent magnet according to any one of claims 5 to 9, wherein the magnet powder is magnet powder containing magnet powder having a single magnetic domain particle diameter.