JP2010238712A - Method for manufacturing rare earth sintered magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a rare earth sintered magnet for simply manufacturing the rare earth sintered magnet having a reduced variation in magnetic characteristic by favorably maintaining the dispersibility of a heavy rare earth powder in a slurry. <P>SOLUTION: The method for manufacturing a rare earth sintered magnet includes: attaching a heavy rare earth powder to a magnet element assembly by immersing the magnet element assembly comprising a sintered body including a light rare earth element in a bubbling-agitated slurry including a heavy rare earth powder including at least one of the heavy rare earth metal and its compound, and a solvent, and heat-treating the magnet element assembly to which the heavy rare earth powder is attached to manufacture the rare earth sintered magnet. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a rare earth sintered magnet.

  In a rare earth sintered magnet, a state in which a heavy rare earth metal such as Dy or Tb or a compound such as a hydride, fluoride or oxide of the heavy rare earth metal is present on the surface of a magnet body containing a rare earth element There is known a means for improving the coercive force by heat-treating and intentionally causing the heavy rare earth metal element to exist at the crystal grain boundary of the sintered magnet.

  In such a method, in order to obtain a rare earth sintered magnet having an excellent coercive force, it is necessary to attach a heavy rare earth metal or a compound thereof to the surface of the magnet body before performing the heat treatment. As a method for efficiently attaching heavy rare earth metal or the like to the surface of the magnet body, a method of immersing the magnet body in a slurry in which a powder of heavy rare earth metal or a compound thereof is dispersed in an organic solvent has been proposed. (For example, refer to Patent Document 1).

International Publication No. 2006/043348

  However, since powders containing heavy rare earth metals and their compounds (heavy rare earth powders) usually have a large specific gravity, it is difficult to maintain good dispersibility of the heavy rare earth powders in the slurry. On the other hand, when a rare earth sintered magnet is manufactured by immersing a magnet body in a slurry in which the dispersibility of the heavy rare earth powder is not uniform, the amount of heavy rare earth metal adhering to the surface of the magnet body varies, and the final Variation of the magnetic properties of the rare earth sintered magnets obtained in a conventional manner.

  Here, as a technique for maintaining good dispersibility of the heavy rare earth powder in the slurry, a method of applying ultrasonic waves or performing mechanical mixing can be considered. However, in these methods, it is difficult to sufficiently maintain the good dispersibility of the heavy rare earth powder having a large specific gravity and a compound thereof.

  As another method for maintaining good dispersibility of the heavy rare earth powder in the slurry, it is conceivable to improve the dispersibility by reducing the particle size of the heavy rare earth powder. However, heavy rare earth element compounds usually have high strength and are not easily pulverized. For this reason, when it is going to obtain the fine heavy rare earth powder of submicron size, there exists a tendency for cost to become high. In addition, heavy rare earth powders containing rare earth elements have a very high activity and become difficult to handle when the particle size is reduced.

  The present invention has been made in view of the above circumstances, and by easily maintaining the dispersibility of the heavy rare earth powder in the slurry, it is possible to easily produce a rare earth sintered magnet with reduced variations in magnetic properties. An object of the present invention is to provide a method for producing a rare earth sintered magnet.

  In order to achieve the above object, in the present invention, a magnet body made of a sintered body containing a light rare earth element, a heavy rare earth powder containing at least one of a heavy rare earth metal and a compound stirred by bubbling, and a solvent are used. A rare earth having an adhesion step in which the heavy rare earth powder is adhered to the magnet body, and a heating step in which the magnet body on which the heavy rare earth powder is adhered is heated to produce a rare earth sintered magnet. A method for producing a sintered magnet is provided.

  According to the production method of the present invention, since the slurry is stirred by bubbling when the magnet body is immersed in the slurry, the dispersibility of the heavy rare earth powder in the slurry can be maintained well. In addition, the stirring by bubbling can reduce the difference in the moving speed of the heavy rare earth powder in the slurry compared to the mechanical mixing such as stirring blades, and suppresses the sedimentation of the heavy rare earth powder. The local adhesion of heavy rare earth powder to can be reduced. By these actions, it is possible to reduce the variation in magnetic characteristics among the rare earth sintered magnets and the variation in magnetic characteristics depending on the location of each rare earth sintered magnet.

  The production method of the present invention preferably has an oxidation step of oxidizing at least a part of the surface of the heavy rare earth powder before the adhesion step. As a result, air can be used as the bubbling gas, and a rare earth sintered magnet with reduced variations in magnetic properties can be manufactured more easily.

  The solvent contained in the slurry in the production method of the present invention is preferably an organic solvent having a relative dielectric constant at 25 ° C. of 10 or more. By using such a solvent, the dispersibility of the heavy rare earth powder in the slurry can be maintained better, and a rare earth sintered magnet with further reduced variation in magnetic properties can be manufactured.

  According to the present invention, a method for producing a rare earth sintered magnet capable of easily producing a rare earth sintered magnet with reduced variations in magnetic properties by maintaining good dispersibility of the heavy rare earth powder in the slurry. Can be provided.

It is the schematic which shows an example of the slurry stirring apparatus used at the adhesion process of this embodiment. It is the schematic which shows another example of the slurry stirring apparatus used at the adhesion process of this embodiment. It is a magnetic hysteresis loop measured using a BH tracer. In the manufacturing process of the rare earth sintered magnet of Example 13, a scanning electron micrograph showing a cross section in the vicinity of the surface of the magnet body before being subjected to heat treatment after being dipped in a slurry containing a heavy rare earth compound and dried. (Magnification: 500 times). In the manufacturing process of the rare earth sintered magnet of Comparative Example 7, a scanning electron micrograph showing a cross section near the surface of the magnet body before being subjected to heat treatment after being dipped in a slurry containing a heavy rare earth compound and dried. (Magnification: 500 times).

  In the following, preferred embodiments of the present invention will be described with reference to the drawings as the case may be.

  The method for producing a rare earth sintered magnet according to the present embodiment includes a preparation step of forming a magnet body made of a sintered body containing a light rare earth element, and a surface of a heavy rare earth powder containing at least one of a heavy rare earth metal and a compound thereof. An oxidation process for oxidizing the catalyst, a slurry preparation process for preparing a slurry by mixing a heavy rare earth powder whose surface has been oxidized and a solvent, and a heavy rare earth containing at least one of the heavy rare earth metal and its compound stirred by bubbling A magnet body is immersed in a slurry containing powder and a solvent to attach a heavy rare earth powder to the magnet body, and the magnet body to which the heavy rare earth powder is attached is heat-treated to produce a rare earth sintered magnet. And a heating step to be manufactured. Details of each step will be described below.

  In the preparation process, a magnet body made of a sintered body containing a light rare earth element is formed as follows. First, an alloy is prepared so that a magnet body having a desired composition can be obtained. Specifically, a simple substance, an alloy, a compound, or the like containing an element such as a metal corresponding to the composition of the magnet body is dissolved in an inert gas atmosphere such as vacuum or argon, and then used for casting or stripping. An alloy having a desired composition is manufactured by performing an alloy manufacturing process such as a casting method.

  Two types of alloys may be used: an alloy having a composition mainly constituting crystal grains (main phase alloy) and an alloy having a composition constituting a grain boundary phase (grain boundary phase alloy) in the magnet body. .

The magnet body is preferably, for example, an R-T-B rare earth sintered magnet whose main component is an R ₂ Fe ₁₄ B ₁ type crystal. Here, R is at least one element selected from rare earth elements including Y, and T represents at least one element of Fe and Co. The mass ratio of the light rare earth element to the entire R element in the magnet body is preferably 70% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more.

  Note that in this specification, rare earth elements refer to scandium (Sc), yttrium (Y), and lanthanoid elements belonging to Group 3 of the long-period periodic table. Examples of lanthanoid elements include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy). ), Holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) and the like. The rare earth elements can be classified into light rare earth elements and heavy rare earth elements. In the present specification, “heavy rare earth element” refers to Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and “light rare earth element” refers to Sc, Y, La, Ce, Pr, Nd, Sm, Eu.

  The magnet body preferably contains Nd and Pr as light rare earth elements. However, in addition to the light rare earth element, a heavy rare earth element or a transition element may be included. For example, a suitable composition of the magnet body includes at least one of Nd and Pr as a rare earth element, 0.5 to 4.5% by mass of B as an essential element, and the balance being Fe and inevitable impurities. The thing which has a composition of R-Fe-B type is mentioned. The magnet body may further contain other elements such as Co, Ni, Mn, Al, Cu, Nb, Zr, Ti, W, Mo, V, Ga, Zn, and Si as necessary.

  After preparing an alloy having a composition equivalent to the above-mentioned composition, the alloy is coarsely pulverized to obtain particles having a particle size of about several hundred μm. The coarse pulverization of the alloy is performed by using a coarse pulverizer such as a jaw crusher, a brown mill, a stamp mill, or the like, or after the alloy has occluded hydrogen, it is self-destructive based on the difference in hydrogen occlusion between different phases. It can be performed by causing pulverization (hydrogen occlusion pulverization).

  Subsequently, the powder obtained by coarse pulverization is further finely pulverized, so that the raw material powder of a rare earth magnet having a particle size of preferably about 1 to 10 μm, more preferably about 3 to 5 μm (hereinafter simply referred to as “raw material powder”) ) Fine pulverization is performed by further pulverizing the coarsely pulverized powder using a fine pulverizer such as a jet mill, a ball mill, a vibration mill, and a wet attritor while appropriately adjusting conditions such as pulverization time. To do.

  In addition, when two types of main phase alloy and grain boundary phase alloy are prepared in the manufacture of the alloy, coarse pulverization and fine pulverization are performed on each alloy, and the two types of fine powder obtained thereby are mixed. The raw material powder may be prepared by this.

Next, the raw material powder obtained as described above is formed into a target shape. The molding is performed while applying a magnetic field, thereby causing the raw material powder to have a predetermined orientation. The molding can be performed, for example, by press molding. Specifically, the raw material powder can be formed into a predetermined shape by filling the raw material powder into the mold cavity and then pressing the filled powder between the upper punch and the lower punch. The shape of the molded body obtained by molding is not particularly limited, and can be changed according to the desired shape of the magnet body, such as a columnar shape, a flat plate shape, or a ring shape. The pressing at the time of molding is preferably performed at 0.5 to 1.4 ton / cm ² . The applied magnetic field is preferably 12 to 20 kOe. As the molding method, in addition to the dry molding in which the raw material powder is molded as it is, wet molding in which a slurry in which the raw material powder is dispersed in a solvent such as oil can be molded.

  Next, the molded body is fired, for example, by performing a treatment of heating at 980 to 1110 ° C. for 2 to 6 hours in a vacuum or in the presence of an inert gas. Thereby, raw material powder carries out liquid phase sintering, and a sintered compact (magnet body) is obtained.

  For the sintered body, it is preferable to perform a surface treatment by treating the surface of the sintered body with an acid solution, for example, after appropriately processing it into a desired size and shape. As the acid solution used for the surface treatment, a mixed solution of an aqueous solution such as nitric acid or hydrochloric acid and an alcohol is suitable. This surface treatment can be performed, for example, by immersing the sintered body in an acid solution or spraying the acid solution on the sintered body.

In the oxidation step, first, a heavy rare earth powder for slurry preparation is prepared separately from the above-described magnet body. In the oxidation step, first, a heavy rare earth powder containing at least one of a heavy rare earth metal and a heavy rare earth compound is prepared. The heavy rare earth element contained in the heavy rare earth powder is preferably Dy or Tb from the viewpoint of obtaining a rare earth sintered magnet having a high coercive force. Examples of heavy rare earth compounds include hydrides, oxides, halides and hydroxides of heavy rare earth elements. Of these heavy rare earth compounds, DyH ₂ , DyF ₃ or TbH ₂ is preferred.

  The heavy rare earth compound can be produced by a usual method. It is possible to prepare heavy rare earth powder by a method of dry pulverizing a heavy rare earth compound or heavy rare earth metal produced by a normal method, or a method of mixing with an organic solvent and wet pulverizing using a ball mill or the like. it can.

  The average particle diameter of the heavy rare earth powder is preferably 100 nm to 50 μm, more preferably 1 to 5 μm. When the particle size of the heavy rare earth powder is less than 100 nm, the amount of the heavy rare earth compound that diffuses into the magnet body due to the heat treatment becomes excessive, and the resulting rare earth sintered magnet has a tendency to decrease in Br. On the other hand, if it exceeds 50 μm, the diffusion of the heavy rare earth compound into the magnet body becomes difficult to occur, and the effect of improving HcJ may not be sufficiently obtained. By setting the average particle size of the heavy rare earth powder to 1 to 5 μm, the dispersibility of the heavy rare earth powder in the slurry can be maintained better.

  The heavy rare earth powder obtained by pulverization retains the heavy rare earth powder in an oxygen-containing atmosphere and oxidizes the surface of the heavy rare earth powder. The oxidation conditions are not particularly limited. However, from the viewpoint of ensuring safety, the surface of the heavy rare earth powder is gradually retained by holding the heavy rare earth powder at room temperature (for example, 20 ° C.) in an atmosphere having an oxygen gas concentration of, for example, 0.1 to 5% by volume. It is preferable to oxidize. By performing such gradual oxidation, it is possible to sufficiently suppress the internal oxidation of the heavy rare earth powder and the heat generation accompanying the rapid oxidation of the heavy rare earth powder. Note that the oxidation step is not necessarily an independent step, and may be performed simultaneously with the pulverization step by adjusting the oxygen gas concentration in the pulverization atmosphere to 0.1 to 5% by volume. By these steps, a rare earth sintered magnet having a sufficiently excellent coercive force can be manufactured more easily.

  The heavy rare earth powder whose surface is oxidized is stable and can be held in the atmosphere, and is easy to handle. In addition, air can be used as a bubbling gas in the adhesion step described later, and the manufacturing cost can be reduced.

  In the slurry preparation step, a slurry is prepared by mixing a heavy rare earth powder whose surface is oxidized and a solvent. The solvent used here is preferably an organic solvent, more preferably an organic solvent having a relative dielectric constant of 10 or more at room temperature. Since the organic solvent having a relative dielectric constant of 10 or more has good wettability of the heavy rare earth powder, the dispersibility of the heavy rare earth powder can be more satisfactorily maintained by using such an organic solvent. Further, as the solvent, a mixed solvent of the above-mentioned organic solvents may be used. Among the above organic solvents, from the viewpoint of good dispersibility of heavy rare earth powder, reduction in production cost and work safety, alcohols such as ethanol, methanol, isopropyl alcohol or butanol, ketones such as acetone or isobutyl methyl ketone, Alternatively, a mixture thereof is preferable.

  The solvent and heavy rare earth powder can be mixed by a normal mixing method using a ball mill or the like. Content of the heavy rare earth powder with respect to the whole slurry becomes like this. Preferably it is 3-30 mass%, More preferably, it is 5-20 mass%, More preferably, it is 8-15 mass%. If the content of the heavy rare earth powder is too high, good dispersibility of the heavy rare earth powder in the slurry may be impaired. On the other hand, when the content of the heavy rare earth powder is too low, it tends to be difficult to sufficiently attach the heavy rare earth powder to the surface of the magnet body.

  In order to improve the dispersibility of the heavy rare earth powder, a commercially available dispersant or thickener may be blended with the slurry as necessary. A general surfactant can be used as the dispersant, and a higher fatty acid ester or the like can be used as the thickener.

  In the attaching step, the magnet body is immersed in the slurry stirred by bubbling, and the heavy rare earth powder is attached to the magnet body. This adhesion process can be performed using a slurry stirring apparatus.

  FIG. 1 is a schematic diagram illustrating an example of a slurry agitation apparatus used in the attaching step of the present embodiment. The slurry agitator 10 includes a tank 12 for storing slurry, and a diffuser plate 14 provided in the tank 12 in parallel with the bottom surface. A gas supply pipe 16 for supplying gas is connected below the location of the diffuser plate 14 in the tank 12. As the diffuser plate 14, a plate having holes to the extent that gas can pass can be used. For example, a porous plate made of a porous body having pores with a pore diameter of about 10 to 300 μm can be used.

  The tank 12 includes a slurry reservoir 17 that stores the slurry 34 above the diffuser plate 14, and a gas supply unit 18 below the diffuser plate 14. That is, the diffuser plate 14 is provided between the slurry storage unit 17 and the gas supply unit 18. A gas supply pipe 16 is connected to the gas supply unit 18. The gas supplied to the gas supply unit 18 through the gas supply pipe 16 passes through the diffuser plate 14 and is supplied to the slurry storage unit 17.

  When the slurry 34 is introduced into the slurry reservoir 17 of the tank 12 while supplying gas from the gas supply pipe 16 to the gas supply unit 18, the gas that has passed through the diffuser plate 14 from the gas supply unit 18 becomes bubbles to form the slurry 34. The slurry 34 is passed through while diffusing, and the slurry 34 is stirred by bubbling. Thus, the slurry 34 is agitated by bubbling, whereby the heavy rare earth powder contained in the slurry 34 is dispersed in the solvent.

  The slurry containing heavy rare earth powder is adhered to the surface-treated magnet body by immersing the magnet body in the slurry 34 while stirring the slurry 34 by bubbling. There is no restriction | limiting in particular in the time which immerses the magnet body in the slurry 34 stirred by bubbling, For example, it can be set as 1 to 10 minutes. This immersion time can be adjusted so that the properties of the finally obtained rare earth sintered magnet are in a desired range.

  The bubbling gas supplied into the slurry 34 is not particularly limited, and for example, an inert gas such as nitrogen gas, argon gas, carbon dioxide gas, or air can be used. In addition, since the surface of the magnet body of the present embodiment is oxidized by the oxidation process, a rare earth sintered magnet having excellent coercive force can be manufactured even if air is used. By using air as the bubbling gas, the manufacturing cost of the rare earth sintered magnet can be reduced.

  The flow rate of the bagling gas may be such that the slurry 34 can be sufficiently stirred. For example, a gas of about 10 to 100 L / min may be supplied to 1 L of the slurry. The pressure of gas can be 0.2-0.5 MPa, for example.

  In this adhesion step, since the slurry 34 is stirred by gas bubbling, the dispersibility of the heavy rare earth powder can be maintained well. And, by immersing the magnet body in the slurry 34 in which the good dispersibility of the heavy rare earth powder is maintained in this way, the slurry, that is, the heavy rare earth powder adheres more uniformly to the surface of the magnet body than before. Can do.

  The amount of heavy rare earth powder deposited on the surface of the magnet body is based on the magnet body before the heavy rare earth powder is deposited from the viewpoint of obtaining a rare earth sintered magnet having a more excellent coercive force and squareness ratio (100 Mass%), in terms of heavy rare earth compound or heavy rare earth metal, preferably 0.05 to 1.0 mass%, more preferably 0.08 to 0.6 mass%.

  FIG. 2 is a schematic view showing another example of the slurry agitator used in the attaching step of the present embodiment.

  The slurry agitation device 20 includes a tank 12 including a slurry reservoir 27 that stores slurry, and a gas supply pipe 26 that supplies gas to the slurry reservoir 27. A part of the gas supply pipe 26 is disposed near the bottom of the slurry reservoir 27, and a plurality of supply holes 24 for supplying gas into the slurry reservoir 27 are provided at that portion. The gas flowing through the gas supply pipe 26 passes through the supply hole 24 and is supplied into the slurry reservoir 27.

  When the slurry 34 is introduced into the slurry reservoir 27 of the tank 12, the gas that has passed through the supply hole 24 of the gas supply pipe 26 passes through the slurry 34 while diffusing, and the slurry 34 is stirred by bubbling. It will be. Thus, the slurry 34 is stirred by bubbling, whereby the heavy rare earth powder contained in the slurry 34 is dispersed in the solvent.

  Also when the slurry agitator 20 shown in FIG. 2 is used, the dispersibility of the heavy rare earth powder in the slurry 34 can be maintained well as in the case where the slurry agitator 100 is used. Thus, by immersing the magnet body in the slurry 34 in which good dispersibility of the heavy rare earth powder is maintained, the slurry, that is, the magnet powder can be adhered more uniformly to the surface of the magnet body than in the past.

  In the heating process, a rare earth sintered magnet is manufactured by heat-treating the magnet body to which the heavy rare earth powder is adhered in the adhesion process. By this heat treatment, the heavy rare earth element adhering to the surface of the magnet body diffuses into the sintered body. The heat treatment can be performed in, for example, a two-stage process. In this case, in the first step, heat treatment (step I) is performed at about 800 to 1000 ° C. for 10 minutes to 10 hours, and in the second step, heat treatment is performed at about 500 to 600 ° C. for 1 to 4 hours (step I). It is preferred to carry out step II). In such a two-stage heat treatment, for example, heavy rare earth elements mainly diffuse into the magnet body in step I, and so-called aging treatment proceeds in step II. Therefore, the coercive force of the rare earth sintered magnet can be further improved by performing the heat treatment in two steps. Note that the heat treatment is not necessarily performed in two stages, and may be performed at least so that the heavy rare earth element diffuses into the magnet body.

  The adhesion process and the heating process described above can be performed a plurality of times. For example, it is possible to repeat the attaching step and step I a plurality of times and then perform step II. At this time, the temperature and time of each step I can be arbitrarily selected within the above-mentioned preferable range, and need not be the same. By performing such heat treatment a plurality of times, it is possible to more efficiently diffuse the heavy rare earth element into the magnet and further improve the coercive force.

Heat treatment causes diffusion of heavy rare earth elements from the surface of the magnet body to the inside. At this time, the heavy rare earth elements diffuse along the boundaries of the crystal grains containing the light rare earth elements that are the main components of the magnet body. I think that. As a result, in the rare earth sintered magnet obtained finally become heavy rare earth elements derived from the heavy rare earth compound or a heavy rare earth metal is unevenly distributed in the outer edge area or the grain boundary of the crystal grains, whereby, for example, R ₂ A core-shell structure is formed in which crystal grains having the Fe ₁₄ B ₁ phase are covered with a layer rich in heavy rare earth elements. By having such a core-shell structure, it becomes a rare earth sintered magnet that is particularly excellent in coercive force and squareness ratio.

  After the above-described heat treatment, it may be cut into a desired size or surface-treated as necessary. Moreover, the obtained rare earth sintered magnet may further be provided with a protective layer for preventing deterioration of a plated layer, an oxide layer, a resin layer, or the like on the surface thereof.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.

[Manufacture of rare earth magnets]
Example 1
A raw material alloy was prepared so as to obtain a magnet body (sintered body) having the following composition.
Nd: 24.50 mass%
Dy: 0.50 mass%
Pr: 5.30% by mass
Co: 0.45 mass%
Al: 0.18% by mass
Cu: 0.06 mass%
B: 1.00% by mass
Fe: balance (including unavoidable impurities of less than 0.1% by mass)

As raw material alloys, two types of alloys were prepared: a main phase alloy mainly forming crystal grains of the magnet body and a grain boundary alloy mainly forming grain boundaries. Each of these raw material alloys was coarsely pulverized by hydrogen pulverization and then jet milled by high-pressure N ₂ gas to prepare fine powders each having an average particle diameter of 4 μm.

The prepared main phase alloy fine powder A and the grain boundary alloy fine powder B are mixed at a mass ratio of fine powder A: fine powder B = 95: 5 to prepare a raw material powder of the magnet body. did. Next, using this raw material powder, molding was performed in a magnetic field under the conditions of a molding pressure of 1.2 t / cm ² and an orientation magnetic field of 20 kOe to obtain a cuboid shaped compact (50 mm × 33 mm × 33 mm). The obtained compact was fired at 1060 ° C. for 4 hours to obtain a magnet body (sintered body) having the above composition.

  The obtained magnet body was cut with a slicer to obtain 30 magnet bodies having a size of 15 mm × 6 mm × 2.3 mm. The cut magnet body was etched with nital, an ethanol solution of nitric acid, and then washed with ethanol.

Next, apart from the magnet body, a slurry was prepared as follows. First, Dy powder was occluded at 350 ° C. for 1 hour in a hydrogen atmosphere, followed by treatment at 600 ° C. for 1 hour in an Ar atmosphere to obtain a Dy hydride. The obtained Dy hydride was confirmed to be DyH ₂ by X-ray diffraction measurement.

Ethanol was blended with this DyH ₂ and wet pulverized using a ball mill to obtain DyH ₂ powder having an average particle size of 3 μm. Thereafter, the DyH ₂ powder was dried in a nitrogen atmosphere to remove ethanol. The DyH ₂ powder from which ethanol was removed was held in nitrogen gas having an oxygen gas concentration of 1% by volume while mixing until no heat was generated. As a result, the DyH ₂ powder was gradually oxidized to oxidize the surface of the DyH ₂ powder. Blended and gradually oxidized DyH ₂ powder and ethanol, and subjected to dispersion treatment for mixed 1 hour in a ball mill to give a solid content of 10% by weight of the slurry.

Slurry (containing DyH ₂ ) in which DyH ₂ as a heavy rare earth compound is dispersed in ethanol in a tank 12 (depth: 5 cm) of a slurry agitator 10 (pore diameter 120 μm of a diffuser plate 14) as shown in FIG. Amount = 10% by mass) was introduced so that the depth was 3 cm. While stirring the slurry introduced into the tank with dry air (flow rate: 50 L / min, pressure: 0.3 MPa) and stirring, the magnet body after ethanol washing was immersed in this slurry, DyH ₂ powder was adhered to the surface of the element body. Thereafter, the magnet body to which the DyH ₂ powder was adhered was dried under a nitrogen atmosphere to remove the solvent. The magnet body was divided into three 10 times and a total of 30 magnet bodies were immersed.

  The dried magnet body is subjected to a heat treatment at 900 ° C. for 6 hours in an argon gas atmosphere, and further subjected to an aging treatment at 540 ° C. for 1 hour. Thirty rare earth sintered magnets having a structure in which Dy is unevenly distributed at a high concentration in the grain boundaries of the crystal grains were produced.

(Example 2)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that DyF ₃ (manufactured by Japan Yttrium Co., Ltd.) was used instead of DyH ₂ as the heavy rare earth compound to be dispersed in the slurry.

Example 3
A rare earth sintered magnet was produced in the same manner as in Example 1 except that TbH ₂ was used instead of DyH ₂ as the heavy rare earth compound to be dispersed in the slurry. The TbH ₂ used was prepared as follows. First, Tb powder was occluded at 350 ° C. for 1 hour under a hydrogen atmosphere, and subsequently treated at 600 ° C. for 1 hour under an argon atmosphere to obtain a Tb hydride. The obtained Tb hydride was confirmed to be TbH ₂ by X-ray diffraction measurement.

Example 4
A rare earth sintered magnet was produced in the same manner as in Example 1 except that nitrogen gas was used instead of air as the bubbling gas.

(Example 5)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that argon gas was used as the bubbling gas instead of air.

(Example 6)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that n-butanol was used in place of ethanol as the solvent for the slurry.

(Example 7)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that acetone was used in place of ethanol as a solvent for the slurry.

(Example 8)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that toluene was used in place of ethanol as a solvent for the slurry.

Example 9
A rare earth sintered magnet was produced in the same manner as in Example 1 except that Dispersant 1 (glyceride monooleate) was added to the slurry. In addition, content of the dispersing agent in a slurry was 1 mass%.

(Example 10)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that the dispersant 2 (higher fatty acid ester) was added to the slurry. In addition, content of the dispersing agent in a slurry was 1 mass%.

(Example 11)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that the thickener 1 (polyvinyl butyral, degree of polymerization: about 300) was added to the slurry. In addition, content of the thickener in a slurry was 3 mass%.

(Example 12)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that the thickener 2 (polyvinyl butyral, degree of polymerization: about 1700) was added to the slurry. In addition, content of the thickener in a slurry was 1 mass%.

(Comparative Example 1)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that the magnet body was not immersed in the slurry.

(Comparative Example 2)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that stirring by bubbling of the slurry was not performed.

(Comparative Example 3)
A rare earth sintered magnet was produced in the same manner as in Example 3 except that stirring by bubbling of the slurry was not performed.

(Comparative Example 4)
A rare earth sintered magnet was produced in the same manner as in Example 2 except that stirring by bubbling of the slurry was not performed.

(Comparative Example 5)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that the stirring of the slurry was performed with stirring blades instead of bubbling.

(Comparative Example 6)
A rare earth sintered magnet was produced in the same manner as in Example 1 except that the stirring of the slurry was performed by a ball mill instead of bubbling.

  Table 1 summarizes the manufacturing conditions for the rare earth sintered magnets of the examples and comparative examples.

[Measurement of heavy rare earth compound adhesion on magnet body]
In the manufacturing process of the rare earth sintered magnet manufactured as described above, the mass W ₀ of the magnet body before immersion in the slurry and the mass W ₁ of the magnet body after being immersed in the slurry containing the heavy rare earth compound and dried. From these measured values, the adhesion amount (mass%) was determined by the following formula (1). Table 2 shows the difference between the maximum value and the minimum value of the obtained adhesion amount and the average value.

Adhesion amount (mass%) = (W ₁ −W ₀ ) / W ₁ × 100 (1)

[Evaluation of magnetic properties]
The magnetic properties of the rare earth sintered magnet produced as described above were measured with a BH tracer. From the obtained results, the residual magnetic flux density (Br) and the coercive force (HcJ) of the rare earth sintered magnet were determined. Table 2 shows the difference between the maximum and minimum values of Br and HcJ, and the average value.

(Example 13)
The adhesion amount of the heavy rare earth compound in the magnet body (DyH _2), was changed to as shown in Table 3 by adjusting the immersion time in the slurry of the magnet body, the same procedure as in Example 1 A rare earth sintered magnet was produced and evaluated in the same manner as in Example 1. The evaluation results are summarized in Table 3.

(Comparative Example 7)
The adhesion amount of the heavy rare earth compound in the magnet body (DyH _2), was changed to as shown in Table 3 by adjusting the immersion time in the slurry of the magnet body is in the same manner as in Comparative Example 5 A rare earth sintered magnet was prepared and evaluated in the same manner as in Comparative Example 5. The evaluation results are summarized in Table 3.

  In addition, the squareness ratio and BHmax in Table 3 were also measured using a BH tracer. Moreover, squareness ratio was calculated | required by following formula (2) using HcJ and Hk. The squareness ratio is an index of magnet performance, and represents the degree of angularity in the second quadrant of the magnetic hysteresis loop measured using a BH tracer. Hk in Equation (2) is the external magnetic field strength when the ratio of magnetization to the residual magnetic flux density is 90% in the second quadrant of the magnetic hysteresis loop.

  Squareness ratio (%) = Hk / HcJ × 100 (2)

  FIG. 3 is a magnetic hysteresis loop measured using a BH tracer. It was confirmed that Example 13 has a larger squareness ratio than Comparative Example 7.

  FIG. 4 is a scan showing a cross section in the vicinity of the surface of the magnet body before being subjected to heat treatment after being dipped in a slurry containing a heavy rare earth compound and dried in the manufacturing process of the rare earth sintered magnet of Example 13. It is a type | mold electron micrograph (magnification: 500 times).

  FIG. 5 is a scan showing a cross section in the vicinity of the surface of the magnet body before being subjected to heat treatment after being dipped in a slurry containing a heavy rare earth compound and dried in the process of manufacturing a rare earth sintered magnet of Comparative Example 7. It is a type | mold electron micrograph (magnification: 500 times).

  In Comparative Example 7 in which the slurry was stirred with the stirring blade, the heavy rare earth compound 40 attached to the surface of the magnet body 50 was distributed in an island shape as shown in FIG. Further, there was a portion where the heavy rare earth compound 40 was not attached to the surface of the magnet body 50.

  On the other hand, in Example 13 where the slurry was stirred by bubbling, it was confirmed that the surface of the magnet body 50 was more uniformly covered with the heavy rare earth compound 40 than in Comparative Example 7, as shown in FIG. Thus, the rare earth sintered magnet excellent in coercive force and squareness ratio was able to be obtained, maintaining a residual magnetic flux density by heat-processing the magnet body to which the heavy rare earth compound 40 adhered more uniformly.

  Next, a reference experiment was conducted to examine the presence or absence of aggregation of heavy rare earth powder using various solvents. Specifically, the heavy rare earth powder used in Example 1 and the solvent shown in Table 4 were mixed for 1 hour using a ball mill to prepare a slurry having a solid content of 10% by mass. Thereafter, the slurry was allowed to stand for 1 hour, and then the presence or absence of aggregation of the heavy rare earth powder was evaluated visually by the presence or absence of separation of the slurry. The case where the slurry was separated was evaluated as “with aggregation”, and the case where the slurry was not separated was evaluated as “without aggregation”. The results are shown in Table 4.

  From the results in Table 4, it was confirmed that the dispersibility of the heavy rare earth powder was kept sufficiently good by using an organic solvent having a relative dielectric constant of 10 or more.

Next, a sedimentation test of heavy rare earth powder was performed according to the following procedure. First, DyH ₂ powder having an average particle diameter of 3 μm was prepared. This was dispersed in various solvents shown in Table 5 to prepare a slurry having a solid content of 10% by mass. In addition, a predetermined amount of the additive used in Examples 9 to 12 was added to some of the slurries. After dispersion, the slurry was introduced to the maximum value of the sedimentation test tube memory and allowed to stand. Every predetermined time, the height of the interface between the precipitation part and the supernatant part was measured, and the sedimentation rate of the interface was calculated. The measurement was terminated when the sedimentation rate at each predetermined time reached a constant value. The results are shown in Table 5.

  From the results of Table 5, it was confirmed that the dispersibility of the slurry can be maintained more satisfactorily when the alcohol is used, since the sedimentation rate becomes low. It was also confirmed that the sedimentation rate can be further reduced by using a dispersant or a thickener.

  DESCRIPTION OF SYMBOLS 10 ... Slurry stirring apparatus, 12 ... Tank, 14 ... Diffusing plate, 16, 26 ... Gas supply pipe, 17 ... Slurry storage part, 18 ... Gas supply part, 20 ... Slurry stirring apparatus, 24 ... Supply hole, 27 ... Slurry Reservoir, 34 ... slurry, 40 ... heavy rare earth compound, 50 ... magnet body.

Claims (3)

A magnet body made of a sintered body containing a light rare earth element is immersed in a slurry containing a heavy rare earth powder and a solvent containing at least one of a heavy rare earth metal and a compound stirred by bubbling, and the magnet body An attachment step of attaching the heavy rare earth powder to
And a heating step of producing a rare earth sintered magnet by heat-treating the magnet body to which the heavy rare earth powder is adhered.   The method for producing a rare earth sintered magnet according to claim 1, further comprising an oxidation step of oxidizing at least part of the surface of the heavy rare earth powder before the attaching step.   The method for producing a rare earth sintered magnet according to claim 1 or 2, wherein the solvent is an organic solvent having a relative dielectric constant of 10 or more at 25 ° C.