JP2008060241A - High resistance rare-earth permanent magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high resistance rare-earth permanent magnet to which high electric resistance is imparted and which exhibits an excellent magnetic characteristic, and to provide its manufacturing method. <P>SOLUTION: The high resistance rare-earth permanent magnet has the excellent characteristic where a relative density is not less than 98%, intrinsic coercitivity is not less than 800 kA/m, and volume resistance ratio is not less than 2 μΩm, by using a rare-earth fluorine compound as an insulating layer and optimizing a magnet composition. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rare earth permanent magnet having a high volume resistivity and constituting a high-speed rotating machine used for an elevator, an electric vehicle, a hybrid vehicle, and the like.

Since rare earth magnets such as R-Fe-B magnets (R: rare earth elements including Y) represented by Nd-Fe-B magnets have high magnetic properties, spindle motors and stepping motors In recent years, the demand for such motors has increased with the miniaturization of motors.
Among them, an HDDR having magnetic anisotropy obtained by heating a rare-earth magnet alloy having a predetermined composition in hydrogen to occlude hydrogen, then dehydrogenating, cooling and then pulverizing. (Hydrogenation-Disproportionation-Desorption-Recombination) Bonded magnets heat-formed into a predetermined shape using magnet powder (see, for example, Patent Document 1 and Patent Document 2) have excellent magnetic properties, so Attention has been focused on the development of applications for products that used conductive rare earth bonded magnets.
However, since the rare earth-based bonded magnet contains a resin binder, the magnetic properties are lower than that of the rare-earth sintered magnet. If it is possible to manufacture a high-density bulk magnet from HDDR magnet powder, it is desirable because it can effectively exhibit its excellent magnetic properties, which is proposed in Patent Document 3 and Patent Document 4. .
However, a high-density bulk magnet has a lower electrical resistance than a bonded magnet using a resin binder. The volume resistivity of a general Nd—Fe—B sintered magnet is about 1.2 μΩm, but the volume resistivity of a high-density bulk magnet is also equivalent to this. For this reason, when it is incorporated in a motor, eddy current loss increases, resulting in a problem of reducing motor efficiency. Thus, various techniques for solving this problem by increasing the electric resistance of rare earth permanent magnets have been proposed.
For example, Patent Document 5 proposes a rare earth permanent magnet having a structure in which powder particles for rare earth permanent magnets are bound to at least one of SiO ₂ particles and Al ₂ O ₃ particles. Based on this proposal, if at least one of SiO ₂ particles and Al ₂ O ₃ particles is present between the magnet particles, the electrical resistance of the magnet can be increased. However, if SiO ₂ particles and Al ₂ O ₃ particles are added alone to a rare earth-based permanent magnet, the electrical resistance of the magnet can be increased, but on the other hand, the magnetic properties are greatly deteriorated. . This is difficult to apply to medium to high output motors.
In order to solve this problem, Patent Document 6 proposes a technique using a rare earth fluoride as an insulating layer in a magnet. Although this technology has been evaluated as excellent, since rare earth fluoride powder is used, the thickness of the insulating layer needs to be 0.1 μm (100 nm) or more in order to ensure sufficient insulation. Since the volume ratio cannot be set low, the volume ratio of the magnet component is relatively lowered, and sufficiently high magnetic properties cannot always be obtained.
Thus, Patent Document 7 discloses a technique capable of forming a rare earth fluoride insulating layer with a thickness of 100 nm or less in a magnet. According to the technique of Patent Document 7, a rare earth-based permanent magnet having a high volume resistivity can be manufactured without extremely reducing the volume ratio of the magnet component. However, since Patent Document 7 focuses on increasing the electrical resistance of a magnet, studies on optimizing a magnet composition for exhibiting excellent magnetic properties after increasing electrical resistance have been made. Not.
Japanese Patent Publication No. 6-82575 Japanese Patent Publication No. 7-68561 JP-A-4-246803 JP-A-4-253304 Japanese Patent Laid-Open No. 10-32427 JP 2006-66853 A JP 2006-66870 A

  Accordingly, an object of the present invention is to provide a high-resistance rare earth-based permanent magnet that has high electrical resistance and exhibits excellent magnetic properties, and a method for manufacturing the same.

  In view of the above points, the inventors have conducted a detailed study on HDDR bulk magnets using rare earth fluoride as an insulating layer in a magnet. In the manufacturing process, the rare earth fluoride layer and HDDR magnet powder chemically react. The chemical reaction seems to affect the magnetic properties of the magnets that can be obtained. Therefore, HDDR bulk magnets that are provided with a high electrical resistance by providing a rare earth fluoride layer exhibit the maximum magnetic properties. It has been found that the magnet composition that can be produced is limited.

The high resistance rare earth-based permanent magnet of the present invention made based on the above knowledge is as described in claim 1.
Mainly composed of magnet particles having an Nd ₂ Fe ₁₄ B type crystal structure and a rare earth fluoride layer present on the surface of the magnet particles,
The relative density is 98% or more of the true density calculated from the sum of the volume ratio of the magnet particles and the volume ratio of the rare earth fluoride layer,
The magnet particles have an average particle size of 20 μm to 150 μm,
Composition _{formula: R x (Fe 1-m} Co m) 1-x-y-z Q y M z (R although at least one of Pr and Nd accounts for 70% or more, the balance lanthanide series if there is balance Q is B or B partially substituted with C. M is Ti, V, Cr, Mn, Ni, Cu, Al, Ga, In, Sn, Ta, Zr. , Nb, Mo, W, at least one selected from the group consisting of.
x is 12 at% to 18 at%,
y is 5.5 at% to 8 at%,
z is 0 at% to 10 at%,
m is 0 to 0.2),
The Nd ₂ Fe ₁₄ B type crystal phase constituting the magnet particles has an average crystal grain size of 200 nm to 700 nm,
The direction of easy magnetization of magnet particles is generally aligned in a specific direction inside the particles,
The intrinsic coercive force as a magnet is 800 kA / m or more, and the volume resistivity is 2 μΩm or more.
The high resistance rare earth based permanent magnet according to claim 2 is the high resistance rare earth based permanent magnet according to claim 1, wherein the volume of the rare earth fluoride layer relative to the sum of the volume ratio of the magnet particles and the volume ratio of the rare earth fluoride layer. The ratio is 0.1% to 10%.
The high resistance rare earth permanent magnet according to claim 3 is the high resistance rare earth permanent magnet according to claim 1 or 2, wherein the rare earth fluoride layer is composed of La, Ce, Pr, Nd, Tb, Dy, It contains at least one selected from the group consisting of Ho, and its content is at least 50 at% or more of the entire rare earth element contained in the rare earth fluoride layer.
The high resistance rare earth based permanent magnet according to claim 4 is the high resistance rare earth based permanent magnet according to any one of claims 1 to 3, wherein the residual magnetic flux density is a volume ratio of magnet particles and a volume of the rare earth fluoride layer. It is characterized by being 80% or more of the saturation magnetic polarization calculated from the sum of the ratios.
The high-resistance rare earth-based permanent magnet according to claim 5 is the high-resistance rare earth-based permanent magnet according to any one of claims 1 to 4, wherein the average thickness of the rare earth fluoride layer is 10 nm to 5 μm. And
Moreover, the manufacturing method of the high resistance rare earth based permanent magnet of the present invention is as described in claim 6.
Composition _{formula: R x (Fe 1-m} Co m) 1-x-y-z Q y M z (R although at least one of Pr and Nd accounts for 70% or more, the balance lanthanide series if there is balance Q is B or B partially substituted with C. M is Ti, V, Cr, Mn, Ni, Cu, Al, Ga, In, Sn, Ta, Zr. , Nb, Mo, W, at least one selected from the group consisting of.
x is 12 at% to 18 at%,
y is 5.5 at% to 8 at%,
z is 0 at% to 10 at%,
m is 0 to 0.2),
Magnet particles having an Nd ₂ Fe ₁₄ B type crystal structure having an average particle diameter of 20 μm to 150 μm are manufactured by the HDDR method,
Forming a rare earth fluoride layer on the surface of the magnet particles;
Magnet particles having a rare earth fluoride layer on the surface are hot-formed by applying a pressure of 20 MPa to 200 MPa after the temperature is set to 600 ° C. to 900 ° C., and the relative density is the volume ratio of the magnet particles to the rare earth fluoride layer. The true density calculated from the total volume ratio is 98% or more.
The manufacturing method according to claim 7 is characterized in that, in the manufacturing method according to claim 6, magnetic field orientation is performed before hot forming.

  According to the present invention, a high-resistance rare earth-based permanent magnet that provides high electrical resistance by using rare earth fluoride as an insulating layer and exhibits excellent magnetic properties by optimizing the magnet composition, A manufacturing method thereof can be provided.

  Hereinafter, the high resistance rare earth based permanent magnet of the present invention and the manufacturing method thereof will be described.

<Composition of starting alloy>
The starting alloy used to produce the high resistance rare earth permanent magnet of the present invention is:
Composition _{formula: R x (Fe 1-m} Co m) 1-x-y-z Q y M z (R although at least one of Pr and Nd accounts for 70% or more, the balance lanthanide series if there is balance Q is B or B partially substituted with C. M is Ti, V, Cr, Mn, Ni, Cu, Al, Ga, In, Sn, Ta, Zr. , Nb, Mo, W, at least one selected from the group consisting of.
x is 12 at% to 18 at%,
y is 5.5 at% to 8 at%,
z is 0 at% to 10 at%,
m is 0 to 0.2). Here, examples of the lanthanide series elements include La, Ce, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Yb.

According to the study by the present inventors, in an HDDR bulk magnet using a rare earth fluoride as an insulating layer, the rare earth fluoride layer formed on the surface of the HDDR magnet particle chemically reacts with the magnet particle, thereby causing magnetism of the magnet particle. It seems to affect the characteristics. Specifically, the rare earth fluoride reacts in a manner that takes away R contained in the HDDR magnet particles (for example, RF ₃ → RF ₂ ). Although the reduction amount of R of the magnet particles due to this reaction can be ignored, in order to obtain an intrinsic coercive force (H _cJ ) of 800 kA / m or more as a high-density bulk magnet, the content of R in the starting alloy is It was found that 12 at% or more is necessary (the amount of R decrease in the magnet particles is negligible, so the R content in the starting alloy corresponds to the R content in the magnet particles). As the R content increases, the residual magnetic flux density (B _r ) decreases, so the upper limit of the R content is 18 at% or less. In order to achieve both an intrinsic coercivity better than 800 kA / m and a high residual magnetic flux density, the R content is preferably 12.6 at% to 18 at%, more preferably 12.6 at% to 14 at%, 12.8 at% to 13.8 at% is more preferable. In order to obtain a high coercive force, it is effective to include Dy or Tb in a part of R. However, since the increase in Dy and / or Tb inhibits the progress of the HDDR reaction, the amount of substitution is R It is preferable to be 30 at% or less with respect to the whole.

  Q is obtained by partially substituting B or B with C, and the content thereof is set to 5.5 at% to 8 at%, but preferably 5.8 at% to 6.5 at%.

  For the purpose of improving the magnetic properties of magnets, iron group transition metals such as Ti, V, Cr, Mn, Ni, Cu, Al, Ga, In, Sn, Ta, Zr, Nb, Mo, and W are used. May be included. However, an increase in the content particularly causes a decrease in magnetization. Therefore, the total content is 10 at% or less of the total.

  Fe is a main component of the Nd—Fe—B permanent magnet, has the largest ferromagnetically coupled atomic magnetic moment, and is inexpensive, so its content is preferably as high as possible. Note that the Curie temperature can be increased by replacing part of Fe with Co. If the Co content is up to about 20% of the total of the Fe content and the Co content, the magnetization in the vicinity of room temperature does not drop significantly.

  Co is an element that directly affects the hydrogenation reaction of the alloy in the HDDR method, and the appropriate reaction conditions vary greatly depending on the Co content. When the Co content is low, the equilibrium hydrogen pressure in the hydrogenation reaction decreases, and when it is high, the equilibrium hydrogen pressure tends to increase. This is equivalent to lowering the appropriate reaction temperature when the Co content is low and increasing it when the hydrogen pressure is constant. When the Co content is less than about 5 at%, the equilibrium hydrogen pressure is below atmospheric pressure in all temperature ranges below the normal temperature at which the hydrogenation reaction proceeds. Therefore, if the temperature is raised at atmospheric pressure, the reaction cannot be performed at an appropriate reaction rate, and as a result, HDDR magnet powder having high magnetic properties cannot be obtained. However, in this case, a method of introducing hydrogen at an appropriate reaction temperature after raising the temperature in a gas having a hydrogen partial pressure equal to or lower than the equilibrium hydrogen pressure or in a vacuum can be employed. Therefore, the lower limit value of the Co content may be 0 at%. On the other hand, the upper limit of the Co content is considered as follows. That is, when the Co content is more than about 20% of the total of the Co content and the Fe content, the equilibrium hydrogen pressure is increased, and accordingly, the amount of hydrogen used is preferably increased in proportion to the pressure. In addition, since it is necessary to design the strength to sufficiently pressurize the inside of the furnace with respect to the processing equipment, the equipment cost increases. Accordingly, the upper limit of the Co content is preferably about 20% of the total of the Co content and the Fe content.

<Preparation method of starting alloy powder>
The starting alloy can be obtained by a known alloy production method such as a book mold method, a centrifugal casting method, a strip casting method, an atomizing method, a diffusion reduction method, or the like.

  An alloy obtained by these methods may be subjected to homogenization heat treatment for the purpose of eliminating macro segregation, coarsening of crystal grains, reduction of α-Fe phase, and the like.

Alloys obtained by these methods have a metal structure in which the Nd ₂ Fe ₁₄ B type compound phase region oriented in the same crystal direction in the alloy structure has a thickness of 20 μm or more. This is important in obtaining the saturation magnetic flux density (Br).

  The alloy obtained by these methods is pulverized by a known method to form a starting alloy powder. As the pulverization method, a mechanical pulverization method using a jaw crusher or the like, and a hydrogen storage / disintegration method are mainly used. In order to sufficiently obtain the effects of the present invention, the average particle size of the starting alloy powder obtained by pulverization is preferably 10 μm to 500 μm, more preferably 30 μm to 150 μm.

<HDDR processing>
The HDDR process consists of an HD process (hydrogenation and disproportionation) and a DR process (dehydrogenation and recombination), which can be continuous or discontinuous (eg, HD processing and DR processing are performed in separate facilities).

The HD treatment is performed at 750 ° C. to 950 ° C. in H ₂ gas or a mixed gas of H ₂ gas and inert gas (for example, Ar, He, etc.). The hydrogen partial pressure during HD treatment is appropriately selected depending on the alloy composition, but is usually 10 kPa to 500 kPa. The treatment time is usually 10 minutes to 10 hours, typically 20 minutes to 5 hours.

  After performing HD processing, DR processing is performed. As a control method (atmosphere gas type, pressure, temperature, time) of the DR treatment, a known method may be adopted as appropriate. For example, in an inert gas (eg, Ar or He) atmosphere or in a vacuum atmosphere , A processing temperature of 750 ° C. to 900 ° C., a processing time of 10 minutes to 5 hours, and the like. Needless to say, the atmosphere during the DR process may be controlled stepwise by, for example, decreasing the hydrogen partial pressure stepwise or decreasing the reduced pressure stepwise.

<Crushing and grinding>
The HDDR magnet powder that has been cooled to room temperature after the completion of the DR treatment may be a weak aggregate. In this case, the magnet powder may be crushed by a known method. Further, the particle size may be adjusted by pulverization according to the final purpose. As a pulverization method, a known pulverization technique can be used. However, in order to suppress oxidation of the magnet powder during pulverization, it is preferable to perform pulverization in an inert gas atmosphere such as Ar.

The magnet particles obtained by the above HDDR treatment have a Nd ₂ Fe ₁₄ B type crystal structure, include a large number of primary particles having an average crystal grain size of 200 nm to 700 nm, and the direction of easy magnetization of these primary crystal grains Are secondary particles having an average particle diameter of 20 μm to 150 μm and having an intrinsic coercive force of 800 kA / m or more.

<Formation of rare earth fluoride layer on the surface of magnet particles>
The rare earth fluoride layer as an insulating layer formed on the surface of the magnet particle is, for example, LaF ₃ , CeF ₃ , PrF ₃ , NdF ₃ , NdF ₂ , SmF ₃ , EuF ₃ , GdF ₃ , TbF ₃ , DyF ₃ , HoF. ₃ , rare earth fluorides such as ErF ₃ , YbF ₃ , and LuF ₃ . By using rare earth fluoride as the compound constituting the insulating layer, it is possible to produce a densified bulk magnet by densification while maintaining the excellent magnetic properties of the Nd-Fe-B HDDR magnet powder. The rare earth element contained in the rare earth fluoride layer may be one kind or plural kinds. The rare earth fluoride layer contains at least one selected from the group consisting of La, Ce, Pr, Nd, Tb, Dy, and Ho as the rare earth element, and the content thereof is at least 50 at least of the entire rare earth element contained in the rare earth fluoride layer. When it is at least%, a bulk magnet having excellent magnetic properties can be easily obtained. Particularly suitable rare earth elements are Pr, Nd, Tb, and Dy. By selecting at least one selected from the group consisting of these rare earth elements, a bonded magnet manufactured by using the HDDR magnet powder in a usual manner. It is possible to obtain a hot-pressed bulk magnet having a coercive force equivalent to or higher than. The rare earth fluoride is composed of a rare earth element and fluorine, but in addition to these, oxygen, nitrogen, carbon and the like may be included as a constituent element. In addition to the rare earth fluoride, the rare earth fluoride layer may contain an alkaline earth fluoride such as MgF ₂ or CaF ₂ . In order to provide high electrical resistance without extremely reducing the volume ratio of the magnet component, the ratio of the volume ratio of the rare earth fluoride layer to the sum of the volume ratio of the magnet particles and the volume ratio of the rare earth fluoride layer is 0. It is preferably 1% to 10%, and the average thickness of the rare earth fluoride layer is preferably 10 nm to 5 μm.

  The rare earth fluoride layer can be formed on the surface of the HDDR-treated magnet particle by a technique such as sputtering, vapor deposition, thermal spraying, or coating using a solution. Among these methods, it is preferable to employ a coating method using a solution from the viewpoints of easy industrial operation and operational efficiency.

  In a coating method using a solution, a rare earth fluoride layer is formed on the surfaces of magnet particles using a solution containing a rare earth fluoride (an alcohol is exemplified as a solvent). According to this method, a film that becomes a rare earth fluoride layer by heating and solidifying in a later step is formed along the surface while growing on the entire surface or part of the surface of the magnet particles in the solution. After removing the solvent on the surface of the magnet particles, the magnet particles having the rare earth fluoride coating on the surface are preferably heated at 400 ° C. to 800 ° C. to solidify the rare earth fluoride coating, To do. The upper limit of the heating temperature is set from the viewpoint of avoiding a decrease in magnetic properties of the HDDR magnet powder and avoiding a decrease in insulation due to the progress of a chemical reaction occurring between the rare earth fluoride layer and the magnet particles. Is done. When a rare earth fluoride film is grown on the surface of a magnet particle in a solution, an oxide layer is previously formed on the surface of the magnet particle, and the rare earth fluoride film is grown on the oxide layer as a base, or a magnet is previously formed. A layer containing a rare earth element having a composition different from that of the particles is formed on the surface of the magnet particle, and the rare earth fluoride layer is grown on the surface of the magnet particle by growing a rare earth fluoride coating on the layer. It may not be formed directly. When a rare earth fluoride film is formed on the surface of such a base and heat-treated, a part of the underlying oxide layer is mixed with the rare earth fluoride layer or contains a rare earth element having a composition different from that of the magnet particles. A part of the layer causes mutual diffusion with the rare earth fluoride layer, and the thickness of the rare earth fluoride layer increases. The relationship between the thickness of the base and the thickness of the rare earth fluoride layer varies depending on the heat history of the heat treatment, but if the thickness of the rare earth fluoride layer becomes thicker than the thickness of the base, the loss reduction effect decreases. Tend. The relationship between the thicknesses of the two is a relationship in a relatively flat place such as the surface of the magnet particle or the surface of the grain boundary, and a relationship in a special place such as the triple point of the grain boundary or the protrusion of the magnet particle. is not. Here, the “relatively flat location” is a portion that is not an acute angle portion of the magnet particle, and is a location where the thickness of the rare earth fluoride layer is within a range of −50% to + 200% of the average thickness. When a coating method using a solution is adopted, the area of the rare earth fluoride layer having a thickness within the range of −50% to + 200% of the average thickness is 50% or more of the entire surface of the magnet particles. Is possible.

<Bulk magnetization using magnet particles having a rare earth fluoride layer on the surface>
It is performed by densifying by hot forming by a known method. In order to improve the performance of the magnet, magnetic field orientation for adding anisotropy may be performed before hot forming. By doing so, the residual magnetic flux density of the magnet can be made 80% or more of the saturation magnetic polarization (Js) calculated from the sum of the volume ratio of the magnet particles and the volume ratio of the rare earth fluoride layer.

  In order to efficiently perform magnetic field orientation, the HDDR magnet powder with the rare earth fluoride layer is sufficiently crushed so that it can flow as powder and the magnet particles can be rotated and oriented with torque by the magnetic field. It is necessary to keep. Such a magnet powder is compression molded in a mold in the presence of a magnetic field to obtain a temporary molded body in which easy magnetization directions are aligned. At this time, it is important to adjust the molding pressure in order to avoid that the rare earth fluoride layer present on the surface of the magnet particles is broken by the rolling force and insulation between the magnet particles cannot be taken.

  Specifically, the HDDR magnet powder is converted into a bulk magnet, for example, in a non-oxidizing atmosphere (for example, an inert gas atmosphere using Ar or the like) in a vacuum vessel, and after the temperature is changed from 600 ° C. to 900 ° C., 20 MPa to It is carried out by applying a pressure of 200 MPa to perform hot forming and densifying. The molding time is typically 30 minutes to 120 minutes. In this way, the molding pressure is not applied from the start of heating or applied in the middle of reaching the molding temperature, but is applied after reaching the molding temperature for the following reason. Since HDDR magnet particles are difficult to plastically deform near room temperature and are brittle, they have the property that when excessive pressure is applied near room temperature, the magnet particles break. Therefore, when molding pressure is applied to HDDR magnet particles having a rare earth fluoride layer on the surface at around room temperature, the rare earth fluoride layer is also destroyed and the continuity as a film is lost. It becomes difficult to maintain electrical resistance. On the other hand, HDDR magnet particles are easily plastically deformed at high temperatures. The deformation mechanism is considered to be grain boundary sliding due to the generation of a liquid phase component rich in Nd inside the magnet particles. The temperature at which the magnet particles can be plastically deformed by this deformation mechanism is about 600 ° C. or higher. In addition to this, the present inventors have now found for the first time through experiments that the rare earth fluoride layer acquires ductility in a temperature range in which HDDR magnet particles can be plastically deformed. Therefore, by applying the molding pressure after reaching the molding temperature, the HDDR magnet particles can be plastically deformed, and the rare earth fluoride layer existing on the surface can be spread. . Therefore, if the molding pressure is applied only after reaching the molding temperature without applying the molding pressure for the purpose of densification below the molding temperature, insulation due to the presence of the rare earth fluoride layer on the surface of the magnet particles is achieved. In such a state, the bulk magnets can be densified by plastically deforming the magnet particles so as to fill the gaps between the magnet particles.

The densified magnet of the present invention thus obtained has an average crystal grain size of the Nd ₂ Fe ₁₄ B type crystal phase constituting the magnet particles of 200 nm to 700 nm, and their easy magnetization direction is oriented in a specific direction. And a component such that a rare earth fluoride layer exists as an insulating layer on the surface of magnet particles having an average particle diameter of 20 μm to 150 μm is obtained by compacting without gaps, The density is 98% or more of the true density calculated from the sum of the volume ratio of the magnet particles having the Nd ₂ Fe ₁₄ B type crystal structure and the volume ratio of the rare earth fluoride layer, and the easy magnetization direction of the magnet particles is specified inside the particles. An internal structure of the magnet is formed that is generally aligned in the direction, has an intrinsic coercive force of 800 kA / m or more, and a volume resistivity of 2 μΩm or more.

  In addition, relative density X (%) with respect to the true density calculated from the sum of the volume ratio of the magnet particles and the volume ratio of the rare earth fluoride layer (containing volume ratio) is obtained by measuring the density V of the obtained magnet, The true density calculated from the sum α of the volume ratio of (true density A) and the volume ratio of the rare earth fluoride layer (true density B) can be calculated by the following formula, assuming that the true density is 100%.

(Equation 1)
X (%) = {V / (A × (100−α) + (B × α))} × 100

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is limited to this and is not interpreted.

Example A:
For example, in accordance with the methods described in Patent Document 1 and Patent Document 2, the composition formula: Nd _x Dy _y Co ₁₆ Zr _0.09 Ga _0.5 B _6.5 Fe _bal (Nd content x is 12.4 at%) Four types of alloys having compositions satisfying ˜12.9 at% and Dy content y of 0 and 0.3 at%) were prepared and subjected to HDDR treatment, and the average particle diameter having magnetic properties shown in Table 1 was about 80 μm magnet particles (HDDR magnet powder) were obtained.

A rare earth fluoride layer was formed on the surface of the magnet particles by the following process.
(1) A NdF ₃ film forming treatment liquid for forming an Nd fluoride layer was prepared as follows. First, an Nd salt having high solubility in water (for example, neodymium acetate hydrate) was mixed with water and dissolved by stirring, and then diluted hydrofluoric acid (1 wt% to 10 wt%) was gradually added. The solution in which the gel-like precipitate Nd fluoride (NdF ₃ ) was generated in the liquid by such operation was further stirred, centrifuged, the supernatant was removed, and methanol was added. The methanol solution containing NdF ₃ thus obtained was stirred, centrifuged, the supernatant was removed, and methanol was added again to obtain a methanol solution containing NdF _{3 from} which corrosive ions had been removed, This was used as a treatment liquid.
(2) 10 mL of NdF ₃ film forming treatment liquid was added to 100 g of HDDR magnet powder and mixed until it was confirmed that the entire magnet powder was wet.
(3) Methanol was removed under reduced pressure of 270 Pa to 670 Pa from HDDR magnet powder (magnet particles with NdF ₃ coating formed on the surface) treated with the NdF ₃ coating forming treatment liquid.
(4) The magnet powder from which methanol was removed was transferred to a quartz boat and subjected to heat treatment at 200 ° C. × 30 minutes and 400 ° C. × 30 minutes under reduced pressure of 1.3 × 10 ⁻³ Pa.
(5) The heat-treated magnet powder was transferred to a lidded container, and heat treatment was performed at 400 ° C. to 800 ° C. for 30 minutes under a reduced pressure of 1.3 × 10 ⁻³ Pa to form the surface of the magnet particles. The NdF ₃ coating was solidified to form an NdF ₃ layer.

The NdF ₃ layer formed on the surface of the magnet particles as described above partially changed to NdF ₂ by reacting with the magnet powder. Ratio of the volume ratio of the NdF ₃ layer to the total volume ratio of the volume ratio and the NdF ₃ layers of magnet particles is about 3%, the average thickness was about 600 nm.

The HDDR magnet powder on which the NdF _three layers are formed is loaded in a hot press mold in a non-oriented manner, and the rate of temperature rise to a set ultimate temperature of 700 ° C. in a vacuum atmosphere (<10 ⁻³ Pa) using a vacuum hot press device Heating was performed at 10 ° C./min, and a press pressure of 50 MPa was applied after reaching the set temperature. The temperature was maintained at 700 ° C. and the pressing pressure of 50 MPa for 60 minutes to produce a dense magnet body. When this magnet body was broken and crushed and analyzed, the obtained magnet body contained about 2000 ppm of oxygen as an inevitable impurity, and according to EPMA analysis of the cross section of the magnet body, Generation was suggested.

  Table 2 shows the magnetic properties and relative densities of the obtained magnet bodies (Examples 1 to 4). As is apparent from Table 2, the intrinsic holding force of the magnet body of the example was an excellent value almost equivalent to that of the HDDR magnet powder used as a raw material. Moreover, the volume resistivity of the magnet body of four types of Examples was 2.2-2.4 microhm. In the magnet body manufactured in the same manner as in the example using an alloy having an Nd content x of 11.8 at%, the intrinsic coercive force and the residual magnetic flux density were low values (Comparative Example 1). On the other hand, in the magnet body produced in the same manner as in the example using an alloy having an Nd content x of 18.1 at%, the intrinsic coercive force was an excellent value, but the residual magnetic flux density was a low value ( Comparative Example 2).

Example B:
For example, following the method described in Patent Document 1, Patent Document 2, and the like, an alloy having a composition satisfying the composition formula: Nd _12.1 Dy _0.9 Co ₈ Ga _0.5 B _6.5 Fe _bal is manufactured. The HDDR process was performed to obtain magnet particles (HDDR magnet powder) having the magnetic properties shown in Table 3 and having an average particle diameter of about 80 μm. As a sample of the magnet powder, a sample in which an NdF ₃ layer having an average thickness of about 800 nm is formed on the surface of the magnet powder and a sample in which the NdF ₃ layer is not formed (that is, the HDDR magnet powder itself) are prepared as in Example A Then, the magnet body was produced by densification using four types of hot forming conditions shown in Table 4 in a vacuum atmosphere.

Table 5 shows the magnetic properties and relative density of the obtained magnet body. As is clear from Table 5, when the HDDR magnet powder with the NdF ₃ layer formed is used, the lower the relative density, the higher the volume resistivity (specific resistance), while the lower the specific holding force, It was found that, in a densified magnet body with a relative density of 98% or more, in order to obtain a specific holding force of 800 kA / m or more, it is necessary to perform hot forming by applying a press pressure after reaching the set temperature. It was. Moreover, the result of having performed the high frequency heat_generation | fever measurement on the conditions of 10 kHz and 2.5A about the obtained magnet body is shown in FIG. As is clear from FIG. 1, it was confirmed that the heat generation due to the eddy current is suppressed as the volume resistivity increases.

  The present invention provides a high-resistance rare earth-based permanent magnet that exhibits high magnetic resistance by using a rare earth fluoride as an insulating layer and that exhibits excellent magnetic properties by optimizing the magnet composition, and its manufacture It has industrial applicability in that it can provide a method.

It is a graph which shows the result of having performed the high frequency heat generation measurement about the magnet body obtained in Example B.

Claims (7)

Mainly composed of magnet particles having an Nd ₂ Fe ₁₄ B type crystal structure and a rare earth fluoride layer present on the surface of the magnet particles,
The relative density is 98% or more of the true density calculated from the sum of the volume ratio of the magnet particles and the volume ratio of the rare earth fluoride layer,
The magnet particles have an average particle size of 20 μm to 150 μm,
Composition _{formula: R x (Fe 1-m} Co m) 1-x-y-z Q y M z (R although at least one of Pr and Nd accounts for 70% or more, the balance lanthanide series if there is balance Q is B or B partially substituted with C. M is Ti, V, Cr, Mn, Ni, Cu, Al, Ga, In, Sn, Ta, Zr. , Nb, Mo, W, at least one selected from the group consisting of.
x is 12 at% to 18 at%,
y is 5.5 at% to 8 at%,
z is 0 at% to 10 at%,
m is 0 to 0.2),
The Nd ₂ Fe ₁₄ B type crystal phase constituting the magnet particles has an average crystal grain size of 200 nm to 700 nm,
The direction of easy magnetization of magnet particles is generally aligned in a specific direction inside the particles,
A high resistance rare earth-based permanent magnet having an intrinsic coercive force of 800 kA / m or more as a magnet and a volume resistivity of 2 μΩm or more.   The high resistance rare earth system according to claim 1, wherein the ratio of the volume ratio of the rare earth fluoride layer to the sum of the volume ratio of the magnet particles and the volume ratio of the rare earth fluoride layer is 0.1% to 10%. permanent magnet.   The rare earth fluoride layer includes at least one selected from the group consisting of La, Ce, Pr, Nd, Tb, Dy, and Ho as the rare earth element, and the content thereof is at least 50 at least of the entire rare earth element contained in the rare earth fluoride layer. The high-resistance rare earth-based permanent magnet according to claim 1, wherein the permanent magnet is at least%.   The high residual magnetic flux density according to any one of claims 1 to 3, wherein the residual magnetic flux density is 80% or more of the saturation magnetic polarization calculated from the sum of the volume ratio of the magnet particles and the volume ratio of the rare earth fluoride layer. Resistive rare earth permanent magnet.   5. The high resistance rare earth permanent magnet according to claim 1, wherein the rare earth fluoride layer has an average thickness of 10 nm to 5 μm. Composition _{formula: R x (Fe 1-m} Co m) 1-x-y-z Q y M z (R although at least one of Pr and Nd accounts for 70% or more, the balance lanthanide series if there is balance Q is B or B partially substituted with C. M is Ti, V, Cr, Mn, Ni, Cu, Al, Ga, In, Sn, Ta, Zr. , Nb, Mo, W, at least one selected from the group consisting of.
x is 12 at% to 18 at%,
y is 5.5 at% to 8 at%,
z is 0 at% to 10 at%,
m is 0 to 0.2),
Magnet particles having an Nd ₂ Fe ₁₄ B type crystal structure having an average particle diameter of 20 μm to 150 μm are manufactured by the HDDR method,
Forming a rare earth fluoride layer on the surface of the magnet particles;
Magnet particles having a rare earth fluoride layer on the surface are hot-formed by applying a pressure of 20 MPa to 200 MPa after the temperature is set to 600 ° C. to 900 ° C., and the relative density is the volume ratio of the magnet particles to the rare earth fluoride layer. A method for producing a high-resistance rare earth-based permanent magnet, characterized in that the density is 98% or more of the true density calculated from the sum of the volume ratios.   The manufacturing method according to claim 6, wherein magnetic field orientation is performed before hot forming.

Images