JP2014017480A - GRAIN BOUNDARY MODIFICATION METHOD OF Nd-Fe-B-BASED MAGNET - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Nd-Fe-B-based magnet having enhanced coercive force.SOLUTION: Under existence of calcium vapor, an Nd-Fe-B-based magnet, and a halide, oxide or acid halide of at least one kind of metal, selected from a group consisting of praseodymium (Pe), dysprosium (Dy), terbium (Tb) and holmium (Ho), is heat treated and reduction of the metal is accelerated, thus causing grain boundary diffusion of the metal from the surface of the Nd-Fe-B-based magnet to the inside thereof, in the grain boundary modification method of Nd-Fe-B-based magnet.

Description

  The present invention relates to a grain boundary modification method for Nd—Fe—B magnets. Specifically, the present invention relates to a high-performance magnet having excellent coercive force, in which a specific heavy rare earth metal element is diffused and infiltrated into a crystal grain boundary phase of an Nd—Fe—B-based magnet from the magnet surface. The present invention relates to a manufacturing method of a high coercivity magnet.

  Conventionally, ferrite magnets, which are permanent magnets, have been mainly used as magnet molded bodies used for motors and the like. However, in recent years, the amount of rare earth magnets having more excellent magnetic properties has been increased in response to higher performance and smaller motors.

  Rare earth magnets, especially rare earth element-iron-boron magnets, are widely used in voice coil motors (VCM) of hard disk drives and magnetic circuits of magnetic tomography apparatuses (MRI). Recently, they are used as drive motors for electric vehicles. The application range is also expanding. In particular, heat resistance is required for automobile applications, and a magnet having high magnetic properties (coercive force) is required to avoid high temperature demagnetization at an environmental temperature of 150 to 200 ° C.

The Nd—Fe—B based sintered magnet has a fine structure in which the Nd ₂ Fe ₁₄ B compound main phase is surrounded by an Nd-rich grain boundary phase, and the component composition and size of the main phase and the grain boundary phase are It plays an important role in developing the coercivity of the magnet. In general sintered magnets, the magnetic properties of Dy ₂ Fe ₁₄ B or Tb ₂ Fe ₁₄ B compounds, which have a larger anisotropic magnetic field than Nd ₂ Fe ₁₄ B compounds, are used to incorporate Dy and Tb in magnet alloys. High coercive force is realized by containing about several weight percent to about 10 weight percent. However, as the content of Dy and Tb increases, there is a problem that the saturation magnetization is suddenly decreased to reduce the maximum energy product ((BH) _max ) and the residual magnetic flux density (Br). Further, since Dy and Tb are rare resources and are several times more expensive than Nd, it is necessary to reduce the amount of use.

  In order to solve the above-mentioned problems, a heavy rare earth metal source is heated to high temperature under normal pressure using a Ca reducing agent to reduce it to a heavy rare earth metal, and at the same time, the metal component is reduced to Nd-Fe-B system. A method of selectively diffusing and penetrating the grain boundary phase inside the magnet has been proposed (Patent Document 1). According to this method, in a Nd-Fe-B magnet, the presence of Dy, Tb, etc. in a high concentration in the grain boundary phase surrounding the main phase, that is, without reducing the residual magnetic flux density by grain boundary modification. It is described that the coercivity can be increased effectively.

International Publication No. 2006/064848

  However, the coercivity of the Nd—Fe—B magnet obtained by the method described in Patent Document 1 is not sufficient, and further improvement in coercivity is required.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide an Nd—Fe—B based magnet with improved coercive force.

  As a result of intensive studies to solve the above problems, the present inventors have conducted the above-mentioned problem by heat-treating the Nd—Fe—B magnet and the heavy rare earth metal element supply source in the presence of Ca vapor. The present invention has been completed.

  According to the method of the present invention, since a desired heavy rare earth metal can be present at a high concentration in the grain boundary phase of the Nd—Fe—B magnet, an Nd—Fe—B magnet having a high coercive force can be obtained. .

It is sectional drawing which shows roughly the crystal structure of the cross section of the Nd-Fe-B type magnet which concerns on this invention. It is sectional drawing which shows roughly the crystal structure of the cross section of the conventional Nd-Fe-B type magnet. It is a color photograph which shows the distribution condition of Tb element in the EPMA image of the magnet of Example 6. It is a graph which shows the relationship between heat processing temperature and coercive force in Examples 1-3 and Comparative Examples 1-3 and 4-6. It is a graph which shows the relationship between heat processing temperature and coercive force in Examples 4-6 and Comparative Examples 7-9 and 10-12. It is a figure which shows the XRD pattern of the Al-Ca alloy of a synthesis example. It is a graph which shows the BH demagnetization curve of the high retention magnets (7) and (8) of Examples 7-8, and an original magnet.

  The present invention relates to a grain boundary modification method for Nd—Fe—B magnets. In the method of the present invention, in the presence of calcium vapor, a halide, oxide or acid halide of an Nd-Fe-B magnet and at least one metal selected from the group consisting of Pr, Dy, Tb and Ho Heat treatment. By this heat treatment, the metal is diffused into the grain boundary from the surface layer of the Nd—Fe—B magnet. Hereinafter, “a halide, oxide or acid halide of at least one metal selected from the group consisting of Pr, Dy, Tb, and Ho” will be collectively referred to as a “heavy rare earth metal source”. Similarly, hereinafter, the “Nd—Fe—B magnet” is also simply referred to as “magnet”.

  In the above-mentioned Patent Document 1, a heavy rare earth metal element is reduced by a solid phase reduction method, a liquid phase reduction method, or a molten salt electrolytic reduction method, and the metal component is selectively diffused from the surface of the magnet to the internal grain boundary phase. It penetrates. However, in the above method, particularly the solid phase reduction method or the liquid phase reduction method, it is difficult to uniformly distribute the reducing agent, and it is difficult to effectively increase the coercive force. In addition, there is a problem that the amount of diffusion and penetration of the desired metal component into the grain boundary phase is small, a sufficient coercive force cannot be achieved, and variations occur.

On the other hand, in the method of the present invention, the magnet and the heavy rare earth metal source are heat-treated in the presence of calcium vapor (Ca vapor) to convert the heavy rare earth metal source to the heavy rare earth metal (for example, DyF ₃ is Dy). To reduce. Ca vapor can diffuse the heavy rare earth metal component more efficiently inside the magnet than when Ca is in a solid or liquid state. Therefore, diffusion of heavy rare earth metal into the magnet is promoted, and a higher concentration of heavy rare earth metal can diffuse from the surface of the magnet into the grain boundary, thereby suppressing / preventing demagnetization at high temperature and reducing the coercive force (Hcj ) Can be improved.

  Further, the Ca vapor comes into uniform and efficient contact with the Nd—Fe—B magnet and the heavy rare earth metal source as compared with the case where Ca is in a solid or liquid state. Therefore, the reduction reaction by Ca vapor occurs uniformly and efficiently in the magnet. Therefore, the magnet obtained by the method of the present invention can exhibit a higher coercive force (Hcj) and its variation is small. In addition to the above, the method of the present invention can avoid a decrease in the residual magnetic flux density (Br) of the magnet.

Here, the mechanism by which the magnetic properties can be improved by the diffusion permeation (grain boundary diffusion) treatment according to the present invention (increasing the coercive force and reducing the decrease in residual magnetic flux density) will be described as follows. The present invention is not limited to the following mechanism. The inside of a general Nd—Fe—B based magnet has a grain boundary phase (approximately 10 to 100 nanometers thick, mainly Nd, around the main crystal of Nd ₂ Fe ₁₄ B having a size of about 3 to 10 microns. It is composed of Fe and O and is called an Nd-rich phase). By the reduction of the heavy rare earth metal source by the Ca vapor, the heavy rare earth metal element is reduced and deposited on the magnet surface, and further diffuses and penetrates evenly into the magnet. In this way, the heavy rare earth metal is uniformly dispersed in the main crystal and the grain boundary phase, particularly the grain boundary phase, thereby cleaning the crystal grain boundary and the magnet surface layer, which are likely to be the source of reverse magnetic domains, and strengthening the magnetism. The coercive force of can be increased. Further, in the reduction process, the heavy rare earth metal element forms a structure selectively enriched in the grain boundary phase without substantially replacing Nd of the Nd ₂ Fe ₁₄ B main crystal, and performs grain boundary modification. It is possible. Furthermore, in the reduction step, the heavy rare earth metal source (for example, Dy ₂ O ₃ ) reacts with the Ca component (reducing agent) and is reduced to the heavy rare earth metal, but the Nd—Fe—B component constituting the magnet and Produces little reduction reaction. For this reason, the fall of a residual magnetic flux density (residual magnetization) can be suppressed, and a high energy product (maximum energy product) can be achieved. Also, the magnet is hardly damaged or not at all.

  Therefore, the magnet according to the present invention can be suitably used for a vehicle driving motor that requires heat resistance. Moreover, a coercive force equivalent to or higher than that of a conventional sintered magnet can be obtained with a small amount of heavy rare earth metal, which can contribute to solving a rare resource problem.

  Embodiments of the present invention will be described below.

The Nd—Fe—B based magnet targeted in the present invention is a sintered magnet. The Nd—Fe—B based sintered magnet has a crystal structure in which a Nd ₂ Fe ₁₄ B main phase crystal is surrounded by an Nd-rich grain boundary phase, and exhibits a typical nucleation type coercive force mechanism. For this reason, the effect of increasing the coercive force according to the present invention can be more effectively exhibited.

The production method of the Nd—Fe—B magnet is not particularly limited, and can be applied in the same manner as known methods or appropriately modified. Although preferable embodiment of the manufacturing method of a Nd-Fe-B type magnet is described below, this invention is not limited to the following. That is, the sintered magnet is formed by pulverizing a raw material alloy into several microns, forming and sintering. In the Nd—Fe—B based sintered magnet, a grain boundary phase is formed when the amount of Nd is larger than the Nd ₂ Fe ₁₄ B composition (= 27.5 wt% Nd). However, considering oxidation in the sintering process, 29 to 30% by weight of Nd is a practical Nd composition with respect to the total weight of the magnet. In a general sintered magnet, Pr, Y, etc. are included as impurities or for cost reduction. For this reason, if the content of the total rare earth metal element is about 28 to 35% by weight with respect to the total weight of the magnet, an effect of improving the magnetic properties is recognized. Here, if the content of the total rare earth metal elements is 35% by weight or less, an appropriate grain boundary phase is formed, and the proportion of the Nd ₂ Fe ₁₄ B main phase that bears the coercive force and the magnetic flux density is appropriately balanced. Practical residual magnetic flux density and maximum energy product can be obtained.

The method of the present invention can be applied to all magnets having a crystal structure surrounding a Nd ₂ Fe ₁₄ B main phase crystal with a grain boundary phase. For this reason, not only the Nd—Fe—B forming component but also other additional components such as Co for improving temperature characteristics, Al and Cu for forming a fine and uniform crystal structure are added. Also good. In addition, the method of the present invention is essentially unaffected by the magnetic properties of the original magnet and the amount of rare earth metal elements other than Nd added. For this reason, even if a sintered magnet (high performance sintered magnet) containing heavy rare earth metal elements in the main phase and the grain boundary phase, which is manufactured by adding heavy rare earth metal to the sintering raw material in advance, is used. Good. Here, the content of the heavy rare earth metal element is not particularly limited, but the total content of the heavy rare earth metal element is about 0.2% by weight to 10% by weight with respect to the total weight of the magnet. preferable. Within such a range, the coercive force can be effectively improved even for a high-performance sintered magnet by the method of the present invention.

In the present invention, at least one metal halide, oxide or acid halide selected from the group consisting of praseodymium (Pr), dysprosium (Dy), terbium (Tb) and holmium (Ho) is used as a heavy rare earth metal source. Use. That is, a heavy rare earth metal (element) selected from Pr, Dy, Tb, and Ho is supplied to the magnet surface and diffuses and penetrates into the magnet. Since these heavy rare earth metal sources are stable and can be easily handled in the air, they can be handled in the atmosphere. In addition, calcium oxide (CaO) and calcium halide (for example, CaF ₂ ) are produced after reduction with Ca vapor, but these can be easily separated from the surface of the magnet body. In addition, the heavy rare earth metal (element) has a larger magnetic anisotropy than Nd constituting the Nd—Fe—B type magnet, and easily diffuses and penetrates into the Nd rich phase surrounding the main phase inside the magnet. For this reason, the coercive force can be significantly improved by reducing and precipitating these heavy rare earth metals on the surface of the Nd—Fe—B system magnet and simultaneously diffusing and penetrating from the magnet surface to the internal grain boundary. The heavy rare earth metal source (heavy rare earth metal) may be used alone or in the form of a mixture of two or more. In the latter case, the heavy rare earth metal source (heavy rare earth metal) may be present separately or in a composite (alloyed) form. Of these, halides, oxides or acid halides of Dy, Tb and Ho are preferred, and halides, oxides or acid halides of Dy and Tb are preferred. In particular, the anisotropic magnetic fields of Dy ₂ Fe ₁₄ B and Tb ₂ Fe ₁₄ B compounds are approximately twice and three times that of Nd ₂ Fe ₁₄ B, respectively. Is particularly preferable because of the large effect.

  Here, examples of the halide include fluorides, chlorides, bromides, and iodides of the above heavy rare earth metals. Of these, fluorides and chlorides of the above-mentioned heavy rare earth metals are preferable when considering the coercive force increasing effect and ease of handling, and fluorides are more preferable when considering safety. Examples of the acid halide (halogen oxoacid salt) include acid fluorides, acid chlorides, acid bromides, and acid iodides of the above heavy rare earth metals. Among these, the oxyfluoride of the heavy rare earth metal is preferable in consideration of the coercive force increasing effect, ease of handling, safety, and the like.

In the present invention, the magnet and the heavy rare earth metal source are heat-treated in the presence of Ca vapor. Here, if Ca vapor is not used, the heavy rare earth metal source reacts with the Nd component on the magnet surface at a high temperature and is reduced by binding to Nd. For this reason, a part of the magnet surface layer becomes an Nd deficient state, and a soft magnetic phase (for example, α-Fe phase, DyFe ₂ phase) is produced as a by-product, and the coercive force is reduced.

  Conventionally, Ca has not been used for reduction of heavy rare earth metal sources with magnets due to its activity in air, particularly at high temperatures.

Here, although the production | generation method of Ca vapor | steam is not restrict | limited in particular, it produces | generates by hold | maintaining Ca vapor | steam source under pressure reduction. Note that, under normal pressure, there is little or no Ca vapor generation even under high temperature conditions. That is, Ca vapor is generated by holding the Ca vapor source under reduced pressure. The Ca vapor source is not particularly limited as long as it generates Ca vapor under reduced pressure, and examples thereof include calcium (Ca metal simple substance) and calcium hydride (CaH ₂ ). Considering the coercive force increasing effect and ease of handling, calcium is preferable. The reduction reaction of the heavy rare earth metal source with calcium or calcium hydride (CaH ₂ ) is shown below. That is, when terbium fluoride (TbF ₃ ) or dysprosium oxide (Dy ₂ O ₃ ) is used as the heavy rare earth metal source, the following reaction formula 1 (in the case of Ca) and reaction formula 2 (in the case of CaH ₂ ) ).

Here, calcium hydride, which is a reducing agent, easily reacts with moisture (see the following reaction formula 3). For this reason, when using calcium hydride, it is preferable to handle and apply calcium hydride to the magnet surface in a glove box in which the amount of moisture and oxygen is controlled to be low or zero. On the other hand, calcium does not require management of moisture and oxygen amount, and can be used particularly suitably in mass production. That is, the calcium vapor is preferably generated by holding calcium or calcium hydride (CaH ₂ ) under reduced pressure, and more preferably generated by holding calcium under reduced pressure.

  Alternatively, an alloy containing calcium and metal A, a composite having a calcium-containing material and a material containing metal A, or a form (mixture) separately including a calcium-containing material and a material containing metal A is a Ca vapor source. It is also preferable to use as. More preferably, an alloy containing calcium and metal A is used as the Ca vapor source. Here, the “calcium-containing material” may be in any form as long as it is a compound containing calcium. Similarly, the “material containing metal A” may be in any form as long as it is a compound containing metal A. In addition, “a form including a calcium-containing material and a material containing metal A separately” means that the calcium-containing material and the material containing metal A exist as separate substances, The mixture with the material containing the metal A is included.

The metal A is preferably a metal having the same melting point as that of calcium or a melting point lower than that of calcium and lower than that of the grain boundary phase of the Nd—Fe—B magnet. That is, in addition to the above form, calcium vapor separates an alloy containing calcium and metal A, a composite having a calcium-containing material and a material containing metal A, or a calcium-containing material and a material containing metal A separately. In this case, the metal A is a metal having the same melting point as that of calcium or having a melting point lower than that of calcium and lower than that of the grain boundary phase of the Nd—Fe—B magnet. It is also preferable. As described above, the inside of a general Nd—Fe—B based magnet has a structure in which the grain boundary phase surrounds the Nd ₂ Fe ₁₄ B main crystal. Here, the grain boundary phase formed using calcium or calcium hydride (CaH ₂ ) has a lower melting point than the Nd ₂ Fe ₁₄ B compound main phase (melting point: 1000 ° C. or higher). However, calcium or a metal A having a melting point lower than the grain boundary phase of the Nd—Fe—B magnet is added as an alloy, a composite, or a separate form (for example, a mixture) (hereinafter, also simply referred to as “calcium source”). As a result, the melting point of the grain boundary phase further decreases. For this reason, by reducing the heavy rare earth metal source by Ca vapor using such a calcium supply source, the heavy rare earth metal source (for example, Dy, Tb) is efficiently reduced and deposited on the magnet surface, and is deposited inside the magnet. It spreads more uniformly until. Therefore, the diffusion of heavy rare earth metal into the magnet is further promoted, and a higher concentration of heavy rare earth metal can diffuse into the grain boundary from the surface of the magnet to the inside, suppressing and preventing demagnetization at high temperature, Hcj) can be further improved. In addition to the above, a decrease in the residual magnetic flux density (Br) of the magnet can be further reduced. Further, the melting point of the metal A is lower than that of calcium or the grain boundary phase of the Nd—Fe—B magnet, that is, the metal A (for example, Al), which is easily volatilized to the same degree as calcium, is combined with calcium to form an alloy or composite. By using a body or a mixture, the amount of the metal A mixed into the magnet can be reduced or reduced to zero, and the amount can be so small that there is no problem even if the metal A is mixed into the magnet. Further, when a metal A such as Al is originally an additive component of the magnet, it also has an effect of simultaneously lowering the melting point of the grain boundary phase, so that a heavy rare earth metal source reduced by calcium (for example, Dy, Tb) Can be effectively diffused and introduced to the deep grain boundary phase of the magnet. Therefore, the magnet thus obtained has a large residual magnetic flux density and coercive force, and is excellent in the squareness of the BH demagnetization curve (JH demagnetization curve) (BH polarity (JH curve). ) Is close to a square).

  Here, the metal A that forms an alloy, composite, or mixture with calcium is approximately the same as calcium (melting point: 842 ° C., boiling point: 1503 ° C.) or has a melting point lower than that of calcium, and particles of Nd—Fe—B magnets. A metal having a melting point lower than that of the boundary phase (hereinafter also referred to as “other metal”) is preferable. Thereby, the melting point of the grain boundary phase can be further reduced, the coercive force (Hcj) can be further improved, and the decrease in the residual magnetic flux density (Br) of the magnet can be further reduced. Further, the amount of metal A mixed into the magnet can be reduced or zero. Specifically, aluminum (Al) (melting point: 660 ° C., boiling point: 2520 ° C.), zinc (Zn) (melting point: about 420 ° C., boiling point: 907 ° C.), antimony (Sb) (melting point: about 631 ° C., boiling point : 1587 ° C), ytterbium (Yb) (melting point: 824 ° C, boiling point: 1196 ° C), indium (In) (melting point: about 157 ° C, boiling point: 2072 ° C), cadmium (Cd) (melting point: 321 ° C, boiling point: 767 ° C.), gallium (Ga) (melting point: about 30 ° C., boiling point: 2208 ° C.), tin (Sn) (melting point: about 232 ° C., boiling point: 2603 ° C.), strontium (Sr) (melting point: 777 ° C., boiling point: 1414 ° C.), cesium (Cs) (melting point: about 28 ° C., boiling point: 658 ° C.), cerium (Ce) (melting point: 799 ° C., boiling point: 3426 ° C.), selenium (Se) (melting point: about 220 ° C., boiling point: About 6 5 ° C), thallium (Tl) (melting point: about 304 ° C, boiling point: 1473 ° C), tellurium (Te) (melting point: about 450 ° C, boiling point: 991 ° C), lead (Pb) (melting point: about 328 ° C, boiling point) : 1750 ° C.), bismuth (Bi) (melting point: about 271 ° C., boiling point: 1561 ° C.) and the like. The melting point of other metals is not particularly limited as long as the above conditions are met. In consideration of the fact that Ca vapor and other metal vapors are easily formed at the same time and that Ca vapor is preferentially formed, the boiling point is preferably higher than that of calcium (1503 ° C.). In consideration of the above points, the other metal is preferably aluminum.

  As long as the calcium source contains calcium and another metal (metal A), the calcium source may contain a metal having a higher melting point than calcium or may further contain a material containing a metal having a higher melting point than calcium. In consideration of uniform diffusion and penetration of rare earth metal (for example, Dy, Tb) into the magnet, it is preferable that the rare earth metal is composed of calcium and another metal (metal A). In addition, the composition of the calcium alloy in the case where the calcium supply source is a calcium alloy is not particularly limited, but considering the effect of lowering the melting point, it is preferable that the other metal (metal A) has a higher atomic ratio than calcium. . Note that the calcium alloy is allowed to contain other inevitable impurities (inevitable impurity elements) derived from the raw materials. This inevitable impurity is a component that is recognized as unnecessary other than the essential components constituting the alloy, and is an impurity that is inevitably mixed in depending on the raw material of the alloy component and the processing step. The content of the inevitable impurities is not particularly limited as long as it does not have a significant influence on the normal alloy.

The degree of pressure reduction when generating Ca vapor is not particularly limited as long as Ca vapor is generated. Ca steam production ease, when considering the operability, the pressure is preferably from 1 to 1 × 10 ^-7 Torr, and more preferably ^{1 × 10 -2 ~1 × 10 -7} Torr. That is, the calcium vapor contains calcium, calcium hydride (CaH ₂ ), an alloy containing calcium and metal A, a composite having a calcium-containing material and a material containing metal A, or a calcium-containing material and metal A. It is preferably produced by keeping the material separately under reduced pressure of 1-1 × 10 ⁻⁷ Torr. More preferably, calcium, calcium hydride (CaH ₂ ), an alloy containing calcium and metal A, a composite having a calcium-containing material and a material containing metal A, or a material containing a calcium-containing material and metal A Are separately maintained under a reduced pressure of 1 × 10 ⁻² to 1 × 10 ⁻⁷ Torr to generate calcium vapor.

  The magnet and the heavy rare earth metal source are heat-treated in the presence of Ca vapor. At this time, the heat treatment step may be performed after the Ca vapor is generated or while the Ca vapor is generated. Here, the amount of calcium source (reducing agent) used to generate Ca vapor is not particularly limited as long as it can sufficiently reduce the heavy rare earth metal source, and is appropriately selected depending on the type of heavy rare earth metal source and calcium source. Is done. For example, when calcium is used as the calcium source and a heavy rare earth metal halide is used as the heavy rare earth metal source, as shown in the above reaction formula, stoichiometrically, calcium is a halogen of the heavy rare earth metal. 1.5 mol is required for 1 mol of the compound. However, from the viewpoint of complete reduction, the amount of calcium charged is preferably 1.5 to 3 moles with respect to 1 mole of heavy rare earth metal halide. When calcium is used as the calcium source and heavy rare earth metal oxide is used as the heavy rare earth metal source, as shown in the above reaction formula, stoichiometrically, the calcium source is the heavy rare earth metal oxide. Three moles are required for one mole. However, from the viewpoint of complete reduction, the amount of calcium charged is preferably 3 to 5 moles per mole of heavy rare earth metal oxide.

When calcium hydride is used as a calcium source and a heavy rare earth metal halide is used as a heavy rare earth metal source, as shown in the above reaction formula, stoichiometrically, calcium hydride is a heavy rare earth metal. Must be equimolar with the halide. However, from the standpoint of complete reduction, the amount of calcium hydride charged is preferably 1 to 2 moles per mole of heavy rare earth metal halide. When calcium hydride is used as a calcium source and an oxide of heavy rare earth metal is used as a heavy rare earth metal source, as shown in the above reaction formula, stoichiometrically, calcium hydride is a heavy rare earth metal. 3 moles are required for 1 mole of the oxide. However, from the viewpoint of complete reduction, the amount of calcium charged is preferably 3 to 5 moles per mole of heavy rare earth metal oxide.

The heat treatment step is preferably performed in a state where the magnet, the heavy rare earth metal source, and the calcium source are sealed with a metal material that does not react with calcium vapor. That is, a magnet, a heavy rare earth metal source, and calcium, calcium hydride (CaH ₂ ), an alloy containing calcium and metal A, a composite having a calcium-containing material and a material containing metal A, or a calcium-containing material and a metal It is more preferable to perform the heat treatment in a state where the mixture with the material containing A is sealed with a metal material that does not react with calcium vapor. Thereby, Ca vapor | steam stays around a magnet and spread | circulates a heavy rare earth metal source efficiently. For this reason, the heavy rare earth metal component can be diffused and penetrated more efficiently into the magnet. Therefore, the diffusion and penetration of heavy rare earth metal into the magnet is promoted, and a higher concentration of heavy rare earth metal can be diffused from the surface of the magnet into the grain boundary to improve the coercive force.

Note that “sealing the magnet, the heavy rare earth metal source, and the calcium source with a metal material” means that these three components are confined in a certain space while maintaining a reduced pressure state. For this reason, a part of Ca vapor and air may circulate with the outside world. Here, the method for sealing the magnet, the heavy rare earth metal source, and the calcium source with a metal material is not particularly limited. In particular,
(A) Wrap the above three components with a metal foil made of an inert metal material;
(A) Put the three components in one container made of an inert metal material;
(C) Put the above three components into a container that is a combination of two types of large and small box-shaped containers made of inert metal materials;
(D) Put the above three components in one container whose inner wall is coated with an inert metal material; and (e) Two large and small box-shaped containers whose inner wall is coated with an inert metal material. Nest in nested containers;
Etc. Of these, (a) is preferred. In the case of (a), once the above three components are wrapped in a metal foil made of an inert metal material, Ca vapor is dissipated from the metal foil even when the pressure is reduced by putting it in another container. Suppress and prevent. For this reason, it can suppress and prevent that Ca adheres to the inner wall of a container. For this reason, the material of a container can be selected freely. Further, the container after the depressurization treatment can be kept clean, and washing / cleaning of the container can be omitted or reduced. In addition, what sealed the three components as mentioned above may be subjected to reduced pressure or heat treatment as it is, or the sealed three components are put in another container (for example, a decompression vessel, a heat treatment vessel). Thereafter, it may be subjected to reduced pressure or heat treatment. In addition, it is preferable to carry out pressure reduction or heat processing, after putting said (A), (U), and (O) into another container (for example, a pressure reduction container, a heat processing container). The above (a) and (d) are preferably subjected to reduced pressure or heat treatment as they are.

  As the metal material that does not react with the calcium vapor, any metal material (inert metal material) that does not react with the Ca vapor can be used, but a metal material having a high melting point is preferable. Specific examples of such a metal material include stainless steel, molybdenum (Mo), niobium (Nb), and the like.

  In the heat treatment step, the heat treatment is preferably performed in a state where the magnet surface is covered with a heavy rare earth metal source. Since the heavy rare earth metal source is in contact with the magnet surface, the heavy rare earth metal component can be diffused more efficiently inside the magnet. Therefore, the diffusion of heavy rare earth metal into the magnet is promoted, and a higher concentration of heavy rare earth metal can be diffused from the surface of the magnet to the grain boundary, demagnetizing at high temperature can be suppressed / prevented, and high coercivity can be achieved. it can. Here, the method of coating the magnet surface with the heavy rare earth metal source is not particularly limited, but there is a method in which the heavy rare earth metal source is added to a suitable solvent to prepare a slurry or solution and this is applied to the magnet. This method is preferable because it can be easily performed in the atmosphere without controlling the amount of moisture and oxygen.

  The solvent that can be used in the above method is not particularly limited as long as it is an inert solvent for the heavy rare earth metal source. Examples thereof include alcohols such as methanol, ethanol, propanol, isopropanol, butanol, and tert-butanol.

  Also, the amount of solution applied to the magnet is not particularly limited. In general, the coercive force of a magnet is affected by a structure having a concentration gradient of heavy rare earth metal elements in the depth direction of the cross section of the magnet, and a larger coercive force is obtained as the depth of the diffusion layer increases. On the other hand, when the heavy rare earth metal element is diffused and infiltrated, the thickness (width) of the grain boundary phase increases, but as the thickness of the grain boundary phase in the diffusion layer portion increases and the depth of the diffusion layer increases, the heavy rare earth element increases. A large amount of metal component is contained, resulting in a decrease in residual magnetic flux density. Therefore, in order to achieve a significant increase in coercive force while suppressing the decrease in residual magnetic flux density, the amount of heavy rare earth metal source used, the heat treatment temperature and time should be appropriate so that the heavy rare earth metal element does not become excessive. It is important to control. From this point of view, the total heavy rare earth metal component that combines the amount diffused in the magnet body and the amount that cannot be diffused and remains on the surface as a metal layer is 0.1 to 10 weights relative to the total weight of the magnet. %, And more preferably 0.2 to 5% by weight. Within such a range, the magnet can exhibit high performance magnetic properties. Within such a range, the magnet can improve the coercive force and further the maximum energy product while suppressing a decrease in the residual magnetic flux density. Also, the squareness of the demagnetization curve can be improved.

  The heat treatment conditions are not particularly limited as long as the conditions can reduce the heavy rare earth metal and diffuse the heavy rare earth metal component into the magnet. For example, the heat treatment temperature is preferably 700 to 1000 ° C, more preferably 800 to 1000 ° C, and particularly preferably 900 to 1000 ° C. The heat treatment time is preferably 10 minutes to 24 hours, more preferably 1 to 5 hours. Under such conditions, the heavy rare earth metal source is efficiently reduced to heavy rare earth metal by Ca vapor, and the heavy rare earth metal component can diffuse into the magnet.

  The depth at which the heavy rare earth metal diffuses can be appropriately adjusted depending on the heat treatment conditions (heating temperature and time). Usually, the depth at which the heavy rare earth metal diffuses may be about 20 to 1000 μm from the magnet surface. The structure of the grain boundary phase after diffusion and penetration was confirmed by the analysis result of EPMA (Electron Probe Micro-Analyzer) to be M-Nd-Fe-O (M = heavy rare earth metal) system. Is estimated to be about 10 to 200 nm. The amount of heavy rare earth metal that is reduced and deposited on the magnet surface and inside can be easily adjusted by the heat treatment temperature and time. In the method of the present invention, the heavy rare earth metal is reduced and deposited on the surface of the magnet, and at the same time, part of it diffuses and penetrates into the magnet. For this reason, it is difficult to clearly determine the thickness of only the heavy rare earth metal on the magnet surface.

  In the present invention, it is preferable to further perform an aging treatment after the heat treatment. Thereby, the coercive force can be further improved. Here, the aging treatment may be performed in the same process as the heat treatment (that is, in the same container following the heat treatment process) or may be performed in another container, but the former simplifies the operation. From the viewpoint of Here, the aging treatment conditions are not particularly limited. For example, the aging treatment temperature is preferably 400 to 700 ° C, more preferably 500 to 650 ° C. The aging treatment time is preferably 10 minutes to 3 hours, more preferably 30 minutes to 2 hours. Under such conditions, the uniform generation of the Nd-rich phase at the grain boundary is promoted, and the coercive force can be further improved. In addition, since the production | generation temperature range of a Nd rich phase is 500-600 degreeC, when an aging treatment temperature is less than a minimum, there exists a possibility that there may be little coercive force improvement effect. On the other hand, if the upper limit is exceeded, the Nd-rich phase may grow excessively, leading to a decrease in coercive force. Moreover, in order to produce | generate Ca vapor | steam, it heat-processes, maintaining a pressure-reduced atmosphere. For this reason, the container (vacuum container) which maintained pressure reduction conditions can be heat-processed in air | atmosphere atmosphere.

  By the heat treatment as described above and, if necessary, the aging treatment, the heavy rare earth metal source is reduced to the heavy rare earth metal and deposited on the magnet surface, and the heavy rare earth metal selectively diffuses into the grain boundary phase inside the magnet. To penetrate. Further, since the heavy rare earth metal does not diffuse on the surface of the magnet but remains on the surface, a heavy rare earth metal layer is formed on the surface of the magnet. The heavy rare earth metal layer on the magnet surface may be removed if necessary. If the removal thickness of the heavy rare earth metal layer on the magnet surface is about 0.05 mm or less, the coercive force is hardly reduced by the removal, and the residual magnetic flux density is not changed even if it is cut. Here, the method for removing the heavy rare earth metal layer on the magnet surface is not particularly limited, and a known method can be used. For example, a surface grinding method using a plane or cylindrical grinder can be preferably used. In addition, it is possible to dissolve and remove the surface layer using an acid, but in that case, it is preferable to sufficiently perform alkali neutralization or washing.

  After the heat treatment and, if necessary, the aging treatment or the heavy rare earth metal layer removal treatment, if necessary, the magnet may be cut to produce a plurality of magnets having a predetermined shape and size. Here, the cutting method is not particularly limited, and a known method can be used. For example, using a disk-shaped cutting blade with diamonds and green corundum abrasive grains fixed to the outer periphery of the cutting blade, fixing the magnet piece and then cutting the magnet one by one, attaching multiple blades A method of cutting a plurality of pieces at the same time with a cutting machine (multi-saw) can be used. For example, when the grain boundary modification treatment according to the present invention is performed on a thin magnet having a thickness of 1 mm or less, it is easy to obtain desired magnetic characteristics by a short time treatment using a small amount of heavy rare earth metal element. It is. On the other hand, in the case of a thick magnet having a thickness of about 5 to 10 mm, it is preferable that the heavy rare earth metal element is sufficiently infiltrated deeply into the magnet so that the entire magnet is in a substantially homogeneous structure. It is also a suitable method to reduce the number of press moldings in the magnet manufacturing process by performing subsequent cutting.

A magnet (high coercive force magnet) obtained by the method of the present invention has a cross-sectional structure as shown in FIG. In FIG. 1, Dy is described as a representative example of heavy rare earth metal, but other heavy rare earth metals have the same structure. As shown in FIG. 1, the Dy element diffuses and penetrates from the magnet surface and penetrates into the magnet particles on the outermost layer of the magnet to form a Dy metal layer, but hardly penetrates into the inner magnet particles. Diffuses at grain boundaries. Thus, the magnet according to the present invention can improve the coercive force because the heavy rare earth metal element selectively permeates the crystal grain boundary. Dy element penetrates into a small portion of the Nd ₂ Fe ₁₄ B crystal in the surface layer of the magnet, but does not penetrate most of the Nd ₂ Fe ₁₄ B crystal inside, and most of the Dy element Invade the Nd-rich grain boundary phase. In addition, the diffusion penetration into the Nd-rich grain boundary phase also has a tissue structure having a concentration gradient in which the Dy element concentration (diffusion penetration degree) is high on the magnet surface side and slightly thinner toward the inside. As described above, in the magnet according to the present invention, although the heavy rare earth metal element penetrates into the main phase crystal of the magnet in the outermost surface layer portion of the magnet, the main phase crystal is substantially heavy (especially inside). Since rare earth metal elements do not enter, it is possible to suppress a decrease in residual magnetic flux density.

On the other hand, the conventional magnet has a structure in which Nd-rich grain boundary phases surround Nd ₂ Fe ₁₄ B crystal grains, as shown in FIG. Even when a small amount of Dy element is contained, the Dy element exists uniformly distributed in each of the Nd ₂ Fe ₁₄ B crystal grains and the Nd-rich grain boundary phase. Absent.

As described above, according to the method of the present invention, the heavy rare earth metal component diffuses and penetrates from the magnet surface to the inside, and the grain boundary phase is enriched with the heavy rare earth metal element. This surface layer is a heavy rare earth metal-rich layer in which Nd and Fe in the magnet are partially incorporated by reaction. For this reason, since it is more stable in air than Nd ₂ Fe ₁₄ B, it is possible to omit a rust preventive film such as nickel plating or resin coating when used in a relatively low humidity environment at several tens of degrees Celsius. Is possible. Further, the heavy rare earth metal exists preferentially in the surface layer portion rather than the inner deep portion of the magnet, and Nd of the Nd ₂ Fe ₁₄ B main crystal is hardly substituted by the M metal element. For this reason, since a structure in which the heavy rare earth metal element is selectively enriched in the grain boundary phase rather than in the main crystal is formed, the occurrence of reverse magnetic domains is suppressed, and an Nd—Fe—B magnet before grain boundary modification is obtained. Thus, the coercive force can be improved.

In addition, the method of the present invention can easily realize reduction to heavy rare earth metal and selective diffusion and penetration of heavy rare earth metal component into the grain boundary phase inside the magnet in a single processing step. Further, since the melting point of the Nd-rich grain boundary phase is lower than the melting point of the Nd ₂ Fe ₁₄ B phase (1000 ° C. or higher), it easily diffuses selectively into the grain boundary phase of the magnet.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

The coercive force (Hcj), the residual magnetic flux density (Br), and the maximum energy product ((BH) _max ) are measured by the following method. In addition, the squareness is evaluated by the following method.

<Measurement of coercive force (Hcj) and residual magnetic flux density (Br)>
Magnetization characteristics were measured using a pulse BH curve tracer manufactured by Nippon Electromagnetic Co., Ltd., and a coercive force (Hcj) and a residual magnetic flux density (Br) were obtained.

<Measurement of maximum energy product ((BH) _max )>
The maximum value of the product of the magnetic flux density and the magnetic field magnitude measured above is defined as the maximum energy product ((BH) _max ).

<Evaluation of squareness>
Magnetization characteristics are measured using a pulse BH curve tracer made by Nippon Electromagnetic Co., Ltd., and the coercive force (Hcj) and the residual magnetic flux density (Br) are obtained. The residual magnetic flux density (Br) with respect to the coercive force (Hcj) Was plotted to prepare a BH demagnetization curve, and the squareness was evaluated based on this curve.

Examples 1-3
According to the following method, an Nd—Fe—B based magnet [composition: Nd ₂ Fe ₁₄ B; Br = 1.48 (T), Hcj = 1.01 (MA / m), (BH) _max = 370 kJ / m ³ ] Was produced. That is, an alloy flake having a thickness of about 0.2 mm was manufactured from an alloy ingot having a composition of Nd _12.5 Fe _79.5 B ₈ by strip casting. Next, this thin piece is filled in a container, and hydrogen gas of 300 kPa is occluded at room temperature and then released to obtain an amorphous powder having a size of 0.1 to 0.2 mm, followed by jet mill pulverization. Thus, a fine powder of about 3 μm was produced. The fine powder was filled in a mold, formed by applying a pressure of 100 MPa while applying a magnetic field of 800 kA / m, charged in a vacuum furnace, and sintered at 1080 ° C. for 1 hour. This sintered body was cut to produce a plurality of plate-like samples having anisotropy in the thickness direction of about 5 mm × about 5 mm × about 4.8 mm. Below, this plate-shaped sample was used as a magnet (original magnet).

A slurry was prepared by adding dysprosium (III) fluoride (DyF ₃ ) to butanol to a concentration of 20% by weight. On the surface of the Nd-Fe-B magnet produced above (size: 5 mm x 5 mm x 4.8 mm), the slurry prepared above was Dy with respect to the amount of Nd component contained in the magnet piece in the air. Coating was performed so that the amount of the component was about 5 atomic%, and a coated magnet was manufactured.

Next, 900 mg of this coated magnet and Ca metal (10 mg: equivalent to 1.5 to ₃ mol with respect to 1 mol of DyF ₃ ) are wrapped with Mo metal foil and placed in a quartz tube (outer diameter 10 mm, length 100 mm). I put it in. The quartz tube was evacuated to 10 ⁻² Torr or less and sealed. Further, this quartz tube was heat-treated at 900 ° C., 950 ° C., or 1000 ° C. for 4 hours in the air, respectively. After this heat treatment, an aging treatment was carried out at 600 ° C. for 1 hour as it was to produce high retention magnets (1) to (3) (Ca vapor-DyF ₃ ). In addition, although the quartz tube inner wall was visually observed after the said heat processing, adhesion of Ca was not recognized.

For the high retention magnets (1) to (3) obtained above, the coercive force (Hcj), the residual magnetic flux density (Br) and the maximum energy product ((BH) _max ) were measured, and the results are shown in Table 1 and FIG. 4 shows.

Comparative Examples 1-3
Nd—Fe—B based magnets were produced in the same manner as in Examples 1 to 3.

In a glove box (oxygen amount 0.03 ppm or less, dew point controlled to −95 ° C. or less), 0.2 g of calcium hydride (CaH ₂ ) and 0.3 g of dysprosium (III) fluoride (DyF ₃ ) are mixed, butanol A slurry was prepared by adding to 1 mL. On the surface of the Nd-Fe-B magnet produced above (size: 5 mm x 5 mm x 4.8 mm), the slurry prepared above was Dy with respect to the amount of Nd component contained in the magnet piece in the air. Coating was performed so that the amount of the component was about 5 atomic%, and a coated magnet was manufactured.

  Each of the coated magnets was heat-treated at 900 ° C., 950 ° C., or 1000 ° C. for 4 hours in the air. After this heat treatment, an aging treatment was carried out at 600 ° C. for 1 hour to produce comparative magnets (1) to (3).

For the comparative magnets (1) to (3) obtained above, the coercive force (Hcj), the residual magnetic flux density (Br) and the maximum energy product ((BH) _max ) were measured, and the results are shown in Table 1 and FIG. Shown in

Comparative Examples 4-6
In Examples 1 to 3, comparative magnets (4) to (6) were produced in the same manner as Examples 1 to 3, respectively, except that no Ca metal was used.

For the comparative magnets (4) to (6) obtained above, the coercive force (Hcj), the residual magnetic flux density (Br) and the maximum energy product ((BH) _max ) were measured, and the results are shown in Table 1 and FIG. Shown in

Examples 4-6
Nd—Fe—B based magnets were produced in the same manner as in Examples 1 to 3.

A slurry was prepared by adding terbium (III) fluoride (TbF ₃ ) to butanol to a concentration of 20% by weight. On the surface of the Nd—Fe—B magnet (size: 5 mm × 5 mm × 4.8 mm) prepared above, the slurry prepared above was added to the surface of the Nd component contained in the magnet piece in the atmosphere by Tb. Coating was performed so that the amount of the component was about 5 atomic%, and a coated magnet was manufactured.

Next, this coated magnet and Ca metal (10 mg) were wrapped with Mo metal foil and placed in a quartz tube (outer diameter 10 mm, length 100 mm). The quartz tube was evacuated to 10 ⁻² Torr or less and sealed. Further, this quartz tube was heat-treated at 900 ° C., 950 ° C., or 1000 ° C. for 4 hours in the air, respectively. After this heat treatment, an aging treatment was carried out at 600 ° C. for 1 hour to produce high retention magnets (4) to (6). In addition, although the quartz tube inner wall was visually observed after the said heat processing, adhesion of Ca was not recognized.

For the high retention magnets (4) to (6) obtained above, the coercive force (Hcj), the residual magnetic flux density (Br) and the maximum energy product ((BH) _max ) were measured, and the results are shown in Table 2 and FIG. As shown in FIG.

  Further, for the high holding magnet (Example 6) heat-treated at 1000 ° C. for 4 hours, Tb element mapping of the magnet cross section by EPMA (Electron Probe Micro-Analyzer) was performed, and the analysis result is shown in FIG. From FIG. 3, it can be seen that the Tb element diffuses from the surface layer into the grain boundary. Further, it can be seen that the Tb element penetrates into the magnet particles on the outermost layer of the magnet to form a Tb metal layer, but diffuses to the grain boundary with almost no penetration into the inner magnet particles. . From this, it is considered that according to the method of the present invention, the coercive force can be improved because the heavy rare earth metal element selectively permeates the crystal grain boundary. Also, according to the method of the present invention, heavy rare earth metal elements penetrate into the main phase crystal of the magnet on the outermost surface layer portion of the magnet, but the heavy phase rare earth metal is substantially contained in most (especially the inside) main phase crystals. Since the element does not enter, it is considered that the decrease in the residual magnetic flux density can be suppressed.

Comparative Examples 7-9
Nd—Fe—B based magnets were produced in the same manner as in Examples 1 to 3.

In a glove box (oxygen amount 0.03 ppm or less, dew point controlled to -95 ° C. or less), 0.2 g of calcium hydride (CaH ₂ ) and 0.3 g of terbium fluoride (III) (TbF ₃ ) are mixed, butanol A slurry was prepared by adding to 1 mL. On the surface of the Nd—Fe—B magnet (size: 5 mm × 5 mm × 4.8 mm) prepared above, the slurry prepared above was added to the surface of the Nd component contained in the magnet piece in the atmosphere by Tb. Coating was performed so that the amount of the component was about 5 atomic%, and a coated magnet was manufactured.

  Each of the coated magnets was heat-treated at 900 ° C., 950 ° C., or 1000 ° C. for 4 hours in the air. After this heat treatment, an aging treatment was carried out at 600 ° C. for 1 hour to produce comparative magnets (4) to (6).

For the comparative magnets (4) to (6) obtained above, the coercive force (Hcj), the residual magnetic flux density (Br) and the maximum energy product ((BH) _max ) were measured, and the results are shown in Table 2 and FIG. Shown in

Comparative Examples 10-12
In Examples 4 to 6, comparative magnets (10) to (12) were produced in the same manner as Examples 4 to 6, respectively, except that no Ca metal was used.

For the comparative magnets (10) to (12) obtained above, the coercive force (Hcj), the residual magnetic flux density (Br) and the maximum energy product ((BH) _max ) were measured, and the results are shown in Table 2 and FIG. Shown in

Tables 1 and 2 and FIGS. 4 and 5 show that a high coercive force (Hcj) can be exhibited at all temperatures by heating the magnet and the heavy rare earth metal source in the presence of Ca vapor. Further, the effect is compared with the case of performing the reduction treatment by CaH ₂ under normal pressure if not used (Comparative Example 1～3,7～9) and Ca metal (Comparative Example 4～6,10～12) It is also shown that the coercivity (Hcj) is significantly higher at all temperatures. From this, the magnet manufactured by the method of this invention can exhibit a high coercive force. In addition, it is estimated that a coercive force can be improved more effectively by covering the whole with Mo foil and keeping Ca vapor | steam around a magnet. It is also shown that no significant decrease in residual magnetic flux density (Br) is observed with the method of the present invention.

  As described above, considering that Tb diffuses from the surface layer to the inside (FIG. 3), a high concentration of Tb exists in the grain boundary phase surrounding the main phase. It is estimated that the coercive force was significantly improved.

Synthesis Example Aluminum powder (Al powder) and calcium powder (Ca powder) were blended so as to have an elemental composition of Al ₂ Ca or Al ₄ Ca, and arc-melted in an argon atmosphere in a glove box, and the alloys were respectively calcium- An aluminum alloy ingot was obtained. This alloy ingot was coarsely pulverized by mortar pulverization in the glove box and then pulverized by a jet mill to obtain a calcium-aluminum alloy powder having a particle size of 10 μm or less. About the obtained calcium-aluminum alloy powder, the phase (solid solution, intermetallic compound) was specified using the X-ray-diffraction apparatus (XRD). These X-ray diffraction patterns are shown in FIG. From Figure 6, calcium was obtained - aluminum alloy, respectively, can be confirmed to have an elemental composition of Al ₂ Ca or Al ₄ Ca.

Example 7
Nd—Fe—B based magnets were produced in the same manner as in Examples 1 to 3.

A slurry was prepared by adding dysprosium (III) fluoride (DyF ₃ ) to butanol to a concentration of 20% by weight. On the surface of the Nd-Fe-B magnet produced above (size: 5 mm x 5 mm x 4.8 mm), the slurry prepared above was Dy with respect to the amount of Nd component contained in the magnet piece in the air. Coating was performed so that the amount of the component was about 5 atomic%, and a coated magnet was manufactured.

Next, about 900 mg of this coated magnet and Ca metal (10 mg: equivalent to 1.5 to ₃ mol with respect to 1 mol of DyF ₃ ) are wrapped with Mo metal foil, and inside a quartz tube (outer diameter 10 mm, length 100 mm) Put in. The quartz tube was evacuated to 10 ⁻² Torr or less and sealed. Further, each of the quartz tubes was heat-treated in the atmosphere at 900 ° C. for 4 hours. After this heat treatment, an aging treatment was carried out at 600 ° C. for 1 hour to produce a high retention magnet (7) (DyF ₃ + Ca vapor). In addition, although the quartz tube inner wall was visually observed after the said heat processing, adhesion of Ca was not recognized.

  The coercive force (Hcj) and residual magnetic flux density (Br) of the high retention magnet (7) obtained above were measured, and the results are shown in Table 3 and FIG. Note that “As-is” in FIG. 7 indicates the characteristics of the original magnet.

Example 8
Nd—Fe—B based magnets were produced in the same manner as in Examples 1 to 3.

A slurry was prepared by adding dysprosium (III) fluoride (DyF ₃ ) to butanol to a concentration of 20% by weight. On the surface of the Nd-Fe-B magnet produced above (size: 5 mm x 5 mm x 4.8 mm), the slurry prepared above was Dy with respect to the amount of Nd component contained in the magnet piece in the air. Coating was performed so that the amount of the component was about 5 atomic%, and a coated magnet was manufactured.

Next, about 900 mg of this coated magnet and the Al ₄ Ca alloy prepared in the above synthesis example (16.5 mg: equivalent to 1.5 to ₃ mol of calcium relative to 1 mol of DyF ₃ ) are wrapped in Mo metal foil, and quartz The tube was placed in an outer diameter of 10 mm and a length of 100 mm. The quartz tube was evacuated to 10 ⁻² Torr or less and sealed. Further, each of the quartz tubes was heat-treated in the atmosphere at 900 ° C. for 4 hours. After this heat treatment, an aging treatment was carried out at 600 ° C. for 1 hour as it was to produce a high retention magnet (8) (DyF ₃ + Al / Ca vapor). In addition, although the quartz tube inner wall was visually observed after the said heat processing, adhesion of Ca was not recognized.

  The coercive force (Hcj) and residual magnetic flux density (Br) of the high retention magnet (8) obtained above were measured, and the results are shown in Table 3 and FIG.

Table 3 and FIG. 7 show that the high retention magnets (7) and (8) of the present invention can exhibit higher coercive force and squareness than the original magnet. In particular, in the high retention magnet (8) obtained by heat-treating the magnet and the heavy rare earth metal source in the presence of Ca vapor generated using the Al ₄ Ca alloy, the coercive force is particularly improved, It is also shown that the squareness can be maintained at a high level.

  According to the method of the present invention, the heavy rare earth metal component can be selectively present in the grain boundary phase while being hardly taken into the main phase of the magnet. For this reason, it becomes possible to improve a coercive force. Furthermore, according to the method of the present invention, a decrease in residual magnetic flux density can be suppressed / prevented. For this reason, saving of scarce resources and reduction of magnet cost can be achieved.

Claims (8)

  Nd-Fe-B magnets in the presence of calcium vapor, and at least one metal halide selected from the group consisting of praseodymium (Pr), dysprosium (Dy), terbium (Tb) and holmium (Ho), Grain boundary modification method for Nd-Fe-B magnets, comprising heat-treating an oxide or acid halide to diffuse the metal from the surface layer of the Nd-Fe-B magnets to the inside. . The method of claim 1, wherein the calcium vapor is generated by holding calcium, calcium hydride (CaH ₂ ) under reduced pressure. The calcium vapor keeps the alloy containing calcium and metal A, a composite having a calcium-containing material and a material containing metal A, or the calcium-containing material and the material containing metal A separately under reduced pressure. Generated by
The method according to claim 1, wherein the metal A has the same melting point as or lower than the melting point of calcium and lower than the melting point of the grain boundary phase of the Nd—Fe—B magnet. The calcium vapor is calcium, calcium hydride (CaH ₂ ), an alloy containing calcium and metal A, a composite having a calcium-containing material and a material containing metal A, or a material containing a calcium-containing material and metal A 4. The method according to claim 2 or 3, wherein is produced separately by keeping them under a reduced pressure of 1-1.times.10.sup.- ⁷ Torr. Contains the Nd-Fe-B magnet, the metal halide, oxide or acid halide, and calcium, calcium hydride (CaH ₂ ), an alloy containing calcium and metal A, a calcium-containing material and metal A The method according to claim 2 or 3, wherein the heat treatment is performed in a state where the composite containing the material to be processed or the mixture of the calcium-containing material and the material containing metal A is sealed with a metal material that does not react with calcium vapor.   The method of any one of Claims 1-4 which heat-processes in the state which coat | covered the said Nd-Fe-B type magnet surface with the halide, oxide, or acid halide of the said metal.   The method according to claim 1, wherein the heat treatment is performed at 700 to 1000 ° C.   The method according to claim 1, wherein an aging treatment is further performed after the heat treatment.