JP2007305691A - Rare earth magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare earth magnet provided with a protecting layer that can be formed with a simplified method and has excellent electric insulation property. <P>SOLUTION: The rare earth magnet 1 is provided with a magnet element material 2 including a rare earth element and a metal element other than the rare earth element, and a protecting layer 4 formed on the front surface of this magnet element material 2. This protecting layer 4 includes inorganic particles, and a compound of a metal element same as at least a kind of the metal elements included in the magnet element material 2, or includes silicon, oxygen, and a metal element same as at least a kind of the metal element included in the magnet element material. In the former protecting layer 4, inorganic particles are included therein in the amount of 90 to 10,000 μg/cm<SP>2</SP>. Moreover, in the latter protecting layer 4, silicon is included in the amount of 90 to 10,000 μg/cm<SP>2</SP>in terms of SiO<SB>2</SB>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rare earth magnet.

  Although a rare earth magnet containing a rare earth element has an excellent magnetic force, it contains a rare earth element that is easily oxidized as a main component, and therefore tends to have low corrosion resistance. Therefore, rare earth magnets are often configured such that a protective layer made of resin, plating, or the like is provided on the surface of a magnet body containing a rare earth element.

  By the way, in recent years, a protective layer capable of imparting a certain degree of corrosion resistance has been provided for the reason that the corrosion resistance of the magnet body itself has been improved and that the corrosion resistance of the rare earth magnet is not required depending on the application. The number of cases where it is required to be easily formed at low cost is increasing.

As a method for forming a protective layer on the surface of the magnet body relatively easily, a method of coating a colloidal solution composed of inorganic fine particles (SiO ₂ ) on the surface of the magnet body and solidifying by heating is known. (See Patent Document 1). According to such a method, since the protective layer can be formed simply by applying a colloidal solution to the magnet body and then heating it, it is possible to obtain a rare earth magnet having the protective layer on the surface at a relatively simple and low cost. It becomes.
JP-A 63-301506

  By the way, in recent years, rare earth magnets have been increasingly applied to applications such as motors. In this case, rare earth magnets have sufficient corrosion resistance and can prevent eddy currents generated in the rare earth magnets. It is required to have. For that purpose, it is preferable that the protective layer has excellent electrical insulation, but the protective layer in the conventional rare earth magnet can always provide sufficient electrical insulation for applications such as motors. It wasn't.

  Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a rare earth magnet that can be formed by a simple method and includes a protective layer having excellent electrical insulation.

In order to achieve the above object, a rare earth magnet of the present invention comprises a magnet body containing a metal element containing at least a rare earth element, and a protective layer formed on the surface of the magnet body. Inorganic particles and a compound of the same metal element as the metal element contained in the magnet element body (hereinafter abbreviated as “metal compound”), and the inorganic particles are 90 to 10,000 μg in the protective layer. / Cm ² so as to be included.

  The protective layer formed by the above-described prior art method is a layer in which inorganic fine particles are aggregated and adhered, so that corrosive components such as moisture and corrosive ions can easily pass through the gaps between the inorganic fine particles. Met. Therefore, in a rare earth magnet having such a protective layer, a corrosive component may pass through the protective layer and adhere to the magnet body, which is one factor that causes rust in the rare earth magnet.

  On the other hand, the protective layer in the rare earth magnet of the present invention contains the above-described metal compound in addition to the inorganic particles. In such a protective layer, the gap between the inorganic particles is filled with the metal compound, whereby the inorganic particles are bonded to each other. For this reason, the protective layer is difficult to pass corrosive components as compared with the conventional protective layer in which only the inorganic fine particles are adhered. Therefore, in the rare earth magnet of the present invention, corrosive components are less likely to adhere to the magnet body through the protective layer, and rust is hardly generated.

  In the rare earth magnet of the present invention, the protective layer contains the same metal element compound (metal compound) as at least one of the metal elements contained in the magnet body as described above. In the rare earth magnet, since the protective layer and the magnet body contain the same metal element as described above, their adhesion is good, and this also increases the corrosion resistance.

Furthermore, the protective layer formed by the above-described conventional method easily absorbs moisture between the inorganic fine particles, and thereby the insulating property is easily lowered. In contrast, the protective layer in the rare earth magnet of the present invention is unlikely to cause such moisture absorption because the gaps between the inorganic particles are filled with the metal compound, and as a result, high insulation can be maintained. In particular, the protective layer has excellent insulating properties by including inorganic particles at 90 to 10000 μg / cm ² . Further, from the viewpoint of obtaining excellent insulating properties, the inorganic particles are more preferably contained in the protective layer so as to be 250 to 3000 μg / cm ² .

  In the rare earth magnet of the present invention, it is preferable that the concentration of at least one of the metal elements contained in the protective layer increases from the surface side of the protective layer toward the magnet body side. If it becomes like this, the content rate of the metal element in the interface part of a protective layer and a magnet element body will become the highest, and, thereby, both adhesiveness will become still higher. Further, with such a configuration, it is difficult for stress to be generated in the protective layer and cracks are hardly generated in the protective layer, and as a result, the corrosion resistance of the rare earth magnet may be further improved. It is more preferable that the metal element in the protective layer is contained at least on the surface side from the center in the thickness direction of the protective layer.

  Furthermore, in the rare earth magnet of the present invention, the inorganic particles contained in the protective layer are composed of at least one element selected from the group consisting of silicon, aluminum, titanium, zirconium, iron and tin, and a compound containing oxygen. Are preferred. According to the protective layer containing such inorganic particles, the generation of rust in the rare earth magnet is further reduced. Among these, as the inorganic particles, those composed of a compound containing silicon and oxygen, that is, silica particles are particularly preferable.

Another rare earth magnet of the present invention includes a magnet body containing a metal element containing at least a rare earth element, and a protective layer formed on the surface of the magnet body. , And at least one of the metal elements contained in the magnet element body, and at least one of the metal elements contained in the protective layer is directed from the surface side of the protective layer toward the magnet element body side. The concentration is increased, and silicon is contained in the protective layer so as to be 90 to 10,000 μg / cm ² in terms of SiO ₂ .

  Thus, in the rare earth magnet of the present invention, the protective layer may contain silicon and oxygen, and the same metal element as the magnet body. The protective layer having such a structure is in a state in which silicon and oxygen (specifically, a compound containing them) are strongly bonded to the metal element, and therefore, it is difficult to pass corrosive components. The generation of rust can be greatly reduced. In addition, since the concentration of at least one of the metal elements in the protective layer is closer to the magnet body, the protective layer has a composition close to that of the magnet body in the vicinity of the interface with the magnet body. As a result, the magnet body is in very good contact. Therefore, the rare earth magnet of the present invention hardly causes peeling of the protective layer and has excellent corrosion resistance from this viewpoint.

Furthermore, in the rare earth magnet of the present invention, the protective layer is in a state in which silicon and oxygen (such as these compounds) are bonded as described above, so that the insulation is not easily deteriorated due to moisture absorption, and excellent insulation is achieved. Can maintain sex. In particular, the protective layer is that it contains so that 90~10000μg / cm ² in terms of silicon to SiO _2, comes to have excellent insulating properties. Further, from the viewpoint of obtaining excellent insulating properties, it is more preferable that silicon is contained in the protective layer so as to be 250 to 3000 μg / cm ² in terms of SiO ₂ .

  In the rare earth magnet of the present invention described above, the magnet body preferably further contains iron as a metal element. In this case, the protective layer more preferably contains an iron compound. Iron tends to have a high affinity for inorganic particles and the like because the electric field strength of ions is high. Therefore, by including an iron compound, inorganic particles are further satisfactorily bonded to each other in the protective layer, and the corrosion resistance of the rare earth magnet is further improved.

  Further, the magnet body preferably includes aluminum as a metal element, and in this case, the protective layer more preferably includes an aluminum compound. Aluminum has higher ion field strength than iron and has extremely good affinity for inorganic particles. Therefore, the protective layer containing an aluminum compound is such that inorganic particles are more strongly bonded to each other, and further excellent corrosion resistance can be imparted. From the viewpoint of obtaining such an effect better, it is more preferable that the protective layer includes a portion in which the aluminum concentration is higher than the aluminum concentration in the magnet body.

  Furthermore, it is preferable that the magnet body further includes copper in addition to the above-described iron and / or aluminum. In this case, it is more preferable that the protective layer contains copper or a copper compound as the metal compound. By doing so, the corrosion resistance of the rare earth magnet is further improved.

  According to the present invention, it is possible to provide a rare earth magnet that can be formed by a simple method and that includes a protective layer having excellent electrical insulation.

Hereinafter, preferred embodiments of the present invention will be described.
[Rare earth magnet]

  FIG. 1 is a diagram showing a rare earth magnet according to a preferred embodiment of the present invention. Moreover, FIG. 2 is a figure which shows typically the cross-sectional structure which follows the II-II line | wire of the rare earth magnet shown in FIG. As illustrated, the rare earth magnet 1 is composed of a magnet body 2 and a protective layer 4 formed on the surface thereof.

(Magnet body)
The magnet body 2 is a permanent magnet containing a rare earth element. In this case, rare earth elements refer to scandium (Sc), yttrium (Y), and lanthanoid elements belonging to Group 3 of the long-period periodic table. Examples of lanthanoid elements include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium. (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) and the like are included.

  Examples of the constituent material of the magnet body 2 include a material containing the rare earth element and a transition element other than the rare earth element in combination. In this case, the rare earth element is preferably at least one element selected from the group consisting of Nd, Sm, Dy, Pr, Ho, and Tb. These elements include La, Ce, Gd, Er, Eu, Tm, Yb, and More preferably, it further contains at least one element selected from the group consisting of Y.

  As transition elements other than rare earth elements, iron (Fe), cobalt (Co), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu) At least one element selected from the group consisting of zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta) and tungsten (W) is preferable, and Fe and / or Co are more preferable. preferable.

  As a constituent material of the magnet body 2, an R—Fe—B constituent material is particularly preferable. When the magnet body 2 is of the R—Fe—B type, excellent magnet characteristics can be obtained, and the effect of improving the corrosion resistance due to the formation of the protective layer 4 can be obtained more favorably.

  The R-Fe-B-based magnet element body 2 has a main phase with a substantially tetragonal crystal structure, and a rare earth-rich phase having a high rare earth element content in the grain boundary portion of the main phase, and boron It has a structure having a boron-rich phase with a high proportion of atoms. These rare earth-rich phase and boron-rich phase are nonmagnetic phases that do not have magnetism. Such a nonmagnetic phase is usually contained in an amount of 0.5 to 50% by volume in the magnet constituting material. Moreover, the particle size of the main phase is usually about 1 to 100 μm.

  In such R—Fe—B-based constituent materials, the rare earth element content is preferably 8 to 40 atomic%. When the rare earth element content is less than 8 atomic%, the crystal structure of the main phase becomes almost the same as that of α-iron, and the coercive force (iHc) tends to decrease. On the other hand, if it exceeds 40 atomic%, a rare earth-rich phase is excessively formed, and the residual magnetic flux density (Br) tends to be small.

  The Fe content is preferably 42 to 90 atomic%. When the Fe content is less than 42 atomic%, the residual magnetic flux density decreases, and when it exceeds 90 atomic%, the coercive force tends to decrease. Furthermore, the B content is preferably 2 to 28 atomic%. If the B content is less than 2 atomic%, a rhombohedral structure is likely to be formed, and this tends to reduce the coercive force. On the other hand, if it exceeds 28 atomic%, a boron-rich phase is excessively formed, and this tends to reduce the residual magnetic flux density.

  In the constituent materials described above, a part of Fe in the R—Fe—B system may be substituted with Co. Thus, if a part of Fe is replaced by Co, the temperature characteristics can be improved without deteriorating the magnetic characteristics. In this case, it is desirable that the amount of substitution of Co not be larger than the content of Fe. If the Co content exceeds the Fe content, the magnetic properties of the magnet body 2 tend to deteriorate.

  A part of B in the constituent material may be substituted with an element such as carbon (C), phosphorus (P), sulfur (S), or copper (Cu). By replacing a part of B in this way, the magnet body can be easily manufactured and the manufacturing cost can be reduced. At this time, the substitution amount of these elements is desirably an amount that does not substantially affect the magnetic properties, and is preferably 4 atomic% or less with respect to the total amount of the constituent atoms.

  Further, from the viewpoint of improving the coercive force and reducing the manufacturing cost, the magnet body 2 is made of aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese (in addition to the above elements). Mn), bismuth (Bi), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), antimony (Sb), germanium (Ge), tin (Sn), zirconium (Zr), nickel ( Ni), silicon (Si), gallium (Ga), copper (Cu), hafnium (Hf) and the like may further be contained. Especially, it is suitable that the magnet body 2 further contains Al and / or Cu. These contents are also preferably in a range that does not affect the magnetic properties, and preferably 10 atomic% or less with respect to the total amount of constituent atoms. In addition, oxygen (O), nitrogen (N), carbon (C), calcium (Ca), and the like are conceivable as other components that are inevitably mixed. It may be contained in an amount of.

(Protective layer)
The protective layer 4 is a layer for protecting the magnet body 2 formed on the surface of the magnet body 2. Here, two preferred forms of the protective layer 4 will be described.

(Protective layer: 1st form)
First, the 1st form of the protective layer 4 is demonstrated. The protective layer 4 according to the first embodiment is a layer containing inorganic particles and a metal compound containing oxygen and a metal element contained in the magnet body. FIG. 3 is an enlarged schematic view showing a cross-sectional configuration near the surface of the protective layer according to the first embodiment.

  As shown in FIG. 3, the protective layer 4 has a structure in which inorganic particles 14 are mainly aggregated and an interparticle phase 24 is formed between the inorganic particles 14. Examples of the inorganic particles 14 include those composed of a metal compound containing a metal. As this metal, silicon (Si), aluminum (Al), titanium (Ti), zirconium (Zr), iron (Fe) or tin (Sn) is preferable. Among these, Si, Al, or Ti is more preferable, and Si is particularly preferable. In this specification, Si is included in the metal.

  The inorganic particles 14 are preferably composed of metal oxide, metal hydroxide, or metal nitride, more preferably composed of metal oxide or metal hydroxide, and composed of metal oxide. More preferred. Examples of the inorganic particles 14 made of a metal oxide include particles of silica, alumina (including boehmite), titania, zirconia, and the like, and silica particles are particularly preferable.

  The inorganic particles 14 included in the protective layer 4 preferably have an average particle size of 200 nm or less, and more preferably 5 to 100 nm. Here, as the average particle diameter, a value measured by a method such as BET method, X-ray small angle scattering method, dynamic light scattering method, observation with a transmission electron microscope can be adopted. When the average particle diameter of the inorganic particles 14 exceeds 200 nm, the gap between the inorganic particles 14 becomes too large, and this gap may not be sufficiently filled with the interparticle phase 24. In addition, when the average particle diameter of the inorganic particles 14 is less than 5 nm, the shrinkage stress is increased when the protective layer 4 is formed, and cracks may easily occur in the layer.

  The interparticle phase 24 is mainly composed of a compound (metal compound) of the same metal element as at least one of the metal elements contained in the magnet body 2. As such a metal compound, a compound containing a metal element and oxygen is suitable, and specifically, a metal oxide or a metal hydroxide can be mentioned. A suitable magnet body 2 includes a plurality of types of metal elements such as rare earth elements and other transition elements as described above. In this case, the interparticle phase 24 is a single type of metal element in the magnet body 2. Or a compound of a plurality of types of metal elements.

  As the metal compound contained in the interparticle phase 24, for example, when the magnet body 2 contains Fe, an Fe compound is preferable. Thus, when the intergranular phase 24 contains a Fe compound, the inorganic particles 14 in the protective layer 4 are further bonded to each other, and the corrosion resistance of the rare earth magnet 1 is further improved. In addition, since Fe can function as a curing catalyst for anaerobic adhesive, the protective layer 4 (interparticle phase 24) contains an Fe compound, so that the anaerobic adhesive can be used for the rare earth magnet 1 as another member. It tends to provide excellent adhesion when used for adhesion.

  Furthermore, when the magnet body 2 contains Al and / or Cu, the interparticle phase 24 preferably contains Al and / or Cu as well. When the protective layer 4 contains Al, further excellent corrosion resistance can be obtained due to the high affinity of the Al to the inorganic particles 14 and the like. Moreover, since Cu can function as a curing catalyst for anaerobic adhesives similarly to Fe, the rare earth magnet 1 including the protective layer 4 further containing Cu is bonded to other members using an anaerobic adhesive. When it does, it comes to be able to exhibit the outstanding adhesiveness.

  Furthermore, when the magnet body 2 further contains a metal element other than the above metal elements, the interparticle phase 24 may further contain a compound of these metal elements.

In the protective layer 4, the mass of the inorganic particles 14 relative to the unit surface area of the protective layer 4 (hereinafter referred to as “unit mass of inorganic particles”) satisfies 90 to 10,000 μg / cm ² . This value is a value indicating the mass of the inorganic particles 14 included in the protective layer 4 constituting a portion of the surface area with respect to a predetermined surface area of the protective layer 4. Therefore, when the inorganic particles 14 are included at the same density, the value increases as the thickness of the protective layer 4 increases.

  The unit mass of such inorganic particles 14 is determined, for example, by measuring the amount of constituent elements (particularly metal elements) of the inorganic particles contained in the protective layer 4 by fluorescent X-ray analysis, It can be calculated by converting to a mass of 14.

In the protective layer 4, when the unit mass of the inorganic particles 14 is less than 90 μg / cm ² , the inorganic particles 14 are too far apart or the protective layer 4 is too thin, and sufficient corrosion resistance and insulation are obtained. It becomes difficult. On the other hand, if it exceeds 10,000 μg / cm ² , the interparticle phase 24 in the protective layer 4 is not sufficiently formed, or the protective layer 4 is too thick, and the protective layer 4 is easily peeled off. Thus, it becomes difficult to obtain good dimensional accuracy. In addition, if the protective layer 4 is too thick, the size of the magnet body 2 is relatively small, so that a problem that sufficient magnetic properties are difficult to be obtained easily occurs.

From the viewpoint of more effectively reducing these disadvantages, the unit mass of the inorganic particles 14 in the protective layer 4 is preferably 250 μg / cm ² or more. Further, preferable to be 3000μg / cm ² or less, more preferably 1000 [mu] g / cm ² or less.

  In the protective layer 4, the metal element (metal element of the metal compound) contained in the interparticle phase 24 is at least from the interface with the magnet body 2 to the surface side from the center in the thickness direction of the protective layer 4. It is preferable that it is included, and it is more preferable that the protective layer 4 is included up to the surface. In this case, in the protective layer 4, it is more preferable that the concentration of the metal element increases from the surface side toward the magnet body 2 side. When the protective layer 4 has such a configuration, the adhesion between the protective layer 4 and the magnet body 2 is further improved. Moreover, it becomes difficult to generate stress in the protective layer 4 and the generation of cracks is reduced. As a result, the corrosion resistance of the rare earth magnet 1 is further improved. The concentration of the metal element in the protective layer 4 can be measured by, for example, Auger electron spectroscopy. The concentration in this case refers to the ratio of the corresponding metal element to the total amount of metal element measured by such a measurement method.

  Furthermore, the protective layer 4 may contain a metal element other than that contained in the magnet body 2. Examples of such metal elements include titanium (Ti), zirconium (Zr), vanadium (V), molybdenum (Mo), tungsten (W), and manganese (Mn). These may be contained in either the inorganic particles 14 or the interparticle phase 24, but are preferably contained in the interparticle phase 24. When the protective layer 4 contains these elements, the corrosion resistance of the rare earth magnet 1 tends to be further improved.

(Protective layer: second form)
Next, the 2nd form of the protective layer 4 is demonstrated. The protective layer 4 according to the second embodiment is a layer having a composition containing silicon (Si), oxygen (O) and at least one of the metal elements contained in the magnet body 2 and the same kind of metal element. In such a protective layer 4, the compound containing silicon and oxygen may constitute inorganic particles as in the first embodiment.

The protective layer 4 of the second form has the following structure, for example. That is, the protective layer 4 contains a silicate represented by the general formula MO _x · nSiO ₂ (M is the same metal element as the magnet body 2). These silicates are considered to be ionic crystals having a structure in which regular tetrahedrons of SiO ₄ are regularly linked and arranged, and metal ions represented by M are contained in the gaps. In addition to these silicates, the protective layer 4 may further contain silicon dioxide, metal element oxides, hydroxides, carbonates, etc. in the magnet body 2.

  In the protective layer 4, at least one of the same kind of metal elements as the magnet body 2 has a concentration from the surface side of the protective layer 4 (the surface side opposite to the magnet body 2) toward the magnet body 2 side. Is getting bigger. The protective layer 4 having such a configuration has a composition close to that of the magnet body 2 in the vicinity of the interface with the magnet body 2 as compared with the case where all the metal elements are contained substantially uniformly. The adhesion to the element body 2 is very good. In addition, the protective layer 4 containing a metal element in this way is less prone to stress, and therefore is less likely to crack. Therefore, the rare earth magnet 1 provided with the protective layer 4 is less deteriorated due to cracks or the like occurring in the protective layer 4. The concentration of the metal element in the protective layer 4 can be measured in the same manner as the concentration of the metal element contained in the interparticle phase 24 in the protective layer 4 of the first embodiment.

  Moreover, it is preferable that the protective layer 4 includes a portion in which the concentration of the same metal element as that of the magnet element body 2 is higher than the concentration of the metal element in the magnet element body 2. Thereby, the denseness of the protective layer 4 and the adhesion to the magnet body 2 are further improved, and the corrosion resistance of the rare earth magnet 1 is further improved. It is more preferable that the concentration of such a metal element increases in the protective layer 4 as it approaches the magnet body as described above. Furthermore, the metal element of the same type as the magnet body 2 included in the protective layer 4 is at least included in a region from the interface portion with the magnet body 2 to the surface side from the center in the thickness direction of the protective layer 4. It is preferable that the protective layer 4 is included up to the surface portion.

In the protective layer 4, the mass of silicon relative to the unit surface area of the protective layer 4 (hereinafter referred to as “unit mass of silicon”) is included so as to be 90 to 10,000 μg / cm ² in terms of SiO ₂ . . This value is a value indicating the mass converted to SiO ₂ of silicon contained in the protective layer 4 constituting the portion of the surface area with respect to the predetermined surface area of the protective layer 4. Such a unit mass of silicon can be calculated, for example, by measuring the amount of silicon contained in the protective layer 4 by fluorescent X-ray analysis and then converting this measurement result to SiO ₂ . When the silicon in the protective layer 4 satisfies such a condition, the protective layer 4 has excellent insulating properties. From the viewpoint of obtaining such an effect better, the unit mass of silicon in the protective layer 4 is preferably 250 μg / cm ² or more. Further, preferable to be 3000μg / cm ² or less, more preferably 1000 [mu] g / cm ² or less.

Further, the protective layer 4 of the second form is composed of one or more metal elements of Fe and Al as the same kind of metal element as that of the magnet body 2 as in the case of the protective layer 4 of the first form described above. It is preferably contained as a metal compound such as a metal oxide or a metal hydroxide. In addition to these, it is more preferable that Cu is contained as a metal simple substance or a metal compound. By including these metal elements, the same effect as in the first embodiment can be obtained. Further, when the magnet body 2 further contains a metal element other than Fe, Al, and Cu, the protective layer 4 may contain such a metal element, and further include a metal element that is not included in the magnet body 2. You may contain.
[Rare earth magnet manufacturing method]

  Next, a preferred method for manufacturing the rare earth magnet 1 having the above configuration will be described.

First, the magnet body 2 can be manufactured by a powder metallurgy method. In this method, first, an alloy having a desired composition is manufactured by a known alloy manufacturing process such as a casting method or a strip casting method. Next, this alloy is pulverized to a particle size of 10 to 100 μm using a coarse pulverizer such as a jaw crusher, a brown mill, or a stamp mill. Thereafter, the particle size is further adjusted to 0.5 to 5 μm by a fine pulverizer such as a jet mill or an attritor. The powder thus obtained is preferably molded at a pressure of 0.5 to ⁵ t / cm ² in a magnetic field having a magnetic field strength of 600 kA / m or more.

  Thereafter, the obtained compact is preferably sintered in an inert gas atmosphere or under vacuum at 1000 to 1200 ° C. for 0.5 to 10 hours and then rapidly cooled. Further, the sintered body is subjected to heat treatment at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere or vacuum, and the sintered body is processed into a desired shape (practical shape) as necessary. A magnet body 2 is obtained.

  After obtaining the magnet body 2 in this way, it is preferable to perform acid cleaning on the magnet body 2 before performing a step of forming a protective layer 4 described later. Nitric acid is preferred as the acid used in the acid cleaning. Usually, when a steel material or the like is subjected to a plating treatment, a non-oxidizing acid having no oxidizing property such as hydrochloric acid or sulfuric acid is often used. However, when a rare earth element is included as in the magnet body 2 in the present embodiment, when processing is performed using these acids, hydrogen generated by the acid is easily occluded on the surface of the magnet body 2, The occlusion site may become brittle and a large amount of powdery undissolved material may be generated. This powdery undissolved product may cause surface roughness, defects and poor adhesion after the surface treatment. For this reason, it is preferable not to contain the non-oxidizing acid as described above in the acid cleaning treatment liquid in the present embodiment. Therefore, in the acid cleaning, it is preferable to use an oxidizing acid that generates little hydrogen, such as nitric acid.

  The amount of dissolution of the surface of the magnet body 2 by such acid cleaning is preferably 5 μm or more, preferably 10 to 15 μm in average thickness from the surface. By so doing, the altered layer and the oxidized layer due to the processing of the surface of the magnet body 2 can be almost completely removed, and the protective layer 4 described later can be formed satisfactorily.

  The concentration of nitric acid used for the acid cleaning is preferably 1 N or less, particularly preferably 0.5 N or less. If the nitric acid concentration is too high, the dissolution rate of the magnet body 2 will be extremely fast, and it will be difficult to control the amount of dissolution. In particular, it will be difficult to maintain the dimensional accuracy of the product due to large variations in mass processing such as barrel processing. Tend to be. Moreover, when the nitric acid concentration is too low, the dissolved amount tends to be insufficient. For this reason, the nitric acid concentration is preferably 1 N or less, and particularly preferably 0.5 to 0.05 N. The amount of Fe dissolved at the end of the treatment is about 1 to 10 g / L.

  After the acid cleaning, in order to remove undissolved substances and residual acid components adhering to the surface of the magnet body 2, it is preferable to further clean the magnet body 2, preferably using ultrasonic waves. This ultrasonic cleaning is preferably performed in pure water with very few chlorine ions that generate rust on the surface of the magnet body 2. Further, before and after the washing and in each process of the treatment with the treatment liquid, washing with water may be performed as necessary.

  Thereafter, when the first protective layer 4 is formed on the surface of the magnet body 2, for example, an acidic aqueous solution (treatment liquid) containing inorganic particles is brought into contact with the inorganic particles and the magnet element on the surface. A protective layer containing a compound of the same metal element as at least one of the metal elements contained in the body is formed.

  The treatment liquid is preferably an aqueous sol in which inorganic particles composed of the above-described metal compound or the like are uniformly dispersed. As such an aqueous sol, Snowtex (manufactured by Nissan Chemical Industries, Ltd.), Quattron (manufactured by Fuso Chemical Industries, Ltd.), alumina sol (manufactured by Nissan Chemical Industries, Ltd.), titania sol STS (manufactured by Ishihara Sangyo Co., Ltd.) It can be illustrated.

For example, when the second protective layer 4 is formed, the surface of the magnet body 2 is brought into contact with an aqueous solution (treatment liquid) containing silicate ions and having acidity, and the second form of the second form is formed on the surface. The protective layer 4 is deposited. The treatment liquid containing silicate ions is obtained, for example, by dissolving silicate in the treatment liquid. Examples of the silicate include alkali metal salts represented by nA ₂ O · mSiO ₂ (A is an alkali metal element) and ammonium salts such as ammonium silicate. Among these, alkali metal silicates are preferable because a protective layer can be easily formed. Examples of the alkali metal silicate include lithium silicate, sodium silicate, potassium silicate, cesium silicate, and the like. The concentration of silicate ions in the treatment solution is preferably a 0.01~4mol / L in terms of SiO _2.

  As described above, all of the treatment liquids are acidic. Specifically, the pH of the treatment liquid is preferably 0 to 6, and more preferably 1 to 5. If the pH of the treatment liquid is too low, the magnet body 2 may be excessively dissolved and it may be difficult to obtain a rare earth magnet having a desired shape. On the other hand, if the pH exceeds 5, the stability of the treatment liquid when coming into contact with the magnet body 2 tends to be low, and the protective layer 4 having a uniform thickness tends to be difficult to be formed.

  The acidity of the treatment liquid can be adjusted by adding an acid to an aqueous solution containing inorganic particles such as the above-described aqueous sol or silicate ions. The acid is not particularly limited, and inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as malic acid, malonic acid, citric acid, and succinic acid can be applied. By adjusting the concentration of this acid, the pH of the treatment liquid can be adjusted to the preferred range as described above.

  More preferably, the treatment liquid contains an acid having an oxidizing property as an acid. Examples of the acid having an oxidizing property include those further containing an oxidizing agent in addition to the acids as described above. Examples of the oxidizing agent include nitric acid or nitrate, nitrous acid or nitrite, hydrogen peroxide, permanganate and the like. When the treatment liquid contains an acid having an oxidizing property, the main phase of the magnet body 2 is well dissolved, and the protective layer 4 having a uniform thickness is formed. In addition, during the treatment with the acidic treatment liquid, there may be a problem of embrittlement of the magnet body 2 with hydrogen as in the case of the above acid cleaning. This makes it possible to reduce problems.

  In particular, the treatment liquid preferably contains nitric acid, perchloric acid, or chromic acid as an acid having an oxidizing property. These can function alone as both acids and oxidants. Therefore, by containing these, the treatment liquid has good acidity and oxidizability without containing an oxidizing agent. Of these, nitric acid is particularly preferable as the acid having oxidizing properties because it has both the properties of an acid and an oxidizing agent. In addition, even if it is a case where a process liquid contains the acid which functions as an acid and an oxidizing agent alone, it may further contain an oxidizing agent.

  Further, in the treatment liquid, since the protective layer 4 contains metal elements other than those contained in the magnet body 2 as described above, these metal elements, specifically, Ti, Zr, V Mo, W or Mn compounds such as salts of these metals can be further added. Examples of such metal salts include titanium sulfate, zirconium sulfate, zirconium chloride oxide, zirconium nitrate oxide, sodium vanadate, potassium vanadate, ammonium vanadate, sodium molybdate, potassium molybdate, ammonium molybdate, sodium tungstate, Examples include potassium tungstate, ammonium tungstate, manganese sulfate, manganese nitrate, manganese formate, and potassium permanganate. The blending amount of these metal salts is preferably 0.01 mol / L to 0.5 mol / L in the treatment liquid.

  Examples of the method of bringing the treatment liquid into contact with the magnet body 2 include an immersion method in which the magnet body 2 is immersed in the treatment liquid, and a spray method in which the treatment liquid is sprayed onto the magnet body 2. Especially, the immersion method which can make a process liquid adhere simply to the whole surface of the magnet element | base_body 2 is suitable. The temperature of the treatment liquid during the treatment is preferably 0 to 90 ° C, and more preferably 10 to 60 ° C. In the case of the immersion method, the time for immersing the magnet body 2 in the treatment liquid is preferably 10 seconds to 30 minutes. These conditions can be appropriately changed according to the desired thickness of the protective layer 4 and the like.

  Thus, the specific mechanism by which the protective layer 4 is formed by contact with the treatment liquid is not necessarily clear. For example, when forming the protective layer 4 according to the first embodiment, the following (1) and (2) is estimated. That is, when an acidic aqueous solution (treatment liquid) comes into contact with the magnet body, first, the magnet body in that portion is dissolved. (1) When dissolution of the magnet body occurs in this way, the acidity of the treatment liquid in that portion is weakened by this reaction (pH increases). If it becomes like this, the dispersibility of inorganic particles will fall in the part in which the acidity in a process liquid became weak, and, thereby, inorganic particles adhere to the surface of a magnet element body. At this time, the metal element eluted from the magnet body reacts with components in the treatment liquid to form the metal compound as described above, and on the surface of the magnet body so as to fill the gaps between the inorganic particles. Precipitate.

  (2) When the magnet body is dissolved by the contact of the treatment liquid, metal ions derived from the metal elements constituting the magnet body are dispersed in the treatment liquid near the magnet body. The metal ions and the like are adsorbed and adhered to the surface of the inorganic particles in the treatment liquid. Inorganic particles to which metal ions are attached tend to aggregate because the zeta potential of the surface changes. Accordingly, the inorganic particles aggregate in the vicinity of the surface of the magnet body, and the aggregated inorganic particles adhere to the surface of the magnet body. At this time, metal ions and the like attached to the inorganic particles react with components in the treatment liquid to form the metal compound and deposit on the surface of the magnet body so as to fill the gaps between the inorganic particles. However, the formation mechanism of a protective layer is not necessarily limited to these.

  After the formation of the protective layer 4, the surface of the protective layer 4 is washed with water in order to remove the treatment liquid adhering to the surface of the protective layer 4, by-products after the reaction, components dissolved from the magnet body 2, and the like. It is preferable. Thereby, excess processing liquid is removed and unevenness in the thickness of the protective layer 4 due to the flow of the processing liquid or the like is reduced. In addition, since the treatment liquid has acidity and tends to corrode the rare earth magnet 1, the corrosion of the rare earth magnet 1 due to the remaining treatment liquid can be reliably prevented by washing with water. More preferably, after the protective layer 4 is washed with water, the protective layer 4 is dried by warm air drying or natural drying.

  Further, the protective layer 4 may be further subjected to heat treatment. By the heat treatment, for example, condensation of the metal compound constituting the intergranular phase 24 proceeds, which may further improve the corrosion resistance of the rare earth magnet 1. The heat treatment can be performed by heating the rare earth magnet 1 after the protective layer 4 is formed. The heating temperature in this case can be 50-450 degreeC, for example. In this way, the rare earth magnet 1 having the protective layer 4 on the surface of the magnet body 2 is obtained.

  As mentioned above, although preferred embodiment of the rare earth magnet of this invention and its manufacturing method was described, this invention is not necessarily limited to embodiment mentioned above. For example, first, in the protective layer 4 of the first form in the rare earth magnet 1, it is not always necessary that the interparticle phase 24 completely fills the gaps between the inorganic particles 14 as described above. A form in which the same metal compound as the interparticle phase 24 is attached to the surface may be used. In addition, the inorganic particles 14 and the metal compound need not be separated in the protective layer 4, and the metal compound may be contained in the inorganic particles 14.

  The rare earth magnet 1 may further include a layer for protecting the rare earth magnet 1 on the surface of the protective layer 4. As such a layer, what is normally formed as a layer which protects the surface of a rare earth magnet can be applied without a restriction | limiting, A resin layer, an inorganic compound layer, a metal layer, etc. are mentioned. Thereby, the corrosion resistance of the rare earth magnet 1 can be further improved.

EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.
[Manufacture of rare earth magnets]

(Production Examples 1-6)
First, an ingot having a composition of 27.6Nd-4.9Dy-0.5Co-0.4Al-0.07Cu-1.0B-remaining Fe (numbers represent weight percentage) is produced by powder metallurgy. This was coarsely pulverized. Thereafter, jet milling with an inert gas was performed to obtain a fine powder having an average particle size of about 3.5 μm. The obtained fine powder was filled in a mold and molded in a magnetic field. Next, after sintering in vacuum, heat treatment was performed to obtain a sintered body. The obtained sintered body was cut into a size of 20 mm × 10 mm × 2 mm and processed to obtain a magnet body. Next, the obtained magnet body was subjected to acid cleaning by immersing in a 2% HNO ₃ aqueous solution for 2 minutes, and then subjected to ultrasonic cleaning.

  Thereafter, the magnet body was immersed in an acidic treatment solution containing inorganic particles for 5 minutes to form a protective layer on the surface of the magnet body to obtain a rare earth magnet. After pulling up the rare earth magnet from the treatment liquid, it was sufficiently washed with water before the treatment liquid was dried, and further subjected to a heat treatment at 180 ° C. for 20 minutes. Thereby, the rare earth magnets of Production Examples 1 to 6 each including a protective layer on the surface of the magnet body were completed.

In Production Examples 1 to 6, various rare earth magnets were produced using inorganic particle-dispersed aqueous solutions (aqueous sols) having the pH shown in Table 1 as the treatment liquid. The pH of these treatment liquids was adjusted by adding nitric acid as an acid. In Table 1, the film thickness of the protective layer formed in each production example is also shown.

  In Table 1, Snowtex C (manufactured by Nissan Chemical Co., Ltd.) is a sol containing silica fine particles having an average particle diameter of 10 to 20 nm by the BET method, and the surface of the fine particles is stabilized with Al. (Made by Kagaku Co.) is a sol containing silica fine particles having an average particle diameter of 10 to 20 nm by BET method, and alumina sol 520 is a sol containing boehmite fine particles having an average particle diameter of 10 to 20 nm by TEM observation. 01 is a sol containing titanium oxide (anatase) fine particles having an average particle diameter measured by X-ray of 7 nm.

  Moreover, the surface composition of the rare earth magnets obtained in Production Examples 1 to 6 was analyzed by fluorescent X-ray analysis (ZSX-100e; manufactured by Rigaku Corporation). As a result, it was confirmed that Si, Al and Cu were deposited on the surfaces of the rare earth magnets of Production Examples 1 to 4, and Al and Cu were deposited on the surface of the rare earth magnet of Production Example 5. It was confirmed that Ti, Al and Cu were deposited on the surface of the rare earth magnet of Production Example 6.

  Furthermore, the profile in the depth direction of the elements contained in the protective layer was analyzed for the rare earth magnets obtained in Production Examples 1 to 6 by Auger electron spectroscopy (SAM680, manufactured by ULVAC-PHI). As a result, it was confirmed that the protective layer further contained Fe and O.

  As an example, FIG. 4 shows the analysis result of the rare earth magnet of Production Example 2 by Auger electron spectroscopy. In FIG. 4, the horizontal axis represents the sputtering time of the rare earth magnet by Ar ions, and is proportional to the depth from the surface. The vertical axis represents the intensity of each element measured at the corresponding sputtering time. In this analysis, it is considered that the protective layer is analyzed at a sputtering time of 0 to 11 minutes, and the magnet body is analyzed at a sputtering time of 20 minutes or more. Moreover, it is thought that the time between these is measuring either a protective layer or a magnet body by a place by the influence of surface roughness.

  In FIG. 4, L11 indicates the strength of Fe, L12 indicates the strength of O, L13 indicates the strength of Si, and L14 indicates the strength of Al. From FIG. 4, it was confirmed that the concentration of Fe and Al gradually increased from the surface of the protective layer toward the interface with the magnet body. Further, it was confirmed that the Al concentration in the protective layer was larger than the Al concentration inside the magnet body, and in particular, increased in the vicinity of the interface with the magnet body.

(Comparative Production Example 1)
The magnet body obtained in the same manner as in Production Examples 1 to 6 was used as a rare earth magnet as it was.

(Comparative Production Example 2)
First, in the same manner as in Production Examples 1 to 6, production of a magnet body, acid cleaning, and ultrasonic cleaning were performed. The obtained magnet body was spray-coated with a treatment solution obtained by adding 10% by weight of methanol to Snowtex C (inorganic particle content: 20% by weight). Thereafter, heat treatment was performed at 180 ° C. for 20 minutes to obtain a rare earth magnet having a colloidal silica coating on the surface of the magnet body.
[Characteristic evaluation]

(High temperature and high humidity test)
The rare earth magnets of Production Examples 1 to 6 and Comparative Production Examples 1 and 2 were subjected to a high-temperature and high-humidity test at 85 ° C., 85% RH, 250 hours, and the appearance of each rare earth magnet was observed. As a result, in the rare earth magnets of Production Examples 1 to 6, no rust was observed, whereas in the rare earth magnet of Comparative Production Example 1, rust occurred 24 hours after the start of the test, and in the rare earth magnet of Comparative Production Example 2, Rust occurred 250 hours after the start of the test. From these results, the rare earth magnets (Production Examples 1 to 6) having a protective layer containing inorganic particles, or silicon and oxygen, and the same metal element contained in the magnet body, have such a protective layer. It was confirmed that rust is less likely to be produced as compared with those that do not (Comparative Production Examples 1 and 2).
[Manufacture of rare earth magnets]

(Examples 1-3, Comparative Examples 1-3)
First, an ingot having a composition of 27.6Nd-4.9Dy-0.5Co-0.4Al-0.07Cu-1.0B-remaining Fe (numbers represent weight percentage) is produced by powder metallurgy. This was coarsely pulverized. Thereafter, jet milling with an inert gas was performed to obtain a fine powder having an average particle size of about 3.5 μm. The obtained fine powder was filled in a mold and molded in a magnetic field. Next, after sintering in vacuum, heat treatment was performed to obtain a sintered body. The obtained sintered body was cut into a size of 20 mm × 10 mm × 2 mm and processed to obtain a magnet body. Next, the obtained magnet body was subjected to acid cleaning by immersing in a 2% HNO ₃ aqueous solution for 2 minutes, and then subjected to ultrasonic cleaning.

  Thereafter, the magnet body was immersed in an acidic treatment solution containing inorganic particles for a predetermined time to form a protective layer on the surface of the magnet body to obtain a rare earth magnet. After pulling up the rare earth magnet from the treatment liquid, it was sufficiently washed with water before the treatment liquid was dried, and further subjected to a heat treatment at 180 ° C. for 20 minutes. Thereby, the rare earth magnets of Examples 1 to 3 and Comparative Examples 1 to 3 each having a protective layer on the surface of the magnet body were completed.

  In Examples 1-3 and Comparative Examples 1-3, while using inorganic particle dispersion aqueous solution (aqueous sol) which has pH shown in Table 2 as a processing liquid, respectively, immersion time was changed as shown in Table 2. Various rare earth magnets were manufactured. The pH of these treatment liquids was adjusted by adding nitric acid as an acid.

And about the obtained rare earth magnets of Examples 1 to 3 and Comparative Examples 1 to 3, the amount of Si contained in the protective layer was measured by X-ray fluorescence analysis (ZSX-100e; manufactured by Rigaku Corporation). From the obtained results, the unit mass of the inorganic particles (silica particles; SiO ₂ ) in the protective layer was calculated. Table 2 also shows the unit mass of the inorganic particles in the protective layer in each rare earth magnet.

  In Table 2, Snowtex C (manufactured by Nissan Chemical Industries, Ltd.) is a sol containing silica fine particles having an average particle diameter of 10 to 20 nm by the BET method, and the surface of the fine particles being stabilized with Al.

  As a result of analysis of the surface composition by fluorescent X-ray analysis of the rare earth magnets obtained in Examples 1 to 3 and Comparative Examples 1 to 3, Si, Al and Cu were deposited on the surface of these rare earth magnets. It was confirmed that

  Moreover, about the rare earth magnet obtained in Examples 1-3 and Comparative Examples 1-3, the profile of the depth direction of the element contained in a protective layer was analyzed by Auger electron spectroscopy (ULVAC-PHI Co., Ltd. SAM680). did. As a result, it was confirmed that the protective layer further contained Fe and O.

(Comparative Example 4)
Magnet bodies obtained in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 3 were used as they were as rare earth magnets.
[Characteristic evaluation]

(Insulation test)
The insulating properties of the rare earth magnets of Examples 1 to 3 and Comparative Examples 1 to 4 were measured by the following method. That is, a conductive tape (manufactured by Sumitomo 3M, 2245) was brought into close contact with two opposing surfaces of the rare earth magnet, and the resistance value between the two surfaces was measured. It means that the greater the resistance value, the greater the insulation of the protective layer of each rare earth magnet. For the measurement of resistance, both an insulation resistance meter (Yokogawa Hewlett-Packard 4329A) and a simple tester were used.

The resistance values obtained with each rare earth magnet are shown in Table 3 for each of the two measuring instruments. Moreover, the graph which plotted the resistance value obtained with these rare earth magnets with respect to the unit mass of the inorganic particle in the protective layer of the rare earth magnets of Examples 1-3 and Comparative Examples 1-3 is shown in FIG. In the figure, black circles correspond to the results obtained in Examples 1 to 3, and x corresponds to the results obtained in Comparative Examples 1 to 3.

From Table 3 and FIG. 5, according to the rare earth magnets of Examples 1 to 3 in which the unit mass of the inorganic particles in the protective layer was 90 μg / cm ² or more, the unit mass of the inorganic particles was smaller than this (82 μg). / Cm ² or less) It was confirmed that extremely excellent electrical insulation was obtained as compared with the rare earth magnets of Comparative Examples 1 to 3 and the rare earth magnet of Comparative Example 4 having no protective layer.

It is a figure which shows the rare earth magnet obtained by the manufacturing method which concerns on suitable embodiment. It is a figure which shows typically the cross-sectional structure which follows the II-II line | wire of the rare earth magnet shown in FIG. It is a schematic diagram which expands and shows the cross-sectional structure of the protective layer of a 1st form. It is a figure which shows the analysis result by the Auger electron spectroscopy of the rare earth magnet of the manufacture example 2. It is a graph which shows the resistance value of the said protective layer with respect to the unit mass of the inorganic particle in the protective layer in the rare earth magnets of Examples 1-3 and Comparative Examples 1-3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rare earth magnet, 2 ... Magnet body, 4 ... Protective layer, 14 ... Inorganic particle, 24 ... Interparticle phase.

Claims (11)

A magnet body containing a metal element including at least a rare earth element, and a protective layer formed on the surface of the magnet body,
The protective layer includes inorganic particles, and a compound of the same metal element as at least one of the metal elements contained in the magnet body, and
The inorganic particles are included in the protective layer so as to be 90 to 10000 μg / cm ² .
Rare earth magnet characterized by that. The rare earth magnet according to claim 1, wherein the inorganic particles are contained in the protective layer so as to be 250 to 3000 μg / cm ² .   3. The rare earth according to claim 1, wherein the concentration of at least one of the metal elements contained in the protective layer increases from the surface side of the protective layer toward the magnet body side. magnet.   The inorganic particles are composed of at least one element selected from the group consisting of silicon, aluminum, titanium, zirconium, iron and tin, and a compound containing oxygen. The rare earth magnet according to claim 1.   The rare earth magnet according to claim 1, wherein the inorganic particles are silica particles. A magnet body containing a metal element including at least a rare earth element, and a protective layer formed on the surface of the magnet body,
The protective layer includes silicon, oxygen, and the same metal element as at least one of metal elements included in the magnet body,
The concentration of at least one of the metal elements contained in the protective layer is increased from the surface side of the protective layer toward the magnet body side,
In the protective layer, silicon is contained so as to be 90 to 10000 μg / cm ² in terms of SiO ₂ .
Rare earth magnet characterized by that. In the protective layer, the silicon is contained as a 250~3000μg / cm ² in terms of SiO _2, rare-earth magnet according to claim 6, wherein a.   The rare earth magnet according to claim 1, wherein the magnet body includes iron as the metal element, and the protective layer includes an iron compound.   The rare earth magnet according to any one of claims 1 to 8, wherein the magnet body includes aluminum as the metal element, and the protective layer includes an aluminum compound.   The rare earth magnet according to claim 9, wherein the protective layer includes a portion in which an aluminum concentration is higher than an aluminum concentration in the magnet body. The rare earth magnet according to any one of claims 8 to 10, wherein the magnet body includes copper as the metal element, and the protective layer includes copper or a copper compound.

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