JP2007273831A - Rare-earth magnet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare-earth magnet in which a separation of a protection layer is low, and its manufacturing method. <P>SOLUTION: The rare-earth magnet 1 comprises a magnet element assembly 2 containing at least a rare-earth element, inorganic particles 6 scattered on and adhered to a surface of this magnet element assembly 2, and a protection layer 4 formed so as to cover the inorganic particles 6 on the surface of this magnet element assembly 2. The rare-earth magnet 1 can be obtained by forming the protection layer 4 so that, after the magnet element assembly 2 is processed with a first processing agent containing metal ions and subsequently a second processing agent having a different pH from the first processing agent, the inorganic particles 6 separated thereby are covered. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rare earth magnet and a method for manufacturing the same.

  Rare earth magnets containing rare earth elements have an excellent magnetic force and are used in a wide range of applications. This rare earth magnet tends to have low corrosion resistance because it contains a rare-earth element that is easily oxidized as a main component, and it is generally configured that a protective layer is provided on the surface of a magnet body having magnetic properties. Is.

  Conventionally, resin layers are widely known as protective layers for rare earth magnets. However, in recent years, rare earth magnets are often applied to motors for automobiles such as drive motors and generators for hybrid cars. However, peeling and blistering occurred due to high temperature and high humidity environment, and sufficient corrosion resistance was often not obtained.

  In order to reduce peeling and blistering in such a high-temperature and high-humidity environment, a rare earth magnet is known in which a protective layer is provided after a predetermined base treatment is performed on the surface of the magnet body. As the base treatment, for example, a chemical conversion treatment of the surface of the magnet body is known. The chemical conversion treatment is a treatment for forming an insoluble salt on the surface of the element body along with the dissolution of the magnet element body. However, in the chemical conversion treatment, since the grain boundary portion is more easily dissolved than the main phase in the magnet body, holes in the depth direction from the surface of the magnet body may be formed. When such a hole is formed, a corrosive component penetrates into the inside of the magnet body from this portion, which may deteriorate the magnet body.

Therefore, as a base treatment, a treatment is known in which a magnet body is immersed in a treatment liquid containing metal ions and a metal element compound derived from the metal ions is deposited on the surface (see Patent Document 1). . According to such a method, the metal compound layer can be formed on the surface without dissolving the magnet body, and the formation of holes as in the chemical conversion treatment is reduced.
JP 2000-199074 A

  However, even with a rare earth magnet that has been subjected to a base treatment of a magnet body by deposition of a metal compound as in Patent Document 1, the adhesion of the protective layer to the magnet body is not sufficient, and the protective layer is peeled off. It has been still difficult to sufficiently reduce the above.

  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 having sufficient corrosion resistance and less protective layer peeling, and a method for manufacturing the same.

  In order to achieve the above object, a rare earth magnet of the present invention includes a magnet element containing a metal element containing at least a rare earth element, inorganic particles dispersed and attached to the surface of the magnet element, and the surface of the magnet element. And a protective layer formed so as to cover the inorganic particles.

  In the rare earth magnet of the present invention, a protective layer is formed on the surface of the magnet body via inorganic particles dispersed and attached on the surface. For this reason, in the rare earth magnet of the present invention, compared with the case where the protective layer is formed directly on the surface of the magnet element body or through the layer of the base treatment, the contact portion of the protective layer to the magnet element body side The area is large, and the adhesion of the protective layer is good. Even if a stress is applied to the contact interface between the protective layer and the magnet body, the stress can be relaxed at the portion of the inorganic particles dispersed and attached to the surface of the magnet body. Accordingly, the rare earth magnet of the present invention is extremely difficult to peel off the protective layer.

  In the rare earth magnet of the present invention, it is preferable that the inorganic particles attached on the surface of the magnet body include a compound of the same metal element as at least one of the metal elements contained in the magnet body. If it carries out like this, a magnet element | base_body and an inorganic particle will contain the same metallic element, and both adhesiveness will become better. As a result, peeling of the inorganic particles from the magnet body is extremely difficult to occur, thereby further reducing the peeling of the protective layer.

  More specifically, the inorganic particles preferably include at least one metal element selected from the group consisting of Fe, Co, Al, and Cu, and more preferably include a compound of these metal elements. Since inorganic particles containing these metal elements are difficult to dissolve in acidic aqueous solutions, the corrosion resistance of rare earth magnets is further improved by having such inorganic particles at the interface between the protective layer and the magnet body. To do.

  Furthermore, the protective layer is more preferably a resin layer. Since the resin layer is flexible, it can adhere well to the uneven surface of the magnet body to which the inorganic particles are attached. In addition, if the protective layer is a resin layer, the stress generated at the interface between the magnet body and the protective layer can be well relaxed by the flexible resin layer. As a result, peeling of the protective layer from the magnet body is more difficult to occur.

  The method for producing a rare earth magnet of the present invention is a method for suitably producing the rare earth magnet of the present invention, wherein the magnet element containing a metal element containing at least a rare earth element contains a metal ion. A step of immersing in the first treatment liquid, and a surface of the magnet body with the first treatment liquid adhered thereto, a second treatment liquid having a pH different from that of the first treatment liquid, and contacting the surface A step of depositing inorganic particles made of a compound of a metal element derived from metal ions contained in the first treatment liquid, and a step of forming a protective layer on the surface of the magnet body so as to cover the inorganic particles; It is characterized by having.

  In the manufacturing method of the present invention, after the first treatment liquid containing metal ions is brought into contact with the magnet body, the pH at which the metal ions in the first treatment liquid adhered to the surface can be precipitated as a compound. By further contacting the second treatment liquid having the above, the inorganic particles are formed in a dispersed state on the surface of the magnet body. As described above, according to the manufacturing method of the present invention, the inorganic particles can be attached on the surface of the magnet body by bringing two kinds of treatment liquids into contact with each other, and a rare earth magnet can be easily manufactured. .

  Here, the method of the ground treatment of the above-mentioned patent document 1 is to deposit the metal compound on the magnet body by causing precipitation of a metal element compound derived from metal ions in the treatment liquid. . However, in this method, since the precipitate is uniformly formed in the treatment liquid, the treatment liquid once used cannot be used again, and is not sufficient in terms of mass productivity. On the other hand, in the method for producing a rare earth magnet of the present invention, the first treatment liquid is attached to the magnet body, and then the second treatment liquid is contacted, thereby causing the metal ions in the first treatment liquid to contact with the metal ions. Since the derived compound is precipitated, the components of the treatment liquid hardly change in these series of steps. Therefore, the production method of the present invention can repeatedly use the first and second treatment liquids, and is excellent from the viewpoint of mass productivity.

  In the method for producing a rare earth magnet of the present invention, the metal ion contained in the first treatment liquid is preferably an ion of the same metal element as at least one of the metal elements contained in the magnet body. Thereby, the inorganic particle which consists of a compound of the same kind of metal element as what is contained in a magnet element body is formed in the surface of a magnet element body, and the adhesiveness of a magnet element body and an inorganic particle becomes favorable. Moreover, it is preferable to form a resin layer as a protective layer. The protective layer made of the resin layer is flexible, and even when stress is generated between the protective layer and the magnet body, it can be satisfactorily relaxed.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the rare earth magnet which has sufficient corrosion resistance, and there are few peeling of a protective layer, and its manufacturing method.

  Preferred embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a perspective view 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. Further, FIG. 3 is a schematic diagram showing an enlarged cross-sectional configuration of a region near the surface of the rare earth magnet shown in FIG. As shown in the drawing, the rare earth magnet 1 is formed so as to cover the inorganic particles 6 on the surface of the magnet body 2, the inorganic particles 6 dispersed and attached on the surface of the magnet body 2, and the surface of the magnet body 2. And a protective layer 4.

  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 the lanthanoid element 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. In addition to these elements, La, Ce, Gd, Er, Eu, Tm, More preferably, it further contains at least one element selected from the group consisting of Yb and 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 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 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.

  The inorganic particles 6 are directly attached to the surface of the magnet element body 2, and no other layers are interposed between the inorganic particles 6 and the magnet element body 2. The inorganic particles 6 are mainly composed of a metal element compound. Such inorganic particles 6 may be primary particles composed of a single particle, secondary particles in which a plurality of particles are aggregated, or the like. Further, the inorganic particles 6 do not have to be dispersed individually on the entire surface of the magnet body 2, and may be partially aggregated to form a layer.

  Examples of the metal element compound constituting the inorganic particles 6 include metal element oxides or hydroxides. The metal element is not particularly limited as long as it can form metal oxide or hydroxide particles. Among these, oxides or hydroxides of Fe, Co, Al, or Cu are particularly suitable from the viewpoint of improving the corrosion resistance of the rare earth magnet 1 because they are stable to solutions in the acidic to neutral range. The inorganic particles 6 may contain a single element of the same metal or a combination of a single element or a compound of another metal in addition to the compound of the metal element that mainly constitutes the inorganic particle 6.

  The inorganic particles 6 preferably contain the same metal element as at least one of the metal elements contained in the magnet body 2, and more preferably contain a compound of this metal element. For example, when the magnet body 2 includes Fe, Co, Al, Cu or the like, the inorganic particles 6 preferably include at least one of these metal elements, and may include a combination of a plurality of types.

  In addition, the magnet body 2 does not necessarily have a flat surface shape and may have holes (surface holes) in the depth direction from the surface. In this case, it is preferable that a large amount of the inorganic particles 6 adhere to the surface pore portions of the magnet body 2 in particular. Corrosion of the magnet body 2 usually tends to proceed due to the entry of corrosive components into the interior from the surface holes. On the other hand, as a result of the large amount of inorganic particles 6 adhering to the surface vacancies as described above, the invasion of corrosive components from the surface vacancies is less likely to occur. It will be greatly suppressed.

  As an example, FIG. 4 shows a scanning electron micrograph of the surface of the magnet body 2 with the inorganic particles 6 attached thereto. In FIG. 4, the white granular deposits are the inorganic particles 6, and the depressions formed near the center are the surface vacancies of the magnet body 2. As shown in the figure, the inorganic particles 6 are dispersed and attached to the surface of the magnet body 2, and in particular, many inorganic particles 6 are attached inside the surface pores.

  The protective layer 4 can be applied without particular limitation as long as it is usually formed as a layer protecting the surface of the rare earth magnet. Examples thereof include a resin layer formed by painting or vapor deposition polymerization method, a metal layer formed by plating or vapor phase method, an inorganic layer formed by coating method or vapor phase method, and the like. In particular, the resin layer can satisfactorily cover the surface of the magnet element body 2 to which the inorganic particles 6 are adhered, and even when stress is applied to the interface between the magnet element body 2 and the resin layer, the resin layer can be well relaxed. This is particularly preferable because it can hardly be peeled off from the magnet body 2.

  As the resin layer, both a layer made of a thermosetting resin or a layer made of a thermoplastic resin can be applied. Thermosetting resins include phenolic resin, epoxy resin, urethane resin, silicone resin, melamine resin, epoxy melamine resin, thermosetting acrylic resin, polyimide resin, polyamideimide resin, polyparaxylylene resin, polyurea resin, epoxy A silicone resin, an acrylic silicone resin, etc. are mentioned. Moreover, as a thermoplastic resin, the vinyl resin which uses vinyl compounds, such as acrylic acid, ethylene, styrene, vinyl chloride, vinyl acetate, as a raw material is mentioned.

Examples of the metal layer include Ni, Ni-P, Cu, Zn, Cr, Sn, Al, or a combination of a plurality of layers made of these. The inorganic layer, alkali _silicates, oxides such as _{SiO 2, Al 2 O 3,} TiN, include those made of nitride or the like such as AlN.

  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 the magnet body 2 is manufactured in this way, the obtained magnet body 2 may be subjected to acid cleaning before being treated with first and second treatment liquids 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 deteriorated layer and the oxide layer due to the processing of the surface of the magnet body 2 can be almost completely removed, and a protective layer 4 and the like to be described later can be satisfactorily formed.

  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, the magnet body 2 may be further cleaned, 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.

  Next, the magnet body 2 is immersed in a first treatment liquid containing metal ions. The first treatment liquid is preferably an aqueous solution containing metal ions, and examples thereof include a solution in which a compound of a metal element is dissolved in water and a solution in which a metal is dissolved in an acidic or basic aqueous solution. Metal element compounds include nitrates, sulfates, chlorides and other metal salts, silicates, aluminates, molybdates, vanadates and other oxoacid salts, metal oxides, metal hydroxides, etc. Can be mentioned. The first treatment liquid may contain a plurality of types of metal ions. In this case, the metal ions include both those obtained by dissolving a compound of a metal element and those obtained by dissolving a metal. May be included.

  The first treatment liquid has a pH at which the metal ions contained therein can stably exist, and this pH is set to an acidic region or a basic region depending on the nature of the metal ions. However, since the metal ions are stably present at a pH in the acidic region and often precipitate as a compound such as a hydroxide in the vicinity of neutrality, the first treatment liquid is preferably an aqueous solution having acidity. . Specifically, an aqueous solution having a pH of 0 to 6 is preferable, and an aqueous solution having a pH of 1 to 5 is more preferable.

  This first treatment liquid preferably contains ions of the same metal element as the metal element contained in the magnet body 2. If it carries out like this, the inorganic particle 6 containing the compound of the metal element of the same kind as the magnet element | base_body 2 will precipitate in the process of making the 2nd process liquid mentioned later contact. The first treatment liquid containing ions of the same kind of metal element as the magnet body 2 is preferably obtained by, for example, immersing the magnet body 2 in an acidic aqueous solution and thereby dissolving a part of the magnet body 2. It is done. In this case, as the magnet body 2, one used for manufacturing the rare earth magnet 1 may be used, or one prepared separately for preparing the first treatment liquid may be used.

  The acidic aqueous solution for dissolving the magnet body 2 is preferably an aqueous solution having a pH of 0 to 6, and more preferably an aqueous solution having a pH of 1 to 5. Such an acidic aqueous solution is not particularly limited, and an aqueous solution containing an inorganic acid such as hydrochloric acid, sulfuric acid or nitric acid, or an organic acid such as malic acid, malonic acid, citric acid or succinic acid can be applied.

  Further, in the acid washing step described above, the acid after washing the magnet body 2 also contains metal element ions dissolved from the magnet body 2 and can therefore be used as the first treatment liquid. When the acid after acid cleaning is used as the first treatment liquid in this way, for example, the magnet body 2 is once pulled up after acid cleaning and washed with water, and then immersed in the acid after acid cleaning again. The first treatment liquid containing metal ions can be attached to the surface of the magnet body 2. In addition, after the acid cleaning, if the acid containing metal ions dissolved from the magnet body 2 is sufficiently adhered to the surface of the magnet body 2, the magnet body 2 is not cleaned (washed with water, etc.). The step of contacting the second treatment liquid described later may be performed as it is. In this case, the acid cleaning also serves as a step of immersing in the first treatment liquid.

Preferred concentration of metal ions in the first processing solution depends pH type and second treatment liquid metal ion, preferable to be ^{1 × 10 -7 ~1mol / L,} 1 × 10 - more preferably a ^{7 ~0.1mol} / L. When the concentration of metal ions is less than 1 × 10 ⁻⁷ mol / L, the amount of metal ions attached to the magnet body 2 is insufficient, and the inorganic particles 6 tend not to be sufficiently formed. On the other hand, if it exceeds 1 mol / L, excessive metal ions may adhere to the surface of the magnet body 2, and the metal element derived from the metal ions may form a layer instead of the inorganic particles 6.

  Thereafter, a second treatment liquid having a pH different from that of the first treatment liquid is brought into contact with the surface of the magnet body 2 in a state where the first treatment liquid is attached. Thereby, the inorganic particles 6 containing the compound of the metal element derived from the metal ions in the first treatment liquid adhering to the surface of the magnet body 2 are deposited on the surface of the magnet body 2. Examples of the metal element compound derived from the metal ion include oxides and hydroxides, and hydroxides are particularly preferable. Thus, the second treatment liquid has a pH at which metal ions in the first treatment liquid can be precipitated as a compound.

ただし、^＊Ｋ_Ｓ０＝Ｋ_Ｓ０／Ｋ_ｗ ^ｎ（Ｋ_Ｓ０：水酸化物の溶解度積、Ｋ_ｗ：水のイオン積、ｎ：金属イオンの価数）であり、^＊Ｋ_１は［Ｍ（ＯＨ）^{（ｚ−１）＋}］×［Ｈ^＋］／［Ｍ^ｚ＋］で表されるモノヒドロキソ錯体の生成定数であり、Ｃ_Ｍは金属イオン濃度である。 The suitable pH of the second treatment liquid can be determined from, for example, the solubility product of the hydroxide and the formation constant of the monohydroxo complex when the precipitated compound is a hydroxide. Specifically, it can be calculated according to the following formula (1).

_{^{However, * K S0 = K S0 /}} K w n (K S0: solubility product of the hydroxide, _{K w:} ionic product of water, n: metal valence of ions) ^is, * _{K 1} is [M (OH ) ^{(Z-1) +} ] × [H ⁺ ] / [M ^{z +} ] is a formation constant of a monohydroxo complex, and C _M is a metal ion concentration.

According to the above formula (1), for example, the pH at which metal ions contained in the first treatment liquid at a concentration of 0.1 mol / L precipitate as hydroxide is 3.1 in the case of Al ³⁺ , Co ²⁺ is 7.3, Cu ²⁺ is 4.6, Dy ³⁺ is 5.7, Fe ²⁺ is 7.3, and Nd ³⁺ is 6.4. Ni ²⁺ is 7.2, Zn ²⁺ is 6.0, and Zr ⁴⁺ is 3.1. Therefore, when these metal ions are contained in the first treatment liquid at 0.1 mol / L, the second treatment liquid having a higher pH than the above is used for each metal ion. The metal element hydroxide derived can be deposited.

  As the second treatment liquid, for example, in the neutral region, water such as ion-exchanged water or pure water is suitable. In the case of an acidic or basic region, a material adjusted to a suitable pH by appropriately adding an acid or base to water can be used. When the second treatment solution is a solution having a buffering action in a specific pH region, the inorganic particles 6 can be stably deposited with less pH fluctuation when the acidic or basic region is used as in the latter case. Therefore, it is more preferable.

  As a method of bringing the second treatment liquid into contact with the magnet element body 2 to which the first treatment liquid has adhered, a dipping method in which the magnet element body 2 is immersed in the second treatment liquid or a treatment to the magnet element body 2 is performed. The spray method which sprays a liquid is mentioned. 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. Further, when the second treatment liquid is water, the inorganic particles 6 can also be precipitated by washing the magnet element body 2 to which the first treatment liquid is attached with running water.

  As described above, the inorganic particles 6 are deposited on the surface of the magnet body 2 in a dispersed state by sequentially performing the treatment with the first treatment liquid and the second treatment liquid on the magnet body 2. . The mechanism by which the inorganic particles 6 are not formed by this method but the metal compound layer derived from the metal ions in the first treatment liquid is not necessarily clear, but is estimated as follows.

  That is, in the state pulled up from the first treatment liquid, the first treatment liquid is attached to the magnet body 2, and metal ions are present in a dispersed state in the attached first treatment liquid. Yes. Next, for example, when the magnet body 2 is immersed in the second processing liquid, the metal ions are dispersed and exist in the second processing liquid in the vicinity of the magnet body 2. Since the metal ions dispersed in this way generate a compound in situ, a particulate compound is thereby formed. And the particle | grains produced | generated in this way adhere to the magnet surface 2, and the magnet base body 2 which the inorganic particle 6 disperse | distributed and adhered is obtained.

  In the formation process of such inorganic particles 6, for example, when the magnet body 2 has holes in the depth direction (surface holes) on the surface thereof, the magnet body 2 from the first treatment liquid is used. When pulling up, a large amount of metal ions tend to remain in the surface hole portion. Therefore, after the contact with the second treatment liquid, more inorganic particles 6 are deposited in the surface pore portion than in the flat surface portion. As described above, the surface vacancies of the magnet body 2 are likely to be a starting point for corrosion of the body 2. Therefore, according to the manufacturing method of the present embodiment, a large number of inorganic particles 6 can be formed in such surface pore portions, and the rare earth magnet 1 having particularly excellent corrosion resistance can be obtained.

  Thereafter, the magnet body 2 having the inorganic particles 6 attached to the surface is appropriately washed and dried, and then the protective layer 4 is formed on the surface of the magnet body 2 so as to cover the inorganic particles 6. . In this way, the rare earth magnet 1 having the structure shown in FIGS.

  For example, in the case of a resin layer, the protective layer 4 is prepared by dissolving the above-described resin in a solvent to prepare a coating solution, which is applied to the surface of the magnet body 2 by dip coating, dip spin coating, spray coating, or the like. After application, it can be formed by baking or drying. The resin layer can also be formed by a so-called polymerization vapor deposition method in which a monomer for forming the resin layer is vaporized and vapor deposited on the surface of the magnet body and polymerized at the same time.

  The metal layer can be formed by subjecting the magnet body 2 to electroplating, electroless plating, or the like. In addition, gas phase methods such as ion plating, sputtering, and vapor deposition can also be applied. In addition, the inorganic layer can be formed by applying an alkali silicate solution such as water glass or a metal alkoxide solution to the surface of the magnet body 2 and then baking or drying, as well as an ion plating method, It can also be formed by using a vapor phase method such as a CVD method.

  The rare earth magnet 1 of the above-described embodiment has a configuration in which the protective layer 4 is formed on the surface of the magnet body 2 via the inorganic particles 6 dispersed and attached to the surface of the magnet body 2. The rare earth magnet 1 having such a configuration has better adhesion between the magnet body 2 and the protective layer 4 as compared with the magnet body 2 provided with the protective layer 4 directly. Further, since the rare earth magnet 1 has a large number of inorganic particles 6 that are stable against corrosive components such as water on the surface of the magnet body 2, the corrosive components have passed through the protective layer 4. Even in this case, the corrosion of the magnet body 2 is difficult to proceed.

  Further, in the rare earth magnet 1, since the inorganic particles 6 are dispersed and attached on the surface of the magnet body 2, even when stress is generated between the magnet body 2 and the protective layer 4. The stress can be sufficiently relaxed in the inorganic particle 6 portion. Therefore, when a base treatment layer such as a chemical conversion treatment layer or a metal compound layer is conventionally formed between the magnet body and the protective layer, these may be caused by a difference in thermal expansion coefficient between the base treatment layer and the protective layer. In the meantime, stress is generated, and the protective layer is easily peeled off, and the rare earth magnet 1 of the present embodiment hardly peels off the protective layer 4.

  Furthermore, according to the manufacturing method of the above-described embodiment, the inorganic particles can be easily obtained in a two-stage process of manufacturing the magnet body 2, dipping in the first processing liquid, and contacting the second processing liquid. Since 6 can be deposited, the rare earth magnet 1 can be easily manufactured. In particular, when an acid solution is used as the first treatment liquid and water is used as the second treatment liquid, normal water washing may be performed after the magnet body 2 is immersed in the first treatment liquid. Inorganic particles 6 can be formed very easily.

  Furthermore, in the manufacturing method according to the present embodiment, the components of these treatment liquids hardly change in a series of treatments using the first and second treatment liquids, and therefore the first and second treatment liquids are repeated. It is possible to use. Therefore, the manufacturing method of the present embodiment can be a suitable method for mass production of the rare earth magnet 1.

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

Example 1
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 prepared 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 magnet body was dipped in the first treatment liquid and then pulled up. The first treatment liquid is obtained by dissolving a similar magnet body in 0.4 mol / L nitric acid. As a result of analysis by the ICP analysis method, the first treatment liquid contained 44 ppm of B, 27 ppm of Al, 4400 ppm of Fe, 25 ppm of Co, 4.9 ppm of Cu, 1500 ppm of Nd, and 240 ppm of Dy.

  Next, the magnet body with the first treatment liquid attached thereto was immersed in ion-exchanged water having a pH of 7 as the second treatment liquid. Thereby, the particles of the metal compound derived from the metal ions contained in the first treatment liquid were dispersed and deposited on the surface of the magnet body. Then, the magnet body was washed with water and then dried.

  As a result of analyzing the surface of the dried magnet body with a laser ablation-ICP mass spectrometer (LA-ICP-MS), a high concentration of a compound containing Al, Cu, Co is present near the surface of the magnet body. It was confirmed that it was precipitated. Further, when the surface of the magnet body was observed with a scanning electron microscope, it was confirmed that fine particles were dispersed and formed.

  Thereafter, an epoxy resin paint is applied to the surface of the magnet body by spray coating, and then cured by heating at 180 ° C. for 30 minutes to form a resin made of an epoxy resin having a thickness of 10 μm on the surface of the magnet body. Layers were formed. Thereby, the rare earth magnet of Example 1 was completed.

(Example 2)
First, a magnet body was formed in the same manner as in Example 1. The obtained magnet body was subjected to acid cleaning by immersing it in a 2% HNO ₃ aqueous solution for 2 minutes, and then subjected to ultrasonic cleaning. Next, the magnet body was dipped in a first treatment liquid obtained by dissolving iron (III) nitrate in ion-exchanged water so as to be 0.01 mol / L, and then pulled up.

  Then, the magnet body with the first treatment liquid adhered thereto was immersed in ion exchange water having a pH of 7 as the second treatment liquid. Thereby, the particles of the iron compound derived from iron contained in the first treatment liquid were dispersed and deposited on the surface of the magnet body. Then, the magnet body was washed with water and then dried.

  As a result of analyzing the surface of the magnet body after drying by LA-ICP-MS, it was confirmed that the Fe compound was deposited at a high concentration in the vicinity of the surface of the magnet body. Further, when the surface of the magnet body was observed with a scanning electron microscope, it was confirmed that fine particles were dispersed and formed.

  And the resin layer was formed on the surface of this magnet element body similarly to Example 1, and the rare earth magnet of Example 2 was completed.

(Comparative Example 1)
First, a magnet body was obtained in the same manner as in Example 1. The obtained magnet body was subjected to acid cleaning by immersing it in a 2% HNO ₃ aqueous solution for 2 minutes, and then subjected to ultrasonic cleaning. Then, a resin layer was formed on the surface of the magnet body in the same manner as in Example 1. Thereby, the rare earth magnet of Comparative Example 1 was completed.

(Comparative Example 2)
First, a magnet body was formed in the same manner as in Example 1. The obtained magnet body was subjected to acid cleaning by immersing it in a 2% HNO ₃ aqueous solution for 2 minutes, and then subjected to ultrasonic cleaning. Then, the magnet body was immersed in a phosphoric acid aqueous solution having a phosphoric acid concentration of 0.07 mol / L, and a chemical conversion treatment was performed on the surface of the magnet body to form a chemical conversion treatment layer on the surface. The conditions for the chemical conversion treatment were 60 ° C., pH 3 (prepared with NaOH), and 5 minutes.

Then, a resin layer was formed on the surface of the magnet body in the same manner as in Example 1. Thereby, the rare earth magnet of Comparative Example 2 was completed.
[Characteristic evaluation]

(PCT test)
A pressure cooker test (PCT test) was performed on the rare earth magnets of Examples 1 and 2 and Comparative Examples 1 and 2 under the conditions of 120 ° C., 0.2 MPa, 100% RH, and 100 hours. While observing (presence or absence of peeling of the protective layer), the amount of decrease in weight after the test relative to before the test was measured. In addition, for each rare earth magnet after the PCT test, in accordance with a grid surface tape test specified in JIS K5600 (1999), cuts penetrating the layer are formed in a grid pattern on the protective layer, and an adhesive tape is applied thereon. The test which evaluates the presence or absence of peeling of a protective layer when peeling after extending | stretching was done. The results obtained are summarized in Table 1.

In Table 1, the evaluation of peeling of the protective layer was described according to A: no peeling, B: partial peeling only at the corners, and C: peeling at the corners and portions other than the corners. Moreover, evaluation of the tape test was performed according to the classification based on JISK5600. In the evaluation, a six-stage evaluation is performed from classification 0 in which no peeling was observed to classification 5 in which most of the peeling occurred, and the smaller the number, the smaller the peeling.

  From Table 1, the rare earth magnets of Examples 1 and 2 had no peeling of the protective layer after the PCT test, and no peeling of the protective layer was observed in the cross cut tape test. It was confirmed that the adhesion was good. In addition, since the rare earth magnets of Examples 1 and 2 did not show a decrease in weight after the PCT test, it was found that deterioration under high temperature and high humidity conditions was small and had excellent corrosion resistance.

(Salt spray test)
The rare earth magnets of Example 1 and Comparative Example 1 were each subjected to a salt spray test. That is, after a cross cut was put in the resin layer of the rare earth magnet, a salt spray test was performed under conditions of 96 hours at 35 ° C. using 5% salt water in accordance with JIS K5600-7-1. As a result, in the rare earth magnet of Example 1, rust was generated only in the crosscut portion, whereas in the rare earth magnet of Comparative Example 1, corrosion progressed from the crosscut portion to the inside, and the swelling of the resin layer was confirmed. It was done. From this, it was found that the rare earth magnet of Example 1 was extremely excellent in adhesion between the protective layer and the magnet element body as compared with that of Comparative Example 1.

It is a figure which shows the rare earth magnet 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 surface vicinity area | region of the rare earth magnet shown in FIG. It is a figure which shows the scanning electron micrograph of the surface of the magnet element | base_body 2 of the state to which the inorganic particle 6 adhered.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rare earth magnet, 2 ... Magnet base body, 4 ... Protective layer, 6 ... Inorganic particle.

Claims (7)

A magnet body containing a metal element including at least a rare earth element;
Inorganic particles dispersed and attached to the surface of the magnet body;
A protective layer formed on the surface of the magnet body so as to cover the inorganic particles;
A rare earth magnet comprising:   The rare earth magnet according to claim 1, wherein the inorganic particles contain a compound of the same metal element as at least one of the metal elements contained in the magnet body.   The rare earth magnet according to claim 1 or 2, wherein the inorganic particles contain at least one metal element selected from the group consisting of Fe, Co, Al, and Cu.   The rare earth magnet according to claim 1, wherein the protective layer is a resin layer. Immersing a magnet body containing a metal element including at least a rare earth element in a first treatment liquid containing metal ions;
A second treatment liquid having a pH different from that of the first treatment liquid is brought into contact with the surface of the magnet body with the first treatment liquid attached, and the first treatment is performed on the surface. A step of precipitating inorganic particles containing a compound of a metal element derived from the metal ions contained in the liquid;
Forming a protective layer on the surface of the magnet body so as to cover the inorganic particles;
A method for producing a rare earth magnet, comprising:   6. The rare earth magnet according to claim 5, wherein the metal ions contained in the first treatment liquid are ions of the same metal element as at least one of the metal elements contained in the magnet body. Method. The method for producing a rare earth magnet according to claim 5, wherein the protective layer is a resin layer.

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