JP2011091313A - Rare earth magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare earth magnet superior in corrosion resistance while superior in adhesion between a magnet element assembly and a coating layer. <P>SOLUTION: A rare earth magnet includes: a magnet element assembly 10 containing a rare earth element; and a coating layer 20 having a first layer 22 and a second layer 24 that are formed on the magnet element assembly from the magnet element assembly 10 side in this order. In the rare earth magnet 100, the first layer 22 contains at least one metal selected from a group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn or an alloy containing the metal, and the second layer 24 contains a compound having silicon, nitrogen and hydrogen as a constituent element. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rare earth magnet having a coating layer.

  Rare earth magnets such as R-Fe-B magnets containing rare earth elements have high magnetic properties and are used in various fields as permanent magnets. Such rare earth magnets usually contain rare earth elements that are relatively easily corroded. For this reason, in order to suppress the deterioration of the magnetic characteristics as a permanent magnet, it has been proposed to provide coating layers of various materials on the magnet body.

  For example, in Patent Document 1 below, an attempt is made to improve the corrosion resistance and hydrogen resistance of a rare earth magnet by providing a hydrogen-containing amorphous carbon film on a base film containing various metals.

Japanese Patent Laid-Open No. 2007-158030

  However, since the hydrogen-containing amorphous carbon film of the rare earth magnet as described in Patent Document 1 has bonds between elements having 4 valence electrons, a strong bond is formed between the elements. Since the degree of freedom of bonding is low, large internal stress (residual stress) is likely to occur, and structural defects tend to occur. For this reason, when used in a corrosive environment, a corrosive substance enters from a structural defect and the magnet body is corroded, making it difficult to maintain the original magnetic properties of the rare earth magnet.

  Another example of the coating layer provided on the surface of the magnet body is a silicon nitride film. However, when the coating layer is a film containing a compound having a metalloid element such as silicon nitride, the adhesion between the magnet body containing the rare earth element and the coating layer is not sufficient, and the coating layer is not formed from the magnet body. It was found that they could be peeled off and could cause corrosion of the magnet body and deterioration of magnetic properties.

  This invention is made | formed in view of the said situation, and it aims at providing the rare earth magnet which is excellent in the corrosion resistance while being excellent in the adhesiveness of a magnet element | base_body and a coating layer.

  In order to achieve the above object, the present inventors have studied various materials and structures of the coating layer. And as a coating layer, by providing a layer containing a specific compound and a layer containing a specific component between the layer and the magnet element body, adhesion between the coating layer and the magnet element body It was found that a rare earth magnet having excellent corrosion resistance and excellent corrosion resistance can be obtained. That is, the present invention is a rare earth magnet comprising a magnet body containing a rare earth element, and a coating layer having a first layer and a second layer on the magnet body side from the magnet body, wherein the first layer comprises: Containing at least one metal selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, or an alloy containing the metal, and the second layer is silicon as a constituent element; A rare earth magnet containing a compound having nitrogen and hydrogen is provided.

  The rare earth magnet of the present invention has excellent adhesion between the coating layer and the magnet body, and also has excellent corrosion resistance. The inventors of the present invention consider the factors that can achieve such an effect as follows. That is, the second layer in the rare earth magnet coating layer of the present invention includes a compound having silicon, nitrogen, and hydrogen as constituent elements, each having 4, 3, and 1 valence electrons. Such a coating layer is more likely to have a dense structure than the coating layer containing a compound having oxygen, boron, carbon, phosphorus, or the like instead of hydrogen as a constituent element, and a dense structure. it is conceivable that. This is thought to be because the number of lattices with unstable bond angles is reduced because the bonds between constituent elements with a large number of valence electrons become dense while the bond ends can be made hydrogen. . Therefore, the rare earth magnet of the present invention has excellent corrosion resistance even in a corrosive environment.

  In the rare earth magnet of the present invention, the first layer disposed on the side of the magnet body with respect to the second layer mainly contributes to improving the adhesion between the magnet body and the coating layer. That is, the magnet body contains a rare earth element having a large atomic weight, whereas the second layer contains an element having a small atomic weight such as silicon, nitrogen, and hydrogen. For this reason, when a 2nd layer is laminated | stacked directly on the surface of a magnet element body, it exists in the tendency for favorable adhesiveness not to be acquired. However, in the present invention, the first metal containing the predetermined metal or alloy excellent in compatibility with both the component contained in the magnet body and the component contained in the second layer is provided between the magnet body and the second layer. A layer is provided. That is, since the first layer contains a metal element, the adhesion with the magnet body is good, and since the first layer contains a metal element having an atomic radius smaller than that of the rare earth element, the first layer is in close contact with the second layer. The property is also good. Such an action is considered to improve the adhesion between the magnet body and the coating layer. However, the reason why the effect of the present invention is obtained is not limited to the above-described factors.

  In the rare earth magnet of the present invention, the hydrogen content in the second layer is preferably 0.1 to 50 atomic%. As a result, the airtightness of the second layer can be made sufficiently high, and the corrosion resistance of the rare earth magnet can be further improved.

  The first layer in the rare earth magnet of the present invention preferably contains a hydride of the metal or the alloy on the contact surface side with the second layer. By containing such a hydride, the adhesion between the first layer and the second layer can be further improved. Therefore, the excellent corrosion resistance of the rare earth magnet can be further improved.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in the adhesiveness of a magnet body and a coating layer, the rare earth magnet excellent in corrosion resistance can be provided.

It is a perspective view which shows typically suitable embodiment of the rare earth magnet of this invention. It is a schematic cross section at the time of cut | disconnecting the rare earth magnet shown in FIG. 1 along the II-II line. It is sectional drawing which shows typically another Embodiment of the rare earth magnet of this invention.

  In the following, preferred embodiments of the present invention will be described with reference to the drawings as the case may be. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a perspective view schematically showing the rare earth magnet of the present embodiment. FIG. 2 is a schematic cross-sectional view when the rare earth magnet 100 shown in FIG. 1 is cut along the line II-II. The rare earth magnet 100 includes a magnet body 10 and a coating layer 20 that covers the surface of the magnet body 10. The covering layer 20 has a stacked structure in which the first layer 22 and the second layer 24 are sequentially stacked from the magnet body 10 side.

  The magnet body 10 includes one or more elements selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoids belonging to Group 3 of the long-period periodic table as rare earth elements. Here, the lanthanoid is 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) and lutetium (Lu).

  The magnet body 10 is, as the rare earth element, at least one element selected from Nd, Pr, Ho and Tb, or La, Sm, Ce, Gd, Er, Eu, Tm, Yb and Y among the elements described above. It is preferable to contain at least one element selected from

The magnet body 10 may be a sintered magnet or a bonded magnet. Examples of the magnetic particles contained in the magnet body include Sm—Co based magnetic particles, Nd—Fe—B based magnetic particles, and Sm—Fe—N based magnetic particles. Among these, as the magnetic particles, Sm—Co based magnetic particles represented by SmCo ₅ and Sm ₂ Co ₁₇ or Nd—Fe—B based magnetic particles represented by Nd ₂ Fe ₁₄ B are used. preferable.

  When the magnet body 10 is an Nd—Fe—B sintered magnet, the content ratio of the rare earth element in the magnet body 10 is preferably 8 to 40% by mass, more preferably 15 to 35% by mass. It is. If the content ratio of the rare earth element is less than 8% by mass, the rare earth magnet 100 having a high coercive force (iHc) tends to be hardly obtained. On the other hand, when the content of the rare earth element exceeds 40% by mass, the R-rich nonmagnetic phase increases, and the residual magnetic flux density (Br) of the rare earth magnet 100 tends to decrease.

  The content ratio of Fe in the magnet body 10 is preferably 42 to 90 mass%, more preferably 60 to 80 mass%. If the Fe content is less than 42% by mass, Br of the rare earth magnet 100 tends to decrease, and if it exceeds 90% by mass, the iHc of the rare earth magnet 100 tends to decrease.

  The content ratio of B in the magnet body 10 is preferably 0.5 to 5% by mass. If the B content is less than 0.5% by mass, the iHc of the rare earth magnet 100 tends to decrease, and if it exceeds 5% by mass, the B-rich nonmagnetic phase increases. It tends to decrease.

  A part of Fe may be substituted with cobalt (Co). As a result, the temperature characteristics can be improved without impairing the magnetic characteristics of the rare earth magnet 100. A part of B may be substituted with one or more elements selected from the group consisting of carbon (C), phosphorus (P), sulfur (S), and copper (Cu). As a result, the productivity of the rare earth magnet 100 can be improved and the production cost can be reduced.

  From the viewpoint of improving the coercive force of the rare earth magnet 100, improving productivity, and reducing the cost, the magnet body 10 is made of aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese (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), and / or hafnium (Hf), and the like.

  The magnet body 10 may contain oxygen (O), nitrogen (N), carbon (C), and / or calcium (Ca) as inevitable impurities.

  The covering layer 20 includes a first layer 22 and a second layer 24 in order from the magnet body 10 side. The first layer 22 contains as a main component at least one metal selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, or an alloy containing the metal. The total content of metals and alloys in the first layer 22 is preferably 90% by mass or more, more preferably 95% by mass or more. The metal elements other than Al described above are metal elements belonging to the D block of the fourth period of the long-period periodic table. Since such a metal element has an atomic radius smaller than that of the rare earth element contained in the magnet body 10, it is between the first layer 22 and the second layer 24 and between the magnet body 10 and the first layer 22. Both adhesiveness can be made high.

  The first layer 22 preferably includes at least one metal selected from the group consisting of Al, Ni, Cu, and Zn or an alloy containing the metal. Since the metal element contained in such a metal or alloy is similar in atomic radius to Si contained in the second layer 24, the adhesion between the first layer 22 and the second layer 24 can be further improved. Can do.

  The first layer 22 may include a hydride of the metal or alloy described above. Such a hydride may be present dispersed in the metal or alloy contained in the first layer 22, or may be formed as a film on the surface portion of the first layer. When the first layer 22 has such a coating on the contact surface with the second layer 24, the compound of the second layer 24 is formed when the second layer 24 is formed (film formation) on the first layer 22. From the initial stage of formation, the distortion of the compound is reduced, and the second layer 24 that is more airtight can be formed.

  When the hydride of the metal or alloy described above is included, the hydrogen content in the contact surface of the first layer 22 with the second layer 24 is preferably 0.1 to 10 atomic%, more preferably 0.3 to 3 Atomic%. When the content of hydrogen at the contact surface is less than 0.1 atomic%, the above-described strain reduction effect tends to be hardly obtained. When the content exceeds 10 atomic%, the hydrogenation process is prolonged. Manufacturing efficiency tends to decrease.

  Specifically, the first layer 22 is preferably a metal plating layer. Various plating layers can be used as the metal plating layer. Examples thereof include an electrolytic Ni plating layer, an electroless Ni plating layer, and an electrolytic Cu plating layer.

  The second layer 24 contains, as a main component, a compound having silicon, nitrogen, and hydrogen as constituent elements. Specific examples of the compound include silicon nitride containing hydrogen as a constituent element. The second layer 24 contains such a compound in a content of preferably 90% by mass or more, more preferably 95% by mass or more.

  The hydrogen content in the second layer 24 is preferably 0.1 to 50 atomic%, more preferably 1 to 45 atomic%, and further preferably 3 to 40, based on the total number of atoms contained in the second layer 24. Atomic%. When the hydrogen content in the second layer 24 exceeds 50 atomic%, or when the hydrogen content in the second layer 24 is less than 0.1 atomic%, the excellent hermeticity of the second layer 24 decreases. Thus, sufficiently good corrosion resistance tends to be impaired. When the hydrogen content in the second layer 24 is 45 atomic% or less, the second layer 24 can be easily formed, and the second layer 24 can be formed with high production efficiency. Further, when the hydrogen content in the second layer 24 is 1 atomic% or more, the second layer 24 becomes a denser layer, and the corrosion resistance of the rare earth magnet 100 can be further improved.

  The silicon content in the second layer 24 is preferably 10 to 80 atomic%, more preferably, based on the total number of atoms contained in the second layer 24 from the viewpoint of making the coating layer more airtight. Is 20-70 atomic%.

  The nitrogen content in the second layer 24 is preferably 10 to 70 atomic%, more preferably, based on the total number of atoms contained in the second layer 24 from the viewpoint of making the coating layer more excellent in airtightness. Is 20 to 60 atomic%.

  The second layer 24 preferably has a low carbon content. This is because if the graphite structure or the like is formed by containing carbon, cracks are likely to occur, and the sufficiently high density of the second layer 24 may be impaired. From such a viewpoint, the carbon content in the second layer 24 is preferably 5 atomic percent or less, more preferably 1 atomic percent or less.

  The interface between the first layer 22 and the second layer 24 can be specified using a commercially available analyzer. For example, the content of the constituent element is measured by glow discharge emission spectroscopic analysis capable of analyzing the composition while cutting the coating layer 20 in the thickness direction (stacking direction), and the content of the constituent element is determined along the thickness direction. Locations that change discontinuously can be identified as layer interfaces.

  Note that the content of each constituent element in the second layer 24 may not be uniform. For example, the content rate of each constituent element may change continuously along the thickness direction (stacking direction) of the second layer 24. Among such structures, it is preferable that the hydrogen content in the second layer 24 decreases as it approaches the magnet body 10. By setting it as such a layer, the airtightness of the coating layer 20 can be improved further.

  The thickness of the first layer 22 is preferably 0.1 μm or more, and more preferably 0.3 μm or more. Usually, since the arithmetic mean roughness Ra of the surface of the magnet body 10 is 0.7 to 3 μm, when the thickness is less than 0.1 μm, particularly in the convex portion of the magnet body 10, the effect of improving the adhesion. Tends to be insufficient. When the thickness of the first layer 22 is 0.3 μm or more, the adhesion between the coating layer 20 and the magnet body 10 can be sufficiently increased.

  The thickness of the first layer 22 is preferably 50 μm or less, more preferably 30 μm or less. When the thickness exceeds 50 μm, the volume ratio of the magnet body in the rare earth magnet of a predetermined size is lowered, and it is difficult to obtain sufficiently excellent magnetic characteristics. When the thickness is 30 μm or less, the rare earth magnet 100 having sufficiently excellent adhesion can be produced at a low production cost.

  The thickness of the second layer 24 is preferably 0.1 μm or more, more preferably 1 μm or more. When the thickness is less than 0.1 μm, sufficiently excellent corrosion resistance and moisture resistance tend to be impaired. When the thickness is 1 μm or more, corrosion resistance and moisture resistance can be further improved.

  The thickness of the second layer 24 is preferably 10 μm or less, and more preferably 5 μm or less. If the thickness exceeds 10 μm, the manufacturing cost of the rare earth magnet 100 tends to increase. When the thickness of the second layer 24 is 5 μm or less, the rare earth magnet 100 having sufficiently excellent corrosion resistance and moisture resistance can be manufactured at a low manufacturing cost.

  The thickness of the entire coating layer 20 is preferably 0.2 μm or more, and more preferably 1.3 μm or more. When the thickness is less than 0.2 μm, sufficiently excellent corrosion resistance and moisture resistance tend to be impaired. When the thickness is 1.3 μm or more, corrosion resistance and moisture resistance can be further improved.

  The thickness of the entire coating layer 20 is preferably 50 μm or less, and more preferably 30 μm or less. If the thickness exceeds 50 μm, the thickness of the coating layer 20 becomes too large, the volume ratio of the magnet body in the rare earth magnet of a predetermined size is lowered, and it is difficult to obtain sufficiently excellent magnetic properties. is there. When the thickness of the entire coating layer 20 is 30 μm or less, the rare earth magnet 100 having sufficiently excellent magnetic properties, excellent corrosion resistance, and moisture resistance can be manufactured at a low manufacturing cost.

  Next, an example of a method for manufacturing the rare earth magnet 100 of the present embodiment will be described. The manufacturing method of the rare earth magnet 100 described here includes a first step of manufacturing the magnet body 10, a second step of forming the first layer 22 on the surface of the magnet body 10, and the surface of the first layer 22. And a third step of forming the second layer 24 thereon. Details of each step will be described below.

  In the first step, when the magnet body 10 is a sintered magnet mainly composed of R-Fe-B based magnetic particles, the magnet body 10 is manufactured by a sintering method described below. First, a composition containing rare earth elements (R), iron (Fe), boron (B), and other elements described above in a predetermined ratio is cast to obtain an ingot. The obtained ingot is roughly pulverized to a particle size of about 10 to 100 μm using a stamp mill or the like, and then finely pulverized to a particle size of about 0.5 to 5 μm using a ball mill or the like to obtain a magnetic powder.

Next, the obtained magnetic powder is preferably molded in a magnetic field to prepare a molded body. In this case, the applied magnetic field strength is preferably 10 kOe or more, and the molding pressure is preferably about 1 to 5 ton / cm ² .

  The prepared molded body is sintered at 1000 to 1200 ° C. for about 0.5 to 5 hours and rapidly cooled. The sintering atmosphere is preferably an inert gas atmosphere such as Ar gas. And preferably, the magnet body 10 is obtained by performing heat treatment (aging treatment) at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere.

  When the magnet body 10 is a bonded magnet, the magnet body 10 can be manufactured by the method described below. First, a magnetic powder is obtained in the same manner as in the production of a sintered magnet. After mixing the obtained magnetic powder, a binder resin, a curing agent, and the like, the mixture is put into a kneader such as a pressure kneader and kneaded to obtain a kneaded product. The mixing ratio of the magnetic powder and the binder resin is preferably 95 to 98 parts by mass of the magnetic powder with respect to 100 parts by mass of the total of the magnetic powder and the binder resin.

  Next, the kneaded product is compression-molded by a compression molding machine or the like. At this time, magnetization may be performed simultaneously by performing compression molding in a magnetic field. Magnetization may be performed separately after compression molding. From the viewpoint of obtaining the magnet body 10 having excellent magnetic properties, it is preferable to perform compression molding at a high pressure of about 784 to 980 MPa.

  As the binder resin, a thermosetting resin or a thermoplastic resin capable of binding magnetic powders can be used. Examples of such binder resins include thermosetting resins such as epoxy resins and phenol resins, styrene-based, olefin-based, urethane-based, polyester-based, polyamide-based elastomers, ionomers, ethylene-propylene copolymers (EPM), and ethylene. -Thermoplastic resins such as ethyl acrylate copolymer. Especially, a thermosetting resin is preferable and an epoxy resin or a phenol resin is more preferable.

  When a thermosetting resin is used as the binder resin, the magnet body 10 can be obtained by curing the binder resin by heating the obtained molded body at about 100 to 250 ° C. after compression molding. . When a thermoplastic resin is used as the binder resin, such thermosetting may not be performed.

  In the second step, at least selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn on the surface of the magnet body 10 obtained as described above. The first layer 22 containing a kind of metal or an alloy containing the metal is formed. When the first layer 22 is a metal plating layer, the first layer 22 can be formed by normal electrolytic plating or electroless plating. Specifically, each plating layer can be formed by electrolytic Ni plating, electroless Ni plating, or electrolytic Cu plating. Moreover, the formation method of the 1st layer 22 is not limited to the above-mentioned manufacturing method, For example, sputtering and vapor deposition may be sufficient.

For example, the electrolytic Ni plating layer can be formed using a plating bath such as a watt bath or a sulfamic acid bath. A preferred plating bath composition is as follows.
_{NiSO 4 · 6H 2 O: 200~500g} / l
NiCl _2: 10~100g / l
H ₃ BO ₄ : 10 to 100 g / l

The electrolytic copper plating layer can be formed by preparing an electrolytic copper plating solution and immersing the magnet body in the electrolytic copper plating solution using a barrel tank or a hooking jig. As the electrolytic copper plating solution, one having a copper sulfate concentration of 20 to 150 g / L and a chelating agent concentration of 30 to 250 g / L such as ethylenediaminetetraacetic acid (EDTA) can be used. The current density in electrolytic copper plating can be 0.1-1.5 A / dm < ² >, and the temperature of an electrolytic copper plating bath can be 10-70 degreeC.

  The electroless Ni plating layer contains a predetermined amount of nickel ions and, for example, a nickel chemical plating solution containing a reducing agent such as sodium hypophosphite, a complexing agent such as sodium citrate, and ammonium sulfate (temperature: It can be formed by immersing the magnet body 10 in about 80 ° C.).

  The first layer 22 may be composed of one type of plating layer, or may be a combination of two or more types of plating layers. In addition, a layer other than the plating layer described above may be formed by a known method to form the first layer 22.

  In the third step, the second layer 24 containing as a main component a compound having silicon, nitrogen and hydrogen as constituent elements is formed. As a method for forming the second layer 24, a vacuum deposition method, a sputtering method, an ion plating method, a vapor phase growth method such as a CVD method or a thermal spraying method, a liquid phase growth method such as a coating method or a solution deposition method, or a sol-gel method. A known film forming technique such as, for example, can be used. Among these, the CVD method is advantageous in that layers having different compositions can be formed continuously, and even if the surface of the magnet body 10 has some irregularities, the coating layer 20 can be reliably formed on the surface. preferable. Examples of the CVD method include a plasma CVD method, a thermal CVD method, and a Cat-CVD method.

In the CVD method, for example, SiH ₄ gas, N ₂ gas, NH ₃ gas, H ₂ gas or the like is used as a raw material gas, and these are reacted under predetermined conditions to form a constituent element on the surface of the magnet body 10. A second layer 24 made of an amorphous material containing silicon, nitrogen and hydrogen is formed. At this time, the supply ratio of SiH ₄ gas, N ₂ gas, NH ₃ gas, and H ₂ gas is adjusted, and the hydrogen content in the second layer 24 is preferably 0.1 to 50 atomic%, more preferably 1 ˜45 atomic%, more preferably 3 to 40 atomic%. In order to easily form the second layer having such a composition, it is preferable to use a mixed gas of SiH ₄ gas, H ₂ gas, and NH ₃ gas as the source gas. When such a mixed gas is used, the volume ratio of NH ₃ gas to the entire raw material gas is preferably 0 to 90% by volume, more preferably from the viewpoint of efficiently forming the second layer 24 having a predetermined hydrogen content. Is 5 to 85% by volume, more preferably 10 to 80% by volume. On the other hand, the volume ratio of H ₂ gas to the entire source gas is preferably 0 to 30 volume, more preferably 0 to 20 volume%, and the volume ratio of SiH ₄ gas to the entire source gas is preferably 1 to 30 volume. %, More preferably 2 to 12% by volume. By using such a source gas, the first layer 22 having a desired hydrogen content can be easily formed.

  In the CVD method, Ar gas or He gas may be used as the carrier gas in addition to the above-described source gas. Note that the flow rate of the carrier gas is not used for calculating the volume ratio of each raw material gas in the mixed gas. That is, regardless of whether or not the carrier gas is used, the preferable range of the volume ratio of each source gas is the above-described range.

  Through the above steps, the rare earth magnet 100 having the covering layer 20 composed of the first layer 22 and the second layer 24 can be manufactured on the magnet body 10. Such a rare earth magnet 100 includes a coating layer 20 having a dense second layer 24 having hydrogen in addition to silicon and nitrogen as constituent elements, and a first layer 22 that is in close contact with the second layer 24. Since this coating layer 20 is excellent in adhesiveness with the magnet body 10, even if it is used in a corrosive environment, the corrosion of the magnet body 10 due to a corrosive substance can be sufficiently suppressed. That is, the rare earth magnet 100 can maintain sufficiently excellent corrosion resistance over a long period of time. The rare earth magnet 100 of this embodiment having such characteristics is suitably used for a rotating element of an electric device that is required to have excellent corrosion resistance, for example.

  Next, another embodiment of the rare earth magnet of the present invention will be described.

  FIG. 3 is a cross-sectional view schematically showing still another embodiment of the rare earth magnet of the present invention. The rare earth magnet 300 includes a magnet body 10 and a coating layer 30 on the magnet body 10. The covering layer 30 has a stacked structure in which a first layer 32, an intermediate layer 34, and a second layer 36 are sequentially stacked from the magnet body 10 side. The first layer 32 and the second layer 36 are the same layers as the first layer 22 and the second layer 24 of the above embodiment. That is, the rare earth magnet 300 is different from the rare earth magnet 100 of the above embodiment in that the intermediate layer 34 is provided between the first layer 32 and the second layer 36.

  The intermediate layer 34 includes at least one metal hydride selected from the group consisting of metals Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn contained in the first layer 32 or the metal. As a main component, a hydride of an alloy containing is contained. Since the intermediate layer 34 contains the hydride of the metal or alloy contained in the first layer 32, the strain generated in the compound contained in the second layer 36 is sufficiently reduced when the second layer 36 is formed. can do.

  Further, since the intermediate layer 34 contains the same metal component as that of the first layer 32, the intermediate layer 34 can be firmly adhered to the first layer 32. Furthermore, since the intermediate layer 34 contains hydrogen, it can be firmly adhered to the second layer 36. Thus, since the coating layer 30 has sufficiently excellent adhesion between layers, the rare earth magnet 300 has sufficiently excellent corrosion resistance, and maintains excellent magnetic properties over a long period of time. be able to.

  The intermediate layer 34 can be formed by performing a hydrogenation treatment in which the first layer 32 is formed and then heated in a hydrogen atmosphere at a temperature of 50 to 300 ° C. for 0.1 to 1 hour.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments. The hydride may be included in the vicinity of the contact surface between the first layer 22 and the second layer 24 of the rare earth magnet 100 without forming a layer like the intermediate layer 34 of the rare earth magnet 300. Moreover, the rare earth magnets 100 and 300 have a layer (for example, a layer made of a compound not containing hydrogen as a constituent element) having a composition different from that of the layer constituting the coating layer on the coating layers 20 and 30. May be.

  The contents of the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Preparation of rare earth magnet and composition analysis of coating layer]
Example 1
<Preparation of magnet body>
An ingot made of an Nd—Dy—B—Fe alloy was obtained by powder metallurgy. The composition of this ingot was Nd content: 27.4% by mass, Dy content: 3% by mass, B content: 1% by mass, and Fe content: 68.6% by mass. The ingot was pulverized by a stamp mill and a ball mill to obtain fine alloy powder having the above composition.

  The obtained alloy fine powder was press-molded in a magnetic field to prepare a compact. The molded body was sintered under the conditions of a holding temperature of 1100 ° C. and a holding time of 1 hour to obtain a sintered body. Thereafter, the sintered body was subjected to an aging treatment under the conditions of a holding temperature of 600 ° C. and a holding time of 2 hours in an Ar gas atmosphere. The sintered body subjected to the aging treatment was processed into a rectangular parallelepiped shape having a size of 20 × 20 × 1 (mm), and chamfered by barrel polishing treatment to obtain a magnet body.

<Pretreatment>
The magnet body was subjected to a pretreatment in which an alkaline degreasing treatment, water washing, acid washing treatment with a nitric acid solution, water washing, smut removal treatment by ultrasonic washing, and water washing were sequentially performed.

<Formation of the first layer>
A plating bath comprising the following components was prepared.
Nickel sulfate hexahydrate: 270 g / L
Nickel chloride hexahydrate: 50 g / L
Boric acid: 45 g / L
Saccharin sodium: 5 g / L
Coumarin: 0.3 g / L

The pre-treated magnet body was immersed in the plating bath (pH: 4.0, temperature: 50 ° C.), and electroplating was performed. The electroplating process was performed at a current density of 0.2 A / dm ² by a barrel plating method, and a Ni plating layer (first layer) having a thickness of 3 μm was formed on the surface of the magnet body.

<Formation of second layer>
After the magnet body having the first layer formed on the surface is placed inside the vacuum film formation chamber, the pressure inside the vacuum film formation chamber becomes a predetermined value (1 × 10 ⁻³ Pa) or less. The vacuum film formation chamber was evacuated.

  A second layer (thickness: 2 μm) made of silicon nitride containing hydrogen as a constituent element was formed on the Ni plating layer by plasma CVD vapor deposition. The conditions of the plasma CVD vapor deposition method were as follows.

Introduced gas: SiH ₄ (silane), N ₂ (nitrogen)
Flow rate of introduced gas: SiH ₄ = 20 ml / min, N ₂ = 600 ml / min (The flow rate of introduced gas is a value obtained by converting temperature and pressure to 25 ° C. and 1 atm.)
Pressure in the chamber: 30Pa
Surface temperature of magnet body: 150 ° C
High frequency power: 300W

  In this way, a rare earth magnet was obtained in which a coating layer composed of a first layer made of nickel and a second layer made of silicon nitride containing hydrogen as a constituent element was formed on the magnet body.

<Composition analysis>
Glow discharge emission spectroscopic analysis (manufactured by JOBIN YVON, device name: GD-PROFILER2) of the obtained rare earth magnet coating layer was performed to analyze the composition of the first layer and the second layer constituting the coating layer. The analysis conditions were glow discharge power: 20 W, discharge range: diameter 2 mm. As a result, the first layer contained nickel and the second layer contained silicon, nitrogen and hydrogen. The hydrogen content in the second layer was 5 atomic%.

(Example 2)
A rare earth magnet was obtained in the same manner as in Example 1 except that the conditions for forming the second layer by the plasma CVD vapor deposition method were as follows.

Introduced gas: SiH ₄ (silane), NH ₃ (ammonia), N ₂ (nitrogen)
Gas flow rate: SiH ₄ = 60 ml / min, NH ₃ = 30 ml / min, N ₂ = 600 ml / min (The flow rate of the introduced gas is a value obtained by converting temperature and pressure into 25 ° C. and 1 atm.)
Pressure in the chamber: 30Pa
Surface temperature of the first layer: 200 ° C
High frequency power: 300W

  In the same manner as in Example 1, the composition of the coating layer formed on the magnet body was analyzed. As a result, the first layer contained nickel and the second layer contained silicon, nitrogen and hydrogen. The hydrogen content of the second layer was 15 atomic%.

(Example 3)
A rare earth magnet was obtained in the same manner as in Example 1 except that the conditions for forming the second layer by the plasma CVD vapor deposition method were as follows.

Introduced gas: SiH ₄ (silane), NH ₃ (ammonia), H ₂ (hydrogen)
Gas flow rate: SiH ₄ = 60 ml / min, NH ₃ = 500 ml / min, H ₂ = 100 ml / min (The flow rate of the introduced gas is a value obtained by converting temperature and pressure into 25 ° C. and 1 atm.)
Pressure in the chamber: 30Pa
Surface temperature of the first layer: 300 ° C
High frequency power: 300W

  In the same manner as in Example 1, the composition of the coating layer formed on the magnet body was analyzed. As a result, the first layer contained nickel and the second layer contained silicon, nitrogen and hydrogen. The hydrogen content of the second layer was 30 atomic%.

Example 4
Instead of the Ni plating layer of Example 1, a rare earth magnet was obtained in the same manner as Example 2 except that the Cu plating layer formed under the following conditions was the first layer.

<Formation of the first layer>
A plating bath comprising the following components was prepared.
Copper pyrophosphate trihydrate: 10 g / L
Potassium pyrophosphate: 200 g / L
Potassium citrate: 60 g / L
28% by mass ammonia water: 1 mL / L,

The pre-treated magnet body was immersed in the plating bath (pH: 10.5, temperature: 40 ° C.), and electroplating was performed. The electroplating process was performed at a current density of 0.2 A / dm ² by barrel plating, and a Cu plating layer (first layer) having a thickness of 3 μm was formed on the surface of the magnet body.

  After forming the second layer in the same manner as in Example 2, the composition of the coating layer formed on the magnet body was analyzed. As a result, the first layer contained copper and the second layer contained silicon, nitrogen and hydrogen. The hydrogen content of the second layer was 15 atomic%.

(Example 5)
Example 2 is the same as Example 2 except that the following hydrogenation step was performed after forming the first layer on the magnet body by Ni plating and then forming the second layer by plasma CVD vapor deposition method. Thus, a rare earth magnet was obtained.

<Hydrogenation process>
The magnet body on which the first layer was formed was held in a hydrogen atmosphere for 30 minutes at 100 ° C. and 1 atm.

  After the holding, the second layer was formed in the same manner as in Example 2, and the composition of the coating layer formed on the magnet body was analyzed. As a result, the first layer contained nickel and the second layer contained silicon, nitrogen and hydrogen. The first layer contained hydrogen in the vicinity of the interface between the first layer and the second layer. The hydrogen content in the vicinity of the interface of the first layer was 1 atomic%, and the hydrogen content in the second layer was 15 atomic%.

(Example 6)
Example 4 except that after the Cu plating layer (first layer) was formed on the magnet body, the following hydrogenation step was performed before the second layer was formed by the plasma CVD vapor deposition method. In the same manner as above, a rare earth magnet was obtained.

<Hydrogenation process>
The magnet body on which the first layer was formed was held in a hydrogen atmosphere for 30 minutes at 100 ° C. and 1 atm.

  After the holding, a second layer was formed in the same manner as in Example 4, and the composition of the coating layer formed on the magnet body was analyzed. As a result, the first layer contained copper and the second layer contained silicon, nitrogen and hydrogen. The first layer contained hydrogen in the vicinity of the interface between the first layer and the second layer. The hydrogen content in the vicinity of the interface of the first layer was 1 atomic%, and the hydrogen content in the second layer was 15 atomic%.

(Comparative Example 1)
A magnet body was prepared in the same manner as in Example 1, and the same pretreatment as in Example 1 was performed.

<Formation of coating layer>
A coating layer (thickness: 5 μm) made of silicon nitride containing hydrogen as a constituent element was formed on the surface of the magnet body by plasma CVD vapor deposition. The conditions for the plasma CVD vapor deposition method were the same as those for forming the second layer of Example 2.

<Composition analysis>
In the same manner as in Example 1, the composition analysis of the coating layer formed on the magnet body was performed. As a result, the coating layer contained silicon, nitrogen and hydrogen, and the hydrogen content was 15 atomic%.

(Comparative Example 2)
A rare earth magnet was obtained in the same manner as in Example 1 except that the second layer was not formed. That is, the rare earth magnet of Comparative Example 2 had a coating layer (thickness: 5 μm) consisting only of the first layer on the magnet body. When the composition analysis of the coating layer was performed in the same manner as in Example 1, the coating layer contained nickel.

(Comparative Example 3)
A rare earth magnet was obtained in the same manner as in Example 4 except that the second layer was not formed. That is, the rare earth magnet of Comparative Example 2 had a coating layer (thickness: 5 μm) consisting only of the first layer on the magnet body. When the composition analysis of the coating layer was performed in the same manner as in Example 1, the coating layer contained copper.

(Comparative Example 4)
A rare earth magnet was obtained in the same manner as in Example 5 except that the second layer was not formed by the plasma CVD vapor deposition method. That is, the rare earth magnet of Comparative Example 4 had a coating layer (thickness: 5 μm) consisting only of the first layer on the magnet body, and the vicinity of the surface of the first layer was hydrogenated. The composition of the coating layer was analyzed in the same manner as in Example 5. As a result, the coating layer contained nickel. Moreover, hydrogen was contained near the surface of the coating layer. The hydrogen content in the vicinity of the surface of the coating layer was 1 atomic%.

[Characteristic evaluation of rare earth magnets]
Using the rare earth magnets obtained in each Example and each Comparative Example as samples, corrosion resistance, moisture resistance and adhesion were evaluated by the following procedures.

<Corrosion resistance evaluation>
In accordance with the standard of JIS C0023, a salt spray test (SST) was performed under conditions of salt water (NaCl concentration: 5 mass%) and a test temperature of 35 ° C. Under this condition, the sample was held for 24 hours, and the surface state of the sample after holding was visually observed to evaluate the presence or absence of rust, peeling of the coating layer, and swelling. A sample in which rust and coating layer peeling and swelling were not observed was judged as “A”, and a sample in which at least one of rust and coating layer peeling and swelling was observed was judged as “B”. The evaluation results are shown in Table 1.

  The rare earth magnets of Examples 1 to 6 had excellent corrosion resistance, with no rust, peeling or swelling of the coating layer observed. On the other hand, in the rare earth magnets of Comparative Examples 2 to 4, rust and swelling occurred. From these results, it was confirmed that the rare earth magnets of Comparative Examples 2 to 4 were inferior in corrosion resistance to the rare earth magnets of Examples 1 to 6.

<Moisture resistance evaluation>
A pressure cooker test (PCT) was performed under the condition of a sample temperature of 121 ° C. in an atmosphere containing saturated water vapor. The sample was held for 300 hours under these conditions, and the surface state of the sample after holding was visually observed to observe the occurrence of rust, peeling of the coating layer, and swelling. A sample in which rust and coating layer peeling and swelling were not observed was judged as “A”, and a sample in which at least one of rust and coating layer peeling and swelling was observed was judged as “B”. The evaluation results are shown in Table 1.

  The rare earth magnets of Examples 1 to 6 had excellent moisture resistance without rusting, peeling or swelling of the coating layer being observed even after being held for 300 hours. On the other hand, in the rare earth magnet of Comparative Example 1, peeling of the coating layer occurred after holding for 100 hours. In addition, the rare earth magnets of Comparative Examples 2 to 4 were swollen. From these results, it was confirmed that the rare earth magnets of Comparative Examples 1 to 4 were inferior in moisture resistance to the rare earth magnets of Examples 1 to 6.

<Adhesion evaluation>
A sample before PCT and a sample after PCT were prepared. And the adhesiveness of each sample was evaluated by the cross-cut tape method according to JIS K5400. Specifically, grid-like cuts (100 locations) with an interval of 1 mm were made in a 10 mm square region on the surface of the rare earth magnet on which the coating layer was formed. On top of that, one tape was applied, and when the tape was peeled off, the number of places where the coating layer did not peel from the magnet body was determined, and the adhesion was evaluated. The results are shown in Table 1. For example, when the number of areas where the coating layer is peeled is one in 100 areas, the adhesion notation in Table 1 is 99/100. Adhesion of 95/100 or higher was considered good. Moreover, in the peeled location, the peeling site | part was pinpointed visually.

  The rare earth magnets of Examples 1 to 6 each had 100/100 adhesion before PCT, and had excellent adhesion. On the other hand, the rare earth magnet of Comparative Example 1 had an adhesion before PCT of 83/100, and it was confirmed that the adhesion of the coating layer was inferior to each example. Further, after the PCT, some peeling was observed at the interface between the first layer and the second layer in the rare earth magnets of Examples 1 to 4. However, in these rare earth magnets, peeling at the interface between the first layer and the magnet body was not observed, and it was confirmed that the magnet body and the coating layer still have excellent adhesion. In the rare earth magnets of Examples 5 and 6, no peeling occurred and it was confirmed that the rare earth magnets had better adhesion.

  On the other hand, in the rare earth magnet of Comparative Example 1, the adhesion was remarkably lowered after PCT. In the rare earth magnets of Comparative Examples 2 to 4, the coating layer swelled after PCT, and the adhesion could not be evaluated.

  DESCRIPTION OF SYMBOLS 10 ... Magnet body, 20, 30 ... Covering layer, 22, 32 ... First layer, 24, 36 ... Second layer, 34 ... Intermediate layer, 100, 300 ... Rare earth magnet.

Claims (3)

A rare earth magnet comprising: a magnet element body including a rare earth element; and a coating layer having a first layer and a second layer from the magnet element side on the magnet element body,
The first layer contains at least one metal selected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, or an alloy containing the metal,
The second layer is a rare earth magnet containing a compound having silicon, nitrogen and hydrogen as constituent elements.   The rare earth magnet according to claim 1, wherein the hydrogen content in the second layer is 0.1 to 50 atomic%.   The rare earth magnet according to claim 1, wherein the first layer includes a hydride of the metal or the alloy on a contact surface side with the second layer.

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