JP2009099968A - Rare earth magnet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a rare earth magnet having a protective layer that can provide sufficient water resistance, and to provide a rare earth magnet obtained by the method. <P>SOLUTION: The method for manufacturing the rare earth magnet comprising a magnet body containing a rare earth element and a protective layer formed on the surface of the magnet body includes: a first step in which a zinc compound soluble in an alkaline solution is dissolved in an alkali silicate solution to obtain a treatment solution; a second step in which the treatment solution is made to adhere to the surface of the magnet body; and a third step in which the treatment solution adhering to the magnet body surface is cured to form a protective layer comprising the cured product of the treatment solution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  Although a rare earth magnet containing a rare earth element has an excellent magnetic force, it contains a rare earth element that is easily oxidized as a main component, and therefore tends to have low corrosion resistance. Therefore, rare earth magnets are often configured such that a protective layer made of resin, plating, or the like is provided on the surface of a magnet body containing a rare earth element. In recent years, in rare earth magnets, when the corrosion resistance of the magnet body itself has been improved, or when it is used for applications that do not require the corrosion resistance as in the past, it is easier and less expensive than before, to a certain extent In some cases, it is required to be able to form a protective layer capable of exhibiting the above corrosion resistance.

Examples of rare earth magnets having such a protective layer include flaky fine powder / alkali silicate obtained by heating a treatment film with a treatment liquid containing flaky fine powder of a predetermined metal and alkali silicate. There is known a corrosion-resistant rare earth magnet having a composite film (see Patent Document 1 below).
JP 2006-49864 A

  By the way, in recent years, the use of rare earth magnets having high characteristics under various conditions has been studied, and the rare earth magnets are increasingly required to have resistance to water (water resistance).

  However, as a result of investigations by the present inventors, the above-described conventional corrosion-resistant rare earth magnet formed with the flaky fine powder / alkali silicate composite film can obtain corrosion resistance under normal conditions. From the viewpoint of safety, the current situation is that they do not have sufficient characteristics.

  Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide a method for producing a rare earth magnet capable of obtaining a rare earth magnet having a protective layer capable of obtaining sufficient water resistance.

  In order to achieve the above object, a rare earth magnet of the present invention is a method for producing a rare earth magnet having a magnet element body containing a rare earth element and a protective layer formed on the surface of the magnet element element. First step of dissolving a zinc compound soluble in an alkali silicate aqueous solution to obtain a treatment liquid, a second step of attaching a treatment liquid to the surface of the magnet body, and a treatment attached to the surface of the magnet body And a third step of forming a protective layer made of a cured product of the treatment liquid by curing the liquid.

  According to such a method for producing a rare earth magnet of the present invention, a protective layer in which zinc elements are uniformly dispersed is satisfactorily formed on a film made of alkali silicate (so-called “water glass”). Such a protective layer has high resistance to water and can sufficiently prevent the permeation of water. Therefore, the rare earth magnet obtained by the production method of the present invention can have excellent water resistance.

  In addition, the flaky fine powder / alkali silicate composite film of the above prior art may have a structure in which zinc is included in the composite film as long as the raw material of the flaky fine powder is zinc. However, as a result of investigations by the present inventors, such a composite coating contains zinc in the form of flaky fine powder to the end, so that the thickness of the coating is uneven and water resistance may be reduced. In addition, it has been found that dropping of particles may adversely affect electronic devices equipped with rare earth magnets.

  On the other hand, in the present invention, as described above, since the treatment liquid in which the zinc compound is dissolved is used, the protective layer to be formed has zinc in an atomic state or a state close to the atomic size (for example, , Zinc compound molecular state). As a result, the rare earth magnet obtained by the present invention has sufficient water resistance since it has a protective layer having a uniform thickness, and it is extremely difficult to cause adverse effects on electronic devices due to dropping of particles and the like. In addition, according to the present invention, since the particles are not included, the thickness of the protective layer can be reduced, and this protective layer can have sufficient water resistance even if it is thin. Therefore, the rare earth magnet obtained by the present invention can make the protective layer relatively thin in a certain size, so that the magnet body can be made relatively large, and thereby high magnetic properties can be obtained while obtaining sufficient water resistance. It will be easy to get.

  Moreover, in a 1st process, after adding a zinc compound to alkali silicate aqueous solution, it is preferable to stir 24 hours or more. Thereby, a zinc compound will be more reliably melt | dissolved in a process liquid, and it becomes easier to acquire the effect of this invention mentioned above.

  The present invention also provides a rare earth magnet suitably obtained by the production method of the present invention. That is, the rare earth magnet of the present invention has a magnet body containing a rare earth element and a protective layer formed on the surface of the magnet body, the protective layer contains an alkali silicate, and Zinc and / or zinc compounds are uniformly dispersed.

  The rare earth magnet of the present invention configured as described above has a protective layer in which zinc is contained in the state of zinc atoms or zinc compound molecules in a film mainly made of alkali silicate. Such a protective layer has a high resistance to water as described above, and can sufficiently prevent the permeation of water, so that it has excellent water resistance and a thin protective layer. Therefore, it can have excellent magnetic properties.

  According to the present invention, it is possible to provide a rare earth magnet that has a protective layer that can provide sufficient water resistance even when thin, and that can exhibit high magnetic properties, and a method for manufacturing the rare earth magnet.

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

  First, a method for producing a rare earth magnet according to a preferred embodiment of the present invention will be described.

  In manufacturing a rare earth magnet, first, a magnet body is formed. The magnet body is a permanent magnet containing a rare earth element, and a composition known as a rare earth magnet can be applied without particular limitation. The rare earth element contained in the magnet body refers to scandium (Sc), yttrium (Y), and a lanthanoid element 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 include those containing the rare earth element and a transition element other than the rare earth element in combination. In this case, as the rare earth element, at least one element selected from the group consisting of Nd, Sm, Dy, Pr, Ho and Tb is preferable, and these elements include La, Ce, Gd, Er, Eu, Tm, Yb and More preferably, it further contains at least one element selected from the group consisting of Y.

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

  More specifically, examples of the constituent material of the magnet body include R—Fe—B and R—Co materials. In the former constituent material, R is preferably a rare earth element mainly composed of Nd. In the latter constituent material, R is preferably a rare earth element mainly composed of Sm.

  As the constituent material of the magnet body, an R—Fe—B constituent material is particularly preferable. When the magnet body is of the R—Fe—B system, excellent magnet characteristics can be obtained, and the effect of improving the corrosion resistance by forming the protective layer can be obtained more favorably.

  The R-Fe-B based magnet body has a main phase with a substantially tetragonal crystal structure, and a rare earth rich phase with a high blending ratio of rare earth elements in the grain boundary portion of the main phase, and boron atoms It has the structure which has a boron rich phase with a high compounding ratio. 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.

  Further, the Fe content is preferably 42 to 90 atomic%. When the Fe content is less than 42 atomic%, Br decreases, and when it exceeds 90 atomic%, iHc tends to decrease. Furthermore, the content of B 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 iHc. On the other hand, if it exceeds 28 atomic%, a boron-rich phase is excessively formed, and this tends to decrease Br.

  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 iHc and reducing manufacturing costs, in addition to the above-described structure, 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) Further, elements such as gallium (Ga), copper (Cu), and hafnium (Hf) may be added. These addition amounts are also preferably in a range that does not affect the magnetic properties, and are preferably 10 atomic% or less with respect to the total amount of constituent atoms. In addition, oxygen (O), nitrogen (N), carbon (C), calcium (Ca), etc. are conceivable as components inevitably mixed, and these are about 3 atomic% with respect to the total amount of constituent atoms. It may be contained in the following amounts.

Such a magnet body can be manufactured by, for example, powder metallurgy. 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 (coarsely pulverized) to a particle size of 10 to 100 μm using a coarse pulverizer such as a jaw crusher, brown mill, stamp mill, and then further finely pulverized using a jet mill, an attritor or the like. Finely pulverize to a particle size of 0.5-5 μm with a machine. Then, the powder thus obtained is molded at a pressure of 0.5 to ⁵ t / cm ² in a magnetic field having a magnetic field strength of preferably 600 kA / m or more to obtain a molded body.

  Thereafter, the obtained molded body is preferably fired in an inert gas atmosphere or in a vacuum at 1000 to 1200 ° C. for 0.5 to 10 hours. After firing, the obtained sintered body may be quenched. Furthermore, this sintered body is subjected to heat treatment at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere or in a vacuum, if necessary, or by cutting or polishing the sintered body. (Practical shape) to obtain a magnet body.

  The magnet body obtained in this manner may be washed as appropriate in order to remove surface irregularities and impurities adhering to the surface. The cleaning is preferably, for example, acid cleaning using an acid solution. According to the acid cleaning, it becomes easy to obtain a magnet body having a smooth surface by dissolving and removing irregularities and impurities on the surface of the magnet body.

  Nitric acid is preferred as the acid used in this acid cleaning. When plating a general steel material, non-oxidizing acids such as hydrochloric acid and sulfuric acid are often used. However, when a rare earth element is contained as in a magnet body, if these acids are used for treatment, hydrogen generated by the acid is occluded on the surface of the magnet body, and the occlusion site becomes brittle and a large amount of There is a possibility of generating powdery undissolved material. This powdery undissolved material is not desirable because it may cause surface roughness, defects, poor adhesion and the like after the surface treatment. Therefore, it is preferable not to include the non-oxidizing acid described above in the treatment liquid used for the acid cleaning. Therefore, in this embodiment, it is preferable to use nitric acid, which is an oxidizing acid that generates little hydrogen.

  When nitric acid is used for the acid cleaning, the nitric acid concentration in the treatment liquid is preferably 1 N or less, particularly preferably 0.5 N or less. If the concentration of nitric acid is too high, the dissolution rate of the magnet body becomes too fast and it becomes difficult to control the amount of dissolution, especially in large-scale processing such as barrel processing, and it is difficult to maintain the dimensional accuracy of the product. Tend to be. On the other hand, if the nitric acid concentration is too low, the amount of dissolution 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 preferably about 1 to 10 g / l.

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

  In addition, after removing the treatment liquid used for the acid cleaning by washing with water after the above acid cleaning, the magnet body is subjected to ultrasonic waves in order to completely remove a small amount of undissolved substances and residual acid components remaining on the surface. It is preferable to carry out washing using This ultrasonic cleaning can be performed, for example, in pure water or an alkaline solution with very little chlorine ions that generate rust on the surface of the magnet body. After the ultrasonic cleaning, water cleaning may be performed as necessary.

  In the production of rare earth magnets, a magnet body is formed in this way, and a treatment liquid to be attached to the surface of the magnet body is prepared. The treatment liquid is obtained by dissolving a zinc compound soluble in an alkaline solution in an aqueous alkali silicate solution. In this treatment liquid preparation step, at least a part of the zinc compound is dissolved in the treatment liquid. The degree of dissolution is determined when the obtained treatment liquid is measured with a turbidimeter (for example, 2100P type manufactured by Hack). The obtained turbidity is preferably 10 NTU or less, and more preferably 20 NTU or less. If it carries out like this, a zinc compound will fully be melt | dissolved in a process liquid, and a protective layer which has high corrosion resistance comes to be obtained.

  In particular, in this embodiment, it is more preferable to completely dissolve the zinc compound in the aqueous alkali silicate solution in the preparation of the treatment liquid. Here, the “completely dissolved state” of the zinc compound means that the turbidity described above is 100 NTU or less. In this case, zinc or zinc compound particles are hardly included in the protective layer, and it becomes easier to obtain better water resistance, and the protective layer can be easily made thinner.

  Examples of the alkali silicate contained in the treatment liquid include lithium silicate, sodium silicate, potassium silicate, ammonium silicate and the like. An alkali silicate may be used individually by 1 type, and may be used in combination of multiple types. Among these, a mixture of sodium silicate and lithium silicate is preferable because a protective layer having high corrosion resistance can be formed.

  The zinc compound is soluble in an alkaline solution, and preferably has a property soluble in an alkaline solution having a pH of about 10 to 11. Such a zinc compound can be completely dissolved in the above-described alkali silicate aqueous solution at approximately room temperature, and is particularly suitable for the method for producing a rare earth magnet of the present invention. Examples of the zinc compound include zinc sulfate, zinc borate, basic zinc carbonate, zinc acetate, zinc chloride, and zinc gluconate. These may be used in the form of hydrates.

  In the preparation of the treatment liquid, the alkali silicate aqueous solution preferably has an alkali silicate concentration of 1 to 50% by mass, more preferably 5 to 40% by mass. According to such an alkali silicate aqueous solution, a protective layer excellent in corrosion resistance can be formed, and a zinc compound can be dissolved well.

  In the treatment liquid, the zinc compound is preferably contained in an amount of 0.001 to 0.05 mol, more preferably 0.002 to 0.02 mol, based on 1 mol of silicon in the alkali silicate. If it carries out like this, zinc will be disperse | distributed uniformly in a protective layer and it will become easy to obtain the outstanding corrosion resistance. When the content of the zinc compound is too small, the corrosion resistance of the rare earth magnet tends to decrease. On the other hand, if the amount is too large, the stability of the treatment liquid tends to deteriorate, which is not preferable.

  Moreover, in preparation of a process liquid, after adding a zinc compound to alkaline silicate aqueous solution, it is preferable to stir for 24 hours or more, and it is more preferable to stir for 48 hours or more. In this way, the zinc compound can be reliably dissolved by the aqueous alkali silicate solution. When the stirring time is less than 24 hours, the zinc compound is not sufficiently dissolved, and water resistance may not be sufficiently obtained. Furthermore, when the temperature at this time is 10 to 50 ° C., the zinc compound can be dissolved more satisfactorily.

  Next, the treatment liquid prepared above is adhered to the surface of the magnet body described above. The treatment liquid can be attached by, for example, dropping or spraying the treatment liquid on the surface of the magnet body or immersing the magnet body in the treatment liquid. From the viewpoint of uniformly attaching the treatment liquid to the entire surface of the magnet body, it is preferable to immerse the magnet body in the treatment liquid. Specifically, the treatment liquid is preferably attached by a dip spin coating method in which the magnet element body is dipped in the solution and then pulled up, and the magnet element body is further rotated to shake off excess treatment liquid.

  After the treatment liquid is attached to the surface of the magnet body in this way, the treatment liquid attached to the surface is cured. This hardening is mainly hardening of the alkali silicate contained in the treatment liquid, and is caused by removing water as a solvent from the aqueous alkali silicate solution.

  The curing of the treatment liquid can be performed, for example, by heating the magnet body to which the treatment liquid is attached. The heating temperature is preferably 100 to 500 ° C, more preferably 120 to 350 ° C. The heating time is preferably 1 minute to 10 hours, and more preferably 5 minutes to 1 hour. If the heating temperature is too low or the heating time is too short, sufficient curing may not occur and it may be difficult to obtain good water resistance. On the other hand, if the heating temperature is too high or the heating time is too long, the magnetic properties are likely to deteriorate, such being undesirable.

  In this way, the treatment liquid adhering to the surface of the magnet body is cured, and a protective layer made of a cured product of the treatment liquid is formed on the surface of the magnet body, thereby obtaining the rare earth magnet of the preferred embodiment. .

  Hereinafter, an example of the structure of the rare earth magnet thus obtained will be described. FIG. 1 is a perspective view showing an example of a rare earth magnet obtained by the production method of the present invention. Moreover, FIG. 2 is a figure which shows typically the cross-sectional structure which follows the II-II line | wire of the rare earth magnet shown in FIG. As shown in the drawing, the rare earth magnet 1 of the present embodiment includes a magnet body 2 and a protective layer 4 formed so as to cover the surface thereof, and has a substantially rectangular parallelepiped shape as a whole.

  In this rare earth magnet 1, the magnet body 2 has the composition described above. On the other hand, the protective layer 4 is a layer formed by curing a treatment liquid in which a zinc compound is dissolved in an aqueous alkali silicate solution. The protective layer 4 has a configuration in which, for example, zinc is dispersed in a state of a metal element alone or a zinc compound used as a raw material in a glassy film made of alkali silicate. In the formation of the protective layer 4, since the treatment liquid in which the zinc compound is almost completely dissolved is used, zinc is contained in the protective layer 4 in an atomic state or a state close to the atomic size.

  Further, in the protective layer 4, since zinc and / or zinc compound is formed by the treatment liquid in which the zinc compound is dissolved as described above, the zinc and / or zinc compound is uniformly dispersed in the glassy film made of alkali silicate. It becomes a state. Here, the “uniformly dispersed state” refers to a state in which zinc and a zinc compound are present not only in a specific region in the protective layer 4 but over the entire region. For example, when the cross section of the protective layer 4 is analyzed by TEM-EDS, even when the region formed by gathering zinc or the zinc compound is the largest, the aspect having no width of 10 nm or more is “uniformly”. Corresponds to "Distributed state".

  The zinc or zinc compound in the protective layer in the rare earth magnet 1 is preferably contained in an amount of 0.001 to 0.05 mol per 1 mol of silicon in the alkali silicate in the proportion of zinc element. More preferably, 02 mol is contained. It should be noted that whether or not zinc or a zinc compound is contained in the protective layer 4 or the content thereof is, for example, XRF (fluorescence X-ray analysis method), EPMA (X-ray microanalyzer method), XPS (X-ray photoelectron). It can be confirmed by measuring using a known composition analysis method such as spectroscopy), AES (Auger electron spectroscopy) or EDS (energy dispersive X-ray fluorescence spectroscopy).

  The thickness of the protective layer 4 in the rare earth magnet 1 is preferably 0.01 to 10 μm, and more preferably 0.1 to 3 μm. If this thickness is too thin, the corrosion resistance mainly of the water resistance of the rare earth magnet 1 tends to decrease. On the other hand, if it is too thick, the magnet element body 1 becomes relatively small at a certain size of the rare earth magnet 1, and sufficient magnetic properties may not be obtained. According to the protective layer 4 of the present embodiment, sufficient water resistance can be obtained as long as it has a thickness of at least the above-described minimum value, so that a protective layer that must be thicker than this is formed. As compared with the case, excellent magnetic properties can be obtained. In applications where corrosion resistance is required rather than magnetic properties, the protective layer 4 may be thicker than the above range.

  The preferred embodiments of the present invention have been described above. However, the present invention is not necessarily limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the above embodiment, the treatment liquid was prepared by adding the zinc compound to the alkali silicate aqueous solution and stirring the solution. However, the order is not limited thereto, and the zinc compound, the alkali silicate, and water are added. You may prepare a process liquid by mixing simultaneously and stirring this. Further, the curing of the treatment liquid is not necessarily performed by heating, and may be performed by leaving it for a predetermined time after application, for example.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.

[Manufacture of rare earth magnets]
(Examples 1-6, Comparative Examples 1-4)
First, an ingot having a composition of 27.6Nd-4.9Dy-0.5Co-0.4Al-0.07Cu-1.0B-remaining Fe (numbers represent weight percentage) is produced by powder metallurgy. This was coarsely pulverized. Thereafter, jet milling with an inert gas was performed to obtain a fine powder having an average particle size of about 3.5 μm. The obtained fine powder was filled in a mold and molded in a magnetic field. Next, after sintering in vacuum, heat treatment was performed to obtain a sintered body. The obtained sintered body was cut into a size of 20 mm × 10 mm × 2 mm and processed to obtain a magnet body. Next, the obtained magnet body was degreased and then subjected to ultrasonic cleaning.

  Moreover, it is processed by mixing and stirring No. 3 sodium silicate (manufactured by Fuji Chemical Co., Ltd.), lithium silicate (lithium silicate 45 manufactured by Nissan Chemical Industries, Ltd.), zinc compound and water in combinations and proportions shown in Table 1 below. A liquid was prepared. The stirring temperature at this time was 25 ° C., and the stirring time was as shown in Table 1. In Table 1, Comparative Example 1 is one in which no zinc compound was added.

Thereafter, each treatment solution was applied to the magnet body to a thickness of 0.7 μm by dip spin coating. After the application, heat treatment was performed at 150 ° C. for 20 minutes to cure the treatment liquid, thereby obtaining a rare earth magnet having a protective layer formed on the surface of the magnet body.

  The rare earth magnets obtained in Examples 1 to 6 were sliced using a focused ion beam processing apparatus, and the structure near the surface was observed with a transmission electron microscope (JEM-3010 manufactured by JEOL) to form a protective layer. The distribution of the contained elements was analyzed using EDS (Voyager III manufactured by Noraan Instruments). As a result, in the protective layer, a portion where the zinc element was formed in a region of 10 nm or more was not observed. Therefore, it was confirmed that zinc was uniformly dispersed in the protective layer.

[Characteristic evaluation]
(High temperature and high humidity test)
A humidity resistance test was performed in which the rare earth magnets of Examples 1 to 6 and Comparative Examples 1 to 4 were left in an atmosphere of 85 ° C. and 85% RH, and each rare earth magnet after the test was observed.

  As a result, in the rare earth magnets of Examples 1 to 6, no rusting was observed even after 400 hours, whereas in the magnet of Comparative Example 1, the film was whitened after 100 hours. Then, rusting was observed after 240 hours. The obtained results are summarized in Table 2.

(Adhesion test)
An aluminum stud pin having a diameter of 4.1 mm was adhered to the surface of each of the rare earth magnets of Examples 1 to 6 and Comparative Examples 1 to 4 with an epoxy adhesive, and this was cured by heating. The magnet was left in an atmosphere of 60 ° C. and 95% RH for 24 hours, and then a tensile test was performed to peel the stud pin from the rare earth magnet.

  As a result, the magnets of Examples 1 to 6 did not peel even at 500 N, but the magnet of Comparative Example 1 was 270 N, the magnet of Comparative Example 2 was 410 N, the magnet of Comparative Example 3 was 320 N, and the magnet of Comparative Example 4 was 370 N. Peeled off. The obtained results are summarized in Table 2.

(Water resistance test)
After the rare earth magnets of Examples 1 to 6 and Comparative Examples 1 to 4 were immersed in 3 ml of pure water at 50 ° C. for 1 hour, the concentration of the silica component eluted in the pure water was measured using Digital Pack Test Multi (trade name) : Kyoritsu Riken Co., Ltd.) and measured by the molybdenum blue method. The obtained results are summarized in Table 2. The greater the amount of elution, the more easily the protective layer is corroded by water, indicating poor water resistance.

  From Table 2, according to the rare earth magnets obtained in Examples 1 to 6, the zinc compound was not sufficiently dissolved in the treatment liquid, or compared with Comparative Examples 1 to 4 in which dissolution was not possible. Rust generation was not observed even in the humidity test, so it has high corrosion resistance, excellent adhesion even after high-temperature and high-humidity treatment, and high durability even when immersed in water There was found.

It is a perspective view which shows an example of the rare earth magnet obtained by the manufacturing method of this invention. 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.

Explanation of symbols

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

Claims (3)

A method for producing a rare earth magnet having a magnet body containing a rare earth element, and a protective layer formed on the surface of the magnet body,
A first step of dissolving a zinc compound soluble in an alkaline solution in an aqueous alkali silicate solution to obtain a treatment liquid;
A second step of attaching the treatment liquid to the surface of the magnet body;
A third step of curing the treatment liquid adhering to the surface of the magnet body to form a protective layer made of a cured product of the treatment liquid;
A method for producing a rare earth magnet, comprising:   The method for producing a rare earth magnet according to claim 1, wherein, in the first step, the zinc compound is added to the alkali silicate aqueous solution and then stirred for 24 hours or more. A magnet body containing a rare earth element, and a protective layer formed on the surface of the magnet body,
2. The rare earth magnet according to claim 1, wherein the protective layer contains an alkali silicate and zinc and / or a zinc compound are uniformly dispersed.

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