JP4483318B2 - Rare earth magnet manufacturing method - Google Patents

Description

The present invention relates to a process for producing a rare earth magnet, in particular to a method for producing a rare earth magnet having a protective layer on the surface.

  Conventionally, rare earth magnets are known as high performance permanent magnets. This rare earth magnet is not only used for household appliances such as air conditioners and refrigerators, but is also being considered for application to drive motors for industrial machines, robots, fuel cell vehicles, hybrid cars, etc. It is expected that energy saving can be realized. Among such rare earth magnets, R—Fe—B (R is a rare earth element) type magnet has attracted attention because it has particularly high magnetic properties. As such R—Fe—B rare earth magnets, for example, those described in Patent Document 1 and Patent Document 2 below are known.

  R—Fe—B rare earth magnets are high performance magnets that exhibit a high energy product, typically exceeding 25 MGOe. However, such rare earth magnets have properties of being easily oxidized and having low heat resistance because they contain rare earth elements and iron as the main components of the magnet. For this reason, such rare earth magnets tend to be inferior in corrosion resistance, and it has been difficult to avoid deterioration of magnetic characteristics over time due to long-term use.

  In recent years, attempts have been made to form a protective layer on the surface of a magnet body for the purpose of improving the corrosion resistance of such R—Fe—B rare earth magnets. As one of the methods for forming the protective layer, a so-called wet film-forming method using a coating solution containing a metal atom such as Ti has been proposed as one of relatively simple and highly practical methods (Patent Documents 3 to 5). reference). For example, in Patent Document 3, the magnet body is surface-treated with a specific organometallic compound containing Si, Ti, or Al in order to improve the oxidation resistance of the magnet. A method for producing a rare earth magnet that forms an oxidation resistant coating on the surface is described.

Patent Document 4 discloses a method for producing a rare earth magnet in which organic titanium is attached to the surface of a magnet body and then heat-treated in an inert atmosphere with the intention of providing a permanent magnet that is not easily oxidized. Is described. Further, the surface of the magnet body, Nd, specific examples of the above _{compounds, FeTiO 3, Fe 2 TiO 5} , Fe 2 Ti 4 O, FeTi, Nd 2 Ti 2 O 7, Ti 2 B, TiO, Ti 2 O ₃ , TiO _{2 and the} like.

Furthermore, Patent Document 5 describes a rare earth magnet in which a coating made of a metal oxide is formed on the surface of a magnet body by a sol-gel method for the purpose of improving the corrosion resistance or alkali resistance of the magnet.
JP 59-46008 A JP-A-60-9852 JP-A-63-192216 JP 63-168209 A JP 2001-76914 A

  The rare earth magnet provided with the conventional protective layers including the above Patent Documents 3 to 5 has higher corrosion resistance than the case where the magnet element body is used alone. However, when the present inventors examined these conventional rare earth magnets in detail, these rare earth magnets have insufficient corrosion resistance due to their insufficient function as a protective layer. It has become clear that it is still not practical for applications where severe conditions such as these are imposed.

  For example, in the method for producing a rare earth magnet described in Patent Document 3, it is necessary to dry a coating liquid composed of a specific organic compound or a solution thereof after applying it to the magnet surface. Reaction, thermal decomposition reaction, etc. proceed. Therefore, volume shrinkage occurs while the coating liquid is dried to obtain the protective layer, and stress is generated inside the resulting protective layer, and cracks are likely to occur due to the stress. When cracks occur in the protective layer, corrosion-causing substances (oxygen, moisture, salt water, sulfides, etc.) easily enter from the cracks. For example, a rare earth magnet is placed in an environment of 80 ° C. and 90% RH (relative humidity). Corrosion resistance of the entire magnet is significantly reduced by corrosion accelerated tests in which the degree of corrosion is examined after exposure for a predetermined time, such as corrosion of the magnet body.

  Further, the protective layer obtained by the method for producing a rare earth magnet described in Patent Document 4 is subjected to heat treatment in an inert atmosphere, and stress due to volume shrinkage, which is the same cause as in Patent Document 3, is generated inside the protective layer. As a result, the corrosion resistance of the entire magnet is significantly reduced. Furthermore, since the heat treatment is performed at a temperature of 700 ° C. or higher, the obtained protective layer has high crystallinity, and corrosion factors such as moisture and sulfide existing in the external atmosphere from the grain boundaries between the crystals. It becomes easy to invade. From this point of view, the corrosion resistance of the entire magnet is significantly reduced.

  Furthermore, in the rare earth magnet described in Patent Document 5, the sol solution for film formation is heated during the formation of the protective layer, thereby causing solvent evaporation, polymerization or thermal decomposition reaction. By passing, the applied sol liquid tends to cause a large volume shrinkage. Therefore, the protective layer is likely to crack due to this, and the corrosion resistance of the entire magnet is significantly reduced.

  The present invention has been made in view of the above circumstances, and provides a rare earth magnet exhibiting sufficiently high corrosion resistance by providing a protective layer having sufficiently excellent protective properties on its surface, and a method for manufacturing the same. With the goal.

  The rare earth magnet of the present invention that solves the above problems comprises a magnet element containing a rare earth element and a protective layer formed on the surface of the magnet element and containing a titanium compound having a peroxo group. It is characterized by.

  The rare earth magnet of the present invention is a first substrate for preparing a first substrate obtained by coating a magnet body containing a rare earth element and a coating solution containing a peroxotitanic acid aqueous solution on the surface of the magnet body. And a protective layer formed on the surface of the magnet body through a preparation step and a drying step of drying the coating solution under a predetermined temperature condition. The protective layer provided in the rare earth magnet is formed on the surface of the magnet body by drying the coating liquid applied on the surface of the magnet body and volatilizing and removing the liquid component. It contains a titanium compound having a peroxo group as its constituent component.

Here, the “peroxotitanic acid aqueous solution” is prepared by adding hydrogen peroxide (H ₂ O ₂ ) to a titanic acid suspension or a peroxotitanium hydrate suspension prepared from an aqueous titanium salt solution. It is. “Peroxotitanium hydrate” is a solid compound that is amorphous at room temperature, usually represented by the chemical formula of Ti ₂ O ₅ (OH) ₂ . The “predetermined temperature condition” means that the liquid component in the coating solution can be volatilized and removed, and even if titanium oxide is generated by the decomposition of peroxotitanium hydrate, at least the coating solution of the titanium oxide is used. This refers to a temperature condition that does not cause crystallization of the material existing in contact with the magnet body.

  In the sol-gel method, which is a conventional wet film formation method, when the coating solution on the surface of the magnet body is dried to form a protective layer, the solvent evaporates from the coating solution and the polycondensation reaction proceeds rapidly. To do. As a result, the protective layer obtained is inferior in flexibility and cannot easily relieve shrinkage stress, so that cracks are likely to occur. On the other hand, in the method for producing a rare earth magnet of the present invention, even when the protective layer on the surface of the magnet body is dried and the solvent is evaporated, the flexible structure is maintained at that point, Even if this occurs, it can be easily mitigated.

  In addition, the peroxotitanium hydrate produced in the drying process gradually changes into an oxide. In this case, since the volumetric shrinkage rate from peroxotitanium hydrate to titanium oxide is small, the shrinkage stress originally generated along with the volumetric shrinkage is very small compared to the conventional case.

  As a result, cracks are hardly generated in the protective layer when the rare earth magnet of the present invention is used, and the corrosion resistance of the rare earth magnet is sufficiently excellent. In particular, the effect of suppressing the occurrence of cracks is greater when the coating solution to be applied at once is thicker or the surface of the magnet body on which the coating solution is formed is more uneven. Therefore, the effect of corrosion resistance as compared with the conventional rare earth magnet appears more remarkably.

  Further, since the rare earth magnet of the present invention includes a protective layer having sufficiently high density and excellent adhesion to the magnet body, from such a viewpoint, a rare earth magnet having sufficiently high corrosion resistance can be obtained. Become.

The titanium compound having a peroxo group contained in the protective layer according to the present invention is derived from a peroxotitanium hydrate having a chemical structure represented by the following formula (1), and may contain a hydroxyl group. . That is, the titanium compound of the present invention may be a compound composed of a titanium atom and an oxygen atom such as a titanium oxide and / or a compound composed of a titanium atom, an oxygen atom and a hydrogen atom such as a titanium hydroxide. . It is presumed that the protective layer containing a titanium compound having such a peroxo group is sufficiently excellent in flexibility.

  In addition, peroxotitanium hydrate has two hydroxyl groups at both ends as represented by the above formula (1). Adhesion between the magnet body and the protective layer by hydrogen bonding of these hydroxyl groups to oxygen or hydroxyl groups present on the surface of the magnet body, or by covalently bonding with hydroxyl groups on the surface of the magnet body. Is considered to be sufficiently high.

  Further, for example, when a protective layer is formed by a sol-gel method as disclosed in Patent Document 5, a coating solution containing an acid catalyst used for a hydrolysis reaction of a metal alkoxide is applied on the surface of a magnet body. It is necessary to apply. However, since the magnet body containing the rare earth element according to the present invention tends to be particularly inferior in acid resistance, when the above-described sol-gel method is adopted for forming the protective layer, the magnet body becomes an acid by the coating solution. Corrosion will occur. On the other hand, the peroxotitanic acid aqueous solution used when forming the protective layer of the rare earth magnet of the present invention is substantially neutral to weakly basic. Therefore, the magnet body is not subjected to acid corrosion as described above when forming the protective layer, and the obtained rare earth magnet can have desired magnetic properties (coercive force, residual magnetic flux density, etc.).

  In addition, since metal alkoxides used in the sol-gel method cause hydrolysis or polymerization reaction relatively easily, the chemical stability of the coating solution used for forming the protective layer by the sol-gel method is low and tends to be difficult to handle. It is in. On the other hand, the aqueous peroxotitanic acid solution according to the present invention has very high stability and safety. Therefore, the peroxotitanic acid aqueous solution is easy to handle and requires less labor when forming the protective layer. Therefore, the rare earth magnet of the present invention tends to be very excellent from the viewpoint of mass productivity and manufacturing cost.

  Furthermore, when it is going to form a protective layer by the method as described in patent document 4, it is necessary to heat at 700 degreeC or more (patent document 4) or 400 degreeC or more. However, such heating is not preferable because the various magnetic properties of the magnet body tend to be significantly reduced as compared to before the protective layer is formed. On the other hand, when the protective layer of the rare earth magnet of the present invention is formed, if it is heated and dried to about 200 ° C. at the highest, the resulting protective layer has a very high density. Therefore, the rare earth magnet of the present invention has sufficiently excellent corrosion resistance, and at the same time, the provided magnet body maintains sufficiently high magnetic properties.

The rare earth magnet of the present invention is a first substrate preparation step of preparing a first substrate obtained by applying a magnet body containing a rare earth element and a coating solution containing a peroxotitanic acid aqueous solution on the surface of the magnet body. And a protective layer formed on the surface of the magnet body by passing through the drying ultraviolet irradiation step of irradiating the coating liquid with ultraviolet rays simultaneously with drying the coating liquid under a predetermined temperature condition. Features. The protective layer provided in the rare earth magnet is used to dry the coating liquid applied on the surface of the magnet body, volatilize and remove the liquid component, and to irradiate the coating liquid with ultraviolet rays to thereby surface the magnet body. It is formed on the top. As its constituent component, peroxotitanium hydrate is partly polycondensed and may contain amorphous titanium oxide (such as TiO ₂ ). There may be no.

  In the rare earth magnet of the present invention, the protective layer is further densified due to the decomposition of peroxo groups in the coating solution or in the dry film generated during drying by ultraviolet light. As a result, the protective layer obtained through the dry ultraviolet irradiation process has further improved protective properties, and thus the corrosion resistance of the rare earth magnet tends to be further improved. Furthermore, it is considered that amorphous titanium oxide is generated in the protective layer through the dry ultraviolet irradiation process. By containing this amorphous titanium oxide, the protective layer tends to be harder. In addition, the protective layer also contains the above-described titanium oxide having a peroxo group, and has both high flexibility and hardness.

  From such a point of view, the rare earth magnet of the present invention includes a protective layer formed by performing an ultraviolet irradiation step of irradiating an ultraviolet ray onto a dry film obtained by drying the coating liquid in the drying step described above. Also good.

  Further, the rare earth magnet of the present invention may be provided with a protective layer further containing a titanium oxide not having a peroxo group, such as crystalline titanium oxide such as anatase, in which case it is contained in the protective layer. Among the titanium oxides, at least those present in contact with the magnet body are preferably amorphous. Thereby, it is possible to sufficiently effectively suppress the magnet body from being oxidized by the photocatalytic action of crystalline titanium oxide. By sufficiently suppressing the oxidation of the magnet body, the obtained rare earth oxide can maintain sufficiently high magnetic properties over a long period of time, coupled with the improvement in corrosion resistance due to the provision of the protective layer.

  The protective layer provided in the rare earth magnet of the present invention preferably has a thickness of 0.2 to 3 μm. Rare earth magnets including conventional protective layers such as those described above do not have sufficient denseness of the protective layer and / or adhesion between the magnet body and the protective layer. Therefore, when the protective layer is set to such a film thickness, pinholes are generated in the protective layer, or there is a tendency that a gap is generated between the protective layer and the magnet body. When such pinholes or gaps are generated, corrosion-causing substances existing in the ambient atmosphere of the rare earth magnet enter from there, and thus the rare earth magnet tends not to exhibit sufficiently excellent corrosion resistance. In addition, if the protective layer is made thicker, the above-mentioned lack of denseness can be compensated, but cracks in the protective layer as described above tend to occur. It tends to be difficult to make it sufficient.

  On the other hand, since the rare earth magnet of the present invention has sufficient denseness of the protective layer and sufficient adhesion to the magnet body, it has sufficient resistance to corrosion even within the thickness range of the protective layer. is there. Furthermore, in the rare earth magnet of the present invention, the occurrence of cracks is further suppressed by making the thickness of the protective layer within the above range. Therefore, such rare earth magnets tend to maintain sufficiently excellent corrosion resistance for a longer period.

  The method for producing a rare earth magnet of the present invention includes a first substrate preparation step of preparing a first substrate by coating a coating solution containing a peroxotitanic acid aqueous solution on the surface of a magnet body containing a rare earth element; A protective layer is formed on the surface of the magnet body through a drying step of drying the coating solution under a predetermined temperature condition.

  In addition, the method for producing a rare earth magnet of the present invention provides a dry film obtained by drying a coating solution containing a peroxotitanic acid aqueous solution under a predetermined temperature condition on the surface of a magnet body containing a rare earth element. A protective layer is formed on the surface of the magnet body through a second substrate preparation step of preparing a second substrate provided and an ultraviolet light irradiation step of irradiating the dried film with ultraviolet light. .

  Furthermore, in the method for producing a rare earth magnet of the present invention, a first substrate preparation step of preparing a first substrate by applying a coating solution containing an aqueous peroxotitanic acid solution on the surface of a magnet body containing a rare earth element. And a drying ultraviolet irradiation step of irradiating the coating liquid with ultraviolet rays simultaneously with drying the coating liquid under a predetermined temperature condition, and forming a protective layer on the surface of the magnet body .

  By using these manufacturing methods, a rare earth magnet having sufficiently excellent corrosion resistance as described above can be obtained. In that case, the protective layer is preferably composed of a compound composed of a titanium atom and an oxygen atom and / or a compound composed of a titanium atom, an oxygen atom and a hydrogen atom. In particular, it is more preferable that the titanium compound is amorphous because the corrosion resistance is further improved.

  According to the present invention, it is possible to provide a rare earth magnet that has a protective layer having sufficiently excellent protective properties on its surface and thereby exhibits sufficiently high corrosion resistance, and a method for manufacturing the same.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as necessary. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

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

  FIG. 1 is a schematic perspective view showing a rare earth magnet according to this embodiment, and FIG. 2 is a diagram schematically showing a cross section that appears when the rare earth magnet of FIG. 1 is cut along the line II. As is clear from FIGS. 1 and 2, the rare earth magnet 100 of this embodiment includes a protective layer 20 that is formed by covering the entire surface of the magnet body 10.

  The magnet body 10 contains R, iron (Fe), and boron (B). R represents one or more rare earth elements, specifically, one or more selected from the group consisting of scandium (Sc), yttrium (Y) and lanthanoids belonging to Group 3 of the long-period periodic table. Indicates an element. 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 composition of the above-described elements in the magnet body 10 is preferably as described below when the magnet body 10 is manufactured by a sintering method.

  R preferably includes one or more elements of Nd, Pr, Ho, and Tb among those described above, and further includes 1 of La, Sm, Ce, Gd, Er, Eu, Tm, Yb, and Y. It is also preferable to include more than one element.

  The content ratio of R in the magnet body 10 is preferably 8 to 40 atomic% with respect to the total amount of atoms constituting the magnet body 10. When the content ratio of R is less than 8 atomic%, the crystal structure has a cubic structure having the same structure as that of α-iron. Therefore, the rare earth magnet 100 having a high coercive force (iHc) tends not to be obtained. Further, when the content ratio of R exceeds 30 atomic%, 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 atomic% with respect to the total amount of atoms constituting the magnet body 10. If the Fe content is less than 42 atomic%, the Br of the rare earth magnet 100 tends to decrease, and if it exceeds 90 atomic%, the iHc of the rare earth magnet 100 tends to decrease.

  The content ratio of B in the magnet body 10 is preferably 2 to 28 atomic% with respect to the total amount of atoms constituting the magnet body 10. If the B content is less than 2 atomic%, the crystal structure has a rhombohedral structure, so the iHc of the rare earth magnet 100 tends to be insufficient. If it exceeds 28 atomic%, there are many B-rich nonmagnetic phases. Therefore, the Br of the rare earth magnet 100 tends to decrease.

  Further, the magnet body 10 may be configured by replacing part of Fe with cobalt (Co). By adopting such a configuration, the temperature characteristics tend to be improved without impairing the magnetic characteristics of the rare earth magnet 100. In this case, the content ratio of Fe and Co after substitution is preferably such that Co / (Fe + Co) is 0.5 or less on an atomic basis. If the amount of substitution of Co is larger than this, the magnetic properties of the rare earth magnet 100 tend to deteriorate.

  Furthermore, even if a part of B is replaced with one or more elements selected from the group consisting of carbon (C), phosphorus (P), sulfur (S), and copper (Cu), the magnet body 10 is configured. Good. By adopting such a configuration, the productivity of the rare earth magnet 100 is improved and the production cost tends to be reduced. In this case, the content of C, P, S and / or Cu is preferably 4 atom% or less with respect to the amount of all atoms constituting the magnet body 10. When the content of C, P, S and / or Cu is more than 4 atomic%, the magnetic properties of the rare earth magnet 100 tend to deteriorate.

  Further, from the viewpoint of improving the coercive force of the rare earth magnet 100, improving productivity, and reducing the cost, 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 ( The magnet body 10 may be configured by adding one or more elements of Si), gallium (Ga), copper (Cu), and / or hafnium (Hf). In this case, it is preferable that the addition amount of the element is 10 atomic% or less with respect to the total amount of atoms constituting the magnet body 10. When the addition amount of these elements exceeds 10 atomic%, the magnetic properties of the rare earth magnet 100 tend to deteriorate.

  In the magnet body 10, oxygen (O), nitrogen (N), carbon (C), and / or calcium (Ca), etc. as unavoidable impurities are included in the amount of all atoms constituting the magnet body 10. And may be contained within a range of 3 atomic% or less.

  As shown in FIG. 3, the magnet body 10 includes a main phase 50 having a substantially tetragonal crystal structure, a rare earth-rich phase 60 containing a relatively large amount of rare earth elements, and a boron rich material containing a relatively large amount of boron. And the phase 70 is formed. The particle size of the main phase 50 which is a magnetic phase is preferably about 1 to 100 μm. The rare earth-rich phase 60 and the boron-rich phase 70 are nonmagnetic phases and exist mainly at the grain boundaries of the main phase 50. These nonmagnetic phases 60 and 70 are usually contained in the magnet body 10 by about 0.5 volume% to 50 volume%.

  The magnet body 10 is prepared, for example, by being manufactured by a sintering method as described below. First, a desired composition containing the elements described above is cast to obtain an ingot. Subsequently, 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 powder. .

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

  Subsequently, the obtained 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 as described above is obtained by performing heat treatment (aging treatment) at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere.

  In addition to the above, the magnet body 10 can be prepared by, for example, a well-known super rapid cooling method, a warm brittle processing method, a casting method, or a mechanical alloying method. Further, a commercially available magnet body 10 may be prepared.

  The protective layer 20 contains a titanium compound having a peroxo group, and is obtained by a method for producing a rare earth magnet described below.

  As shown in FIG. 4, the manufacturing method of the rare earth magnet 100 according to the preferred first embodiment of the present invention includes a first base preparation step S10 and a drying step S3. Furthermore, the first substrate preparation step S10 includes a step of preparing a coating solution containing a peroxotitanic acid aqueous solution (peroxotitanic acid aqueous solution preparation step) S1 and a magnet body prepared by using the obtained coating solution as described above. Application process S2 apply | coated on the surface of 10. FIG.

  In the peroxotitanic acid aqueous solution preparation step S1, the peroxotitanic acid aqueous solution is prepared according to Ichinose, M. Terasaki and H. Katsuki, J. Ceram. Soc. Japan, 104, 715 (1996), H. Ichinose, A. Kawahara and H. Katsuki, J. Ceram. Soc. Japan, 104, 914 (1996), H. Ichinose and H. Katsuki, J. Ceram. Soc. Japan, 106, 344 (1998), Hiromichi Ichinose, Ceramics, 36, 586 (2001) ), Or the method described in H. Ichinose, M. Terasaki and H. Katsuki, J. Sol-Gel Sci. Tech., 22, 33 (2001) or a method analogous thereto. Below, the suitable preparation method of peroxotitanic acid aqueous solution is demonstrated.

  The aqueous solution of peroxotitanic acid according to this embodiment is obtained by adding a basic substance having an excess hydroxyl group to the molar amount of titanium to a solid titanium compound made of metal titanium, titanium oxide or titanium hydrate, and further Removal treatment of titanium ions, titanium-containing ions and cations other than hydrogen ions in the aqueous solution generated after dissolution by the action of hydrogen oxide water, and decomposition treatment of excess hydrogen peroxide present in the solution It is obtained by carrying out the treatment a plurality of times while maintaining the pH of the aqueous solution at 3-10. The thus obtained peroxotitanic acid aqueous solution of the present embodiment has, for example, a cation concentration other than titanium ion, titanium-containing ion, and hydrogen ion in the aqueous solution that is ½ or less of the titanium concentration. A peroxo group is stably present.

  Conventionally, aqueous solutions obtained by adding a basic substance and hydrogen peroxide solution to titanium compounds such as titanium, titanium oxide, and titanium hydrate are generally transparent for several minutes to several days after the solution is prepared. The state of the correct solution. However, the degree varies depending on the type and amount of the basic substance used for dissolution, or the amount of hydrogen peroxide solution added, but over time, the aqueous solution becomes cloudy or gelled, which is unstable. There was a tendency to become something. Moreover, although this aqueous solution can be stored by cooling, it tends to be unsuitable for long-term storage.

  Such instability of the titanium-containing aqueous solution is caused by the basic substance remaining in the aqueous solution and hydrogen peroxide. Therefore, when the peroxotitanic acid aqueous solution of this embodiment is prepared, the basicity in the aqueous solution is reduced. The basic substance is removed from the aqueous solution so as to bring the substance to a predetermined concentration or less, and hydrogen peroxide is decomposed to finally obtain a stable protective layer 20.

  In the method for preparing a peroxotitanic acid aqueous solution according to the present embodiment, by maintaining the pH of the aqueous solution at 3 or more, the titanium component is sufficiently left in the aqueous solution, and the titanium ions and titanium-containing ions in the aqueous solution are also retained. In addition, cations other than hydrogen ions can be removed. In other words, titanium dissolved in a titanium-containing solution prepared by adding a basic substance having an excess hydroxyl group to titanium and hydrogen peroxide exists in the form of an anion composed of a complex having a hydroxyl group bonded thereto. It is thought that. Therefore, after adding substances that exchange or capture cations such as cation exchange resin and zeolite into the solution, these substances are removed, so that dissolved titanium is present in the solution without affecting it. Cations derived from basic substances can be removed.

  However, when the cation derived from the basic substance is removed by a cation exchange resin or the like, the pH of the aqueous solution changes with the ion exchange between the cation derived from the basic substance and the hydrogen ion. When the pH is lower than a certain value, titanium-containing ions such as peroxotitanate ions in the aqueous solution become cations such as titanium ions, and are captured by the cation exchange resin and the titanium is removed from the aqueous solution. It will end up. Therefore, the removal of the cation derived from the basic substance in the solution needs to be performed by adjusting the pH of the aqueous solution to 3 or more, and the pH is more preferably 4 or more.

  Further, in the decomposition treatment of hydrogen peroxide added excessively in the solution, when hydrogen peroxide is rapidly decomposed, there is a tendency that the pH is increased or the dissolved titanium compound is precipitated. Therefore, the pH of the aqueous solution needs to be adjusted so as not to increase to 10 or more, and more preferably adjusted so as not to increase to 9 or more.

  In order to make it possible to adjust the pH as described above, in the present embodiment, the basic substance is maintained so that the pH of the aqueous solution in the removal process of the basic substance and the decomposition process of hydrogen peroxide is maintained within a predetermined range. It is preferable to carry out the removal of the cation derived therefrom and the decomposition of hydrogen peroxide in several steps.

  A more specific example of the method for preparing the peroxotitanic acid aqueous solution of the present embodiment is illustrated below.

  First, a cation exchange resin is added to a titanium-containing aqueous solution obtained by adding a basic substance and a hydrogen peroxide solution to metal titanium or a titanium compound containing titanium and hydrogen or oxygen, and pH Is removed in the state of 3 to 6 weak acid or in the neutral range (cation removal treatment).

  Next, the obtained titanium-containing aqueous solution is allowed to stand as it is within a range in which the pH can be maintained at 7 to 10, stirred, ultrasonically irradiated or heat-treated to decompose hydrogen peroxide (hydrogen peroxide decomposition treatment). .

  Thereafter, a desired peroxotitanic acid aqueous solution can be obtained by repeating the above-described cation removal treatment and hydrogen peroxide decomposition treatment an appropriate number of times.

  In the initial removal treatment of the cation derived from the basic substance, it is preferable to adjust the pH in the titanium-containing aqueous solution within a range of about 3 to 6, and it is more preferable to adjust it to a range of 4 to 6. Thereby, it exists in the tendency which can suppress inhibition of the cation removal by the influence of the hydrogen peroxide which exists in a solution in large quantities.

  In the initial decomposition treatment of hydrogen peroxide, it is preferable to adjust the pH in the titanium-containing aqueous solution to about 7 to 9. Thereby, since precipitation of a polymer of peroxotitanium hydrate when a large amount of hydrogen peroxide is decomposed can be suppressed, the protective layer 20 having a more uniform film thickness and / or film quality tends to be obtained. This tendency leads to further improving the corrosion resistance of the rare earth magnet 100 finally obtained.

  The cation removal treatment and hydrogen peroxide decomposition treatment repeated as described above may cause loss of titanium in the titanium-containing aqueous solution or precipitation of peroxotitanium hydrate forming a polymer. If there is no such, it is preferable for the same reason as above. From such a viewpoint, the concentration of the cation derived from the basic substance in the obtained aqueous solution is preferably small with respect to the titanium concentration, and more preferably half or less.

  Examples of the titanium metal or titanium compound used in the present embodiment include titanium compounds containing hydrogen or oxygen such as metal titanium obtained from a titanium mineral or the like, or titanium dioxide. In addition, from a titanium hydrate or titanium oxide obtained by adding a hydrogen peroxide solution to an aqueous solution of a soluble titanium compound such as titanium tetrachloride and then adding a basic substance such as ammonia water, chloride ions, etc. What was obtained by removing the anion of may be used.

  In the present embodiment, examples of the basic substance used for dissolving metallic titanium or a titanium compound include ammonia water, an aqueous alkali metal hydroxide solution, and an aqueous tetraalkylammonium solution. Among these, when forming the protective layer by applying the obtained peroxotitanic acid aqueous solution on the surface of the magnet body 10, it can be removed relatively easily by volatilization or decomposition. It is preferable to use a material that does not contain any metal element, and it is particularly preferable to use ammonia water.

  The amount of the basic substance used for dissolving the metal titanium or the titanium compound is preferably 2 times or more, more preferably 4 times or more the molar amount of titanium in the titanium-containing aqueous solution. Moreover, when using the titanium compound which does not contain a hydroxyl group, it is preferable that the quantity of the basic substance is 4 times or more of a titanium compound, and it is more preferable that it is 6 times or more. The cation removal treatment and the hydrogen peroxide removal treatment may be performed at room temperature or may be performed by heating.

In the present embodiment, the cation derived from the basic substance is removed by using, for example, electrodialysis using an ion exchange membrane, dialysis, reverse osmosis or the like, in addition to using a cation exchange resin such as H ⁺ substitution type or zeolite. A method may be adopted.

  In the present embodiment, the concentration of the cation in the aqueous solution does not mean the concentration of the dissociated in the aqueous solution, but is measured in the analysis even if it is not dissociated or coordinated. It shall refer to the total concentration of what is being done. Similarly, regarding the titanium concentration, it refers to the total concentration of titanium present in the solution regardless of the form in which the solution is present.

  The method for measuring the cation concentration in the aqueous solution is not particularly limited as long as it is a known method. For example, a method in which a color-forming compound whose color intensity changes depending on the cation concentration and absorption spectroscopy is used. Can be mentioned. The method for measuring the titanium concentration in the aqueous solution is not particularly limited as long as it is a conventionally known method. For example, an ICP emission analysis method can be used.

  In the application step S <b> 2, the above-described peroxotitanic acid aqueous solution is applied onto the surface of the magnet body 10. As a coating method, any conventionally known method can be adopted without any particular limitation. Specific examples include a dip coating method, a spray coating method, and a spin coating method.

  At this time, the application of the coating liquid is preferably adjusted in consideration of solvent volatilization or volume shrinkage in the drying step described later so that the film thickness of the protective layer 20 to be obtained has a desired value. For example, when the application is performed by the dip coating method, the thickness of the applied application liquid can be adjusted by immersing the magnet body 10 in the application liquid and appropriately setting the pulling speed and time.

  In addition, from the viewpoint of easily performing such application and improving the adhesion of the protective layer 20 to be formed, a predetermined treatment is performed on the surface of the magnet body 10 before performing the application process. Is desirable. As this predetermined treatment, for example, after the surface of the magnet body 10 is smoothed by barrel polishing or the like, the surface of the body is degreased and further cleaned with an acid solution or washed with water, etc. Thus, the magnet body 10 having the following can be obtained.

  In this way, the 1st base | substrate formed by apply | coating a coating liquid on the surface of the magnet element | base_body 10 is obtained.

  In the drying step S3, the coating liquid applied on the surface of the magnet body 10 in the coating step S2 is dried under a predetermined temperature condition. As a drying method, any known method can be employed without any particular limitation. Specifically, for example, a method in which the first base is placed on a heating base with a built-in heater and dried by heating, or from above the coating solution applied to the magnet body 10 (on the side opposite to the magnet body 10). And a method of heating and drying by irradiating the coating liquid with radiant heat.

  The predetermined temperature (drying temperature) in the drying step S3 can volatilize and remove the liquid component in the coating solution, and even if titanium oxide is generated by the decomposition of peroxotitanium hydrate, at least coating of the titanium oxide is performed. Although it will not specifically limit if what exists in contact with the magnet element body in a liquid does not raise | generate crystallization, It is preferable in it being 30-300 degreeC. If the drying temperature is below this lower limit, the drying time tends to be too long, which is not preferable from the viewpoint of mass productivity or manufacturing cost. Further, when the drying temperature exceeds the upper limit value, titanium oxide is generated and the crystallization of titanium oxide tends to be promoted, and the corrosion resistance of the obtained rare earth magnet 100 tends to be lowered. Furthermore, when the drying temperature is 100 to 250 ° C., the resulting protective layer 20 tends to become more dense and further suppress crystallization of titanium oxide or the like. Note that whether or not solid crystals are present in the dry film (protective layer) can be confirmed by X-ray diffraction (XRD) or the like.

  In the drying step S3, the drying temperature may be maintained at a desired constant temperature within the above temperature range, or the drying temperature may be appropriately changed within the above temperature range. For example, in the drying step S3, first, the drying temperature is set to about 30 ° C., and a certain amount of liquid components are volatilized and removed. Then, the drying temperature is set to about 150 ° C. and further dried. By this further drying, the peroxo group present in the dried film is decomposed, and the resulting protective layer 20 tends to be hardened while improving the denseness.

In this way, a dry film, that is, a protective layer 20 containing a titanium compound having a peroxo group is formed on the surface of the magnet body 10, and the rare earth magnet 100 according to the first embodiment of the present invention is obtained. In addition, the presence of the titanium compound having a peroxo group in the protective layer 20 may be confirmed by having a peak in the vicinity of 890 cm ^{−1 of a} spectrum obtained by FT-IR (Fourier transform infrared spectroscopy). it can.

  The thickness of the protective layer 20 is preferably 0.2 to 3 μm, and more preferably 0.5 to 2 μm. If the thickness of the protective layer 20 is less than this lower limit value, it tends to be extremely difficult to sufficiently cover the magnet surface. As a result, the corrosion resistance of the obtained rare earth magnet 100 tends to decrease. On the other hand, when the film thickness exceeds the above upper limit value, cracks and peeling are likely to occur in the protective layer 20, and the reliability as the protective layer 20 tends to decrease. In addition, the film thickness of the protective layer 20 in this case shall mean the average film thickness of the protective layer 10 formed on the surface of the magnet body 10.

  Moreover, as shown in FIG. 5, the manufacturing method of the rare earth magnet 100 according to the second preferred embodiment of the present invention includes a second substrate preparation step S20 and an ultraviolet irradiation step S4. Furthermore, the second substrate preparation step S20 includes a peroxotitanic acid aqueous solution preparation step S1 similar to that in the first embodiment and an application step S2 similar to that in the first embodiment. Here, the second substrate is obtained through the drying step S <b> 3, and is provided with a dry film on the surface of the magnet body 10.

  In the ultraviolet irradiation step S4, the dry film is irradiated with ultraviolet rays. The protective layer 20 obtained through this step S4 tends to be harder and more dense because some of the peroxo groups in the dried film are decomposed to produce amorphous titanium oxide. . Therefore, the obtained rare earth magnet 100 has a tendency to further improve the corrosion resistance because it is difficult for an external corrosion factor substance to enter the magnet body 10 through the protective layer 20.

  The ultraviolet ray irradiation method is not particularly limited as long as it is a known method, and examples thereof include an excimer lamp and a mercury lamp.

  Furthermore, the method for manufacturing the rare earth magnet 100 according to the preferred third embodiment of the present invention includes, as shown in FIG. 6, a first substrate preparation step S10 similar to the first embodiment and a dry ultraviolet irradiation step S5. I have it. In the drying ultraviolet irradiation step S5, the coating liquid applied on the surface of the magnet body 10 is dried under a predetermined temperature condition similar to that in the drying step S2, and at the same time as in the ultraviolet irradiation step S4. The coating solution is irradiated with ultraviolet rays by the above irradiation method. When this manufacturing method is used, the resulting rare earth magnet 100 tends to have further improved corrosion resistance, as in the manufacturing method of the rare earth magnet 100 according to the second embodiment.

  In the rare earth magnet 100 of the preferred embodiment of the present invention described above, even if the protective layer 20 on the surface of the magnet body 10 is dried to evaporate the solvent, a flexible structure is maintained at that time. Therefore, even if stress occurs in the protective layer 20, it can be easily relaxed. In addition, the peroxotitanium hydrate produced in the drying process gradually changes into an oxide. In this case, since the volumetric shrinkage rate from peroxotitanium hydrate to titanium oxide is small, the shrinkage stress originally generated along with the volumetric shrinkage is very small compared to the conventional case. Furthermore, since the protective layer is obtained by drying the coating solution under the predetermined temperature condition, the titanium compound having a peroxo group contained therein has higher flexibility than titanium oxide. Therefore, even if stress occurs in the protective layer 20, the stress can be relaxed with high flexibility. As a result, cracks are unlikely to occur in the protective layer 20, so that the corrosion resistance of the rare earth magnet 100 of this embodiment is sufficiently excellent.

  In particular, when the thickness of the coating liquid applied at one time becomes thicker or the surface of the magnet body 10 on which the coating liquid is formed is more uneven, the effect of suppressing the occurrence of cracks is more pronounced. Since it becomes large, the effect of the corrosion resistance compared with the conventional rare earth magnet appears more remarkably.

  Furthermore, since the rare earth magnet 100 of the present embodiment includes the protective layer 20 having sufficiently high density and excellent adhesion to the magnet body 10, the corrosion resistance is sufficient from such a viewpoint. It will be expensive.

  Moreover, since the above-mentioned peroxotitanic acid aqueous solution has very high stability and safety, it is easy to handle and requires less labor when forming the protective layer 20. Therefore, the rare earth magnet 100 obtained using such an aqueous solution of peroxotitanic acid tends to be very excellent from the viewpoint of mass productivity and manufacturing cost.

  Furthermore, when the rare earth magnet 100 of this embodiment forms the protective layer 20, if it heat-drys at about 200 degreeC at the highest, the protective layer 20 obtained will become the thing excellent in the density | concentration very much. Therefore, since the rare earth magnet 100 has sufficiently excellent corrosion resistance and does not require heating at a relatively high temperature, the magnet body 10 maintains sufficiently high magnetic characteristics.

  Rare earth magnets are used for line printers, automotive starters and motors, special motors, servo motors, disk drives for magnetic recording devices, linear actuators, voice coil motors, motors for devices, industrial motors, speakers and nuclear magnetic resonance diagnostics. Such as a magnet. In particular, when used in an environment where oil such as an automobile motor is splashed, it is difficult to obtain a rare earth magnet having sufficiently excellent corrosion resistance if the protective layer has only oxidation resistance. Also in this point of view, the rare earth magnet 100 obtained according to the present embodiment has resistance to various corrosion factors such as oxygen, moisture, salt water, sulfides, etc., and therefore has sufficiently excellent corrosion resistance. It is.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, instead of the above-described peroxotitanic acid aqueous solution preparation step S1, a commercially available peroxotitanic acid aqueous solution may be prepared.

  In addition, in the peroxotitanic acid aqueous solution preparation step, in addition to the method of adding a basic substance to titanium metal or a titanium compound without performing a precipitation treatment, and further adding a hydrogen peroxide solution to obtain a peroxotitanic acid aqueous solution, By leaving or heating a titanium-containing aqueous solution in which titanium or a titanium compound is dissolved as it is, a precipitate of the titanium compound is deposited, and then washing is performed to reduce the cation derived from the basic substance to a desired concentration or less. After the reduction, a peroxotitanic acid aqueous solution may be obtained by further acting a hydrogen peroxide solution.

Other substances to be included in the protective layer include metal fine powders such as Al, Mg, Ca, Zn, Si, and Mn, metal oxide fine powders such as SiO ₂ , TiO ₂ , ZrO ₂ , and Al ₂ O ₃ , Examples thereof include resin components such as acrylic resin and epoxy resin, and clay minerals such as montmorillonite.

  Furthermore, the protective layer 20 does not have to be directly laminated on the magnet body 10. After preparing the magnet body 10, one or more functional layers are formed on the surface of the magnet body 10, and then In addition, the protective layer 20 may be formed on the surface of the outermost functional layer. The functional layer has a function of improving adhesion between the magnet body 10 and the protective layer 20 and a function of preventing excessive reaction between the magnet body 10 and the protective layer 20 (for example, titanium oxide is crystallized). And a function of preventing the magnet body 10 from being oxidized) and a function of controlling the surface roughness of the magnet body 10 are preferable. Examples of the constituent material include metals such as Al, Cr, Si, Ti and Ni, resins such as epoxy resins and polyimide resins, and metal oxides. As the formation method, a conventionally known dry method (evaporation method, sputtering method, etc.) or wet method (coating method, plating method, chemical conversion film method, etc.) can be employed.

  Further, a film having a further function may be formed on the surface of the protective layer 20. This makes it possible to adjust the wettability of the adhesive when adhering the magnets or to ensure the insulation of the surface of the magnet body.

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

( Reference Example 1)
A sintered body having a composition of 14Nd-1Dy-7B-78Fe (numbers are atomic ratio) prepared by powder metallurgy is heat-treated at 600 ° C. for 2 hours in an argon gas atmosphere, and then 56 × 40 × 8 (mm ) And then chamfered by barrel polishing to obtain a magnet body.

  Next, the magnet body was washed with an alkaline degreasing solution, then the surface was activated with an aqueous nitric acid solution, and then sufficiently washed with water.

  Next, a peroxotitanic acid aqueous solution (PTA-170, trade name, manufactured by Seiko Co., Ltd.) having a solid content concentration of 1.7% by mass is prepared and applied to the entire surface of the magnet body by a dip coating method ( Application step), a first substrate was obtained (first substrate preparation step).

Thereafter, the coating liquid applied on the surface of the magnet body was dried by heating at 200 ° C. for 20 minutes using an electric furnace (drying step) to form a protective layer, whereby the rare earth magnet of Reference Example 1 was obtained. . In addition, when the infrared spectrum was measured about the protective layer formed on the glass substrate on the same conditions using general purpose FT-IR, the peak was recognized by 890 cm < ^-1 > vicinity.

  About the protective layer of the obtained rare earth magnet, when the film thickness was measured by electron microscope observation, the average film thickness was 1.5 micrometers. Moreover, when the surface of the protective layer was observed using an electron microscope, no cracks or pinholes were confirmed.

When the rare earth magnet of Reference Example 1 was subjected to an accelerated corrosion resistance test under the conditions of 80 ° C. and 90% RH, generation of rust was not confirmed even after 200 hours from the start of the test.

(Comparative Example 1)
The coating solution used during the coating process, instead of the aqueous solution peroxotitanate, except that the one obtained by dissolving titanium tetraisopropoxide in 2-methoxy ethanol, in Comparative Example 1 in the same manner as in Reference Example 1 A rare earth magnet was obtained.

  When the film thickness of the protective layer of the obtained rare earth magnet was measured by observation with an electron microscope, the average film thickness was 1.0 μm. Moreover, when the protective layer surface was observed using the electron microscope, the crack was confirmed.

  The rare earth magnet of Comparative Example 1 was subjected to an accelerated corrosion resistance test under the conditions of 80 ° C. and 90% RH. After 200 hours had elapsed from the start of the test, generation of rust was confirmed in the magnet body.

It is a schematic perspective view which shows the rare earth magnet obtained by the manufacturing method of the rare earth magnet which concerns on embodiment of this invention. It is a schematic sectional drawing which shows the rare earth magnet obtained by the manufacturing method of the rare earth magnet which concerns on embodiment of this invention. It is a model enlarged view which shows the phase structure of a R-Fe-B type magnet. It is a flowchart of the manufacturing method of the rare earth magnet which concerns on 1st Embodiment. It is a flowchart of the manufacturing method of the rare earth magnet which concerns on 2nd Embodiment. It is a flowchart of the manufacturing method of the rare earth magnet which concerns on 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Magnet body, 20 ... Protective layer, 100 ... Rare earth magnet, S3 ... Drying process, S4 ... Ultraviolet irradiation process, S5 ... Dry ultraviolet irradiation process, S10 ... First base preparation process, S20 ... Second base preparation process.

Claims (4)

A second substrate for preparing a second substrate comprising a dry film obtained by drying a coating solution containing an aqueous peroxotitanic acid solution under a predetermined temperature condition on the surface of a magnet element body containing a rare earth element A preparation process;
An ultraviolet light irradiation step of irradiating the dry film with ultraviolet light;
Then, a protective layer is formed on the surface of the magnet body. A first substrate preparation step of preparing a first substrate by coating a coating solution containing a peroxotitanic acid aqueous solution on the surface of a magnet body containing a rare earth element;
A drying ultraviolet irradiation step of irradiating the coating liquid with ultraviolet rays simultaneously with drying the coating liquid under a predetermined temperature condition;
Then, a protective layer is formed on the surface of the magnet body. The protective layer is a titanium compound of titanium and oxygen atoms, and / or titanium atom, titanium compounds consisting of oxygen atom and hydrogen atom, according to claim 1 or 2, characterized in that the constituent materials A method for producing a rare earth magnet. The method for producing a rare earth magnet according to claim 3, wherein the titanium compound is amorphous.

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