JP4419245B2 - Rare earth permanent magnet and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rare earth permanent magnet having a thin and dense Zr oxide film on the surface of a magnet, which is excellent in corrosion resistance and alkali resistance, and a method for producing the magnet.
[0002]
[Prior art]
Rare earth permanent magnets such as R—Fe—B permanent magnets typified by Nd—Fe—B permanent magnets and R—Fe—N permanent magnets typified by Sm—Fe—N permanent magnets are Sm -Compared to Co-based permanent magnets, resource-rich and inexpensive materials are used, and because they have high magnetic properties, R-Fe-B-based permanent magnets are used in various fields today. Has been.
However, since rare earth permanent magnets contain highly reactive R, they are prone to oxidative corrosion in the atmosphere, and when used without surface treatment, corrosion proceeds from the surface due to slight acid and moisture effects. As a result, rust is generated, which causes deterioration and variation in magnet characteristics. Furthermore, when a magnet in which rust is generated is incorporated in an apparatus such as a magnetic circuit, the rust may be scattered to contaminate peripheral components.
In view of the above points, it has been proposed to form, for example, a Si oxide film, an Al oxide film, or a Ti oxide film as a corrosion-resistant film on the magnet surface (see JP-A-63-192216).
[0003]
[Problems to be solved by the invention]
In recent years, in the electronics industry and household electrical appliance industry in which rare earth permanent magnets are used, parts are downsized and downsized, and accordingly, the magnet itself is also required to be downsized and reduced in cost. In order to satisfy this requirement, the surface treatment of the magnet must be performed with higher dimensional accuracy (thinning, high corrosion resistance in the thin film), increasing the effective volume of the magnet, and at low cost.
Also, consideration for the environment is indispensable today, and it is necessary to consider the influence of the treatment liquid and the coating itself on the environment. In addition, as for the cleaning agent used for cleaning the magnet, an alkaline cleaning agent has attracted attention in place of the environmentally undesirable chlorine-based cleaning agent.
However, metal oxide coatings such as Si oxide coatings known so far have excellent corrosion resistance, but do not have sufficient alkali resistance, so that the coating deteriorates when washed with an alkaline detergent. As a result, there is a problem of causing deterioration of magnetic properties and rusting.
Accordingly, the present invention provides a rare earth-based permanent magnet having excellent corrosion resistance and alkali resistance, having a thin and dense coating on the surface of the magnet, and a simple manufacturing method of the magnet at low cost with little environmental impact. It is aimed.
[0004]
[Means for Solving the Problems]
In order to obtain a thin film having excellent corrosion resistance and alkali resistance, the present inventors have a high alkali resistance in addition to being dense in relation to a highly reactive rare earth magnet. As a result of various investigations from the viewpoint that it is important, it was found that excellent corrosion resistance and alkali resistance can be imparted by forming a Zr oxide film on the magnet surface.
[0005]
The present invention has been made on the basis of such knowledge, and the rare earth permanent magnet of the present invention is, as described in claim 1 , coated by thermal decomposition after applying a Zr compound solution having a viscosity of less than 100 cP to the magnet surface. A Zr oxide film that is amorphous and has a C content of 100 ppm to 1000 ppm (wt / wt) is directly formed as a corrosion-resistant and alkali-resistant film by a method (excluding the sol-gel method) ( However, except for a magnet in which another film is laminated on the Zr oxide film) .
The rare earth permanent magnet according to claim 2 is the rare earth permanent magnet according to claim 1, wherein the rare earth permanent magnet is an R-Fe-B permanent magnet.
The rare earth permanent magnet according to claim 3 is the rare earth permanent magnet according to claim 1, wherein the rare earth permanent magnet is an R-Fe-N permanent magnet .
Also, rare earth metal-based permanent magnet according to claim 4, wherein, in the rare earth metal-based permanent magnet according to claim 1及至6, wherein the thickness of the Zr oxide film is 0.01μm~5μm to.
Also, method for preparing a rare earth-based permanent magnet having a corrosion resistance and alkali resistance of the present invention, as claimed in claim 5, wherein, the coating thermal decomposition method viscosity magnet surface is heat treated after coating a solution of a Zr compound of less than 100cP (However, except for the sol-gel method) , an amorphous Zr oxide film having a C content of 100 ppm to 1000 ppm (wt / wt) is directly formed as a corrosion resistance and alkali resistance film (however, Excluding magnets in which another film is laminated on the Zr oxide film) .
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, as a method of forming a Zr oxide film on the surface of a rare earth-based permanent magnet, for example, a thermal decomposition reaction or a polymerization reaction is performed by applying a heat treatment after applying a Zr compound solution as a treatment liquid on the magnet surface. Examples include dry coating methods such as coating pyrolysis, plasma spraying, sputtering, vacuum deposition, and chemical vapor deposition to form a Zr oxide film. The method is not limited to the above method as long as the method is obtained.
However, the coating pyrolysis method can be performed with a simple apparatus, the stability of the treatment liquid is excellent, the water is not used at all, and thus the corrosion of the magnet during film formation can be prevented, and the treatment temperature is relatively high. Since it is low temperature, it can prevent the magnetic properties of the magnet from degrading at high temperature, can form a dense film with excellent corrosion resistance and alkali resistance despite being a thin film, and has few environmental problems. Convenient because it has.
[0007]
Hereinafter, a method of forming a Zr oxide film on the surface of the rare earth permanent magnet by the coating pyrolysis method will be described.
[0008]
The treatment liquid used in the coating pyrolysis method is a Zr compound solution.
Here, as the Zr compound, alkoxides such as ethoxide of Zr, propoxide, butoxide, oxalate, acetate, octylate, stearate, 2-ethylhexanoate, acrylate, naphthenic acid of Zr Carboxylates such as salts, chelate compounds (such as acetylacetonate) of Zr with β-diketones (such as acetylacetone) and β-keto acid esters (such as ethyl acetoacetate), inorganic salts such as nitrates and chlorides of Zr A salt, an ethanolamine complex of Zr, or the like can be used, but considering the stability and cost of the treatment liquid, an alkoxide having an alkoxyl group having 3 to 4 carbon atoms, such as Zr propoxide or butoxide, It is desirable to use carboxylates such as acetates and octylates.
[0009]
The mixing ratio of Zr compound to the treatment liquid is preferably in the range of 0.1wt% ~30wt% (ZrO ₂ conversion). If the blending ratio is less than 0.1 wt%, it may be necessary to repeat the film forming process many times in order to obtain a film thickness having sufficient performance. If the blending ratio exceeds 30 wt%, the viscosity of the treatment liquid increases. This is because film formation may be difficult.
[0010]
You may mix | blend a stabilizer with a process liquid as needed. Stabilizers are appropriately selected according to the chemical stability of the Zr compound used, β-diketones including acetylacetone, β-keto acid esters including ethyl acetoacetate, etc. Compounds that form chelates with Zr are desirable. By blending the stabilizer, in the actual mass production process, it is possible to prevent a change in the processing solution over time due to the reaction of the Zr compound with moisture in the air.
[0011]
For example, when β-diketone is used, the blending amount of the stabilizer is preferably 3 or less in terms of molar ratio (stabilizer / Zr compound). When the molar ratio exceeds 3, it is difficult to form a uniform film, and a dense film cannot be obtained, or cracks may occur during heat treatment.
[0012]
The organic solvent used for preparing the treatment liquid is not particularly limited as long as it can uniformly dissolve the Zr compound and the stabilizer. For example, a lower alcohol represented by ethanol, Hydrocarbon ether alcohol represented by ethylene glycol monoalkyl ether, acetate ester of hydrocarbon ether alcohol represented by ethylene glycol monoalkyl ether acetate, acetate ester of lower alcohol represented by ethoxyethyl acetate, represented by ethyl acetate In addition to acetic acid esters and ketones typified by acetone, glycols such as ethylene glycol, aromatic hydrocarbons such as toluene and xylene, and halogenated hydrocarbons such as trichloromethane can be used. These may be used alone or in combination of two or more.
[0013]
The viscosity of the treatment liquid is generally less than 100 cP, although it depends on the combination of treatment liquid components. If it exceeds 100 cP, it is difficult to form a uniform film, and cracks may occur during heat treatment.
[0014]
As a method for applying the treatment liquid to the magnet surface, a dip coating method, a spray method, a spin coating method, or the like can be used.
[0015]
After applying a Zr compound solution as a treatment liquid to the magnet surface, heat treatment is performed. In the case of a sintered magnet, if the heat treatment temperature exceeds 450 ° C., the magnetic properties of the magnet may be deteriorated. Further, when the heat treatment temperature is less than 150 ° C., there is a possibility that the film is not sufficiently densified. Therefore, the heat treatment temperature is desirably 150 ° C to 450 ° C.
[0016]
According to the above method, 100 ppm to 1000 ppm (wt / wt) of C is contained in the coating, and the presence of this C makes it easy to obtain an amorphous coating excellent in corrosion resistance and alkali resistance.
[0017]
The present invention is directed to rare earth permanent magnets having various configurations such as sintered magnets and bonded magnets. The rare earth element (R) in the rare earth based permanent magnet is at least one of Nd, Pr, Dy, Ho, Tb, Sm, or La, Ce, Gd, Er, Eu, Tm, Yb, Lu, Y. Among them, those containing at least one kind are desirable.
Usually, one type of R is sufficient, but in practice, a mixture of two or more types (such as misch metal and didymium) can also be used for reasons of convenience.
[0018]
If the content of R in the R—Fe—B permanent magnet is less than 10 atomic%, the crystal structure has the same cubic structure as that of α-Fe, so that high magnetic properties, particularly high coercive force (HcJ) can be obtained. On the other hand, if it exceeds 30 atomic%, the R-rich non-magnetic phase increases, the residual magnetic flux density (Br) decreases, and an excellent permanent magnet cannot be obtained. % To 30 atomic% is desirable.
[0019]
If the Fe content is less than 65 atomic%, Br decreases, and if it exceeds 80 atomic%, high HcJ cannot be obtained. Therefore, the content of 65 atomic% to 80 atomic% is desirable.
In addition, by replacing part of Fe with Co, the temperature characteristics can be improved without impairing the magnetic characteristics of the obtained magnet. However, when the amount of Co substitution exceeds 20% of Fe, the magnetic characteristics are improved. Undesirable because it deteriorates. When the amount of Co substitution is 5 atom% to 15 atom%, Br increases as compared with the case where it is not substituted, and thus it is desirable for obtaining a high magnetic flux density.
[0020]
When the B content is less than 2 atomic%, the rhombohedral structure is the main phase, and high HcJ cannot be obtained. When the B content exceeds 28 atomic%, the B-rich nonmagnetic phase increases and Br decreases, resulting in excellent characteristics. Since a permanent magnet cannot be obtained, the content is preferably 2 atomic% to 28 atomic%.
Further, in order to improve the manufacturability of permanent magnets and to reduce the price, at least one of P of 2.0 wt% or less and S of 2.0 wt% or less is contained in a total amount of 2.0 wt% or less. It may be. Furthermore, the corrosion resistance of the magnet can be improved by replacing a part of B with C of 30 wt% or less.
[0021]
Furthermore, at least one of Al, Ti, V, Cr, Mn, Bi, Nb, Ta, Mo, W, Sb, Ge, Sn, Zr, Ni, Si, Zn, Hf, and Ga is added. It is effective in improving the squareness of the demagnetization curve, improving manufacturability, and reducing the price. It should be noted that Br is required to be added in a range satisfying the condition because Br is required to be at least 0.9 T in order to make the maximum energy product (BH) max 159 kJ / m ³ or more.
The R—Fe—B permanent magnet may contain impurities inevitable for industrial production in addition to R, Fe, and B.
[0022]
Further, among the R—Fe—B permanent magnets used in the present invention, a compound having a tetragonal crystal structure having an average crystal grain size in the range of 1 μm to 80 μm is a main phase, and the volume ratio is 1%. Permanent magnets characterized by containing ˜50% nonmagnetic phase (excluding oxide phase) show HcJ ≧ 80 kA / m, Br> 0.4T, (BH) max ≧ 80 kJ / m ³ , ( The maximum value of BH) max reaches 199 kJ / m ³ or more.
[0023]
As the R—Fe—N permanent magnet, for example, (Fe _1-x R _x ) _1-y N _y (0.07 ≦ x ≦ 0.3, 0.001 ≦ ₁ ) described in Japanese Patent Publication No. 5-82041. and permanent magnets characterized by y ≦ 0.2).
[0024]
The rare earth permanent magnet having a Zr oxide film on the magnet surface of the present invention has strong adhesion and is dense even if the film thickness is very thin, so that the film thickness is 0.01 μm or more. Sufficient corrosion resistance and alkali resistance can be obtained. The upper limit of the film thickness that can be produced by the present invention is not limited, but is 5 μm or less, preferably 3 μm or less, which is suitable for practical use because of the demand based on miniaturization of the magnet itself. .
Here, it goes without saying that the application of the treatment liquid to the magnet surface and the subsequent heat treatment may be repeated a plurality of times as necessary.
[0025]
Note that the rare earth metal-based permanent magnet in the magnet surface of the present invention having the Zr oxide film is, there is the Zr oxide film is formed directly on the magnet surface, on the Zr oxide film, is further coating It is assumed that they are not laminated.
[0026]
Hereinafter, based on an Example, this invention is demonstrated in detail. In the following examples, application to a sintered magnet is taken as an example, but the present invention is not limited to application to a sintered magnet, and can also be applied to a bonded magnet.
[0027]
【Example】
A known cast ingot is pulverized, and after fine pulverization, molding, sintering, heat treatment, and surface processing are performed to produce a magnet body test piece having a composition of 17Nd-1Pr-75Fe-7B and a size of 23 mm × 10 mm × 6 mm. The following examples and comparative examples were performed using
[0028]
Example:
As a treatment liquid, a 5 wt% toluene solution of zirconium octylate (ZrO ₂ equivalent: viscosity 0.7 cP) was prepared.
A treatment liquid was applied by a dip coating method at a lifting speed of 30 cm / min to the test piece whose surface was cleaned by shot blasting and solvent degreasing, and heat treatment was performed at 350 ° C. for 20 minutes. This treatment liquid application and heat treatment were further repeated 4 times (5 times in total) to form a Zr oxide film on the surface of the test piece.
The resulting Zr oxide film (ZrO _x film: 0 <x ≦ 2) was measured by electron microscopy the thickness of the fracture surface was 0.8 [mu] m. When the amount of C in the film was measured using a glow discharge mass spectrometer, it was 380 ppm. Further, as a result of structural analysis of the obtained Zr oxide film using an X-ray diffractometer, the film was amorphous.
[0029]
The obtained magnet having the Zr oxide film on the surface was immersed in a 1 mol / l NaOH aqueous solution at a temperature of 65 ° C. for 2 hours, and then washed and dried. Thereafter, the sample was left under high temperature and high humidity conditions of a temperature of 60 ° C. and a relative humidity of 90%, and an accelerated corrosion resistance test was performed. As a result of appearance observation, rusting was not observed even after 200 hours passed from the start of the test, and the magnet having the obtained Zr oxide coating on the surface was immersed in an alkaline aqueous solution, It was found that even after standing for a long time, the required corrosion resistance and alkali resistance were sufficiently satisfied.
[0030]
Comparative example:
A 5 wt% ethanol solution of tetraethoxysilane (SiO ₂ equivalent: viscosity 1.2 cP) was prepared as a treatment liquid.
A treatment liquid was applied by a dip coating method at a pulling rate of 20 cm / min to the test piece whose surface was cleaned by shot blasting and solvent degreasing, and heat treatment was performed at 200 ° C. for 20 minutes. Application of this treatment liquid and heat treatment were further repeated 4 times (total 5 times) to form a Si oxide film on the surface of the test piece.
The film thickness of the obtained Si oxide film (SiO _x film: 0 <x ≦ 2) was measured by electron microscope observation of the fracture surface and found to be 0.9 μm. Further, as a result of structural analysis of the obtained Si oxide film using an X-ray diffractometer, the film was amorphous.
The obtained magnet having the Si oxide film on the surface was immersed in a 1 mol / l NaOH aqueous solution at a temperature of 65 ° C. for 2 hours, and then washed with water and dried. Thereafter, the sample was left under high temperature and high humidity conditions of a temperature of 60 ° C. and a relative humidity of 90%, and an accelerated corrosion resistance test was performed. As a result of external observation, rust was generated 100 hours after the start of the test.
[0031]
【The invention's effect】
The rare earth-based permanent magnet having a Zr oxide film on the magnet surface of the present invention has high adhesion to the magnet even if the Zr oxide film is very thin, and peeling between the film and the magnet is difficult. Corrosion hardly occurs. Moreover, since the coating is very dense, pinholes are difficult to form. From these effects, it has very excellent corrosion resistance and alkali resistance.
Furthermore, from the above advantages, even when the film thickness is thin, sufficient corrosion resistance and alkali resistance can be obtained, so that high dimensional accuracy can be achieved and the effective volume of the magnet can be improved.
In particular, when manufactured by a coating pyrolysis method, it can be performed with a simple apparatus, the stability of the treatment liquid is excellent, the water is not used at all, and corrosion of the magnet during film formation can be prevented, the processing temperature Because it is relatively low temperature, it can prevent deterioration of the magnetic properties of the magnet under high temperature, can form a dense film with excellent corrosion resistance and alkali resistance despite being a thin film, and there are few environmental problems Has the advantage of

Claims (5)

With a coating pyrolysis method (except for the sol-gel method) in which a Zr compound solution having a viscosity of less than 100 cP is applied to the magnet surface and then heat-treated, the amorphous C content is 100 ppm to 1000 ppm (wt / wt). A rare earth permanent magnet characterized in that a certain Zr oxide film is directly formed as a corrosion-resistant and alkali-resistant film (except for a magnet in which another film is laminated on the Zr oxide film) .   The rare earth permanent magnet according to claim 1, wherein the rare earth permanent magnet is an R—Fe—B permanent magnet. 2. The rare earth permanent magnet according to claim 1, wherein the rare earth permanent magnet is an R—Fe—N permanent magnet . Rare earth metal-based permanent magnet according to claim 1及至3 the thickness of the Zr oxide film is characterized in that it is a 0.01 m to 5 m. With a coating pyrolysis method (except for the sol-gel method) in which a Zr compound solution having a viscosity of less than 100 cP is applied to the magnet surface and then heat-treated, the amorphous C content is 100 ppm to 1000 ppm (wt / wt). A method for producing a rare earth permanent magnet having corrosion resistance and alkali resistance , characterized in that a Zr oxide film is directly formed as a corrosion resistance and alkali resistance film (however, another film is laminated on the Zr oxide film). Excluding magnets) .