JP3740551B2 - Method for manufacturing permanent magnet - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a permanent magnet containing R (where R is one or more rare earth elements including Y), Fe and B.
[0002]
[Prior art]
A permanent magnet having high performance is an Sm-Co magnet by powder metallurgy and has an energy product of 250 kJ / m.^ThreeIs mass-produced. However, the Sm—Co magnet has a drawback that the raw material price of Sm and Co is high. Among rare earth elements, rare earth elements having a small atomic weight, such as cerium, praseodymium, and neodymium, are more abundant and less expensive than samarium. Fe is inexpensive.
[0003]
In recent years, therefore, Nd-Fe-B magnets have been developed. JP-A-59-46008 discloses a sintered magnet, and JP-A-60-9852 discloses a high-speed quenching method. . Nd-Fe-B magnets are 200 kJ / m^ThreeAlthough it is a high-performance magnet exhibiting the above high energy product, it contains rare earth elements that are easily oxidized and iron as the main components, and therefore has low corrosion resistance and has problems such as deterioration in performance and variation.
[0004]
For the purpose of improving the low corrosion resistance of such R-Fe-B magnets, there have been proposed permanent magnets having various protective layers having corrosion resistance on the surface or a method for producing the same (Japanese Patent Laid-Open No. 60/1990). No. -54406, No. 60-63901, No. 60-63902, No. 61-130453, No. 61-150201, No. 61-166115, No. 61-166116, No. 61- 166117, 61-185910, 61-270308, 62-120004, etc.).
[0005]
Such a protective layer is composed of a metal, a compound such as a metal oxide or a metal nitride, an organic material such as glass or resin, or a mixture thereof. The layering method includes liquid phase plating such as electroplating, vapor phase plating such as sputtering, ion plating and vacuum deposition, coating methods such as dip coating, brush coating, pouring, hot dipping, electrodeposition coating, etc. Has been applied. Among the protective layers formed by these methods, the metal protective layer by electroplating is useful because it is excellent in mass productivity and not only improves corrosion resistance but also exhibits a reinforcing effect in mechanical strength. .
[0006]
[Problems to be solved by the invention]
In general, the protective layer formed by electroplating is formed of a metal that is electrochemically nobler than the R-Fe-B magnet body, such as Cu / Sn / Ni, and thus a plating bath in which such a metal is dissolved. Shows a corrosive action on the magnet body. Therefore, until the protective layer is completely formed, some dissolution of the magnet body in the plating bath occurs.
[0007]
Of the magnet body components that dissolve in this way, most of Fe can be converted into trivalent Fe ions that are easily precipitated by air oxidation, and therefore can be easily removed by continuous filtration treatment usually performed in a plating apparatus. is there. B is trivalent BO_ThreeAlthough it becomes an ion, this also has little effect on the performance of the protective layer, as expected because boric acid or borate is often added to the plating bath as a pH buffer.
[0008]
However, ions of rare earth elements (hereinafter sometimes referred to as element R or simply R) do not change their precipitation due to oxidation, and are electrochemically very basic. Also does not happen. Therefore, if the plating bath is used continuously, it accumulates in the plating bath. When the increased R ion concentration becomes a certain level or more, appearance abnormalities such as stains, pinholes, and delamination occur in the protective layer to be formed, resulting in a problem that the corrosion resistance is lowered.
[0009]
For such accumulation of R ions, Japanese Patent Application Laid-Open No. 7-34300 proposes a method of removing R ions by adding phosphoric acid alkyl ester and reacting them. However, in this method, the reaction product is a gel-like ion aggregate, and the ion aggregate has a low specific gravity and floats on the plating bath, so that it is difficult to remove from the bath by filtration. There is. Moreover, since the process which removes unreacted phosphoric acid alkylester with activated carbon is required after a process, there also exists a problem that R ion removal cannot be performed during plating bath operation.
[0010]
An object of the present invention is to provide a method of stably producing a permanent magnet having a protective layer that prevents accumulation of R ions in the plating bath as described above and exhibits a certain appearance and corrosion resistance. .
[0011]
[Means for Solving the Problems]
Such an object is achieved by the present inventions (1) to (10) below.
(1) A permanent magnet having a step of forming a protective layer by electroplating in close contact with the surface of a permanent magnet body containing R (where R is one or more of rare earth elements including Y), Fe and B A manufacturing method comprising:
In the electroplating, a sulfamic acid plating bath substantially not containing a chloride component is used, and R ions in the plating bath that increase with repetition of electroplating are continuously or intermittently added by azodisulfonic acid. A method for manufacturing a permanent magnet, which prevents defects and appearance defects of the protective layer by removing.
(2) The method for producing a permanent magnet according to (1), wherein azodisulfonic acid is added to the plating bath or azodisulfonic acid is generated in the plating bath in order to remove R ions in the plating bath.
(3) The method for producing a permanent magnet according to (1), wherein azodisulfonic acid is generated in the plating bath while the plating bath is in operation.
(4) The method for producing a permanent magnet according to any one of (1) to (3) above, wherein the azodisulfonic acid is generated chemically, electrochemically or photochemically.
(5) The method for producing a permanent magnet according to (4), wherein the azodisulfonic acid is produced by adding an oxidizing agent to a solution containing a sulfamate.
(6) The method for producing a permanent magnet according to (4) above, wherein the azodisulfonic acid is produced by subjecting a solution containing a sulfamate to an electrolytic treatment using an insoluble anode.
(7) The method for producing a permanent magnet according to (4), wherein the azodisulfonic acid is produced by subjecting a solution containing a sulfamate to electrolytic treatment using a Ni-containing anode.
(8) During the electrolytic treatment, the anode current density is 6 A / dm.²The manufacturing method of the permanent magnet according to (7) above.
(9) The method for producing a permanent magnet according to (4) above, wherein the azodisulfonic acid is produced by subjecting a solution containing sulfamate to an oxidation treatment using a photocatalyst containing titanium oxide.
(10) Any one of (1) to (9) above, wherein sulfate ions in the plating bath, which are increased by hydrolysis of sulfamic acid by repeated electroplating, are removed by adding a barium compound to the plating bath. Of manufacturing permanent magnets.
[0012]
[Action]
R ions may precipitate as hydroxides from almost neutral solutions, but are usually removed by filtration in order to maintain dissolution in acidic and basic plating baths where plating operations are performed. Is impossible. In addition, there is a plating bath that can perform a plating operation near neutrality. In this case, since a complexing agent is added for the purpose of preventing precipitation of metal ions to be plated, R ions do not precipitate. Removal by filtration is not possible.
[0013]
However, the present inventor, while continuously monitoring the R ion concentration in the plating bath in the continuous operation in the plating baths having various compositions, increases the R ion concentration in a specific bath composition and specific processing conditions. Has been found to be abnormally reduced, leading to the present invention.
[0014]
Specifically, the increase in the R ion concentration was small when the sulfamic acid-based plating bath contained no chloride and was plated with a relatively large anode current density. However, in the case of a model experiment in which an R compound was simply dissolved in a sulfamic acid plating bath containing no chloride and the filtration operation was performed, the R ion concentration did not decrease.
[0015]
Therefore, when an electrolysis treatment using an insoluble anode is performed on a sulfamic acid-based plating bath not containing chloride, a precipitate is generated and removed by a filtration operation. Along with this, R ions in the plating bath are generated. It was found that the concentration decreased. Therefore, this precipitate is considered to be an R compound. Since it was confirmed that the precipitate obtained in this experiment was easily dissolved in dilute hydrochloric acid, the increase in the R ion concentration was suppressed in the sulfamic acid plating bath containing no hydrochloric acid component. I can explain.
[0016]
Moreover, when the oxidation treatment with permanganate or ozone was applied to the plating bath, a decrease in the R ion concentration was also observed.
[0017]
When plating is performed using a sulfamic acid-based plating bath, depending on conditions, sulfamic acid ions are oxidized at the anode and azodisulfonic acid ions (SO_ThreeNNSO_Three ^2-) Is known to produce. Based on this and the conditions under which the R ions decrease, the present inventor found that azodisulfonic acid produced at the anode by the plating operation under specific conditions in a sulfamic acid-based plating bath not containing chlorine ions. It was considered that the increase in the R ion concentration was partially suppressed. Actually, when the above-described oxidation treatment was performed on the plating bath so that azodisulfonic acid was formed, a precipitate was formed and the R ion concentration in the bath was significantly reduced.
[0018]
Therefore, in the present invention, azodisulfonic acid is added to the plating bath, or azodisulfonic acid is generated in the plating bath, thereby forming a precipitate by bonding of azodisulfonic acid and R ions, thereby removing R ions. The configuration. Thereby, in this invention, R ion concentration itself can be reduced rather than reducing the increase rate of R ion concentration in a plating bath. Conventionally, a sulfamic acid-based plating bath containing no chloride has a relatively long life. However, by applying the present invention to this plating bath, it is not necessary to discard and renew the plating bath for a very long period of time. In the present invention, it is also possible to produce azodisulfonic acid in the plating bath during operation of the plating bath. In this case, the plating bath can be continuously operated over a long period of time, so that productivity is improved. And it is extremely effective for cost reduction.
[0019]
In addition, when using a sulfamic acid bath for a long period, it is known that a part of sulfamic acid will hydrolyze and it will become a sulfate ion and an ammonium ion. Since the precipitate produced by the present invention is dissolved in dilute sulfuric acid, the accumulation of sulfate ions in the bath inhibits the formation of the precipitate. However, the sulfate ions generated in the bath can be removed by adding a barium compound, precipitating as barium sulfate, and filtering. Therefore, if the increased sulfate ion is removed by the barium compound, the effect of lowering the R ion concentration by azodisulfonic acid can be maintained over a long period of time.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, before the protective layer is formed on the permanent magnet body, pretreatment is performed using a predetermined treatment liquid.
[0021]
Non-oxidizing acids such as hydrochloric acid and sulfuric acid are often used for the plating pretreatment. However, when a permanent magnet body containing rare earth elements is treated with these acids, hydrogen generated by the acid is occluded on the surface of the permanent magnet body, and the occlusion site becomes brittle, resulting in a large amount of powdery undissolved matter. Occurs. Since this powdery undissolved substance causes a defect of the protective layer or causes a decrease in adhesion, it is preferable not to include a non-oxidizing acid in the treatment liquid. Therefore, the acid used is preferably nitric acid, which is an oxidizing acid that generates little hydrogen. By using nitric acid, the surface of the magnet body is chemically etched by the oxidation action, and a fine uneven structure that cannot be confirmed with the naked eye is formed.
[0022]
The amount of dissolution of the magnet body by such pretreatment is preferably 5 μm or more, more preferably 10 to 15 μm in average thickness from the surface. When the dissolution amount is less than 5 μm, the deteriorated layer and the oxide layer cannot be completely removed by processing the surface of the magnet body, so that sufficient adhesion cannot be obtained. The average depth of the irregularities (depth from the valley to the mountain) is preferably about 1 to 5 μm. Moreover, it is preferable that the average pitch of unevenness | corrugation is about 10-50 micrometers. These improve adhesion.
[0023]
The concentration of nitric acid in the treatment solution used for such pretreatment is desirably 1 N or less, particularly 0.6 N or less, and more preferably 0.5 N or less. When the nitric acid concentration exceeds 1N, the dissolution rate of the magnet body becomes extremely fast, and it becomes difficult to control the amount of dissolution and to obtain a product with a desired dimensional accuracy. In addition, when a large amount of processing is performed, such as barrel processing, variation in processing state becomes large.
[0024]
The amount of Fe dissolved at the end of the treatment is about 1 to 10 g / L (liter). That is, the dissolution treatment is performed by batch processing, and the treatment liquid may be discarded when the amount of dissolved Fe becomes this level.
[0025]
The treatment temperature with the treatment liquid is preferably 40 ° C. or less, more preferably 30 ° C. or less, and further preferably 20 ° C. or less. The treatment time may be appropriately adjusted depending on the treatment liquid composition, temperature, and target etching amount, but it is usually preferably 1 to 20 minutes.
[0026]
In order to completely remove a small amount of undissolved substances and residual acid components from the pretreated magnetic body surface, it is preferable to perform cleaning using ultrasonic waves. This ultrasonic cleaning is preferably performed in water having a low chloride ion content such as ion-exchanged water or a solution in which a small amount of a basic compound is dissolved for the purpose of neutralizing residual acid. When chlorine ions are contained in the cleaning liquid, it causes rust generation on the magnet surface, and it is brought into the plating bath to inhibit precipitation of azodisulfonic acid and R ions. If necessary, the same immersion cleaning with water or a basic aqueous solution may be performed before and after the ultrasonic cleaning. Furthermore, before performing the pretreatment, depending on the processing method and storage state of the magnet body, mechanical polishing treatment and dipping or electrolytic degreasing treatment or alkali derusting treatment usually performed as plating pretreatment may be performed. .
[0027]
In the pretreatment with the acid, it is preferable not to apply ultrasonic waves. This is because the unevenness may become too large due to the erosion action.
[0028]
A protective layer is formed on the cleaned magnet body surface by electroplating. By forming the protective layer by electroplating, a high-performance corrosion-resistant film having excellent mass productivity can be formed.
[0029]
In the present invention, the protective layer contains Ni as a main component. By using Ni for the protective layer, the strength of the protective layer is increased and an excellent antirust effect can be obtained. In the present invention, this protective layer is formed by electroplating. For this electroplating, an anode containing Ni and a nickel sulfamate bath substantially free of chloride components are used.
[0030]
Examples of the composition of the sulfamic acid bath include, for example,
Ni (NH₂SO_Three)₂・ 4H₂O: 150-600 g / L,
NiBr₂・ 6H₂O: 0 to 30 g / L,
Boric acid: 30-60g / L
Is preferred. When the plating bath is constructed, it is preferable that the water used does not contain chlorine, and the amount of chlorine in the bath is preferably 0.01 g / L or less. Thus, by removing the chlorine component from the plating bath, the occurrence of swelling due to aging can be prevented, and the effect of removing R ions by azodisulfonic acid can be sufficiently exhibited.
[0031]
As for the plating conditions, the pH (hydrogen ion concentration) is preferably 3 to 6, particularly 4.0 to 5.0, and the temperature is preferably 30 to 70 ° C. If the pH is too low, the magnet body is dissolved, and sulfate ions increase in the bath due to hydrolysis of sulfamic acid, thereby inhibiting the R ion removal effect of azodisulfonic acid. If the pH is too high, nickel hydroxide will precipitate and the plating film will become brittle.
[0032]
In the present invention, R ions in the plating bath during operation are periodically analyzed, and the concentration is preferably controlled to be 3 g / L or less, more preferably 1 g / L or less. Although the analysis method is arbitrary, plasma emission spectroscopy can be preferably used. The frequency of analysis varies depending on the capacity of the plating bath, the shape of the magnet body, and the processing amount, but may be about once per week.
[0033]
When the above analysis shows that the upper limit concentration of R ions is acceptable, azodisulfonic acid is added to the plating bath. As a result, R ions in the plating bath combine with azodisulfonic acid to form a precipitate, and the R ion concentration in the bath decreases. However, since azodisulfonic acid itself is difficult to obtain, sulfamate solution is chemically, electrochemically or photochemically oxidized to produce azodisulfonic acid, and this solution is added to the plating bath. It is preferable to do. The sulfamate used in this case is preferably an alkali metal sulfamate such as Li, Na, or K. The amount of azodisulfonic acid added may be appropriately determined so that the amount of R ions in the plating bath decreases to the target amount.
[0034]
In addition, since the sulfamic acid plating bath itself is a sulfamate solution, the oxidation bath is chemically, electrochemically, or photochemically applied to the plating bath that is the target for removing R ions. Can also produce azodisulfonic acid. In this method, the amount of the plating bath does not fluctuate as compared with the method of adding the azodisulfonic acid-containing solution from the outside, and the plating bath is operated continuously or intermittently in the plating bath during the operation of the plating bath. Since azodisulfonic acid can be produced, it is a more preferable method.
[0035]
When chemically oxidizing the sulfamate solution, an oxidizing agent may be added to the solution. As the oxidizing agent, permanganate such as potassium permanganate and / or ozone is preferable. When using a permanganate, azodisulfonic acid is sufficiently produced by adding and stirring for several hours, and then hydrogen peroxide is added to decompose the remaining permanganate, and the produced dioxide. Manganese is removed by filtration. On the other hand, when ozone is used as the oxidizing agent, ozone may be blown into the sulfamate solution. When the azodisulfonic acid production treatment with ozone is directly applied to the plating bath, for example, if an ozone generator is installed on the suction side of the blower for stirring the air in the plating bath, ozone is continuously blown into the plating bath. Therefore, it is possible to generate azodisulfonic acid in the plating bath during operation. On the other hand, in the method of adding permanganate to the plating bath, as described above, batch processing is performed to remove permanganate. Therefore, ozone is preferable as the oxidizing agent. In addition, ozone may be blown into the plating bath intermittently. What is necessary is just to determine the addition amount of an oxidizing agent suitably according to the amount of R ion in a plating bath.
[0036]
When electrochemically oxidizing the sulfamate solution, it is preferable to use the first electrolytic treatment or the second electrolytic treatment described below.
[0037]
In the first electrolytic treatment, it is preferable to generate azodisulfonic acid by inserting an insoluble anode and a dummy cathode into the sulfamate solution and performing an empty electrolytic treatment for several minutes to several tens of minutes. As the insoluble anode, for example, a platinum-plated titanium anode or a carbon anode can be used. The anode current density in this case is not particularly limited, but it is possible to generate azodisulfonic acid even when the anode current density is relatively low, and that the generation of gas increases when the anode current density is increased. The anode current density is 1A / dm²The following is preferable.
[0038]
When the first electrolytic treatment is directly applied to the plating bath, a power source independent of the power source used for normal plating operation (plating operation for forming the protective layer) is installed, and the insoluble anode and If it is set as the structure which supplies an electric current with respect to the said dummy cathode, an azodisulfonic acid production | generation process can be performed with respect to the plating bath in operation.
[0039]
On the other hand, in the second electrolytic treatment, a Ni-containing anode used for a normal plating operation is used, and the anode current density is made higher than that of a normal plating operation. As a result, the oxidation of the anode cannot catch up. As a result, a part of the supplied current is consumed for the oxidation of the sulfamate ion, so that azodisulfonic acid is generated. The anode current density in this case is preferably 6 A / dm.²Or more, more preferably 10 A / dm²That's it. However, if the anode current density is remarkably increased, the voltage required for energization increases and a large power supply device is required. Therefore, the anode current density is 15 A / dm.²The following is preferable.
[0040]
In addition, the anode current density in normal plating in which a plating bath is repeatedly used, such as formation of a protective layer on a magnet body, is 1 to 5 A / dm.²(See, for example, Table 4-10 on page 111 of the “Plating Technology Guide” issued by the National Association of Plating Materials Association). Therefore, also in the present invention, the anode current density when forming the protective layer is preferably within this range. On the other hand, the cathode current density is a condition that greatly affects the film quality of the plating film, and what is simply described as the current density as the plating condition is this cathode current density. In the present invention, the cathode current density at the time of forming the protective layer may be the same as the conventional one. For example, as described in JP-A-4-283911, 0.1-10 A / dm²It should be about. If the cathode current density is too low, the number of impurities folded into the plating film increases, and a film with poor appearance and low corrosion resistance tends to be formed. On the other hand, if the cathode current density is too high, hydrogen generation near the cathode increases, and hydrogen is occluded in the magnet body, causing a decrease in adhesion.
[0041]
When the second electrolytic treatment is directly applied to the plating bath, a magnet body to be plated may be used for the cathode. However, it is preferable to use a dummy cathode because the cathode current density is excessive and there is a high possibility that a good quality protective layer cannot be formed. On the other hand, when the second electrolytic treatment is performed on a sulfamate solution different from the plating bath, a dummy cathode may be used.
[0042]
When the second electrolytic treatment is directly applied to the plating bath, azodisulfonic acid can be generated during the operation of the plating bath or simply by replacing the dummy cathode, so that the influence on productivity is small.
[0043]
When the second electrolytic treatment is performed, the pH of the plating bath may be lowered to an extent that falls outside the preferred range. Therefore, it is preferable to adjust the pH after completion of the treatment, if necessary. When the second electrolytic treatment is applied to a sulfamate solution different from the plating bath, the pH is increased by adding an alkali metal carbonate or hydroxide such as lithium or sodium into the solution, What is necessary is just to throw this solution in a plating bath. On the other hand, when the second electrolytic treatment is performed on the plating bath, for example, nickel carbonate can be added to the plating bath to adjust the pH.
[0044]
In addition, what is necessary is just to determine suitably the process time in the case of performing an electrochemical oxidation process intermittently so that the amount of R ion in a plating bath may fall to the target quantity.
[0045]
When photochemically oxidizing the sulfamate solution, azodisulfonic acid is generated by bringing a photocatalyst containing titanium oxide into contact with the sulfamate solution. Titanium oxide may be either anatase type or rutile type, but anatase type titanium oxide is preferred in terms of obtaining stronger catalytic activity. When the photochemical oxidation treatment is performed on the plating bath, for example, at least a part of the continuous filtration pipe is a translucent portion made of a transparent material such as glass, and a film containing a photocatalyst on the inner surface of the translucent portion And azodisulfonic acid may be generated by irradiating the light transmitting part with ultraviolet rays. Since continuous filtration is performed during operation of the plating bath, azodisulfonic acid can be continuously supplied into the plating bath during operation by generating azodisulfonic acid in the piping for continuous filtration.
[0046]
In any of the above oxidation treatment means, in order to remove the precipitate generated in the plating bath, a continuous filtration treatment apparatus provided in the plating apparatus can be used. May be performed.
[0047]
Note that the presence of the azodisulfonic acid produced by each oxidation treatment can be confirmed in a transparent solution by specific light absorption based on an azo bond (N = N). On the other hand, in a plating bath containing a large amount of colored nickel ions, it is difficult to accurately monitor the increase or decrease in azodisulfonic acid. However, azodisulfonic acid is known to have the effect of changing the stress of the nickel plating film to the compressive stress side. Therefore, by periodically measuring the stress of the nickel plating film formed, the increase or decrease can be increased. It can also be monitored indirectly. However, when carrying out the present invention, it is not necessary to accurately grasp the azodisulfonic acid content in the sulfamate solution added to the plating bath or the azodisulfonic acid content in the plating bath. That is, the degree of each oxidation treatment may be controlled so that the R ion concentration in the plating bath is reduced by a desired amount.
[0048]
Even if the plating treatment is performed under proper operating conditions, a part of sulfamic acid is hydrolyzed and sulfate ions accumulate in long-term use. As a result, R ions having a concentration substantially equal to the accumulated sulfate ion concentration remain after the oxidation treatment. In that case, it is preferable to add a barium salt such as barium hydroxide to the bath to precipitate sulfate ions as barium sulfate, and remove the precipitate by filtration. This makes it possible to fully function the R ion removing action of azodisulfonic acid over a long period of time. The sulfate ion concentration can be analyzed by an ion chromatograph or the like.
[0049]
In the present invention, multilayer plating for the purpose of improving corrosion resistance such as known double nickel plating and trinickel plating having different natural potentials can be preferably used as necessary. In the case of multilayer plating, the present invention is applied at least when forming an electroplated film that is in close contact with the magnet body.
[0050]
In forming the protective layer by electroplating, a rack plating method or a barrel plating method is appropriately applied according to the size and shape of the magnet body. In general, a magnet body having a large size that is processed by a rack plating method has a large area that requires a defect-free protective layer, so that the protective layer needs to be relatively thick. In this case, the thickness of the protective layer made of an electroplated film is preferably 20 to 30 μm. On the other hand, in a magnet body having a weight of several tens of grams or less that is processed in a large amount by barrel plating, there is no problem even if the protective layer is relatively thin because the surface area is small. In this case, the thickness of the protective layer is preferably 10 to 20 μm.
[0051]
In addition, if necessary, a protective layer by another technique, such as an electroless plating layer, a resin layer by various coating methods, etc. can be provided on the protective layer by electroplating. It is possible to make the protective layer by electroplating thinner.
[0052]
In the present invention, the permanent magnet body having the protective layer on the surface thereof contains R (where R is one or more of rare earth elements including Y), Fe and B.
[0053]
The contents of R, Fe and B are in atomic percentages
5.5 ≦ R ≦ 30,
42 ≦ Fe ≦ 90,
2 ≦ B ≦ 28
In particular, when a permanent magnet body is produced by a sintering method, R is preferably 8 atomic% or more.
[0054]
The rare earth element R includes at least one of Nd, Pr, Ho, and Tb, or further includes one or more of La, Sm, Ce, Gd, Er, Eu, Pm, Tm, Yb, and Y. preferable. In addition, when using 2 or more types of elements as R, mixtures, such as a misch metal, can also be used as a raw material. If the R content is too small, the crystal structure becomes a cubic structure having the same structure as that of α-Fe, so that high coercive force (HcJ) cannot be obtained. On the other hand, if the R content is too large, the R-rich non-magnetic phase increases and the residual magnetic flux density (Br) decreases. If the Fe content is too low, Br will be low, and if it is too high, HcJ will be low. If the B content is too small, the rhombohedral fabric is formed, so that HcJ is insufficient. If the B content is too large, the B-rich nonmagnetic phase increases, so the Br becomes low.
[0055]
Note that by replacing part of Fe with Co, the temperature characteristics can be improved without deteriorating the magnetic characteristics. In this case, if the Co substitution amount exceeds 50% of Fe, the magnetic properties deteriorate, so the Co substitution amount is preferably 50% or less.
[0056]
Furthermore, by replacing a part of B with one or more of C, P, S, and Cu, productivity can be improved and cost can be reduced. In this case, the amount of substitution is preferably 4 atomic% or less. In addition, Al, Ti, V, Cr, Mn, Bi, Nb, Ta, Mo, W, Sb, Ge, Sn, Zr, Ni, Si are used to improve coercivity, improve productivity, and reduce costs. One or more of Hf and the like may be added. In this case, the total amount added is preferably 10 atomic% or less.
[0057]
The permanent magnet body in the present invention has a main phase having a substantially tetragonal crystal structure. The particle size of the main phase is preferably about 1 to 100 μm. And it usually contains 1-50% nonmagnetic phase by volume ratio.
[0058]
Such a permanent magnet body is disclosed in Japanese Patent Laid-Open No. 61-185910 described above.
[0059]
The permanent magnet body as described above is preferably manufactured by a sintering method as described below. First, an alloy having a desired composition is cast to obtain an ingot. The obtained ingot is coarsely pulverized to a particle size of about 10 to 100 μm by a stamp mill or the like, and then finely pulverized to a particle size of about 0.5 to 5 μm by a ball mill or the like. The obtained powder is preferably shaped in a magnetic field. In this case, the magnetic field strength is preferably 800 kA / m or more, and the molding pressure is preferably about 100 to 500 MPa. The obtained molded body is sintered at 1000 to 1200 ° C. for 0.5 to 5 hours and rapidly cooled. The sintering atmosphere is preferably an inert gas atmosphere such as Ar gas. Thereafter, an aging treatment is preferably performed at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere.
[0060]
【Example】
Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.
[0061]
Common conditions
A flat ring-shaped sintered body having a composition of 14Nd-1Dy-7B-78Fe (numbers are atomic ratios), an outer diameter of 35 mm, an inner diameter of 20 mm, and a height of 2 mm was produced by a powder metallurgy method. The sintered body was subjected to barrel polishing to obtain a magnet body. As a pretreatment for plating, the magnet body was subjected to a surface layer dissolution treatment with a 0.5 N nitric acid solution and an ultrasonic cleaning treatment in ion-exchanged water.
[0062]
The plating bath has a total capacity of 0.5m^Three4 each of the above-mentioned pre-treated samples and 4 hexagonal columnar barrels with a diameter of 0.3 m and a length of 0.5 m, charged with 2 kg of steel balls with a diameter of 3 mm and with Ni plating for assisting energization. Then, barrel plating was performed for 4 hours at a current value of 50 A per barrel. The pH of the plating bath is 4.5 ± 0.2, the temperature of the plating bath is 50 ± 3 ° C., and the anode current density is 2 A / dm as the anode.²An electrolytic nickel plate having an area to be used was used.
[0063]
The barrel plating process was performed 3 times / day while updating the sample, and the plating solution was sampled every weekend to measure the R ion concentration in the plating bath. In addition, a total number of appearance inspections were performed on the samples after plating. Further, n = 10 samples extracted from each batch were put into a pressure cooker test at a temperature of 120 ° C., a pressure of 0.2 MPa, a relative humidity of 100%, and 24 hours to perform a corrosion resistance test.
[0064]
Example 1
Ni (NH₂SO_Three)₂・ 4H₂O: 600 g / L,
NiBr₂・ 6H₂O: 15 g / L,
Boric acid: 40 g / L
The sample was plated for 3 months using a plating bath containing, and the R ion concentration (total concentration of Nd ions and Dy ions) in the bath was continuously measured. The transition of the R ion concentration in the plating bath is shown in FIG.
[0065]
As shown in FIG. 1, the R ion concentration was 1 g / L or less even after 3 months. In addition, the plating film formed had an appearance defect rate of 1% or less such as pinholes and spots, and no occurrence of defects was observed in the pressure cooker test. However, from FIG. 1, it is expected that the R ion concentration exceeds 3 g / L by continuous operation for about one year.
[0066]
Electrochemical oxidation treatment
1 liter of sodium sulfamate solution with a concentration of 100 g / L is prepared, and the anode current density is 1 A / dm using a platinum-plated titanium plate as an anode and a stainless plate as a cathode.²A part of sulfamic acid was electrochemically oxidized by applying an electrolytic treatment for 10 minutes to prepare an azodisulfonic acid-containing solution.
[0067]
0.05 liter of the azodisulfonic acid-containing solution was added to 1 liter of the plating solution sampled from the plating bath after 3 months of use, and the mixture was stirred for 2 hours. When filtration was performed using 5C filter paper, a pale white precipitate was observed. When the R ion concentration in the plating solution after filtration was analyzed, it was reduced to 0.02 g / L.
[0068]
In order to simulate a state in which the R ion concentration further increased, an R compound (neodymium oxide) was added so that the R ion concentration in the plating bath was 4 g / L. Subsequently, after performing the same treatment as the above electrochemical oxidation treatment except that the amount of the azodisulfonic acid-containing solution added was 0.2 liter, the R ion concentration after filtration was 0. Reduced to 05 g / L.
[0069]
Example 2
Ni (NH₂SO_Three)₂・ 4H₂O: 150 g / L,
NaNH₂SO_Three              : 200 g / L,
NiBr₂・ 6H₂O: 5 g / L,
Boric acid: 40 g / L
A plating bath containing was used to plate the sample for 3 months and the R ion concentration in the bath was continuously measured. The transition of the R ion concentration in the plating bath is also shown in FIG.
[0070]
As shown in FIG. 1, the R ion concentration was 0.5 g / L or less even after 3 months. In addition, the plating film formed had an appearance defect rate of 1% or less such as pinholes and spots, and no occurrence of defects was observed in the pressure cooker test.
[0071]
Chemical oxidation treatment
0.03 liter of 1N potassium permanganate solution was added to 1 liter of plating solution sampled from the plating bath after 3 months of use, and stirred for 4 hours. A hydrogen peroxide solution having a concentration of 30% by mass was added until the reddish purple color of the plating solution disappeared, and the remaining potassium permanganate was decomposed. Filtration was performed using 5C filter paper. When the R ion concentration in the plating solution after filtration was analyzed, it was less than the detection limit (0.001 g / L).
[0072]
In addition, in order to simulate the state where the R ion concentration further increased, the R compound was added in the same manner as in Example 1. Next, treatment was performed in the same manner as the above chemical oxidation treatment except that the amount of potassium permanganate solution added was 0.15 liter, and filtration was performed. The R ion concentration after filtration was 0.05 g / L. It was decreasing until.
[0073]
Electrochemical oxidation treatment
One liter of plating solution is sampled from the above plating bath after 3 months of use, and the anode current density is 12 A / dm using a high-purity electrolytic nickel plate as the anode and a stainless steel mesh as the cathode.²No. 10 was subjected to electrolytic treatment for 10 minutes and stirred for 2 hours after removing both electrodes. Filtration was performed using 5C filter paper. When the R ion concentration in the plating solution after filtration was analyzed, it was less than 0.001 g / L.
Sulfate ion removal treatment
One liter of plating solution is sampled from the plating bath after 3 months of use, 5 g of ammonium sulfate is added to simulate the state in which sulfate ions are generated by hydrolysis of sulfamic acid, and then the electrochemical oxidation treatment is performed. And filtration was performed. When the R ion concentration in the plating solution after filtration was analyzed, almost no decrease was observed.
[0074]
Therefore, when 6.5 g of barium hydroxide was added to the plating solution after filtration, and the plating solution after filtration was again subjected to the electrochemical oxidation treatment and filtration, the R ion concentration was 0. It decreased to less than 0.001 g / L.
[0075]
Comparative Example 1
Ni (NH₂SO_Three)₂・ 4H₂O: 600 g / L,
NiCl₂・ 6H₂O: 15 g / L,
Boric acid: 40 g / L
Using the plating bath containing, the sample was plated for 3 months in the same manner as in Example 1 and the R ion concentration in the bath was continuously measured. The only difference from the composition used in Example 1 is that nickel bromide was replaced with nickel chloride. The transition of the R ion concentration in the plating bath is also shown in FIG.
[0076]
As shown in FIG. 1, the R ion concentration increased at a rate about 3 times that of Example 1 and exceeded 3 g / L after 3 months. In addition, the appearance defect rate of pinholes, spots, etc. of the formed plating film gradually increases and reaches 5% after 3 months. At this point, the occurrence of defects in the pressure cooker test is recognized. It was.
[0077]
Electrochemical oxidation treatment
0.05 liter of the azodisulfonic acid-containing solution prepared in Example 1 was added to 1 liter of the plating solution sampled from the plating bath after use for 3 months, and after stirring for 2 hours, Filtration was performed using 5C filter paper, but no precipitation was confirmed. When the R ion concentration in the plating solution after filtration was analyzed, it was hardly reduced to 3 g / L or more. This is because chloride was contained in the plating bath.
[0078]
【The invention's effect】
According to the present invention, it is not necessary to frequently discard and renew the plating bath for forming the protective layer. Therefore, a permanent magnet having few appearance defects and good corrosion resistance can be stably manufactured over a long period of time.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the number of days of plating and the concentration of R (rare earth element) ions in a plating bath.

Claims (4)

R (wherein, R is one or more rare earth elements including Y), in close contact with the surface of the permanent magnet body containing Fe and B, have a step of forming a protective layer by electroplating,
In the electroplating, a sulfamic acid plating bath substantially not containing a chloride component is used, and R ions in the plating bath that increase with repetition of electroplating are continuously or intermittently generated by azodisulfonic acid. A method of manufacturing a permanent magnet that prevents defects in the protective layer and appearance defects by removing ,
A method for producing a permanent magnet, wherein the azodisulfonic acid is produced by adding an oxidizing agent to a solution containing a sulfamate. R (where R is one or more of rare earth elements including Y), having a step of forming a protective layer by electroplating in close contact with the surface of a permanent magnet body containing Fe and B;
In the electroplating, a sulfamic acid plating bath substantially not containing a chloride component is used, and R ions in the plating bath that increase with repetition of electroplating are continuously or intermittently generated by azodisulfonic acid. A method of manufacturing a permanent magnet that prevents defects in the protective layer and appearance defects by removing,
When the azodisulfonic acid is a Ni-containing anode for a solution containing sulfamate, an anode current density of 6 A / dm ² The manufacturing method of the permanent magnet which is produced | generated by performing an electrolysis process on the above conditions. R (where R is one or more of rare earth elements including Y), having a step of forming a protective layer by electroplating in close contact with the surface of a permanent magnet body containing Fe and B;
In the electroplating, a sulfamic acid plating bath substantially not containing a chloride component is used, and R ions in the plating bath that increase with repetition of electroplating are continuously or intermittently added by azodisulfonic acid. A method of manufacturing a permanent magnet that prevents defects in the protective layer and appearance defects by removing,
A method for producing a permanent magnet, wherein the azodisulfonic acid is produced by subjecting a solution containing sulfamate to an oxidation treatment using a photocatalyst containing titanium oxide. The method for producing a permanent magnet according to any one of claims 1 to 3 , wherein sulfate ions in the plating bath, which are increased by hydrolysis of sulfamic acid by repeated electroplating, are removed by adding a barium compound to the plating bath. .

Images