JPH0963833A - Highly corrosion resistant permanent magnet and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a highly corrosion resistant R-Fe-B based permanent magnet whose magnetic characteristics do not deteriorate inexpensively and conveniently as compared with a conventional surface treating method by coating the surface of an R-Fe-B based permanent magnet with a glass-like protective layer. SOLUTION: An R-Fe-B based permanent magnet (R is at least one kind of rare earth element including Y) is immersed into or coated with a treating liquid comprising an aqueous solution of alkaline silicate dispersed with ultrafine silica particles of average grain size in the range of 5-50nm having a silanol group (≡Si-OH) on the surface thereof. It is then heat treated to cause dehydration condensation of a silanol group. According to the method, a highly corrosion resistant permanent magnet coated with a glass-like protective layer can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth permanent magnet having high corrosion resistance and a method for producing the same, and more particularly to a glassy protective layer made of an alkali silicate aqueous solution in which ultrafine particle silica is dispersed on the surface of a sintered magnet. R-Fe coated
-A B-type high corrosion-resistant permanent magnet and a method for manufacturing the same.

[0002]

2. Description of the Related Art Rare earth permanent magnets are widely used in the field of electric and electronic devices because of their excellent magnetic properties and economical efficiency, and in recent years, their performance has been required to increase. Of these R-F
Compared to rare earth cobalt magnets, e-B system permanent magnets are richer in Nd, which is the main element, than Sm, and do not use a large amount of Co, so the raw material cost is low, and the magnetic properties of rare earth cobalt magnets are low. Since it is a far superior permanent magnet material, it not only replaces the small magnetic circuit where rare earth cobalt magnets have been used up until now, but also widely applied to the field where hard ferrites or electromagnets were used. Is about to be done. But,
Since the R-Fe-B system permanent magnet contains rare earth elements and iron as main components, it has a drawback that it is easily oxidized in a humid air in a short time, and is incorporated in a magnetic circuit. In such a case, there is a problem that the output of the magnetic circuit is lowered due to these oxidations, or the surroundings of the equipment are contaminated.

[0003]

[Problems to be Solved by the Invention] Such R-Fe
Various surface treatment methods such as resin coating, vapor-phase plating such as ion plating, and wet plating such as Ni plating have been proposed for improving the corrosion resistance of B-type permanent magnets. But,
Since these surface treatment methods require complicated steps, R
There is a problem that the surface treatment cost for the -Fe-B system permanent magnet is expensive. Further, as a simpler surface treatment method, there is proposed a technique in which only the chromic acid treatment is applied to the R-Fe-B system permanent magnet (see Japanese Patent Application Laid-Open No. 6-302420), but nitric acid or the like is used before the chromic acid treatment. Since the pickling treatment is necessary and the waste liquid treatment of the chromic acid treatment liquid is not easy, it cannot be said that the surface treatment cost is necessarily low. The present invention has been made to solve the above problems, and an object of the present invention is to provide an R-Fe-B system permanent magnet having high corrosion resistance in a cheaper and simpler method than conventional surface treatment methods. .

[0004]

The present inventor has proposed that R-Fe-B
As a result of diligent studies on a corrosion resistant coating for a system permanent magnet and a method of forming the same, an R-Fe-B system permanent magnet is immersed in a treatment solution comprising an alkali silicate aqueous solution in which ultrafine particle silica is dispersed, or the treatment solution. After applying to the surface of the magnet, a heat treatment is performed to form a glass-like protective layer on the surface of the permanent magnet, so that the aesthetic appearance is maintained for a long period of time, and it can be processed at a lower cost than conventional surface treatment methods. And, it was found that the waste liquid treatment is easy, and the present invention has been completed by establishing various conditions.
Average particle size 5 with silanol groups (≡Si-OH) on the surface
R-Fe-B system permanent magnet (where R is at least one of rare earth elements containing Y) is immersed in a treatment liquid consisting of an alkali silicate aqueous solution in which ultrafine silica particles having a particle size of up to 50 nm are dispersed, or the treatment is performed. After applying the liquid, by heat treatment to cause dehydration condensation of silanol groups, a method for producing a highly corrosion-resistant permanent magnet characterized by coating the glass surface protective layer on the magnet surface, and by the above production method. A highly corrosion-resistant permanent magnet having a glass-like protective layer produced.

Hereinafter, the present invention will be described in detail. The method for adjusting the treatment liquid in the method for forming the glassy protective layer, which is the greatest feature of the present invention, first, ion-exchanged water is added to the alkali silicate aqueous solution to adjust the concentration, and further a predetermined amount of ultrafine silica particles is added. Added. When the ultrafine silica is a powder, it is dispersed using ultrasonic waves. The alkali silicate concentration is adjusted so as to be 3 to 200 g / L as SiO _{2 in} order to obtain the following film thickness (5 nm to 10 μm) of the glassy protective layer. If it is less than 3 g / L, sufficient corrosion resistance cannot be obtained, and 200 g / L
If it exceeds, the viscosity of the alkali silicate aqueous solution will increase,
The film thickness becomes uneven after the heat treatment, which is not preferable in appearance. Specific examples of the alkali silicate include water glass (mainly composed of SiO ₂ and Na ₂ O), potassium silicate, lithium silicate, and the like.
O ₂ and Na ₂ O molar ratio of _{(Si O 2 / Na 2 O} ) is 1.5 to 2
0.0 is preferable. When it is less than 1.5, the concentration of alkali ions in the glass-like protective layer is high, and the glass-like protective layer has low water resistance, and sufficient corrosion resistance cannot be obtained. If it exceeds 20.0, the alkali ion concentration is low, so that the glass-like protective layer excessively shrinks due to dehydration condensation of silanol groups during heat treatment, and cracks occur in the glass-like protective layer, so that sufficient corrosion resistance cannot be obtained.

The ultrafine particle silica to be added to the above aqueous solution of alkali silicate has a silanol group (≡Si-OH) on the surface and has an average particle diameter of 5 to 50 nm. Examples of commercially available products include Aerosil (trade name of Nippon Aerosil Co., Ltd.), Snowtex (trade name of Nissan Chemical Co., Ltd.), etc., all containing 1 to 15 mol% of silanol groups and having an average particle size of 5
~ 50 nm. In particular, since Aerosil (described above) is manufactured by a high temperature flame hydrolysis method, it hardly contains alkali components such as Na. Therefore, since it is possible to add the ultrafine particle silica without increasing the concentration of alkali ions in the treatment liquid, it is possible to obtain a glassy protective layer having good corrosion resistance. Alternatively, it may be made of water glass or a metal alkoxide such as tetraethoxysilane. In the case of water glass, there are a method of forcibly removing Na ₂ O through a cation exchange resin or a semipermeable membrane and then polymerizing, a method of neutralizing with an acid to remove by-product salts, and the like. is there. The metal alkoxide can be produced by diluting with an alcohol, adding water, and further hydrolyzing in the presence of an acid or an alkali.

The amount of the ultrafine silica particles added may be 1/50 to 1/2 of the SiO ₂ concentration of the alkali silicate in the treatment liquid. When the ultrafine particle silica is a powder, it is dispersed in the treatment liquid using ultrasonic waves after addition. During heat treatment, the ultrafine silica particles dispersed in the treatment liquid cause dehydration condensation between the silanol groups on the surface of the ultrafine silica particles and the silanol groups of the alkali silicate, resulting in a siloxane bond (≡S
i-O-Si ≡) is produced and aggregated to form a glassy protective layer. As a result, the ultrafine silica particles are taken into the glassy protective layer, but this state is not a state in which the ultrafine silica particles are dispersed alone in the glassy protective layer, but it is bonded to the alkali silicate to form ultrafine particles. The fine silica particles are also a part of the glass-like protective layer. Therefore, alkali ions do not exist in the portion of the glassy protective layer obtained by the present invention which was the ultrafine particle silica. Moisture in the atmosphere reacts with alkali ions in the glass-like protective layer to form a hydroxide and corrodes the glass-like protective layer, so that the glass-like protective layer obtained by the present invention has a portion where alkali ions do not exist. Thus, a glassy protective layer having better water resistance than a glassy protective layer obtained from an aqueous alkali silicate solution is obtained.

When the amount of the ultrafine silica particles added is less than 1/50 of the SiO ₂ concentration in the alkali silicate, the amount of the ultrafine silica particles taken into the glassy protective layer is small, so that the glassy glass with low water resistance is obtained. It becomes a protective layer, so that a glass-like protective layer having sufficient corrosion resistance cannot be obtained. In addition, since alkali ions that have reacted with water further react with carbon dioxide in the atmosphere to precipitate a carbonate on the surface of the glass-like protective layer, there is a problem of contamination around the equipment, which is not preferable. Furthermore, in general, when using an R-Fe-B system magnet,
It is incorporated into the magnetic circuit by adhesion using various adhesives such as epoxy resin adhesives and acrylic adhesives, but glass-like protection coated with a treatment liquid with an addition amount of less than 2% (= 1/50). When a magnet having a layer is adhered, the adhesive strength is deteriorated due to a change with time, and the magnet cannot be used.

When the amount of the ultrafine silica added exceeds 1/2 of the SiO ₂ concentration in the alkali silicate, the content of the ultrafine silica increases, and the glassy glass is formed by dehydration condensation of silanol groups during heat treatment. Excessive shrinkage of the protective layer causes cracks in the glassy protective layer. Therefore, a glassy protective layer having sufficient corrosion resistance cannot be obtained. Further, the viscosity of the treatment liquid becomes high, and the film thickness becomes uneven after the heat treatment, which is not preferable in appearance. Furthermore, if the amount of addition is large, the dispersibility of the ultrafine silica particles deteriorates, and the ultrafine silica particles aggregate and precipitate, resulting in poor stability of the treatment liquid. For the above reason, the amount of ultrafine silica added is 1% of the SiO ₂ concentration of the alkali silicate added.
It is preferable to add it so that it becomes / 50 to 1/2, and 1/20 to 1
The range of / 3 is preferable because the effect of the present invention is more remarkably exhibited.

In the surface treatment method of the present invention, the heat treatment after dipping or coating in the treatment liquid is performed at a temperature of 50 in order to sufficiently evaporate water and dehydrate and condense silanol groups.
It is desirable that the temperature is ˜450 ° C., more preferably 120 to 450 ° C. The treatment time is preferably 1 to 120 minutes. If the temperature is lower than 50 ° C, the evaporation of water and the dehydration condensation of silanol groups are not sufficient, and the treatment time is long, which is not preferable in terms of cost. At 120 ° C or higher, evaporation of water and dehydration condensation of silanol groups will be more sufficient. On the other hand, if the temperature exceeds 450 ° C, the structure of the R-Fe-B system magnet is affected and the magnetic properties are deteriorated, which is not preferable. Further, if the treatment time is less than 1 minute, evaporation of water and dehydration condensation of silanol groups do not proceed sufficiently, and if it exceeds 120 minutes, there is no problem in practical use, but productivity is lowered, which is not preferable in terms of cost. It is also possible to repeat the above-mentioned steps of dipping or coating and heat treatment twice or more.

In the present invention, the film thickness of the glassy protective layer formed from an aqueous solution of alkali silicic acid in which ultrafine particle silica is dispersed is preferably 5 nm to 10 μm. If the thickness is less than 5 nm, sufficient coverage cannot be obtained for the irregularities on the magnet surface, and sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 10 μm, there is no problem in practical use in terms of corrosion resistance, but it is difficult to obtain a uniform film thickness, which is not preferable in appearance. Furthermore, if the glass-like protective layer is thickened, it can be used even if the external shape is the same.
Since the volume of the Fe-B system permanent magnet becomes small, it is not preferable in using the magnet.

In the surface treatment method of the present invention, as pretreatment, immediately before immersion of the R-Fe-B system permanent magnet in the treatment liquid,
Alternatively, it is desirable to perform ultrasonic cleaning immediately before applying the treatment liquid to the magnet surface. By removing the minute machining debris and magnetic powder that are physically adsorbed or magnetically attracted and remain on the magnet surface, which causes the adhesion and corrosion resistance of the glassy protective layer, from the magnet surface by ultrasonic cleaning. ,
The adhesion and corrosion resistance of the glassy protective layer can be improved. Usually, in a wet plating method such as Ni plating or a chemical conversion treatment method such as zinc phosphate treatment, as a pretreatment, a degreasing step for removing oil, a layer of a rare earth element oxide or the like which is hard to cover the protective layer is removed. The surface of the magnet is covered with a protective layer having high adhesion and corrosion resistance by performing complicated pretreatments such as the acid pickling step and the activation step for surely forming the protective layer. However, unlike the protective layer obtained by wet plating, chemical conversion treatment, etc., the glass-like protective layer obtained by the present invention can easily form a protective layer even on a rare earth element oxide, etc. Since the magnet surface and the treatment liquid do not react to form a protective layer, the pretreatment such as the above-mentioned pickling step and activation step is not always necessary, and fine magnetic powder and processing waste on the magnet surface are not necessarily required. A glass-like protective layer having sufficient adhesion and corrosion resistance can be formed even by a pretreatment of only removing the. Therefore,
As the pretreatment of the present invention, a degreasing step, a pickling step, an activating step and the like may be followed by ultrasonic cleaning, but the pretreatment of only ultrasonic cleaning is more simple in terms of steps and cost. It can be said that it is preferable.

In the present invention, R used in the R-Fe-B system permanent magnet occupies 5 to 40% by weight of the composition, and as R, Y or La, Ce, Pr, Nd, Pm, Sm,
One or more selected from Gd, Tb, Dy, Ho, Er, Lu and Yb are used. Among them, it is preferable to contain at least one of Ce, La, Nd, Pr, Dy and Tb. B is in the range of 0.2 to 8% by weight. Fe is in the range of 50 to 90% by weight. However, Fe
The temperature characteristics can be improved by substituting a part of Co for Co. However, if the addition amount of Co is less than 0.1% by weight, a sufficient effect cannot be obtained. On the other hand, if it exceeds 15% by weight, the coercive force decreases, so the amount is preferably 0.1 to 15% by weight. Further, Ni, Nb, Al, Ti, Zr, Cr, V, and M are used to improve the magnetic characteristics or reduce the cost.
n, Mo, Si, Sn, Cu, Ca, Mg, Pb, Sb
At least one selected from Ga, Zn and Zn can be added.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The action of the present invention is that ultrafine silica particles added to an aqueous alkali silicate solution are
The silanol groups on the surface of the ultrafine silica and the silanol groups of the alkali silicate cause dehydration condensation to form siloxane bonds (≡Si-O-Si≡) and aggregate to form a glass-like protective layer. Alkali ions do not exist in the portion of the glassy protective layer that was the ultrafine silica. Moisture in the atmosphere reacts with alkali ions in the glass-like protective layer to form a hydroxide and corrodes the glass-like protective layer, so that the glass-like protective layer obtained by the present invention has a portion where alkali ions do not exist. Thus, a glassy protective layer having better water resistance than a glassy protective layer obtained from an aqueous alkali silicate solution is obtained.

[0015]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited thereto. (Examples 1 to 6 and Comparative Examples 1 to 3) 32 Nd-1.2B-59.8Fe-7Co by weight ratio by high frequency melting in an Ar atmosphere.
An ingot having the following composition was produced. The ingot was coarsely crushed with a jaw crusher and then finely crushed with a jet mill using nitrogen gas to obtain fine powder having an average particle size of 3.5 μm. Next, this fine powder was filled in a mold to which a magnetic field of 10 kOe was applied, and molded at a pressure of 1.0 t / cm ² . Then in a vacuum
Sintering was performed at 1100 ° C for 2 hours, and aging treatment was performed at 550 ° C for 1 hour to obtain a permanent magnet. Diameter 21 mm from the obtained permanent magnet
B. A magnet test piece having a thickness of 5 mm was cut out, and barrel polishing treatment was further performed. The obtained test piece was subjected to ultrasonic cleaning as a pretreatment, and then ultrafine silica particles having an average particle diameter of 12 nm shown in Table 1 were added to water glass having a concentration of 30 g / L as SiO ₂ and ultrasonic waves were applied. After being dipped in the treatment liquid dispersed in step 1, heat treatment was performed at 150 ° C. for 20 minutes in a hot air oven.
The corrosion resistance was evaluated by observing the appearance after 100 hours at 80 ° C. and 90% RH. Further, after the test piece was adhered to the iron piece using an epoxy resin adhesive, the shearing force was measured at 80 ° C., 90% RH for about 100 hours, and the adhesive strength deterioration rate was obtained. The results of the corrosion resistance evaluation and the adhesive strength evaluation of Comparative Examples 1 and 2 immersed in a treatment liquid to which an addition amount outside the applicable range was added, and Comparative Example 3 of untreated test pieces are shown. As can be seen from Table 1, it can be seen that the corrosion resistance is improved when the addition amount of ultrafine particle silica is within the range of 1/50 to 1/2 of the SiO ₂ concentration in water glass. Also, regarding the adhesive force, it can be seen that the deterioration of the adhesive force is small if the addition amount is in the range of 1/50 to 1/2. Furthermore, the addition amount is 1/20 ~
It can be said that the effect of the present invention is more remarkable when it is in the range of 1/3.

[0016]

[Table 1]

(Examples 7 to 11, Comparative Examples 4 to 5) Example 1
After ultrasonic cleaning as a pretreatment for the test piece prepared in the same manner as above, 5 g / L of ultrafine silica was added to water glass adjusted to the concentration shown in Table 2 to prepare a treatment liquid which was dispersed using ultrasonic waves. After the immersion, heat treatment was performed at 150 ° C. for 20 minutes in a hot air oven. The film thickness of the glassy protective layer formed on the test piece was measured using XPS (X-ray photoelectron spectroscopy). The corrosion resistance was evaluated by observing the appearance after 100 hours at 80 ° C. and 90% RH. Table 2 shows the treatment conditions and the results of corrosion resistance evaluation. As can be seen from Table 2, it can be seen that the corrosion resistance is improved when the film thickness of the glassy protective layer is 5 nm or more.

[0018]

[Table 2]

(Examples 12 to 15, Comparative Examples 6 to 7) Example 1
After ultrasonic cleaning as a pretreatment of the test piece prepared in the same manner as above, 5 g / L of ultrafine silica particles with an average particle diameter of 12 nm was added to water glass containing 30 g / L of SiO ₂ as the test piece and ultrasonically applied. After soaking in the dispersed treatment liquid, in a hot air oven, Table 3
Heat treatment was performed for 20 minutes at the temperature shown in. However, when the treatment temperature was 30 ° C., heat treatment was performed for 40 minutes. The corrosion resistance was evaluated by observing the appearance after 100 hours at 80 ° C. and 90% RH. The magnetic property deterioration rate was obtained by measuring the magnetic properties before and after coating the glassy protective layer by a coil drawing method using a flux meter. Table 3 shows the processing conditions, the corrosion resistance evaluation, and the magnetic property deterioration rate. As can be seen from Table 3, the corrosion resistance is considerably improved even when the heat treatment temperature is 120 ° C. or lower, but it is understood that the glassy protective layer having better corrosion resistance is formed at 120 ° C. or higher. Also, it can be seen that at a temperature higher than 450 ° C, the magnetic properties are greatly deteriorated and the product cannot be used.

[0020]

[Table 3]

[0021]

According to the present invention, by coating the surface of the R-Fe-B system permanent magnet with the glass-like protective layer, it is possible to perform a simple process, at low cost, and with high corrosion resistance and permanent sintering without deterioration of magnetic properties. A magnet can be provided, and its utility value is extremely high in industry.

Claims (2)

[Claims] 1. A R-Fe-B permanent magnet is added to a treatment liquid comprising an aqueous alkali silicate solution in which ultrafine silica particles having a silanol group (≡Si-OH) and having an average particle size of 5 to 50 nm are dispersed. (Wherein R is at least one of rare earth elements including Y) or after applying the treatment liquid, heat treatment is carried out to cause dehydration condensation of silanol groups, whereby a glass-like protective layer is formed on the surface of the magnet. A method for producing a highly corrosion-resistant permanent magnet, characterized in that: 2. A highly corrosion-resistant permanent magnet having a glass-like protective layer manufactured by the manufacturing method according to claim 1.