JPH097867A - High corrosion-resistant permanent magnet and manufacture thereof - Google Patents

Abstract

PURPOSE: To obtain a high corrosion-resistant permanent magnet which is much enhanced in corrosion resistance by a method wherein a glassy protective layer is provided onto the surface of an R-Fe-B permanent magnet which is liable to deteriorate in magnetic properties due to oxidation. CONSTITUTION: An R-Fe-B permanent magnet (R denotes one of rare earth elements including Y) is dipped into treatment solution of alkaline silicate water solution or treatment solution is applied onto the magnet, and then the magnet is heat-treated, whereby the surface of the permanent magnet is coated with a glassy protective layer as thick as 5nm to 10μm. Or the surface of a permanent magnet is subjected to an ultrasonic rinsing pretreatment before the permanent magnet is dipped into treatment solution.

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 an R-Fe-B permanent magnet in which the surface of a sintered magnet is uniformly covered with a protective layer of an aqueous alkali silicate solution. A magnet and a manufacturing method thereof.

[0002]

2. Description of the Related Art Rare earth permanent magnets have been widely used in the field of electric and electronic devices because of their excellent magnetic properties and economic efficiency, and in recent years, their performance has been required to increase. R of these
The --Fe--B system permanent magnet has a larger amount of Nd, which is a main element, than Sm, as compared with the rare earth cobalt magnet.
Raw materials cost is low because a large amount of o is not used,
Since it is a permanent magnet material with excellent magnetic properties far superior to those of rare earth cobalt magnets, it not only replaces the small magnetic circuit where rare earth cobalt magnets have been used until now, but also uses hard ferrites or electromagnets. It is about to be widely applied to other fields.
However, 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 humid air in a short period of time, and thus it has a drawback in magnetic circuits. When incorporated, there is a problem in that the output of the magnetic circuit is reduced due to these oxide films and 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 the above surface treatment method requires 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, a technique has been proposed in which only the chromic acid treatment is applied to the R-Fe-B system permanent magnet (see JP-A-6-302420). Since the washing treatment is necessary and the waste liquid of the chromic acid treatment liquid is difficult to treat easily, the surface treatment cost is not 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 for forming the same, an R-Fe-B system permanent magnet was dipped in a treatment solution consisting of an alkali silicate aqueous solution, or after the treatment solution was applied to the magnet surface, By performing a heat treatment to form a glassy protective layer on the surface of the permanent magnet, the aesthetic appearance is maintained for a long time, the treatment can be performed at a lower cost than conventional surface treatment methods, and waste liquid treatment is easy. Therefore, the present invention has been completed by establishing various conditions, and the gist of the invention is to provide an R-Fe-B system permanent magnet (where R contains Y) in a treatment liquid composed of an aqueous alkali silicate solution. Highly corrosion-resistant permanent magnet characterized by coating the surface of the magnet with a glass-like protective layer having a thickness of 5 nm to 10 μm by dipping at least one rare earth element) or applying the treatment liquid and then performing heat treatment. Or a pretreatment by ultrasonic cleaning is applied to the surface of the R-Fe-B system permanent magnet, and then the magnet is immersed in a treatment solution containing an aqueous alkali silicate solution, or the treatment solution is applied to the magnet surface. A method for producing a highly corrosion-resistant permanent magnet, characterized by coating the surface of the magnet with a glass-like protective layer having a thickness of 5 nm to 10 μm by applying heat treatment, and the thickness produced by the above two methods. A highly corrosion-resistant permanent magnet having a glass-like protective layer of 5 nm to 10 μm.

Hereinafter, the present invention will be described in detail. In the method for forming a glassy protective layer, which is the greatest feature of the present invention,
As a treatment liquid for the surface treatment method, ion-exchanged water is added to an alkali silicate aqueous solution to adjust the concentration. To obtain the following glassy protective layer film thickness (5 nm to 10 μm), SiO _{2 is used.}
Adjust to be 3 to 200 g / L. If it is less than 3 g / L, sufficient corrosion resistance cannot be obtained, and if it exceeds 200 g / L, the viscosity of the aqueous alkali silicate solution becomes high and the film thickness becomes uneven after heat treatment, which is not preferable in appearance. Specific examples of the alkali silicate include water glass (mainly composed of Na ₂ O and SiO ₂ ), potassium silicate, lithium silicate and the like.

In the present invention, the glass-like protective layer formed from an aqueous solution of alkali silicic acid preferably has a thickness of 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. Also, 10μm
If it exceeds, there is no practical problem in 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 made thick, the volume of the R-Fe-B system permanent magnet that can be used will be small even if the outer appearance is the same, which is not preferable in terms of magnet usage. further,
When the thickness of the glassy protective layer is in the range of 100 nm to 3 μm, the effect of the present invention is remarkably exhibited, which is preferable. In the surface treatment method of the present invention, the heat treatment after dipping in an alkali silicate aqueous solution or coating on the surface of the magnet is carried out 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. 50 ° C
If the amount is less than this, evaporation of water and dehydration condensation of silanol groups are not sufficient, and the treatment time becomes 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, when the treatment time is less than 1 minute, water evaporation and dehydration condensation of silanol groups do not proceed sufficiently, and when 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 steps twice or more.

In the surface treatment method of the present invention, as pretreatment, ultrasonic waves are applied immediately before the immersion of the R-Fe-B system permanent magnet in the alkaline silicic acid aqueous solution or immediately before the application of the alkaline silicic acid aqueous solution onto the magnet surface. It is desirable to perform cleaning. The minute processing dust or magnetic powder that is physically adsorbed or magnetically attracted and remains on the magnet surface, which causes the adhesion and corrosion resistance of the glass-like protective layer to desorb from the magnet surface by ultrasonic cleaning The adhesion and corrosion resistance of the protective layer can be improved. Usually, in a wet plating method such as Ni plating and a chemical conversion treatment method such as zinc phosphate treatment, a degreasing step for removing oil and a phase such as a rare earth element oxide that is difficult to cover the protective layer are performed as pretreatment. The surface of the magnet is coated 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, the glass-like protective layer obtained by the present invention is different from the protective layer obtained by wet plating, chemical conversion treatment, etc., and it is possible to easily form a film on a rare earth element oxide or the like, and Since it is not a method of forming a protective layer by reacting the magnet surface with the treatment liquid, 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 required. Even if the pretreatment is performed only for removal, the glass-like protective layer having sufficient adhesion and corrosion resistance can be formed. Therefore, as the pretreatment of the present invention, ultrasonic cleaning may be performed after performing a degreasing step, a pickling step, an activation step, etc. However, the pretreatment only with ultrasonic cleaning simplifies the steps and costs. Can be said to be more preferable.

In the present invention, the rare earth element R of the R-Fe-B system permanent magnet occupies 5 to 40% by weight of the composition.
As Y or La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, D
1 or 2 selected from y, Ho, Er, Lu and Yb
More than one species are used, among which Ce, La, Nd, Pr, Dy, T
It is preferable to contain at least one of b. B is 0.2 ~
The range is 8% by weight. Fe is in the range of 50 to 90% by weight, but the temperature characteristics can be improved by substituting a part of Fe for Co. However, the addition amount of Co is 0.1
If it is less than 10% by weight, the sufficient effect cannot be obtained, while 15% by weight
If it exceeds 0.1%, the coercive force will decrease, so the amount is preferably 0.1 to 15% by weight. Further, Ni, Nb, Al, Ti, Zr, Cr, V, Mn, Mo, for improving the magnetic characteristics or reducing the cost.
At least one selected from Si, Sn, Cu, Ca, Mg, Pb, Sb, Ga and Zn can be added.

[0009]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. (Examples 1 to 7 and Comparative Examples 1 to 3) Ingots having a composition of 32 Nd-1.2B-59.8Fe-7Co in weight ratio were produced by high frequency melting in an Ar atmosphere. This ingot was roughly crushed with a jaw crusher and further 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 vacuum at 1100 ℃
Sintered for 2 hours and further aged at 550 ° C for 1 hour to obtain a permanent magnet. A magnet test piece having a diameter of 21 mm and a thickness of 5 mm was cut out from the obtained permanent magnet, and further subjected to barrel polishing treatment. The obtained test piece was subjected to ultrasonic cleaning in pure water as a pretreatment, immersed in a treatment solution whose water glass had a concentration shown in Table 1, and then placed in a hot air oven for 150 hours.
A heat treatment was performed at 20 ° C. for 20 minutes. 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 a pressure cooker test (120 ° C., 100% RH) by weight reduction of the sample after 100 hours. However, after the test was completed, the rust and the like formed on the test piece were sufficiently removed and the weight was measured to determine the weight reduction per unit surface area. The test conditions and the results are shown in Table 1. The appearance after 100 hours at 80 ° C. and 90% RH was observed and the results are shown in Table 1. As Comparative Examples 1 to 3, the results of the corrosion resistance evaluation of the ones immersed in the treatment liquid outside the applicable range and the untreated test pieces are shown. As you can see from Table 1,
Compared with the untreated product, the test piece having the glassy protective layer has significantly improved corrosion resistance.

[0010]

[Table 1]

(Examples 8 to 13 and Comparative Example 4) A test piece prepared in the same manner as in Example 1 was subjected to ultrasonic cleaning in acetone as a pretreatment, and then the test piece was treated with water glass of SiO ₂ at 40 g / L
After soaking in the treatment liquid containing it, a heat treatment was carried out for 20 minutes at the temperature shown in Table 2 in a hot air oven. The film thickness of the glass-like protective layer formed on the test piece is measured by using XPS.
It was 200 nm. The corrosion resistance was evaluated by a pressure cooker test (120 ° C., 100% RH) by weight reduction of the sample after 100 hours. However, after the test was completed, the rust and the like formed on the test piece were sufficiently removed and the weight was measured to determine the weight reduction per unit surface area. Also, 80 ℃, 90% RH, 1
The appearance after 00 hours and the magnetic properties before and after coating the glassy protective layer with the coil drawing method using a flux meter were measured to determine the deterioration rate, and the results are shown in Table 2. As can be seen from Table 2, even when the heat treatment temperature is lower than 120 ° C, the corrosion resistance is considerably improved, but at 120 ° C or higher, the glassy protective layer having better corrosion resistance is formed. Also, 450
It can be seen that at a high temperature exceeding ℃, the magnetic properties are greatly deteriorated and it cannot be used.

[0012]

[Table 2]

(Examples 14 to 16 and Comparative Examples 5 to 6) Example 1
After performing the pretreatment shown in Table 3 on the test piece prepared in the same manner as above, after dipping in a treatment liquid containing 40 g / L of water glass as SiO ₂ ,
Heat treatment was performed at 150 ° C for 20 minutes in a hot air oven. The film thickness of the glass-like protective layer formed on the test piece is XPS
The measurement was carried out by using a measuring instrument and it was 200 nm. The corrosion resistance was evaluated by a pressure cooker test (120 ° C., 100% RH) by weight reduction of the sample after 100 hours. However, after the test was completed, the rust and the like formed on the test piece were sufficiently removed and the weight was measured to determine the weight reduction per unit surface area. The adhesion of the glass-like protective layer was evaluated by adhering the test piece to the iron piece with an epoxy resin adhesive and then measuring the shearing force. For comparison, a test piece which was ultrasonically washed with water and was not coated with the glassy protective layer was used in Comparative Example 5 which was subjected to degreasing treatment, pickling treatment (3 vol% nitric acid 30 seconds immersion), and ultrasonic water washing which was not coated with the glassy protective film. A piece is shown in Comparative Example 6. From Table 3, it is possible to improve the adhesion and corrosion resistance of the glass-like protective layer by removing the magnetic powder and processing wastes on the surface of the R-Fe-B system permanent magnet before dipping in the aqueous solution of alkali silicate or before coating. I know that Further, it can be seen that there is no problem regarding the adhesion and the corrosion resistance of the glassy protective layer regardless of the presence or absence of the pickling treatment.

[0014]

[Table 3]

[0015]

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 (3)

[Claims] 1. An R-Fe-B system permanent magnet (where R is at least one rare earth element containing Y) is dipped in a treatment solution comprising an alkali silicate aqueous solution, or after the treatment solution is applied. A method for producing a highly corrosion-resistant permanent magnet, which comprises coating the surface of the magnet with a glass-like protective layer having a thickness of 5 nm to 10 μm by performing heat treatment. 2. A pretreatment by ultrasonic cleaning is applied to the surface of an R-Fe-B system permanent magnet, and then the magnet is dipped in a treatment solution containing an alkali silicate aqueous solution, or the treatment solution is applied to the magnet surface. Then, a heating treatment is performed to coat the surface of the magnet with a glass-like protective layer having a thickness of 5 nm to 10 μm. 3. A highly corrosion-resistant permanent magnet having a glass-like protective layer having a thickness of 5 nm to 10 μm, which is produced by the method according to claim 1.