JPH0412603B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a powder permanent magnet which has a high coercive force and is extremely stable with small magnetic fluctuations due to temperature changes. Permanent magnets are broadly classified into alloy magnets made of bulk magnetic alloys and powder magnets made of magnetic powder, and powder magnets are further classified into sintered magnets and composite magnets. Composite magnets are obtained by combining rubber, plastic, or metal with ferromagnetic powder, and it is possible to produce complex-shaped magnets at low cost.
In recent years, its use has been increasing in particular. Most conventional composite magnets utilize single domain size high coercive force powders such as barium ferrite, strontium ferrite, and rare earth cobalt compounds, which have large crystal magnetic anisotropy. These magnetic powders with large magnetocrystalline anisotropy have the advantage of producing a high coercive force magnet because the interaction between powder particles is so small that it can be ignored during powder compaction. It has the disadvantage of large fluctuations in magnetic properties. On the other hand, as high coercive force magnetic powders that exhibit little variation in magnetic properties due to temperature changes, alnico alloy powders, Fe-Cr-Co alloy powders, etc., which can obtain high coercive forces due to shape anisotropy, are known. However, magnetic powders that obtain high coercive force due to shape anisotropy have the disadvantage that when compacted, the coercive force rapidly decreases due to magnetic interaction between powder particles. One way to solve this problem is to coat single-domain particles with large shape anisotropy with a non-magnetic material, and then disperse the single-domain particles in the non-magnetic material so that the magnetic interaction between the particles is reduced. is possible. A composite magnet that realizes this idea
ESD (Elongated Single Domain) magnets are the only known. ESD magnets are manufactured, for example, by the following method (“J.Appl.phys.,” 1966, 37
(See Volume 108). First, elongated fine particles of iron or iron-cobalt alloy are precipitated on a mercury electrode in a metal salt solution, grown into an appropriate shape, such as a single magnetic domain size, by heat treatment, and then mixed with non-magnetic lead powder and placed in a magnetic field. After the mercury is removed by vacuum distillation, it is crushed into a magnetic powder in which elongated single-domain size iron or iron-cobalt alloy is dispersed and aligned in non-magnetic lead, which is then compression-molded in a magnetic field. Manufactured by FIG. 1 is a schematic diagram showing a magnetic powder 1 in which iron or iron-cobalt alloy 2 of elongated single-domain size used in an ESD magnet is dispersed and aligned in non-magnetic lead 3. Usually, the elongated iron or iron-cobalt alloy has a diameter of about 0.02 μm and a length of about 0.1 μm, and a single magnetic domain mechanism based on its shape anisotropy provides a high coercive force. However, the manufacturing process of ESD magnets is complicated and has the drawback of evaporating and removing mercury, which is harmful to manufacturing. The present invention provides a method for manufacturing a powdered permanent magnet which, unlike the above-mentioned conventional magnets, has less magnetic fluctuation due to temperature changes, does not have a coercive force decrease even during powder processing, and is easy to manufacture. In this method, fine particles of porous aluminum oxide whose pores are filled with a ferromagnetic metal or a ferromagnetic alloy are compression molded in a magnetic field in which the direction of pressure and the direction of the applied magnetic field are approximately perpendicular to each other, and then solidified. It is characterized by obtaining a permanent magnet. The present invention will be explained in detail below along with examples.
FIG. 2 shows an enlarged schematic diagram of the magnetic powder used in the present invention. As shown in the figure, the magnetic particles 4 are powder particles in which the pores of porous aluminum oxide 6 are filled with a ferromagnetic material 5 of a single metal or an alloy. The above-mentioned magnetic powder 4 can be easily obtained by the manufacturing method shown in Japanese Patent Application No. 141211/1982. The outline of this manufacturing method is that an aluminum or aluminum alloy substrate is first anodized to form a porous aluminum oxide film, and then a ferromagnetic metal or ferromagnetic material is electroplated into the pores of the porous aluminum oxide film. By precipitating the alloy and crushing the porous aluminum oxide film in which the pores are filled with the ferromagnetic metal or ferromagnetic alloy into fine particles, with or without separating from the aluminum or aluminum alloy substrate. This is a manufacturing method for obtaining the above magnetic powder. The magnetic powder obtained in this way may be used as it is, but since it contains water, it is preferable to heat it at a temperature between room temperature and 200°C, or to degas it in a vacuum while heating it. is good. The ferromagnetic material 5 in the magnetic powder obtained by the above manufacturing method has a diameter of about 0.01 to 0.04 μm,
The length depends on the particle size of the magnetic powder, but is usually 0.1 to 1 μm.
It is. Further, these ferromagnetic materials 5 are arranged in one direction in the aluminum oxide at intervals of about 0.02 to 0.08 μm. In this way, the magnetic powder 4 is filled with ferromagnetic substances 5 made of metal or alloy aligned in one direction, and each ferromagnetic substance 5 is coated with the surrounding aluminum oxide 6, so that it is strong. The magnetic bodies 5 do not directly coalesce, and a sudden drop in coercive force due to magnetic interaction can be prevented. In general, a porous aluminum oxide film obtained by an anodic oxidation method has fine pores arranged in alignment, and since aluminum oxide is a nonmagnetic material, it is suitable as a base for the ferromagnetic material 5. When the porous aluminum oxide film is plated with cobalt or the like by electroplating, cobalt etc. are deposited in the pores of the aluminum oxide film,
If this is pulverized into powder, a magnetic powder suitable as a raw material for the present invention can be obtained. The present invention comprises compression molding the above magnetic powder in a magnetic field,
Solidify to produce permanent magnets. At this time, favorable results can be obtained even if the magnetic properties are set such that the direction of pressure and the direction of the applied magnetic field are perpendicular to each other. still,
Good magnetic properties can be obtained even with isotropic compression molding such as a rubber press because sufficient magnetic field orientation is performed. In order to improve the mechanical strength of such a compression-molded magnet, the molded body is impregnated with a binder and solidified at room temperature or by heating. At this time, it is desirable to subject the molded magnet to vacuum treatment immediately before impregnation. The impregnation binder is a liquid organic resin, and impregnation is carried out at room temperature or by heating to an appropriate temperature for the purpose of lowering the resin viscosity.
It is carried out by immersion in a liquid organic resin in the atmosphere or under high pressure conditions. Furthermore, in order to improve the mechanical strength of the powdered permanent magnet of the present invention, kneading or mixing the magnetic powder and the binder after degassing treatment,
This mixture is preferably placed in a mold, compression molded in a magnetic field, and then heated and solidified at an appropriate temperature. In this case, a powdered organic resin is used as the binder. The organic resin used in the above two manufacturing methods may be either a thermosetting resin (eg, epoxy resin, phenolic resin) or a thermoplastic resin (eg, nylon resin, vinyl chloride resin). Next, examples of the present invention will be shown. Example 1 Acicular cobalt fills and precipitates into the pores of aluminum oxide. Particle size is approximately 0.5 μm, saturation magnetization is 23 emu/g.
of magnetic powder in a vacuum of 4 x 10 ^-5 mmHg at 150°C.
After being degassed for a period of time, it was placed in a mold, the direction of pressure and the direction of the applied magnetic field were made perpendicular, and compression molding was performed in the magnetic field while varying the pressure and strength of the magnetic field to obtain a powder permanent magnet. Table 1 shows the magnetic properties of the powdered permanent magnet obtained. As is clear from the results in Table 1, when only compression molding is performed without an applied magnetic field, the residual magnetization, squareness ratio, and coercive force are low due to the random orientation of the powder, but when compression molding is performed with the addition of a magnetic field, the squareness ratio is low. Good high coercive force magnet characteristics can be obtained. In addition, as the pressure increases, the density improves, so the saturation magnetization increases,
The residual magnetization also increases.

[Table] Example 2 Acicular cobalt-iron alloy (Co70wt% - Fe30wt%) was filled and precipitated into the pores of aluminum oxide. Magnetic powder with a particle size of about 0.7 μm and a saturation magnetization of 20 emu/g was mixed into 100 μm.
After degassing in a vacuum at 4×10 ^-5 mmHg for 2 hours, it was placed in a mold and a magnetic field was applied with a pressure of 3 ton/ ^cm2.
Compression molding was performed under 15kG conditions. The obtained molded body was treated at room temperature in a vacuum of 2 x 10 ^-4 mmHg for 1 hour, and then immersed in a one-component epoxy adhesive heated to 50°C, while applying a pressure of about 3 atm. It was soaked for 2 hours. After this, take it out from the soaking tank and let it stand in the air.
It was heated at 130°C for 1 hour to solidify. The density of the magnet thus obtained was 2.3 g/cm ² , and the magnetic properties were saturation magnetization (4πIs) 360G, residual magnetization (4πIr) 328G,
The coercive force (IHc) was 2100 Oe. Further, while it was impossible to cut the compression-molded magnet without impregnation treatment, it was possible to cut the magnet with impregnation treatment. Example 3 Acicular cobalt fills and precipitates into the pores of aluminum oxide. Particle size is approximately 0.5 μm, saturation magnetization is 2.3 emu/g.
After degassing in a vacuum at 150°C and 4 x 10 ^-5 mmHg for 1 hour, 95% by weight of magnetic powder and 5% by weight of powdered epoxy resin were mixed and placed in a mold, and the mixture was heated at 3.5ton/ ^cm2 . 150℃ while applying pressure and 13kG magnetic field intermittently
It was heated for 1 hour and compression molded. The density of the obtained magnet is 2.4 g/cm ² and the magnetic property is saturation magnetization (4πIs).
390G, residual magnetization (4πIr) 353G, and coercive force 1800Oe. Furthermore, the magnet manufactured in this manner could be machined. As mentioned above, the permanent magnet obtained by the manufacturing method of the present invention exhibits a high coercive force based on the shape-anisotropic single domain mechanism, and since it uses magnetic powder with almost no magnetic interaction, it can be compressed and molded. The magnet does not lose its high coercive force even when exposed to heat, has high mechanical strength, exhibits little magnetic fluctuation due to temperature changes, and has a small density, making it suitable for use in equipment such as precision instruments and artificial satellites.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of magnetic powder used in ESD magnets. FIG. 2 is a schematic diagram of magnetic powder used in the powder permanent magnet of the present invention. In the figure, 1...magnetic powder in which elongated iron or iron-cobalt alloy is dispersed and aligned in lead, 2... elongated iron or iron-cobalt alloy, 3... lead, 4... needle-shaped ferromagnetic metal or strong Magnetic powder in which a magnetic alloy is dispersed in aluminum oxide, 5... Acicular ferromagnetic metal or ferromagnetic alloy, 6... Aluminum oxide.

Claims (1)

[Claims] 1. Fine particles of porous aluminum oxide whose pores are filled with a ferromagnetic metal or a ferromagnetic alloy are compression-molded in a magnetic field such that the direction of pressure and the direction of the applied magnetic field are approximately perpendicular to each other. A method for producing a powdered permanent magnet, characterized in that a permanent magnet is obtained by solidifying the powder. 2. A method for manufacturing a powder permanent magnet according to claim 1, characterized in that during compression molding, aluminum oxide fine particles are impregnated with a binder made of an organic resin. 3. A method for manufacturing a powder permanent magnet according to claim 1, characterized in that when solidifying after compression molding, the molded body is impregnated with a binder made of an organic resin and solidified.