JPH10265260A - Production of calcined ferrite powder and production of ferite magnet using the powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce calcined ferrite powder for a high performance ferrite magnet having a small particle diameter and almost uniform narrow particle size distribution by granulating starting material giving a specified compsn. after calcination to a specified particle diameter range and carrying out calcination at a specified temp. in a fluidized bed. SOLUTION: An aq. PVA soln. having 0.1-10 wt.% concn. is added by 0.1-1 wt.% to a slurry of an Fe2 O3 -MO mixture giving a basic compsn. represented by the formula MO.nFe2 O3 [where M is one or more kinds of metals selected from among Ba, Sr and Pb and (n) is 5-6] after calcination and the mixture is granulated to 20-10O μm particle diameter by a granulating means such as spray drying. The granulated mixture is fed into a fluidized bed and calcined at 1,000-1,200 deg.C under fluidization to obtain the objective calcined ferrite powder. This powder is pulverized to 0.5-1 μm average particle diameter, further wet- pulverized to 0.3-0.8 μm average particle diameter, concentrated, kneaded, wet- molded in a magnetic field and sintered to obtain the objective ferrite magnet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a calcined powder for a ferrite sintered magnet capable of obtaining higher magnetic properties than before and a method for producing a ferrite magnet using the same.

[0002]

2. Description of the Related Art In general, strontium ferrite magnets are widely used in electric motors and the like because of their high magnetic properties, economical efficiency and environmental resistance. But,
Demands for further miniaturization and higher performance are increasing. In order to obtain a ferrite sintered magnet having high magnetic properties, the ferrite crystal grain size of the sintered body should be close to a single domain grain size (improved intrinsic coercive force iHc), and the ferrite crystal grains should be aligned in the direction of magnetic anisotropy. (Improvement of residual magnetic flux density Br) and high density (improvement of Br) are important.
In order to achieve the above, it is necessary to reduce the size of the finely pulverized particles before sintering to a particle diameter of a single magnetic domain or less, improve the degree of orientation of the compact during compaction in a magnetic field, and further sinter at an appropriate temperature. It is. In order to mass-produce such high-performance ferrite magnets, it is generally necessary to produce a relatively large calcined body at the calcining stage, pulverize it by a mechanical pulverization method, and reduce the raw material to a single magnetic domain particle size. . This fine powder raw material is formed in a magnetic field and fired to obtain a product. Generally, it is effective to grow ferrite crystals to some extent to improve Br, but this immediately leads to a decrease in iHc. In order to simultaneously improve both contradictory magnetic properties, additives,
Optimization studies on particle size distribution and the like have been made. However, it is very difficult to produce a ferrite magnet excellent in both Br and iHc. This is mainly because there is a distribution in the pulverized particle diameter, and as a result, there are many crystal particles in the magnet structure that are larger than the single magnetic domain particle diameter. For example, the presence of ultrafine particles in the pulverized particles promotes abnormal grain growth and leads to a decrease in iHc. Also, the presence of coarse particles also results in a low iHc.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a calcined coarse powder for a high-performance ferrite magnet having a small particle size and a narrow particle size distribution without relying too much on conventional particle size control by pulverization. It is an object of the present invention to provide a method for manufacturing a high-performance ferrite magnet using the same.

[0004]

Means for Solving the Problems The present inventors granulate a ferrite raw material and calcine it while flowing it to obtain a high-performance ferrite powder having a finer primary particle diameter and a narrower particle diameter distribution than before. It has been found that calcined coarse powder for a magnet can be obtained. Further, they have found that a finer ferrite magnet with higher performance than before can be obtained by finely pulverizing and kneading the coarse powder. That is, the present invention relates to MO.nFe ₂ O ₃ (M: B
Manufacture of calcined ferrite powder having a basic composition of at least one of a, Sr, and Pb (n = 5 to 6) and obtained by calcining a granulated material of 20 to 100 μm in a fluidized state. In this method, the calcined powder is roughly pulverized as appropriate to obtain a calcined ferrite powder having an average particle size of 0.5 to 1 μm. Further, the present invention relates to MO.nFe ₂ O ₃ (M: Ba,
One or more of Sr and Pb, n = 5 to 6), and the calcined coarse powder having an average particle diameter of 0.5 to 1 μm is reduced to an average particle diameter of 0.3 to 0.8 μm. After wet pulverization, concentration,
This is a method for producing a high-performance ferrite magnet that is kneaded, wet-formed in a magnetic field, and sintered.

The above calcined coarse powder according to the present invention is obtained by the following production method. MO ・ nFe ₂ O after calcination
₃ (M: one or more of Ba, Sr, Pb, n = 5
Fe ₂ O ₃ were mixed so as to have a basic composition of 6) and SrC
The mixture slurry consisting O ₃ Prefecture, 0.1 a PVA aqueous solution having a concentration of 0.1 to 10% by weight relative to the mixed raw material powder
After adding 1% by weight, the mixture is granulated to a sieving particle diameter of 20 to 100 μm by a granulation means such as a spray drier. 20
If it is less than μm, it is difficult to maintain a fluidized state under calcination heating, and if it exceeds 100 μm, the heat conductivity during fluidized bed heating decreases. Next, the granulated product is calcined using an apparatus generally called a fluidized bed. That is, the fluidized bed is a device that sends air from below into a powder particle layer on a perforated plate and fluidizes it (in a state where each particle is moving randomly due to a drag received from an airflow). The temperature at which the particles in the fluidized state can be turned into ferrite is 10
Calcination is performed by heating and holding at 00 to 1200 ° C. If the calcination is less than 1000 ° C., the ferrite-forming reaction is insufficient. If the calcination exceeds 1200 ° C., the grain growth proceeds, and the pulverization efficiency in the subsequent step is undesirably reduced. Since the particles in the fluidized bed are moving violently, the temperature in the fluidized bed is maintained almost uniformly, and the heat transfer capacity is high. For this reason, the temperature required for calcination can be suppressed lower than the conventional calcination method. The calcined powder thus obtained is coarsely pulverized to a mean particle size of 0.5 to 1 μm using a device such as a vibration mill. When the average particle size of the coarsely ground powder is less than 0.5 μm, when the coarsely ground powder is wet-milled, it is over-milled, and a large amount of ultrafine powder having a particle size of less than 0.5 μm is generated, and the particle size distribution is widened, resulting in magnetic properties. The characteristics also deteriorate. On the other hand, if the average particle diameter of the coarsely pulverized powder exceeds 1 μm, large particles of about 1 μm remain even after wet pulverization, which causes a decrease in the degree of orientation of the sintered ferrite magnet.

Then, the calcined coarse powder according to the present invention is finely wet-pulverized by an apparatus such as a ball mill or an attritor. The average particle diameter of the finely pulverized powder is desirably 0.3 to 0.8 μm. When it is less than 0.3 μm, physical and magnetic aggregation of the particles becomes strong, the degree of orientation during magnetic field forming is remarkably reduced, and coarse particles are easily generated, so that the holding power is apt to be reduced. On the other hand, if the thickness exceeds 0.8 μm, the coercive force also decreases, and it is difficult to realize high magnetic properties.

Next, the obtained slurry of the finely ground ferrite powder is dried and pulverized, and then the solid content concentration is 75 to 88 by weight.
A high-concentration slurry by weight is prepared and kneaded with a device such as a kneader that applies mechanical shearing force. At the time of kneading, it is desirable to use a dispersant for the purpose of improving the dispersibility in the finely pulverized slurry. At the time of kneading, a dispersant of 0.5 to 5.0% by weight based on the solid content is used. The addition improves the dispersibility of the ferrite particles in the slurry and improves the magnetic properties.

According to the present invention, the granulated ferrite raw material before calcining is calcined while being fluidized in an air stream, so that a ferrite phase can be obtained at a calcining condition lower than before,
A calcined body having a primary particle diameter of 0.5 to 1 μm in average particle diameter is obtained. Furthermore, by coarsely pulverizing the powder, a calcined ferrite powder having a smaller particle size and a narrower particle size distribution than before can be obtained. A ferrite magnet having the same can be obtained. Here, the average particle diameter in the present invention is a powder particle diameter measured by an air permeation method (Fisher sub-sieve sizer).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to examples. (Example 1) after calcination in _{SrO · nFe 2 O 3, n} = 5~6
0.5% by weight of a 5% by weight aqueous PVA solution was added to a raw material obtained by mixing SrCO ₃ and Fe ₂ O ₃ so as to have a basic composition of It was granulated to a particle size of 50 μm. The particle size of the granulated product may be confirmed by a scanning electron microscope. Next, the granulated product was calcined at 900 to 1300 ° C. as shown in Table 1 while fluidizing. Each calcined powder was ground with a vibration mill for 6 hours to obtain a ferrite coarse powder. 0.5 wt% of SrCO ₃ and CaC
After adding 0.8% by weight of O ₃ and 0.3% by weight of SiO ₂ and further adding water to form a slurry having a solid content of 40% by weight, the slurry was adjusted to an average particle diameter of 0.82 to 0.85 μm. It was wet-milled with a lighter. This slurry is applied with a magnetic field strength of 8k.
The magnetic properties (Br, iHH) of each ferrite magnet obtained by compression-molding under a pressure of 400 kgf / cm ² in a magnetic field of Oe and then sintering at 1100 to 1200 ° C. for 2 hours.
c) is shown in Table 1.

[0010]

[Table 1] M: Macnetophranite phase (SrO.nFe2O3)

According to Table 1, the higher the calcining temperature, the larger the primary particle diameter of the coarse powder. Therefore, if the calcining temperature is higher than 1200 ° C., the features of the present invention cannot be utilized. When the calcination temperature is low, hematite is formed, so that the primary particle size is small, but the obtained magnetic properties are low. That is, if the calcination temperature is 1
It can be seen that excellent magnetic properties can be obtained at 000 to 1200 ° C.

[0012] For the ferrite coarse powder (Example 2) Example 1, SrCO ₃ 0.5% by weight, the CaCO ₃ 0.8
% By weight, SiO ₂ was added in an amount of 0.3% by weight, and water was further added to form a slurry having a solid concentration of 40% by weight. Then, the slurry was wet-milled to an average particle diameter of 0.72 to 0.84 μm using an attritor. . After heating and drying this finely pulverized slurry, water and a dispersant were added, and the mixture was kneaded with a kneader for 1 hour as a slurry having a solid content concentration of 84% by weight. After kneading, water was added for dilution to obtain a slurry having a solid content of 75% by weight. This slurry is placed in a magnetic field with a magnetic field strength of 8 kOe for 400
compression molding at a pressure of kgf / cm ² ,
Table 2 shows the magnetic properties of the ferrite magnet obtained by sintering at 00 ° C. for 2 hours.

[0013]

[Table 2]

From Table 2, it can be seen that as compared with the case where the conventional coarse powder was used, the one using the coarse powder of the present invention exhibited higher magnetic properties.

Next, the particle size distribution of the finely pulverized powder obtained by drying the finely pulverized slurry of Example 2 is shown in FIG. FIG. 1 also shows the particle size distribution of the conventional fine powder obtained by pulverizing the conventional coarse powder of Table 2 in the same manner as the finely pulverized powder of Example 2. From FIG. 1, it can be seen that the finely pulverized powder according to the present invention has a smaller particle size peak and a narrower particle diameter distribution than the conventional finely pulverized powder, and is suitable for obtaining high magnetic properties.

[0016]

According to the present invention, the mixed raw material granulated in the method for producing a high-performance ferrite magnet is fluidized and calcined to obtain a narrower particle diameter distribution with a smaller particle diameter and a substantially uniform particle diameter than the conventional one. Ferrite coarse powder and finely pulverized ferrite powder can obtain almost uniform finely pulverized powder with a narrow particle size distribution, and can improve the magnetic properties of ferrite sintered magnets manufactured using this powder as compared to conventional products. .

[Brief description of the drawings]

FIG. 1 is a diagram showing the effect of improving the particle size distribution of pulverized particles by a fluid calcining method.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yoshiro Adachi 2-24-16 Nakamachi, Koganei-shi, Tokyo Graduate School of Biosystems and Applied Sciences, Tokyo University of Agriculture and Technology (72) Inventor Masatoshi Horio 2-24 Nakamachi, Koganei-shi, Tokyo −16 Tokyo University of Agriculture and Technology Graduate School of Biological Sciences

Claims (2)

[Claims] 1. After calcination, MO.nFe ₂ O ₃ (M: Ba,
One or more of Sr and Pb, n = 5 to 6) The raw materials mixed so as to have a basic composition of 20 to 100 μm are granulated to 1000 to 100 μm while being fluidized in a fluidized bed.
A method for producing a calcined ferrite powder, wherein the calcined powder is calcined at 1200 ° C. 2. A coarsely pulverized ferrite calcined powder having an average particle diameter of 0.5 to 1 μm obtained by coarsely pulverizing the calcined powder according to claim 1 to wet pulverization to an average particle diameter of 0.3 to 0.8 μm. After, concentration,
A method for producing a ferrite magnet, comprising kneading, wet forming in a magnetic field, and sintering.