JPH08293424A - Manufacture of oxide permanent magnet - Google Patents

Abstract

PURPOSE: To develop a technique for stably providing an oxide permanent magnet with high iHc as high Br. CONSTITUTION: In manufacture of an oxide permanent magnet by crushing pre-sintered ferrite powder into fine particles, molding the fine particles within a magnetic field, and then sintering the resulting molding, the temperature rise speed at least in a temperature range of 700-900 deg.C of temperature rise in sintering is set to 0.1-2 deg.C/minute. Subsequently, heating is maintained at a holding temperature above 900 deg.C, or the temperature within the range of 700-900 deg.C of the temperature rise in sintering is maintained at least once or more for one or more hours. Subsequently, heating at a holding temperature above 900 deg.C is maintained.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a residual magnetic flux density (hereinafter,
The present invention relates to a manufacturing method for stably obtaining an oxide permanent magnet having a high "Br" and a high coercive force (hereinafter, "iHc").

[0002]

2. Description of the Related Art Generally, oxide permanent magnets such as Sr are used.
In a ferrite magnet, first, raw material powders of iron oxide and strontium carbonate are mixed and mixed, and then calcined to produce Sr ferrite crystals, and then,
The calcinated product thus obtained is pulverized into a fine powder,
After that, the fine powder is wet-molded in a magnetic field and then main-baked to manufacture.

In such a known method for producing an oxide permanent magnet, in order to improve the magnetic properties, in order to achieve a high Br, the ferrite ratio, the sintering density, the crystal orientation degree, or the constituent ferrite particles themselves are changed. It is known that increasing the abundance of single domain particles (crystals) in the sintered body is effective for increasing Is (saturation magnetization) and increasing iHc.

Therefore, as for the Sr ferrite magnet,
Conventionally, various magnet compositions, additives, manufacturing conditions, and the like have been studied based on the above findings in order to achieve high Br and high iHc. Increasing the density of the aggregates inevitably promotes crystal growth and coarsens the crystal grains, resulting in multi-magnetization of the crystal grains, reducing the proportion of single domain grains, and ultimately improving Br and iHc at the same time. It was extremely difficult.

Under these circumstances, in recent years, there has been proposed a method for improving both magnetic properties by classifying fine powders or mixing two or more kinds of fine powders to control the particle size distribution of the fine powders. Has been done. For example, JP-A-4-320009
The invention is disclosed in Japanese Patent Laid-Open No. 6-20819.

[0006] In these methods, the presence of coarse particles is reduced, the proportion of single domain particles is increased, and the amount of ultrafine powder having high sinterability is reduced. The abnormal grain growth of the crystal grains caused by the above is suppressed, and the deterioration of the magnetic characteristics and the variation are reduced. Here, the reason why the ultrafine powder is slightly left is that if the ultrafine powder is extremely small, the density of the compact during compaction is lowered, and the firing that acts as a sintering aid during sintering is performed. This is because if the amount of the ultrafine powder having a high binding property is small, the density of the sintered body after sintering is lowered, and the magnetic characteristics of the sintered body, especially Br and strength are lowered.

[0007]

However, even in these methods, the ultrafine powder having a high sinterability, which acts as a sintering aid during sintering for the reason of improving the sinterability as described above, is also used. Due to the fact that it contains a small amount (diameter <0.1 μm) and that a temperature difference occurs between the surface and the inside of the compact depending on the temperature rise rate during temperature rise As a result, variations in the magnetic properties, and cracks, cracks, and deformations due to the difference in shrinkage between the surface of the molded body and the inside or the difference in local sintering behavior may occur.

The object of the present invention is to improve the Br and iH by reducing the above problems of the prior art.
It is to develop a technique for stably manufacturing the oxide permanent magnet of c.

[0009]

Means for Solving the Problems As means for solving the above problems, the present inventor has found variations in magnetic characteristics when the temperature rising rate during sintering is high and cracks, cracks and deformation during sintering. The following findings were obtained as a result of intensive research on the cause of occurrence of the phenomenon.

(1) When the temperature rising rate during sintering is slow, particles having high sinterability such as ultrafine powder contained in the compact are gradually sintered / disappeared from a low temperature due to surface diffusion and the like. However, while the sintering gradually progresses as a whole, there is a tendency that the sintering becomes uneven and locally occurs as the heating rate increases. Then, as a result of further research on the heating rate and the sintering behavior, the following points were found.

(2) In the method of producing an oxide permanent magnet by pulverizing a calcined raw material powder into a fine powder, molding the fine powder in a magnetic field, and then subjecting the powder to a fine powder Temperature increase rate of at least 700 to 900 ℃
By setting the rate to 0.1 to 2 ° C./minute, almost uniform sintering is caused, and an oxide permanent magnet having high Br and high iHc can be stably obtained.

(3) 700 to 900 ° C. at the time of temperature rise during main firing
The same effect can be obtained by holding the temperature at least once in the temperature range of 1 hour or more.

Here, the gist of the present invention is that the calcinated ferrite powder is pulverized into a fine powder, the fine powder is molded in a magnetic field, and then the fine powder is sintered to produce an oxide permanent magnet. In the method,
A method for producing an oxide permanent magnet, characterized in that a temperature rising rate in a temperature range of 700 to 900 ° C. is set to 0.1 to 2 ° C./min, and then heating and holding is performed at a holding temperature of more than 900 ° C.

From still another aspect, in the present invention, the calcinated ferrite powder is pulverized into a fine powder, the fine powder is molded in a magnetic field, and then the powder is sintered to produce an oxide permanent magnet. In the method, the oxide is characterized by holding at least once in the temperature range of 700 to 900 ° C. at the time of temperature rise during the main calcination for 1 hour or more, and then heating and holding at a holding temperature of more than 900 ° C. It is a manufacturing method of a permanent magnet.

The fine powder used in the manufacturing method according to the present invention, the particle size distribution thereof and the molding method are not particularly limited, and for example, variations in magnetic properties, cracks, and the like due to ultrafine powder having a diameter of <0.1 μm. Any fine powder that causes cracking or deformation may be used. However, in order to obtain an oxide permanent magnet with higher magnetic properties, high Br and high iH
It is desirable to apply a fine powder and a molding method whose particle size is further adjusted so that c can be realized.

[0016]

Next, the reason why the manufacturing conditions are limited as described above in the present invention and the operation thereof will be described more specifically.

First, according to the present invention, the calcinated raw material powder is pulverized into a fine powder, and the obtained fine powder is molded in a magnetic field. In the method for producing a permanent magnet, the heating rate in the temperature range of at least 700 to 900 ° C at the time of heating in the main firing is set to 0.
1 to 2 ° C / min.

There is no particular limitation on the fine powder used for molding in the present invention, but the object of the present invention is to reduce deterioration and variations in magnetic properties after sintering and defects such as cracks, cracks, and deformations, Since it is intended to stably manufacture an oxide permanent magnet having high Br and high iHc, high Br and high i
It is desirable to use fine powders tuned for Hc.

Specifically, an ultrafine powder having a diameter of <0.1 μm is used in 3.
The ferrite fine powder contains 0% by volume or less, preferably 0.5 to 2.0% by volume, and has an average particle size of 0.5 to 1.0 μm as a whole. When using such fine powder for high magnetic properties, the effect of the present invention is more significant.

Also, there is no particular limitation on the molding of such ferrite fine powder, and a conventional method such as pressing in a wet magnetic field can be used. However, from the viewpoint of improving the magnetic properties, it is preferable to use a molding method having excellent particle orientation, for example, a molding method in which the magnetic field direction at the time of molding is orthogonal to the pressing direction, a hydrostatic press in a magnetic field, or the like.

Next, according to the present invention, the rate of temperature increase is 0.1 to within a temperature range of at least 700 to 900 ° C. during temperature increase during the sintering process.
The rate is 2 ° C./minute, but other sintering conditions (holding temperature, holding time, temperature rising rate, etc.) are not particularly limited. For example
Up to 700 ° C, the temperature may be raised at 5 ° C / minute as in the conventional method. The reason why the temperature range in which the rate of temperature rise during the temperature rise of sintering is limited in this way is described below.

As described above, as a result of studying the causes of variations in magnetic properties and cracks, cracks, deformation, etc., it was found that fine powders with a diameter of 0.1 μm or less and a large amount of ultrafine powder, which were not subjected to particle size distribution adjustment, were used. If the formed compact is sintered under conditions where the temperature rise rate is high, where variations in magnetic properties and cracks, cracks, and deformation are likely to occur, the compact is locally burned at a temperature lower than the sintering holding temperature. In the sintered body in which there was a part where the binding progressed and further the sintering proceeded completely, an abnormal grain growth part that was considered to correspond to the above-mentioned local sintering progress part was recognized. Therefore, it was considered that the ultrafine powder contained in the compact had an effect as one of the main causes of the variation in magnetic properties and the occurrence of cracks, cracks, deformation, and the like. However, as described above, if the content of the ultrafine powder in the fine powder to be molded is extremely reduced, it leads to a decrease in the molding density and thus the sintering density. Rather than attempting to achieve this, it was thought that in the sintering stage, this ultrafine powder disappears or is reduced before it contributes to abnormal grain growth and the like.

As is conventionally known, ultrafine powder having a larger specific surface area and larger surface energy than fine powder has excellent sinterability, and surface sintering is dominant in sintering that occurs at low temperature. In consideration of the fact that the neck growth between particles is prioritized, and the increase in crystal grain size and sintering shrinkage are small, the pre-heat treatment in the low temperature part of the molded body causes the ultra-fine powder inside the molded body included at the time of molding. Is reduced. However, if a preliminary heat treatment step for eliminating or reducing the ultrafine powder in such a compact is newly added before the conventional main firing step, the number of steps is increased and the productivity is lowered. It was considered desirable to perform this heat treatment during the existing sintering process.

In addition to this, productivity decreases,
There was a fact that when the temperature rising rate was lowered to 2 ° C./min or less, variations in magnetic characteristics and occurrence of cracks, cracks, deformation, etc. were small as in the case of performing the preliminary heat treatment.

Therefore, variations in magnetic characteristics and cracks,
In order to suppress the occurrence of cracking, deformation, etc., the step of performing the heat treatment for eliminating or reducing the ultrafine powder in the compact should be performed during the current sintering step, except for the portion corresponding to the preliminary heat treatment. In this temperature range, the rate of temperature increase is not particularly limited so as not to cause a decrease in productivity, and the method for producing an oxide permanent magnet is limited to a specific temperature range only.

Therefore, in the present invention, the temperature range defining the cooling rate is set to 700 to 900 ° C. because the sintering reaction rate is greatly influenced by the particle size in that temperature range.

The upper limit of the rate of temperature rise is 2 ° C./min. If the rate of temperature rise is made higher than this, the temperature difference between the inside of the compact during sintering will cause a difference between the center and the periphery of the compact. In addition to the difference between the sintering states of the above, the time required for the ultrafine powder to sufficiently disappear before reaching the temperature that adversely affects the sintering, resulting in variations in magnetic properties and cracks, This is because sufficient stabilization such as cracking and deformation cannot be obtained. The lower limit rate of 0.1 ° C./min means that if the temperature raising rate is lower than this, the temperature raising time will be extremely long and the productivity will be significantly reduced.
Even if the heating rate is further decreased below ℃ / min, no further improvement in magnetic property variations and cracks, cracks, deformations, etc. is observed, so from the viewpoint of productivity, the lower limit heating rate is 0.1 ℃ / min. Minutes

In the present invention, the heating rate in the limited temperature range is shown only in that range, but it is desirable to slow down the heating rate on the low temperature side in the limited temperature range and to increase it on the high temperature side. It is better to change the heating rate such as increasing the heating rate, because it reduces the dispersion of magnetic properties due to the disappearance or reduction of ultrafine powder and reduces cracks, cracks, deformation, etc. and shortens the sintering time. This is desirable because it improves both productivity.

Further, the same effect is obtained as shown in another embodiment of the present invention, in the sintering process, at least once or more in the temperature range of 700 to 900 ° C. for the purpose of eliminating or reducing the ultrafine powder, This can also be achieved by providing a temperature holding step for 1 hour or more.

The limitation of the temperature range in the temperature holding step is the same as the above reason. If the holding time in the holding step in this mode is less than 1 hour, sufficient reduction of the ultrafine powder cannot be expected, and sufficient effect of holding the temperature cannot be recognized. The upper limit is not particularly limited, but from the economical viewpoint, holding for a very long time is not desirable and may be 5 hours or less.

Then, the temperature is raised at a specific heating rate in the temperature range of 700 to 900 ° C., preferably further held, and then heated and held at a temperature higher than 900 ° C.,
Complete the sintering. Usually, the holding temperature at this time is 1000 ~
It is 1300 ° C. The holding time is until sintering is completed,
This is usually about 30 minutes to 2 hours. Next, the working effects of the present invention will be described more specifically by way of examples.

[0032]

【Example】

(Example 1) Sr ferrite calcination powder having a molar ratio of Fe ₂ O ₃ and SrO of 5.8 was wet pulverized by a ball mill to obtain a slurry. At this time, the average particle diameter of the ferrite crystal fine powder was 0.72 μm as determined by the air permeation measurement method. Next, after adjusting the concentration of this slurry to 60%, it was molded in a wet magnetic field at a molding pressure of 0.5 ton / cm ² and a magnetic field strength of 7 kOe using a wet magnetic field press machine, and a cylindrical shape with a diameter of 25 and a height of about 15 mm was used. A molded body of was obtained. The magnetic field orientation direction was the same as the pressing direction.

Next, after drying the molded body, the temperature rising rate of 700 to 900 ° C. was changed according to the firing profile shown in FIG. 1 to produce 10 sintered bodies under each condition, and the magnetic characteristics were obtained. And visual inspection for cracks, cracks, deformation, etc. was performed.

The results are summarized in Table 1. The firing profile in the conventional example was as shown in FIG. As is clear from the results of Table 1, in the temperature rising profile of the present invention, stabilization of magnetic properties and reduction of appearance defects are recognized.

[0035]

[Table 1]

(Example 2) A molded body was prepared under the same conditions as in Example 1 and dried, and then the holding temperature T was changed by keeping the holding temperature 90 minutes constant in the firing profile shown in FIG. We made a 10P sintered body under the conditions,
A visual inspection such as cracking or deformation was performed.

As a result, as shown in Table 2, in the comparative example, the magnetic characteristics could not be sufficiently stabilized and the appearance was poor, whereas in the inventive example, the magnetic characteristics were stabilized and the appearance was poor. Reduction is observed.

[0038]

[Table 2]

Example 3 A molded body was prepared under the same conditions as in Example 1 and dried, and then the holding temperature was kept constant at 800 ° C. and the holding time t was changed according to the firing profile shown in FIG. Ten sintered bodies were produced under each condition, and the magnetic properties and the appearance inspections such as cracks, cracks, and deformations were performed.

As a result, as shown in Table 3, the retention time is 60
If it is less than a minute, sufficient stabilization cannot be achieved, and 90 minutes, which is a long holding time, is a good result almost equal to the holding time of 60 minutes. The baking profile in the conventional method was as shown in FIG.

[0041]

[Table 3]

[0042]

As described above, according to the present invention,
The ultrafine particles contained in the compact during sintering disappear or decrease before the temperature range that causes coarsening of crystal grains, and the temperature distribution in the compact in the temperature range in which the ultrafine particles are present is almost uniform. Therefore, the deformation due to the difference in local sintering rate due to the temperature difference is reduced, the deterioration of iHc due to the coarsening of the crystal particles due to the ultrafine particles is suppressed, and the magnetic characteristics due to the sintering are suppressed. Variation, cracks, cracks, and deformation can be reduced. The method of the present invention is effectively applied not only to Sr-based ferrite magnets but also to oxide permanent magnets such as Ba-based ferrite magnets.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a firing profile of Example 1 of a method for manufacturing an oxide permanent magnet according to the present invention.

FIG. 2 is an explanatory view of a firing profile in Examples 2 and 3 of the method for producing an oxide permanent magnet according to the present invention.

FIG. 3 is an explanatory diagram of a firing profile of a conventional example in Examples 1 to 3.

Claims (2)

[Claims] 1. A method for producing an oxide permanent magnet by pulverizing a calcinated ferrite powder into a fine powder, molding the fine powder in a magnetic field, and then subjecting the fine powder to a fine powder in the magnetic field. At a temperature rising rate of at least 700 to 900 ° C. of 0.1 to 2 ° C./min, and then heating and holding at a holding temperature of more than 900 ° C., a method for producing an oxide permanent magnet. 2. A method for producing an oxide permanent magnet by pulverizing a calcinated ferrite powder into a fine powder, molding the fine powder in a magnetic field, and then subjecting the powder to a permanent magnet to increase the temperature during the main firing. At least once in the temperature range of 700-900 ℃,
A method for producing an oxide permanent magnet, which comprises holding for 1 hour or more, and then heating and holding at a holding temperature of more than 900 ° C.