JPH0661029A - Manufacture of oxide permanent magnet - Google Patents

Abstract

PURPOSE:To obtain a method of manufacturing easily an Sr ferrite magnet, which is superior in both of Br and iHc. CONSTITUTION:In the case of a method of manufacturing an oxide permanent magnet, which calcinates a raw material at a temperature of 1200 to 1350 deg.C, obtains Sr ferrite calcinated powder by grinding the calcinated material and thereafter, grinds the calcinated powder, molds the ground powder in a magnetic field and thereafter, calcinates finally the molded powder, calcinated powder obtainable by adding further 5 to 25wt.% of Sr ferrite powder calcinated at 1150 deg.C or higher and at a temperature region of a calcinating temperature of lower to the Sr ferrite calcinated powder is used as calcinated powder which is supplied to the molding. Thereby, it becomes possible to manufacture easily a high-Br and high-iHc Sr 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 manufacturing an oxide permanent magnet, and more particularly to a residual magnetic flux density (hereinafter simply referred to as "Br") and a coercive force (hereinafter simply referred to as "i").
Hc ”) is excellent, and a method for advantageously producing a high-performance oxide permanent magnet suitable for use in a rotating machine segment and the like is proposed.

[0002]

2. Description of the Related Art Oxide permanent magnets, especially Sr ferrite magnets, are widely used as various magnet materials because of their abundant raw material resources and low cost. There is one.

Generally, this Sr ferrite magnet is manufactured through the steps of raw material mixing, calcination, pulverization, molding and firing. That is, first, the main components of iron oxide and strontium oxide or strontium carbonate are represented by the chemical formula SrO
・ Weigh nFeO _{3 so} that n = 5.2 to 6.2,
Wet mix and dry. Next, this dry mixture is mixed with 12
Calcination at a temperature of 00 to 1350 ℃ for about 1 hour, then crushing and S
r Calcinated powder of ferrite is obtained. After that, the obtained calcined powder was pulverized after adding a predetermined amount of a component capable of becoming a sintering accelerator or a crystal growth inhibitor, and an average particle size of 0.7 to 1.0.
A micronized powder of μm is obtained. After that, the finely pulverized powder obtained is subjected to molding in a wet magnetic field and then fired in a temperature range of 1200 to 1260 ° C. to produce an Sr ferrite magnet.

The Sr ferrite magnet manufactured in this way is not necessarily excellent in Br and iHc. Therefore, for example, when the Sr ferrite magnet is used as a motor segment, when the motor is started, When restrained, a large demagnetizing field may act due to an excessive current flowing through the armature, resulting in a decrease in magnetic force. From this,
Conventionally, it has been desired that the Sr ferrite magnet has excellent Br and iHc.

However, in order to obtain a magnet material exhibiting a high Br value that can meet the demands of the field, it is necessary to use a raw material having a high saturation magnetic flux density to form a highly oriented and high density sintered body. Mandatory. That is, in order to cope with the high Br, a high-purity raw material has a high molar ratio (n = 5.8 to 6.
0)), calcined at a temperature higher than the final sintering temperature to promote the ferritic reaction sufficiently, and then pulverize the calcined product, and magnetize the fine powder obtained by molding in a wet magnetic field. A method of orienting in the easy axis direction and then firing at a temperature that can sufficiently increase the sintered density is adopted.

On the other hand, in order to cope with high iHc, it is necessary to suppress the crystal grain size to a single domain grain size or less. That is, the single domain limit grain size of Sr ferrite is generally about 0.94μ.
It is said that the average particle size of the Sr ferrite calcined product is at least about 0.1 in order to achieve high iHc.
It is necessary to suppress grain growth during firing by pulverizing to 7 to 0.9 μm and adding a crystal growth inhibitor.

From the above, it is understood that it is necessary to simultaneously realize high density and suppression of grain growth in order to simultaneously realize high Br and high iHc of the magnet material. For this purpose, for example, CaO and _{PbO, Bi 2 O 3, B} 2 O 3 is a method of crystal growth inhibitor is calcined by combined addition of such a sintering accelerator SiO ₂ or Al ₂ O _3, such as but From the viewpoint of at least high Br, it is desirable to suppress the non-magnetic component as low as possible, and it is not preferable to use an additive more than necessary. Therefore, in this method, it is not possible to improve both Br and iHc at the same time. There was a limit.

On the other hand, there is also a conventional method for improving both Br and iHc of the magnet material by making the crushed particle size of the Sr ferrite powder fine. However, in this conventional method, when the average particle size is 0.7 μm or less, the time required for the pulverization becomes long, so that the composition variation and the abrasion of the pulverizer become remarkable, and the pulverized particle size is small, so that the molding in the wet magnetic field is performed. However, there was a problem in that the moldability in Example 2 deteriorated and the productivity extremely deteriorated.

As described above, simultaneous improvement of Br and iHc of the magnetic material has been difficult to realize because it is necessary to use phenomena that are mutually contradictory in a normal sintering mechanism.

[0010]

On the other hand, in recent years,
By mixing two types of pulverized powders with an average particle size of 1.0 to 1.3 μm and 0.75 to 1.0 μm and molding in a magnetic field, the orientation and the sintering density are improved without compromising the moldability and high Br is achieved. And an attempt to achieve high iHc have been proposed (see Japanese Patent Publication No. 60-50324).

However, in this known method, in order to obtain two kinds of finely pulverized powder, it is necessary to perform the pulverization treatment in two steps, and further, these finely pulverized powders cause the occurrence of secondary aggregation. It has been a problem that productivity is significantly impaired due to problems such as easy occurrence and very difficult uniform mixing.

An object of the present invention is to propose an advantageous method for producing an oxide permanent magnet, which can solve the problems of the above-mentioned prior art. In particular, it is a very simple method with high Br and high An object of the present invention is to provide a technique capable of manufacturing an iHc Sr ferrite magnet.

[0013]

In order to improve the orientation during sintering and promote densification, it is essential for the pulverized powder to contain fine powder to some extent, while the coercive force is increased. Based on the finding that it is necessary to suppress the content of coarse powder of 2 μm or more as much as possible in order to keep the value high, further intensive research was conducted toward the realization of the above object. As a result, focusing on the particle size adjustment in the calcination step, by adding and mixing the calcinated powder at the normal temperature and the calcinated powder calcined at a lower temperature than that, it is possible to increase the Br of the magnetic material and the iHc. The inventors have found that a particle size distribution of pulverized powder suitable for conversion can be easily obtained, and have conceived the present invention.

That is, in the present invention, the raw material is 1200 to 1350 ° C.
The Sr ferrite calcined powder obtained by calcination and pulverization at the temperature of 10 is then pulverized and molded in a magnetic field, and then main-calcined to produce an oxide permanent magnet. Oxidation characterized by using, as powder, 5 to 25 wt% of Sr ferrite powder calcined at a temperature range of 1150 ° C. or higher and not higher than the calcination temperature is added to the Sr ferrite calcined powder. It is a method of manufacturing a permanent magnet.

[0015]

Now, in the production of a general Sr ferrite magnet, it is desirable to completely advance the ferritization in the calcination step in order to sufficiently enhance the orientation in the molding in the magnetic field. Usually, the calcination is performed at 1200 ° C to 1350 ° C. Temperature is used.
The reason for this is that if calcination is performed at a temperature higher than 1350 ° C., it is difficult to pulverize the calcinated product obtained, resulting in a large particle size distribution of coarse powder and a decrease in iHc.
If it is less than the above, as described later, the ferritization is insufficient, and unreacted components that are not ferritized remain, so that it becomes difficult to obtain a high orientation by molding in a wet magnetic field.

According to a study conducted by the inventors on the calcination temperature, the change in the calcination powder structure with the change in the calcination temperature was observed by a scanning electron microscope.
Below 00 ° C, there is almost no change compared to the raw powder, 1250 ° C
It has been found that when the temperature exceeds 1300 ° C., the particle size increases remarkably, and when the temperature exceeds 1300 ° C., the particle size increases and the binding between particles becomes significant, and the particles having a particle size of more than 2 μm become conspicuous.

From the above research results, in order to pulverize the calcined powder to obtain a finely pulverized powder having a large amount of fine powder and a small amount of coarse powder, Sr ferrite calcined powder calcined at a low temperature However, it can be seen that so-called low temperature calcined powder is advantageous. However, as a result of the phase analysis of the low-temperature calcined powder by X-ray diffraction, some residual α-Fe ₂ O ₃ phase was observed in the low-temperature calcined powder. Therefore, it was also found that it is difficult to obtain high Br in high magnetic field compaction with only a single powder of low-temperature calcined powder, and it is difficult to obtain high Br.

Therefore, the inventors of the present invention have proposed a normal calcination temperature of 1200
Based on Sr ferrite calcined powder that has been fully calcined at ℃ to 1350 ℃ and has been sufficiently ferriticized, add low temperature calcined powder that has a certain degree of ferriticization and a particle size similar to that of the calcined raw material powder, and mix I tried to crush it.

That is, according to such a calcination compounded powder, it is possible to obtain a finely pulverized powder having a particle size distribution containing a large amount of fine powder which does not deteriorate the orientation in the molding in a magnetic field. It becomes possible to easily manufacture a Sr ferrite magnet having a high Br and a high iHc.

Here, the calcination temperature for obtaining the above-mentioned low-temperature calcination powder is 1150 ° C. or higher and the normal calcination temperature.
The temperature range is from 00 ℃ to 1350 ℃ or below. This temperature is 1150 ℃
If it is less than the above, unreacted components that do not become ferrite increase,
This is because high orientation cannot be obtained by molding in a wet magnetic field.
On the other hand, the above temperature is the normal calcination temperature of 1200 ℃ ~ 13
This is because if the temperature exceeds 50 ° C., the particle size of the calcined powder increases, the particle size distribution becomes large with coarse powder, and iHc decreases.

The addition amount of the low temperature calcined powder to the Sr ferrite calcined powder calcined at a calcining temperature of 1200 ° C to 1350 ° C is
5 to 25 wt%. The reason for this is that if it is less than 5 wt%, the effect of addition is not remarkable because a particle size distribution containing a large amount of fine powder cannot be obtained, while if it exceeds 25 wt%, the characteristics deteriorate conversely.

[0022]

【Example】

(Example 1) A raw material powder having a molar ratio of Fe ₂ O ₃ / SrO of 5.8 was calcined at 1275 ° C. for 1 hour to obtain a calcined Sr ferrite powder. Then, the obtained calcined powder was calcined for 1 hour at variously changed temperatures in the range of 1100 to 1300 ° C.
wt%, 0.36 wt% SiO ₂ and 0.45 wt% CaO were added to obtain various mixed calcined powders. Then, the various mixed calcined powders obtained were crushed and molded in a wet magnetic field according to a conventional method, and further sintered at 1225 ° C. for 1 hour to obtain an Sr ferrite sintered body.

Table 1 shows the magnetic characteristics of the Sr ferrite sintered body thus obtained. As is clear from the results shown in this table, a low temperature calcined powder calcined at a temperature of 1150 ° C. or higher and the calcined temperature of 1275 ° C. or lower is added to the calcined powder calcined at a normal calcining temperature of 1275 ° C. By doing so, an Sr ferrite magnet with high Br and high iHc can be obtained.

(Example 2) Fe ₂ O ₃ / SrO is 5.8 in molar ratio.
Was calcined at 1275 ° C. for 1 hour to obtain a calcined powder. Then, the low-temperature calcined powder obtained by calcining the obtained calcined powder at 1200 ° C. for 1 hour with various addition amounts in the range of 0 to 30 wt%, 0.36 wt% SiO ₂ and 0.45 wt% CaO was added to obtain various mixed calcined powders. Then, the various mixed calcined powders obtained were pulverized and molded in a wet magnetic field according to a conventional method, and further calcined at 1200 to 1260 ° C. for 1 hour to obtain an Sr ferrite sintered body.

The magnetic characteristics of the Sr ferrite sintered body thus obtained are shown in FIG. As is clear from the results shown in this figure, by adding 5 to 25 wt% of low temperature calcined powder to the calcined powder calcined at a normal calcining temperature of 1275 ° C, high B
It is possible to obtain an Sr ferrite magnet having r and high iHc.

FIG. 2 shows the results of particle size distribution measurement of finely pulverized powder in this example. This particle size distribution shows the case of the present invention example in which 20 wt% of the low temperature calcinated powder calcined at 1200 ° C. is added to the calcinated powder calcined at 1275 ° C. and the case of the conventional example in which the low temperature calcinated powder is not added. It is a comparison. As is clear from the results shown in this figure, the distribution shifts to the fine powder side by adding the low-temperature calcined powder calcined at 1200 ° C to the calcined powder calcined at the normal calcination temperature of 1275 ° C. I understood.

[0027]

[Table 1]

[0028]

As described above, according to the manufacturing method of the present invention, as the Sr ferrite calcined powder, the normal calcining temperature 12
Since Sr ferrite calcined powder calcined at 00 ℃ to 1350 ℃ is added with low temperature calcined powder calcined at a temperature that does not deteriorate the orientation in molding in a magnetic field, a large amount of fine powder is used. It is possible to obtain a finely pulverized powder showing the particle size distribution contained,
Therefore, it is possible to easily manufacture the Sr ferrite magnet having high Br and high iHc.

Moreover, since this low-temperature calcined powder is added during the crushing process together with the sintering promoter and grain growth promoter, the conventional process can be used as it is, and Sr can be used in an extremely simple manner. It is possible to improve the characteristics of the ferrite magnet.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the amount of low-temperature calcined powder added and magnetic properties.

FIG. 2 is a diagram showing a particle size distribution of finely pulverized powder.

Claims (1)

[Claims] 1. An Sr ferrite calcined powder obtained by calcining and pulverizing a raw material at a temperature of 1200 to 1350 ° C., then pulverizing and molding in a magnetic field, and then main-calcining the oxide permanent magnet. In the method for producing, as the calcined powder to be subjected to the molding, 5 to 25 wt% of Sr ferrite powder calcined in the temperature range of 1150 ° C. or higher and the calcining temperature or lower is added to the Sr ferrite calcined powder. A method for producing an oxide permanent magnet, characterized in that an additive is used.