JP2000323317A - Ferrite magnet and manufacture of powder thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Sr ferrite magnet having excellent magnetic characteristic and a manufacturing method of powder of the magnet. SOLUTION: An Sr ferrite magnet has practically a magneto plumbite type crystal structure. A part of Sr site is substituted by at least one kind out of La, Nd and Pr, and a part of Fe site is substituted by at least one kind out of Mn, Co and Ni. In a manufacturing method of the above Sr ferrite magnet, at least one kind of compound out of La, Nd and Pr and at least one kind of compound out of Mn, Co and Ni are mixed with carbonate of Sr whose compounding ratio is shown by SrO/nFe2O3 (where n is mole ratio) and iron oxide, and calcination is performed. The calcined object is smashed. Molding is performed in a magnetic field by using the obtained smashed powder, and then sintering is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention has a higher residual magnetic flux density or a higher residual magnetic flux density and coercive force as compared with the prior art,
The present invention relates to a high-performance ferrite magnet having a substantially magnetoplumbite crystal structure and a method for producing powder thereof.

[0002]

2. Description of the Related Art Ferrite magnets are used in various applications including rotating machines such as motors and generators. Recently, ferrite magnets having higher magnetic properties have been demanded especially in the field of rotating machines for automobiles for the purpose of reduction in size and weight, and in the field of rotating machines for electric equipment for the purpose of improving efficiency.

Conventionally, Sr ferrite or Ba ferrite
High performance sintered magnets are manufactured as follows. Ma
After mixing iron oxide and Sr or Ba carbonate, calcining
Perform a lightening reaction. The calcined clinker is roughly pulverized,
Additives that control the sintering behavior (SiO_Two, SrCO_Three, CaCO_Three
Etc.) and additives (Al_TwoO_ThreeOr Cr _TwoO
_ThreeEtc.) and wet until the average particle size becomes 0.7-1.0 μm.
Pulverize by the formula. In a magnetic field using the obtained fine powder slurry
Wet molding is performed while orienting at a temperature to obtain a molded body. Finally
After firing the shape, it is processed into a product shape.

[0004]

On the premise of such a manufacturing method, methods for improving the performance of ferrite magnets can be roughly classified into the following five methods.

[0005] The first method is an atomization method. M (Magnetoplumbite) type Sr
Since the coercive force iHc increases as the diameter of the ferrite magnet approaches the critical single magnetic domain particle diameter (about 0.9 μm), the finely pulverized average particle diameter is reduced to, for example, 0.7 μm or less in anticipation of crystal grain growth during firing. However, this method has a problem in that the finer the particles, the worse the dewatering characteristics during wet molding, and the lower the production efficiency.

The second method is to make the size of the crystal grains of the fired body as uniform as possible. Ideally, the particle diameter should be uniform and the value should be the critical single magnetic domain particle diameter (about 0.9 μm). Coercive force iH for both larger and smaller grains
This is because it leads to a decrease in c. The specific means of improving the performance by this method is to improve the particle size distribution of the finely pulverized powder, but in the case of industrial production, an existing pulverizer such as a ball mill or an attritor must be used. However, the degree of improvement is naturally limited. In recent years, an attempt to produce ferrite fine particles having a uniform particle size by a chemical precipitation method has been disclosed, but this method cannot be said to be suitable for industrial mass production.

[0007] A third method is to improve the degree of crystal orientation which affects magnetic anisotropy. Specific means in this method include adding a surfactant to the finely pulverized slurry to improve the dispersibility of the ferrite particles in the slurry, or to increase the magnetic field strength during orientation.

A fourth method is to improve the density of the fired body. The theoretical density of the sintered Sr ferrite is 5.15 g / cc. The density of currently marketed Sr ferrite sintered magnets is generally in the range of 4.9-5.0 g / cc, which corresponds to a theoretical density ratio of 95-97%. Residual magnetic flux density with higher density
Although improvement of Br is expected, a special high-density means such as HIP is required to increase the density beyond the current value. However, the introduction of such a special process leads to an increase in manufacturing cost, and may lose the characteristics of the ferrite magnet as a low-cost magnet.

A fifth method is to improve the saturation magnetization s of the ferrite compound itself, which is the main composition constituting the ferrite magnet. This is because the improvement of the saturation magnetization s has a possibility of directly leading to the improvement of the residual magnetic flux density Br. Although a W-type ferrite having a larger saturation magnetization than a conventional M (magnet plumbite) -type ferrite magnet has been studied, mass production has not been realized due to difficulty in controlling the atmosphere.

Under these circumstances, high performance ferrite magnets have been achieved by the first to fourth methods, and at present, high performance ferrite magnets having typical characteristics (Br = 4100G, iHc = 4000Oe) To commercialization. However, if the compound represented by SrO.n Fe ₂ O ₃ (where n is a molar ratio) is used as the main composition, further improving the performance by the above-described first to fourth methods cannot be achieved (a). ) These methods are not suitable for mass production, and (b) the magnetic properties, in particular, the residual magnetic flux density Br has already reached a level close to the theoretical value.

[0011] Accordingly, an object of the present invention is to adopt the above-mentioned fifth method to obtain a much better magnetic property, especially a higher residual magnetic flux density (or a higher residual magnetic flux density and coercive force) than conventional ferrite magnets. It is an object of the present invention to provide a Sr ferrite magnet having the same and a method for producing the powder.

[0012]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors found that SrO.nFe ₂ O ₃ (where n
Is the molar ratio. It has been found that by substituting a part of the Sr and Fe elements of the composition which can be represented by the above) with a different element, a Sr ferrite magnet having more excellent magnetic properties can be obtained.

The magnetic properties of magnetoplumbite-type Sr ferrite depend on the magnetic moment of Fe ions. Sr ferrite has the magnetic structure of a ferrimagnetic material in which this magnetic moment is partially arranged in an antiparallel direction by Fe ion sites. Have. There are two ways to improve saturation magnetization in this magnetic structure. The first method is to add Fe ions at sites corresponding to magnetic moments oriented in the antiparallel direction,
The substitution of another element that has a smaller magnetic moment than the Fe ion or is non-magnetic. A second method is to replace the Fe ion at the site corresponding to the magnetic moment oriented in the parallel direction with another element having a larger magnetic moment than the Fe ion.

With the above knowledge in mind, the present inventors have made Fe
As a result of studying the replacement of ions with various elements, Mn,
It has been discovered that Co or Ni is an element that improves the magnetic properties (especially saturation magnetization) of Sr ferrite. However, it has been found that a mere addition of the above elements does not provide a sufficient effect of improving magnetic properties. This is because, when the Fe ion is replaced with another element, the balance of the ionic valence is lost, and a different phase harmful to the magnetic properties is generated in the Sr ferrite. To avoid this phenomenon, it is necessary to replace the Sr site with another element for the purpose of charge compensation, and for that purpose, La, Nd or Pr have been found to be effective, and the present invention has been completed.

That is, the first method of the present invention for producing an Sr ferrite magnet has a substantially magnetoplumbite type crystal structure, and a part of the Sr site is replaced with at least one of La, Nd and Pr. And manufactures an Sr ferrite magnet in which a part of the Fe site is replaced by at least one of Mn, Co and Ni, and SrO.nFe ₂ O ₃ (where n
Is the molar ratio. ), At least one compound of La, Nd, and Pr, and at least one compound of Mn, Co, and Ni are mixed with the carbonate and iron oxide of Sr in the compounding ratio represented by The obtained calcined product is pulverized, molded in a magnetic field using the obtained pulverized powder, and then sintered. It is preferable to set the average particle size of the pulverized powder to 0.4 to 0.7 μm because the magnetic properties can be enhanced.

In the second method of the present invention for producing an Sr ferrite magnet, a part of the Sr site is replaced by at least one of La, Nd and Pr, and a part of the Fe site is Mn and
It produces Sr ferrite magnets substituted with at least one of Co and Ni, and contains Sr carbonate and oxide in a compounding ratio represented by SrO.nFe ₂ O ₃ (where n is a molar ratio). Iron, at least one compound of La, Nd and Pr, and M
n, at least one compound of Co and Ni is mixed, calcined, and the obtained calcined product is pulverized, and the slurry of the obtained pulverized powder is molded in a magnetic field without kneading, and then sintered. It is characterized by the following. Sr ferrite magnets obtained by molding in a magnetic field without kneading the slurry have higher magnetic properties than conventional ferrite magnets. It is preferable to set the average particle size of the pulverized powder to 0.4 to 0.7 μm because the magnetic properties can be enhanced.

The third method of the present invention for producing an Sr ferrite magnet has a substantially magnetoplumbite type crystal structure, wherein a part of the Sr site is replaced with at least one of La, Nd and Pr. In addition, it produces an Sr ferrite magnet in which a part of the Fe site is substituted by at least one of Mn, Co and Ni, and is represented by SrO · nFe ₂ O ₃ (where n is a molar ratio). At least one compound of La, Nd and Pr, Mn, Co
And at least one compound of Ni and calcined,
The obtained calcined product is pulverized, a sintering aid is added in the pulverization stage, and the slurry of the obtained pulverized powder is molded in a magnetic field, and then sintered. As a sintering aid
The addition of SiO ₂ is preferable because the growth of crystal grains during sintering is suppressed and the coercive force can be increased. Further, it is preferable that the average particle size of the pulverized powder is 0.4 to 0.7 μm because the magnetic characteristics can be enhanced.

The method of the present invention for producing a Sr ferrite magnet powder has a substantially magnetoplumbite type crystal structure, wherein a part of the Sr site is substituted with at least one of La, Nd and Pr. , Some of the Fe sites are Mn, Co and
It produces Sr ferrite magnet powder substituted with at least one kind of Ni. The compounding ratio of Sr carbonate and iron oxide is represented by SrO · nFe ₂ O ₃ (where n is a molar ratio). At least one compound of La, Nd and Pr, and Mn,
After mixing with at least one compound of Co and Ni, the mixture is calcined, and the obtained calcined product is pulverized.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The ferrite magnet or its powder obtained by the production method of the present invention is preferably of the following general formula: (Sr _1-x R _x ) On · n [(Fe _1-y M _y ) ₂ O ₃ ] (atomic ratio) (where R is at least one of La, Nd and Pr,
M is at least one of Mn, Co and Ni, and n = 5.7 to 6.
0 (molar ratio). ). x is the substitution amount (atomic ratio) of the R element in the Sr site
And y is the substitution amount (atomic ratio) of the M element in the Fe site.

It is preferable that the substitution amount (atomic ratio) x of the R element in the Sr site is 0.05 to 0.5. If x is less than 0.05, it is difficult to improve the magnetic properties, and if it exceeds 0.5, the magnetic properties will be reduced. In addition, in order to realize charge compensation and improve magnetic properties, the substitution amount (atomic ratio) y of the M element in the Fe site is [x / (2.2n)] ≦ y ≦ [x / (1.8n)]
It is preferred that

In order to produce an Sr ferrite magnet according to the present invention, it is preferable to go through a standard production process (mixing → calcination → crushing → molding → sintering). In this case, it is desirable that the basic composition of the Sr ferrite magnet is substantially set in the calcination stage, and the Sr ferrite calcined powder having the basic composition is subjected to pulverization. For this purpose, the R element and the M element are added in a mixing stage. As a result, the Sr ferrite having the basic composition undergoes two high-temperature steps of calcination and sintering, and the diffusion of the R element and the M element into the solid proceeds, whereby a more uniform composition is obtained.

In order to obtain a high-performance ferrite fired body,
SiO ₂ and CaO (or CaC) as additives to control the sintering phenomenon
It is desirable to add O ₃ ) during the milling stage. SiO ₂ is an additive that suppresses crystal grain growth during sintering, and its content is 0.
Preferably it is 4 to 0.5% by weight. If it is less than 0.4% by weight, the effect of suppressing the growth of crystal grains during sintering is insufficient, and the coercive force decreases. On the other hand, if the content exceeds 0.5% by weight, the growth of crystal grains is excessively suppressed, and the improvement of the degree of orientation that proceeds with the growth of crystal grains becomes insufficient, and the residual magnetic flux density decreases. On the other hand, CaO is an additive that promotes crystal grain growth, and its content is preferably 0.35 to 0.55% by weight. If it exceeds 0.55% by weight, crystal grain growth during sintering proceeds excessively, and the coercive force decreases. If the content is less than 0.35% by weight, the growth of crystal grains is excessively suppressed, the degree of orientation progressing along with the growth of crystal grains is insufficiently improved, and the residual magnetic flux density decreases.

In order to obtain a high-performance ferrite fired body from the above composition, it is desirable to carry out the following steps after the pulverization in the standard production process. That is, as a pulverizing step, the composition is finely pulverized by a wet method until the average particle diameter is in the range of 0.4 to 0.6 μm. Although wet molding is performed using the obtained fine powder slurry, a concentration or drying step, a crushing step, and a kneading step may be performed before the wet molding, if necessary. In any case, sintering is performed after wet molding. Pulverization to an average particle size of less than 0.4 μm causes abnormal crystal grain growth during sintering, so that not only high magnetic properties cannot be obtained, but also dehydration properties during wet molding deteriorate. On the other hand, when the average particle size exceeds 0.6 μm, the existence ratio of coarse crystal grains in the structure of the sintered body increases.

In order to enhance the magnetic properties of the Sr ferrite magnet, it is important to prepare a pulverized powder adjusted to an optimum composition and an average particle size, and it is important that the pulverized powder does not agglomerate in the slurry. Therefore, the present inventors have made various studies to create a state in which the pulverized powder can exist independently in the slurry. As a result, after drying or concentrating the slurry containing the pulverized powder, a high-concentration slurry state is obtained, and then a shearing force is applied by adding and kneading a dispersant, whereby coagulation is released and the orientation is improved, It has been found that the magnetic properties are improved. It is considered that by adding the dispersant, the dispersant is adsorbed on the pulverized powder, the surface is modified, a good dispersion state is obtained, and the magnetic properties are improved.

As the dispersant, a surfactant, a higher fatty acid, a higher fatty acid soap, a higher fatty acid ester and the like are known, but by using a polycarboxylic acid dispersant which is a kind of anionic surfactant. It was found that the dispersibility of the pulverized powder could be significantly improved. Although there are various polycarboxylic acid-based dispersants, ammonium polycarboxylate is particularly effective for improving dispersibility. The amount of the dispersant added is effective if the solid content ratio is 0.2% or more, but if it exceeds 2.0%, the residual magnetic flux density decreases.

[0026]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Examples 1 to 3, Reference Examples 1 to 9, and Comparative Example 1 La, Pr, Nd, Sm, and R are used as R elements (Sr site substitution elements) on the basis of having an ionic radius similar to that of Sr ions.
Eu and Gd were selected, and Ti, V, Mn, Co, Ni, Cu and Zn were selected as M elements (Fe site substitution elements) on the basis that they had an ionic radius similar to that of Fe ions. SrCO
₃ , Fe ₂ O ₃ , an oxide of the R element and an oxide of the M element, respectively, using the following chemical formula: (Sr _1-x R _x ) On · n [(Fe _1-y M _y ) ₂ O ₃ ] , N = 5.85, x = 2ny, and x = 0.117 in atomic ratio
And wet-mixed. The resulting mixture
Calcination was performed in the air at 1200 ° C. for 2 hours. Further, as Comparative Example 1, calcination was carried out in the same manner as described above except that the composition was such that n = 5.85 and x = y = 0 in the above chemical formula, and they were mixed.

Each calcined powder obtained was dry-pulverized by a roller mill. The magnetic properties of the obtained coarsely pulverized powder were measured with a sample vibration magnetometer. The measurement was performed at the maximum field strength 12 kOe, were determined saturation magnetization σs and the coercive force Hc of 1 / H ² plot (H is the applied magnetic field strength). The product phase was identified by X-ray diffraction. Table 1 shows the results. In Table 1, M
The phase is a phase having a magnetoplumbite type crystal structure.

As is clear from Table 1, Comparative Example 1 was obtained when the combination of the R element and the M element was La + Mn (Example 1), La + Co (Example 2), and La + Ni (Example 3). , The saturation magnetization σs and the coercive force Hc are higher. It was also found that the balance between the saturation magnetization s and the coercive force Hc was better than in Reference Examples 1 to 9. In particular, in the case of La + Co (Example 2), both the saturation magnetization s and the coercive force Hc were excellent. From the above results, it can be seen that the Sr ferrite magnets of Examples 1 to 3 have better characteristics than the Sr ferrite magnet of Comparative Example 1.

[0030]

[Table 1]

[0031]Reference Example 10 Select La as R element and Zn as M element
And SrCO_Three, Fe_TwoO_Three, La_TwoO _ThreeUsing ZnO and ZnO
Formula: (Sr_1-xLa_x) O ・ n [(Fe_1-yZn_y)_TwoO_Three], N = 5.85, x = 2ny, and x = 0-0.
6 and wet-mixed. Then at 1200 ° C
It was calcined in the air for 2 hours. The obtained calcined powder was used in Example 1.
It was coarsely ground in the same manner as described above.

The magnetic properties of the resulting coarsely pulverized powder were measured.
The results are shown in FIG. As is clear from FIG. 1, the saturation magnetization σs was improved by simultaneously adding La ₂ O ₃ and ZnO. Also, it can be seen that when the La content x is 0.05 or more, the effect of improving σs is recognized, and when the content exceeds 0.5, σs decreases conversely. Therefore, x is preferably from 0.05 to 0.5, more preferably from 0.07 to 0.4.

Example 4 A coarsely pulverized powder was prepared in the same manner as in Reference Example 10 except that Pr or Nd was selected as the R element and any of Mn, Co and Ni was selected as the M element, and the magnetic properties were evaluated. did. As a result, FIG.
Almost the same result was obtained. No significant difference was observed when n was in the range of 5.7 to 6.0, confirming that the same effect was obtained.

[0034]Examples 5 to 7, Reference Example 11 Select La as the R element and Mn as the M element
(Example 5), Co (Example 6), Ni (Example 7), and
Zn (Reference Example 11) was selected. SrCO_Three, Fe_TwoO_Three, La_TwoO _Threeas well as
Using an oxide of each M element, a chemical formula shown below: (Sr_1-xLa_x) O ・ n [(Fe_1-yM_y)_TwoO_Three], N = 5.85, x = 2ny, and x = 0.117 in atomic ratio
And wet-mixed. Then at 1200 ℃ 2
It was calcined in air for hours. Roller mill the obtained calcined powder
To obtain a coarsely pulverized powder.

Thereafter, wet pulverization was performed using an attritor to obtain a slurry containing finely pulverized powder having an average particle diameter of 0.7 μm. Early in the milling, 0.45% respectively by weight relative to the coarsely pulverized powder of SiO ₂ and CaCO ₃ as a sintering aid, 0.80% (Ca
(0.45% in terms of O). 10kOe using this slurry
Wet molding was performed in a magnetic field of 5 to obtain a molded body. Next, the molded body was sintered at a temperature range of 1180 to 1230 ° C. for 2 hours to obtain a fired body. A conventional material was prepared in the same manner as described above except that the composition of the fired body was such that x = y = 0. Each of these fired bodies was processed into a shape of about 10 mm × 10 mm × 20 mm, and the magnetic properties were measured with a BH tracer. The results are shown in FIG.

FIG. 2 shows that La + Mn (Example 5), La + Co
(Example 6), La + Ni (Example 7) and La + Zn (Reference example)
It is judged that all of the replacement materials of 11) have a higher elongation of the residual magnetic flux density Br in the low iHc region than the conventional material, and also have an effect of improving the saturation magnetization s. Therefore, La + Mn, La
+ Ni and La + Zn substitutes are suitable for high Br materials. Among them, the replacement material of La + Co (Example 6) is high with high Br.
It has iHc and is very useful as a high performance material.

[0037]

As is clear from the above, the Sr ferrite magnet produced by the method of the present invention has high saturation magnetization (or high saturation magnetization and coercive force), and has higher performance than conventional ferrite magnets.

[Brief description of the drawings]

FIG. 1 is a graph showing a correlation example between a substitution amount (atomic ratio) x of an R element and a saturation magnetization σs in an Sr ferrite magnet.

FIG. 2 is a graph showing an example of magnetic properties of an Sr ferrite magnet used in the present invention.

Claims (8)

[Claims] 1. It has a substantially magnetoplumbite type crystal structure, a part of Sr site is substituted by at least one of La, Nd and Pr, and a part of Fe site is Mn,
A method for producing an Sr ferrite magnet substituted with at least one of Co and Ni, comprising a carbonate of Sr having a compounding ratio represented by SrO · nFe ₂ O ₃ (where n is a molar ratio) and Iron oxide, at least one compound of La, Nd and Pr,
Mixing at least one compound of Mn, Co and Ni, calcining, pulverizing the obtained calcined product, molding in a magnetic field using the obtained pulverized powder, and then sintering. Sr
Manufacturing method of ferrite magnet. 2. The method for producing a Sr ferrite magnet according to claim 1, wherein said pulverized powder has an average particle size of 0.4 to 0.7 μm.
m, a method for producing an Sr ferrite magnet. 3. It has a substantially magnetoplumbite type crystal structure, wherein a part of Sr site is replaced by at least one of La, Nd and Pr, and a part of Fe site is Mn,
A method for producing an Sr ferrite magnet substituted with at least one of Co and Ni, comprising a carbonate of Sr having a compounding ratio represented by SrO · nFe ₂ O ₃ (where n is a molar ratio) and Iron oxide, at least one compound of La, Nd and Pr,
A mixture of at least one compound of Mn, Co and Ni is calcined, the calcined product is pulverized, the slurry of the pulverized powder is molded in a magnetic field without kneading, and then sintered. A method for producing an Sr ferrite magnet, comprising: 4. The method for producing an Sr ferrite magnet according to claim 3, wherein the average particle size of the pulverized powder in the slurry is 0.4 to 0.7 μm. 5. It has a substantially magnetoplumbite type crystal structure, wherein a part of Sr site is substituted by at least one of La, Nd and Pr, and a part of Fe site is Mn,
A method for producing an Sr ferrite magnet substituted with at least one of Co and Ni, comprising a carbonate of Sr having a compounding ratio represented by SrO · nFe ₂ O ₃ (where n is a molar ratio) and Iron oxide, at least one compound of La, Nd and Pr,
A mixture of at least one compound of Mn, Co, and Ni is calcined, and the obtained calcined product is pulverized, and a sintering aid is added in the pulverization step. A method for producing an Sr ferrite magnet, comprising forming and then sintering. 6. The method for producing an Sr ferrite magnet according to claim 5, wherein SiO ₂ is added as the sintering aid. 7. The method for producing an Sr ferrite magnet according to claim 5, wherein the average particle size of the pulverized powder in the slurry is 0.4 to 0.7 μm. 8. It has a substantially magnetoplumbite type crystal structure, wherein a part of Sr site is substituted by at least one of La, Nd and Pr, and a part of Fe site is Mn,
A method for producing a Sr ferrite magnet powder substituted with at least one of Co and Ni, wherein SrO.nFe ₂ O ₃ (where n
Is the molar ratio. ) Is mixed with at least one compound of La, Nd and Pr and at least one compound of Mn, Co and Ni, and then calcined. And a method for producing Sr ferrite magnet powder, characterized by pulverizing the obtained calcined product.