JP3506174B2 - Method for producing ferrite magnet and powder thereof - Google Patents

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 type crystal structure and a method for producing a powder thereof.

[0002]

Ferrite magnets are used in various applications including rotating machines such as motors and generators. Recently, there has been a demand for ferrite magnets having higher magnetic properties for the purpose of downsizing and weight reduction, especially in the field of rotary machines for automobiles, and in the field of rotary machines for electrical equipment, for higher efficiency.

Conventionally, Sr ferrite or Ba ferrite
The high performance sintered magnet is manufactured as follows. Well
After mixing ferrous oxide and Sr or Ba carbonate, calcining
Perform a light-up reaction. Coarsely crushed clinker,
In addition, additives that control the sintering behavior (SiO₂, SrCO₃, CaCO₃
Etc.), and additives that control the coercive force iHc (Al₂O₃Or Cr ₂O
₃Etc.), and wet until the average particle size reaches 0.7-1.0 μm.
Finely grind with a formula. In a magnetic field using the obtained fine powder slurry
Wet-molding while orienting to form a molded body. Finally successful
After firing the shaped body, it is processed into a product shape.

[0004]

On the premise of such a manufacturing method, it is considered that methods for improving the performance of ferrite magnets can be broadly classified into the following five.

The first method is an atomization method. The size of the crystal grains in the fired body is M (magnetoplumbite) type Sr.
The coercive force iHc increases as it approaches the critical single domain particle size (about 0.9 μm) of the ferrite magnet. Therefore, the average particle size of finely pulverized particles is reduced to, for example, 0.7 μm or less in consideration of crystal grain growth during firing. However, this method has a problem that the finer the particles, the worse the dehydration characteristics during wet molding, and the lower the production efficiency.

The second method is to make the grain size of the fired body as uniform as possible. Ideally, the particle size should be uniform and the value should be the critical single domain particle size (about 0.9 μm). Coercive force iH
This is because it leads to a decrease in c. A concrete means of improving performance by this method is to improve the particle size distribution of finely pulverized powder, but in the case of industrial production, there is no choice but to use an existing pulverizer such as a ball mill or an attritor. However, the degree of improvement is naturally limited. Further, in recent years, an attempt to produce ferrite fine particles having a uniform particle diameter by a chemical precipitation method has been published, but it cannot be said to be a method suitable for industrial mass production.

The third method is to improve the degree of crystal orientation that influences 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 and to increase the magnetic field strength during orientation.

The fourth method is to improve the density of the fired body. The theoretical density of the Sr ferrite fired body is 5.15 g / cc. The density of Sr ferrite sintered magnets currently on the market is generally in the range of 4.9 to 5.0 g / cc, which corresponds to 95 to 97% in theoretical density ratio. Residual magnetic flux density if densified
Although it is expected that Br will be improved, a special densification method such as HIP is required to increase the density above the current value. However, the introduction of such a special process leads to an increase in manufacturing cost, and there is a possibility that the features of the ferrite magnet as an inexpensive magnet will be lost.

The fifth method is to improve the saturation magnetization σs of the ferrite compound itself which is the main composition constituting the ferrite magnet. This is because the improvement of the saturation magnetization σs may directly lead to the improvement of the residual magnetic flux density Br. A W-type ferrite having a saturation magnetization larger than that of a conventional M (magnetoplumbite) type ferrite magnet has been studied, but mass production has not been realized due to the difficulty of atmosphere control.

Under these circumstances, the high performance of the ferrite magnet was achieved by the first to fourth methods, and at present, the high performance ferrite magnet having typical characteristics (Br = 4100G, iHc = 4000Oe). Is being commercialized. _{However, SrO · n Fe 2 O 3} ( where n is a molar ratio.) The compound as a main composition represented by, achieving higher performance by the first to fourth methods, (b ) It was found that these methods are not suitable for mass production, and (b) the residual magnetic flux density Br among the magnetic properties has already reached a level close to the theoretical value, which proves to be difficult.

Therefore, an object of the present invention is to adopt the fifth method described above and to obtain remarkably excellent magnetic characteristics, particularly a high residual magnetic flux density (or high residual magnetic flux density and coercive force) as compared with conventional ferrite magnets. An object of the present invention is to provide a method for producing an Sr ferrite magnet and a powder thereof.

[0012]

[Means for Solving the Problems] As a result of earnest research to achieve the above object, the present inventors have found that SrO.nFe ₂ O ₃ (where n
Is the molar ratio. It has been discovered that by substituting some of the Sr and Fe elements of the composition that can be represented by) with different elements, Sr ferrite magnets with even better magnetic properties can be obtained.

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

With the above knowledge in mind, the present inventors have
As a result of studying substitution of various elements for ions, Mn,
It was 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 sufficient effect of improving the magnetic properties cannot be obtained by simply adding the above element. This is because if the Fe ions are replaced by another type of element, the ionic valences will be out of balance, and a heterogeneous phase detrimental to the magnetic properties will occur in the Sr ferrite. To avoid this phenomenon, it was necessary to replace the Sr site with another element for the purpose of charge compensation, and it was discovered that La, Nd or Pr is effective for that purpose, and the present invention was completed.

[0015] That is, the first method of the present invention for producing a Sr ferrite magnet has a substantially magnetoplumbite-type crystal structure, in SrO · nFe ₂ O ₃ (where n is the molar ratio,
5.7 to 6. ), The Sr site is partially substituted with at least one of La, Nd, and Pr, and the Fe site is partially substituted with at least one of Mn, Co, and Ni. Manufactures ferrite magnets,
At least 1 of La, Nd and Pr for Sr carbonate and iron oxide
Seed compound and at least one compound of Mn, Co and Ni are mixed, calcined, the calcined product obtained is crushed, and a slurry of the crushed powder obtained is molded in a magnetic field and then sintered. It is characterized by doing. The average particle size of crushed powder is 0.4 to 0.6 μm
It is preferable because the magnetic properties can be improved by making

[0016]

The second method of the present invention for producing the Sr ferrite magnet has a substantially magnetoplumbite-type crystal structure, in SrO · nFe ₂ O ₃ (where n is the molar ratio, in 5.7 to 6
is there. ), The Sr site is partially substituted with at least one of La, Nd, and Pr, and the Fe site is partially substituted with at least one of Mn, Co, and Ni. A ferrite magnet is manufactured by mixing Sr carbonate and iron oxide with at least one compound of La, Nd and Pr and at least one compound of Mn, Co and Ni, It is characterized in that it is calcined, the obtained calcined product is crushed, a sintering aid is added in the crushing step, the slurry of the crushed powder obtained is molded in a magnetic field, and then sintered. It is preferable to add SiO ₂ as a sintering aid because the growth of crystal grains during sintering can be suppressed and the coercive force can be increased. Further, it is preferable to set the average particle size of the pulverized powder to 0.4 to 0.6 μm because the magnetic characteristics can be enhanced.

The method of the present invention for producing the Sr ferrite magnet powder has a substantially magnetoplumbite type crystal structure, and a part of the Sr site is substituted with at least one of La, Nd and Pr. , Part of Fe site is Mn, Co and
Sr ferrite magnet powder substituted with at least one kind of Ni is produced, and Sr carbonate and iron oxide having a compounding ratio represented by SrO · nFe ₂ O ₃ (where n is a molar ratio). And at least one compound of La, Nd and Pr, and Mn,
It is characterized in that it is mixed with at least one compound of Co and Ni, calcined, and the calcined product obtained is pulverized.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The ferrite magnet or powder thereof obtained by the production method of the present invention preferably has the following general formula: (Sr _1-x R _x ) O.n [(Fe _1-y M _y ) ₂ O ₃ ] (atomic ratio) (wherein 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.
It is 0 (molar ratio). ) Has a basic composition represented by x is the substitution amount of R element at the Sr site (atomic ratio)
And y is the substitution amount (atomic ratio) of the M element at the Fe site.

The substitution amount (atomic ratio) x of the R element at the Sr site is preferably 0.05 to 0.5. When x is less than 0.05, it is difficult to improve the magnetic properties, and when x exceeds 0.5, the magnetic properties are deteriorated. In order to realize charge compensation and improve magnetic characteristics, the substitution amount (atomic ratio) y of the M element at the Fe site is [x / (2.2n)] ≦ y ≦ [x / (1.8n)]
Is preferred.

In order to manufacture the Sr ferrite magnet according to the present invention, it is preferable to go through a standard manufacturing process (mixing → calcination → grinding → molding → sintering). In this case, it is desirable that the Sr ferrite magnet has a basic composition substantially at 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 at the mixing stage. As a result, the Sr ferrite having a basic composition undergoes two high-temperature processes of calcination and sintering, and diffusion of the R element and the M element in the solid progresses to obtain a more uniform composition.

In order to obtain a high-performance ferrite fired body,
SiO ₂ and CaO (or CaC) are added as additives to control the sintering phenomenon.
It is advisable to add O ₃ ) at the grinding stage. SiO ₂ is an additive that suppresses crystal grain growth during sintering, and its content is 0.
It is preferably 4 to 0.5% by weight. If it is less than 0.4% by weight, the effect of suppressing the crystal grain growth during sintering is insufficient and the coercive force decreases. On the other hand, if it exceeds 0.5% by weight, the crystal grain growth is excessively suppressed, the improvement of the degree of orientation that progresses with the crystal grain growth 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 coercive force decreases. On the other hand, if it is less than 0.35% by weight, the crystal grain growth is excessively suppressed, the degree of orientation progressing with the crystal grain growth is not sufficiently improved, and the residual magnetic flux density is lowered.

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

In order to enhance the magnetic properties of the Sr ferrite magnet, it is important to prepare a pulverized powder adjusted to have an optimum composition and an average particle size, and it is important that the pulverized powder does not aggregate 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 added, shearing force is added by kneading by adding a dispersant, the aggregation is released, and the orientation is improved, It has been discovered that the magnetic properties are improved. It is considered that the addition of the dispersant causes the dispersant to be adsorbed to the pulverized powder, and the surface is modified to be in a good dispersed state, thereby improving the magnetic properties.

As the dispersant, a surfactant, a higher fatty acid, a higher fatty acid soap, a higher fatty acid ester or the like is known, but by using a polycarboxylic acid type dispersant which is a kind of anionic surfactant. It has been found that the dispersibility of the ground powder can be significantly improved. Although there are various polycarboxylic acid-based dispersants, ammonium polycarboxylic acid salts are 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 by the following examples, but the present invention is not limited thereto.

Examples 1 to 3, Reference Examples 1 to 9 and Comparative Example 1 La, Pr, Nd, Sm as the R element (Sr site substituting element), based on having an ionic radius close to that of Sr ion,
Eu and Gd were selected, and Ti, V, Mn, Co, Ni, Cu and Zn were selected as M elements (Fe site substituting elements) on the basis of having an ionic radius close to that of Fe ions. SrCO
₃ , Fe ₂ O ₃ , an oxide of the R element and an oxide of the M element are used, respectively, and have the following chemical formulas: (Sr _1-x R _x ) O · n [(Fe _1-y M _y ) ₂ O ₃ ]. In atomic ratio n = 5.85, x = 2ny, and x = 0.117
And were wet mixed. The resulting mixture
It was calcined in the air at 1200 ° C for 2 hours. Further, as Comparative Example 1, calcination was performed 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 that they were mixed.

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

As is clear from Table 1, when the combination of R element + M element is La + Mn (Example 1), La + Co (Example 2) and La + Ni (Example 3), Comparative Example 1 Saturation magnetization σs and coercive force Hc are higher than those of. It was also found that the saturation magnetization [sigma] s and the coercive force Hc were better balanced than in Reference Examples 1 to 9. Particularly in the case of La + Co (Example 2), both the saturation magnetization σs and the coercive force Hc were excellent. From the above results, it is understood that the Sr ferrite magnets of Examples 1 to 3 have excellent characteristics as compared with the Sr ferrite magnet of Comparative Example 1.

[0030]

[Table 1]

[0031]Reference example 10 La is selected as the R element and Zn is selected as the M element.
And SrCO₃, Fe₂O₃, La₂O ₃Using ZnO and ZnO
Scientific formula: (Sr_1-xLa_x) O ・ n [(Fe_1-yZn_y)₂O₃] In atomic ratio, n = 5.85, x = 2ny, and x = 0 to 0.
The ingredients were blended so as to be 6 and wet-mixed. Then at 1200 ℃
It was calcined in the atmosphere for 2 hours. The obtained calcined powder was used in Example 1.
Coarsely crushed in the same manner as in.

The magnetic properties of the obtained coarsely crushed powder were measured.
The results are shown in Fig. 1. As is clear from FIG. 1, the saturation magnetization σs was improved by simultaneously adding La ₂ O ₃ and ZnO. Further, it can be seen that when the La content x is 0.05 or more, the effect of improving σs is recognized, and when it exceeds 0.5, σs decreases conversely. Therefore, x is preferably 0.05 to 0.5, and more preferably 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 one of Mn, Co and Ni was selected as the M element, and the magnetic properties were evaluated. did. As a result,
Almost the same result was obtained. In addition, no significant difference was observed when n was in the range of 5.7 to 6.0, confirming that similar effects were obtained.

[0034]Examples 5-7, 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. SrCO₃, Fe₂O₃, La₂O ₃as well as
Using the oxide of each M element, the chemical formula shown below: (Sr_1-xLa_x) O ・ n [(Fe_1-yM_y)₂O₃] In atomic ratio n = 5.85, x = 2ny, and x = 0.117
And were wet mixed. Then at 1200 ℃ 2
It was calcined in the atmosphere for an hour. Roller mill the resulting calcined powder
Dry pulverization was performed to obtain coarsely pulverized powder.

After that, wet pulverization was performed with an attritor to obtain a slurry containing finely pulverized powder having an average particle size of 0.7 μm. In the initial stage of fine pulverization, SiO ₂ and CaCO ₃ were added as sintering aids in a weight ratio of 0.45% and 0.80% (Ca
0.45% in terms of O) was added. 10kOe with this slurry
Wet molding was carried out in the magnetic field of 1 to obtain a molded body. Next, the molded body was sintered in the 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 x = y = 0. Each of these fired bodies was processed into a shape of about 10 mm × 10 mm × 20 mm, and the magnetic characteristics were measured by a BH tracer. The results are shown in Figure 2.

From FIG. 2, La + Mn (Example 5), La + Co
(Example 6), La + Ni (Example 7) and La + Zn (Reference Example)
It is considered that all of the replacement materials of 11) have a better elongation of the residual magnetic flux density Br in the low iHc region than the conventional materials and have an effect of improving the saturation magnetization σs. Therefore, La + Mn, La
The substitution materials of + Ni and La + Zn are suitable for high Br materials. Among them, the substitution 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 apparent from the above, the Sr ferrite magnet manufactured 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 drawings]

FIG. 1 is a graph showing an example of a correlation 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 characteristics of an Sr ferrite magnet used in the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References Patent 2922864 (JP, B2) Patent 3266187 (JP, B2) Denpa Shimbun, October 17, 1966, p. 23-24 (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01F 1/11 C01G 49/00 C04B 35/26 H01F 41/02

Claims (6)

(57) [Claims] 1. A substantially has a magnetoplumbite-type crystal structure, SrO · nFe ₂ O ₃ (where n is the molar ratio, from 5.7 to 6
Is. ), The part of the Sr site is La, Nd.
And at least one of Pr and Fe,
A method for producing an Sr ferrite magnet, wherein a part of the sites is replaced with at least one of Mn, Co and Ni, wherein the carbon content of Sr is
The acid salt and iron oxide are mixed with at least one compound of La, Nd and Pr and at least one compound of Mn, Co and Ni, calcined, and the calcined product obtained is crushed to obtain A method for producing an Sr ferrite magnet, which comprises forming the slurry of the obtained pulverized powder in a magnetic field, and then sintering. 2. The method for manufacturing an Sr ferrite magnet according to claim 1, wherein the crushed powder has an average particle size of 0.4 to 0.6 μm.
A method for manufacturing an Sr ferrite magnet, characterized in that m is set. Wherein substantially the magnetoplumbite-type crystal structure, SrO · nFe ₂ O ₃ (where n is the molar ratio, from 5.7 to 6
Is. ), The part of the Sr site is La, Nd.
And at least one of Pr and Fe,
A method for producing an Sr ferrite magnet, wherein a part of the sites is replaced with at least one of Mn, Co and Ni, wherein the carbon content of Sr is
At least one compound of La, Nd and Pr and at least one compound of Mn, Co and Ni are mixed with acid salt and iron oxide and calcined, and the calcined product obtained is crushed and crushed. A method for producing an Sr ferrite magnet, which comprises adding a sintering aid in a step, molding the obtained slurry of ground powder in a magnetic field, and then sintering. 4. The method for producing an Sr ferrite magnet according to claim 3, wherein SiO ₂ is added as the sintering aid. 5. The method for producing an Sr ferrite magnet according to claim 3, wherein the crushed powder in the slurry has an average particle size of 0.4 to 0.6 μm. 6. have a substantially magnetoplumbite-type crystal structure, SrO · nFe ₂ O ₃ (where n is the molar ratio, from 5.7 to 6
Is. ), The part of the Sr site is La, Nd.
And at least one of Pr and Fe,
Some sites A method of manufacturing a Sr ferrite magnet powder is substituted with at least one Mn, Co and Ni, Sr
After mixing at least one compound of La, Nd, and Pr and at least one compound of Mn, Co, and Ni with the carbonate and iron oxide of, the resulting calcined product is pulverized. A method for producing an Sr ferrite magnet powder, comprising: