JP2002141212A - Rotating machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-performance rotating machine, which utilizes an anisotropic Sr ferrite sintered magnet that has a higher residual magnetic flux density and a higher coercive force than the conventional ferrite magnets. SOLUTION: A rotating machine uses an anisotropic Sr ferrite sintered magnet, having a magnet plumbite crystalline structure, where the anisotropic Sr ferrite sintered magnet has basic composition composed of a composition represented by SrO.nFe2O3 (where n is 5.7 to 6.0 (molar ratio)), at least a rare- earth element selected from La, Nd, and Pr, and Co, the amount x of substitution (atomic ratio) of rare-earth element at an Sr site in the anisotropic Sr ferrite sintered magnet is 0.05 to 0.5, the amount y of substitution (atomic ratio) of Co at an Fe site is set so as to satisfy the formula, [x/(2.2n)]<=y<=[x/(1.8n)], and the anisotropic Sr ferrite sintered magnet has a residual magnetic flux density Br of 4,200 G or larger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotating machine using a high-performance anisotropic Sr ferrite sintered magnet having a high residual magnetic flux density and a coercive force as compared with the prior art and having a magnetoplumbite type crystal structure. .

[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, high-performance anisotropic sintered magnets of Sr ferrite or Ba ferrite have been manufactured as follows. First, after mixing iron oxide and a carbonate of Sr or Ba, a ferrite-forming reaction is performed by calcination. The calcined clinker is coarsely pulverized, and additives (SiO ₂ , SrCO
₃ , CaCO ₃ etc.) and additives (Al
₂ O ₃ or Cr ₂ O ₃ ), and the average particle size is 0.7 to 1.
Finely pulverize with a wet method until it reaches 0 μm. The obtained fine powder slurry is wet-formed while being oriented in a magnetic field to obtain a formed body. Finally, after firing the molded body, it is processed into a product shape.

[0004]

On the premise of such a manufacturing method, the methods for improving the performance of the sintered anisotropic ferrite magnet are considered to 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 particle diameter becomes closer to the critical single domain particle diameter (about 0.9 μm) of the ferrite magnet, the 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 for both larger and smaller grains
This is because it leads to a decrease in iHc. 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, and increasing the magnetic field strength during orientation.

A fourth method is to improve the density of the fired body. The theoretical density of sintered Sr ferrite is 5.15 g / cc
It is. 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%. If the density is increased, the residual magnetic flux density Br is expected to be improved. However, to increase the density beyond the current value, a special high-density means such as HIP is required. 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 in the saturation magnetization s has a possibility of directly leading to an increase in 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, the performance of ferrite magnets has been improved by the above-described first to fourth methods. At present, high-performance ferrite magnets having typical characteristics (Br = 4100 G, iHc = 4000 Oe) have been developed. Production of ferrite magnets is in progress. However, when a compound represented by SrO.nFe ₂ O ₃ (where n is a molar ratio) is used as a main composition, further improvement in performance by the above-described first to fourth methods can be achieved.
(A) These methods are unsuitable for mass production, and (B) Among the magnetic properties, in particular, the residual magnetic flux density Br has already reached a level close to the theoretical value.

Accordingly, an object of the present invention is to adopt the above-described fifth method to provide an anisotropic Sr ferrite sintered body having remarkably excellent magnetic properties, particularly a high residual magnetic flux density and a high coercive force as compared with conventional ferrite magnets. An object is to provide a high-performance rotating machine using a magnet.

[0012]

Means for Solving the Problems As a result of intense research in order to achieve the above object, the present inventors have SrO · nFe ₂ O ₃ (where n is from 5.7 to 6.0 (mole ratio).) Represented by By substituting some of the Sr and Fe elements of the composition with different elements, an anisotropic Sr ferrite sintered magnet having more excellent magnetic properties can be obtained. For example, it has been found that a rotating machine having excellent characteristics 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, Co
It has been discovered that Sr ferrite is an element that improves the magnetic properties. However, it has been found that a mere addition of the above elements does not provide a sufficient effect of improving magnetic properties. The reason is that if you replace the Fe ion with another element,
This is because 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, for which La, Nd or Pr
Was found to be effective. The present invention has been completed based on the above findings.

That is, the rotating machine of the present invention uses an anisotropic Sr ferrite sintered magnet having a magnetoplumbite type crystal structure, and the anisotropic Sr ferrite sintered magnet is SrO
A basic composition obtained by blending Co with at least one rare earth element of La, Nd and Pr in a composition represented by nFe ₂ O ₃ (where n is 5.7 to 6.0 (molar ratio)); The substitution amount (atomic ratio) x of the rare earth element at the Sr site in the sintered anisotropic Sr ferrite magnet is 0.05 to 0.
5 and the substitution amount (atomic ratio) of Co at the Fe site y
Satisfies [x / (2.2n)] ≦ y ≦ [x / (1.8n)], and is characterized in that the residual magnetic flux density Br is 4200 G or more.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Anisotropic Sr used in the rotating machine of the present invention
The ferrite sintered magnet has the following general formula: (Sr _1-x R _x ) O · n [(Fe _1-y Co _y ) ₂ O ₃ ] (atomic ratio) (where R is at least La, Nd and Pr) One kind,
n = 5.7 to 6.0 (molar ratio). ). x is the substitution amount (atomic ratio) of the R element at the Sr site, and y is the substitution amount (atomic ratio) of Co at the Fe site.

The substitution amount (atomic ratio) x of the R element at 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 deteriorate. Further, in order to realize charge compensation and improve magnetic properties, the substitution amount (atomic ratio) of Co at the Fe site is [x / (2.2n)] ≦ y ≦ [x / (1.8n)].

The sintered anisotropic Sr ferrite magnet used in the present invention can be manufactured through standard manufacturing steps (mixing → calcination → crushing → molding in a magnetic field → sintering). In this case, it is desirable to make the base composition of the anisotropic Sr ferrite sintered magnet substantially at the calcination stage, and to subject the Sr ferrite calcined powder of the base composition to pulverization. For this purpose, the R element and Co are added in the mixing stage. As a result, the Sr ferrite having the basic composition undergoes two high-temperature steps of calcination and sintering, and the R element and
The diffusion of Co into the solid proceeds, and a more uniform composition is obtained.

In order to obtain a high-performance sintered anisotropic Sr ferrite used in the present invention, it is desirable to add SiO ₂ and CaO (or CaCO ₃ ) as additives for controlling the sintering phenomenon in the pulverization stage. SiO ₂ is an additive that suppresses the growth of crystal grains during sintering, and its content is preferably 0.4 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, when the content exceeds 0.5% by weight, the growth of crystal grains is excessively suppressed, the degree of orientation progressing along 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 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 anisotropic Sr ferrite sintered body from the above composition, it is desirable to carry out the following steps after the pulverization in the standard manufacturing process. That is, as a pulverizing step, the composition is finely pulverized by a wet method until the average particle size is in the range of 0.4 to 0.6 μm, concentrated or dried, then crushed and kneaded. Subsequently, it is preferable to perform wet molding in a magnetic field and sinter.
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 forming in a magnetic field deteriorate. On the other hand, if the average particle size exceeds 0.6 μm, the proportion of coarse crystal grains in the structure of the sintered body increases.

In order to enhance the magnetic properties of the sintered anisotropic Sr ferrite magnet used in the present invention, in addition to preparing a pulverized powder adjusted to an optimum composition and an average particle size, it is necessary that the pulverized powder does not agglomerate in the slurry. is important. 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 is formed, and then a dispersing agent is added and kneaded, whereby a shearing force is applied, aggregation is released, and 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. It is effective if the amount of the dispersant added is 0.2% or more in terms of solid content, but if it exceeds 2.0%, the residual magnetic flux density decreases.

[0023]

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.

REFERENCE EXAMPLES 1-12, COMPARATIVE EXAMPLE 1 La, Pr, Nd, Sm, and R are used as R elements (Sr site substitution elements) on the basis of having an ion 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 ] In the above, n = 5.85, x = 2ny, and x = 0 in atomic ratio.
117 and wet-mixed. The obtained mixture was calcined at 1200 ° C. for 2 hours in the air. 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 they were mixed.

Each of the calcined powders 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 a maximum magnetic 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,
The M phase is a phase having a magnetoplumbite type crystal structure.

As is clear from Table 1, when the combination of the R element and the M element is La + Mn (Reference Example 3), when the combination is La + Co (Reference Example 4), and when the combination is La + Ni (Reference Example 5), Comparative Example 1 is used. The saturation magnetization σs and the coercive force Hc are higher than those of. In particular
In the case of La + Co (Reference Example 4), the saturation magnetization s and the coercive force Hc
Both were excellent.

[0027]

[Table 1]

Reference Example 13 La was selected as the R element and Zn was selected as the M element, and SrCO ₃ , Fe ₂ O ₃ , La ₂ O ₃ and ZnO were used, and the following chemical formula was used: (Sr _1-x R _x ) O.n [(Fe _1-y M _y ) ₂ O ₃ ], where n = 5.85, x = 2ny, and x = 0 in atomic ratio
0.60.6 and wet-mixed. Then 1200
Calcination was performed in air at ℃ for 2 hours. The obtained calcined powder was roughly pulverized in the same manner as in Reference Example 3.

The magnetic properties of the obtained coarsely pulverized powder were measured.
The results are shown in FIG. As is clear from FIG. 1, La ₂ O ₃
And ZnO were added at the same time, the saturation magnetization σs was improved. Also, it can be seen that the improvement effect of σs is recognized when the La content x is 0.05 or more, and that the σs decreases when it exceeds 0.5. Therefore, x is preferably 0.05 to 0.5, and 0.07 to 0.
4 is more desirable.

REFERENCE EXAMPLE 14 Coarsely pulverized powder was prepared in the same manner as in Reference Example 13 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.

Example 1, Reference Examples 15 to 17 La was selected as the R element, and Mn was selected as the M element.
(Reference Example 15), Co (Example 1), Ni (Reference Example 16), and
Zn (Reference Example 17) was selected. SrCO ₃ , Fe ₂ O ₃ , La ₂ O
Using the oxides of ₃ and each M element, the following chemical formula: (Sr _1-x R _x ) O · n [(Fe _1-y M _y ) ₂ O ₃ ], n = 5.85 in atomic ratio, x = 2ny and x = 0.
117 and wet-mixed. Then 1200 ° C
For 2 hours in the air. The resulting calcined powder was dry-pulverized with a roller mill to obtain a coarsely pulverized powder.

Thereafter, wet pulverization was performed with an attritor to obtain a slurry containing finely pulverized powder having an average particle diameter of 0.7 μm. At the beginning of the milling, SiO ₂ and CaCO _{3 were} used as sintering aids.
Are 0.45% and 0.80%, respectively, by weight to the coarsely ground powder
(0.45% in terms of CaO). Using this slurry
Wet molding was performed in a magnetic field of 10 kOe 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. After processing each of these fired bodies into a shape of about 10 mm × 10 mm × 20 mm, BH
The magnetic properties were measured with a tracer. The results are shown in FIG.

FIG. 2 shows that La + Mn (Reference Example 15), La + Ni
The replacement materials of (Reference Example 16) and La + Zn (Reference Example 17) were both residual magnetic flux density Br in the low iHc region as compared with the conventional material.
Has good elongation. The replacement material for La + Co (Example 1)
It has both high Br and high iHc.
Rotating machines using Sr ferrite sintered magnets have higher performance than those using conventional materials.

[0034]

As is clear from the above, the sintered anisotropic Sr ferrite magnet used for the rotating machine of the present invention has both higher Br and higher iHc than the conventional material, so that a high-performance rotating machine that has never existed before can be used. Can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing a correlation example between the 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 the sintered anisotropic Sr ferrite magnet used in the present invention.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H01F 7/20 C04B 35/26 F (72) Inventor Yasunobu Ogata 5200 Sankajiri, Kumagaya-shi, Saitama Hitachi Metals, Ltd. In-house F term (reference) 4G002 AA08 AA09 AA10 AE02 4G018 AA08 AA09 AA11 AA13 AA15 AA17 AA21 AA22 AA23 AA24 AA25 AA31 AB04 AC03 AC07 AC11 AC16 5E040 AB04 BD01 CA01 NN00

Claims (1)

[Claims] 1. A rotating machine using an anisotropic Sr ferrite sintered magnet having a magnetoplumbite type crystal structure, wherein the anisotropic Sr ferrite sintered magnet is SrO.nFe ₂ O
₃ (where n is 5.7 to 6.0 (molar ratio)) having a basic composition obtained by blending Co with at least one rare earth element of La, Nd and Pr, and Co. The substitution amount (atomic ratio) x of the rare earth element at the Sr site in the anisotropic Sr ferrite sintered magnet is 0.05 to 0.5, and Fe
The substitution amount (atomic ratio) of Co at the site y is [x / (2.2n)]
≦ y ≦ [x / (1.8n)], so that the residual magnetic flux density Br is 4200
A rotating machine characterized by being at least G.