JP2005072186A - Ferrite magnet powder, method for manufacturing ferrite magnet, and method of forming hexagonal system w type ferrite phase - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a ferrite magnet which can improve coercive force of a hexagonal system W type ferrite magnet. <P>SOLUTION: A first temporary baking process wherein material powder containing A (where A is at least one kind of element selected out of Sr, Ba and Pb) and Fe is held at 1,220-1,320°C for a predetermined time, a pulverization process which pulverizes first temporarily baked member obtained by the first temporary baking process, and a second temporary baking process is installed wherein pulverized powder obtained by the pulverization process is held in a temperature range of 1,220-1,320°C for a predetermined time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ferrite magnet, and more particularly to a method for producing a hexagonal W-type ferrite magnet powder.

Conventionally, magnetoplumbite type hexagonal ferrite represented by SrO.6Fe ₂ O ₃ , that is, M-type ferrite has been the mainstream of ferrite magnets. With regard to this M-type ferrite magnet, efforts have been made to improve the performance, focusing on making the ferrite crystal grain size close to the single domain grain size, aligning the ferrite crystal grains in the direction of magnetic anisotropy, and increasing the density. I came. As a result, Non-Patent Document 1 discloses that an M-type ferrite magnet having a saturation magnetization (σs) of 74 emu / g can be obtained. It is difficult to improve the characteristics.

  A W-type ferrite magnet is known as a ferrite magnet having the possibility of exhibiting magnetic properties that surpass those of an M-type ferrite magnet. A W-type ferrite magnet has an anisotropic magnetic field similar to that of an M-type ferrite magnet and has a high saturation magnetization. For example, Patent Document 1 describes a W-type ferrite magnet having a saturation magnetization (σs) of 78 emu / g.

  Patent Document 1 aims to obtain a fine powder in a state where it has undergone calcination for the generation of W phase. For that purpose, the final temperature is 1500K (1250 ° C) to 1650K (1377 ° C), It has been proposed that the temperature rising rate in the temperature range of 1000 K (727 ° C.) or higher is 0.40 K / s or higher and the temperature lowering rate is 1 K / s or higher.

JP 2001-284112 A Proc. ICF, C1-299 (1997)

  However, the magnet powder obtained in Patent Document 1 has a coercive force (HcJ) of about 1.3 kOe, and its improvement is strongly desired. In Patent Document 1, it is necessary to strictly control the temperature increase and temperature decrease rates during calcination, but it is desirable to omit such control in consideration of industrial production.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a method for producing a ferrite magnet capable of improving the coercive force of a hexagonal W-type ferrite magnet.

  The present inventor has studied to improve the coercive force of a hexagonal W-type ferrite magnet, particularly a hexagonal W-type ferrite magnet having a powder form. As is well known, the smaller the particle size, the higher the coercive force can be obtained. In order to reduce the particle size of the powder obtained by pulverization after calcination, the calcination temperature may be set lower in order to suppress particle growth. However, if the calcining temperature is low, the W phase necessary for obtaining high magnetic properties is not generated or even if generated. That is, in order to solve the problem of the present invention, a process capable of sufficiently generating the W phase even by calcination at a lower temperature is necessary.

  As the treatment, the present inventor studied to lengthen the calcination time or to perform the calcination a plurality of times. However, it is difficult to sufficiently generate the W phase at a low temperature even by performing calcination for a long time or by performing calcination a plurality of times. However, it was found that the W phase can be sufficiently generated even at a low temperature by pulverizing the calcined body obtained by calcining and then performing calcining again.

Accordingly, the present invention provides a composition formula: AFe ²⁺ _a Fe ³⁺ _b O ₂₇ (wherein A is at least one element selected from Sr, Ba and Pb, 1.7 ≦ a ≦ 2.2). 14 ≦ b ≦ 18), the first calcined body obtained by the first calcining process and the first calcining process in which the raw material powder having the composition represented by 14 ≦ b ≦ 18 is held at 1220 to 1320 ° C. for a predetermined time. There is provided a method for producing a ferrite magnet comprising: a pulverizing step for pulverizing; and a second calcining step for holding the pulverized powder obtained in the pulverizing step for a predetermined time in a temperature range of 1220 to 1320 ° C.

  The ferrite magnet according to the present invention can have a structure in which a hexagonal W-type ferrite phase (hereinafter simply referred to as W phase) forms a main phase.

  In the method for producing a ferrite magnet of the present invention, the first calcination step and the second calcination step are both aimed to produce a W phase, but usually the second calcination step obtained in the second calcination step. The amount of W phase generated in the fired body is greater than the amount of W phase generated in the first calcined body obtained in the first calcining step. That is, in the method for producing a ferrite magnet according to the present invention, since the W phase cannot be sufficiently generated in the first calcination step because the calcination is performed at a relatively low temperature, the second calcination step is performed after pulverization. Thus, the W phase is sufficiently obtained, preferably a W phase single phase structure is obtained. In addition, this invention includes grind | pulverizing a 2nd calcined body after a 2nd calcining process, and performing a 3rd calcining process and also a 4th calcining process ... after that.

Magnet powder can be obtained by crushing or pulverizing the ferrite magnet (second calcined body) obtained in the present invention. The magnet powder obtained by crushing can be used for, for example, a bonded magnet, and the magnet powder obtained by crushing can be used for a sintered magnet. The difference between crushing and crushing will be described later.
The ferrite magnet powder obtained by the present invention has a composition formula: AFe ²⁺ _a Fe ³⁺ _b O ₂₇ (in the composition formula, A is at least one element selected from Sr, Ba and Pb; 7 ≦ a ≦ 2.2 and 14 ≦ b ≦ 18), the average particle size is 2.5 μm or less, the saturation magnetization (σs) is 75 emu / g or more, and the coercive force (HcJ). Can have characteristics of 3 kOe or more.

In the past, calcination (W phase generation processing) was completed once, whereas the present inventors newly proposed that the W phase generation processing be repeated twice or more. As described later, it is important to modify the dispersion state of the particles of the product obtained in the preceding W phase generation process between the W phase generation process to be performed and the subsequent W phase generation process. Therefore, in the present invention, the composition formula: AFe ²⁺ _a Fe ³⁺ _b O ₂₇ (wherein A is at least one element selected from Sr, Ba and Pb, 1.7 ≦ a ≦ 2.2 14 ≦ b ≦ 18), and a method for producing a hexagonal W-type ferrite phase in a magnet material in which a hexagonal W-type ferrite phase is a main phase, Applying a W phase generation process for generating a hexagonal W-type ferrite phase, modifying the dispersion state of each component in the product obtained from the W phase generation process, and further performing a W phase generation process on the product The present invention provides a method for producing a characteristic hexagonal W-type ferrite phase.

According to the present invention, a ferrite magnet powder having a W phase as a main phase and a coercive force (HcJ) exceeding 3 kOe can be obtained. Moreover, as shown in the examples described later, according to the present invention, it is possible to have a coercive force (HcJ) exceeding 3 kOe and 70, and further to have a saturation magnetization (σs) exceeding 75 emu / g.

Hereinafter, specific embodiments of the present invention including the best mode will be described.
The manufacturing method of a ferrite magnet by this invention, a compounding process, and a W phase production | generation process are included. Hereinafter, each step will be described.
<Mixing process>
First, when Sr is selected as the Fe ₂ O ₃ (hematite) powder and the A element, SrCO ₃ powder is prepared. Then, the Fe ₂ O ₃ powder and the SrCO ₃ powder are weighed so that the main composition becomes the composition formula described above. Specifically, the molar ratio of SrCO ₃ powder and Fe ₂ O ₃ powder is 1: 8.
. The range may be 0 to 1: 8.6. At this time, C, Si or the like may be mixed as a reducing agent. Further, CaCO ₃ and SiO ₂ can be added to improve the coercive force and adjust the crystal grain size. It may be further added a powder, such as Al ₂ O ₃ or Cr ₂ O _3.

After weighing each raw material, it is mixed and pulverized for about 1 to 3 hours with a wet attritor or the like.
Although an example in which SrCO ₃ powder and Fe ₂ O ₃ powder are used will be described here, the A element can be added as an oxide in addition to the form of adding as a carbonate. The same applies to Fe, and it can be added as a compound other than Fe ₂ O ₃ (hematite). Furthermore, it is possible to use a compound containing element A and Fe.

In the present invention, it is also effective to make Fe ₃ O ₄ (magnetite) part or all of Fe ₂ O ₃ added as a raw material powder. W-type ferrite is characterized by containing a divalent atom at the Fe site. When all Fe atoms are Fe ³⁺ hematite, it is necessary to reduce a part of Fe ³⁺ to Fe ²⁺ , but a magnetite composed of two Fe ³⁺ and one Fe ²⁺ is suitable. By using it as a raw material instead of hematite, it is possible to produce W-type ferrite without going through a reduction process. At this time, depending on the atmosphere of the W phase generation treatment, it is possible to obtain the same effect as when the reducing agent is added by changing the ratio of hematite and magnetite to increase the amount of magnetite. That is, since Fe ²⁺ ions contained in Fe ₃ O ₄ act as a reducing agent, the same effect as when C or Si is added can be obtained. In addition, by appropriately setting the amount of Fe ₃ O ₄ , impurities from the reducing agent do not remain in the magnet powder, so that the magnetic characteristics are not deteriorated.

<W phase generation process>
The sufficiently mixed raw material powder is then subjected to a W phase generation step.
In the W phase generation step, a process generally referred to as calcination is performed a plurality of times. In addition, the present invention is characterized in that a pulverization process is performed between the preceding calcination and the subsequent calcination.
In the present invention, this calcination is performed in a temperature range of 1230 to 1320 ° C. As described above, the present invention is premised on calcining at a relatively low temperature. However, as shown in the examples to be described later, at 1200 ° C., the W phase is generated even if the calcining is performed a plurality of times according to the present invention. Can not do it. Therefore, the temperature of calcination shall be 1230 degreeC or more. On the other hand, when calcined at 1350 ° C., the W phase can be easily generated, but the particles grow coarsely in the calcined body, and even if this is crushed, a high coercive force can be obtained. It is not possible. A desirable calcination temperature is 1230 to 1280 ° C, and a more desirable calcination temperature is 1240 to 1260 ° C. The holding time may be appropriately selected within the range of 0.2 to 5 hours. In the present invention, the calcining performed a plurality of times may be performed under the same conditions or different conditions. For example, the present invention includes performing the preceding calcination and the subsequent calcination at different temperatures or at different holding times. In the present invention, the cooling after holding at the calcining temperature for a predetermined time may be performed at a rate of 50 ° C./min or less, and further 30 ° C./min or less.

The calcination is performed in a non-oxidizing atmosphere such as nitrogen gas, argon gas, or a mixed gas thereof. By heating and holding in a non-oxidizing atmosphere, Fe ³⁺ in Fe ₂ O ₃ (hematite) powder is reduced to generate Fe ²⁺ constituting W-type ferrite, and W-type ferrite is generated. However, if a sufficient amount of Fe ²⁺ cannot be secured at this stage, an M phase or a hematite phase is present in addition to the W phase. In order to obtain W single-phase ferrite, it is effective to adjust the oxygen partial pressure. When the oxygen partial pressure is lowered, Fe ³⁺ is reduced and Fe ²⁺ is easily generated.

  In the present invention, the calcined body obtained in each calcining step is pulverized during calcining performed a plurality of times. Compared with the fact that W phase generation at low temperature is not realized even if the calcination time is extended as shown in the examples described later, this pulverization process can generate W phase by low temperature calcination. It is a factor to make. The reason why the W phase can be generated by calcination at a low temperature by pulverization is not clear, but the inventor presumes as follows. In the blending step before calcination, each component of the raw material powder is uniformly distributed. Needless to say, it is advantageous that the components are uniformly distributed for the generation of the W phase. When each component reacts by calcination and a W phase or another phase is generated, each component is consumed to generate the phase. That is, the reaction part and the unreacted part are mixed in the whole raw material powder, and the initial uniform component distribution state collapses. Therefore, the generation of the W phase does not proceed. However, by pulverizing the calcined body, the distribution of each component is modified to a uniform state, and by performing calcination again, generation of the W phase proceeds.

  A known pulverizing apparatus such as a ball mill, an attritor, or a vibration mill can be used for pulverization performed between a plurality of calcinations. For example, after coarse pulverization with a vibration mill, fine pulverization can be performed with a ball mill. The calcined body has a form in which a large number of particles are aggregated, and the purpose of pulverization is to solve this aggregated state and make the distribution state of each component uniform as described above. Therefore, it is necessary to spend time accordingly. Naturally, depending on the pulverizing apparatus, etc., when a ball mill is used, pulverization is carried out for about 10 to 50 hours.

<Process after W phase generation process>
Although a calcined body is obtained by the W phase generation step, the subsequent treatment differs depending on the type of product to be applied. Hereinafter, the outline of the process after the W-phase generation step will be described for a case where it is applied to a sintered magnet and a case where it is applied to a bonded magnet.

<Sintered magnet>
When applied to a sintered magnet, the calcined body is pulverized. This pulverization may be basically considered in the same manner as the above-described pulverization, but it is necessary to consider that the particle size is suitable for firing performed later. Specifically, it is wet or dry pulverized by an attritor, ball mill, jet mill or the like and pulverized to 1 μm or less, preferably 0.1 to 0.8 μm, and more preferably 0.1 to 0.6 μm. Further, at this stage, carbon powder having a reducing effect can be added. Also, CaCO ₃ and SiO ₂ can be added prior to pulverization in order to improve the coercive force and adjust the crystal grain size.

The powder obtained by pulverization needs to be formed into a predetermined shape. This shaping is performed with a magnetic field applied. Molding in a magnetic field is performed dry or wet. Since it is preferable to perform wet molding in order to increase the degree of orientation, the case of performing wet molding will be described below.
When employing wet molding, the slurry after wet pulverization is concentrated to prepare a slurry for wet molding. Concentration may be performed by centrifugation, filter press, or the like. At this time, it is desirable that the ferrite magnet powder occupies 30 to 80 wt% in the wet forming slurry. Further, it is desirable to add a surfactant such as gluconic acid (salt) and sorbitol to water as a dispersion medium. Next, magnetic field molding is performed using the slurry for wet molding. Molding pressure is 0.1
The applied magnetic field may be about 5 to 15 kOe and about 0.5 ton / cm ² . The dispersion medium is not limited to water and may be non-aqueous. When a non-aqueous dispersion medium is used, an organic solvent such as toluene or xylene can be used. When using toluene or xylene as the non-aqueous dispersion medium, it is desirable to add a surfactant such as oleic acid.

After the molding in the magnetic field, a heat treatment can be performed in which the compact is held at a low temperature of 100 to 450 ° C., more preferably 200 to 350 ° C. for 1 to 4 hours. By performing this heat treatment in the atmosphere, a part of Fe ²⁺ is oxidized to Fe ³⁺ . That is, in this step, by a certain extent the reaction proceeds from Fe ²⁺ to Fe ^3+, is to control the amount of Fe ²⁺ to a predetermined amount. In this step, the dispersion medium is removed.
The heat-treated molded body is fired by holding at a temperature of 1100 to 1270 ° C, more preferably 1160 to 1240 ° C for 0.5 to 3 hours. The firing atmosphere is a non-oxidizing atmosphere for the same reason as in the calcination step.

<Bond magnet>
When applied to a bonded magnet, the calcined body is crushed. As described above, the calcined body is an aggregate of a large number of particles, but crushing should be limited to solving the aggregated state of the particles. It can be said that less mechanical energy is applied as compared with the pulverization in which the particles whose aggregation state is released are further refined. Although crushing is ideally a process that only stops the agglomeration state between particles, it cannot be denied that some particles are pulverized in an actual process.

The calcined body obtained by the present invention is composed of fine particles having an average particle size of 2.5 μm or less. Therefore, the magnet powder obtained by crushing is also fine with an average particle size of 2.5 μm or less.
This fine magnet powder is kneaded with a binder such as rubber or plastic of about 10 wt% and a plasticizer, a cross-linking agent, and other additives, and is molded into a predetermined shape by a molding method such as roll, compression, extrusion, or injection. Get. About this molded object, when a binder is a thermosetting resin, a cure can be performed, and when it is a rubber type | system | group, it can vulcanize | cure and a bond magnet can be obtained. As the binder, it is desirable to use NBR (acrylonitrile butadiene) rubber, chlorinated polyethylene, or polyamide resin.

<Composition>
The ferrite magnet to which the present invention is applied has a main composition having the following composition formula.
AFe ²⁺ _a Fe ³⁺ _b O ₂₇
However, A is at least one element selected from Sr, Ba and Pb, 1.7 ≦ a ≦ 2.2, and 14 ≦ b ≦ 18.
A is preferably at least one of Sr and Ba, and Sr is particularly preferable from the viewpoint of magnetic properties.
“A” indicating the proportion of Fe ²⁺ is in the range of 1.7 ≦ a ≦ 2.2. When a is less than 1.7, an M phase and an Fe ₂ O ₃ (hematite) phase whose saturation magnetization is lower than that of the W phase are generated, and the saturation magnetization is lowered. On the other hand, if a exceeds 2.2, a spinel phase is generated and the coercive force is reduced. Therefore, a is in the range of 1.7 ≦ a ≦ 2.2. A desirable range of a is 1.8 ≦ a ≦ 2.1, and a more desirable range is 1.9 ≦ a ≦ 2.1.

“B” indicating the proportion of Fe ³⁺ is in the range of 14 ≦ b ≦ 18. This is because if b is less than 14 and exceeds 18, coercive force and residual magnetic flux density at a high level cannot be obtained. A desirable range of b is 14.5 ≦ b ≦ 16.9.

Hereinafter, the present invention will be described based on specific examples.
Fe ₂ O ₃ powder (primary particle size: 0.3 μm) and SrCO ₃ powder (primary particle size: 2 μm) were prepared as raw material powders. The raw material powder was weighed so that a = 2.0 and b = 16.0 in the above composition formula. After weighing, it was mixed and pulverized with a wet attritor for 2 hours.

Next, calcination was performed. The calcination was performed using a tubular furnace under the condition of holding in an N ₂ gas atmosphere for 1 hour. The heating and holding temperatures were 1200 ° C., 1250 ° C., and 1350 ° C., and the temperature rising rate to the heating holding temperature and the rate of temperature falling from the heating holding temperature were 5 ° C./min. In addition, the calcination was performed 1 to 3 times, and the calcined body obtained by the preceding calcination was pulverized before performing the second and third calcinations. The pulverization was performed in two stages: coarse pulverization using a vibration mill and fine pulverization using a ball mill. Coarse pulverization using a vibration mill is performed for 10 minutes on 220 g of the calcined body, and fine pulverization using a ball mill is performed by adding 400 ml of water to 210 g of the coarsely pulverized powder and treating for 40 hours.

Composition analysis, phase composition, magnetic properties, and particle size were measured each time one to three calcinations were completed. The results are shown in Table 1.
In addition, when the heating and holding temperature of calcination is 1250 ° C., an experiment in which the holding time is 2 hours (Table 1 Experiment 5), an experiment in which the pulverization treatment is not performed before the second and third calcinations (Table 1). Experiment 6
) Also went.
The composition analysis was performed by fluorescent X-ray quantitative analysis (where Fe ²⁺ is a chemical analysis). The a and b values of the composition formula: AFe ²⁺ _a Fe ³⁺ _b O ₂₇ are shown in Table 1. As shown in Table 1, the values of a and b fluctuate depending on the number of times of calcination because of the inclusion of substances from the media used for pulverization. In this embodiment, since the media of the ball mill is made of stainless steel, Fe is mainly mixed.
The phase composition was identified by X-ray diffraction results. The conditions for X-ray diffraction are as follows. In the present invention (this example), the case where the W phase is 80% or more by molar ratio is defined as the W phase being the main phase.
X-ray generator: 3 kW, tube voltage: 45 kV, tube current: 40 mA
Sampling width: 0.02 deg, scanning speed: 4.00 deg / min
Divergence slit: 1.00 deg, scattering slit: 1.00 deg
Receiving slit: 0.30mm
The magnetic properties (saturation magnetization (σs) and coercivity (HcJ)) were measured on the calcined body. Specifically, it is obtained based on a magnetization curve in the easy axis direction and a magnetization curve in the hard axis direction measured with a maximum applied magnetic field of 20 kOe using a VSM (vibrating magnetometer).
The particle size is shown as the average particle size of the powder obtained by crushing 220 g of the calcined body for 1 minute using a vibration mill (4 inches).

As shown in Table 1, even if calcination was performed twice and three times after pulverization, a W phase could not be generated at a calcination temperature of 1200 ° C.
On the other hand, when the calcining temperature is 1250 ° C., the W phase is generated by the first calcining. However, although the W phase is generated until the second calcination, the amount thereof is insufficient, so that the magnetic properties are low. However, after the third calcination, the W phase forms the main phase, and a coercive force (HcJ) of 3000 Oe or more and a saturation magnetization (σs) of 75 emu / g or more can be obtained.
Experiment 3 in Table 1 is an experimental example similar to Experiment 2 except that C (carbon) as a reducing agent was added at the time of blending, but the same effect can be obtained even when C is added. I understand.
When the calcining temperature reaches 1350 ° C., the phase composition becomes a W-phase single phase after the first calcining, but the particles constituting the calcined body are semi-molten and coarsened to obtain only a low coercive force (HcJ). I found it impossible.
Also, as shown in Experiment 5 of Table 1, the calcination holding time is lengthened, or even if calcination is performed a plurality of times without performing pulverization as in Experiment 6, the W phase is defined as the main phase. It is not possible to improve the magnetic properties, particularly the coercive force (HcJ).

Fe ₂ O ₃ powder (primary particle size: 0.3 μm), SrCO ₃ powder (primary particle size: 2 μm) were a = 2.0 and b = 15.1 (experiment 7) in the above composition formula, a = The same treatment and measurement as in Example 1 were performed except that the weight was 2.0 and b = 14.2 (Experiment 8). The results are shown in Table 2.
In Experiments 7 and 8, Fe / Sr is smaller than Experiment 2 of Example 1, and the amount of Fe is small. Thus, it can be seen that when the amount of Fe is small, a W-phase single-phase structure can be obtained by the second calcination.

  According to the present invention, a fine magnet material having a W phase as a main phase can be obtained by calcining at a low temperature. Since this magnet material has a high coercive force and saturation magnetization, the application of ferrite magnets is expanded. Contribute to.

Claims (6)

Composition formula: AFe ²⁺ _a Fe ³⁺ _b O ₂₇ (in the composition formula, A is at least one element selected from Sr, Ba and Pb, 1.7 ≦ a ≦ 2.2, 14 ≦ b ≦ 18), an average particle diameter of 2.5 μm or less, a saturation magnetization (σs) of 75 emu / g or more, and a coercive force (HcJ) of 3 kOe or more. Powder. Composition formula: AFe ²⁺ _a Fe ³⁺ _b O ₂₇ (in the composition formula, A is at least one element selected from Sr, Ba and Pb, 1.7 ≦ a ≦ 2.2, 14 ≦ b ≦ A first calcining step of holding a raw material powder having a composition represented by (18) at 1220 to 1320 ° C. for a predetermined time;
A crushing step of crushing the first calcined body obtained in the first calcining step;
And a second calcination step of holding the pulverized powder obtained in the pulverization step in a temperature range of 1220 to 1320 ° C. for a predetermined time.   The amount of hexagonal W-type ferrite phase generated in the second calcined body obtained in the second calcined step is equal to the hexagonal W-type ferrite phase in the first calcined body obtained in the first calcined step. The method for producing a ferrite magnet according to claim 2, wherein the production amount of the ferrite magnet is larger than that of the ferrite magnet.   The method for producing a ferrite magnet according to claim 2 or 3, wherein magnet powder is obtained by crushing or pulverizing the second calcined body obtained in the second calcining step.   5. The method for producing a ferrite magnet according to claim 4, wherein the magnet powder has an average particle size of 2.5 [mu] m or less. Composition formula: AFe ²⁺ _a Fe ³⁺ _b O ₂₇ (in the composition formula, A is at least one element selected from Sr, Ba and Pb, 1.7 ≦ a ≦ 2.2, 14 ≦ b ≦ 18), and a hexagonal W-type ferrite phase in a magnet material in which a hexagonal W-type ferrite phase forms a main phase,
The raw material powder is subjected to a W phase generation process for generating a hexagonal W type ferrite phase,
Modify the distribution state of each component in the product obtained from the W-phase generation treatment,
A method for producing a hexagonal W-type ferrite phase, wherein the product is further subjected to a W-phase production treatment.