JP2007290956A - Method of manufacturing ferrite magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a ferrite magnet by which the pass of a dispersion medium in slurry is reduced in order to shorten hours required in a molding step and the elution of metallic ions to the dispersion medium is suppressed in order to reduce the occurrence of pin holes in a sintered compact. <P>SOLUTION: The method of manufacturing the ferrite magnet is provided with a finely grinding step of pulverizing a composition including ferrite powder and SiO<SB>2</SB>powder having 50-150 m<SP>2</SP>/g specific surface to obtain pulverized powder, a molding step of compacting the slurry in which the pulverized powder is dispersed in the dispersion medium in a magnetic field to obtain a compact and a step of firing the compact. It is preferable that the specific surface of SiO<SB>2</SB>powder is ≥100 m<SP>2</SP>/g and the composition contains 0.05-2.5 wt.% SiO<SB>2</SB>powder per the ferrite powder. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a ferrite magnet.

  In order to manufacture a ferrite (sintered) magnet, which has become the mainstream magnet, a mixture of raw materials mixed at a predetermined mixing ratio is calcined to form a ferrite, and the resulting calcined body is coarsely pulverized to produce ferrite A coarsely pulverized powder is obtained. The coarsely pulverized powder is further pulverized to a submicron size to obtain a finely pulverized powder. Next, the finely pulverized powder is compression-molded by a mold in a magnetic field to obtain a compact, and then the compact is sintered to obtain a ferrite magnet. About the manufacturing method of such a ferrite magnet, patent document 1 has description, for example.

  The molding process is roughly divided into a dry type in which the finely pulverized powder is dried and then molded, and a wet type in which the finely pulverized powder is dispersed in a dispersion medium and molded into a slurry. When the forming step is performed in a wet manner, the orientation of the finely pulverized powder can be increased as compared with the case where the forming step is performed in a dry manner, so that a ferrite magnet having excellent magnetic properties can be manufactured.

  If the ferrite particles are in a single domain state, in order to reverse the magnetization, it is necessary to reverse the magnetization against the anisotropic magnetic field, so that the maximum coercive force is expected. The single domain critical diameter of the ferrite particles is about 1 μm. In order to obtain a high coercive force, it is important to make ferrite particles into single domain particles and to make the particle size uniform.

  For the pulverization of the calcined body, mechanical pulverization means such as an attritor or a ball mill is used. However, when mechanical pulverization is performed, there are not a few ultrafine particles that are much smaller than the target particle size and coarse particles that are not sufficiently pulverized. If the pulverization time is extended to prevent the generation of coarse particles for the purpose of improving the magnetic properties of the ferrite magnet, the number of ultrafine particles increases. When ultrafine particles increase, clogging of the filter occurs during wet molding, and resistance when the dispersion medium passes between particles increases, so that the removal of the dispersion medium worsens and the cycle time of the molding process becomes longer, resulting in production. There is a problem that the performance is lowered.

  In addition, when a considerable amount of time elapses after the finely pulverized powder is dispersed in the dispersion medium to form a slurry, alkaline earth metal ions such as Sr and Ca eluted in the dispersion medium are contained in the air. It reacts with oxygen and carbon dioxide and precipitates as a solid such as carbonate. When this is vaporized by sintering, pinholes are generated in the sintered body, causing insufficient strength of the obtained ferrite magnet.

Japanese Patent No. 3088236

  The present invention has been made on the basis of such a technical problem, and can improve the escape of the slurry dispersion medium to shorten the molding process time, and further to the dispersion medium to reduce pinholes in the sintered body. It aims at providing the manufacturing method of the ferrite magnet which can suppress that alkaline earth metal ion elutes.

For this purpose, as a result of intensive investigations, the present inventors specified the particle size distribution of the SiO ₂ powder added to the ferrite powder to produce a finely pulverized powder, and dispersed the finely pulverized powder in a dispersion medium. It has been found that forming the slurry can improve the escape of the dispersion medium at the time of forming without lowering the magnetic properties of the ferrite magnet, and further suppress the elution of alkaline earth metal ions into the dispersion medium. In the present invention, the specific surface area obtained by the BET method is used as an index representing the particle size of the SiO ₂ powder.

Therefore, the present invention provides a fine pulverization step of pulverizing a composition containing ferrite powder and a SiO ₂ powder having a specific surface area of 50 to 150 m ² / g to obtain a pulverized powder, and a slurry in which the pulverized powder is dispersed in a dispersion medium. It is a manufacturing method of a ferrite magnet characterized by including the forming process which obtains a forming object by carrying out pressure forming in a magnetic field, and the process of baking a forming object.

In the present invention, the specific surface area of the SiO ₂ powder is preferably 100 m ² / g or more.
In the present invention, the composition preferably contains 0.05 to 2.5% of SiO ₂ powder to the ferrite powder.

  As described above, according to the present invention, it is possible to improve the escape of the dispersion medium of the slurry during molding, and it is possible to further suppress the alkaline earth metal ions from eluting into the dispersion medium.

Hereinafter, the present invention will be described in detail based on embodiments.
FIG. 1 is a diagram showing an example of the flow of a manufacturing process of a ferrite magnet in the present embodiment. In addition, it cannot be overemphasized that the manufacturing process of the ferrite magnet shown in this Embodiment is only an example, and can change suitably.

  As shown in FIG. 1, in order to manufacture a ferrite magnet, first, a mixture of raw materials in a predetermined blending ratio is calcined to be converted into ferrite (steps S101 and S102). As the raw material, oxide powder or a compound that becomes an oxide by firing, for example, carbonate, hydroxide, nitrate, or the like is used. The calcination is usually performed in an oxidizing atmosphere such as air.

Next, the obtained calcined body is pulverized through a coarse pulverization step (step S103) to obtain a ferrite coarsely pulverized powder (powder).
The coarse pulverization may be a dry pulverization method or a wet pulverization method. However, since the calcined body is generally composed of granules, the coarse pulverization step is preferably performed by a dry method. The coarse pulverization may be a batch type or a continuous type, and may be performed using a vibration mill, a roller mill, an atomizer or the like.
The coarse pulverization step is preferably performed until the average particle size is about 1 to 10 μm.

  The ferrite powder may be a powder mainly composed of ferrite, and includes a raw material composition other than ferrite for constituting the intended ferrite magnet composition, an unreacted raw material composition in the calcination step, and the like. Also good. The ferrite is preferably a hexagonal ferrite such as a magnetoplumbite type M phase or W phase.

Next, SiO ₂ powder is added to the ferrite coarsely pulverized powder and pulverized to a submicron size through a fine pulverization step (step S104) to obtain a finely pulverized powder mainly composed of ferrite (hereinafter referred to as finely pulverized powder). This SiO ₂ powder is added as an additive that suppresses the growth of crystal grains at the same time as a liquid phase component at the time of firing, promoting a sintering reaction and densifying the sintered body together with a compound that produces CaO by a reaction such as CaCO ₃ Is done.

The pulverization may be performed wet or dry, but is preferably performed wet. In the fine pulverization by wet, a pulverized slurry containing coarsely pulverized powder and water coarsely pulverized until the particle size becomes a predetermined particle size or less is prepared, and fine pulverization is performed until the particle size becomes a predetermined particle size or less. The fine pulverization may be performed using a ball mill, an attritor, a vibration mill or the like.
In the fine pulverization step, the pulverization is preferably performed until the average particle size is about 0.3 to 1.2 μm.

As an example of the object to which the SiO ₂ powder is added, the ferrite coarsely pulverized powder has been described. However, the ferrite powder obtained by subjecting the calcined body to heat treatment after coarsely pulverizing, the ferrite powder obtained by subjecting the calcined body to finely pulverized and heat treated, etc. Needless to say, various types of ferrite powders can be used.

  Thereafter, slurry of a predetermined concentration is prepared by dispersing finely pulverized powder in a dispersion medium, and this is magnetically shaped. When wet pulverization is performed in the fine pulverization step, a slurry having a predetermined concentration may be prepared by concentrating the slurry in the dehydration step (step S105).

The present invention is characterized in that the specific surface area of the SiO ₂ powder added to the ferrite powder is 50 m ² / g or more. Thereby, without dropping the magnetic properties of the ferrite magnet, it is possible to improve the removal of the dispersion medium of the slurry at the time of molding, and the effect of suppressing the alkaline earth metal ions from eluting into the dispersion medium is obtained.

The reason why the dispersion medium is better removed from the slurry is that when the SiO ₂ powder having a specific surface area of 50 m ² / g or more is added, the specific surface area of the entire finely pulverized powder after pulverization is reduced. Although the reason for this is not clear, the present inventors presume that this is due to the adsorption of the SiO ₂ powder to the ferrite particles. Large (finer granularity) SiO ₂ powder having a specific surface area as compared to SiO ₂ powder (larger particle size) small specific surface area, the surface of the SiO ₂ powder has a higher physical adsorption capacity in activity. It is conceivable that the surface of the ferrite particle is smoothed by the adsorption of SiO ₂ on the surface of the ferrite particle and the specific surface area is reduced. Further, since the fine pulverization process performs mechanical pulverization, not a few ultrafine particles finer than the target particle size are generated. The presence of such ultrafine particles in an aggregated state due to the adsorption of SiO ₂ powder results in particles having a small specific surface area (large particle size), and the apparent specific surface area of the finely pulverized powder as a whole is reduced. It is also possible that By these, since the resistance when a dispersion medium passes between particles at the time of wet molding becomes small, the escape of the dispersion medium is improved.
This reduction in specific surface area also occurs by adding a water-soluble silicate such as sodium silicate, so that the solubility is increased by using fine SiO ₂ powder, and a part of the SiO ₂ powder is silicic acid. There is also a possibility that it is dissolved as ions and reprecipitated on the surface of the ferrite particles.

Further, conventionally, the reduction in the specific surface area of the finely pulverized powder means that the ferrite particles are coarsened, and the magnetic properties of the ferrite magnet are reduced. However, in the present invention, the apparent specific surface area is reduced by physical adsorption between the SiO ₂ powder and the ferrite particles, and the ferrite particles themselves are not coarsened. Therefore, the magnetic properties are not deteriorated.

In addition, the inventors of the present invention also show that when the SiO ₂ powder having a specific surface area of 50 m ² / g or more is added, elution of alkaline earth metal ions into the dispersion medium is suppressed, the surface is active and the adsorption capacity is high. High SiO ₂ powder with high specific surface area adsorbs to the ferrite particle surface to suppress elution of alkaline earth metal ions into the dispersion medium, and SiO ₂ powder disperses by adsorbing alkaline earth metal ions. It is estimated that alkaline earth metal ions in the medium are reduced. Moreover, it is also conceivable that elution of alkaline earth metal ions is suppressed by dissolving a part of the SiO ₂ powder as silicate ions. Thereby, the pinhole of a sintered compact can be reduced.

The specific surface area of the SiO ₂ powder is set to 50 m ² / g or more in order to obtain the above effect, but the addition amount of the SiO ₂ powder is sufficient to improve the removal of the dispersion medium and reduce the alkaline earth metal ion elution. the specific surface area of the SiO ₂ powder to get the is preferably 100 m ² / g or more. Further, since expensive when SiO ₂ powder has a specific surface area becomes larger, in order to suppress the production cost, it is preferable to 150 meters 2 / ^g or less.

It is preferable to add 0.05 to 2.5 wt% of SiO ₂ powder. Addition of less than 0.05 wt% requires the use of SiO ₂ powder having a larger specific surface area in order to obtain the effect, which increases production cost. Therefore, it is preferable to add 0.05 wt% or more. It is more preferable to add 5 wt% or more. If added over 2.5 wt%, the SiO ₂ powder not involved in adsorption may increase the specific surface area of the entire finely pulverized powder. Therefore, it is preferable to add 2.5 wt% or less. % Or less is more preferable.

As described above, the SiO ₂ powder promotes a sintering reaction as a liquid phase component at the time of firing together with a compound that generates CaO by a reaction such as CaCO ₃ to increase the density of the sintered body and simultaneously suppress the growth of crystal particles. It also has an effect as an additive. If the amount of SiO ₂ powder added is less than 0.1 wt%, the crystal grains of the sintered body are likely to become coarser, and the coercive force (HcJ) tends to decrease. If the amount exceeds 1.0 wt%, the density of the sintered body decreases. The residual magnetic flux density (Br) easily deteriorates. Therefore, in order to obtain the effect of improving the escape of the dispersion medium and high magnetic properties, it is most preferable to add in the range of 0.1 to 1.0 wt%.

In order to obtain the effect of improving the escape of the dispersion medium and the reduction of alkaline earth metal ion elution by adding the SiO ₂ powder, the SiO ₂ powder is used before the pulverization step in order to obtain a sufficient effect as a sintering aid. Although the addition, the addition of part of the SiO ₂ powder to be added during calcining, may be added to the remainder before the milling process. Even in this case, in order to obtain the effect of improving the escape of the dispersion medium of the slurry by the SiO ₂ powder and reducing the alkaline earth metal ion elution, the SiO ₂ powder of 0.05 wt% or more should be added before the pulverization step. It is preferable to add.

  As a dispersion medium for the slurry, water, hexane, toluene, p-xylene, methanol, or the like can be used, but water is preferably used in order to reduce the burden on the environment.

Then, after this slurry is kneaded (step S106), the slurry is poured into a mold and molded by compression molding while applying a magnetic field in a predetermined direction (step S107). The molding conditions are preferably a magnetic field strength of about 5 to 15 kOe and a pressure of about 0.1 to 0.6 Ton / cm ² .
In the present invention, the addition of the SiO ₂ powder improves the escape of the dispersion medium from the slurry. If the dispersion medium is well removed, the cycle time of the molding process can be shortened by reducing the time for filling the mold of the molding machine with the slurry and reducing the internal pressure of the slurry inside the mold. improves.

Thereafter, the obtained molded body is fired and sintered to obtain a ferrite magnet (step S108).
Prior to firing, a drying step is performed, and it is preferable to control the moisture content of the molded body (amount of dispersion medium contained in the molded body) to 7 wt% or less, more preferably 4 wt% or less of the molded body. It is preferably carried out at a temperature of 1150 to 1250 ° C. in the atmosphere, preferably 1200 to 1250 ° C. for about 30 minutes to 3 hours.
Thereafter, a ferrite magnet as a product is completed through processing into a predetermined shape (steps S109 to S110).

The ferrite magnet to which the present invention is applied is an anisotropic ferrite magnet, which is mainly a hexagonal ferrite such as a magnetoplumbite type M phase or W phase. Such a ferrite is particularly preferably MO.nFe ₂ O ₃ (M is preferably one or more of Sr and Ba, n = 4.5 to 6.5). Such ferrite further contains rare earth elements, Ca, Pb, Si, Al, Ga, Sn, Zn, In, Co, Ni, Ti, Cr, Mn, Cu, Ge, Nb, Zr, and the like. May be.

  More preferably, A represents at least one element selected from Sr, Ba, Ca and Pb, R represents at least one element selected from rare earth elements (including Y) and Bi, and Co and / Alternatively, when Zn is L, the total constituent ratio of the metal elements of A, R, Fe and L is A: 1 to 13 atomic%, R: 0.05 to 10 atomic% with respect to the total amount of metal elements. , Fe: 80 to 95 atomic%, L: 0.1 to 5 atomic%, hexagonal magnetoplumbite type (M type) ferrite having a main phase is preferable.

In this case, a main phase represented by the formula IA _1-x R _x (Fe _12-y L _y ) _z O ₁₉ expressed as R is present at the A site and L is present at the Fe site is formed. It is preferable to do. Note that x, y, and z are values calculated from the above amounts.
Further, A: 3 to 11 atomic%, R: 0.2 to 6 atomic%, Fe: 83 to 94 atomic%, L: 0.3 to 4 atomic%, particularly preferably A: 3 -9 atomic%, R: 0.5-4 atomic%, Fe: 86-93 atomic%, L: 0.5-3 atomic%.

In each of the above constituent elements, A is at least one element selected from Sr, Ba, Ca, and Pb, and preferably necessarily contains Sr. If A is too small, M-type ferrite will not be produced, or nonmagnetic phases such as α-Fe ₂ O ₃ will increase. If A is too large, M-type ferrite will not be formed, or nonmagnetic phases such as SrFeO _3-x will increase. The ratio of Sr in A is preferably 51 atomic% or more, more preferably 70 atomic% or more, and further preferably 100 atomic%. If the ratio of Sr in A is too low, it becomes impossible to obtain both the saturation magnetization and the significant improvement in coercive force.

  R is at least one element selected from rare earth elements (including Y) and Bi. R preferably contains La, Pr, and Nd, and particularly preferably contains La. If R is too small, the solid solution amount of L will be small, and the effect will be difficult to obtain. When R is too large, nonmagnetic heterogeneous phases such as orthoferrite increase. The proportion of La in R is preferably 40 atomic% or more, more preferably 70 atomic% or more, and it is most preferable to use only La as R in order to improve saturation magnetization. This is because La is the largest when the solid solution limit amount for hexagonal M-type ferrite is compared. Therefore, if the ratio of La in R is too low, the solid solution amount of R cannot be increased. As a result, the solid solution amount of element L cannot be increased, and the effect becomes small. Further, if Bi is used in combination, the calcination temperature and the sintering temperature can be lowered, which is advantageous in production.

  The element L is Co and / or Zn, and it is particularly preferable that Co is necessarily contained. The ratio of Co in the element L is preferably 10 atomic% or more, more preferably 20 atomic% or more. If the Co ratio is too low, the coercive force will be insufficiently improved.

Hereinafter, the present invention will be described based on specific examples.
Fe ₂ O ₃ powder and SrCO ₃ powder were prepared as starting materials. Fe ₂ O ₃ powder and SrCO ₃ powder are weighed so that Fe and Sr are in a ratio of 6.2: 1 (molar ratio), and SiO ₂ and CaCO ₃ are added to this mixture to obtain a raw material composition Got. The raw material composition was wet-mixed with an attritor, dried and sized, and calcined at 1200 to 1310 ° C. for 2 hours with a rotary kiln to obtain a granular calcined body.

After roughly pulverizing the obtained calcined body with a vibration mill, two kinds of SiO ₂ powders having different specific surface areas were added to 0.31 wt%, respectively, and CaCO ₃ and Al ₂ O ₃ were also added at the same time. Finely pulverized powder was obtained by finely pulverizing with an attritor. The fine pulverization was performed in a slurry state using water as a dispersion medium, and was performed under the same conditions.
In addition, as two types of SiO ₂ powders having different specific surface areas, a SiO ₂ powder having a specific surface area of 126 m ² / g by BET method (average particle size 1 μm) and a SiO ₂ powder having an average particle size of 1.3 m ² / g (average particle size) 5 μm) was used.
Table 1 shows the results of measuring the specific surface area of the entire finely pulverized powder (specific surface area of the finely pulverized powder) by the BET method.

  The finely pulverized slurry was dehydrated with a filter press and kneaded with a kneader. At this time, the solid content concentration in the molding slurry was adjusted to 75 wt%.

  The molding slurry was poured into a mold, and compression molding was performed while removing water. This molding was performed while applying a magnetic field of about 10 kOe (800 kA / m) in the compression direction.

The molded body thus obtained was fired by holding at an elevated temperature rate of 5 ° C./min and 1200 ° C. for 1 hour to obtain a fired body.
The composition of the obtained sintered _{body, Al 2 O 3: 0.12wt%} , SiO 2: 0.31wt%, CaCO 3: 0.57wt%, SrO: 9.36wt%, and the balance _Fe 2 _{O 3} .

Table 1 shows the magnetic properties of the obtained fired body as residual magnetic flux density Br (mT), coercive force Hcj (kA / m), Br. Indicates potential. In addition, Br. The potential is a value obtained by converting Hcj to 278 (kA / m) and converting Br (Br: HcJ = + 1 (mT):-2.4 (kA / m)) in order to compare magnetic characteristics.
Table 2 shows the time required to fill the mold with the slurry during molding (material filling time during molding) and the internal pressure of the slurry inside the molding machine (slurry internal pressure during molding).

From Table 1, in the case of the present invention example using a fine SiO ₂ powder having a specific surface area of 126 m ² / g, it was finely pulverized as compared with the conventional example using a conventional SiO ₂ powder having a specific surface area of 1.3 m ² / g. It can be seen that the specific surface area of the entire powder is small (the particle size is large), and the magnetic properties are equivalent or better.
From Table 2, it can be seen that the inventive example has a shorter material filling time and lower slurry internal pressure than the conventional example. As described above, the specific surface area of the finely pulverized powder is reduced, and the removal of the dispersion medium of the slurry at the time of molding is improved. Therefore, the cycle time of the molding process can be shortened by the present invention.

Fine pulverization is performed by changing the amount of SiO ₂ powder added before the pulverization step in the range of 0 to 3.2 wt% to obtain fine pulverized powder, and the specific surface area of the entire fine pulverized powder is obtained by the BET method. It was. The results are shown in Table 3 and FIG.
The specific surface area by the BET method of SiO ₂ powder used was as in Example 1, 126m ² / g (fine SiO ₂ powder), which is 1.3 m ² / g (prior art SiO ₂ powder).

From Table 3 and FIG. 2, it can be seen that when a fine SiO ₂ powder having a specific surface area of 126 m ² / g is used, the specific surface area of the entire finely pulverized powder is small, that is, the particle size becomes coarse. On the other hand, if the specific surface area using a conventional SiO ₂ powder 1.3 m ² / g, a specific surface area of the entire milling powder is equivalent to the case of not adding SiO ₂ powder, whole milled powder in the conventional SiO ₂ powder It can be seen that the effect of reducing the specific surface area cannot be obtained. Since it is better for the dispersion medium to escape during molding when the specific surface area is smaller (grain size is coarse), the use of fine SiO ₂ powder improves the dispersion medium removal.

In addition, paying attention to the change in the specific surface area of the finely pulverized powder with respect to the added amount of fine SiO ₂ powder in FIG. 2, the specific surface area of the finely pulverized powder increases at the peak when 0.8 wt% of fine SiO ₂ powder is added. When the added amount exceeds 2.5 wt%, the specific surface area of the finely pulverized powder exceeds that when no SiO ₂ powder is added. This is considered that the effect of reducing the specific surface area of the finely pulverized powder obtained by adsorption of the fine SiO ₂ powder is saturated, and the fine SiO ₂ powder itself having a large specific surface area increases the total specific surface area.

In the present embodiment 2, in addition amount 3.2 wt% of fine SiO ₂ powder, greater than if the specific surface area of the finely pulverized powder is not added SiO ₂ powder, but the specific surface area of SiO ₂ powder used, the material Since the addition amount of the SiO ₂ powder may be appropriately set depending on the composition, fine grinding conditions, etc., the fine ground powder may be added even if the SiO ₂ powder exceeds 3.2 wt% when the conditions are different from those in Example 2. It is possible to obtain the effect of reducing the specific surface area.

The amount of SiO ₂ powder added before the pulverization step was changed in the range of 0 to 0.6 wt%, and pulverization was performed to obtain a slurry containing the pulverized powder. As the dispersion medium, water was used in the same manner as in Example 1. BET specific surface area of the SiO ₂ powder used was as in Example 1, fine SiO ₂ powder according to the present invention is 126m ² / g, the conventional SiO ₂ powder 1.3 m ² / g.

  Alkaline earth metal ions (Sr ions, Ca ions) eluted in the finely pulverized slurry were measured by ICP (plasma emission analyzer). Table 4 shows the elution amount of alkaline earth metal ions (Sr ions, Ca ions).

From Table 4, when the fine SiO ₂ powder having a specific surface area of 126 m ² / g is used, the amount of alkaline earth metal ions eluted compared to the case of using the conventional SiO ₂ powder having a specific surface area of 1.3 m ² / g. It can be seen that decreases. Thereby, it becomes possible to reduce the pinhole of a sintered compact.

SiO ₂ powder having a specific surface area ^{1.3m 2 /g,41.7m 2 /g,62.2m 2 /g,81.3m 2} / g to be added prior to the milling step, 126m ² / g and 149m ² A slurry containing finely pulverized powder was obtained in the same manner as in Example 1 except that fine pulverization was performed and the calcination temperature was changed to 1215 ° C. The amount of SiO ₂ powder added at this time is 0.15 wt%. The specific surface area of the entire finely pulverized powder was determined by the BET method. The results are shown in Table 5.

Alkaline earth metal ions (Sr ions, Ca ions) eluted in the finely pulverized slurry were measured by ICP (plasma emission analyzer). The amounts of alkaline earth metal ions (Sr ions, Ca ions) eluted are shown in Table 5, FIG. 3 and FIG.
Furthermore, as magnetic characteristics of the obtained fired body, residual magnetic flux density Br (mT), coercive force Hcj (kA / m), Br. The potential was measured. The results are shown in Table 5. In addition, Br. The potential was determined in the same manner as in Table 1 of Example 1.

Table 5 shows that the elution amount of alkaline earth metal ions decreases as the specific surface area of the SiO ₂ powder increases. Thereby, it becomes possible to reduce the pinhole of a sintered compact. On the other hand, even if the specific surface area of the SiO ₂ powder is increased, the magnetic properties of the sintered body are not adversely affected.

  In the above embodiment, a strontium ferrite magnet is used as the ferrite magnet. The configuration can be changed as appropriate.

It is a figure which shows the manufacturing process of the ferrite magnet in this Embodiment. Is a graph showing the specific surface area of the finely divided powder to the specific surface area of the conventional SiO ₂ addition of finely ground powder to fine SiO ₂ added. It is a graph showing the amount of elution of the relationship of the specific surface area of the SiO ₂ powder and Sr ions. It is a graph showing the amount of elution of the relationship of the specific surface area of the SiO ₂ powder and Ca ions.

Claims (3)

A pulverizing step of pulverizing a composition containing ferrite powder and a SiO ₂ powder having a specific surface area of 50 to 150 m ² / g to obtain a pulverized powder;
A molding step of obtaining a molded body by pressure molding a slurry in which the pulverized powder is dispersed in a dispersion medium in a magnetic field;
Firing the molded body;
A method for producing a ferrite magnet, comprising: The method for producing a ferrite magnet according to claim 1, wherein the specific surface area of the SiO ₂ powder is 100 m ² / g or more. The composition, method for producing a ferrite magnet according to claim 1, wherein the ferrite powder to containing 0.05 to 2.5% of the SiO ₂ powder.

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