JP2005162498A - Manufacturing method of oxide sintered compact and composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for improving sintered density while benefiting from carbon addition. <P>SOLUTION: The manufacturing method of an oxide sintered compact comprises a molding step wherein a mixture containing a raw material powder, a carbon powder and a dispersant is molded and a sintering step wherein the obtained molded product is sintered to obtain the sintered compact. The dispersant used here is an organic compound having a hydroxy or carboxy group, its neutralized salt or its lactone, an organic compound having a hydroxymethylcarbonyl group or an organic compound having an enolic hydroxy group which can dissociate as an acid or its neutralized salt, wherein the organic compound has 3-20 carbons and has hydroxy groups bound to ≥50% of carbon atoms that are not forming double bonds with oxygen atoms. The dispersant (e.g. gluconic acid) inhibits segregation of the carbon powder and therefore inhibits increase in pinholes and the resulting decrease in sintered density, even when the carbon powder disappears at sintering. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing an oxide sintered body, and particularly to an oxide sintered body such as a ferrite magnet.

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 made of an oxide sintered body 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 discloses a W-type ferrite magnet having a composition satisfying SrO · 2 (FeO) · n (Fe ₂ O ₃ ) and n satisfying 7.2 to 7.7. In Patent Document 1, the composition is within the above-described range, and carbon is added to the raw material powder before calcining, and CaO, SiO ₂ , and carbon are further added after calcining, so that the magnetic properties of the W-type ferrite magnet are obtained. We are trying to improve. In Patent Document 1, (1) it is possible to generate W-type ferrite in a wide temperature range by adding carbon to the raw material powder before calcination, and (2) carbon is a raw material powder during calcination. (3) By adding carbon after calcination and before pulverization, the optimum range of drying temperature is expanded to the high temperature side, and excellent maximum energy product That ((BH) max) can be obtained stably is cited as the reason for adding carbon.

JP 2000-501893 (Claims, pages 4 to 8)

As described above, when manufacturing an oxide sintered body such as a W-type ferrite magnet, the effect of reducing action and improving magnetic properties can be expected by adding carbon. In particular, in the Fe ₂ W type ferrite magnet, it is difficult to control the amount of divalent iron to a desired value. However, as proposed in Patent Document 1, it is possible to add two by adding carbon after calcination. Control of the amount of valence iron becomes easy.
However, carbon added as a fine powder tends to agglomerate and therefore segregates. If carbon powder in a segregated state is present in the molded body before being subjected to sintering, the oxide sintered body obtained after sintering has a low sintered density. This is because the segregated carbon powder disappears during sintering, so that pinholes increase in the sintered body and the sintered density decreases.
Then, this invention makes it a subject to provide the technique for improving a sintered density, enjoying the effect by carbon addition.

The present inventor has made various studies in order to suppress segregation of the carbon powder. As a result, it was found that the segregation of the carbon powder can be suppressed by adding a certain type of dispersant, and the dispersibility of the carbon powder is improved. That is, the present invention comprises a molding step of molding a mixture containing raw material powder, carbon powder, and a dispersing agent, and a sintering step of sintering the obtained molded body to obtain a sintered body, the dispersing agent Is an organic compound having a hydroxyl group and a carboxyl group or a neutralized salt or lactone thereof, an organic compound having a hydroxymethylcarbonyl group, an organic compound having an enol-type hydroxyl group that can be dissociated as an acid, or a neutralization thereof It is a salt, wherein the organic compound has 3 to 20 carbon atoms, and a hydroxyl group is bonded to 50% or more of carbon atoms other than carbon atoms double-bonded to oxygen atoms. A method for producing an oxide sintered body is provided. The dispersant used in the present invention not only improves the dispersibility of the particles constituting the raw material powder, but also suppresses segregation of the carbon powder. For this reason, even if carbon powder lose | disappears at the time of sintering, the increase in a pinhole and the fall of the sintering density resulting from it can be suppressed. Here, the oxide sintered body includes the above-described Fe ₂ W type ferrite, as well as other W type ferrites, and other types of ferrites (for example, other hexagonal ferrites such as M type, Mn-based and Ni-based cubic ferrite) are also included. An oxide sintered body other than ferrite, for example, a sintered body having dielectric properties, is also included in the oxide sintered body of the present invention. The applicant of the present application has already filed an application as Japanese Patent No. 3137658 (International Publication Number: WO98 / 25278) for the above-described dispersant effectively contributing to the improvement of the dispersibility of the particles constituting the raw material powder.

In the present invention, the mixture containing the raw material powder, the carbon powder, and the dispersant described above is obtained by stirring. In other words, the timing of adding the carbon powder and the dispersant to the raw material powder may be the same or different, but it is desirable to use the agitated one in the molding step of the present invention. This is to improve the dispersibility of the carbon powder.
An independent stirring step is not essential depending on the timing of adding the dispersant. For example, when a dispersant is added in the pulverization step, a stirring process proceeds with the pulverization, so that an independent stirring step is not required.

By selecting a powder that can develop a magnetic ferrite phase as the raw material powder, the oxide sintered body in the present invention can have a magnetic ferrite phase. An oxide sintered body having a magnetic ferrite phase can be used as a ferrite magnet by magnetization. Here, residual magnetic flux density (Br) is mentioned as one of the magnet characteristics. As is clear from the formula Br = σs × density × magnetic orientation (where σs is saturation magnetization per unit weight), density is a factor that greatly affects the residual magnetic flux density (Br). Therefore, in order to manufacture a W-type ferrite magnet having a high residual magnetic flux density (Br), improving the density is one key. As described above, according to the method for manufacturing an oxide sintered body in the present invention, since the sintered density can be improved, a ferrite magnet having a finally high residual magnetic flux density (Br) can be obtained.
The oxide sintered body in the present invention is a hexagonal W-type ferrite, particularly a composition formula: AFe ²⁺ _a Fe ³⁺ _b O ₂₇ (in the composition formula, A is at least one selected from Sr, Ba, and Pb). Fe ₂ W type ferrite having a composition represented by a seed element (1.5 ≦ a ≦ 2.1, 12.5 ≦ b ≦ 16.5) is desirable. Fe ₂ W type ferrite is known as hard ferrite, and by magnetizing Fe ₂ W type ferrite having the above composition, excellent magnetic properties surpassing M type ferrite, especially residual magnetic flux density (Br). ) Can be obtained.
In order to obtain the above-described Fe ₂ W type ferrite, the compact is sintered in a non-oxidizing atmosphere, for example, a nitrogen atmosphere in order to control the amount of divalent iron. In this case, the carbon powder contributes effectively as a reducing agent.
As the dispersant used in the present invention, gluconic acid is desirable.
It is effective to add the dispersant used in the present invention as a calcium salt. For example, when selecting gluconic acid as a dispersing agent, adding as gluconic acid Ca is desirable.
In addition, since Ca gluconate exists as a solid at normal temperature, it can be added as a powder.

Although the oxide sintered body has been described in detail above, the knowledge of the present invention that the above-described dispersant is effective in suppressing segregation of carbon powder can also be grasped as the following composition. That is, the present invention is a composition used for sintering, wherein carbon powder is dispersed in the composition, and is an organic compound having a hydroxyl group and a carboxyl group, or a neutralized salt thereof or a lactone thereof? An organic compound having a hydroxymethylcarbonyl group, an organic compound having an enol-type hydroxyl group that can be dissociated as an acid, or a neutralized salt thereof, wherein the organic compound has 3 to 20 carbon atoms, Provided is a composition comprising a dispersant having a hydroxyl group bonded to 50% or more of carbon atoms other than double-bonded carbon atoms.
Here, Ca gluconate is desirable as the dispersant. As shown in the examples described later, by using Ca gluconate, a high-density and high-characteristic oxide sintered body can be obtained.
An example of the first form of the composition is a molding slurry. It is already known that a sintered magnet having a high degree of magnetic orientation can be obtained by employing wet magnetic field forming. Slurry containing raw material powder is used for wet magnetic field molding, but by using the molding slurry of the present invention in which carbon powder is dispersed as this slurry, sintering with a high sintering density and residual magnetic flux density is finally achieved. A magnet can be obtained.
The molding slurry is a liquid composition, but the composition of the present invention can also be regarded as a solid molded body.
This molded product has a CV value (CV: Coefficient of Variation) of carbon powder in a 200 μm × 200 μm visual field as small as 0.5 or less, and is excellent in dispersibility. For this reason, an oxide sintered body having a high sintering density can be obtained by subjecting the formed body to sintering. Therefore, if the oxide sintered body has magnetism, a sintered magnet having a high residual magnetic flux density can be finally obtained. In addition, it shows that the dispersion degree of carbon powder is so high that CV value is small. As is well known, the CV value is a value (percentage) obtained by dividing the standard deviation by the arithmetic average value. The CV value in the present invention is a value determined by the measurement conditions of the examples described later.

  According to the present invention, segregation of carbon powder can be suppressed, and a high-density oxide sintered body can be obtained while enjoying the effects of carbon addition. By applying the present invention to a W-type ferrite magnet, a W-type ferrite magnet having a high residual magnetic flux density (Br) can be obtained.

Hereinafter, specific embodiments of the present invention including the best mode will be described.
The method for producing an oxide sintered body according to the present invention suppresses segregation of the carbon powder by using a certain dispersant when carbon powder is added in the production process, and the sintered density of the oxide sintered body. It is characterized by improving. Here, the dispersant used in the present invention is an organic compound having a hydroxyl group and a carboxyl group or a neutralized salt or lactone thereof, an organic compound having a hydroxymethylcarbonyl group, or an enol capable of dissociating as an acid. An organic compound having a type hydroxyl group or a neutralized salt thereof, wherein the organic compound has 3 to 20 carbon atoms, and hydroxyl groups are bonded to 50% or more of carbon atoms other than carbon atoms double-bonded to oxygen atoms. It is what.
The present invention as described above can be applied to the production of various oxide sintered bodies. However, since a particularly remarkable effect is obtained, the following description will be given by taking the case of application to the production of an Fe ₂ W type ferrite magnet as an example. To explain.

<Composition>
When the present invention is applied to a W-type ferrite magnet, it is desirable to use a main composition having the following composition formula.
AFe ²⁺ _a Fe ³⁺ _b O ₂₇ Formula (1)
In formula (1),
1.5 ≦ a ≦ 2.1,
12.5 ≦ b ≦ 16.5. A is at least one element selected from Sr, Ba and Pb.

  A is preferably at least one of Sr and Ba. In the above formula (1), a and b each represent a molar ratio.

Next, the reasons for limiting a and b in the above composition formula will be described.
“A” indicating the proportion of Fe ²⁺ is in the range of 1.5 ≦ a ≦ 2.1. When a is less than 1.5, an M phase and Fe ₂ O ₃ (hematite) phase having a saturation magnetization (4πIs) lower than that of the W phase are generated, and the saturation magnetization (4πIs) is lowered. On the other hand, if a exceeds 2.1, a spinel phase is generated and the coercive force (HcJ) is lowered. Therefore, a is in the range of 1.5 ≦ a ≦ 2.1. A desirable range of a is 1.6 ≦ a ≦ 2.1, and a more desirable range is 1.6 ≦ a ≦ 2.0.
“B” indicating the ratio of Fe ³⁺ is set in the range of 12.5 ≦ b ≦ 16.5. When b is less than 12.5, a spinel phase is generated and the coercive force (HcJ) decreases. On the other hand, when b exceeds 16.5, an M phase and an Fe ₂ O ₃ (hematite) phase are generated, and the saturation magnetization (4πIs) decreases. Therefore, b is set to a range of 12.5 ≦ b ≦ 16.5. A desirable range of b is 13.0 ≦ b ≦ 16.0, and a more desirable range is 13.0 ≦ b ≦ 15.5.

  The composition of the ferrite magnet powder can be measured by fluorescent X-ray quantitative analysis or the like. Further, the present invention does not exclude the inclusion of an element other than the A element (at least one element selected from Sr, Ba and Pb) and Fe. In addition to these elements, for example, elements such as Si and Ca may be contained.

FIG. 1 is a flowchart showing a manufacturing process when an Fe ₂ W type ferrite magnet is obtained as an oxide sintered body.
As shown in FIG. 1, the manufacturing method of the Fe ₂ W type ferrite magnet of the present invention includes a blending step (step S100), a calcining step (step S110), a coarse crushing step (step S120), and a fine crushing step (step S130). , A magnetic field forming step (step S140), a compact heat treatment step (step S150), and a firing step (step S160). Since Fe ²⁺ tends to become Fe ³⁺ in the atmosphere, in the method for producing an Fe ₂ W type ferrite magnet of the present invention, carbon powder acting as a reducing agent is added at least before the magnetic field forming step (step S140). The above-mentioned dispersant effective for suppressing the segregation of the carbon powder is added at least before the magnetic field forming step. Moreover, in order to stably control Fe ²⁺ , the heat treatment temperature, the firing atmosphere, and the like are controlled, and the firing step (step S160) is performed in a non-oxidizing atmosphere, and in this step, the carbon powder functions as a reducing agent.
Hereinafter, each step will be described.

<Combination process (step S100)>
After weighing each raw material, it is mixed and pulverized for about 1 to 3 hours with a wet attritor or the like. As the raw material powder, an oxide or a compound that becomes an oxide by sintering can be used. 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.

<Calcination process (step S110)>
The mixed powder material obtained in the blending step (step S100) is calcined at 1100 to 1350 ° C. By performing this calcination in a non-oxidizing atmosphere such as nitrogen gas or argon gas, Fe ³⁺ in the Fe ₂ O ₃ (hematite) powder is reduced to generate Fe ²⁺ constituting W-type ferrite. W-type ferrite is formed. 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. This is because when the oxygen partial pressure is lowered, Fe ³⁺ is reduced and Fe ²⁺ is generated.

<Rough grinding process (step S120)>
Since the calcined body is generally granular, it is preferable to coarsely pulverize the calcined body. In the coarse pulverization step (step S120), pulverization is performed using a vibration mill or the like until the average particle size becomes 0.5 to 10 μm.

<Fine grinding step (Step S130)>
In the subsequent fine pulverization step (step S130), the coarsely pulverized powder 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. Although depending on the pulverization method, when the coarsely pulverized powder is wet pulverized by a ball mill, the coarsely pulverized powder may be pulverized for 30 to 50 hours with respect to 200 g. In order to improve the coercive force and adjust the crystal grain size, powders such as CaCO ₃ and SiO ₂ , or Al ₂ O ₃ and Cr ₂ O ₃ may be added prior to fine pulverization.

Carbon powder having a reducing effect can be added in this fine pulverization step (step S130). The addition of carbon powder is effective for generating W-type ferrite in a state close to a single phase (or a single phase).
Here, the addition amount of carbon powder (hereinafter referred to as “carbon amount”) is 0.15 to 0.45 wt% with respect to the raw material powder. By setting the amount of carbon within this range, it is possible to sufficiently expect the effect of the carbon powder as a reducing agent in the firing step (step S160) described later, and higher saturation magnetization (σs) than in the case where no carbon powder is added. ) Can be obtained. When the present invention is applied to an Fe ₂ W type ferrite magnet, the more desirable carbon amount is 0.2 to 0.45 wt%, and the more desirable carbon amount is 0.3 to 0.4 wt%. In addition, when applying this invention to oxide sintered compacts other than a magnet, since it is not necessary to consider saturation magnetization ((sigma) s), carbon content should just be about 0.05-1.0 wt%.
The size of the carbon powder to be added may be about 0.01 to 1.0 μm.

In the present invention, in order to suppress segregation of the carbon powder, at least one of the following dispersants is added.
(A) an organic compound having a hydroxyl group and a carboxyl group, a neutralized salt thereof, or an lactone (b) an organic compound having a hydroxymethylcarbonyl group (c) an organic compound having an enol-type hydroxyl group that can be dissociated as an acid A compound or its neutralized salt

In addition, the kind of neutralization salt used as a dispersing agent is not specifically limited, Although calcium salt, sodium salt, etc. can be used, Preferably calcium salt is used. In the manufacturing process of ferrite magnets, SiO ₂ and CaCO ₃ are usually added to improve the coercive force and adjust the crystal grain size. However, when hydroxycarboxylic acid or its lactone is used as a dispersant, a molding slurry is used. SiO ₂ and CaCO ₃ may partly flow out when preparing the liquid or during wet magnetic field molding. However, by using the calcium salt as the dispersant, it is possible to prevent and suppress the outflow of SiO ₂ and CaCO _3, the characteristic deterioration of the coercive force (HcJ) decreases like experience when SiO ₂ and CaCO ₃ is leaked .

  In the present invention, the organic compounds mentioned in the above (a) to (c) have 3 to 20, preferably 4 to 12, carbon atoms other than carbon atoms that are double-bonded to oxygen atoms. Those having a hydroxyl group bonded to 50% or more are used. When the carbon number is 2 or less, the effect of suppressing segregation of the carbon powder becomes insufficient. Moreover, even if the number of carbon atoms is 3 or more, the segregation suppressing effect of the carbon powder is still insufficient if the bonding ratio of hydroxyl groups to carbon atoms other than carbon atoms double-bonded to oxygen atoms is less than 50%. Become.

  In addition, the bonding ratio of the hydroxyl group is limited with respect to the organic compound, and is not limited with respect to the dispersant itself. For example, when a lactone of an organic compound (hydroxycarboxylic acid) having a hydroxyl group and a carboxyl group is used as the dispersant, the limitation on the bonding ratio of the hydroxyl group is applied not to the lactone but to the hydroxycarboxylic acid itself. Two or more of the above-described dispersants may be used in combination. In addition to the dispersant used in the present invention, other known dispersants may be further used.

  The basic skeleton of the organic compound described above may be a chain or a ring, and may be a saturated bond or an unsaturated bond.

  Specifically, a hydroxycarboxylic acid or a neutralized salt thereof or a lactone thereof is preferable as the dispersant. In particular, gluconic acid (C = 6; OH = 5; COOH = 1) or a neutralized salt or lactone thereof, lactobionic acid (C = 12; OH = 8; COOH = 1), tartaric acid (C = 4; OH = 2; COOH = 2) or a neutralized salt thereof, glucoheptonic acid γ-lactone (C = 7; OH = 5) is preferable. Among these, gluconic acid or a neutralized salt thereof or a lactone thereof is preferable because it has a high effect of suppressing segregation of carbon powder and a high effect of improving the degree of orientation of particles constituting the raw material powder. Moreover, gluconic acid (or its neutralized salt or its lactone) is inexpensive. The kind of the neutralized salt is not particularly limited, and it is as described above that a calcium salt, a sodium salt, or the like can be used, but a calcium salt is preferably used. As shown in Examples described later, by using Ca gluconate, a sintered magnet having a high sintered density and excellent magnetic properties can be obtained.

As the organic compound having a hydroxymethylcarbonyl group, sorbose is preferable.
Ascorbic acid is preferable as the organic compound having an enol-type hydroxyl group that can be dissociated as an acid. Here, the structure of gluconic acid used in Examples described later is shown in FIG.

  Note that the structure of the dispersant used in the present invention may change during pulverization, molding slurry preparation, and the like. For example, free gluconic acid and its two types of lactones (γ- and δ-) do not exist alone in an aqueous solution, but exist in a mixed state because they change into the other two. Furthermore, the structure of the dispersant may change due to a mechanochemical reaction caused by pulverization. Furthermore, there is a possibility that the object of the present invention can be achieved by adding a compound that generates the same organic compound as the dispersant used in the present invention, for example, by hydrolysis reaction.

The addition amount of a dispersing agent shall be 0.05-3.0 wt% with respect to raw material powder. When the added amount of the dispersant is less than 0.05 wt%, the segregation suppressing effect of the carbon powder is insufficient. The dispersant used in the present invention also has a function of improving the degree of orientation of the particles constituting the raw material powder, but if the amount added is less than 0.05 wt%, the degree of orientation of the particles constituting the raw material powder can also be improved. It becomes insufficient.
On the other hand, when the added amount of the dispersant exceeds 3.0 wt%, cracks are likely to occur in the molded body and the sintered body. Therefore, the addition amount of a dispersing agent shall be 0.05-3.0 wt% with respect to raw material powder. A desirable addition amount of the dispersant is 0.1 to 2.0 wt%, and more desirably 0.3 to 2.0 wt%.

  By selecting Ca gluconate as a dispersant and adding 0.05 to 3.0 wt% of the raw material powder, the residual magnetic flux density (Br) of 4500G or more and the degree of magnetic orientation of 94% or more are used. It is also possible to obtain a sintered magnet showing Desirable addition amount of Ca gluconate is 0.1 to 2.5 wt%, more desirably 0.1 to 2.0 wt%, and still more desirably 0.5 to 1.8 wt%. By adding 0.1 to 2.5 wt% of gluconate Ca, the residual magnetic flux density (Br) of 4500 G or more, the magnetic orientation degree of 94% or more, and the coercive force (HcJ) of 3000 Oe or more and 94 A sintered magnet exhibiting a magnetic orientation degree of at least% can be obtained.

  When the dispersant is ionizable in an aqueous solution, such as an acid or a metal salt, the added amount of the dispersant is an ion conversion value. That is, the amount added is calculated in terms of organic components excluding hydrogen ions and metal ions. Moreover, when a dispersing agent is a hydrate, an addition amount is calculated | required except crystal water. For example, the amount of addition when the dispersant is calcium gluconate monohydrate is calculated in terms of gluconate ions.

  When the dispersant is made of lactone or contains lactone, the amount of addition is calculated in terms of hydroxycarboxylic acid ions, assuming that the lactone is all ring-opened to become hydroxycarboxylic acid.

  If it is before the magnetic field shaping | molding process (step S140) mentioned later, the timing which adds a dispersing agent will not be specifically limited, For example, it can add at the following timing.

(1) After calcination step (step S110) and before coarse pulverization step (step S120) (2) At coarse pulverization step (step S120) (3) After coarse pulverization step (step S120) and fine pulverization step (step S130) Before (4) At the time of the fine grinding step (step S130) (5) After the fine grinding step (step S130) and before the magnetic field forming step (step S140)

In any case, the dispersant in the present invention is present in the molding slurry used in the magnetic field molding step (step S140), but in order to fully exhibit the effect of suppressing segregation of the carbon powder. In addition, stirring is performed after the dispersant is added. This stirring is not necessarily performed immediately after the dispersant is added, and may be performed at the latest before the magnetic field forming step (step S140).
Moreover, you may add a dispersing agent in multiple times. For example, a part may be added at the timing (4) and the remaining may be added at the timing (5). When the dispersant is added in a plurality of times, the addition amount of each time may be set so that the total addition amount is in the above-described desirable range, that is, 0.05 to 3.0 wt% with respect to the raw material powder. .

Most of the added dispersant is decomposed and removed in the compact heat treatment step (step S150) performed after the magnetic field forming step (step S140). The dispersant remaining without being decomposed and removed in the compact heat treatment step (step S150) is also decomposed and removed in the subsequent firing step (step S160).
In addition, although it mentioned above about the case where carbon powder is added at the time of a fine grinding | pulverization process (step S130), what is necessary is just to add carbon powder at the stage in any one of said (1)-(5) similarly to a dispersing agent. Further, the carbon powder may be added in a plurality of times.

  Although this invention does not exclude performing the magnetic field shaping | molding process (step S140) mentioned later by a dry type, in order to make a magnetic orientation degree high, it is preferable to perform wet shaping | molding. Therefore, after describing the preparation of the slurry for wet molding, the subsequent magnetic field molding process (step S140) will be described.

<Preparation of molding slurry>
Prior to the subsequent magnetic field forming step (step S140), a forming slurry is prepared. A slurry for molding (composition) can be obtained by concentrating the slurry after wet pulverization by means of centrifugal separation or a filter press. When the dispersant is not added in the above step, the molding slurry may be obtained by adding the dispersant to the molding slurry before or after concentration and stirring. It is desirable that the ferrite magnet powder occupies 30 to 80 wt% in the molding slurry after concentration.
Note that both the molding slurry before concentration and the molding slurry after concentration are included in the composition (molding slurry) in the present invention. Moreover, although water can be used as a dispersion medium, you may use nonaqueous dispersion media, such as toluene and xylene.
In the present invention, when a dispersant (hydroxycarboxylic acid or the like) that exhibits acid properties in an aqueous solution is used, it is desirable to add a basic compound to increase the pH of the molding slurry supernatant. Thereby, a magnetic orientation degree can be improved further. As the basic compound, ammonia and sodium hydroxide are preferable. Ammonia may be added as aqueous ammonia. In addition, pH fall can also be prevented by using the sodium salt of hydroxycarboxylic acid.

<Magnetic field forming step (step S140)>
Next, magnetic field molding is performed using a molding slurry. The molding pressure may be about 0.1 to 0.5 ton / cm ² and the applied magnetic field may be about 5 to 15 kOe.

<Molded Body Heat Treatment Step (Step S150)>
In this step, heat treatment is 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. Further, in this step, the dispersion medium is removed, and most of the dispersant is decomposed and removed.

<Baking process (step S160)>
In the subsequent firing step (step S160), the molded body is fired 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 (step S110). Moreover, carbon powder lose | disappears in this process.

Through the above steps, an Fe ₂ W type ferrite magnet as the oxide sintered body of the present invention can be obtained. In the present invention, the above-described dispersant is added to suppress segregation of the carbon powder. For this reason, the oxide sintered compact of the present invention obtained after the firing step has a high sintered density of 5.0 g / cm ³ or more. Moreover, according to the Fe ₂ W type ferrite magnet as the oxide sintered body of the present invention, the residual magnetic flux density (Br) of 90% or more, further 92% or more, magnetic orientation of 4000G or more, further 4200G or more. ) Can be obtained. Further, by going through the above-described composition and process, sintered magnet as a main phase and W-phase, it is possible to further obtain Fe ₂ W-type ferrite magnets have a single phase W phase. In addition, according to the sintered magnet of the present invention, a coercive force (HcJ) of 2200 Oe or more, further 2500 Oe or more can be obtained with the W phase as the main phase. In addition, saturation magnetization (σs) of 70 emu / g or more, further 72 emu / g or more, and desirably 75 emu / g or more can be obtained.

FIG. 3 is a flowchart showing another manufacturing process of the Fe ₂ W type ferrite magnet as the oxide sintered body of the present invention. The blending step (step S100), calcination step (step S110), coarse pulverization step (step S120), magnetic field forming step (step S140), compact heat treatment step (step S150), and firing step (step S160) shown in FIG. ) May be performed according to the procedure described above. Therefore, hereinafter, the first fine pulverization process (step S200), the heat treatment process (step S210), and the second fine pulverization process (step S220), which are characteristic parts in the flowchart shown in FIG. 3, will be described.

<First fine grinding step (step S200)>
In the first fine pulverization step (step S200), the coarsely pulverized powder is wet or dry pulverized by an attritor, ball mill, jet mill or the like to be 0.8 μm or less, preferably 0.1 to 0.4 μm, more preferably 0. . Grind to 1-0.2 μm. The first fine pulverization is performed for the purpose of eliminating coarse powder.
Although depending on the pulverization method, when the coarsely pulverized powder is wet pulverized with a ball mill, it may be treated for 60 to 100 hours per 200 g of the coarsely pulverized powder.
In order to improve the coercive force and adjust the crystal grain size, CaCO ₃ and SiO ₂ , or SrCO ₃ , BaCO ₃ , Al ₂ O ₃ , Cr ₂ , prior to the first pulverization step (step S200). A powder such as O ₃ may be added.

<Heat treatment process (step S210)>
In the heat treatment step (step S210), a heat treatment is performed in which the finely pulverized powder is held at 600 to 1200 ° C., more preferably 700 to 1000 ° C., for 1 second to 10 hours.
The first fine pulverization process produces a large amount of ultrafine powder of less than 0.1 μm. However, if the ultrafine powder is present, problems may occur in the subsequent molding process. For example, when there is a large amount of ultrafine powder during wet molding, problems such as poor water drainage and molding cannot occur. Therefore, in the present embodiment, heat treatment is performed prior to the molding process. That is, this heat treatment is performed for the purpose of reducing the ultrafine powder of less than 0.1 μm generated in the first fine pulverization step by reacting with the fine powder (0.1 to 0.2 μm). By this heat treatment, ultrafine powder is reduced and the moldability can be improved.
The heat treatment atmosphere is a non-oxidizing atmosphere for the same reason as in the calcination step (step S110).

<Second fine grinding step (step S220)>
In the subsequent second fine pulverization step (step S220), the heat-treated fine pulverized powder is wet or dry pulverized by an attritor, ball mill, jet mill or the like, and is 0.8 μm or less, preferably 0.1 to 0.4 μm, More preferably, it grind | pulverizes to 0.1-0.2 micrometer. The second pulverization is performed for the purpose of adjusting the particle size, removing necking, and improving the dispersibility of the additive.
Depending on the pulverization method, when wet pulverization is performed with a ball mill, the treatment may be performed for 10 to 40 hours per 200 g of finely pulverized powder.

After performing the second pulverization step (step S220), the magnetic field forming step (step S140), the compact heat treatment step (step S150) and the firing step (step S160) are performed according to the above-described procedure. An Fe ₂ W type ferrite magnet as an oxide sintered body can be obtained. Based on the flowchart shown in FIG. 3, the fine pulverization is divided into a first fine pulverization step (step S200) and a second fine pulverization step (step S220), and the first fine pulverization step (step S200) and An Fe ₂ W type ferrite magnet that exhibits higher magnetic properties than the case where the manufacturing process shown in FIG. 1 is performed by performing the heat treatment process (step S210) between the second pulverization process (step S220). Can be obtained. Specifically, it has a high sintered density of 5.0 g / cm ³ or more and a magnetic orientation degree of 95% or more, more preferably 96% or more, and a residual magnetic flux density (Br) of 4500 G or more, further 4600 G or more. Can be obtained. Further, through the above-described composition and the process shown in FIG. 3, a sintered magnet having a W phase as a main phase and an Fe ₂ W type ferrite magnet having a W phase as a single phase can be obtained.
According to the sintered magnet of the present invention, a coercive force (HcJ) of 2800 Oe or more, further 3000 Oe or more, more desirably 3200 Oe or more can be obtained with the W phase as the main phase. In addition, saturation magnetization (σs) of 70 emu / g or more, or 75 emu / g or more can be obtained.

Hereinafter, the present invention will be described based on specific examples.
In Example 1, an Fe ₂ W type ferrite magnet was produced based on the flowchart shown in FIG.
First, Fe ₂ O ₃ powder (primary particle diameter: 0.3 μm) and SrCO ₃ powder (primary particle diameter: 2 μm) were prepared as raw material powders. After this raw material powder was weighed, 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 temperature was 1300 ° C., and the rate of temperature increase to the heating and holding temperature and the rate of temperature decrease from the heating and holding temperature was 5 ° C./min. 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.
(Sample No. 1-5)
In this fine pulverization stage, SiO ₂ powder (primary particle diameter: 0.01 μm) is added to the coarsely pulverized powder by 0.3 wt%, and CaCO ₃ powder (primary particle diameter: 1 μm) is added by 0.7 wt%. In addition, 0.9 wt% of Ca gluconate (primary particle size: 10 μm) was added as the dispersant described above. Moreover, the addition amount of carbon powder (primary particle diameter: 0.05 micrometer) is 0.1 wt% (sample No. 1), 0.2 wt% (sample No. 2), 0.3 wt% (sample No. 3). , 0.4 wt% (sample No. 4), and 0.5 wt% (sample No. 5).
A wet milling slurry was obtained by wet milling for 40 hours using a ball mill. Next, the slurry for wet molding was concentrated with a centrifugal separator, and molding was performed in a magnetic field using the concentrated slurry for wet molding. In addition, the applied magnetic field (longitudinal magnetic field) is 12 kOe (1000 kA / m), and the molded body has a cylindrical shape with a diameter of 30 mm and a height of 15 mm. This molded body was heat-treated in the atmosphere at 300 ° C. for 3 hours, and then fired in nitrogen at a heating rate of 5 ° C./min and a maximum temperature of 1190 ° C. for 1 hour to obtain five types of sintered bodies. The composition of the obtained sintered body was a = 2.0 and b = 16.0 in the above composition formula. The composition analysis was performed using a fluorescent X-ray quantitative analyzer SIMULTIX 3550 manufactured by Rigaku Corporation (the same applies to Examples 2 and 3 described later).

(Sample No. 6)
Except that no carbon powder was added, the above sample No. The sintered compact was produced on the conditions similar to 1-5.
(Sample No. 7)
Except that neither carbon powder nor Ca gluconate was added, the above sample No. The sintered compact was produced on the conditions similar to 1-5.
(Sample Nos. 8-12)
Except for not adding Ca gluconate, the above sample No. The sintered compact was produced on the conditions similar to 1-5. Sample No. The amount of carbon powder added in 8 to 12 is the same as that of Sample No. This corresponds to the amount of carbon powder added in 1-5.
(Sample No. 13)
Except for the addition of Ca gluconate and the addition amount of carbon powder of 0.7 wt%, the above sample No. The sintered compact was produced on the conditions similar to 1-5.

  Sample No. The sintered density of each of the sintered bodies 1 to 13 was measured. The results are shown in Table 1 and FIG. Note that FIG. Sample Nos. The sintered density of 1-12 is plotted.

As shown in FIG. 4, when Ca gluconate is not added, the sintering density decreases as the amount of carbon increases, and when Ca gluconate is 0.4 wt%, the sintering density is 5.0 g / cm ³ . Below. However, when Ca gluconate is added, a sintered density of 5.05 g / cm ³ or more is exhibited even if the amount of carbon is increased.
From the above results, it was found that by adding Ca gluconate, it is possible to suppress a decrease in sintered density associated with the addition of carbon.

Subsequently, the above-mentioned sample No. The sintered bodies of 2, 4, 6, 7, 9, 11, and 13 were observed with an optical microscope. Sample No. with no addition of Ca gluconate. 7, 9, 11, and 13 are micrographs shown in FIGS. The micrographs of 6, 2, and 4 are shown in FIGS.
As shown in FIGS. 5A to 5D, in the case where Ca gluconate is not added, as the amount of carbon increases, the black spots in the micrographs increase. This black spot is a pinhole formed after the carbon powder disappears during sintering. When the carbon powder disappears while being segregated, pinholes are formed, and black spots are noticeably observed in the micrographs. However, as shown in FIGS. 11 (carbon amount: 0.4 wt%), Sample No. In 13 (carbon amount: 0.7 wt%), many large and small black spots were observed.
On the other hand, as shown in FIGS. 6A to 6C, when Ca gluconate is added, the black spots are hardly increased even if the amount of carbon is increased. When Ca gluconate is added, segregation of the carbon powder is suppressed, so pinholes are difficult to form even when the carbon powder disappears, and as a result, there is almost no increase in sunspots even if the amount of carbon increases. it is conceivable that.
The observation results of the above micrographs correspond to the results shown in FIG.

  Next, the dispersibility of the carbon powder on the analysis screen is changed to the CV value (coefficient of variation) from the result of elemental mapping by EPMA for two types of molded articles produced under the same conditions except for the presence or absence of Ca gluconate addition. And evaluated. These two types of molded products are sample Nos. With both carbon addition amounts of 0.4 wt%. 4, 11 (molded body before being subjected to sintering). The CV value is a value (percentage) obtained by dividing the standard deviation of all analysis points by the average value of all analysis points, and the smaller this value, the better the dispersibility. In addition, EPMA-1600 manufactured by Shimadzu Corporation was used as the EPMA, and the measurement conditions were as follows. The analysis screen and CV value of each molded body are shown in FIGS. 7 and 8 respectively show analysis screens in a 200 μm × 200 μm visual field and a 500 μm × 500 μm visual field.

Measurement conditions of CV value in FIG. 7 Acceleration voltage: 15 kV
Beam size: 1μm
Irradiation current: 0.13 μA
Irradiation time: 40 msec / point Measurement point: X → 200 points (1,000 μm step)
Y → 200 points (1.000 μm step)
Range: 200 μm × 200 μm

Measurement condition of CV value in FIG. 8 Acceleration voltage: 15 kV
Beam size: 1μm
Irradiation current: 0.13 μA
Irradiation time: 40 msec / point Measurement point: X → 250 points (2,000 μm step)
Y → 250 points (2.000μm step)
Range: 500μm × 500μm

As shown in FIG. 7, in the 200 μm × 200 μm visual field, the CV value is 0.606 when Ca gluconate is not added, whereas the CV value is only 0.182 when Ca gluconate is added. It is. In addition, as shown in FIG. 8, in the 500 μm × 500 μm visual field, the CV value is 0.206 when Ca gluconate is not added, whereas the CV value is 0.2 when Ca gluconate is added. 146. That is, it can be seen from FIGS. 7 and 8 that when Ca gluconate is added, the dispersibility of the carbon powder is improved as compared with the case where Ca gluconate is not added. Thus, the good dispersibility by adding Ca gluconate seems to be the cause which suppresses the fall of the pinhole at the time of sintering, and the sintering density resulting from it.
From the above results, it was confirmed that when Ca gluconate was added, the carbon powder was dispersed at the stage before sintering. And it was found that by adding Ca gluconate, the CV value of the carbon powder in the field of view of 200 μm × 200 μm can be 0.5 or less, further 0.3 or less, and desirably 0.2 or less.

  Subsequently, the above-mentioned sample No. The saturation magnetization (σs) was measured for each of the sintered bodies 1 to 13. The results are shown in Table 1 and FIG. The saturation magnetization (σs) is measured based on the magnetization curve in the easy axis direction and the magnetization curve in the hard axis direction measured with a maximum applied magnetic field of 20 kOe using a VSM (vibrating magnetometer). Note that FIG. Sample Nos. The saturation magnetization (σs) of 1 to 12 is plotted.

  FIG. 9 shows that the saturation magnetization (σs) is maximized when the carbon content is 0.3 to 0.4 wt% regardless of whether Ca gluconate is added. Here, as shown in FIG. 1, when Ca gluconate is added, even if the amount of carbon is increased, there is no problem that the sintered density is lowered. Therefore, by setting the carbon amount to 0.15 to 0.45 wt%, desirably 0.2 to 0.45 wt%, it is possible to combine the characteristics of high saturation magnetization (σs) and high density.

Next, the above sample No. The degree of magnetic orientation was measured for 1 to 12 sintered bodies. Sample No. The coercive force (HcJ), residual magnetic flux density (Br), and squareness ratio (Hk / HcJ) were also measured for the sintered bodies of 1 to 5. The results are shown in Table 1. The coercive force (HcJ) and the residual magnetic flux density (Br) were evaluated using a BH tracer with a maximum applied magnetic field of 25 kOe after processing the upper and lower surfaces of the obtained sintered body. Hk is the external magnetic field strength when the magnetic flux density is 90% of the residual magnetic flux density (Br) in the second quadrant of the magnetic hysteresis loop. When Hk is low, a high maximum energy product cannot be obtained. Hk / HcJ is an index of magnet performance and represents the degree of angularity in the second quadrant of the magnetic hysteresis loop.
The degree of magnetic orientation was measured with a BH tracer.

  From Table 1, the sample No. It can be seen that 1 to 5 not only have a high sintered density, but also have good values for each magnetic property.

  Subsequently, sample No. About 1-5, the phase state was identified using the X-ray-diffraction apparatus. As a result of X-ray diffraction, it was confirmed that the molar ratio of the W phase was 70% or more. The conditions for X-ray diffraction are as follows. Further, the molar ratio in the present embodiment was calculated by mixing W-type ferrite, M-type ferrite, hematite, and spinel powder samples at a predetermined ratio and comparatively calculating from their X-ray diffraction intensities.

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

In Example 2, an Fe ₂ W type ferrite magnet was produced based on the flowchart shown in FIG.
First, Fe ₂ O ₃ powder (primary particle diameter: 0.3 μm) and SrCO ₃ powder (primary particle diameter: 2 μm) were prepared as raw material powders. After this raw material powder was weighed, it was mixed and pulverized with a wet attritor for 2 hours.

Next, calcination and rough pulverization using a vibration mill were performed under the same conditions as in Example 1. The fine pulverization was performed in two stages using a ball mill. The first fine pulverization is performed by adding 400 ml of water to 210 g of the coarsely pulverized powder and treating for 88 hours. After the first fine pulverization, the finely pulverized powder was heat-treated in a N ₂ gas atmosphere at 800 ° C. for 1 hour. The rate of temperature increase to the heating and holding temperature and the rate of temperature decrease from the heating and holding temperature was 5 ° C./min. Subsequently, a second fine pulverization was performed by using a ball mill for 25 hours to obtain a slurry for wet molding. At the time of the second fine pulverization, the SiO ₂ powder (primary particle size: 0.01 μm) is 0.6 wt% and the CaCO ₃ powder (primary particle size: 1 μm) with respect to the first finely pulverized powder. ) 0.7 wt%, SrCO ₃ powder (primary particle size: 2 μm) 0.7 wt%, carbon powder (primary particle size: 0.05 μm) 0.4 wt%, and glucone as a dispersant. Acid Ca (primary particle diameter: 10 μm) was added at 0.9 wt%. Next, the slurry for wet molding is concentrated in the same manner as in Example 1, and using the concentrated slurry for wet molding, molding in a magnetic field, heat treatment of the molded body and firing are performed under the same conditions as in Example 1. A sintered body (Sample No. 14) was obtained. The composition of the obtained sintered body was a = 2.0 and b = 14.8 in the above composition formula.

(Sample No. 15)
Except for not adding Ca gluconate, the above sample No. A sintered body was produced under the same conditions as in No.14.

  The obtained sample No. For 14 and 15, the sintering density, saturation magnetization (σs), coercive force (HcJ), residual magnetic flux density (Br), squareness ratio (Hk / HcJ), and degree of magnetic orientation were measured under the same conditions as in Example 1. did. The results are shown in Table 1.

Sample No. in Table 1 4 and 14, the first fine pulverization (step S200), the heat treatment (step S210), and the second fine pulverization (step S220) shown in FIG. It is possible to obtain a sintered magnet showing a higher coercive force (HcJ), residual magnetic flux density (Br), squareness ratio (Hk / HcJ) and magnetic orientation than when a sintered magnet is obtained based on the flowchart. I understand.
Next, sample No. 14 and Sample No. 15 were compared, Sample No. to which Ca gluconate was added was obtained. Sample No. 14 with no addition of Ca gluconate was used. It can be seen that the sintered density, saturation magnetization (σs), residual magnetic flux density (Br) and magnetic orientation degree higher than 15 are obtained. Sample no. 14 has a high sintered density of 5.0 g / cm ³ or more, a coercive force (HcJ) of 2800 Oe or more, a saturation magnetization (σs) of 75 emu / g or more, and a residual magnetic flux density (Br) of 4700 G or more. , 80% or higher squareness ratio (Hk / HcJ), and 96% or higher magnetic orientation degree.

  Sample No. About 14, the phase state was identified on the same conditions as Example 1 using the X-ray-diffraction apparatus. As a result of X-ray diffraction, it was confirmed that the molar ratio of the W phase was 70% or more.

An experiment conducted for confirming fluctuations in magnetic properties and the like with the addition amount of Ca gluconate is shown as Example 3. In Example 3, an Fe ₂ W type ferrite magnet was produced based on the flowchart shown in FIG. In Example 3, Sr and Ba were selected as the A element.

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. After this raw material powder was weighed, it was mixed and pulverized with a wet attritor for 2 hours.

Next, calcination and rough pulverization using a vibration mill were performed under the same conditions as in Example 1. The fine pulverization was performed in two stages using a ball mill. The first fine pulverization is performed by adding 400 ml of water to 210 g of the coarsely pulverized powder and treating for 88 hours. After the first fine pulverization, the finely pulverized powder was heat-treated in a N ₂ gas atmosphere at 800 ° C. for 1 hour. The rate of temperature increase to the heating and holding temperature and the rate of temperature decrease from the heating and holding temperature was 5 ° C./min. Subsequently, a second fine pulverization was performed by using a ball mill for 25 hours to obtain a slurry for wet molding. At the time of the second fine pulverization, the SiO ₂ powder (primary particle size: 0.01 μm) is 0.6 wt% and the CaCO ₃ powder (primary particle size: 1 μm) with respect to the first finely pulverized powder. ) 0.7 wt%, BaCO ₃ powder (primary particle size: 2 μm) 1.75 wt%, carbon powder (primary particle size: 0.05 μm) 0.4 wt%, and glucone as a dispersant. Acid Ca (primary particle diameter: 10 μm) was added at 0.6 wt%, 0.9 wt%, 1.2 wt%, and 1.5 wt%. Next, the slurry for wet molding was concentrated in the same manner as in Example 1. Using the concentrated slurry for wet molding, molding in a magnetic field, heat treatment of the compact and firing were performed under the same conditions as in Example 1. Sintered body (sample No. 16: Ca gluconate 0.6 wt% added, sample No. 17: Ca gluconate 0.9 wt% added, sample No. 18: gluconic acid Ca 1.2 wt% added, sample No. 19: gluconic acid Ca 1.5 wt% addition) was obtained.
The composition of the obtained sintered body was a = 2.0 and b = 13.7 in the above composition formula. The ratio of Sr to Ba was Sr: Ba = 0.88: 0.12.

(Sample No. 20)
Except for not adding Ca gluconate, the above sample No. The sintered compact was produced on the conditions similar to 16-19.

  The obtained sample No. For 16 to 20, the sintering density, saturation magnetization (σs), coercive force (HcJ), residual magnetic flux density (Br), squareness ratio (Hk / HcJ), and degree of magnetic orientation were measured under the same conditions as in Example 1. did. The results are shown in Table 1.

As shown in Table 1, it can be seen that the sintering density increases as the amount of Ca gluconate added increases.
Sample No. Focusing on the coercive force (HcJ), residual magnetic flux density (Br), squareness ratio (Hk / HcJ), and magnetic orientation of 16-20, by adding Ca gluconate, the coercive force (HcJ), residual It was confirmed that the magnetic flux density (Br), the squareness ratio (Hk / HcJ), and the degree of magnetic orientation were improved. Sample no. According to 16 to 19, it has a high sintered density of 5.0 g / cm ³ or more, a coercive force (HcJ) of 3200 Oe or more, a saturation magnetization (σs) of 74.5 emu / g or more, and a residual magnetic flux of 4500 G or more. The magnetic properties of density (Br), squareness ratio (Hk / HcJ) of 70% or more, and magnetic orientation degree of 95% or more can be combined. In particular, sample no. 17-19, coercive force (HcJ) of 3400 Oe or more, saturation magnetization (σs) of 74.5 emu / g or more, residual magnetic flux density (Br) of 4600 G or more, squareness ratio of 80% or more (Hk / HcJ) ), And a magnetic property of 96% or more of magnetic orientation.
Here, sample No. From comparison between 14 and 17, it can be seen that by selecting Sr and Ba as the A element, a sintered magnet having higher characteristics than when only Sr is selected as the A element can be obtained.

  Sample No. About 16-19, the phase state was identified on the conditions similar to Example 1 using the X-ray-diffraction apparatus. As a result of X-ray diffraction, it was confirmed that the molar ratio of the W phase was 70% or more.

It is a flowchart showing manufacturing steps in the case of obtaining the Fe ₂ W-type ferrite magnets as the oxide sintered body. It is a chemical formula showing the structure of gluconic acid. It is a flowchart showing another manufacturing process of the case of obtaining the Fe ₂ W-type ferrite magnets as the oxide sintered body. Sample No. It is the graph which plotted the sintered density of 1-12. (A) to (d) are sample Nos. With no Ca gluconate added. 7 is an optical micrograph of 7, 9, 11, and 13; (A) to (c) are sample Nos. Added with Ca gluconate. 6 is an optical micrograph of 6, 2, and 4. It is a photograph which shows the EPMA analysis screen in a visual field of 200 micrometers x 200 micrometers. It is a photograph which shows the EPMA analysis screen in a visual field of 500 micrometers x 500 micrometers. Sample No. It is the graph which plotted the saturation magnetization ((sigma) s) of the sintered compact of 1-12.

Claims (12)

A molding step of molding a mixture containing raw material powder, carbon powder, and a dispersant;
Sintering the obtained molded body to obtain a sintered body,
With
The dispersant is an organic compound having a hydroxyl group and a carboxyl group or a neutralized salt or lactone thereof, an organic compound having a hydroxymethylcarbonyl group, an organic compound having an enol-type hydroxyl group that can be dissociated as an acid, or The neutralized salt, wherein the organic compound has 3 to 20 carbon atoms, and a hydroxyl group is bonded to 50% or more of carbon atoms other than carbon atoms double-bonded to oxygen atoms. A method for producing a featured oxide sintered body.   The method for producing an oxide sintered body according to claim 1, wherein the mixture is obtained by stirring.   The method for producing an oxide sintered body according to claim 1, wherein the oxide sintered body has a magnetic ferrite phase. The oxide sintered body 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, 1.5 ≦ a ≦ 2 1 and 12.5 ≦ b ≦ 16.5). The method for producing an oxide sintered body according to claim 1, wherein   The method for producing an oxide sintered body according to claim 4, wherein the compact is sintered in a non-oxidizing atmosphere in the sintering step.   The method for producing an oxide sintered body according to any one of claims 1 to 5, wherein the dispersant is gluconic acid.   The method for producing an oxide sintered body according to claim 1, wherein the dispersant is a calcium salt. A composition that is subjected to sintering,
While carbon powder is dispersed in the composition,
An organic compound having a hydroxyl group and a carboxyl group or a neutralized salt thereof or a lactone thereof, an organic compound having a hydroxymethylcarbonyl group, an organic compound having an enol-type hydroxyl group that can be dissociated as an acid, or a neutralized salt thereof The organic compound has 3 to 20 carbon atoms and contains a dispersant in which hydroxyl groups are bonded to 50% or more of carbon atoms other than carbon atoms double-bonded to oxygen atoms. And a composition.   9. The composition of claim 8, wherein the dispersant is calcium gluconate.   The composition according to claim 8 or 9, wherein the composition is a molding slurry.   The composition according to claim 8 or 9, wherein the composition is a molded body.   The composition according to claim 11, wherein a CV value (CV: Coefficient of Variation) of the carbon powder in a visual field of 200 μm × 200 μm is 0.5 or less.

Images