JP2006076860A - Method of manufacturing oxide sintered compact and composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the segregation of carbon to improve the sintering density even when carbon powder is added as the need arises. <P>SOLUTION: This method of manufacturing an oxide sintered compact is provided with a forming process for forming a mixture containing raw material powder, carbon powder, a non-aqueous solvent and a surfactant and a sintering process for sintering the resultant formed body to obtain the sintered compact. The segregation of the carbon powder is suppressed by incorporating the non-aqueous solvent and the surfactant. In the resultant formed body, low CV (coefficient of variation) value and excellent dispersibility of the carbon powder are attained. <P>COPYRIGHT: (C)2006,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.

Special Table 2000-501893

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 the non-aqueous solvent and the surfactant, and the dispersibility of the carbon powder is improved. That is, the present invention includes a molding step of molding a mixture containing raw material powder, carbon powder, a non-aqueous solvent, and a surfactant, and sintering to obtain a sintered body by sintering the obtained molded body And a process for producing an oxide sintered body.
In the present invention, the non-aqueous solvent and the surfactant suppress the segregation of the carbon powder without reducing the dispersibility of the particles constituting the raw material 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 mixture in the present invention preferably contains carbon powder: 0.15 to 0.45 wt% and surfactant: 0.05 to 10 wt% with respect to the raw material powder, and the surfactant includes oleic acid and olein. It is preferable that it is 1 type, or 2 or more types of the salt of an acid, a stearic acid, and the salt of a stearic acid.
In the present invention, the mixture containing raw material powder, carbon powder, non-aqueous solvent and surfactant is obtained by stirring. That is, the timing of adding the carbon powder, the non-aqueous solvent and the surfactant to the raw material powder may be the same or different, but it is desirable to use the agitated material 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 non-aqueous solvent and the surfactant. For example, when a non-aqueous solvent and a surfactant are added in the pulverization step, a stirring process proceeds with the pulverization, so that an independent stirring step is not necessary.

  By selecting the above-mentioned raw material powder that can develop a magnetic ferrite phase, 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 (1.1 ≦ a ≦ 2.4, 12.3 ≦ b ≦ 16.1) 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.
According to the present invention, an Fe ₂ W type ferrite magnet having a W phase as a main phase can be obtained. Here, in the present invention, when the molar ratio of the W phase is 50% or more, the W phase is referred to as the main phase. From the viewpoint of magnetic properties, the molar ratio of the W phase is preferably 70% or more, preferably 80% or more, more preferably 90% or more. The molar ratio in the present application is calculated by mixing W-type ferrite, M-type ferrite, hematite, and spinel powder samples at a predetermined ratio, and comparing and calculating from their X-ray diffraction intensities.

  Although the oxide sintered body has been described in detail above, the knowledge of the present invention that the non-aqueous solvent and the surfactant are effective in suppressing the segregation of the 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 a non-aqueous solvent and a surfactant are contained.

One form of this 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. In wet magnetic field molding, a slurry containing raw material powder is used. By using a molding slurry containing carbon powder, a non-aqueous solvent and a surfactant as this slurry, the sintered density and residual magnetic flux density are finally reduced. A high sintered 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 field of view of 500 μm × 500 μm as small as 0.2 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 of the present invention suppresses segregation of the carbon powder by using a non-aqueous solvent and a surfactant when carbon powder is added during the production process, and the oxide sintered body is sintered. It is characterized by improving the consolidation density. Although the present invention can be applied to the production of various oxide sintered bodies, a particularly remarkable effect is obtained. Therefore, in the following description, the case where the present invention is applied to the production of an Fe ₂ W type ferrite magnet will be described as an example. I do.

<Composition>
When the present invention is applied to a W-type ferrite magnet, it is desirable to have a main composition having the following composition formula.
AFe ²⁺ _a Fe ³⁺ _b O ₂₇ Formula (1)
In formula (1), 1.1 ≦ a ≦ 2.4 and 12.3 ≦ b ≦ 16.1. 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.
In the above formula (1), a indicating the proportion of Fe ²⁺ is 1.1 ≦ a ≦ 2.4. When a is less than 1.1, an M phase and an 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 2.4, a spinel phase is generated and the coercive force (HcJ) is lowered. Therefore, a is set to a range of 1.1 ≦ a ≦ 2.4. The preferable range of a is 1.5 ≦ a ≦ 2.4, the more preferable range is 1.6 ≦ a ≦ 2.1, and the still more preferable range is 1.6 ≦ a ≦ 2.0.
Further, b indicating the ratio of Fe ²⁺ and Fe ³⁺ is in the range of 12.3 ≦ b ≦ 16.1. In the range of 1.1 ≦ a ≦ 2.4, if b is less than 12.3, a spinel phase is generated and the coercive force (HcJ) decreases. On the other hand, if b exceeds 16.1, the M phase and Fe ₂ O ₃ (hematite) phase are generated, and the saturation magnetization (4πIs) decreases. Therefore, b is set to a range of 12.3 ≦ b ≦ 16.1. A preferable range of b is 13.0 ≦ b ≦ 15.8, and a more preferable range is 14.4 ≦ b ≦ 15.0.

The composition of the W-type ferrite magnet can be measured by fluorescent X-ray quantitative analysis or the like. Further, the present invention does not exclude the inclusion of elements other than the A element (at least one element selected from Sr, Ba and Pb) and Fe. For example, in the Fe ₂ W type ferrite, a part of the Fe ²⁺ site or the Fe ³⁺ site can be substituted with another element. In addition to the elements other than the A element and Fe, for example, a Ca component and / or a Si component derived from CaCO ₃ and SiO ₂ may be contained. By including these components, it is possible to adjust the coercive force (HcJ), the crystal grain size, etc., and obtain a ferrite sintered magnet having both high coercive force (HcJ) and residual magnetic flux density (Br). Can do.

Ca component in the W-type ferrite magnet, a Si component in CaCO _3, SiO _{2 conversion, CaCO 3: 0~3.0wt%, SiO} 2: It is desirable to include a range of 0.2~1.4wt%.
When SiO ₂ is less than 0.2 wt%, the effect of adding SiO ₂ is insufficient. On the other hand, if CaCO ₃ exceeds 3.0 wt%, Ca ferrite that causes a decrease in magnetic properties may be generated. Furthermore, when SiO ₂ exceeds 1.4 wt%, the residual magnetic flux density (Br) tends to decrease. From the above, Ca component in the present invention, the amount of Si component is CaCO _3, SiO _{2 conversion, CaCO 3: 0~3.0wt%, SiO} 2: a 0.2~1.4wt%. CaCO ₃ and SiO ₂ are desirably contained in the ranges of CaCO ₃ : 0.2 to 1.5 wt%, SiO ₂ : 0.2 to 1.0 wt%, respectively, and further CaCO ₃ : 0.3 to 1 .2 wt%, SiO ₂ : It is desirable to contain in the range of 0.3 to 0.8 wt%.

  The W-type ferrite magnet as an oxide sintered body according to the present invention is processed into a predetermined shape and used for a wide range of applications as described below. For example, for automobiles such as fuel pump, power window, ABS (anti-lock brake system), fan, wiper, power steering, active suspension, starter, door lock, electric mirror, etc. It can be used as a motor. Also for FDD spindle, VTR capstan, VTR rotary head, VTR reel, VTR loading, VTR camera capstan, VTR camera rotary head, VTR camera zoom, VTR camera focus, radio cassette etc. , CD, LD, MD spindle, CD, LD, MD loading, CD, LD optical pickup, etc. Also, motors for home appliances such as air conditioner compressors, refrigerator compressors, electric tool drive, electric fan, microwave oven fan, microwave plate rotation, mixer drive, dryer fan, shaver drive, electric toothbrush, etc. Can also be used. Furthermore, it can also be used as a motor for FA devices such as a robot shaft, joint drive, robot main drive, machine tool table drive, and machine tool belt drive. Other applications include motorcycle generators, speaker / headphone magnets, magnetron tubes, MRI magnetic field generators, CD-ROM clampers, distributor sensors, ABS sensors, fuel / oil level sensors, magnet latches, isolators. Etc. are preferably used.

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). A non-aqueous solvent and a surfactant effective for suppressing segregation of the carbon powder are added at least before the magnetic field forming step (step S140). 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 main phase or 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.

It is desirable to add carbon powder having a reducing effect in this fine pulverization step (step S130).
The addition of carbon powder is effective for making W-type ferrite a main phase or a single phase. Stirring is required after adding the carbon powder, but the stirring method may be either wet or dry. This stirring need not be performed immediately after the addition of carbon, but may be performed before the magnetic field forming step (step 140) at the latest.
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%. When applying the present invention to Fe ₂ W type ferrite sintered oxide other than magnets, since it is not necessary to consider the saturation magnetization ([sigma] s), the carbon amount is about 0.05 to 1.0% And it is sufficient.
The size of the carbon powder to be added may be about 0.01 to 1.0 μm.

The present invention is characterized by adding a non-aqueous solvent and a surfactant in order to suppress segregation of the carbon powder. And it is desirable to add a non-aqueous solvent and surfactant in a pulverization process (step S130).
As the non-aqueous solvent used in the present invention, a liquid organic compound may be used at room temperature such as various organic solvents, but hydrocarbons such as hebutane, industrial gasoline, coconut oil, cyclohexanone, toluene, xylene, ethylbenzene, turpentine oil and the like; Halogenated hydrocarbons such as 1,2-dibromoethane, tetrachloroethylene, perchloroethylene, dichloropentane, monochlorobenzene, etc .; monohydric alcohols, phenols, ethers such as methanol, ethanol, n-propyl alcohol, n-butyl alcohol, cyclohexanol, phenol, n-butyl ether, etc .; acids, esters, such as butyl acetate; polyhydric alcohols and their ethers, esters, such as ethylene glycol; aldehydes, acetals, ketones Kind, For example, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc .; silicone oils such as low viscosity silicone oils; nitrogen-containing compounds such as ethylenediamine; sulfur compounds such as carbon disulfide; paint thinners such as lacquer A thinner or the like or a mixed solvent thereof can be used.

  When the amount of the non-aqueous solvent added is small, there is a problem in pulverization when the non-aqueous solvent is used alone. If the amount of the non-aqueous solvent added is too large, the slurry concentration during pulverization becomes too low, which is inconvenient for pulverization. Therefore, the addition amount of the non-aqueous solvent is preferably 10 to 2000 wt%, particularly preferably 20 to 500 wt% with respect to the raw material powder.

  The present invention further uses a surfactant. This surfactant is generally amphiphilic and can be adsorbed on the surface of the ferrite particles of the raw material powder in the slurry and is solubilized in the non-aqueous solvent used in the adsorbed state. That is, it usually has a hydrophilic group that can be adsorbed on the surface of the ferrite particles and an affinity group (hydrophobic group) that dissolves in the non-aqueous solvent used. And the thing with which the solubility parameter (SP value) of the surfactant to be used and the solubility parameter (SP value) of the non-aqueous solvent to be used are approximated is preferable. Further, it is preferable that substantially all of the added material is adsorbed to the raw material powder in the slurry. By performing such adsorption and solubilization to form micelles, the carbon powder is well dispersed in the slurry after the wet pulverization.

As the surfactant to be used, any of a cationic type, an anionic type, a nonionic type and an amphoteric type may be used. In particular, a carboxylic acid or a salt thereof such as stearic acid, oleic acid, Zn stearate, Ca stearate, 4 to 4 carbon atoms such as stearic acid Sr, stearic acid Ba, magnesium stearate, Al stearate, Zn oleate, Ca oleate, Sr oleate, Ba oleate, Mg oleate, Al oleate, ammonium oleate Those containing about 30 saturated or unsaturated fatty acids or salts thereof are preferably used.
In particular, an organic substance containing an effective additive element that may be added to ferrite such as Ca, Ba, Sr, Al, Cr, Ga, Cu, Zn, Mn, Co, and Ti (an organic interface such as a metal salt of the above fatty acid) By adding a metal salt of an activator, such an element can be highly dispersed around the ferrite particles. In addition, known sulfonic acid or salt thereof; sulfate ester or salt thereof; phosphate ester or salt thereof; aliphatic amine salt or quaternary ammonium thereof; aromatic quaternary ammonium salt; biridinium salt; imidazolinium salt; Aminocarboxylates; imidazoline derivatives; and at least one of natural surfactants is also preferably used.

  If the added amount of the surfactant is small, the dispersion effect cannot be enjoyed. On the other hand, if the amount of the surfactant added is too large, the dispersion effect is lowered, and the water drainage during molding and the degreasing during firing tend to be hindered. Therefore, the addition amount of the surfactant is preferably 0.05 to 10 wt%, particularly preferably 0.1 to 5 wt% with respect to the raw material powder.

  If such a surfactant is added to the non-aqueous solvent slurry of the raw material powder and wet pulverized, then this slurry can be used for wet molding as it is. Alternatively, a part or all of this surfactant may be added at the time of coarse pulverization of the calcined powder, which is performed prior to wet molding or performed alone. Further, a part or all of the surfactant may be added after wet pulverization of the non-aqueous solvent slurry. Furthermore, a slurry for wet molding may be prepared by adding a surfactant and a non-aqueous solvent after coarse pulverization of the calcined powder. In any case, since the surfactant is present in the slurry during the wet magnetic field molding, the effect of improving the degree of orientation of the molded body in the present invention is similarly realized. In addition, what is necessary is just to set the addition amount of surfactant in each step so that it may finally become said addition amount in the slurry at the time of wet molding.

  When carbon is used in the manufacturing process of an oxide sintered body (W-type ferrite or the like), the carbon causes a decrease in the density of the sintered body. The carbon in the molded body is oxidized in the firing step (step S160), and the solid carbon disappears as gaseous carbon dioxide. Due to the disappearance of carbon, the space occupied by carbon before firing is vacant, and when this “vacant space” remains after firing (pinhole), the density of the sintered body is affected. Although the volume occupied by the “vacant space” depends on the amount of carbon added, the “vacant space” that occurs when the carbon aggregates is large, and the “vacant space” that occurs when the carbon is dispersed is small. Become. If the vacant space is sufficiently small, there is no vacant space in the middle of firing due to shrinkage during firing, so no pinholes remain in the sintered body. That is, when the carbon aggregates to reach a certain size, there is no empty space due to shrinkage during firing, and pinholes remain in the sintered body, whereas the non-aqueous solvent and surfactant recommended by the present invention Since carbon does not agglomerate up to the size where pinholes can remain by adding, the density of the oxide sintered body obtained after sintering is improved according to the present invention.

If it is before the magnetic field shaping | molding process (step S140) mentioned later, the timing which adds a non-aqueous solvent and surfactant is not 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 non-aqueous solvent and the surfactant are present in the molding slurry used in the magnetic field molding step (step S140), but the effect of suppressing the segregation of the carbon powder is fully exhibited. Therefore, stirring is performed after adding the non-aqueous solvent and the surfactant. This stirring is not necessarily performed immediately after the addition of the non-aqueous solvent and the surfactant, and may be performed at the latest before the magnetic field forming step (step S140).
Moreover, you may add a non-aqueous solvent and surfactant 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 non-aqueous solvent and the surfactant are added in a plurality of times, the total addition amount may be within the desirable range described above.

Most of the added non-aqueous solvent and surfactant are removed in the compact heat treatment step (step S150) performed after the magnetic field forming step (step S140). The non-aqueous solvent and the surfactant remaining without being decomposed and removed in the molded body heat treatment step (step S150) are also 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), it adds at the stage in said (1)-(5) also about carbon powder similarly to a non-aqueous solvent and surfactant. do it. Further, the carbon powder may be added in a plurality of times.

<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 non-aqueous solvent and the surfactant are not added in the above process, the molding slurry is obtained by adding the non-aqueous solvent and the surfactant to the molding slurry before or after the concentration and stirring. Also good. It is desirable that the ferrite magnet powder occupies 30 to 80 wt% of 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.

<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 polyhydric alcohol 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, a non-aqueous solvent and a surfactant are added to suppress segregation of the carbon powder.

FIG. 2 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 process (step S100), calcination process (step S110), coarse pulverization process (step S120), magnetic field forming process (step S140), compact heat treatment process (step S150), and firing process (step S160) shown in FIG. ) May be performed according to the procedure described above. Therefore, hereinafter, the first fine pulverization step (step S200), the powder heat treatment step (step S210), and the second fine pulverization step (step S220), which are characteristic parts in the flowchart shown in FIG. 2, 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.

<Powder heat treatment process (step S210)>
In the powder heat treatment step (step S210), 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 step (step S200) generates a large amount of ultrafine powder of less than 0.1 μm. However, if the ultrafine powder is present, a problem may occur in the subsequent magnetic field forming step (step S140). 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 magnetic field forming step (step S140). 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 grinding step (step S200) by reacting with the fine powder (0.1 to 0.2 μm). is there. 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. 2, 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 Fe ₂ W type ferrite showing higher magnetic characteristics than the case where the manufacturing process shown in FIG. 1 is performed by performing the powder heat treatment process (step S210) between the second pulverization process (step S220). A magnet can be obtained.

Hereinafter, the present invention will be described based on specific examples.
Based on the flowchart shown in FIG. 1, xylene was selected as the non-aqueous solvent, and oleic acid was selected as the surfactant to produce an Fe ₂ W type ferrite magnet.
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 rise to the heating and holding temperature and the rate of temperature drop 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.

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 using a ball mill for 25 hours or 50 hours to obtain a slurry for wet molding. At the time of the second pulverization, 0.6 wt% of SiO ₂ powder (primary particle diameter: 0.01 μm) and CaCO ₃ powder (primary particle diameter) with respect to the pulverized powder subjected to the first pulverization. 1 μm) 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 non-aqueous 400 ml of xylene as a solvent and 1.5 wt% of oleic acid as a surfactant were added.

Next, the wet molding slurry obtained above was concentrated with a centrifugal separator, and magnetic field molding was performed using the concentrated wet molding slurry. 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 a sintered body. A sintered body obtained by performing the second fine pulverization for 25 hours was referred to as Sample No. The sintered body obtained by performing for 1 and 50 hours is referred to as Sample No. 2
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.

  Further, the same conditions as described above, except that xylene as a non-aqueous solvent and oleic acid as a surfactant were not added, and water was added during the second pulverization to produce a slurry (hereinafter referred to as water slurry). A sintered body was prepared. This sintered body was referred to as Sample No. Let's say 3.

  Next, the dispersibility of the carbon powder on the analysis screen was evaluated by the CV value (coefficient of variation) from the results of element mapping by EPMA for the molded bodies in the process of producing samples 1, 2, and 3. 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 FIG. 3 (Sample No. 1), FIG. 4 (Sample No. 2) and FIG. 5 (Sample No. 3).

CV value measurement conditions in FIGS. 3 to 5 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 FIGS. 3 to 5, the CV value of the molded body made of water slurry in the field of view of 500 μm × 500 μm is 0.2, whereas the CV value of the molded body to which xylene and oleic acid are added is Only about 0.1. Thus, it can be seen from FIGS. 3 to 5 that the addition of xylene and oleic acid improves the dispersibility of the carbon powder.
From the above results, it was confirmed that when xylene and oleic acid were added, the dispersion state of the carbon powder was improved at the stage before sintering.

Next, the sintered body obtained above was observed with an optical microscope. Sample No. The micrographs of 1, 2, and 3 are shown in FIGS.
Black spots in the micrographs shown in FIGS. 6 to 8 are pinholes formed after the carbon powder disappeared during sintering. When the carbon powder disappears while being segregated, a pinhole is formed, and a black spot is remarkably observed in the micrograph. Sample No. produced using a slurry using water as a dispersion medium. In FIG. 1, many large and small black spots were observed as shown in FIG. On the other hand, as shown in FIGS. 6 and 7, the number of sunspots is extremely small by adding xylene and oleic acid. It is considered that when xylene and oleic acid were added, segregation of the carbon powder was suppressed, so that pinholes were hardly formed even when the carbon powder disappeared.

  A molded body was produced in the same manner as in Example 1 except that toluene was used as a non-aqueous solvent and 4 wt% of stearic acid as a surfactant was added, and the CV value was determined. As a result, the CV value of the molded product obtained by pulverization for 25 hours was 0.117, and the CV value of the molded product obtained by pulverization for 55 hours was 0.125.

In this embodiment is a flowchart showing manufacturing steps of the Fe ₂ W-type ferrite magnets. It is a flowchart showing another manufacturing process of the Fe ₂ W-type ferrite magnets of the present embodiment. The analysis screen by EPMA of the molded object produced with the slurry which added xylene and oleic acid is shown. The analysis screen by EPMA of the molded object produced with the slurry which added xylene and oleic acid is shown. The analysis screen by EPMA of the molded object produced with the water slurry is shown. The structure photograph by the optical microscope of the sintered compact produced with the slurry which added xylene and oleic acid is shown. The structure photograph by the optical microscope of the sintered compact produced with the slurry which added xylene and oleic acid is shown. The structure photograph by the optical microscope of the sintered compact produced by the water slurry is shown.

Claims (10)

A molding step of molding a mixture containing raw material powder, carbon powder, a non-aqueous solvent, and a surfactant;
Sintering the obtained molded body to obtain a sintered body,
A method for producing an oxide sintered body characterized by comprising:   2. The oxide according to claim 1, wherein the mixture includes the carbon powder: 0.15 to 0.45 wt% and the surfactant: 0.05 to 10 wt% with respect to the raw material powder. A method for producing a sintered body.   3. The oxide sintered body according to claim 1, wherein the surfactant is one or more of oleic acid, a salt of oleic acid, stearic acid, and a salt of stearic acid. 4. Method.   The said mixture is obtained by stirring, The manufacturing method of the oxide sintered compact in any one of Claims 1-3 characterized by the above-mentioned.   The said oxide sintered compact has a magnetic ferrite phase, The manufacturing method of the oxide sintered compact in any one of Claims 1-4 characterized by the above-mentioned. 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, 1.1 ≦ a ≦ 2 .4, 12.3 ≦ b ≦ 16.1). The method for producing an oxide sintered body according to any one of claims 1 to 5, wherein:   The method for producing an oxide sintered body according to any one of claims 1 to 6, wherein the compact is sintered in a non-oxidizing atmosphere in the sintering step. A composition that is subjected to sintering,
While carbon powder is dispersed in the composition,
A composition comprising a non-aqueous solvent and a surfactant.   The composition according to claim 8, wherein the composition is a molding slurry.   The composition according to claim 8, wherein the composition is a molded body.

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