JP2001322865A - Alumina sintered body with high strength and high toughness and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alumina sintered body having a dense and fine sintered structure, high strength and toughness as high as >=5 MPa.m1/2 fracture toughness as measured by to JIS-R1607 and more preferably >=6 MPa.m1/2. SOLUTION: A high purity alumina calcined body having pores with 40 to 63% relative density is impregnated with a solution of a metal salt of Ca, Sr or Ba. The body is then sintered at 1,350 to 1,600 deg.C to thermally decompose the metal salt so that alumina grains are anisotropically grown by the effect when the metal oxide is formed on the intergranular faces and that anisotropic particles having <=3 μm major diameter and >=2 aspect ratio occupies an area of >=20% based on observation of the cross section. The structure of the sintered body is homogenous, dense and fine, and the fracture toughness can be significantly improved while high strength is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alumina sintered body having high strength and high toughness and useful as a tool material, a structural material, a high-temperature structural material, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, alumina-based sintered bodies have excellent properties such as heat resistance, environmental resistance, and strength. For example, electronic materials represented by packages for housing semiconductor elements, ceramics for living bodies, cast iron, etc. It is used as a highly functional material for cutting tools and the like.

[0003] In addition to the above-mentioned excellent thermal and mechanical properties, an alumina-based sintered body is inherently excellent in oxidation resistance and corrosion resistance, and has been used in various fields. Due to its low fracture toughness, it has not been widely applied as a structural material.

Therefore, in order to further expand the application field of the alumina-based sintered body, it is necessary to further increase its fracture toughness. In order to maintain the strength of the alumina-based sintered body and to improve its fracture toughness, Various means have been developed.

As a means for improving the toughness of an alumina sintered body, Japanese Patent Application Laid-Open No. 9-87008 discloses that Al ₂ O ₃ powder contains Na, M having a eutectic point with Al ₂ O ₃ of 1600 ° C. or less.
g, Ca, Sr, Ba, Ti, Fe, Mn, W, Si or an oxide of an element of Group 3A of the periodic table are added and mixed, and when firing after molding, the temperature is increased from room temperature to the firing temperature by 8 ° C. / m
In a method of raising the temperature at a high temperature rising rate of at least in, a constant amount of a liquid phase is generated during firing, so that isotropic Al ₂
O ₃ and major diameter 10μm or more, a method for a sintered body having an aspect ratio of 3 or more anisotropic Al ₂ O ₃ crystal grains are mixed in a proportion of 20 to 85 vol% in the total amount is disclosed.

[0006] Also, Japanese Patent Application Laid-Open No. Hei 10-158055,
Japanese Patent Application Laid-Open No. Hei 10-212157 discloses that alumina is made of Ti.
By mixing and sintering O ₂ , MgO and SiO ₂ at a predetermined ratio, the formation of a liquid phase is promoted, and the highly anisotropic growth of Al ₂ O ₃ crystals is promoted. A method for forming a sintered body containing the above plate-like Al ₂ O ₃ crystal in an amount of 20% by volume or more is disclosed.

Further, JP-A-11-71167 discloses that a sintered body mainly composed of alumina contains one or more elements selected from Group 3A and one or more elements selected from Group 4A. An element that mixes and sinters an oxide compound and disperses the grain boundary phase composition in the form of a film at the grain boundaries to facilitate crack diffraction and promote Al ₂ O ₃ shape anisotropy growth. Al ₂ O _{3 with} an aspect ratio of 3 or more by adding magnesium or silicon
A method of improving toughness by forming crystal grains is disclosed.

In addition, Japanese Patent Application Laid-Open No. H11-1365 discloses that aluminum hydroxide produced by the Bayer method is used as a raw material and fine α-aluminum oxide powder of 0.1 μm or less is used as a seed crystal of α-aluminum oxide. .01-2
By sintering the aluminum oxide powder obtained by calcining the mixture added with 0 mass% at 900 to 1200 ° C., the ratio of the anisotropic crystal grains having a major axis of 10 μm or less and an aspect ratio of 2 or more is 20% or less. An alumina sintered body having an area% or more is disclosed.

[0009]

As shown in the above-mentioned patent documents, various oxides are mixed with alumina to promote the formation of a liquid phase to promote the highly anisotropic growth of Al ₂ O ₃ crystals. By doing so, the fracture toughness can be improved to about 5 to 5.5 MPa · m ^1/2 , but these sintered structures have coarse grains whose major axis has grown to 10 μm or more due to the highly anisotropic growth of the particles. This material contains particles, and since these coarse particles act as defect sources, this material is inferior in strength, and it is difficult to achieve both strength and toughness. Also,
If the grain boundary phase composition contains a large amount of Group 3A and Group 4A elements so as to be in the form of a film or particles, the strength is reduced.

The method disclosed in Japanese Patent Application Laid-Open No. 11-1365 discloses an inexpensive α produced by the Bayer method, which is a commercially available powder commonly used as a raw material for an alumina sintered body.
-Using aluminum oxide powder as a raw material and suppressing the abnormal growth of particles by using fine α-aluminum oxide powder of 0.1 μm or less as a seed crystal, and achieving a certain fine structure despite containing coarse particles. It has gained. But,
Since the ball mill polishing powder is used as a fine powder serving as a seed crystal, all impurities in the process, such as the powder to be polished, are mixed, and the components and particle diameter are unclear. It is difficult to stably control the sintering structure freely for a long time in production.

In order to solve the above-mentioned problems of the prior art, the present invention has a dense and fine sintered structure, ensures high strength, and has a fracture toughness specified by JIS-R1607 of 5 MPa · m ^{1. / 2} or more, more preferably 6MPa
-To provide an alumina-based sintered body having a toughness higher than m1 / ² .

[0012]

The present inventors have repeatedly studied a method for improving the fracture toughness without impairing the strength characteristics of the alumina-based sintered body. Ca, S throughout the pores of the sintered body
By sintering after impregnating with a solution of at least one metal salt of r or Ba, most alumina crystal grains have shape anisotropy without coarsening of crystal grains. The fracture toughness value defined by JIS-R1607 is 5 MPa · m ^1/2 or more, and furthermore 6 MPa
-It has been found that an alumina-based sintered body higher than m1 / ² can be obtained.

That is, according to the present invention, Ca, S
A ratio of anisotropic crystal particles having a major axis of 3 μm or less and an aspect ratio of 2 or more, which is an alumina sintered body sintered by impregnating at least one metal salt of r or Ba. Is a high-strength and high-toughness alumina-based sintered body characterized by having a dense and fine structure that is not less than 20 area% in observation of a cut surface and has substantially no major particles having a major diameter exceeding 3 μm. is there.

Further, the present invention relates to a method for producing Ca, S
An oxide of the metal formed by thermal decomposition and oxidation of at least one metal salt of any one of r and Ba is used at the grain boundary in an amount of 0.02 to 2. The above high-strength and high-toughness alumina-based sintered body characterized by containing 0% by mass.

Further, the present invention provides a method for producing a resin having a relative density of 40% or more.
Ca, Sr, or Ba on 3% or less alumina
Impregnated with a solution of one or more metal salts of
The method for producing an alumina-based sintered body according to the above, wherein the impregnated temporary sintered body is sintered in an oxidizing atmosphere at a temperature of 1350 to 1600 ° C. Further, in the present invention, the pre-sintered body is sintered at 800 to 1000 ° C. using a high-purity alumina powder having a purity of 99.5% or more and an average particle size of 0.5 μm or less by a wet molding method. A method for producing the above-mentioned alumina-based sintered body, characterized in that the sintered body is a sintered body.

Further, the present invention is characterized in that the wet molding method is a high-speed centrifugal molding method in which alumina slurry is charged into a mold and then molded by applying a high centrifugal force of a gravity multiple of 10 kG to 20 kG. This is a method for producing an alumina sintered body. Further, the present invention is the above-described method for producing an alumina-based sintered body, characterized by impregnating an aqueous solution of Ca nitrate into the temporarily-sintered alumina.

The alumina sintered body of the present invention has a small degree of intermixing of large particles and small particles, that is, a high homogeneity, and a dense and fine sintered structure. And an anisotropic crystal particle having an aspect ratio of 2 or more formed by anisotropic growth of particles while maintaining a fine sintered structure. Further, such a sintered structure can be easily controlled by changing the amount of addition of a crystal grain growth controlling agent comprising at least one metal salt of Ca, Sr, or Ba. It is a new manufacturing method that is excellent in cost performance without using special chemicals or equipment.

[0018]

It is generally known that the finer the structure of the sintered body, the better the strength and toughness of the ceramic. In addition, when particles having a shape anisotropy, that is, particles having a large aspect ratio, are dispersed in the crystal grain boundaries of the alumina-based sintered body, the cracks are diffracted when the cracks propagate through the grain boundaries, resulting in toughness. Is also known to improve.

However, even if the particles have a large aspect ratio, if the particle size is large, the structure of the sintered body becomes coarse and the defects are larger than the advantages. When particles are grown so as to promote shape anisotropy during sintering, the particles usually grow to 10 μm or more, and the structure of the sintered body cannot be kept fine. The present invention maintains the strength by maintaining the structure of the sintered body finely, and by adding the effect brought by the anisotropy of the particles thereto, toughness without impairing the original properties of the alumina sintered body. Is further improved.

In the present invention, the alumina temporarily sintered body is C
By sintering a material impregnated with at least one metal salt of a, Sr, or Ba, an oxide of the metal is formed at a crystal grain boundary by thermal decomposition and oxidation during sintering of the metal salt. The major axis can be maintained at 3 μm or less even when almost all crystal grains are grown up to an aspect ratio of 2 or more when viewed three-dimensionally by promoting anisotropic growth of the particles.
Substantially no coarse particles exceeding m.

It is desirable that almost all of the sintered bodies are particles having a major axis of 3 μm or less and an aspect ratio of 2 or more.
The greater the amount of such particles in the observation of the cut surface, the greater the amount in the sintered body, but if the particles satisfying such conditions are at least 20 area%, the toughness will be improved. Contribute. It is more preferable that the area be 40% by area or more. Coarse particles having a major axis of more than 3 μm are not desirable because they reduce the strength. If the aspect ratio is 2
Particles with less than a small extent contribute to an improvement in toughness.

In order to maintain the homogeneity of the sintered structure, the homogeneity of the structure of the compact must be high. The method for producing an alumina-based sintered body according to the present invention is characterized in that a solution impregnation method is combined with a method for adding a crystal grain growth controlling agent to a molded article having extremely high homogeneity without impairing homogeneity.

In the production method of the present invention, during sintering, the alumina of the pre-sintered body grows crystal grains and the pores disappear. At the same time, the metal salt impregnated in the temporary sintered body as a crystal grain growth controlling agent is thermally decomposed during sintering, but the metal remaining without being scattered during decomposition is oxidized by an oxidizing atmosphere during the growth of crystal grains. The oxide of the metal is formed at the grain boundary,
Most of the crystal grains have shape anisotropy by changing the surface energy of the crystal grains and acting on the direction of crystal growth. It should be noted that, as far as observed by an electron microscope, no trace of the solidified oxide is observed, and it is presumed that the generated oxide is present at the grain boundaries as atomic units or at least as very fine crystals. You.

In the production method of the present invention, the alumina used as the starting material of the pre-sintered body is made to be fine enough to have a particle size of 0.5 μm or less, so that the coarse particles due to the growth of crystal grains at a high temperature of 1350 ° C. or more are sintered. Despite the change, the crystal grain size after sintering can be kept sufficiently fine to an average grain size of 3 μm or less, more preferably 1-2 μm. Thereby, the strength of the sintered body can be maintained high.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the production method of the present invention, high-purity alumina is used as a starting material. In order to obtain a sintered structure having both strength and toughness, a purity of 99.95%
Or more, the average particle size is 0.5 μm or less, more preferably 0.2 μm or less.
Alumina powder of μm or less is desirable. Before forming the temporary sintered body, the powder is used to form an alumina powder molded body.

The alumina powder compact has a particle filling rate of 40
Any molding method can be used as long as the structure is uniform in the range of not less than% and not more than 63%. The highest packing fraction obtained when particles of uniform size are randomly packed is 63%. When the high-purity alumina powder described above is used, almost this particle packing density can be obtained stably. Filling with a powder having a particle size distribution increases the apparent density, but is not preferred from the viewpoint of tissue homogeneity. If the filling ratio is less than 40%, the relative density after high-temperature sintering decreases, and it becomes difficult to secure sufficient strength. Even if the filling rate is 63% of the random close packing, there is no problem in the impregnation step.

In order to maintain the homogeneity of the structure of the alumina sintered body, the homogeneity of the structure of the formed body must be high. It is very difficult to ensure the homogeneity of the structure by the dry mixing method in which the additive component is mixed with the alumina main powder as another powder. A wet molding method such as pressure casting or centrifugal molding is a more preferable method than the dry mixing method in order to ensure homogeneity of powder filling of the alumina powder molded body. In particular, a high-speed centrifugal molding method in which a slip is loaded into a mold and then molded by applying a high centrifugal force of about 10 kG to 20 kG by a gravity multiple is a preferable method.

This high-speed centrifugal molding method is a method developed by the present inventors (centrifugal molding of high-purity alumina ultrafine powder;
"Powder and Powder Metallurgy," Vol. 39, No. 1, 39-4
3, January 1992, Microstructure dependence of mechanical properties of high-purity alumina sintered body by high-speed centrifugal molding; "Powder and Powder Metallurgy", Vol. 46, No. 4, pp. 331-338, 1
Apr. 999, JP-A-8-47907), 60%
A compact having a high filling rate and a low moisture content as described above was obtained, and Ca,
High-purity alumina ultra-fine powder
It can be fired even at a low temperature of 220 ° C. In addition, since molding, drying, and firing can be performed in a short time, productivity is high.

More specifically, in this method, the slip or colloidal slurry of ultrafine ceramic powder is settled by high-speed centrifugal molding at an acceleration of 10,000 to 20,000 times the gravity (10 kG to 20 kG). It is. In this method, a mold may be used as a mold, but by using a wax mold, the mold can be melted and removed after molding, and a precise molded body having a complicated shape can be taken out. For the preparation of the slurry, alumina powder, alumina balls, a predetermined amount of a solvent (for example, ion-exchanged water) and a dispersant (for example, ammonium polycarboxylate) were added to an alumina pot, followed by dispersion treatment in a ball mill. A predetermined amount of a binder (for example, an acrylic polymer) is added, and the dispersion treatment is performed again to obtain a slurry.

The alumina powder compact is 8
Temporary sintering is performed at 00 to 1000 ° C. for about 1 hour to give necessary strength. If the temperature is lower than this, the strength of the temporary sintered body decreases, and if the temperature is higher than this, the densification proceeds and the area of the pore network decreases. Alumina can be sintered more stably in an oxidizing atmosphere such as the air. The structure of the pre-sintered body has a skeletal structure in which the particles are slightly in contact with each other, that is, a structure in which all pores are connected to the outside, so that the impregnating liquid can spread throughout the inside of the formed body.

The pre-sintered body is impregnated with an impregnating material which acts as a crystal grain growth controlling agent, and it is necessary to adjust the impregnation time in accordance with the porosity and size of the pre-sintered body. As the metal salts of Ca, Sr, and Ba as the impregnating materials, inorganic salts such as nitrates and carbonates are suitable. These can be used not only as an aqueous solution but also as a non-aqueous solution such as ethanol. Considering the generation of gas components in the sintering step, nitrates are more preferable. Nitrates
Since hydrates are usually formed at room temperature, they are dissolved by heating to form a high-concentration solution, or diluted with ion-exchanged water to obtain a solution having a required concentration.

Although Ca, Sr, and Ba have a common function in the sintered body of the present invention as a Group 2A metal of the periodic table, Mg among the Group 2A metals of the periodic table is not suitable because it does not provide an equivalent function. It is. Be, Cd, and Hg are not preferable to use because of work safety. Ca, Sr, or B
The addition amount of the metal salt of a is 0.02 to 2.0% by mass of the total amount of the sintered body in terms of metal. When the content is less than 0.02% by mass, the effect of forming anisotropic alumina crystal grains does not appear,
There is no effect of improving toughness. If the content exceeds 2.0% by mass, the strength is reduced.

By drying the pre-sintered body after the impregnation, the nitrate hydrate is uniformly deposited in the pre-sintered body.
Note that a sufficient amount of Ca, Sr, or Ba metal salt can be added to the temporary sintered body by a single impregnation process even in a randomly close-packed temporary sintered body having a density of 63%.

After drying, the temporarily sintered body is sintered. As the sintering method, atmospheric pressure sintering in the atmosphere is sufficient. However, a hot press method, a gas pressure sintering method, or a microwave sintering method may be used. In the production method of the present invention, C
Since the metal salt of a, Sr, or Ba is thermally decomposed and simultaneously forms an oxide of the metal, the sintering atmosphere is an oxidizing atmosphere. Sintering means such as hot isostatic pressure (HIP) treatment after sintering by each of the above methods and HIP treatment after glass sealing can be used as appropriate, although the process is complicated.

In the present invention, 1,623K (1,350K)
C.) to 1,873K (1,600C). Preferably, 1,673 to 1,773K (1,
(400 to 1,500 ° C.), and the crystal grains can be grown anisotropically at a relatively low sintering temperature as compared with a normal sintering temperature. At a sintering temperature lower than 1,623 K (1,350 ° C.), the anisotropy of the crystal grains cannot be sufficiently ensured, so that the toughness does not increase. At a sintering temperature exceeding 1,873 K (1,600 ° C.), the crystal grains become unnecessarily large, and the homogeneity of the structure is lost.

[0036]

Hereinafter, the present invention will be described in more detail with reference to Examples 1 to 5 and Comparative Examples A and B. (1) Materials used As starting materials, the purity is 99.99% and the average particle size is 0.
Alumina powder having a narrow particle size distribution of 2 μm (manufactured by Daimei Chemical Co., Ltd., trade name: Taimicron TM-DAR) was prepared.
In addition, calcium nitrate hydrate (Ca (NO ₃ ) ₂ .4H ₂ O) was prepared as a metal salt for impregnation.

(2) Molding of Alumina Powder Compact Ultra-pure water was used as a dispersion medium, and 75% by mass of the above alumina powder was added thereto. Further, ammonium polycarboxylate was used as a dispersant, and an acrylic polymer was used as a binder. 0.6% by mass and 0.1% by mass were added to the respective alumina powder amounts, and the mixture was stirred and mixed by a ball mill for 48 hours to obtain alumina slurry.

Next, molding is performed by a high-speed centrifugal molding method (High-Spee
d Centrifugal Compaction Process, HCP).
4.5 cm ³ of slurry was poured into a cylindrical mold having a bottom plate attached to one side of an aluminum cylinder having an inner diameter of 8 mm and a height of 90 mm, and was rotated at 11,500 rpm for 1 hour with a swing type high-speed centrifuge having a rotor radius of 120 mm. It was molded to obtain a cylindrical molded body having a height of about 60 mm.

(3) Preparation of Temporary Sintered Body After the molded body was sufficiently dried, it was heated at 1,073 K (800 ° C.) for 1 hour.
Temporarily sintered for a time. The particle filling rate of this temporary sintered body is about 63%
Met.

(4) Impregnation of impregnated material An aqueous solution containing 10 to 50% by mass of calcium nitrate hydrate is prepared, put in a container, and the pre-sintered body is immersed in the aqueous solution of calcium nitrate in the container, and the whole container is Was put into a reduced pressure impregnation apparatus, and the pressure was reduced to about 3 kPa, and the pressure was maintained for 5 minutes to remove air from the temporarily sintered body. Next, the container was returned to the atmospheric pressure and held for 5 minutes to impregnate the temporary sintered body with the nitrate solution.

At this time, the calcium nitrate concentration of the solution
From the measured increase in mass of the pre-sintered body before and after the impregnation, the amount of calcium ions impregnated in the pre-sintered body can be calculated. The impregnated temporary sintered body was dried in a drying furnace for 24 hours. In Comparative Example B, no impregnation treatment was performed on the temporary sintered body.

(4) Sintering temperature: 1,573 to 1,773K (1,300 to 1,50K)
(0 ° C.) for 1.5 hours in the air. During the sintering process, calcium nitrate decomposes and components other than calcium volatilize,
Calcium combines with oxygen to form calcia, which plays a role in growing alumina particles anisotropically.

(5) Evaluation of the sintered body The density of the obtained sintered body was measured by the Archimedes method, and the cut surface was mirror-polished and heat-corroded, and then observed with a scanning electron microscope. , Average particle size, and particle aspect ratio were measured. In addition, Vickers hardness and fracture toughness were measured as mechanical properties. Vickers hardness is 98N test weight based on JIS-R1610,
The loading speed was 70 μm / s, the loading time was 15 seconds, and the fracture toughness value KIC was determined by the IF method based on JIS-R1607.
Each test was performed at a test weight of 196N.

(6) Results Table 1 shows the conditions for producing the sintered body, and Table 2 summarizes the characteristics.
FIG. 1 shows the structure of the sintered body of Example 1 observed with a scanning electron microscope.

[0045]

[Table 1]

In Table 1, the column of calcium nitrate aqueous solution concentration indicates the solution concentration in the impregnation treatment of each of the pre-sintered bodies, and the column of calcium ion concentration indicates the amount of calcium ions added to the pre-sintered body. In Table 2, the numerical values described in the column of the aspect ratio of the particles represent the area ratio (%) of the particles having an aspect ratio of 2 or more in the visual field observed by a scanning electron microscope after the cut surface is mirror-polished and thermally corroded. I asked.

[0047]

[Table 2]

As is clear from the above, Comparative Examples A and B
Has a high hardness of Hv 1712 to 2037 and is assumed to have sufficient strength as an alumina sintered body, but has a small area ratio of particles having an aspect ratio of 2 or more and has a fracture toughness of about 4.
It is as low as 5 MPa · m ^1/2 or less. On the other hand, Example 1 of the present invention
As shown in FIG. 1, all of the calcium-added sintered bodies have uniform and high-density particles, and most of the crystal grains are anisotropic and grow in a plate or rod shape.

Examples 1 and 2 are 1.1% calcium additives. In Example 1, the area ratio of particles having an average particle diameter of 0.2 μm and an aspect ratio of 2 or more was 47%, and the Vickers hardness H
v1841, a fracture toughness value of 6.1 MPa · m ^1/2 ,
In Example 2, the area ratio of particles having an average particle diameter of 0.9 μm and an aspect ratio of 2 or more was 68%, and Vickers hardness Hv165
2. The fracture toughness is 5.0 MPa · m ^1/2 .

In Example 2 in which the sintering temperature was high, the hardness and fracture toughness values were lowered although the area ratio of particles having an aspect ratio of 2 or more was large. It is. Conversely, Example 1 having a low sintering temperature
It can be seen that in the case of the above, the refinement of the structure contributed to the area ratio of the particles having an aspect ratio of 2 or more, and both the hardness and the fracture toughness were improved.

The amount of calcium added is 0.66 to 0.5.
07% and a temperature of 1,773K (1,500
C), the area ratio of particles having an aspect ratio of 2 or more was 20% or more, the fracture toughness was 5.7 MPa · m ^1/2 or more, and a small amount of calcium was added. Is sufficient effect.

[0052]

As described in detail above, the alumina-based sintered body of the present invention has both high strength and high toughness and has excellent properties as a structural material having excellent wear resistance or a high-temperature structural material. Further, the production method is a highly versatile production method in which the sintering reaction conditions are easily controlled and any complex shaped product can be easily applied.

[Brief description of the drawings]

FIG. 1 is a drawing substitute photograph showing a sintered structure obtained by observing a sintered body of Example 1 with a scanning electron microscope.

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[Procedure amendment]

[Submission Date] August 15, 2000 (2008.1.
5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

[0018]

It is generally known that the finer the structure of the sintered body, the better the strength and toughness of the ceramic. In addition, when particles having a shape anisotropy, that is, particles having a large aspect ratio, are present in the alumina-based sintered body, when the cracks propagate through the crystal grain boundaries, the cracks are diffracted, thereby improving toughness. It is also known.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0030

[Correction method] Change

[Correction contents]

The alumina powder compact is 8
Temporary sintering is performed at 00 to 1000 ° C. for about 1 hour to give necessary strength. At a temperature lower than this, the strength of the temporary sintered body decreases, and at a temperature above this, the densification proceeds and the volume of the pore network decreases. Alumina can be sintered more stably in an oxidizing atmosphere such as the air. The structure of the pre-sintered body has a skeletal structure in which the particles are slightly in contact with each other, that is, a structure in which all pores are connected to the outside, so that the impregnating liquid can spread throughout the inside of the formed body.

Claims (6)

[Claims] An alumina sintered body obtained by impregnating a temporary sintered body with at least one metal salt of Ca, Sr, or Ba and having a major axis of 3 μm or less and an aspect ratio of 2 The ratio of the above anisotropic crystal grains is 20 area% or more in the observation of the cut surface, and has a dense and fine structure substantially free of coarse particles whose major axis exceeds 3 μm. High-strength, high-toughness alumina-based sintered body. 2. Ca, Sr, or Ba during sintering
The oxide of the metal formed by the thermal decomposition and oxidation of any one or more metal salts is contained in the crystal grain boundary in an amount of 0.02 to 2.0% by mass in terms of metal with respect to the total amount of the sintered body. The high-strength, high-toughness alumina-based sintered body according to claim 1, wherein 3. A pre-sintered alumina having a relative density of 40% or more and 63% or less is impregnated with a solution of at least one metal salt of Ca, Sr, or Ba. The method for producing a high-strength and high-toughness alumina-based sintered body according to claim 1 or 2, wherein the sintered body is sintered at a temperature of 1350 to 1600 ° C in an oxidizing atmosphere. 4. A pre-sintered body is sintered at 800 to 1000 ° C. using a high-purity alumina powder having a purity of 99.5% or more and an average particle size of 0.5 μm or less by a wet molding method. 4. The method for producing a high-strength and high-toughness alumina-based sintered body according to claim 3, wherein 5. The wet molding method is a high-speed centrifugal molding method in which alumina slurry is charged into a mold and then molded by applying a high centrifugal force of a gravity multiple of 10 kG to 20 kG. The method for producing a high-strength, high-toughness alumina-based sintered body according to the above description. 6. The method for producing a high-strength and high-toughness alumina-based sintered body according to claim 3, wherein the alumina-temporarily sintered body is impregnated with an aqueous solution of Ca nitrate.