JP2000169254A - Air permeable ceramic structure and fluid permeating member using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an air permeable ceramic structure and a fluid permeating member having isotropically excellent strength, isotropic fluid permeation characteristics, excellent heat resistance, corrosion resistance and excellent characteristics as a filter and a catalyst carrier. SOLUTION: In this air permeable structure 1 comprising a skeleton body 2 provided with isotropically communicating gap parts 2b having <=1 mm average diameter in skeleton parts 2a composed of a dense sintered compact such as alumina, mullite or Si3N4 having >=90% relative density and a porous sintered compact 3 composed of alumina, mullite or Si3N4 packed in the gap parts 2b of the skeleton body, the specific surface area of the air permeable ceramic structure 1 is >=100 m2/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a fluid supply member used in the high-temperature energy field, a filter for high-temperature exhaust gas and other corrosive fluids, and a catalyst carrier for decomposing harmful substances. The present invention relates to a permeable ceramic structure and a fluid permeable material.

[0002]

2. Description of the Related Art In recent years, environmental pollution due to harmful substances such as dioxin has become a serious problem, and there is a demand for detoxification of exhaust gas after incineration in garbage incineration plants and the like. Therefore, a filter and a catalyst carrier for decomposing toxic gas are required to collect dust and the like in the exhaust gas. Conventionally, low heat-resistant filters such as polymer resin fibers represented by PPS have been used as dust collection filters in incineration plants, so high-temperature exhaust gas must be cooled, and the cost of cooling equipment and the like is reduced. There was a problem of bulking.

On the other hand, ceramic porous materials have heat resistance,
Attention has been paid to its excellent corrosion resistance, and it is used as a heat insulating material and a refractory, and is also used as a filter for fluid filtration, a catalyst carrier and the like, particularly in a high-temperature energy field, for example, a combustor liner,
Applications to high-temperature combustion exhaust gas filters and the like are being studied.

Specifically, for example, a cordierite ceramic porous body is coated as a high-temperature exhaust gas filter, and a γ-alumina having a specific surface area of about 20 m ² / g is coated on a honeycomb structure sintered body as a catalyst carrier. One that has been formed is proposed.

[0005] Recently, the conditions of use have become severe. Particularly, the filter and the catalyst carrier have high performance, high heat resistance and corrosion resistance, and high strength and thermal shock resistance. There is a demand for a reliable porous body.

Therefore, as a method of reinforcing a porous body, it is known to form a reinforcing body in the porous body. For example, Japanese Patent Publication No. 4-59273 discloses a heat insulating material in which heat-resistant cellulose is supported in the voids of a skeletal structure having a three-dimensional network structure made of ceramic. the reaction sintering matrix such as lightweight high stiffness ceramic are dispersed hollow particles or hollow fibers, furthermore, in Japanese Patent Laid-Open No. 8-40779, a lattice shape made of dense ceramic made of Si ₃ N ₄ or sialon There has been proposed a ceramic structure having low thermal conductivity in which a gap between the reinforcing members is filled with a porous body containing Si, O, and N. These are all made of a composite material of a porous body and a reinforcing body, and have an effect of improving the strength as a structure.

[0007]

However, conventional filters and catalyst carriers have low heat resistance and corrosion resistance, and the porous body is granular, so that the specific surface area as a structure is limited. In addition, since it is necessary to increase the permeation amount and permeation efficiency of the fluid, the pore diameter formed in the structure is about several hundreds μm, and for fine dust of about several nm to several tens nm, It could not be captured, and its performance as a filter or a catalyst carrier was low.

Furthermore, in the ceramic heat insulating material disclosed in Japanese Patent Publication No. 59259/1992, since the porous body is formed by filling with heat-resistant fiber, it is difficult to control the pore diameter of the porous body. Since the skeletal structure is to form a porous skeletal structure by impregnating the urethane foam with metallic silicon and a sintering aid and then nitriding, the strength as the skeletal structure is insufficient. However, the strength required for fluid permeation was insufficient.

In addition, the lightweight and high-rigidity ceramics disclosed in Japanese Patent Application Laid-Open No. 4-37667 are designed to realize high rigidity.
Since the porosity of the reaction sintered matrix was limited to 40% or less, it could not be used as a heat-resistant structure, but was not suitable for fluid permeation.

Further, in the ceramic composite structure disclosed in JP-A-8-40779, the reinforcing member is formed of a lattice-like structure, that is, a honeycomb-like structure. There was a problem that only the shape application could be used.

Accordingly, the present invention provides a gas-permeable ceramic structure having excellent heat resistance and corrosion resistance, excellent isotropic strength and isotropic fluid permeability, and particularly high performance as a filter or a catalyst carrier. It is to provide a body and a fluid permeable member.

[0012]

Means for Solving the Problems As a result of intensive studies on the above-mentioned problems, the present inventors have found that a porous material having a high specific surface area is provided in a gap of a dense sintered body having a gap communicating discontinuously. By applying a gas-permeable ceramic structure supporting, it is possible to obtain excellent heat resistance, corrosion resistance, isotropic strength and fluid permeation characteristics, and in particular, to obtain high performance as a filter or catalyst carrier. I learned.

That is, the air-permeable ceramic structure of the present invention comprises a skeleton having gaps which are irregularly communicated between skeletons made of a dense sintered body, and filling the gaps of the skeleton with the gaps. Characterized by having a total specific surface area of 100 m ² / g or more.

Here, the four-point bending strength of the gas-permeable ceramic structure is 10 MPa or more, and the volume ratio of the porous sintered body to the whole gas-permeable ceramic structure is 70 to 95% by volume. desirable.

The porous sintered body has a porosity of 70%.
As described above, it is desirable to use a ceramic mainly composed of a metal oxide, and it is desirable that the average pore diameter be 1 μm or less.

The skeleton is desirably made of ceramics containing a metal oxide as a main component. In particular, in order to enhance the strength of the skeleton, the main crystal phase made of the first metal oxide and the main crystal phase are preferably used. It is desirable that the second metal oxide particles be dispersed in the grains of the crystal phase or in the grain boundaries.

It is preferable that the first metal oxide is made of an Al-containing oxide, and the second metal oxide contains Ti or Mg.

According to the present invention, by using the gas-permeable ceramic structure as a fluid-permeable member, it has excellent heat resistance and durability, and has three-dimensional isotropic fluid permeability and high strength. In addition, a fluid permeable member having excellent characteristics as a filter or a catalyst carrier can be obtained.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an air-permeable ceramic structure according to the present invention will be described with reference to the schematic diagram of FIG. As shown in FIG. 1, a gas-permeable ceramic structure 1 of the present invention basically includes a skeleton 2 and a porous sintered body 3 filled in a gap in the skeleton 2. .

The skeleton 2 of the present invention has a relative density of 9
It has a skeleton portion 2a made of a dense sintered body of 0% or more, and a gap portion 2b irregularly communicating between the skeleton portions 2a. The porous sintered body 3 is filled in the gap 2b existing between the skeletons 2a.

According to the present invention, the porous sintered body 3 having a high specific surface area is filled in the gap 2b, so that the total specific surface area of the permeable ceramic structure 1 is 100 m ² / g or more.
In particular, it is a significant feature that the thickness is 300 m ² / g or more, and more preferably 500 m ² / g or more. Thereby, especially, the performance as a catalyst carrier is dramatically improved.

As for the air-permeable ceramic structure 1,
In order to enhance the mechanical reliability of the structure, the four-point bending strength is desirably 10 MPa or more, particularly preferably 15 MPa or more.

For this reason, in the permeable ceramic structure 1, the volume ratio of the skeleton 2 to the porous sintered body 3 is a factor that determines the strength of the entire structure 1 and the amount of fluid permeation.
As the ratio of the porous sintered body 3 decreases, the strength of the structure increases, but the amount of fluid permeation decreases, and the permeation efficiency as a fluid permeable member decreases. From this viewpoint, the volume ratio of the porous sintered body in the air-permeable ceramic structure is 70 to
It is desirable that it be present in a proportion of 95% by volume, especially 80 to 90% by volume, so that the skeleton 2
Is preferably present at a ratio of 5 to 30% by volume, particularly 10 to 20% by volume.

The porosity of the porous sintered body 3 filled in the gap 2b of the skeleton 2a determines the fluid permeability, but according to the present invention, the fluid permeability is good. Is preferably 70% or more, especially 75% or more.

Further, regarding the skeletal body 2, in order to improve the performance as a filter, by increasing the porosity of the porous sintered body 3, the fluid permeation efficiency can be improved. Even if the pore diameter of the unit 3 is reduced, gas can be transmitted. From such a viewpoint, the pore diameter of the porous sintered body 3 is desirably 1 μm or less, whereby fine particles of about ten and several nm can be captured.

In order to keep the porosity of the porous sintered body 3 in the above range, it is desirable that the average particle size of the porous sintered body 3 is 1 μm or less.

According to the present invention, the skeleton 2a is formed of a dense sintered body having a relative density of 90% or more.
It is important that the gaps 2b existing between the skeletons 2a do not have regularity but exist isotropically. That is, the skeleton 2a
Having a relative density of 90% or more, particularly 92% or more,
By forming the sintered body of 5% or more, the strength of the entire skeleton 2 and further the entire structure 1 can be increased.

Also, in the structure 1 of the present invention, the gaps 2b are isotropically, in other words, randomly present between the skeleton parts 2a, so that the gaps 2b of any shape from a simple-shaped article to a complicated-shaped article are formed. Since it can be applied to a member and has no anisotropy in mechanical characteristics and transmission characteristics, the reliability as a structure such as a transmission member is greatly improved.

Further, as the size of the gap 2b between the skeletons 2a is larger, the strength of the skeleton 2 itself is reduced and the gap 2b is liable to be broken by an external impact or impact by a fluid. According to the present invention, the average diameter of the gap 2b is 1 mm or less, and from the viewpoint of improving fluid permeability and strength, particularly, 0.1 to 1
mm, more preferably 0.1 to 0.5 mm.

In the air-permeable ceramic structure of the present invention, the sintered body forming the skeleton 2a or the porous sintered body 3 filled in the gap 2b is made of Al ₂ O ₃ , Z
oxides such as rO ₂ , mullite, cordierite, and aluminum titanate; nitrides such as Si ₃ N ₄ , AlN and TiN; carbides such as SiC and TiC; TiB ₂ and AlB
Borides such as ZrB _2, such as _2, SiAlON, Al
A sintered body mainly composed of one or two or more selected from the group consisting of oxynitrides such as ON and carbonitrides such as TiCN is preferably used. From the viewpoint of suppressing corrosion resistance and increasing corrosion resistance, it is most desirable to use an oxide-based sintered body.

Further, for example, by carrying a catalyst such as gold on the porous sintered body 3, particularly on the surface of the particles, for example, harmful substances such as dioxins can be decomposed.

Further, since the oxide-based sintered body constituting the skeleton 2a is required to have excellent strength at room temperature and high temperature, the oxide-based sintered body constituting the skeleton 2a is particularly preferable. As a body, a main crystal phase composed of a first metal oxide and a second crystal within the grains or grain boundaries of the main crystal phase are formed.
By dispersing the metal oxide particles of
At room temperature and high temperature.

In particular, in the second metal oxide particles, a part or all of the components thereof are dissolved in the first oxide crystal which is the main phase and are precipitated from the first oxide crystal. 0.
The presence of fine particles of 3 μm or less can further improve the strength due to the effect of forming a nanocomposite.

The first oxide particles are desirably composed of an oxide containing AL. For example, at least one of alumina and mullite, and the second oxide crystal particles include Ti or Mg. Composite oxide particles are preferred.

In order to produce the air-permeable ceramic structure of the present invention, first, a skeleton 2a made of a dense sintered body having a relative density of 90% or more and irregularly connected between the skeleton 2a. The skeleton 2 having the gap 2b is produced.

Such a skeleton 2 can be formed by a conventionally known method for forming a three-dimensional network structure. Specifically, 1) a foaming material is added to and mixed with the raw material powder of the sintered body, and the mixture is molded by, for example, a die press, a cold isostatic press, a casting molding, an injection molding, an extrusion molding, and the like, followed by firing 2) a method of adding an organic powder to a raw material powder of a sintered body, mixing, shaping, and firing to eliminate the organic powder;
3) An organic base material having a three-dimensional network structure is prepared in advance, and the organic base material is immersed in a slurry containing raw material powder of the sintered body, and the slurry is filled in the voids in the organic base material. Drying and baking to burn off organic matter.

Examples of the firing method include normal-pressure firing, gas-pressure firing, and microwave heating firing. After firing, hot isostatic pressing (HIP) can be performed to increase the density of the skeleton. It is.

Next, the porous sintered body 3 is filled in the gaps 2b that are irregularly communicated between the skeleton parts 2a made of the dense sintered body manufactured as described above. According to the present invention,
As a method for filling the porous sintered body 3, for example, a sol solution containing a component for forming the porous sintered body 3 is prepared, and the skeleton 2 is immersed in the sol solution to thereby form the inside of the gap of the skeleton. Is impregnated with a sol solution. Thereafter, the skeleton 2 impregnated with the sol solution is gelled and dried.

As a method for drying the gel, a freeze-drying method or the like can be used, but in order to increase the specific surface area of the porous sintered body 3, it is most preferable to use drying under supercritical conditions. desirable.

In a usual drying method, for example, a hot-air drying method, the surface of the particles is smoothed by the influence of the surface tension and the contact angle of the solvent, and the particles are easily aggregated in the particles. The surface area will be lower.

On the other hand, when the solvent is dried in a supercritical state, the surface tension and contact angle generated on the surface of the solvent droplet when the solvent evaporates become small, so that the surface state of the particles before drying is reduced. While maintaining the above, it is possible to prevent agglomeration between particles, so that the specific surface area of the porous sintered body is dramatically improved, and fine pores can be formed in the porous sintered body. is there.

In the supercritical state, the substance is in a critical state of gas and liquid, and has a viscosity similar to that of a gas, a density similar to that of a liquid, and an intermediate diffusion coefficient between gas and liquid. The tension and contact angle can be made very small.

Further, after drying under the above-mentioned conditions, by firing under predetermined firing conditions, a chemically stable ceramic porous sintered body can be formed, and the porous sintered body is firmly bonded to the skeleton. At the very least, the mechanical reliability of the structure can be improved.

If the firing temperature is lower than the predetermined temperature, the bonding strength of the porous sintered body to the skeleton is weak, and the porous sintered body may be degranulated. If it is higher, the sintering of the porous sintered body proceeds too much, and the desired specific surface area and pores cannot be obtained.
In addition, the above-mentioned firing conditions are appropriately adjusted according to the material of the ceramic. For example, alumina is preferably fired at 500 to 1100 ° C. in the air.

The average particle size of the obtained porous sintered body is desirably 1 μm or less for controlling the specific surface area and the pore diameter of the structure.

For the purpose of increasing the strength of the skeleton, the second phase is formed within the crystal grains of the main phase composed of the first metal oxide.
As a method for precipitating the metal oxide particles, the heat treatment is performed under the condition that the second metal oxide dissolves in the first metal oxide during firing, and then the second metal oxide is subjected to the first metal oxide. The heat treatment is performed under conditions that do not form a solid solution with the metal oxide, in other words, under the condition that the second metal oxide precipitates from the first metal oxide crystal.

For example, a Ti-containing oxide is added to a raw material such as alumina or mullite, mixed, molded, and then fired at a temperature of 1300 to 1700 ° C. in a reducing atmosphere such as hydrogen to convert Ti into alumina or mullite crystal. Solid solution inside. Next, the above solid solution is placed in an oxidizing atmosphere having a low solubility of Ti in alumina or mullite in an oxidizing atmosphere.
By performing heat treatment at ６００1600 ° C., Ti oxide can be precipitated and dispersed in the crystal grains of alumina or mullite.

Next, the formed body is heated by a known heating method, for example, a normal pressure firing method, a gas pressure firing method, a microwave heating firing method, and a hot isostatic pressure treatment (HIP) after firing.
Sintering and subsequent heat treatment are performed by various sintering techniques such as treatment.

Further, a Ti-containing compound and a Mg-containing compound are added to alumina or mullite at the same molar ratio, mixed and molded, and then heat-treated at 1300 to 1700 ° C. in an oxidizing atmosphere to convert Ti and Mg into alumina or mullite. To form a solid solution. Thereafter, the solid solution is heat-treated at 1100 to 1600 ° C. in a reducing atmosphere such as hydrogen to precipitate MgAl ₂ O ₄ as fine particles of 0.3 μm or less in alumina or mullite crystals.

[0050]

EXAMPLE 1 An alumina (Al ₂ O ₃ ) powder having an average particle size of 0.7 μm was
An organic binder and water were added and mixed to obtain a slurry.

Next, the impregnation / drying of the urethane foam in the slurry was repeated to impregnate the raw material of alumina into the voids of the urethane foam, and then fired at 1500 ° C. in the air. The urethane component was burned off by firing, and a skeleton of a three-dimensional network structure having irregularly connected gaps was obtained using the alumina-based sintered body as a skeleton. The relative density was 98% as measured by Archimedes' method.
Met. As a result of SEM observation, the average diameter of the gap was 0.55 mm.

Next, ethanol was added to a predetermined amount of aluminum butoxide (Al (OC ₄ H ₉ ) ₃ ), and after stirring, hydrochloric acid solution was added dropwise to carry out hydrolysis to produce a transparent boehmite sol.

Then, the above skeleton was immersed in the alumina sol and dried five times. After filling the gaps in the skeleton with the boehmite sol, the skeleton was allowed to stand at room temperature to gel the sol.

The obtained gel-containing skeleton was inserted into a pressure-resistant container, and 55 kg / cm ² of liquefied carbon dioxide was introduced to replace the solvent. / Cm ² for 48 hours to remove the solvent, and further fired in the air at the temperature shown in Table 1 for 2 hours, so that a porous sintered body made of alumina is filled in the gaps of the skeleton. Quality structure was obtained.

The total specific surface area of the obtained structure was measured by a nitrogen adsorption method. Further, the area ratio of the porous sintered body in the structure was measured by Luzex image analysis, and the ratio was calculated assuming the volume ratio of the structure. Further, the porosity and the average pore diameter of the structure were measured by a mercury intrusion method, and were set as the porosity and the average pore diameter of the porous sintered body. Further, this structure was processed into a shape of 3 mm × 4 mm × 40 mm, and the four-point bending strength was measured based on JISR1601. The results are shown in Table 1.

Example 2 The alumina (Al ₂ O ₃ ) powder of Example 1 was replaced with TiO 2
And 1 mol% of ₂ powder, the MgO powder was added in an amount of 1 mol%, the atmosphere in the same manner as in Example 1, after firing at 1500 ° C., in a hydrogen atmosphere, except that the calcined 5 hours at 1400 ° C. Example It was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1 (Sample No. 9).

Comparative Example 1 The gel used in Example 1 was dried under supercritical conditions in the same manner as in Example 1 to obtain a powder, and a predetermined amount of water and an organic binder were added to the powder, followed by casting. It was molded at 800 ° C. in air and evaluated in the same manner as in Example 1.
(Sample No. 10).

Comparative Example 2 The gel-containing skeleton used in Example 1 was treated at 80 ° C. for 4 hours.
After removing the solvent by hot air drying treatment for 8 hours,
Except for baking at 800 ° C. for 2 hours, the same as in Example,
A porous sintered body in which alumina was filled in the space between the skeletons was obtained. The obtained porous sintered body was evaluated in the same manner as in Example 1 and shown in Table 1 (Sample No. 11).

Comparative Example 3 A slurry was prepared by adding a small amount of a binder and a solvent to alumina (Al ₂ O ₃ ) powder having an average particle size of 1.5 μm and mixing them.
The skeleton of Example 1 was impregnated in the slurry and dried, and the skeleton was impregnated with the slurry. The solvent was removed by hot-air drying at 80 ° C. for 48 hours.
Calcination was carried out at a temperature of 2 ° C. for 2 hours to obtain a porous sintered body in which the space between the frameworks was filled with alumina. The obtained porous sintered body was evaluated in the same manner as in Example 1 and shown in Table 1 (Sample N
o. 12).

[0060]

[Table 1]

As is clear from Table 1, the samples filled with the porous sintered body in the skeleton body according to the present invention have a high bending strength of 10 MPa or more, particularly 15 MPa or more. Total specific surface area by critical drying is 10
A porous sintered body of 0 m ² / g or more could be produced.

Example 3 The aluminum butoxide of Example 1 (Al (OC
₄ H ₉ ) ₃ ), chloroauric acid is converted to alumina (Al
A porous structure in which alumina and gold were filled in the gaps of the skeleton was obtained in exactly the same manner as in Example 1 except that the metal conversion amount was 1.5% by weight based on ₂ O ₃ ). . The structure was fired at 800 ° C.

The obtained structure was evaluated in the same manner as in Example 1. As a result, the specific surface area of the structure was 430 m ² / g, the porosity of the porous sintered body was 74%, and the average pore diameter was 22.1 nm. .

Using the evaluation device shown in FIG. 2, the obtained structure was evaluated for filter characteristics and characteristics as a catalyst carrier.

First, the obtained structure was cut out into a shape of φ50 mm × thickness 80 mm, and this test piece 11 was mounted in a tubular body 12 made of alumina ceramic.
While heating the sample No. 2 to 200 ° C. by the heater 13, a simulation gas containing dust and harmful substances of dioxins was introduced from the gas inlet 14. Then, the gas transmitted through the tubular body 12 and the test piece 11 was sampled at the gas outlet 15 and the particle diameter of the dust contained in the gas was measured. I knew it was done.

At the same time, the concentration x of the harmful substance is measured, and the tubular body 16 on which no sample piece is mounted is placed in the evaluation device as a reference, and the concentration x ₀ of the harmful substance in the permeated gas is measured in the same manner as described above. Then, the ratio of x ₀ to x (1
-X) / x ₀ (%) was determined as the harmful substance decomposition rate, and as a result, the harmful substance decomposition rate was 96%, indicating a good decomposition efficiency.

Comparative Example 4 In Example 3, the gel was dried by hot air drying at 80 ° C. for 48 hours to remove the solvent.
A porous sintered body was prepared in which alumina and gold were filled in the gaps of the skeleton in the same manner as in Example 3 except that the structure was fired at 2 ° C. for 2 hours. The specific surface area is 52 m ² / g, the porosity of the porous sintered body is 38%,
The average pore diameter was 68.8 nm, and the filter characteristics and the characteristics as a catalyst carrier were not able to capture dust having a maximum dust of 28 nm or about several tens of nm, and the decomposition rate of harmful substances was as low as 64%. .

Comparative Example 5 Chloroauric acid was added to alumina (Al ₂ O ₃ ) in the slurry containing alumina powder of Comparative Example 2 instead of the gel of Comparative Example 4.
A porous structure in which alumina and gold were filled in the gaps of the skeleton was obtained in exactly the same manner as in Comparative Example 4 except that the metal conversion amount was 1.5% by weight based on the weight of the metal. As a result of evaluation in the same manner as in Comparative Example 4, the specific surface area of the structure was 13 m.
² / g, porosity of porous sintered body 32%, average pore diameter 18
In addition, the filter characteristics and the characteristics as a catalyst carrier were such that the maximum dust was only 2.5 μm, and only the dust of the order of μm could be captured, and the harmful substance decomposition rate was as low as 23%.

[0069]

As described in detail above, the gas-permeable ceramic structure of the present invention has high strength and fluid permeability characteristics isotropically and has excellent characteristics as a filter and a catalyst carrier. Body can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the structure of a gas-permeable ceramic structure of the present invention.

FIG. 2 is a schematic diagram of an evaluation apparatus for evaluating filter characteristics and characteristics as a catalyst carrier using the gas-permeable ceramic structure of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Air-permeable ceramic structure 2 Skeleton 2a Skeleton 2b Gap 3 Porous sintered body

Claims (11)

[Claims] 1. A skeletal body in which gaps communicating irregularly are formed between skeletons made of a dense sintered body, and a porous sintered body filled in the gaps of the skeletal body. And a total specific surface area of 100 m ² / g or more. 2. The gas-permeable ceramic structure according to claim 1, wherein the four-point bending strength is 10 MPa or more. 3. The gas-permeable ceramic structure according to claim 1, wherein a volume ratio of the porous sintered body to the whole gas-permeable ceramic structure is 70 to 95% by volume. 4. The gas-permeable ceramic structure according to claim 1, wherein the porosity of the porous sintered body is 70% or more. 5. The method according to claim 1, wherein the porous sintered body is made of a ceramic containing a metal oxide as a main component.
5. The air-permeable ceramic structure according to any one of items 1 to 4. 6. The gas-permeable ceramic structure according to claim 1, wherein the average pore diameter of the porous sintered body is 1 μm or less. 7. The gas-permeable ceramic structure according to claim 1, wherein said skeleton portion is made of a ceramic mainly composed of a metal oxide. 8. The method according to claim 1, wherein the skeleton comprises a main crystal phase composed of a first metal oxide, and second metal oxide particles dispersed in the grains of the main crystal phase or in grain boundaries. The air-permeable ceramic structure according to claim 7, wherein 9. The gas-permeable ceramic structure according to claim 7, wherein said first metal oxide is made of an Al-containing oxide. 10. The method according to claim 10, wherein the second metal oxide is Ti or M
The gas-permeable ceramic structure according to claim 7 or 8, wherein g is contained. 11. A fluid-permeable member comprising the gas-permeable ceramic structure according to claim 1.