JP5429526B2 - Method for producing ceramic porous body - Google Patents

Description

  The present invention relates to a method for producing a ceramic porous body and a ceramic porous body. Specifically, fine pores are formed on the surface and in the vicinity of the surface, and pores having a shape larger than the fine pores are formed inside. The present invention relates to a method for manufacturing a porous ceramic body in which through holes are formed in communication, and the porous ceramic body.

Conventionally, a ceramic porous body has a structure including a large number of pores in ceramics, and has been widely used as a ceramic filter, a heat insulating material, and the like using the structure.
For example, a ceramic porous body having a through hole is widely used as a ceramic filter. Such a ceramic filter tends to reduce the pore size of the filter layer in order to increase the collection efficiency of dust and the like.

However, if the pore diameter is reduced, the gas permeation resistance (pressure loss) increases. Therefore, in order to prevent the gas permeation resistance from increasing while reducing the pore diameter, a method of thinning the filter is adopted. It was. However, if the filter is simply thinned, the mechanical strength of the filter itself cannot be maintained, so a multilayer structure in which a filter layer having fine pores is provided on a substrate layer having a large pore diameter is performed. Yes.
Furthermore, in order to further improve the collection efficiency, the pore diameter is further reduced and the filter layer is being made thinner.
That is, in ceramic filters, a ceramic porous body in which thin layers having different pore diameters and porosity are sequentially formed and sintered is often used.

Such ceramic porous bodies having different pore diameters and porosityes were used, for example, to form a base layer having a large pore diameter by mixing and sintering a powder and an organic substance, and then forming a base layer. A mixture of a granular material having a particle diameter smaller than that of the granular material and an organic material is formed on a base layer, sintered, and formed by a method of forming a filter layer on the base layer.
However, since this method uses a granular material having a small particle diameter when forming the filter layer, the granular material having a small particle diameter enters the large pores formed in the base layer or the like. There was a problem that it might end up.

Therefore, as a method for solving such a problem, various methods for producing a porous ceramic body having a structure in which the pore diameter and the porosity can be controlled and the base layer and the filter layer are integrated have been proposed.
For example, by mixing a plurality of ceramic powder particles with different particle diameters, arranging particles with different sizes stepwise by centrifugal force, and sintering in this state, the pore size is inclined. A method for producing different ceramic porous bodies has been proposed (see Patent Document 1).

Further, as an improvement of the method described in Patent Document 1, ceramic porous bodies having different pore diameters so as to be inclined using a pressure generated by heating and a pressure gradient generated by centrifugal force are used. A manufacturing method has been proposed (see Patent Document 2).
These methods are effective means for manufacturing a ceramic porous body in which the pore diameter and the porosity are controlled so as to change in a certain direction in the porous body, and the pore diameters are different so as to be inclined. Therefore, a constant pore distribution is obtained and the cost is excellent.

Furthermore, a method for producing a porous ceramic body has been proposed in which the pore diameter is increased and the porosity is increased by adding a foaming agent or the like to the ceramic slurry, but the pore diameter is different so that the pore diameter is inclined. (See Patent Document 3).
Specifically, when a foaming agent or the like is added to the ceramic slurry and agitated, bubbles are generated in the ceramic slurry, but these bubbles are decomposed or aggregated over time, resulting in bubbles of different sizes. Is formed. The location of the bubbles varies in the ceramic slurry depending on the size of the bubbles. For example, the size of the bubbles changes in the ceramic slurry, for example, the bubbles near the surface are small and the bubbles inside are large. And when this ceramic slurry is sintered, the ceramic porous body which is different so that the magnitude | size of a pore diameter may incline can be manufactured.

This method is an effective means when the pore diameter is inclined in the uniaxial direction, and the porosity is high.
Furthermore, a method of joining a metal porous body and a ceramic porous body by joining the metal porous body and the ceramic porous body and diffusing the metal has been proposed (see Patent Document 4).
Moreover, as a method of producing a ceramic porous body having a high porosity and macroporous communication holes, a slurry in which a ceramic raw material is dispersed in an aqueous solution of a water-soluble polymer that can be gelled is gelled, frozen, thawed, A method of drying and sintering has been proposed (see Patent Document 5).

On the other hand, unlike ceramic filters, it has not been considered to use a ceramic porous body having a pore diameter and a porosity in accordance with the temperature to be used and its distribution.
The mechanism of heat conduction usually differs depending on the operating temperature.For example, in a high temperature region, heat conduction due to radiation increases. Therefore, the pore diameter that minimizes the thermal conductivity according to the temperature used and its distribution, It is considered preferable to use a heat insulating material having porosity or the like.

Japanese Patent No. 2997542 JP 2004-359529 A JP 2000-264755 A JP 2006-204990 A JP 2008-201636 A

In the methods described in Patent Documents 1 and 2, since the pore diameter and the porosity depend on the particle diameter of the ceramic granular material, the degree of freedom of the pore diameter and the porosity is limited, the pore diameter is large, and the porosity is It was difficult to produce a high ceramic porous body.
Further, in the method described in Patent Document 3, bubbles are connected before the ceramic slurry is solidified, the pore diameter and pore distribution are likely to be uneven, and the pores are also likely to be closed pores.

Furthermore, in the method described in Patent Document 4, since the base material to be joined is a metal, its use is limited to the low temperature field.
In this regard, it is conceivable that instead of the metal porous body, ceramic porous bodies having different pore diameters are bonded or joined together so that the pore sizes are inclined.
However, since it is a porous body, the area to be bonded or bonded becomes very small. Therefore, there is a problem that the strength of the ceramic porous body becomes weak or the pores are blocked at the bonded or bonded interface. Yes, not put into practical use.
Further, in the method described in Patent Document 5, there is no description of a method for making pores in a ceramic porous body different in size so that the pores are inclined. For example, a filter is manufactured using this ceramic porous body. For this purpose, it is necessary to fabricate a ceramic porous body serving as a base layer having a different pore diameter and porosity and a ceramic porous body serving as a filter layer, and laminating them as usual.

Therefore, in the method for producing a ceramic porous body of the present invention, pores are formed on a specific surface and in the vicinity of the surface, pores larger than the pores are formed on the other surface and inside, and these pores communicate with each other. An object of the present invention is to provide a method for producing a porous ceramic body having through holes and a high porosity.
Furthermore, the method for producing a ceramic porous body according to the present invention includes a thermal conductivity for controlling the particle diameter and content of the ceramic powder, and the freezing rate in the gel-like formed body of the ceramic powder as a production intermediate. By selecting variously the freezing temperature, freezing time, etc. of the member that has been adjusted, the pore diameter near the surface of the ceramic porous body, the internal pore diameter, and further the porosity of the ceramic porous body It aims at providing the manufacturing method of the ceramic porous body which can be adjusted.
In the ceramic porous body of the present invention, pores are formed on a specific surface and in the vicinity of the surface, pores larger than the pores are formed on the other surface and inside, and these pores form through holes. An object of the present invention is to provide a ceramic porous body having a high porosity.

As a result of intensive studies to achieve the above object, the inventors of the present invention have a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more at 0 ° C. of a part of the gel-like molded body of ceramic powder particles. In a state where it is in contact with the member, the gel-shaped molded body is frozen to produce a frozen molded body, ice (solid water) is precipitated in the frozen molded body, the ice is removed from the frozen molded body, By drying and sintering, pores are formed on the surface where the thermal conductivity at 0 ° C. is in contact with a member having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more and in the vicinity thereof. It was found that a ceramic porous body in which pores larger than the pores are formed can be produced. The present invention has been completed based on such findings.

That is, the present invention
(1) A gel-like molded body containing ceramic powder particles, water, and a gelling agent and containing 10 to 40% by volume of the ceramic powder granules is prepared. By freezing the part in contact with a member having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more at 0 ° C., thereby precipitating ice in the frozen molded body in which the gel-like molded body is frozen, A method for producing a porous ceramic body, which removes the ice from the frozen molded body, dries and sinters;
(2) The method for producing a ceramic porous body according to (1), wherein the gelling agent is a non-reversible water-soluble polymer that can be gelled,
(3) The method for producing a ceramic porous body according to (1) or (2), wherein the freezing temperature is minus 10 ° C. or lower,
(4) In any one of the above (1) to (3), the ice is removed by a water-soluble organic solvent and / or vacuum substitution while substantially maintaining the structure of the frozen molded body other than the ice. A method for producing the ceramic porous body according to the description,
(5) A gel-like molded body containing ceramic powder particles, water, and a gelling agent and containing 10 to 40% by volume of the ceramic powder granules is prepared. A frozen molded body in which the gel-shaped molded body is frozen by freezing the portion in contact with a member having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more at 0 ° C. In this case, ice is deposited on and near the surface in contact with the member having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more at 0 ° C., and ice larger than the ice is present on the other surfaces and inside. These ices are deposited, and each particle becomes a continuous particle by bringing a part of its surface into contact with each other. After removing these ices from the frozen molded body, these ice particles A green porous body with pores corresponding to the shape and Ceramic porous body obtained by sintering the green porous body,
(6) The ceramic porous body according to (5), wherein the porosity is 60 to 90% by volume of the ceramic porous body,
Is to provide.

According to the method for producing a porous ceramic body of the present invention, pores are formed on a specific surface and in the vicinity of the surface, pores larger than the pores are formed on the other surface and inside, and these pores communicate with each other to penetrate. A ceramic porous body having pores and a high porosity can be produced.
In addition, according to the method for producing a ceramic porous body of the present invention, the particle size and content of the ceramic granular material, and the cooling rate when freezing the gel-like formed body of the ceramic granular material as a production intermediate are controlled. By selecting variously the members having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or higher at 0 ° C., the freezing temperature of the gel-like molded body, the freezing time, etc. The pore diameter, the internal pore diameter, and the porosity of the ceramic porous body can be adjusted.
Further, according to the ceramic porous body of the present invention, pores are formed on a specific surface and in the vicinity of the surface, pores larger than the pores are formed on the other surface and inside, and these pores communicate with each other to form a through-hole. By forming a ceramic porous body having a high porosity.

3 is an external view photograph of a ceramic porous body of Example 2. 4 is a SEM photograph of a cross section of the ceramic porous body of Example 2. 3 is an enlarged SEM photograph of a portion indicated by A in the SEM photograph of FIG. 2. 3 is an enlarged SEM photograph of a portion indicated by B in the SEM photograph of FIG. 2. 3 is an enlarged SEM photograph of a portion indicated by B in the SEM photograph of FIG. 2. 3 is an appearance photograph of a porous ceramic body of Example 3. 4 is a SEM photograph of a cross section of the ceramic porous body of Example 3. 4 is an external view photograph of a ceramic porous body of Comparative Example 2. 4 is a SEM photograph of a cross section of a ceramic porous body of Comparative Example 2. 4 is a SEM photograph of a cross section of a ceramic porous body of Comparative Example 2.

Hereinafter, although the form for implementing this invention is demonstrated in detail, this form is made to understand the meaning of invention better, and does not limit this invention.
Hereafter, the manufacturing method of the ceramic porous body of this invention is demonstrated concretely.

First, a gel-like molded body containing ceramic powder particles, water and a gelling agent and containing 10 to 40% by volume of the ceramic powder particles is prepared.
The ceramic powder particles used in the present invention are ceramic powders that are dispersed in water and can be easily gelled. The type of the ceramic powder particles is not limited and should be selected in consideration of the environment used, cost, and the like. Can do.
For example, known oxide ceramic particles and non-oxide ceramic particles can be used alone or in combination of two or more. Examples of oxide ceramics include alumina ceramics, zirconia ceramics, mullite ceramics, and non-oxide ceramics include silicon carbide ceramics, silicon nitride ceramics, boron nitride ceramics, and graphite ceramics. Can be mentioned.

Further, the particle shape and particle diameter of the ceramic powder are not particularly limited, and can be selected in consideration of the environment in which it is used. For example, in order to uniformly disperse the ceramic powder particles, the particle diameter is preferably 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.6 μm or less.
In particular, by containing an appropriate amount of particles of 0.1 μm or less, sintering is promoted and the strength as a ceramic sintered body can be increased. Therefore, even if the porosity is increased, sufficient strength as a ceramic porous body can be obtained. In addition, since sintering is promoted, sintering at a low temperature is also possible. The content of these particles is preferably 0.5 to 20% by mass, more preferably 0.5 to 10% by mass in the ceramic powder.

Furthermore, in order to promote the sintering of the ceramic porous body, if necessary, a trace amount of an inorganic compound suitable for the kind of the ceramic powder particles can be added as a sintering aid. Examples of the sintering aid include alumina, yttria, magnesia, calcia, silica, boron, and carbon. The amount of the sintering aid added is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the ceramic powder particles, for example.
Since the water used in the present invention acts as a solvent and serves as an ice source for forming pores, it is preferable to use pure water such as distilled water or ion exchange water.

The gelling agent used in the present invention is a water-soluble polymer that can be gelled, and is preferably an irreversible gel polymer that does not return to the tissue structure before freezing once frozen. Examples of such gelling agents include gelatin, agar, N-alkylacrylamide polymers, N-isopropylacrylamide polymers, sulfomethylated acrylamide polymers, N-dimethylaminopropyl methacrylamide polymers, polyalkylacrylamides. Examples of the polymer include alginic acid, polyethyleneimine, starch, carboxymethylcellulose, hydroxymethylcellulose, sodium polyacrylate, polyvinyl alcohol, polyethylene glycol, and polyethylene oxide. Of these gelling agents, gelling in the atmosphere is preferred, and gelatin and agar that do not leave ash such as carbon during sintering are particularly preferred.
The kind and addition amount of the gelling agent can be appropriately selected depending on the kind of ceramic powder.

Further, if necessary, a crosslinking agent such as a compound having an amine group, a compound having an aldehyde group, a compound having a hydrazide group, a compound having an epoxy group, or a compound having methylol can be added. As the crosslinking agent, for example, diglycerol glycidyl ether which is a compound having an epoxy group is preferable. It is preferable that the addition amount of a crosslinking agent shall be 5-20 mass parts with respect to 100 mass parts of gelatinizers, for example.
And these ceramic powder granules, water, and a gelatinizer are mixed, and a gel-like molded object with content of ceramic powder granules of 10-40 volume% is produced.
Here, when the above sintering aid is added, a sintering aid that does not exist in the sintered ceramic such as carbon is not included in the content of the ceramic powder, Sintering aids such as alumina, yttria, magnesia, calcia, silica, boron, etc., which are present in the ceramics even after the sintering, are included in the content of the ceramic powder particles.

In order to obtain a gel-like molded product having a ceramic powder particle content of 10 to 40% by volume, the ceramic powder particle content is 10 to 40% by volume, the water content is 50 to 89% by volume, gel The content of the agent is preferably 1 to 10% by volume.
If the content of the ceramic powder is 10 to 40% by volume, the strength of the ceramic porous body can be maintained even if the porosity of the produced ceramic porous body is as high as 60 to 90% by volume. Because.
Further, if the water content is 50 to 89% by volume and the gelling agent content is 1 to 10% by volume, a gel can be formed and the water in the gel is frozen by freezing. This is because the pores finally obtained can be formed as communication holes by separating and precipitating from the polymer forming the gel as well as the ice particles contacting each other.

In order to produce a gel-like formed body, first, ceramic powder particles and water are mixed to form a ceramic slurry, and a gelling agent is added thereto to adjust the above-described volume% ceramic slurry. And this slurry is poured into a shaping | molding die, it solidifies in the state hold | maintained in the gel, and is gelatinized.
By this gelation, ceramic powder particles are fixed in the gel. This gel-like molded body is preferably formed in the shape of a ceramic porous body that will be the final product because the post-process can be simplified. In addition, the ceramic slurry to which the gelling agent has been added is once molded into an appropriate size and gelled to obtain a gel body, and a gel mold is pressed against the gel body to form a gel-like molded body. A forming method can also be employed.

The temperature and time for gelation can be appropriately determined depending on the gelling agent used, and can be, for example, 15 ° C. or more and 10 hours or less at a temperature of 1 ° C. or more and 90 ° C. or less.
For example, in the case of agar or methylcellulose, after heating at a temperature of 60 ° C. or higher and 80 ° C. or lower, it can be gelated by standing at room temperature for 2 hours or longer in the air. In the case of polyethyleneimine, it can be gelated by standing at a temperature of 50 ° C. or higher and 60 ° C. or lower for 1 hour to 2 hours. Further, in the case of gelatin, gelation can be achieved by first holding at a temperature of 20 ° C. or more and 25 ° C. or less for 30 minutes or more and 1 hour, and then allowing to stand at a temperature of 2 ° C. or more and 10 ° C. or less for 1 hour or more. it can.

Next, the gel-like molded body is frozen by at least partly freezing it in contact with a member having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more at 0 ° C. In addition to the frozen molded body, ice is deposited in the frozen molded body.
The freezing method may be a known method such as a normal freezer, quick freezer or supercooled freezer. In any case, since the cooling is performed from the outside of the gel-shaped molded body, the surface of the gel-shaped molded body is usually first frozen and the freezing proceeds inside.

  The freezing temperature for producing the freeze-formed body is not particularly limited as long as the water is frozen, but the freezing temperature is in the range of −5 ° C. to −10 ° C. In order to prevent the ice from growing more than necessary during cooling, the temperature is preferably set to −10 ° C. or lower.

Here, in the portion where the gel-like molded body and a member having a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more are in contact and in the vicinity thereof, this member is present, so that this member is in contact A cooling rate can be made faster than the part which is not and the inside of a gel-like molded object. If the cooling rate is high, the time for staying in the ice generation temperature region is short. Therefore, a large number of fine particles of ice are deposited at and near the frozen molded body portion in contact with this member.
On the other hand, in the part where the member having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more at 0 ° C. is not in contact, and in the gel-like molded body, the time spent in the ice generation temperature region is this member. It is longer than the part in contact with and its vicinity. Therefore, in the freeze-formed body, ice particles having a particle size larger than the ice formed in the portion where the member having a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more is in contact with it. ing.

In this way, by changing the cooling rate of the gel-like molded body, the size of ice obtained in the frozen molded body can be changed. Therefore, the size of the ice obtained in the frozen molded body can be changed by the contact form of the member having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more at 0 ° C. to the gel-like molded body.
For example, if a member having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more at 0 ° C. is brought into contact with the entire surface of the gel-like molded body and frozen, the entire surface of the frozen molded body and the vicinity thereof are fine. Ice of a large particle is formed, and ice of a particle larger than the surface is formed inside the frozen molded body, so that a frozen molded body in which the ice particle diameter is changed between the surface and the inside can be obtained.

Further, a part of the surface of the gel-like molded body is brought into contact with a member having a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more, and the other surface has a thermal conductivity at 0 ° C. of 50 W · m ^−1.・ If frozen in a state of contact with a member of less than K ^−1, fine particles are present on the surface where the member with a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more is in contact with the surface. The surface and the inside of the surface other than that (a member with a thermal conductivity of less than 50 W · m ⁻¹ · K ^{−1 at} 0 ° C. is in contact) is formed. A frozen molded body in which fine ice is formed only on the surface can be obtained.
In particular, when a member having a thermal conductivity lower than 50 W · m ⁻¹ · K ^{−1 at} 0 ° C. is selected as a member having a thermal conductivity lower than that of the gel-like molded body, the thermal conductivity at 0 ° C. is The surface of the gel-like molded body that is in contact with a member of less than 50 W · m ⁻¹ · K ⁻¹ is not substantially cooled, and a member having a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more is in contact. It was to become the cooling and freezing only the part 0 thermal conductivity at 0 ℃ from a surface thermal conductivity in contact 50W · m ^-1 · K ^-1 or more members at ° C. is 50 W · m ^-1 · K A frozen molded body in which ice particles expand in one direction toward the surface with which a member of less than ⁻¹ contacts can be obtained.

Further, a part of the surface of the gel-like molded body is brought into contact with a member having a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more, and the other surface has a thermal conductivity different from that of the member. thermal conductivity may be frozen in a state in contact with the 50W · m ^-1 · K ^-1 or more members in ° C.. In this way, it is possible to obtain a frozen molded body in which fine ice having different particle diameters is formed on each surface according to the thermal conductivity of each member.

Here, the method for bringing the gel-like molded body into contact with a member having a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more is not particularly limited. It is possible to employ a means in which a member having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more is brought into contact with the surface of the gel-like molded body. Further, projections or partitions made of members having a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more may be provided inside the mold so that the molded body has a honeycomb shape or the like. .
The reason for providing a member having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more at 0 ° C. is to quench the gel-like molded body using this member. The structure needs to be cooled directly from a cooling source. A shape in which the entire member is included in the gel-like molded body is not preferable because the member is cooled only after the gel-like molded body is cooled.

  In addition, since the water content in the gel-like molded body is 50 to 89% by volume and the content of the gelling agent is 1 to 10% by volume, the formed ice has particles on the surface. It is the continuous particle | grains formed by contacting a part mutually. Therefore, by removing the ice in a later step and making the ice part a pore, a through hole in which the pores communicate can be obtained.

Here, as a material of a member having a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more used in the present invention, for example, iron (thermal conductivity at 0 ° C. is 84 W · m ⁻¹ · K ^{− 1} ), aluminum (thermal conductivity at 0 ° C. 236 W · m ⁻¹ · K ⁻¹ ), copper (thermal conductivity at 0 ° C. 403 W · m ⁻¹ · K ⁻¹ ), gold (heat conduction at 0 ° C.) rate is ^{320W · m -1 · K -1)} , silver (0 thermal conductivity at ℃ is ^{430W · m -1 · K -1)} , nickel (0 thermal conductivity at ℃ is 94W · m ^-1 · K ^{- 1),} brass (0 thermal conductivity at ℃ is ^{106W · m -1 · K -1)} , gun metal (0 thermal conductivity at ℃ is ^{53W · m -1 · K -1)} , and the like. Can also be used as these not only to a single, 0 thermal conductivity 50W · m ^-1 · K ^-1 or more alloys in ° C..

Among these, when gunmetal or iron is used, the particle diameter of ice at the part where the member is in contact is smaller than the inside, but the difference is small. On the other hand, when aluminum or copper is used, the particle diameter of the ice at the part where the member is in contact is clearly smaller than the inside. Thus, as the member used in the present invention may be any thermal conductivity at 0 ℃ is 50W · m ^-1 · K ^-1 or more but, 100W · m ^-1 · K ^-1 or more, further 200 W · m ^{- 1} · K ⁻¹ or more is more preferable.
Therefore, when pores formed on a specific surface and in the vicinity of the surface are made fine and pores formed on the other surface and inside are relatively large, the thermal conductivity is high, for example, 0 The thermal conductivity at 100 ° C. is preferably 100 W · m ⁻¹ · K ⁻¹ or more, and it is particularly preferable to use a member having 200 W · m ⁻¹ · K ⁻¹ or more.

On the other hand, SUS304 (having a thermal conductivity at 0 ° C. of about 20 W · m ⁻¹ · K ⁻¹ ) is preferably a member having a thermal conductivity at 0 ° C. lower than 50 W · m ⁻¹ · K ^−1. Absent. Also, resins such as polyethylene and vinyl chloride generally have a thermal conductivity at 0 ° C. of 1 W · m ⁻¹ · K ⁻¹ or less. Therefore, even if these members are used, it is difficult to change the size of pores formed on a specific surface and in the vicinity of the surface, and the size of pores formed on the other surface and inside. Absent.

By freezing the gel-like molded body in this way, the water in the gel is separated from the polymer forming the gel and precipitated as ice, and the ice whose particle diameter is controlled is separated and precipitated from the gel. A molded body can be produced.
The ice particle size is reflected in the pore size of the ceramic porous body. For the freezing method and selection of members with a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more, the target ceramics It is necessary to examine and select the shape and size of the porous body itself and the shape, size and distribution of pores.

Next, ice is removed from the frozen molded body, dried, and sintered.
First, before removing the ice, it is preferable to remove the frozen molded body from the mold in a frozen state. If the mold is removed after removing the ice, it becomes difficult to keep the pores as it is, or it becomes difficult to maintain the shape of the molded body itself.
If the ice particles formed in the frozen molded body are removed, pores will be formed in the removed parts, so remove only the ice without breaking the skeletal structure of the frozen ceramic powder particles. is important.

Examples of such ice removal methods include substitution with water-soluble organic solvents such as acetone and methanol, or vacuum substitution. By these methods, the structure of the frozen molded body other than ice is substantially maintained. The ice can be removed.
For replacement with a water-soluble organic solvent, first, the frozen molded body is immersed in a water-soluble organic solvent cooled to the same temperature as the frozen molded body, and the temperature is gradually raised to room temperature to bring water into this organic solvent. By transferring to a solvent, the portion where the ice was present is replaced with an organic solvent, and the ice is removed.
The time for immersing in a water-soluble organic solvent can be appropriately determined depending on the shape of the freeze-formed body. For example, in the case of an alumina ceramic freeze-formed body having a length of 100 mm, a width of 100 mm, and a thickness of 10 mm, the freezing temperature is −17 ° C. In a freezer, the substitution can be terminated by immersing in an acetone solvent at the same temperature for 6 hours, then in an acetone solvent at 10 ° C. for 6 hours, and further in an ordinary temperature acetone solvent for 6 hours or more.

  Further, the replacement by vacuum replacement can be performed by a vacuum high-temperature rapid drying or a thawing method using an atmosphere-controlled replacement drying method that removes ice by a freeze drying method. That is, it is a method of removing only ice by directly sublimating the ice in the frozen molded body by heating the frozen molded body weakly under vacuum or reduced pressure. According to this method, the ice is liquefied and the generated water does not move and evaporate from the surface of the molded body, so that the structure is not damaged or deformed due to liquefaction, water movement or evaporation.

In the case of substitution with a water-soluble organic solvent, drying is preferably performed under mild conditions because the water-soluble organic solvent remains. Specifically, it is preferably performed at 25 ° C. or more and 80 ° C. or less, particularly preferably 70 ° C. Further, the temperature raising time is preferably 1 ° C./min or more and 2 ° C./min or less, particularly preferably 1 ° C./min. Further, the dry holding time is preferably 1 hour or longer, particularly preferably 6 hours or longer.
Further, in the case of replacement by vacuum replacement, only a small amount of water vapor remains in the void from which the ice has been removed, and therefore a certain high temperature is desirable. Specifically, it is preferably 80 ° C. or higher and 120 ° C. or lower, particularly preferably 100 ° C. Further, the temperature raising time is preferably 1 ° C./min or more and 2 ° C./min or less, particularly preferably 1 ° C./min. Further, the dry holding time is preferably 1 hour or longer, particularly preferably 6 hours or longer.
The compact from which the ice has been removed by such a method is a sintered body in which the ceramic powder particles are the skeleton, the portions where the ice was present are formed as pores, and the pores corresponding to the ice particle shape are formed. It becomes the previous green porous body.

In the present invention, since a water-soluble polymer that can be gelled is added as a gelling agent when the gel-like molded body is formed, it is preferable to perform a heat degreasing treatment to remove remaining organic substances.
The temperature, time and atmosphere of this heat degreasing treatment are set according to the type and amount of the ceramic component used and the organic substance used. For example, when polyethyleneimine is used as the gelling agent, it is held at 650 ° C. for 4 hours. It is preferable to degrease.

Next, the green porous body subjected to the heat degreasing treatment is sintered.
The sintering temperature, time and atmosphere are set in consideration of the type of ceramic component used, particle size distribution, etc., and can be set by applying the normal ceramic temperature, time and atmosphere sintering conditions. For example, it can be fired under conditions such as 1300 ° C. or more and 2000 ° C. or less, 30 minutes or more and 20 hours or less, in the air, in an argon atmosphere, or in a nitrogen atmosphere.
If the green porous body is sintered in this manner, defects such as cracks can be prevented during the sintering and in the sintered ceramic porous body.

By this method, the produced ceramic porous body has fine pores formed on the specific surface and in the vicinity of the surface, and pores having a shape larger than the fine pores are formed on the other surface and inside. At the same time, these pores communicate with each other to form a porous ceramic body in which through holes are formed.
That is, this ceramic porous body contains a ceramic powder, water, and a gelling agent, and a gel-like molded body containing 10 to 40% by volume of the ceramic powder is produced. Is frozen in a state where at least a part thereof is in contact with a member having a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or more at 0 ° C., thereby producing a frozen molded body in which the gel-like molded body is frozen. In the frozen molded body, ice is deposited on the surface in contact with a member having a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more and in the vicinity thereof, Ice larger than ice is precipitated, and these ice particles are continuous particles by bringing a part of the surface into contact with each other. After removing these ice pieces from the frozen molded body, Corresponding to these ice particle shapes There will have been formed green porous body, the obtained ceramic porous body by sintering the green porous body.

  Conventionally, since the formation of the ceramic skeleton and the formation of pores are performed in the same process, it is necessary to balance the formation conditions of both, and therefore it is difficult to increase the strength of the ceramic skeleton. According to the method for producing a ceramic porous body, the strength of the ceramic skeleton can be improved by forming the ceramic skeleton and the pores by separate processes, and the porosity is increased to 60 to 90% by volume. be able to.

EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to these Examples.
Example 1
90% by mass of silicon carbide particles having an average particle size of 0.8 μm and 10% by mass of silicon carbide particles having an average particle size of 0.03 μm are weighed, and then 100 parts by mass of these silicon carbide particles. 2 parts by mass of alumina particles having an average particle diameter of 0.2 μm were added as a sintering aid. These silicon carbide particles and alumina particles become ceramic particles.

Next, the ceramic particles are first put in pure water so that the content of the ceramic particles is 10% by volume, the content of water is 89% by volume, and the content of the gelling agent is 1% by volume. This was put into a stirrer and mixed with a ball mill at a rotation speed of 40 rpm for 12 hours to obtain a slurry.
Thereafter, polyethyleneimine was added to this slurry as a gelling agent and further mixed for 1 hour. And this slurry was taken out from the stirrer and the bubble was removed by vacuum stirring defoaming.

Thereafter, 12 parts by mass of diglycerol glycidyl ether as a crosslinking agent was added to the slurry with respect to 100 parts by mass of the gelling agent, and this was put into a stirrer and further mixed for 1 hour to obtain a final slurry. The frame is made of aluminum (thermal conductivity at 0 ° C .: 236 W · m ⁻¹ · K ⁻¹ ), and the upper and lower plates are made of copper (thermal conductivity at 0 ° C .: 403 W · m ⁻¹ · K ⁻¹ ). The final slurry was poured into a mold having a length of 100 mm, a width of 100 mm, and a height of 10 mm. Then, this mold was placed in a hot air heating apparatus and treated at 50 ° C. for 1 hour to gel the final slurry in the mold to produce a gel-like body.

  Next, this gel-like body was put in a freezer set to −17 ° C. together with the mold, cooled and frozen at −17 ° C. for 1 hour, and ice was deposited in the frozen molded body. Thereafter, the frozen molded body was removed from the mold while frozen, placed in a vacuum drying apparatus, and vacuum-replaced at 35 ° C. for 12 hours to remove ice from the frozen molded body. Then, this compact is put into a warm air heating device, heated from 30 ° C. to 100 ° C. at 1 ° C. per minute, held at 100 ° C. for 1 hour, dried, and pores corresponding to the ice particle shape are formed. A green porous body was obtained.

  Then, this green porous body is put in an atmosphere furnace, and the atmosphere in the furnace is changed to a nitrogen atmosphere. The temperature is raised to 650 ° C. at a rate of 1 ° C. per minute and held at 650 ° C. for 4 hours. And the heat degreasing process of diglycerol glycidyl ether which is a crosslinking agent was performed. After the heat degreasing treatment, the furnace atmosphere is changed to an argon atmosphere, the furnace temperature is raised to 1800 ° C. at a rate of 15 ° C. per minute, and held at 1800 ° C. for 2 hours for sintering to produce a ceramic porous body. did.

  The produced ceramic porous body had a porosity of 90% and was all through-holes. Fine pores having an average pore diameter of 10 μm were formed on the surface in contact with copper, and had a network structure in which pores having the pore diameter continued to a depth of about 10 μm from the surface. Further, in the interior deeper than about 10 μm from the surface, the pore diameter gradually increased, and the pore size was different so as to be inclined. For example, at about 5 mm from the surface, there was a continuous pore having an average pore diameter of about 190 μm.

Example 2
97 mass% of silicon carbide particles having an average particle size of 0.7 μm and 3 mass% of silicon carbide particles having an average particle size of 0.03 μm were weighed, and then 100 mass parts of these silicon carbide particles. 6 parts by mass of alumina particles having an average particle size of 0.1 μm and yttria particles having an average particle size of 0.6 μm (mass ratio of alumina particles to yttria particles is 1: 1) Added as an agent. These silicon carbide particles, alumina particles, and yttria particles are ceramic particles.

Next, the ceramic particles are first put in pure water so that the content of the ceramic particles is 15% by volume, the content of water is 84% by volume, and the content of the gelling agent is 1% by volume. This was put into a stirrer and mixed with a ball mill at a rotation speed of 20 rpm for 12 hours to obtain a slurry. And this slurry was taken out from the stirrer, and the bubble was removed by vacuum stirring defoaming.
Thereafter, gelatin was added as a gelling agent to this slurry, and further mixed for 15 minutes to obtain a final slurry. And so that the obtained molded body has a honeycomb structure, a plurality of columnar honeycomb hole-forming projections having a honeycomb shape dimension of 10 mil are arranged inside the mold, and are 30 mm in length, 30 mm in width, and 50 mm in height. This final slurry was poured into a mold. The mold frame, the upper and lower plates, and the honeycomb hole forming protrusions are made of copper. And this mold was put into a 10 degreeC refrigerator, and it hold | maintained at 10 degreeC for 1 hour, the last slurry in a mold was gelatinized, and the gel-like body was produced.

Next, this gel-like body was placed in a freezer set to −20 ° C. together with the mold, cooled and frozen at −20 ° C. for 1 hour, and ice was deposited in the frozen molded body. Thereafter, the frozen molded body is removed from the mold while frozen, immersed in acetone cooled to −20 ° C. for 6 hours, then immersed in acetone at 10 ° C. for 6 hours, and further immersed in acetone at room temperature for 6 hours. Was replaced with acetone to remove ice from the frozen molded body. Then, this molded body is put in an explosion-proof dryer, heated to 70 ° C. at 1 ° C. per minute, kept at 70 ° C. for 1 hour, dried, and formed with pores corresponding to ice particle shapes. A porous body was obtained.
Then, this green porous body is put in an atmosphere furnace, the atmosphere in the furnace is changed to an argon atmosphere, the temperature is raised to 1700 ° C. at a rate of 15 ° C. per minute, and the honeycomb structure is sintered by holding at 1700 ° C. for 1 hour. A ceramic porous body was produced.

  The produced ceramic porous body had a porosity of 85% and was all through-holes. Then, fine pores having an average pore diameter of 5 μm were formed on the surface in contact with copper, and had a network structure in which pores having the pore diameter continued to a depth of about 20 μm from the surface. Also, in the interior deeper than 20 μm from the surface, the pore diameter gradually increased, and the pore size was different so as to be inclined. For example, in the place about 125 μm from the surface, it was a continuous pore having an average pore diameter of about 80 μm.

  An appearance photograph of the ceramic porous body having this honeycomb structure is shown in FIG. An SEM photograph of a cross section of the ceramic porous body having the honeycomb structure is shown in FIG. 2 (magnification: 30 times). Further, an enlarged SEM photograph of the portion indicated by A in FIG. 2 is shown in FIG. 3 (magnification: 100 times), and an enlarged SEM photograph of the portion indicated by B in FIG. 2 is shown in FIG. 4 (magnification: 200 times) and FIG. 5 (magnification: 2500 times) shows.

Example 3
96 mass% of silicon carbide powder particles having an average particle diameter of 0.5 μm and 4 mass% of silicon carbide powder particles having an average particle diameter of 0.03 μm were weighed, and then 100 mass parts of these silicon carbide particles. 3 parts by mass of an alumina granule having a uniform particle size of 0.1 μm and an yttria granule having a uniform particle size of 0.6 μm (the mass ratio of the alumina granule to the yttria granule is 7: 3) Added as an agent. These silicon carbide particles, alumina particles, and yttria particles are ceramic particles.

Next, the ceramic particles are first put in pure water so that the content of the ceramic particles is 20% by volume, the content of water is 77% by volume, and the content of the gelling agent is 3% by volume. This was put into a stirrer and mixed with a ball mill at a rotation speed of 20 rpm for 12 hours to obtain a slurry. And this slurry was taken out from the stirrer, and the bubble was removed by vacuum stirring defoaming.
Thereafter, cellulose was added as a gelling agent to this slurry, and further mixed for 15 minutes to obtain a final slurry. The final slurry was poured into a mold having a frame made of copper and upper and lower plates made of aluminum and having a length of 100 mm, a width of 100 mm, and a height of 10 mm. Then, this mold was put into a warm air heating device, treated at 60 ° C. for 1 hour, and then the mold was gelated by moving it into the atmosphere and leaving it at room temperature to produce a gel-like body. .

Next, this gel-like body was placed in a freezer set to −25 ° C. together with the mold, cooled and frozen at −25 ° C. for 1 hour, and ice was deposited in the frozen molded body. Thereafter, the frozen molded body is removed from the mold while frozen, immersed in acetone cooled to −25 ° C. for 6 hours, then immersed in acetone at 10 ° C. for 6 hours, and further immersed in acetone at room temperature for 6 hours. Was replaced with acetone to remove ice from the frozen molded body. Thereafter, this compact was put into a warm air dryer, heated to 1 ° C. per minute up to 70 ° C., held at 70 ° C. for 1 hour, dried, and pores corresponding to the ice particle shape were formed. A green porous body was obtained.
Then, this green body is put into an atmosphere furnace, and the atmosphere in the furnace is changed to an argon atmosphere. The temperature is raised to 1750 ° C. at a rate of 20 ° C. per minute and held at 1750 ° C. for 1 hour to produce a ceramic porous body. did.

  The produced ceramic porous body had a porosity of 80% and was all through-holes. Fine pores having an average pore diameter of 25 μm were formed on the surface in contact with copper, and had a network structure that continued from the surface to a depth of about 15 μm. Further, in the interior deeper than 15 μm from the surface, the pore diameter gradually increased, and the pore size was different so as to be inclined. For example, at about 5 mm from the surface, there was a continuous pore having an average pore diameter of about 90 μm.

Moreover, when the compressive strength of this ceramic porous body was measured, the compressive strength was 10 Mpa, and it was confirmed that a ceramic porous body with high strength was obtained.
An appearance photograph of this ceramic porous body is shown in FIG. Moreover, the SEM photograph of the cross section of this ceramic porous body is shown in FIG. 7 (magnification: 30 times).

Example 4
90% by mass of alumina particles having an average particle size of 0.2 μm and 10% by mass of silicon carbide particles having an average particle size of 0.03 μm were weighed. These alumina powder and silicon carbide powder become ceramic powder.
Next, the ceramic particles are first put in pure water so that the content of the ceramic particles is 40% by volume, the content of water is 59% by volume, and the content of the gelling agent is 1% by volume. This was put into a stirrer and mixed with a ball mill at a rotation speed of 40 rpm for 12 hours to obtain a slurry.
Thereafter, polyethyleneimine was added to this slurry as a gelling agent and further mixed for 1 hour. And this slurry was taken out from the stirrer and the bubble was removed by vacuum stirring defoaming.

  Thereafter, 12 parts by mass of diglycerol glycidyl ether as a crosslinking agent was added to the slurry with respect to 100 parts by mass of the gelling agent, and this was put into a stirrer and further mixed for 1 hour to obtain a final slurry. Then, this final slurry was poured into a mold having a frame ring made of copper and upper and lower plates made of aluminum and having a diameter of 100 mm and a length of 150 mm. Then, this mold was placed in a hot air heating apparatus and treated at 50 ° C. for 1 hour to gel the final slurry in the mold to produce a gel-like body.

Next, this gel-like body was put in a freezer set to −15 ° C. together with the mold, cooled and frozen at −15 ° C. for 1 hour, and ice was deposited in the frozen molded body. Thereafter, the frozen molded body is removed from the mold while frozen, and the molded body is immersed in acetone cooled to −15 ° C. for 6 hours, then immersed in acetone at 10 ° C. for 6 hours, and further immersed in acetone at room temperature for 6 hours. Then, the ice was removed from the frozen molded body by replacing the ice with acetone. Thereafter, this compact was put into a warm air dryer, heated to 1 ° C. per minute up to 70 ° C., held at 70 ° C. for 1 hour, dried, and pores corresponding to the ice particle shape were formed. A green porous body was obtained.
Then, this green porous body is put into an atmosphere furnace, and the atmosphere in the furnace is changed to an argon atmosphere. Manufactured.

  The produced ceramic porous body had a porosity of 60% and was all through-holes. Then, fine pores having an average pore diameter of 8 μm were formed on the surface in contact with copper, and had a network structure in which pores having the pore diameter continued to a depth of about 10 μm from the surface. Further, in the interior deeper than about 10 μm from the surface, the pore diameter gradually increased, and the pore size was different so as to be inclined. For example, at a distance of 10 mm from the surface, it was a continuous pore having an average pore diameter of about 65 μm.

Example 5
100% by mass of alumina particles having an average particle size of 0.1 μm was weighed. Next, 0.3 parts by weight of magnesia powder having an average particle diameter of 0.1 μm was added as a sintering aid to 100 parts by weight of the alumina powder. These alumina particles and magnesia particles become ceramic particles.
Next, the ceramic particles are first put in pure water so that the content of the ceramic particles is 10% by volume, the content of water is 87% by volume, and the content of the gelling agent is 3% by volume. This was put into a stirrer and mixed with a ball mill at a rotation speed of 20 rpm for 12 hours to obtain a slurry. And this slurry was taken out from the stirrer, and the bubble was removed by vacuum stirring defoaming.

  Thereafter, gelatin was added as a gelling agent to this slurry, and further mixed for 15 minutes to obtain a final slurry. Then, the frame was made of copper, and the upper and lower plates were poured into a mold made of aluminum having a length of 100 mm, a width of 100 mm, and a height of 5 mm. And this mold was put into a 10 degreeC refrigerator, and it hold | maintained at 10 degreeC for 1 hour, the last slurry in a mold was gelatinized, and the gel-like body was produced.

Next, this gel-like body was placed in a freezer set to −20 ° C. together with the mold, cooled and frozen at −20 ° C. for 30 minutes, and ice was deposited in the frozen molded body. Thereafter, the frozen molded body is removed from the mold while frozen, and the molded body is immersed in acetone cooled to −20 ° C. for 6 hours, then immersed in acetone at 10 ° C. for 6 hours, and further immersed in acetone at room temperature for 6 hours. Then, the ice was removed from the frozen molded body by replacing the ice with acetone. Thereafter, this compact was put into a warm air dryer, heated to 1 ° C. per minute up to 70 ° C., held at 70 ° C. for 1 hour, dried, and pores corresponding to the ice particle shape were formed. A green porous body was obtained.
And this green porous body was put into the heating furnace, and it heated up to 1300 degreeC in the air | atmosphere at the speed | rate of 5 degree-C / min, hold | maintained at 1300 degreeC for 1 hour, and sintered and manufactured the ceramic porous body.

  The produced ceramic porous body had a porosity of 80% and was all through-holes. The surface in contact with copper had fine pores with an average pore diameter of 7 μm, and had a network structure in which pores having the pore diameter continued to a depth of about 35 μm from the surface. Further, in the interior deeper than about 35 μm from the surface, the pore diameter gradually increased, and the pore size was different so as to be inclined. For example, at an area of about 35 mm from the surface, the average pore diameter was a continuous pore of about 65 μm.

Example 6
100% by mass of alumina particles having an average particle size of 0.6 μm was weighed. Next, 0.3 parts by weight of magnesia powder having an average particle diameter of 0.1 μm was added as a sintering aid to 100 parts by weight of the alumina powder. These alumina particles and magnesia particles become ceramic particles.
Next, the ceramic particles are first put in pure water so that the content of the ceramic particles is 20% by volume, the content of water is 76% by volume, and the content of the gelling agent is 4% by volume. This was put into a stirrer and mixed at a rotation speed of 40 rpm with a ball mill for 4 hours to obtain a slurry. And this slurry was taken out from the stirrer, and the bubble was removed by vacuum stirring defoaming.

Thereafter, agar was added as a gelling agent to the slurry, and the slurry was stirred for 15 minutes in a 70 ° C. hot water bath to obtain a final slurry. Then, the frame and the upper and lower plates were poured into a mold having a length of 100 mm, a width of 100 mm, and a height of 3 mm made of seven-three brass (the thermal conductivity at 0 ° C. was 106 W · m ⁻¹ · K ⁻¹ ). The mold is left in a room at 25 ° C. for 2 hours, then placed in a refrigerator at 10 ° C. and held at 10 ° C. for 1 hour to gel the final slurry in the mold to produce a gel-like body. did.

Next, this gel-like body was put in a freezer set to −15 ° C. together with the mold, cooled and frozen at −15 ° C. for 1 hour, and ice was deposited in the frozen molded body. Thereafter, the frozen molded body is removed from the mold while frozen, and the mold is immersed in acetone cooled to −15 ° C. for 6 hours, then immersed in acetone at 10 ° C. for 6 hours, and further immersed in acetone at room temperature for 6 hours. Then, the ice was removed from the frozen molded body by replacing the ice with acetone. Thereafter, this compact was put into a warm air dryer, heated to 70 ° C. in 1 minute per minute, held at 70 ° C. for 1 hour, dried, and pores corresponding to ice particle shapes were formed. A green porous body was obtained.
Then, this green porous body was put into a heating furnace, heated to 1650 ° C. at a rate of 2 ° C. per minute in the atmosphere, held at 1650 ° C. for 2 hours, and sintered to produce a ceramic porous body.

  The produced ceramic porous body was all through-holes with a porosity of 76%. On the surface in contact with the Nansan brass, pores having an average pore diameter of 30 μm were formed, and had a network structure in which pores having the pore diameter continued to a depth of about 20 μm from the surface. Further, in the interior deeper than about 20 μm from the surface, the pore diameter gradually increased, and the pore size was different so as to be inclined. For example, at an area of about 20 μm from the surface, the average pore diameter was a continuous pore of about 110 μm.

Example 7
100% by mass of zirconia powder having an average particle size of 0.5 μm and containing 3 mol% of yttria was weighed. This zirconia granular material becomes a ceramic granular material.
Next, the ceramic particles are first put in pure water so that the content of the ceramic particles is 25% by volume, the content of water is 70% by volume, and the content of the gelling agent is 5% by volume. This was put into a stirrer and mixed with a ball mill at a rotation speed of 30 rpm for 12 hours to obtain a slurry. And this slurry was taken out from the stirrer, and the bubble was removed by vacuum stirring defoaming.

Thereafter, gelatin previously dissolved as a gelling agent was added to this slurry with stirring for 15 minutes to obtain a final slurry. Then, it was poured into a pipe-shaped mold having an inner diameter of 30 mm, a height of 5 mm, and a thickness of 15 mm made of gunmetal (having a thermal conductivity of 53 W · m ⁻¹ · K ^{−1 at} 0 ° C.) that can be divided into two parts. The mold is left in a room at 25 ° C. for 1 hour, then placed in a refrigerator at 10 ° C. and held at 10 ° C. for 1 hour to gel the final slurry in the mold to produce a gel-like body. did.

Next, this gel-like body was put in a freezer set to −17 ° C. together with the mold, cooled and frozen at −17 ° C. for 1 hour, and ice was deposited in the frozen molded body. Thereafter, the frozen molded body was removed from the mold while frozen and placed in a vacuum drying apparatus, followed by vacuum replacement for 12 hours to remove ice from the frozen molded body. Then, this molded body is put into a warm air heating apparatus, heated from 20 ° C. to 100 ° C. at 1 ° C. per minute, held at 100 ° C. for 1 hour, dried, and pores corresponding to ice particle shapes are formed. A green porous body was obtained.
Then, this green porous body was put into a heating furnace, heated to 1550 ° C. at a rate of 2 ° C. per minute in the atmosphere, held at 1550 ° C. for 2 hours, and sintered to produce a ceramic porous body.

  The produced ceramic porous body had a porosity of 71% and was all through-holes. On the surface in contact with the gun metal, pores having an average pore diameter of 50 μm were formed, and had a network structure in which pores having the pore diameter continued to a depth of about 10 μm from the surface. Further, in the interior deeper than about 10 μm from the surface, the pore diameter gradually increased, and the pore size was different so as to be inclined. For example, at an area of about 10 μm from the surface, the average pore diameter was a continuous pore of about 170 μm.

Comparative Example 1
Example except that the frame and upper and lower plates were made of polyethylene (thermal conductivity at 0 ° C .: about 0.4 W · m ⁻¹ · K ⁻¹ ) as a mold into which the slurry added with the gelling agent was poured. In the same manner as in Example 1, a ceramic porous body was produced.
The obtained ceramic porous body had a porosity of 80% and was all through-holes. However, the pore diameter was almost the same from the surface to the inside, and the average pore diameter was a continuous pore of about 200 μm.

Comparative Example 2
As a mold into which a slurry added with a gelling agent is poured, the frame ring and upper and lower plates are made of vinyl chloride (thermal conductivity at 0 ° C .: about 0.2 W · m ⁻¹ · K ⁻¹ ) Produced a ceramic porous body in the same manner as in Example 4.
The obtained ceramic porous body had a porosity of 80% and was all through-holes. However, the pore diameter was almost the same from the surface to the inside, and the pores were continuous with an average pore diameter of about 250 μm.
An appearance photograph of this ceramic porous body is shown in FIG. Moreover, the SEM photograph of the cross section of the surface vicinity of this ceramic porous body is shown in FIG. 9 (magnification: 30 times), and the SEM photograph of the cross section about 2.5 mm from the surface is shown in FIG. 10 (magnification: 30 times).

Comparative Example 3
As a mold into which a slurry added with a gelling agent is poured, the frame and upper and lower plates are made of lead (thermal conductivity at 0 ° C .: 35 W · m ⁻¹ · K ⁻¹ ) 25 mm long, 25 mm wide, 3 mm high A porous ceramic body was produced in the same manner as in Example 6 except that. The frame and the upper and lower plates used were bent lead sheets.
The obtained ceramic porous body had a porosity of 73% and was all through-holes. However, the pore diameter was almost the same from the surface to the inside, and the pores were continuous with an average pore diameter of about 180 μm.

As described above, from the results of Examples 1 to 7, the particle size and content of the ceramic powder particles, 0 for controlling the cooling rate when freezing the gel-like formed body of the ceramic powder particles as the production intermediate. By selecting various factors such as the freezing temperature and freezing time of members with a thermal conductivity of 50 W · m ⁻¹ · K ⁻¹ or higher at ⁰ ° C., the pore diameter near the surface and the inside of the ceramic porous body It was found that the pore diameter of the ceramic porous body and the porosity of the ceramic porous body can be adjusted.

In the present invention, pores are formed on a specific surface and in the vicinity of the surface, pores larger than the pores are formed on the other surface and inside, and these pores communicate with each other to form a through hole. Ceramic porous bodies with high pores formed on the surface and in the vicinity of the specific surface and in the vicinity of the surface can be used as the base layer. Can be preferably used.
In addition, fine pores are formed on a specific surface and in the vicinity of the surface, and pores larger than the fine pores are formed on the other surface and inside. These pore diameters, and further the porosity of the ceramic porous body Therefore, it can be preferably used as a heat insulating material corresponding to various temperatures from a low temperature to a high temperature.

Claims (4)

A gel-like molded body containing ceramic powder, water, and a gelling agent and containing 10 to 40% by volume of the ceramic powder is produced, and at least part of the gel-shaped molded body is 0 By freezing in contact with a member having a thermal conductivity at 50 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more, ice is precipitated in the frozen molded body in which the gel-shaped molded body is frozen, and the frozen molded body In which the ice is removed, dried and sintered, wherein the ceramic porous body is in contact with a member having a thermal conductivity at 0 ° C. of 50 W · m ⁻¹ · K ⁻¹ or more. Fine pores were formed on the surface and in the vicinity of the surface, pores having a shape larger than the fine pores were formed on the other surfaces and inside, and these pores communicated with each other to form through holes. Ceramics Method of manufacturing the hole body.   The method for producing a ceramic porous body according to claim 1, wherein the gelling agent is an irreversible water-soluble polymer that can be gelled.   The method for producing a ceramic porous body according to claim 1 or 2, wherein the freezing temperature is minus 10 ° C or lower.   The porous ceramic body according to any one of claims 1 to 3, wherein the ice is removed by a water-soluble organic solvent and / or vacuum substitution while substantially maintaining a structure of the freeze-formed body other than the ice. Production method.