JP6614505B2 - Ceramic porous body manufacturing method and ceramic porous body - Google Patents

Description

  The present invention relates to a porous ceramic body that has excellent mechanical properties and can be used under high temperature conditions, and a method for producing the same.

  Conventionally, various ceramic porous bodies that can be used under high temperature conditions and methods for producing the same have been proposed. For example, a heat insulating material manufactured by adding a foaming agent to a slurry prepared with a ceramic powder and a dispersion medium such as water and solidifying the slurry with a large amount of pores introduced therein has been proposed (Patent Document 1). ). Furthermore, there has been proposed a porous body produced by adding foam having a shaped shape to a slurry and solidifying it (Patent Document 2). Further, a porous material produced by slurrying a calcium phosphate compound as a biomaterial together with a surfactant, stirring and foaming, and further heating and gelling is then dried and fired (patent) Reference 3).

  In addition, a method has been proposed in which a slurry prepared by dispersing ceramic raw material powder in water is frozen to grow ice in one direction, and then freeze-dried to sublimate ice to produce a ceramic porous body ( Patent Document 4). Furthermore, a method for producing a ceramic porous body with high handling strength in which communicating holes are formed by gelling a slurry of ceramic raw material powder to which a gelling agent has been added, followed by freeze-drying and firing is proposed. (Patent Document 5).

  In addition, using ceramic material powder slurry added with gelling agent and water-soluble polymer as raw material, partition wall structure is formed inside, and there is a communication hole partially blocked, and it has high heat insulation characteristics A method for producing a porous ceramic body is disclosed (Patent Document 6).

JP-A-5-170571 JP 2004-75444 A JP 2013-79172 A JP 2001-192280 A JP 2008-201636 A JP 2011-195437 A

  The methods proposed in Patent Documents 1 to 6 can be applied to various materials. Moreover, since it is excellent in shape imparting property and water is used as a pore forming means, it can be said that there is almost no harmful gas generated at the time of production, and it is an extremely excellent production method in terms of cost and environment.

  However, since the porous material proposed in Patent Document 1 uses sodium silicate or the like as a starting material, soda may remain even after leaching treatment, and it is difficult to use under high temperature conditions. It was. Furthermore, since the porous body proposed in Patent Document 2 has pores independently, the air permeability cannot be expected so much. In addition, since it is manufactured by a method of adjusting the size of the foam in advance, there were some problems when industrialization was assumed, such as avoidance of bonding between bubbles and dispersibility of foam in slurry. . Furthermore, since the pores existing in the porous body proposed in Patent Document 3 are independent, the air permeability, which is one of important characteristics when used as a filter, is low.

  Moreover, when it was going to apply the ceramic porous body manufactured by the method proposed by patent documents 4-6 to structural materials, such as a filter and a heat insulating material, there existed a subject as shown below. That is, since the pores are formed to extend in one direction, the pore extending direction (horizontal direction: H direction) and the direction orthogonal to the pore extending direction (vertical direction: V direction) The characteristics are very different. For example, the air permeability, which is an important characteristic as a filter, and the strength required for the heat insulating material are “20 or less” in the V direction when the H direction is “100”. For this reason, when practical application was assumed, there existed a subject that a characteristic had a difference by direction.

  Moreover, since the ceramic porous body manufactured by the method proposed in Patent Documents 4 and 5 has a structural feature that macroporous communication holes are formed, heat and gas are easily generated. It passed and was difficult to use as a heat insulating material. On the other hand, the ceramic porous body manufactured by the method proposed in Patent Document 6 is expected to be used as a heat insulating material because the ceramic porous body has a communication hole partially blocked by a partition wall structure formed therein. However, as described above, there is a problem as a structural material in which mechanical characteristics and the like vary greatly depending on directions.

  The present invention has been made in view of such problems of the prior art, and the problem is that the air permeability is high, the thermal conductivity is low, and the structure material has an appropriate strength. An object of the present invention is to provide a production method capable of producing a ceramic porous body that has a small difference in physical properties depending on orientation (direction) and can be used under high-temperature conditions in a simple and inexpensive manner.

  In addition, the subject of the present invention is that the air permeability is high, the thermal conductivity is low, the structure material has an appropriate strength, and the difference in physical properties depending on the direction (direction) is small, under high temperature conditions. The object is to provide a usable ceramic porous body.

That is, according to this invention, the manufacturing method of the ceramic porous body shown below is provided.
[1] material powder made of a ceramic, a gelling agent, and a ceramic slurry containing water, and foam prepared using a surfactant and a polyhydric alcohol, obtained by mixing the content of the foam A step of obtaining a gel body by gelling a raw material slurry having a volume of 30 to 90% by volume, a step of freezing the gel body to obtain a frozen body, and a dried body obtained by removing ice from the frozen body Firing to enclose a large number of spherical pores and obtaining a ceramic porous body having an open-cell structure in which through-holes communicating adjacent spherical pores are formed in partition walls constituting the spherical pores; A method for producing a ceramic porous body.
[2] The method for producing a porous ceramic body according to [1], except that the raw slurry contains an organic monomer.
[3] Said [1] or [2] which prepares the said foam with an average diameter of 30-200 micrometers using the foam raw material containing the said surfactant 5-10 mass% and the said polyhydric alcohol 5-20 mass%. The manufacturing method of the ceramic porous body as described in 2.
[4] The surfactant is a fatty acid alkali salt, an amine compound, an alkylbenzene sulfonate, a higher alcohol sulfate, a polyoxyethylene alkyl ether sulfate, a sulfo fatty acid ester, an olefin sulfonate, an alkyl phosphate salt, Alkyltrimethylammonium salt, amine salt, alkylamino fatty acid salt, polyoxyethylene alkyl ether, alkylglycoside, sorbitan fatty acid ester, and fatty acid alkanolamide are at least one selected from the group consisting of glycerin, [1] to [1], which is at least one selected from the group consisting of propylene glycol, butylene glycol, pentylene glycol, hexanediol, polyethylene glycol, and sorbitol. 3] The method for producing a ceramic porous body according to any one of.
[5] The above-mentioned [1] to [4], wherein the ceramic is at least one selected from the group consisting of mullite, alumina, zirconia, silica, silicon carbide, silicon nitride, boron nitride, cordierite, and carbon. The manufacturing method of the ceramic porous body in any one.

Moreover, according to this invention, the ceramic porous body shown below is provided.
[6 ] It is formed of ceramics and includes a large number of spherical pores, and has an open cell structure in which through holes communicating with the adjacent spherical pores are formed in the partition walls constituting the spherical pores. The compressive strength ratio between the stretching direction of the crystal-derived pores and the direction orthogonal to the stretching direction of the pores is 0.3 or more, the porosity is 50 to 99%, and the air permeability is 1 × 10 ⁻⁸ to 1 Ceramic porous body having a size of × 10 ⁻¹⁵ m ² .
[7] The ceramic, mullite, alumina, zirconia, silica, silicon carbide, silicon nitride, boron nitride, cordierite, and porous ceramic according to at least one type of the [6], which is selected from the group consisting of carbon body.

  According to the present invention, a ceramic porous material having a high air permeability, a low thermal conductivity, an appropriate strength as a structural material, a small difference in physical properties depending on directions (directions), and usable under high temperature conditions. The manufacturing method which can manufacture a body simply and cheaply can be provided.

  In addition, according to the present invention, the air permeability is high, the thermal conductivity is low, the structure material has an appropriate strength, and the difference in physical properties depending on the direction (direction) is small, so that it can be used under high temperature conditions. A ceramic porous body can be provided.

2 is a SEM photograph of a cross section of the ceramic porous body obtained in Example 1. 3 is a SEM photograph of a cross section of a ceramic porous body obtained in Comparative Example 1.

  Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

<Method of manufacturing ceramic porous body>
The present inventors have repeatedly studied to solve the above-described problems. As a result, the conventional gelation freezing method for producing a porous body using a raw material powder made of ceramics and a gelling agent has been modified to have a unique structure, thereby enclosing a large number of spherical pores and adjacent. It has been found that it is possible to produce a ceramic porous body having an open cell structure in which through-holes communicating with spherical pores are formed in partition walls constituting the spherical pores. And it discovered that the ceramic porous body which has such a peculiar open cell structure is very useful as various filters and heat insulating materials which do not have direction dependence. More specifically, it is derived from the added foam by a simple method of adding foam (mouse-like foam) derived from a surfactant other than the gelling agent to the ceramic slurry containing the gelling agent. The present invention has been completed by finding that a large number of spherical pores are formed and a through-hole derived from the gelling agent that connects adjacent spherical pores is formed.

  The method for producing a ceramic porous body according to the present invention comprises mixing a ceramic slurry containing ceramic raw material powder, a gelling agent, and water, and a foam prepared using a surfactant and a polyhydric alcohol. A step of obtaining a gel body by gelling the obtained raw slurry (gelation step), a step of freezing the gel body to obtain a frozen body (freezing step), and a dry body obtained by removing ice from the frozen body And a step of obtaining a ceramic porous body having a specific open cell structure (firing step). In addition, about the technical matters other than the material used at a gelling process, the technical matter described in Unexamined-Japanese-Patent No. 2008-201636 (patent document 5) can be utilized fundamentally. Hereinafter, the detail of the manufacturing method of the ceramic porous body of this invention is demonstrated.

  In the gelation step, a raw material powder made of ceramics, a gelling agent, and water are mixed to prepare a ceramic slurry containing these components. The amount of the raw material powder in the ceramic slurry is usually 1 to 30% by volume. The raw material powder may be any powder made of ceramics and dispersed in water (including carbon powder in the present invention). One feature of the production method of the present invention is that it does not depend on the type of raw material. For this reason, the kind of ceramics constituting the raw material powder can be appropriately selected in consideration of the cost and the strength of the final product. Specific examples of the ceramic constituting the raw material powder include mullite, alumina, zirconia, silica, silicon carbide, silicon nitride, boron nitride, cordierite, and carbon. These ceramics can be used individually by 1 type or in combination of 2 or more types. A small amount of sintering aid can be added to the ceramic slurry.

  The production method of the present invention is characterized in that a high porosity ceramic porous body having a unique open cell structure and a small difference in characteristics due to a difference in direction can be produced without depending on the type of starting material. One. For this reason, the shape and size of the raw material powder are not particularly limited. However, the particle size (diameter) of the raw material powder is preferably 0.01 to 100 μm, and more preferably 0.01 to 5 μm. By using the raw material powder having a particle size in such a range, the raw material powder can be easily crushed and can be more uniformly dispersed in the prepared ceramic slurry or raw material slurry. In addition, since it will become easy to settle when the particle size of raw material powder is too large, it may become difficult to prepare a homogeneous gel body.

  As the gelling agent, a water-soluble polymer compound capable of preparing a gel body can be used. Examples of the gelling agent include N-alkyl acrylamide polymers, N-isopropyl acrylamide polymers, sulfomethylated acrylamide polymers, N-dimethylaminopropyl methacrylamide polymers, polyalkyl acrylamide polymers, alginic acid. And polyethyleneimine, starch, carboxymethylcellulose, gelatin, hydroxymethylcellulose, sodium polyacrylate, polyvinyl alcohol, polyethylene glycol, agar, and polyethylene oxide.

  In the gelation step, foam (mousse foam) is prepared using a surfactant and a polyhydric alcohol. The method for preparing the foam is not particularly limited. For example, by using a former that blows a high-pressure gas into an aqueous solution (foam raw material) containing a surfactant and a polyhydric alcohol, fine bubbles, specifically, bubbles having an average diameter of 30 to 200 μm can be prepared. . Moreover, when preparing foam, it is preferable to use the foam raw material (aqueous solution) containing 5-10 mass% of surfactant and 5-20 mass% of polyhydric alcohol. By foaming a foam material having such a composition, the foam having the above average diameter can be prepared.

  Examples of the surfactant include fatty acid alkali salts, amine compounds, alkylbenzene sulfonates, higher alcohol sulfates, polyoxyethylene alkyl ether sulfates, sulfo fatty acid esters, olefin sulfonates, alkyl phosphate esters, alkyls. Mention may be made of trimethylammonium salts, amine salts, alkylamino fatty acid salts, polyoxyethylene alkyl ethers, alkyl glycosides, sorbitan fatty acid esters, and fatty acid alkanolamides. These surfactants can be used singly or in combination of two or more.

  Examples of the polyhydric alcohol include glycerin, propylene glycol, butylene glycol, pentylene glycol, hexanediol, polyethylene glycol, and sorbitol. These polyhydric alcohols can be used singly or in combination of two or more.

  A raw material slurry can be obtained by mixing the prepared ceramic slurry and foam. In order to make the porosity of the finally obtained ceramic porous body within a preferable range of 50 to 99%, the content of each component in the raw material slurry is preferably set to the following ranges, respectively. That is, the content of the raw material powder in the raw material slurry is preferably 50% by volume or less. Moreover, it is preferable that content of the water in a raw material slurry shall be 48.9 volume% or less. Furthermore, it is preferable that content of the gelatinizer in a raw material slurry shall be 1-5 volume%. If the content of the gelling agent in the raw material slurry is too small, gelation may be difficult to proceed. On the other hand, when the amount of the gelling agent in the raw slurry is too large, the gel strength of the gel body obtained tends to be excessively increased, and the water separation property during freezing tends to be lowered.

  The foam content in the raw slurry is preferably 30 to 90% by volume. By setting the content of foam in the raw material slurry within the above range, mechanical properties are maintained, and a ceramic porous body more useful as a structural material can be produced. If the content of the foam in the raw material slurry is too large, handling may be difficult, and the high temperature characteristics of the resulting ceramic porous body may be slightly deteriorated due to the influence of the surfactant.

  If the raw material slurry obtained by mixing the ceramic slurry and the foam is poured into a mold having a desired shape and cooled as necessary, the raw material slurry can be gelled to obtain a gel body. The obtained gel body is solidified in a state where water is retained. Furthermore, the raw material powder which consists of ceramics is being fixed to the gel body.

  In the freezing step, the gel body obtained in the gelation step is frozen to obtain a frozen body. Specifically, a frozen body in which ice is oriented in the gel body can be obtained by cooling from a part or the entire surface of the mold. As a freezing method, a known cooling method such as a normal freezer or a freezing tank may be used. For example, when a mold containing a gel body is placed on a cooling plate or the like in a freezer or a frozen layer and cooled, ice crystals can be grown upward from the contact surface with the cooling plate. The freezing temperature at the time of producing the frozen body may be a temperature at which water retained in the gelling agent is frozen. However, at temperatures around −10 ° C., the growth of ice may be delayed due to the influence of chemical substances contained in trace amounts in the bubbles. In this case, there is a tendency that through-holes that communicate with adjacent spherical pores constituting the open-cell structure of the resulting ceramic porous body are less likely to be formed. For this reason, the freezing temperature is preferably −20 ° C. or less, and preferably −30 to −50 ° C.

  In the firing step, the dried body obtained by removing ice from the frozen body is fired. By firing the dried body, a ceramic porous body having a specific open cell structure can be obtained. When removing the ice from the frozen body, it is preferable to remove only the ice so as not to destroy the structure of the raw material powder and ice crystals that are constituents of the frozen body. That is, it is preferable to employ an ice removing method (drying method) that has little dimensional change and less risk of sample destruction. It is preferable to employ a freeze-drying method as a drying method with less risk of dimensional change and sample destruction. The freeze-drying method is a method for removing only ice by directly sublimating ice in a frozen body under reduced pressure. This method is preferable since the ice is sublimated from the surface of the frozen body, and the dimensional change can be reduced.

  The firing temperature of the dried body can be set according to the type of ceramics constituting the raw material powder used. Furthermore, the firing temperature can be set from the viewpoint of securing the strength of the obtained ceramic porous body. For example, in the case of mullite, 1,500 to 1,700 ° C, in the case of alumina, 1,100 to 1,600 ° C, in the case of zirconia, 1,200 to 1,600 ° C, in the case of silica, 1,000 to 1 , 300 ° C., 1,500 to 2,300 ° C. for silicon carbide and silicon nitride, 1,400 to 2,500 ° C. for boron nitride, 1,300 to 1,500 ° C. for cordierite, In the case of carbon, it is preferably fired at 1,000 to 2,500 ° C.

<Ceramic porous body>
The ceramic porous body of the present invention is manufactured by the above-described manufacturing method. More specifically, the ceramic porous body of the present invention is formed of ceramics such as mullite, alumina, zirconia, silica, silicon carbide, silicon nitride, boron nitride, cordierite, and carbon. And while having many spherical pores, the through-hole which connects adjacent spherical pores has the open cell structure formed in the partition which comprises a spherical pore.

The porosity of the ceramic porous body of the present invention is preferably 50 to 99%, more preferably 70 to 99%. The air permeability of the ceramic porous body is preferably 1 × 10 ⁻⁸ to 1 × 10 ⁻¹⁵ m ² , more preferably 1 × 10 ^{−8 to} 5 × 10 ⁻¹² m ² . The compressive strength ratio between the stretching direction of the pores derived from ice crystals and the direction orthogonal to the stretching direction of the pores is preferably 0.3 or more, and more preferably 0.5 or more. In addition, when the mold containing the gel body is placed on a cooling plate in a freezer or frozen layer and cooled, the formed ice crystals grow upward from the contact surface with the cooling plate. To do. For this reason, the extending direction of pores derived from ice crystals is the H direction, and the direction perpendicular to the extending direction of the pores is the V direction. And since the ceramic porous body of the present invention has the specific open cell structure as described above, it has high air permeability, low thermal conductivity, moderate hardness, and can be used under high temperature conditions. It is. Furthermore, since a large number of spherical pores are included, the difference in physical characteristics depending on the direction (direction) is small. Therefore, the ceramic porous body of the present invention is suitable as a structural material.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, this invention is not limited to these Examples.

<Manufacture of porous ceramics>
Example 1
After mixing kaolin (trade name “EPK”, manufactured by Edgar Minerals) and aluminum hydroxide (trade name “BF013”, manufactured by Nippon Light Metal Co., Ltd.), calcined and ground to obtain mullite powder having an average particle size of 1.1 μm A body (raw material powder) was obtained. 5 parts by volume of the obtained mullite powder, 92 parts by volume of distilled water, and 3 parts by volume of a gelling agent (gelatin, manufactured by Wako Pure Chemical Industries, Ltd.) were mixed to obtain a ceramic slurry. On the other hand, a foam prepared by mixing 9 parts by volume of a surfactant (main component: trade name “Amilite GCK-11”, manufactured by Ajinomoto Healthy Supply Co., Ltd.) and 10 parts by volume of polyhydric alcohol (glycerin, manufactured by Wako Pure Chemical Industries, Ltd.) Gas was blown into the raw material to prepare bubbles with an average diameter of 80 μm. Foam was added to the ceramic slurry and mixed to prepare a raw material slurry having a foam content of 50% by volume. The prepared raw material slurry was cast into a mold and placed in a refrigerator for gelation. The mold was placed on a shelf (cooling plate) in the frozen layer and cooled at −40 ° C. for 1 hour to obtain a frozen body. The obtained frozen body was removed from the mold and dried for 12 hours using a freeze drying apparatus to obtain a dried body. The obtained dried body was put into a firing furnace and fired at 1,600 ° C. for 2 hours to obtain a ceramic porous body. The SEM photograph of the cross section of the obtained ceramic porous body is shown in FIG. As shown in FIG. 1, it can be seen that there are a large number of substantially spherical pores, and that the partition walls forming each pore have a structure in which through holes that connect adjacent pores are formed. .

(Examples 2 to 10)
Except that the amount of raw material powder in the ceramic slurry (% by volume) and the amount of foam in the raw material slurry (% by volume) are the values shown in Table 1, the same as in Example 1 above, A ceramic porous body was produced.

(Comparative Example 1)
Using the mullite powder prepared in Example 1, a ceramic porous body was produced by a gelation freezing method using a gelling agent disclosed in JP 2008-201636 A (Patent Document 5). In this method, the foam added to the ceramic slurry in Example 1 is not used. The SEM photograph of the cross section of the obtained ceramic porous body is shown in FIG. As shown in FIG. 2, a large number of communicating holes are formed, but it is understood that the open cell structure as shown in FIG. 1 is not formed.

<Evaluation>
(1) Porosity The porosity was calculated by calculating the density from the dimensions and mass of the ceramic porous body and dividing by the density of the ceramic powder. Table 1 shows the calculated porosity.

(2) Air permeability Based on JIS K7126-1, the air permeability of the ceramic porous body was measured. The measurement results are shown in Table 1.

(3) Thermal conductivity The thermal conductivity of the ceramic porous body was measured by a measurement method called a hot disk method. Specifically, a special measuring element in which a heater unit in which a thin wire heater is wound in a double spiral shape and a temperature sensor is sandwiched between two ceramic porous bodies. And it heated by energizing a heater part for a short time, the temperature change by electricity supply was measured with the temperature sensor, and the heat conductivity was computed. Table 1 shows the calculated thermal conductivity.

(4) Strength In accordance with JIS R2615, the strength in the stretching direction (H direction) of pores derived from ice crystals of the ceramic porous body and the direction (V direction) perpendicular to the stretching direction of the pores were measured. The measurement results are shown in Table 1. Further, the ratio of the intensity in the V direction to the intensity in the H direction (V / H) was calculated. Table 1 shows the calculated V / H values.

  The method for producing a ceramic porous body according to the present invention can apply raw material powders made of various types of ceramics, has low physical direction dependency, low thermal conductivity, and high strength. A porous body can be produced.

Claims (7)

The content of the said foam obtained by mixing the raw material powder which consists of ceramics, the ceramic slurry containing a gelatinizer, and water, and the foam prepared using surfactant and a polyhydric alcohol is 30- A step of gelling a raw material slurry of 90% by volume to obtain a gel body;
Freezing the gel body to obtain a frozen body;
The dried body obtained by removing ice from the frozen body was baked to enclose a large number of spherical pores, and through holes communicating with the adjacent spherical pores were formed in the partition walls constituting the spherical pores. Obtaining a ceramic porous body having an open-cell structure;
A method for producing a ceramic porous body having: The method for producing a ceramic porous body according to claim 1, excluding a case where the raw slurry contains an organic monomer.   3. The ceramic porous body according to claim 1, wherein the foam having an average diameter of 30 to 200 μm is prepared using a foam raw material containing 5 to 10 mass% of the surfactant and 5 to 20 mass% of the polyhydric alcohol. Manufacturing method. The surfactant is a fatty acid alkali salt, an amine compound, an alkylbenzene sulfonate, a higher alcohol sulfate, a polyoxyethylene alkyl ether sulfate, a sulfo fatty acid ester, an olefin sulfonate, an alkyl phosphate, an alkyl trimethyl ammonium. At least one selected from the group consisting of a salt, an amine salt, an alkylamino fatty acid salt, a polyoxyethylene alkyl ether, an alkyl glycoside, a sorbitan fatty acid ester, and a fatty acid alkanolamide,
The said polyhydric alcohol is at least 1 type selected from the group which consists of glycerin, propylene glycol, butylene glycol, pentylene glycol, hexanediol, polyethylene glycol, and sorbitol. A method for producing a ceramic porous body.   5. The ceramic according to claim 1, wherein the ceramic is at least one selected from the group consisting of mullite, alumina, zirconia, silica, silicon carbide, silicon nitride, boron nitride, cordierite, and carbon. A method for producing a ceramic porous body. Formed of ceramics,
A large number of spherical pores are included, and a through-hole communicating with the adjacent spherical pores has an open cell structure formed in the partition walls constituting the spherical pores, and the extending direction of pores derived from ice crystals, and the pores The porous ceramics has a compressive strength ratio in the direction orthogonal to the stretching direction of 0.3 or more, a porosity of 50 to 99%, and an air permeability of 1 × 10 ⁻⁸ to 1 × 10 ⁻¹⁵ m ^2. body. The ceramic porous body according to claim 6 , wherein the ceramic is at least one selected from the group consisting of mullite, alumina, zirconia, silica, silicon carbide, silicon nitride, boron nitride, cordierite, and carbon.