JP2006176347A - Porous ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous ceramic body in which columnar open pores or closed pores are formed and which has desired water-retaining property, filtration property and air permeability since the pore shape, the pore arrangement, and the pore density of the pores can be controlled. <P>SOLUTION: The porous ceramic has columnar open pores or closed pores having pore diameters of 5-30 μm. A method for producing the porous ceramic comprises sintering a sea-island form formed body containing, as sea structure, a body for the ceramics and, as island structure, fibers in an oxidizing gas atmosphere. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a porous ceramic body that can be used as a removal filter, a building material, a water purification material, an insulator, an insulating plate, a plant and animal growth base, a soil modifying material, a refractory material, and the like made of particulate matter.

  Porous ceramic body is lightweight, heat and oxidation resistant, and has excellent functions such as breathability, water absorption, water permeability, heat insulation, adsorptivity, soundproofing, chemical resistance, In recent years, it has attracted attention as a support material for water purification microorganisms, particulate matter (PM) catalyst, and an adsorbing material for environmental hormones.

  In general, a porous ceramic body is obtained by kneading and sintering a finely pulverized powder of charcoal made of particles of several tens of μm, rice husk, sawdust, wood chips, etc., in a kneaded material as a raw material. However, these organic materials themselves are in a non-uniform form, or when a molded body containing these materials is sintered, the generated gas such as water vapor and carbon dioxide escapes through the molded body being sintered. However, the pore shape collapses and the pores are randomly scattered inside the ceramic body. Although the apparent porosity and bulk density can be controlled to some extent, the arrangement of the pores has not been controlled. The porous ceramics thus obtained have inaccurate control of filtration characteristics, ventilation characteristics, and water retention, which is one reason why the use of ceramic bodies using ceramic clay for various functional materials is limited. It has become.

Furthermore, these powders, rice husks, sawdust, wood chips, natural fibers, etc. have water absorption, so a lot of moisture is required to improve plasticity, cracks occur during drying, and uneven shrinkage occurs. A ceramic body with high dimensional accuracy has not been obtained. (For example, Patent Document 1)
In addition, as other methods, a method using a resin filler or a phenol resin or a urethane resin foam material is generally used. However, when these techniques are used, the resin filler and the carbon component are kept at a relatively low temperature during sintering. Oxidation disappears, so there are problems such as generation of large amounts of cracked gas before the clay particles forming the ceramic body are combined, or tarring of the cracked gas in the pores, making it impossible to form clean pores. (For example, Patent Document 2).

Therefore, fine ceramic molded bodies are used in fields that require highly controlled porous bodies such as high-performance filters and insulators, and a method for producing porous ceramics having through-holes by compression molding is used. Although disclosed (for example, Patent Document 3), the through-hole is a large one having a diameter of about 10 μm to 100 μm, and the manufacturing method is to form a rod-shaped molded body having an outer diameter of 1 mm or less, A method of bundling and compressing to form pores is adopted. Therefore, a dedicated compression facility for obtaining porous ceramics by further compression-molding the rod-shaped molded body is required, and thus the molded body obtained is expensive.
JP 2003-20290 A JP 2002-274929 A Japanese Patent Application Laid-Open No. 11-13987

  An object of the present invention is to form cylindrical open pores or closed pores in a porous ceramic body, and to control the hole shape, the hole arrangement, and the hole density. It is in providing the manufacturing method of a body.

Porous ceramics having cylindrical open pores or closed pores having an average pore diameter of 5 to 30 μm in the ceramics.
A method for producing porous ceramics, in which a sea island-shaped molded body containing ceramic clay for the sea structure and fibers for the island structure is sintered in an oxidizing gas atmosphere.

  According to the present invention, it is possible to form cylindrical open pores or closed pores in a porous ceramic body, and to control the pore shape, the pore arrangement, and the pore density. It is possible to provide a porous ceramic body that can have ventilation characteristics and the like.

  The ceramic body of the present invention is a porous ceramic body having cylindrical open pores or closed pores having an average pore diameter of 5 to 30 μm. When it exceeds 30 μm, there is a possibility of affecting functions such as removal of fine particles.

  On the other hand, when the average pore diameter is less than 5 μm, depending on the characteristics of the clay, the surface tension with water droplets may increase and water absorption may be reduced.

The hole density observed on the cut surface of the ceramic body in the direction perpendicular to the axial direction of the columnar pores is preferably 10 / mm ² or more and 10000 / mm ² or less. If it is less than 10 pieces / mm ² , the performance as a porous body is not exhibited, and the water absorption rate is not improved. If it is 10,000 pieces / mm ² or more, the water absorption rate is improved, but the bending strength may be lowered.

  The pores observed on the cut surface of the ceramic body in the direction perpendicular to the axial direction of the columnar pores have a roundness (La / Lb) of 2 consisting of the major axis (La) / minor axis (Lb) of the pore diameter. It is suitable that it is 0.0-1.0. When the roundness exceeds 2.0, that is, when an ellipse far from the perfect circle is observed, the degree of parallelism of the pores is low, or the pores are greatly curved. If the degree of parallelism of the pores is low, two or more pores may be bonded to each other, and the size of the pores cannot be controlled, which may cause a decrease in filter performance or catalyst support performance.

  The water absorption of the ceramic body of the present invention is preferably 5.0 wt% or more. If it is less than 5.0 wt%, the performance as a porous material may not be satisfied.

  Here, the water absorption refers to the weight (Ma) of the object to be measured which has been dried at 105 ° C. for 2 hours to become a constant weight state, and the object to be measured is impregnated in pure water for 24 hours to wipe off the water on the surface. It is calculated by the following formula 1 from the subsequent weight (Mb).

Water absorption rate = (Mb−Ma) / Ma × 100 (Equation 1)
The ceramic body of the present invention can be obtained by sintering a sea-island raw material containing a ceramic clay for a sea structure and fibers for an island structure in an oxidizing gas atmosphere.

  The clay for ceramics of the present invention may be any material generally used for ceramics, for example, diatomaceous earth, silica sand, quartzite, kaolin mineral, serpentine, clay, lizardite, chrysotile, mica mineral, vermiculite, smectite, foamed shirasu. , Perlite, obsidian, leechite, shale, sand figure, glitter, feldspar, glass, alumina, fly ash, quartz, amphibole, and the like can be used.

  The average particle size of the clay for ceramics is preferably in the range of 0.01 μm to 1000 μm. When the average particle size exceeds 1000 μm, there may be a problem that the bonding force by water becomes weak and the plasticity is lowered.

  The fibers used in the present invention may be organic synthetic fibers such as nylon, polyester and acrylic, or fibers such as cotton and silk, but they are kneadable with clay, heat loss characteristics, and gas generated and formed during sintering. In view of the cleanliness of pores, carbon fiber bundles and chopped and milled yarns can be suitably used.

  The carbon fiber used for the extrusion molding method in this invention is explained in full detail.

  The carbon fiber used in the present invention may be either acrylic or pitch, and its mechanical properties are not limited. The carbon content obtained by organic elemental analysis is preferably 90 wt% or more and the ash content is 1 wt% or less. When there is much ash, residues such as tar may remain in the pores formed. In order to prevent abnormal color development of the ceramic body, the content of iron or alkali metal derivative is preferably 1 wt% or less.

  Moreover, the temperature at which the heating loss under air condition does not fall below 200 ° C is suitable.

  When heating loss starts at a temperature below 200 ° C., the carbon fiber disappears before the formation of the basic skeleton of the ceramic body due to the evaporation of the bound water in the clay for ceramics and the adhesion of the clay particles, and the porous structure is lost. It may be uniform and is not preferable.

  The fiber diameter of the carbon fiber is not particularly limited. For example, when a normal polyacrylonitrile-based carbon fiber is used, the diameter is 10 μm or less.

  The fiber length is preferably 10 mm or less. If the fiber length of the carbon fiber exceeds 10 mm, the dispersibility of the carbon fiber in the clay during kneading deteriorates. For this reason, carbon fibers are localized inside the ceramic, making it difficult to control the orientation of the pores, and the formability during subsequent extrusion molding is deteriorated.

  On the other hand, when the fiber length of the carbon fiber is less than 100 μm, the kneadability is improved, but the orientation of the island-structured carbon fiber may be lost during subsequent extrusion molding, and a controlled porous body can be obtained. It is not preferable because it disappears.

  The amount of carbon fiber added is preferably 50 parts by weight or less with respect to 100 parts by weight of the ceramic material.

  If the amount of carbon fiber exceeds 50 parts by weight, the dimensional change after drying will increase, the common stickiness will disappear, the plasticity of the clay will decrease, clogging inside the extruder and cracking during the drying process will occur Therefore, it is not preferable.

  If it is 50 parts by weight or less, it is possible to adjust the amount of carbon fiber added in accordance with the desired pore density, and if it does not affect the plasticity or pore formation, a powder such as a filler having a desired function Can also be mixed. In addition, the carbon fiber kneading and forming method may use a normal kneading machine, and is not particularly limited.

  Next, the carbon fiber used for the casting method of the present invention will be described in detail.

  The carbon fiber used in the present invention may be either acrylic or pitch, and its mechanical properties are not limited. The carbon content obtained by organic elemental analysis is preferably 90 wt% or more and the ash content is 1 wt% or less. When there is much ash, residues such as tar may remain in the pores formed. In order to prevent abnormal color development of the ceramic body, the content of iron or alkali metal derivatives is preferably 1 wt% or less, and those having the same properties as those used in the extrusion molding method are suitable.

  It is preferable that the temperature at which heating loss under air conditions begins does not fall below 200 ° C.

  When heating loss starts at a temperature below 200 ° C, the carbon fiber disappears before the formation of the basic skeleton of the ceramic body by bonding water evaporation in the clay for ceramics and adhesion of clay particles, and the porous structure is uneven. This is not preferable.

  Although the fiber diameter of carbon fiber is not specifically limited, For example, the diameter in the case of using a normal polyacrylonitrile-type carbon fiber is 10 micrometers or less.

  The carbon fiber used for the casting method is preferably a strand-like continuous fiber. The fiber length is 100 mm as long as it is possible to cast strands by placing a strand in a normal casting mold, or to pass through the slurry and impregnate the slurry between carbon fiber single yarns. The above is preferable.

  In order to sufficiently cast the slurry between single strands of strands, the number of constituents per strand is preferably 100 to 50000 / piece.

  For the production of the ceramic body of the present invention, any of an extrusion molding method and a casting molding method may be used.

  In the case of the extrusion molding method, a process of kneading carbon fibers into clay, a process of extrusion molding, a drying process after molding, a process of unbaking a molded product obtained by drying, and a main baking process as required Consists of.

  In the step of kneading carbon fiber with clay used for extrusion molding, a normal clay kneader can be used, and the water content is preferably 20 wt% to 30 wt% with respect to the clay.

  In the process of extrusion molding, a vacuum extrusion molding machine used for ordinary ceramic molding can be used. An extruder type extrusion method is suitable, and the degree of vacuum is preferably 0.1 kPa or more, and a perforated plate that does not clog can be inserted into the extruded portion.

  The extrusion die may be any of a polygon, a rectangle, a diamond, an ellipse, and a circle. The thickness of the molded body is preferably 200 mm or less. By this extrusion molding, a molded body having a clay in a sea structure and a carbon fiber in an island structure can be obtained. An example of the molded body before sintering is shown in FIGS.

  The casting molding method includes a step of casting slurry into carbon fiber strands, a molding step of impregnating slurry, a drying step after molding, a step of baking the dried molded product, and a main baking step as necessary.

The mold used for molding is not particularly limited as long as the maximum thickness of the molded body is 200 mm or less.
By applying a tension of about 1 kg / st to the carbon fiber strand, the parallelism of the single yarn can be maintained.

  As the impregnation method, a pressure method, a bending roller method, a curved roller method, a fixed guide method, and the like can be used, but the method is not limited thereto.

  The molded product obtained by each molding method can be dried for about a week at room temperature, as in the case of ordinary ceramics, but if it contains a lot of moisture, it may be dried for a longer period of time. .

  The step of baking the molded product obtained by drying is preferably performed at a temperature of 800 ° C. to 1300 ° C. for about 8 to 20 hours under oxidizing conditions.

  Here, the oxidizing condition is an atmosphere containing at least oxygen. The temperature increase rate in the sintering step is preferably 100 ° C./hr to 200 ° C./hr, but is not particularly limited, as in the usual method for producing ceramics. By sintering under such oxidizing conditions, the bonded water in the clay is released, and then the carbon fibers disappear, so that the island structure where the carbon fibers existed has a diameter of 5 to 30 μm and a length of 100 μm or more. It is possible to obtain a ceramic body having the following pore structure.

  In order to adjust the disappearance temperature and conditions of the carbon fibers, it is possible to combine sintering methods including an inert gas such as nitrogen, carbon monoxide, and argon before, during or after oxidation sintering.

  The temperature increase rate in this sintering process is the same as that of a normal ceramic manufacturing method, and is 100 ° C./hr to 200 ° C./hr. The obtained unglazed product may be subjected to main baking after painting or glaze application, and the method may be the same as that for ordinary ceramics.

  The porcelain body thus obtained can be observed in an array state and an array direction of the pores by cutting in a direction perpendicular to the axial direction of the columnar pores using a diamond cutter or the like. The direction perpendicular to the axial direction of the columnar pore is, for example, in the case of the extrusion molding method, the direction perpendicular to the extrusion direction of the molded body. In the casting molding method, the carbon fiber strand fiber length before sintering The direction perpendicular to the vertical direction. The ceramic cut surface is observed with an electron microscope (× 400 times), and the number of holes confirmed in 10 shooting fields (250 μm × 300 μm) and the major axis and minor axis of each hole are measured. An example taken with an electron microscope is shown in FIG.

The ceramic body thus obtained is a particulate matter removal filter, building material, water purification material, insulator,
It can be suitably used for insulation plates, animal and plant growth bases, soil modifiers and fireproof materials.

Hereinafter, the present invention will be described specifically by way of examples. In the examples, each characteristic value was measured by the following method.
<Water absorption rate>
The weight (Ma) of the object to be measured which was dried at 105 ° C. for 2 hours to be in a constant weight state and the weight (Mb) after the measurement body was impregnated in pure water for 24 hours and the moisture on the surface was wiped off Is calculated by the following formula 1.

Water absorption rate = (Mb−Ma) / Ma × 100 (Equation 1)
<Pore density>
The central part of the ceramic body is cut with a diamond cutter in a direction perpendicular to the axial direction of the columnar pores, magnified 400 times using an electron microscope manufactured by JEOL Ltd., and SEM image of 10 fields (250 μm × 300 μm) Did. The number of holes in the image was counted, and the average value (pieces / mm ² ) was defined as the hole density.
<Average pore diameter and roundness>
The central part of the ceramic body is cut with a diamond cutter in a direction perpendicular to the axial direction of the columnar pores, magnified 400 times using an electron microscope manufactured by JEOL Ltd., and SEM photography of 250 μm × 300 μm is performed. Perform 5 fields per cross section and repeat this twice. The major axis (La) and minor axis (Lb) of the pores on the image are measured, and the average value thereof is taken as the average pore diameter. All roundness values observed in the field were calculated by dividing the major axis (La) by the minor axis (Lb).

<Example 1>
1 kg of carbon fiber (MLD-300, average fiber length 300 μm) manufactured by Toray Industries, Inc. is added to about 5 kg of clay (sanuki soil 60 wt%, godomi soil 40 wt%) having an average particle size of 100 μm, and stirred and kneaded for 20 minutes while adding water. A clay containing 17 wt% carbon fiber was obtained. This clay was further obtained by using a vacuum extrusion molding machine. After air-drying for 1 week, the temperature was raised at 200 ° C./hr using an electric kettle, and when the maximum temperature reached 1100 ° C., the temperature was maintained for 1 hr, and then the temperature naturally decreased, and the furnace temperature fell below 100 ° C. At that time, the ceramic body 1 was collected. The dimensions of the ceramic body were 120 mm long × 50 mm wide × 15 mm thick.

  Table 1 shows the results of measuring the average pore diameter, pore density, roundness, and water absorption rate.

<Example 2>
Carbon fiber (MLD-300, average fiber length 300 μm) 0.5 kg made by Toray Co., Ltd. is put into 5 kg of clay (sanuki soil 60 wt%, gomi clay 40 wt%) having an average particle size of 100 μm, and stirred and kneaded for 20 minutes while adding water. As a result, a clay containing 8 wt% of carbon fibers was obtained. This clay was molded and sintered in the same manner as in Example 1 to obtain a ceramic body 2.

  The results of measuring the average pore diameter, pore density, roundness, and water absorption rate according to Example 1 are shown in Table 1.

<Example 3>
0.5kg of carbon fiber (chopped yarn: average fiber length 6mm) made by Toray Industries, Inc. is put into 5kg of clay (sanuki soil 60wt%, gomi soil 40wt%) with an average particle size of 100μm, and stirred and kneaded for 20 minutes while adding water. A clay containing 8 wt% carbon fiber was obtained. This clay was molded and sintered in the same manner as in Example 1 to obtain a ceramic body 3.

  The results of measuring the average pore diameter, pore density, roundness, and water absorption rate according to Example 1 are shown in Table 1.

<Example 4>
2 kg of water glass was added to 1 kg of clay having a mean particle size of 100 μm (60 wt. A carbon fiber (T300-3K) manufactured by Toray Industries, Inc. was expanded to a width of 2 cm on a square mold, and placed with a tension of 1.0 kg / st. It was installed in a casting molding machine, and casting was performed for 20 minutes to obtain a molded body. After air-drying for 1 week, the temperature was raised at 200 ° C./hr using an electric kettle, and when the maximum temperature reached 1100 ° C., the temperature was maintained for 1 hr, and then the temperature naturally decreased, and the furnace temperature fell below 100 ° C. At that time, the ceramic body 4 was collected. The dimensions were length 100 mm × width 25 mm × thickness 10 mm.

  The results of measuring the average pore diameter, pore density, roundness, and water absorption rate according to Example 1 are shown in Table 1.

<Comparative Example 1>
Only a clay having a mean particle size of 100 μm (Sanuki soil 60 wt%, turquoise soil 40 wt%) was molded and sintered in the same manner as in Example 1 using a vacuum extrusion molding machine to obtain a ceramic body 5.

  Table 1 shows the results of measuring the average pore diameter, pore density, roundness, and water absorption rate according to Example 1. The results are shown in Table 1.

<Comparative example 2>
Carbon fiber (MLD-300, average fiber length 300 μm) 0.5 kg made by Toray Co., Ltd. is put into 5 kg of clay (sanuki soil 60 wt%, gomi clay 40 wt%) having an average particle size of 100 μm, and stirred and kneaded for 20 minutes while adding water. As a result, a clay containing 8 wt% of carbon fibers was obtained. This clay was placed in a molding die having a length of 100 mm × width of 25 mm × thickness of 10 mm, press-molded, and dried and sintered in the same manner as in Example 1 to obtain a ceramic body 6.

Table 1 shows the results of measuring the average pore diameter, pore density, roundness, and water absorption rate according to Example 1.
<Comparative Example 3>
Carbon fiber (average fiber length 20mm) 0.5kg made by Toray Co., Ltd. is put into 5kg of clay with average particle size of 100μm (Sanuki soil 60wt%, Gomi soil 40wt%), carbon fiber is stirred and kneaded for 20 minutes while adding water. A clay containing 8 wt% was obtained. When this clay was put into an extrusion molding machine, slit clogging occurred and a molded body could not be obtained.

It is the schematic of a porous body (closed pore) after sintering. It is the schematic of a pre-sintering molded object.

Explanation of symbols

1 Cylindrical pore part 2 Sintered part
3 An example of a line perpendicular to the axial direction of the cylindrical pore (AA ′)
4 Carbon fiber part (island structure)
5 Clay (Midori) part (Sea structure)

Claims (10)

Porous ceramics having cylindrical open pores or closed pores having an average pore diameter of 5 to 30 μm in the ceramics. ^2. The porous ceramic according to claim 1, wherein the pore density of the ceramic section cut in a direction perpendicular to the axial direction of the columnar pores is 10 / mm ² or more and 10000 / mm ² or less. The roundness (La / Lb) composed of a major axis (La) and a minor axis (Lb) of a ceramic section cut in a direction perpendicular to the axial direction of the cylindrical pore is 2.0 or less. Porous ceramics according to 1 or 2. The porous ceramic according to claim 1, wherein the water absorption is 5.0 wt% or more. A method for producing porous ceramics, in which a sea-island-shaped molded body containing ceramic clay for the sea structure and fibers for the island structure is sintered in an oxidizing gas atmosphere. 6. The method for producing a porous ceramic according to claim 5, wherein the fiber used for the island structure is a carbon fiber. 7. The method for producing a porous ceramic according to claim 6, wherein the clay kneaded with carbon fibers is molded by an extrusion method to form a sea-island structure and then sintered. The method for producing a porous ceramic according to claim 7, wherein the carbon fiber forming the island structure is made of short fibers having a fiber length of 10 mm or less. 7. The method for producing a porous ceramic according to claim 6, wherein a carbon fiber strand is formed on the sea structure and the island structure is formed by casting or impregnation molding, followed by sintering. The method for producing a porous ceramic according to claim 9, wherein the carbon fiber forming the island structure has a fiber length of 100 mm or more and is composed of 100 to 50,000 carbon fiber strands.

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