JPWO2015025951A1 - Porous ceramics and method for producing the same - Google Patents

Abstract

An object of the present invention is to provide a porous ceramic that can be processed in a complicated shape and with high accuracy, and that can control the pore diameter and the porosity at the same time, and has high strength, and a method for producing the same. Porous ceramics comprising ceramic particles containing at least one selected from the group consisting of aluminum nitride, silicon carbide, and silicon nitride, wherein the ceramic wall 2 is formed by bonding a part of the ceramic particles; A plurality of independent pores 1 formed by being surrounded by a ceramic wall, and the plurality of independent pores 1 are communicated with each other by a gap 3 having a pore diameter smaller than that of the independent air 1. Is 10 nm or more and 5 μm or less.

Description

  The present invention relates to a novel porous ceramic and a method for producing the same.

  As a method for producing porous ceramics, a method in which ceramic particles are sintered and pores are formed as particle gaps is the most common and widely used. However, in this manufacturing method, since pores are formed by the gaps between the ceramic particles, it is difficult to independently control the pore diameter and the porosity. Moreover, since a hole is formed with sintering, the deformation | transformation at the time of sintering was large, and the complicated shape and the highly accurate process were difficult.

  Also, recently, a method of forming a molded body by molding powder containing alumina hollow particles into a predetermined shape, and sintering the obtained molded body (Patent Document 1), true spherical resin beads as a pore forming agent (Patent Document 2) has been proposed in which ceramic granulated powder is mixed, pressed and molded, degreased and sintered.

JP 2001-002479 A JP 2006-036624 A

  However, in the manufacturing method of Patent Document 1, pores are formed by the crystal phase transition (shape transition) of the alumina hollow particles to the alumina solid particles during the sintering, so that the deformation during the sintering is large and complicated. Shape and high-precision processing were difficult. Further, since the thickness of the ceramic wall is not uniform, there is a problem that the strength is low as compared with a porous ceramic having the same bulk density and a uniform thickness of the ceramic wall.

  In addition, since the manufacturing method of Patent Document 2 uses resin beads as a pore-forming agent and sinters after degreasing, the ceramic granulated powder penetrates into the pores during sintering, resulting in deformation, complicated shape and high Precision machining was difficult.

  Therefore, the present invention provides a porous ceramic that can be processed in a complicated shape and with high accuracy, and that can control the pore diameter, the pore shape, and the porosity independently, and has high strength, and a method for producing the same. It is an object.

  In order to achieve the above object, the present invention provides ceramic particles containing at least one selected from the group consisting of aluminum nitride, silicon carbide, and silicon nitride, and carbonaceous particles on the surface of the carbonaceous particles. After mixing the two so that the ceramic particles adhere uniformly, while pressing the mixture or pressing the mixture, sintering is performed to obtain a sintered body, and then the carbon contained in the sintered body It is characterized by being a porous ceramic produced by oxidizing and burning the porous particles.

  According to the present invention, it is possible to provide a porous ceramic having a high strength and capable of independently controlling the pore diameter, the pore shape and the porosity, and capable of processing a complicated shape and high precision, and a method for producing the same. There are excellent effects.

1 is a structural diagram of a porous ceramic of the present invention. FIG. 6 is a structural diagram of another embodiment of the porous ceramic of the present invention, where (a) is a porous ceramic in which carbonaceous particles are present in some independent pores, and (b) is a carbon for a ceramic material. Porous ceramics in which the weight ratio of the porous material is reduced in the thickness direction. SEM (scanning electron microscope) photograph of material A1 ((a) is 1000 times magnification, (b) is an enlarged view of part B of FIG. 1 (a), and is 5000 times magnification). The graph which shows the relationship between the diameter of the space | gap in material A1, a difference pore volume, and an accumulation pore volume. The X-ray-diffraction figure of material A1. SEM (scanning electron microscope) photograph of material Z1 ((a) is 100 times magnification, (b) is an enlarged view of part C of FIG. 1 (a), and magnification is 1000 times). The graph which shows the relationship between the radius of the space | gap in material A3, and differential pore volume. The graph which shows the relationship between the radius of the space | gap in material A3, and an accumulation pore volume. The graph which shows the relationship between the radius of the space | gap in material Z1, and a difference pore volume. The graph which shows the relationship between the radius of the space | gap in material Z1, and an integrated pore volume.

In the present invention, ceramic particles containing at least one selected from the group consisting of aluminum nitride, silicon carbide, and silicon nitride, and carbonaceous particles are adhered uniformly to the surface of the carbonaceous particles. After mixing the two in this manner, while pressing the mixture or pressing the mixture, the sintered body is obtained by sintering, and then the carbonaceous particles contained in the sintered body are oxidized and burned off. It is manufactured by.
The porous ceramic produced in this manner is obtained by mixing and sintering the carbonaceous particles as the pore-forming agent and the ceramic particles as the raw material of the porous ceramic, that is, after forming the ceramic wall, Since it is oxidized and burned off, it can be processed with a complicated shape and high accuracy with almost no deformation during the formation of porous ceramics.
In the present invention, that the ceramic particles are uniformly attached to the carbonaceous particles means that the ceramic particles are attached to 90% or more of the entire surface of the carbonaceous particles.

  In addition, when carbonaceous particles and ceramic particles, which are pore formers, are mixed, the ceramic thickness due to the ceramic particles adhering around the carbonaceous particles becomes uniform, so that the thickness of the ceramic wall is uniform even after sintering. Become. Therefore, the strength is higher than that of porous ceramics having the same bulk density but non-uniform ceramic wall thickness. As described above, since the strength is very high despite the same bulk density, the porous ceramic of the present invention can be used in various fields (for example, high-strength heat insulating materials, artificial bones, oil filters, crucibles, vacuum chucks, catalysts). Carrier, spray nozzle, lubricating liquid impregnated bearing, etc.).

  Furthermore, by selecting the particle diameter, shape and amount of carbonaceous particles which are pore forming agents, the pore diameter, the pore shape and the porosity can be independently controlled to desired values.

  The porous ceramic of the present invention comprises ceramic particles containing at least one selected from the group consisting of aluminum nitride, silicon carbide, and silicon nitride, and carbonaceous particles. The ceramic particles are on the surface of the carbonaceous particles. A first step of obtaining a mixture by mixing so as to adhere uniformly, and sintering while pressing the mixture, or after pressing the mixture and sintering to obtain a sintered body It can be manufactured through step 2 and a third step of oxidizing and burning out the carbonaceous particles contained in the sintered body.

  The carbonaceous particles are preferably spherical or plate-like natural graphite and artificial graphite, or carbon fiber. The carbonaceous particles may include only one type or a plurality of types. The particle size of the carbonaceous particles is preferably 1 μm or more and 500 μm or less, more preferably 5 μm or more and 50 μm or less, and further preferably 10 μm or more and 30 μm or less. If the particle size of the carbonaceous particles becomes too small, there is a possibility of aggregation. If the carbonaceous particles are agglomerated too much, the ceramic particles cannot uniformly adhere to the surface of the carbonaceous particles when the carbonaceous particles and the ceramic particles are mixed (that is, where the carbonaceous particles and the carbonaceous particles are in close contact). Since ceramic particles are difficult to adhere to), the thickness of the ceramic wall may not be uniform, and the strength of the structure of the porous ceramic may be reduced. On the other hand, if the particle size of the carbonaceous particles becomes too large, the porosity and the pore size of the independent pores become too large, and the strength of the structure of the porous ceramics may be lowered. Furthermore, the particle diameter of the carbonaceous particles is preferably constant. Specifically, the particle size distribution of the carbonaceous particles is preferably 80% or more in the range of ± 10% from the average particle size, and 90% or more in the range of ± 10% from the average particle size. More preferred. When the particle diameter of the carbonaceous particles is constant, the pore diameter of the independent pores existing in the produced porous ceramic is constant, so that a homogeneous porous structure is obtained and the strength is improved.

  The ceramic particles may include all of aluminum nitride, silicon carbide, and silicon nitride, may include any two of them, or may include only one of them. However, the ceramic particles are preferably only one of aluminum nitride, silicon carbide, and silicon nitride. The particle diameter of the ceramic particles is preferably 100 nm or more and 50 μm or less, more preferably 200 nm or more and 5 μm or less, and further preferably 300 nm or more and 1 μm or less. If the particle size of the ceramic particles becomes too small, they may aggregate. If the ceramic particles are too agglomerated, the ceramic particles cannot uniformly adhere to the surface of the carbonaceous particles when the carbonaceous particles and the ceramic particles are mixed (that is, the location where the agglomerated ceramic particles are attached is the amount of the ceramic particles. However, the thickness of the ceramic wall is not uniform, and the strength of the porous ceramic structure may be reduced. On the other hand, if the particle size of the ceramic particles is too large, the carbon particles cannot be covered uniformly, and the strength of the structure of the porous ceramics may be reduced. Further, the particle diameter of the ceramic particles is preferably constant. Specifically, the particle size distribution of the ceramic particles is preferably 80% or more in the range of ± 10% from the average particle size, and more preferably 90% or more in the range of ± 10% from the average particle size. preferable. When the particle diameter of the ceramic particles is constant, the thickness of the ceramic wall existing in the produced porous ceramic becomes more uniform, and the pore diameter of the voids becomes constant, so that the strength is improved.

  The particle size of the ceramic particles is preferably 1/5 or less, more preferably 1/10 or less, of the particle size of the carbonaceous particles. By making the particle size of the ceramic particles sufficiently smaller than the particle size of the carbonaceous particles, the ceramic particles can adhere uniformly to the surface of the carbonaceous particles when the ceramic particles and the carbonaceous particles are mixed. . Therefore, since the thickness of the ceramic wall of the produced porous ceramic becomes uniform, the strength is improved.

  In the first step, the mixing ratio of the carbonaceous particles and the ceramic particles is preferably such that the weight of the carbonaceous particles: the weight of the ceramic particles is 95: 5 to 20:80, and 80:20 to 40: 60 is more preferable. When the weight ratio of the ceramic particles is less than 20 wt% (particularly less than 5 wt%), the amount of ceramic is reduced, so that it is difficult to form the thickness of the ceramic wall uniformly, and the strength may be too low. On the other hand, when the weight ratio of the ceramic particles exceeds 60 wt% (particularly, exceeds 80 wt%), the amount of the ceramic increases, so that it becomes hard and processing may be difficult. By making the weight ratio of the carbonaceous particles and the ceramic particles 95: 5 to 20:80 (particularly 80:20 to 40:60), the porous ceramic having higher strength and easier processing Become.

Further, a sintering aid may be added when mixing the carbonaceous particles and the ceramic particles. Examples of the sintering aid include yttrium oxide such as Y ₂ O ₃ , aluminum oxide such as Al ₂ O _3, calcium oxide such as CaO, silicon oxide such as SiO ₂ , and other rare earth oxides.

  The method for mixing the carbonaceous particles and the ceramic particles is not particularly limited. For example, a gas phase method, a liquid phase method, a solvent mixing method, a mechanical mixing method, a slurry method, or a combination of these methods can be given. Specific examples of the vapor phase method include a chemical vapor deposition method (CVD method) and a conversion method (CVR method). Specific examples of the liquid phase method include a chemical precipitation method. Specific examples of the slurry method include a gel casting method, slip casting, tape casting, and the like.

  In the second step, the method for obtaining the sintered body is not particularly limited. Examples thereof include a discharge plasma sintering method and a hot press method. The firing temperature, firing time, kind of firing atmosphere, firing pressure, and the like can be appropriately set according to the kind, shape, size, and the like of the material to be used. The firing temperature may be 1700 ° C. or higher, for example. The firing temperature is preferably 1700 ° C. or higher and 2100 ° C. or lower, and more preferably 1800 ° C. or higher and 2000 ° C. or lower. The firing time can be, for example, 5 minutes or more and 2 hours or less. The kind of baking atmosphere can be made into inert gas atmosphere, such as a vacuum, nitrogen, argon, for example. The pressure of baking can be 0.01 MPa or more and 50 MPa or less, for example.

  During the sintering, the ceramic particles uniformly adhered to the surface of the carbonaceous particles are sintered to form a ceramic layer that covers the carbonaceous particles three-dimensionally. The ceramic layer preferably has a continuous structure, and more preferably has a three-dimensional network structure. That is, the plurality of carbonaceous particles are preferably integrated by a ceramic wall having a three-dimensional network structure.

  Further, when silicon nitride is included in the ceramic particles, silicon carbide is formed on the surface of the carbonaceous particles by a reaction during sintering. This silicon carbide is formed between a plurality of carbonaceous particles. That is, the plurality of carbonaceous particles are covered with silicon carbide and bonded by silicon carbide by sintering. Note that silicon nitride may remain in the porous ceramic.

  In the third step, all the carbonaceous particles are oxidized and burned, and as shown in FIG. 1 (in FIG. 1, 1 is an independent pore, 2 is a ceramic wall, and 3 is a void communicating between the independent pores). A method for obtaining a porous ceramic is not particularly limited. For example, the method etc. which heat with an atmospheric furnace are mentioned. The temperature and time for oxidizing and burning, the type of atmosphere, the pressure of the atmosphere, and the like can be appropriately set according to the type, shape, size, etc. of the material used. The oxidation burning temperature may be, for example, 500 ° C. or higher, and is preferably 500 ° C. or higher and 1000 ° C. or lower. The oxidation burning time can be, for example, 5 minutes or more and 48 hours or less. The type of the oxidation burnout atmosphere can be, for example, an oxygen pressure controlled atmosphere in which an inert gas such as air, vacuum or nitrogen is mixed. The pressure of the oxidation burnout atmosphere can be set to, for example, 0.01 MPa or more and 10 MPa or less. Further, before performing the third step, the sintered body may be formed into a desired shape by machining, or may be near-net molded by mold molding.

  In the third step, the method for obtaining a porous ceramic as shown in FIGS. 2A and 2B by oxidizing and burning only a part of the carbonaceous particles is not particularly limited (FIG. 2A). In b), 1 is independent pores, 2 is a ceramic wall, 3 is a void communicating between the independent pores, and 4 is a remaining carbonaceous material). For example, rapid heating in an atmospheric furnace, surface oxidation method using a burner flame, and the like can be mentioned. When the porous ceramic shown in FIG. 2B is obtained using a burner flame, the burner flame is sprayed from the direction of the arrow A. Further, before performing the fourth step, the sintered body may be formed into a desired shape by machining, or near-net formed by mold forming.

The porous ceramic of the present invention is a porous ceramic comprising ceramic particles containing at least one selected from the group consisting of aluminum nitride, silicon carbide, and silicon nitride, and a part of the ceramic particles is A ceramic wall formed by bonding and a plurality of independent pores formed by being surrounded by the ceramic wall, the plurality of independent pores being communicated with each other by a gap having a pore diameter smaller than the independent pore diameter, The pore diameter of the void is from 10 nm to 5 μm.
Since the porous ceramic has independent pores and there are voids communicating between the independent pores, for example, when used as an artificial bone, the connectivity between the pores becomes high. Therefore, the new bone can invade to the deep part of the pores at an early stage, and the function as a bone can be recovered early.

When the cumulative pore volume is calculated using the mercury intrusion method, it is desirable that 60% or more of the total cumulative pore volume exists in the range of ± 50% from the average pore diameter of the voids, and particularly 75% or more. It is desirable to exist.
If it is such a structure, when a liquid and gas permeate | transmit and penetrate | invade in porous ceramics, it can permeate | transmit and penetrate smoothly.

The porosity of the porous ceramic is desirably 50% or more and 80% or less. When the porosity is 50% or more and 80% or less, the number of pores is increased, and the advantage of having the structure of the porous ceramic of the present invention having independent pores and voids is further increased. For this reason, when it uses, for example as a high intensity | strength heat insulating material, the heat insulation effect becomes higher. In the present invention, the porosity is a value represented by the following formula (1).
Porosity = [(volume of independent pores + volume of voids) / volume of porous ceramics] × 100 (1)

  The pore diameter of the void is preferably 20% or less of the pore diameter of the independent pore, and the pore diameter of the independent pore is preferably 5 μm or more and 50 μm or less. The independence of the independent pores is maintained when the pore diameter is 20% or less of the pore diameter of the independent pores. Moreover, when the pore diameter of the independent pores is less than 5 μm, the pore diameter of the independent pores becomes too small. For example, when used as a high-strength heat insulating material, air cannot be sufficiently retained in the independent pores. There is a case. On the other hand, if the pore diameter of the independent pores exceeds 50 μm, the pore diameter becomes too large, and the strength of the porous ceramics may be lowered. Furthermore, it is desirable that the pore diameter of the independent pores is constant. When the pore diameter of the independent pores is constant, a homogeneous porous structure is obtained and the strength is improved.

  The thickness of the ceramic wall is preferably 0.1 μm or more and 7 μm or less. When the thickness of the ceramic wall is less than 0.1 μm, the strength of the porous ceramic may become too low. On the other hand, if the thickness of the ceramic wall exceeds 7 μm, the strength becomes too high, and processing may be difficult. Since the ceramic wall has a thickness of 0.1 μm or more and 7 μm or less, it can be easily processed and has a high strength, and thus is particularly suitable for applications such as a high-strength heat insulating material.

  It is desirable that the inner walls of the independent pores have a fine uneven shape. When the inner walls of the independent pores have a fine uneven shape, it becomes easy to carry a catalyst or the like.

  The three-point bending strength is desirably 1 MPa or more and 200 MPa or less. When the three-point bending strength is 1 MPa or more and 200 MPa or less, it can be used for various applications.

  In the porous ceramic of the present invention, a carbonaceous material may remain in some of the independent pores. Further, when the carbonaceous material remains in some of the independent pores, the weight of the carbonaceous material with respect to the ceramic wall from the front surface to the back surface of the porous ceramic as shown in FIG. The ratio may be decreased in an inclined manner. In this way, a part consisting of ceramics only and having a high heat resistance property, and a part having carbonaceous particles as a pore-forming agent remaining in the independent pores of the porous ceramic material and having a high strength property, Porous ceramics laminated without a joint surface are required to have heat resistance and non-carbonization on the outermost surface of the material, and as a whole material, metal surface heat treatment is desired that has a larger surface area and higher strength. It is particularly suitable for applications such as mounts and high-efficiency radiant heat dissipation materials.

Example 1
As carbonaceous particles, spherical graphite particles (average particle size 20 μm, manufactured by Toyo Tanso Co., Ltd.) were used. As ceramic particles, silicon nitride fine particles (average particle diameter 500 nm, manufactured by Ube Industries) were used. Further, as a sintering aid _was used Y 2 _{O 3} and _Al 2 _{O 3.}

Silicon nitride fine particles, Y ₂ O ₃ , and Al ₂ O ₃ were mixed at a weight ratio of 91: 3: 6. Further, these and spherical graphite particles were prepared at a weight ratio of 35:65, and mixed by a solvent mixing method using 1-propanol as a solvent to obtain a mixture. The weight ratio of carbonaceous particles to ceramic particles in this mixture was 63:37. Further, silicon nitride fine particles were uniformly attached to the surface of the spherical graphite particles of the mixture. Next, the obtained mixture was put in a mold and dried to obtain a molded body. Furthermore, the obtained molded body was sintered in a vacuum atmosphere at 1900 ° C. for 5 minutes by a discharge plasma sintering method to obtain a sintered body. As a result of oxidizing this sintered body in an atmospheric furnace at 1000 ° C. for 5 hours, porous silicon carbide was obtained. Carbon disappeared and there was no dimensional change.
The porous ceramic produced in this manner is hereinafter referred to as material A1.
In addition, when the thickness of the ceramic wall of the material A1 was measured at two places, they were 1.3 μm and 6.1 μm.

(Example 2)
As the carbonaceous particles, spherical graphite particles (particle diameter 20 μm, manufactured by Toyo Tanso Co., Ltd.) were used. Silicon carbide fine particles (average particle diameter 600 nm, manufactured by Shinano Denki Smelting Co., Ltd.) were used as ceramic particles. Further, as a sintering aid _was used Y 2 _{O 3} and _Al 2 _{O 3.}

Silicon carbide fine particles, Y ₂ O ₃ , and Al ₂ O ₃ were mixed at a weight ratio of 91: 3: 6. Further, these and spherical graphite particles were prepared at a weight ratio of 50:50, and mixed by a solvent mixing method using 1-propanol as a solvent to obtain a mixture. The weight ratio of carbonaceous particles to ceramic particles in the mixture was 55:45. Further, silicon carbide fine particles were uniformly attached to the surface of the spherical graphite particles of the mixture. Next, the obtained mixture was put in a mold and dried to obtain a molded body. Further, the obtained molded body was sintered by a hot press method at 2000 ° C. for 1 hour in a nitrogen atmosphere to obtain a sintered body. As a result of oxidizing this sintered body at 1000 ° C. for 10 hours in an atmospheric furnace, porous silicon carbide was obtained. Carbon disappeared and there was no dimensional change.
The porous ceramic produced in this manner is hereinafter referred to as material A2.

(Example 3)
As the carbonaceous particles, spherical graphite particles (particle diameter 20 μm, manufactured by Toyo Tanso Co., Ltd.) were used. As ceramic particles, aluminum nitride fine particles (average particle size 500 nm, manufactured by Tokuyama Corporation) were used. Y ₂ O ₃ was used as a sintering aid.

Aluminum nitride fine particles and Y ₂ O ₃ were mixed at a weight ratio of 95: 5. Further, these and spherical graphite particles were prepared at a weight ratio of 20:80, and mixed by a solvent mixing method using 1-propanol as a solvent to obtain a mixture. The weight ratio of carbonaceous particles to ceramic particles in the mixture was 74:26. Further, aluminum nitride fine particles were uniformly attached to the surface of the spherical graphite particles of the mixture. Next, the obtained mixture was put in a mold and dried to obtain a molded body. Furthermore, the obtained molded body was sintered in a vacuum atmosphere at 1900 ° C. for 5 minutes by a discharge plasma sintering method to obtain a sintered body. As a result of oxidizing this sintered body in an atmospheric furnace at 600 ° C. for 24 hours, porous aluminum nitride was obtained. Carbon disappeared and there was no dimensional change.
The porous ceramic produced in this manner is hereinafter referred to as material A3.

(Comparative Example 1)
As carbonaceous particles, spherical graphite particles (average particle size 20 μm, manufactured by Toyo Tanso Co., Ltd.) were used. As ceramic particles, silicon nitride fine particles (average particle diameter 500 nm, manufactured by Ube Industries) were used. Further, as a sintering aid _was used Y 2 _{O 3} and _Al 2 _{O 3.}

Silicon nitride fine particles, Y ₂ O ₃ , and Al ₂ O ₃ were mixed at a weight ratio of 91: 3: 6. Further, these and spherical graphite particles were prepared at a weight ratio of 35:65, and mixed for 24 hours by a dry mixing method using a ball mill to obtain a mixture. The weight ratio of carbonaceous particles to ceramic particles in the mixture was 63:37. Further, the silicon nitride fine particles were not uniformly adhered to the surface of the spherical graphite particles of the mixture, and were partially agglomerated. Next, the obtained mixture was put in a mold and dried to obtain a molded body. Furthermore, the obtained molded body was sintered in a vacuum atmosphere at 1900 ° C. for 5 minutes by a discharge plasma sintering method to obtain a sintered body. As a result of oxidizing this sintered body in an atmospheric furnace at 1000 ° C. for 5 hours, porous silicon carbide was obtained. Carbon disappeared and there was no dimensional change.
The porous ceramic thus produced is hereinafter referred to as material Z1.
In addition, when the thickness of the ceramic wall of the material Z1 was measured in two places, they were 1.8 μm and 11.1 μm.

(Experiment 1)
The average pore diameter, porosity, average pore diameter of independent pores, bulk density, ceramic wall thickness, and three-point bending strength in the materials A1 to A3 and Z1 were examined. The results are shown in Table 1. In addition, each said physical property was measured in the following way.

[Average pore diameter]
The average pore diameter of the voids was measured by a mercury intrusion method according to JIS R 1655: 2003. The measurement pressure was 0.003 to 379 MPa. For material A1, the pore size distribution of the voids is shown in FIG.

[Porosity]
The porosity was measured according to JIS R 1655: 2003 by the mercury intrusion method. The measurement pressure was 0.003 to 379 MPa.

[Average pore diameter of independent pores]
The pore diameter of the independent pores was obtained from the microstructural observation photograph of the porous ceramics by SEM, and the average value was calculated.

[Bulk density]
The bulk density was measured by the Archimedes method. Specifically, it measured based on JIS A1509-3.

[Ceramic wall thickness]
Two ceramic wall thicknesses were measured from SEM (scanning electron microscope) photographs. In addition, the SEM (scanning electron microscope) photograph of the material A1 is shown in FIGS. 3A and 3B [(a) magnification 1000 times (b) magnification 5000 times)], and the SEM (scanning electron microscope) photograph of the material Z1. Is shown in FIGS. 6 (a) and 6 (b) [(a) magnification 100 times (b) magnification push 1000 times].

[3-point bending strength]
The bending strength was measured by a three-point bending strength test. Specifically, it measured based on JIS A1509-4.

  Moreover, since the X-ray diffraction of material A1 was performed, the result is shown in FIG.

  In Table 1, when comparing the material A1 and the material Z1, the three-point bending strength is about 1.4 times that of the material Z1 even though the porosity and bulk density are the same. It can be seen that this is a porous ceramic. Further, when comparing the material A2 and the material Z1, the material A2 has a porosity reduced by 20% and the bulk density is only about 1.7 times that of the material Z1, but the bending strength is 10 times. As described above, it can be seen that the porous ceramics has a very high strength. In addition, although the material A3 has a bending strength as low as 2 MPa, it was difficult to obtain porous ceramics having a porosity of 80% with the prior art. Therefore, in the method for producing porous ceramics according to the present invention, It was found that porous ceramics having a rate of 80% or more can be produced.

As is clear from FIG. 3A, in the material A1, it is understood that spherical independent pores having a diameter of about 20 μm are formed by ceramic walls that are three-dimensionally connected. Moreover, it turns out that the thickness of a ceramic wall is 1.3-6.1 micrometers. Furthermore, it can be seen from FIG. 3B that the inner walls of the independent pores have a fine uneven shape.
On the other hand, as is apparent from FIGS. 6A and 6B, the material Z1 does not have a structure formed by ceramic walls in which spherical independent pores are three-dimensionally connected, and has an uneven pore structure. It can be seen that

  As is clear from FIG. 4, in the material A1, the average pore diameter of the voids is 2.1 μm from the Incremental Intrusion curve (differential pore volume distribution curve), and all the fine pores are within the range of ± 50% from the average pore diameter. It can be seen that 62% of the pore volume is present. In addition, the distribution of Incremental Intrusion having a pore diameter of about 100 to 400 μm is due to mercury pressed into the concave portion of the sample surface. Moreover, it turned out that the hole diameter of a space | gap has a magnitude | size of 10.5% of an independent pore compared with said independent pore diameter. The total porosity was analyzed as 70% from the Cumulative Induction curve (integrated pore volume distribution curve).

  As is clear from FIG. 5, the material A1 of the present invention has a peak at the position shown in Table 2, and therefore it can be seen that the material A1 of the present invention is composed only of silicon carbide.

(Experiment 2)
In the materials A3 and Z1, the relationship between the radius of the void and the accumulated pore volume and the relationship between the radius of the void and the differential pore volume were examined, and the results are shown in FIGS. In addition, the experiment method was performed by the method similar to the method shown in the above [Experiment 1 average pore diameter]. Further, when the integrated pore volume is calculated using the mercury intrusion method, the ratio (%) of the integrated pore volume to the total integrated pore volume in the range of ± 50% from the average pore diameter of the voids is shown in FIGS. It calculated using.

As shown in FIG. 8, in the case of the material A3, the average pore diameter (radius) of the void is 2.16 μm, −50% of the average pore diameter of the void is 1.08 μm, and + 50% of the average pore diameter of the void is 3.24 μm. It is. The cumulative pore volume when the average pore diameter of the voids is 1.08 μm is 1.02 mL / g, and the cumulative pore volume when the average pore diameter of the voids is 3.24 μm is 0.07 mL / g, Furthermore, the total cumulative pore volume is 1.19 mL / g. Therefore, the ratio (%) of the cumulative pore volume in the range of ± 50% from the average pore diameter of the voids with respect to the total cumulative pore volume is as shown in the following formula (2).
[(1.02-0.07) /1.19] × 100 = 79.8 (%) (2)

As shown in FIG. 10, in the case of the material Z1, the average pore diameter is 2.18 μm, −50% of the average pore diameter is 1.09 μm, and + 50% of the average pore diameter is 3.27 μm. is there. Further, the cumulative pore volume when the average pore diameter of the voids is 1.09 μm is 0.58 mL / g, and the cumulative pore volume when the average pore diameter of the voids is 3.27 μm is 0.18 mL / g, Furthermore, the total cumulative pore volume is 0.73 mL / g. Therefore, the ratio (%) of the cumulative pore volume in the range of ± 50% from the average pore diameter of the voids with respect to the total cumulative pore volume is as shown in the following formula (3).
[(0.58−0.18) /0.73] × 100 = 54.8 (%) (3)
It is obvious from the graphs of FIGS. 7 and 9 that such a result is obtained.

  The porous ceramics of the present invention include a high-strength heat insulating material, an artificial bone, an oil filter, a crucible, a vacuum chuck, a catalyst carrier, a spray nozzle, a lubricant-impregnated bearing, a metal heat treatment stand, a high-efficiency radiation heat dissipation material, and a reactor wall It can be used as a material, a containment vessel, etc.

1: independent pores 2: ceramic wall 3: voids communicating between independent pores 4: carbonaceous material remaining in independent pores

[0008]
A combined oxygen pressure controlled atmosphere can be obtained. The pressure of the oxidation burnout atmosphere can be set to, for example, 0.01 MPa or more and 10 MPa or less. Further, before performing the third step, the sintered body may be formed into a desired shape by machining, or may be near-net molded by mold molding.
[0025]
In the third step, the method for obtaining a porous ceramic as shown in FIGS. 2A and 2B by oxidizing and burning only a part of the carbonaceous particles is not particularly limited (FIG. 2A). In b), 1 is independent pores, 2 is a ceramic wall, 3 is a void communicating between the independent pores, and 4 is a remaining carbonaceous material). For example, rapid heating in an atmospheric furnace, surface oxidation method using a burner flame, and the like can be mentioned. When the porous ceramic shown in FIG. 2B is obtained using a burner flame, the burner flame is sprayed from the direction of the arrow A. Further, before performing the fourth step, the sintered body may be formed into a desired shape by machining, or near-net formed by mold forming.
[0026]
The porous ceramic of the present invention is a porous ceramic comprising ceramic particles containing at least one selected from the group consisting of aluminum nitride, silicon carbide, and silicon nitride, and a part of the ceramic particles is A ceramic wall formed by bonding and a plurality of independent pores formed by being surrounded by the ceramic wall, the plurality of independent pores being communicated with each other by a gap having a pore diameter smaller than the independent pore diameter, The pore diameter is 10 nm or more and 5 μm or less, and the pore diameter is 20% or less of the pore diameter of the independent pores.
Since the porous ceramic has independent pores and there are voids communicating between the independent pores, for example, when used as an artificial bone, the connectivity between the pores becomes high. Therefore, the new bone can invade to the deep part of the pores at an early stage, and the function as a bone can be recovered early. In addition, the independence of the independent pores is maintained when the pore diameter is 20% or less of the pore diameter of the independent pores.
[0027]
When the cumulative pore volume is calculated using the mercury intrusion method, it is desirable that 60% or more of the total cumulative pore volume exists in the range of ± 50% from the average pore diameter of the voids, and particularly 75% or more. It is desirable to exist.
With such a configuration, liquid or gas can permeate and immerse into the porous ceramics.

[0009]
When entering, it can penetrate and penetrate smoothly.
[0028]
The porosity of the porous ceramic is desirably 50% or more and 80% or less. When the porosity is 50% or more and 80% or less, the pore portion is increased, and the advantage of having the structure of the porous ceramic of the present invention having independent pores and voids is further increased. For this reason, when it uses, for example as a high intensity | strength heat insulating material, the heat insulation effect becomes higher. In the present invention, the porosity is a value represented by the following formula (1).
Porosity = [(volume of independent pores + volume of voids) / volume of porous ceramics] × 100 (1)
[0029]
The pore diameter of the independent pores is preferably 5 μm or more and 50 μm or less. When the pore size of the independent pores is less than 5 μm, the pore size of the independent pores becomes too small. For example, when used as a high-strength heat insulating material, the air may not be sufficiently retained in the independent pores. is there. On the other hand, if the pore diameter of the independent pores exceeds 50 μm, the pore diameter becomes too large, and the strength of the porous ceramics may be lowered. Furthermore, it is desirable that the pore diameter of the independent pores is constant. When the pore diameter of the independent pores is constant, a homogeneous porous structure is obtained and the strength is improved.
[0030]
The thickness of the ceramic wall is preferably 0.1 μm or more and 7 μm or less. When the thickness of the ceramic wall is less than 0.1 μm, the strength of the porous ceramic may become too low. On the other hand, if the thickness of the ceramic wall exceeds 7 μm, the strength becomes too high, and processing may be difficult. Since the ceramic wall has a thickness of 0.1 μm or more and 7 μm or less, it can be easily processed and has a high strength, and thus is particularly suitable for applications such as a high-strength heat insulating material.
[0031]
It is desirable that the inner walls of the independent pores have a fine uneven shape. The inner walls of the independent pores have a fine uneven shape, which makes it easier to support a catalyst or the like.

Claims (14)

  Ceramic particles containing at least one selected from the group consisting of aluminum nitride, silicon carbide, and silicon nitride, and carbonaceous particles are bonded together so that the ceramic particles are uniformly attached to the surface of the carbonaceous particles. After mixing, while pressing the mixture or after pressing the mixture, it is sintered to obtain a sintered body, and then manufactured by oxidizing and burning out the carbonaceous particles contained in the sintered body. Porous ceramics characterized by that.   The porous ceramic according to claim 1, wherein a part of the carbonaceous particles remains. Porous ceramics comprising ceramic particles containing at least one selected from the group consisting of aluminum nitride, silicon carbide, and silicon nitride,
A ceramic wall formed by bonding a part of the ceramic particles;
A plurality of independent pores formed by being surrounded by the ceramic wall;
Have
The plurality of independent pores are communicated with each other by a gap having a pore size smaller than the independent pore size,
A porous ceramics characterized in that the pore diameter of the voids is 10 nm or more and 5 μm or less.   The porous ceramics according to claim 3, wherein when the cumulative pore volume is calculated using a mercury intrusion method, 60% or more of the total cumulative pore volume exists in a range of ± 50% from the average pore diameter of the voids. .   The porous ceramics according to claim 4, wherein when the cumulative pore volume is calculated using a mercury intrusion method, 75% or more of the total cumulative pore volume exists in a range of ± 50% from the average pore diameter of the voids. .   The porous ceramics according to any one of claims 3 to 5, wherein the porosity is 50% or more and 80% or less.   The porous ceramics according to any one of claims 3 to 6, wherein a pore diameter of the voids is 20% or less of a pore diameter of the independent pores, and a pore diameter of the independent pores is 5 µm or more and 50 µm or less.   The porous ceramic according to any one of claims 3 to 7, wherein a thickness of the ceramic wall is 0.1 µm or more and 7 µm or less.   The porous ceramic according to any one of claims 3 to 8, wherein an inner wall of the independent pore has a fine uneven shape.   The porous ceramic according to any one of claims 3 to 9, wherein a three-point bending strength is 1 MPa or more and 200 MPa or less.   The porous ceramic according to any one of claims 3 to 10, wherein a carbonaceous material is present in some of the independent pores.   The porous ceramic according to claim 11, wherein a weight ratio of the carbonaceous material with respect to the ceramic wall is gradually decreased in a thickness direction. Ceramic particles containing at least one selected from the group consisting of aluminum nitride, silicon carbide, and silicon nitride, and carbonaceous particles are mixed so that the ceramic particles uniformly adhere to the surface of the carbonaceous particles. A first step of obtaining a mixture;
Sintering while pressing the mixture, or sintering after pressing the mixture to obtain a sintered body;
A third step of oxidizing and burning out the carbonaceous particles contained in the sintered body;
A method for producing porous ceramics, comprising:   The method for producing porous ceramics according to claim 13, wherein in the third step, the carbonaceous particles are oxidized and burned so as to leave a part of the carbonaceous particles.

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