JP4980299B2 - Silicon carbide based porous material - Google Patents

Description

  The present invention relates to a silicon carbide based porous material, and more particularly to a silicon carbide based porous material used as a base for a diesel particulate filter.

  A diesel particulate filter (hereinafter referred to as “DPF”) that collects and removes particulate matter (particulate matter, hereinafter referred to as “PM”) contained in gas discharged from a diesel engine is a ceramic. A honeycomb structure in which a plurality of cells partitioned by porous body partition walls are arranged. When gas passes through the partition walls of the honeycomb structure, PM is collected and removed in the pores of the ceramic porous body. . As the porous ceramic body serving as the DPF substrate, a silicon carbide based porous ceramic body is frequently used because of its low thermal expansion coefficient and excellent heat resistance, thermal conductivity, and thermal shock resistance. Further, since silicon carbide is a semiconductor, when a predetermined amount of collected PM is deposited, a regeneration process is performed in which heat is generated by energization to burn the PM.

  In the DPF, if the pore size of the ceramic porous body is too large, PM that passes through the partition without being collected increases, and the collection efficiency decreases. On the other hand, if the pore diameter is too small, the pressure loss increases due to the resistance to the passage of gas, and the engine is loaded. Therefore, a filter in which the pore diameter of the ceramic porous body constituting the partition wall is controlled has been proposed (see, for example, Patent Document 1 and Patent Document 2).

  These filters are generally suitable for collecting PM with a particle size (diameter) of 0.1 to 0.3 μm by setting the pore diameter of the partition walls to be within a limited narrow range. The average number of pore diameters measured by mercury porosimetry is 1 μm to 15 μm in the former (Patent Document 1), and 20 μm to the latter (Patent Document 2). The standard deviation in the pore size distribution when the pore size is expressed as a common logarithm is 60 μm, and both are 0.20 or less.

Japanese Patent No. 3272746 JP 2002-242655 A

  However, high collection efficiency and suppression of an increase in pressure loss are contradictory requirements, and it has been insufficient to achieve the harmony even with the above-described filter. In recent years, environmental regulations have been tightened to limit the number of PMs in exhaust gas, and PM collection leakage in new DPFs or DPFs immediately after regeneration, that is, DPFs in the initial stage of use, has been reduced. There is a strong demand for reduction.

  Therefore, in view of the above circumstances, the present invention is a silicon carbide based porous material used as a base of a diesel particulate filter, which has a high collection efficiency and suppresses an increase in pressure loss, and is an initial stage of use. It is an object of the present invention to provide a silicon carbide based porous material that can reduce PM collection leakage.

  In order to solve the above-mentioned problems, the silicon carbide based porous material according to the present invention is “a silicon carbide based porous material used as a base of a diesel particulate filter and measured as an equivalent circular area diameter by an image analysis method. The mode diameter of the pore number distribution with respect to the pore diameter is 8 ± 1 μm, and the total volume of the pores having the pore diameter of 40 μm to 50 μm occupies 10% or more of the total pore volume ”. The “silicon carbide based porous material” of the present invention means “a porous body of silicon carbide based ceramic material”.

  According to the above configuration, the porous silicon carbide of the present invention has a pore mode diameter (most frequent diameter) as small as 8 ± 1 μm, and a large pore having a pore diameter of 40 μm to 50 μm is 10% by volume. Since it is the structure included above, it is the structure in which many small pores and large pores are mixed. In other words, the large pores are present in a relatively dense matrix in which many small pores are dispersed.

  As described above, in the conventional DPF, it has been desirable to control the pore diameter “within a limited narrow range” and “equalize the pore diameter”. Contrary to such conventional common knowledge, the inventors of the present invention have a collection efficiency by making a silicon carbide porous material in which large pores are intentionally dispersed in a relatively dense matrix having small pore sizes. It has been found that a DPF can be realized in which the increase in pressure loss is suppressed to a high level and the PM collection leakage in the initial stage of use is reduced.

  Here, the silicon carbide based porous material in which large pores are dispersed in a relatively dense matrix is composed of a silicon nitride powder as a silicon source that causes silicon carbide to react with a silicon carbide powder as an aggregate, and a carbon source as a carbon source. In the method of forming and firing by adding a mixed powder of carbonaceous material, it can be produced by using a carbonaceous solid powder having a large particle size as a carbon source and simultaneously using the carbonaceous solid powder as a pore-forming agent. .

  This production method is a novel method for producing a silicon carbide based porous material researched and developed by the present inventors, and is proposed separately from the present application. Conventionally, when silicon carbide is reactively sintered from a silicon source and a carbon source, it has been common knowledge of those skilled in the art that it is easier to react with a silicon source if fine particles are used as the carbon source. Use carbon solid powder with a large particle size as a carbon source, although the initiation reaction of silicon carbide is slower than when the carbon source is a fine particle, but the generated silicon carbide particles can form a neck. It has been found that it can grow rapidly and can form a strong neck, and has led to the invention of the above production method. In this production method, large particles having an average particle diameter of 10 to 50 μm can be suitably used as the carbonaceous solid powder. Further, as the carbonaceous solid, graphite, coal, coke, charcoal, etc. can be used, but high purity graphite is desirable, natural or various particle shapes such as scaly, granular, massive, amorphous, spherical, etc. Synthetic graphite can be used. The shape of the carbonaceous solid powder is not limited to a spherical shape, but the “average particle diameter” can be obtained as a diffraction scattering diameter.

  Next, the silicon carbide based porous material according to the present invention has a ant nest-like shape in which “the large pores having a pore diameter of 40 μm to 50 μm are connected by small pores having a pore diameter of 5 μm to 20 μm”. Having a pore structure ".

  The term “ant's nest” refers to a structure in which large pores are intricately connected by a large number of small pores, resembling an insect ant nest in which multiple small chambers are intricately connected by a passageway. It is what was expressed.

  Here, the speed of the fluid flowing through the flow path is high when the diameter of the flow path is small, and is slow when the diameter of the flow path is wide. Therefore, in the present invention configured as described above, the PM carried by the gas flowing through the narrow flow path formed by the small-diameter pores is decelerated by the gas flowing into the large-diameter pores and decelerating. Easy to adhere to the inner wall. And since the volume of a large diameter pore is large, many PM can be collected inside. Further, PM that has not been collected by the large-diameter pores is further carried downstream by the gas that is accelerated in the flow path by the small-diameter pores communicating with the large-diameter pores, and is collected downstream. As described above, the silicon carbide based porous material of the present invention has an extremely high trapping efficiency due to the complex connection of small-sized pores and large-sized pores to form an ant nest-like pore structure. If it is high, an increase in pressure loss is suppressed at that time.

  As described above, the effect of the present invention is a silicon carbide based porous material used as a base for a diesel particulate filter, which has a high collection efficiency and suppresses an increase in pressure loss, and at an initial stage of use. It is possible to provide a silicon carbide based porous material that can reduce PM leakage.

  Hereinafter, a silicon carbide based porous material and a method for producing the silicon carbide based porous material according to the best embodiment of the present invention will be described. The silicon carbide based porous material of the present embodiment is a silicon carbide based porous material used as a base of a diesel particulate filter, and the mode diameter of the pore number distribution with respect to the pore diameter measured as a circular area equivalent diameter by an image analysis method. Is 8 ± 1 μm, and the total volume of pores having a pore diameter of 40 μm to 50 μm occupies 10% or more of the total pore volume. In addition, the silicon carbide based porous material of the present embodiment has an ant nest-like pore structure in which large pores having a pore diameter of 40 μm to 50 μm are connected by small pores having a pore diameter of 5 μm to 20 μm. Have.

  The silicon carbide based porous material having the above structure can be manufactured by the following manufacturing method. That is, in the method for producing a silicon carbide based porous material of the present embodiment (hereinafter simply referred to as “production method”), the silicon carbide powder 65 to 95 mass% as an aggregate is mixed with a molar ratio of silicon and carbon (Si / C) A molding step of mixing and molding a silicon nitride powder and a carbonaceous solid powder having a ratio of 0.5 to 1.5, a drying step of drying the molded body obtained in the molding step, and a dried molded body of 1800 A firing step of firing only once in a non-oxidizing atmosphere at ˜2200 ° C. and a decarburizing step performed in an oxidizing atmosphere after the firing step and burning the remaining carbonaceous solid powder. The carbonaceous solid powder has an average particle diameter (diameter) of 10 to 50 μm, and the blending amount thereof is 1 to 1 based on the total mass of the silicon carbide powder, the silicon nitride powder, and the carbonaceous solid powder as an aggregate. 10% by weight is used.

  The manufacturing method will be described in more detail. In the molding process, an organic binder such as methylcellulose and an additive such as moisture are added to the silicon carbide powder, silicon nitride powder, and carbonaceous solid powder as aggregates, and mixed and mixed. A molded product is obtained by extruding the smelted raw material kneaded product. Moreover, a drying process can be performed by the ventilation drying in a temperature control humidity control tank, external heating drying, internal heating drying by microwave irradiation, etc.

  In the firing step, the heating furnace is set to a non-oxidizing atmosphere, the temperature is raised at a speed that does not give a thermal shock to the molded body, and the temperature is maintained at a predetermined firing temperature of 1800 to 2200 ° C. for a certain period of time. The firing time can be, for example, 30 minutes to 4 hours, depending on the size of the molded body. In this firing step, silicon nitride as a silicon source and a carbonaceous solid as a carbon source react to form silicon carbide, and reactive sintering is performed so as to surround the silicon carbide as an aggregate. At the same time, pores are formed in the trace of the carbonaceous solid used in the silicon carbide production reaction. Further, silicon carbide particles grow to such an extent that necks can grow between the particles. After holding at the firing temperature for a predetermined time, the temperature is lowered at a speed that does not give a thermal shock.

  In the decarburization step, the sintered body is heated at a speed that does not give a thermal shock in a heating furnace in an oxidizing atmosphere, held at 650 to 900 ° C. for 1 to 3 hours, and then cooled at a speed that does not give a thermal shock. In this decarburization step, carbonaceous solids that remain without being used in the silicon carbide production reaction are burned and removed, and pores are also formed in the traces.

  In the forming step, the formed body can be formed into a honeycomb structure including a plurality of cells partitioned by a plurality of partition walls extending in a single direction. Further, in the honeycomb structure formed body, when sealing one end of the cell so that the cell opened in one direction and the cell opened in the other direction are alternated, between the molding process and the drying process, or A sealing step can be provided after the drying step.

  In addition, a plurality of honeycomb structure sintered bodies obtained through the firing step are bonded with an adhesive, and the outer peripheral surface is processed, and a coating step is applied to the outer peripheral surface to form a coating layer. be able to. In that case, it can replace with said decarburization process and can be set as the decarburization and joining part heat processing process which performs heat processing, such as heat hardening of an adhesive agent and a coating agent, simultaneously with decarburization.

  Next, the DPF of a specific example using the silicon carbide based porous material of the present embodiment will be described in comparison with the DPF (commercial product) of the control example using the same silicon carbide based porous material. The DPF of this example (hereinafter referred to as “Filter-A”) was manufactured as follows. First, the kneaded product of the raw materials shown in Table 1 was extruded into a honeycomb structure, and one end of the cells of the honeycomb structure was sealed with substantially the same raw material to obtain a filter element molded body. About the obtained molded object, the above-mentioned baking process and decarburization process were performed through the drying process and the degreasing process, and the sintered compact of the filter element was obtained. The obtained sintered body of filter elements was canned after joining a predetermined number and providing a coating layer of cement on the outer peripheral surface. Here, the size of Filter-A was 5.66 inch in diameter × 6 inch in length, the partition wall thickness was 0.38 mm, and the cell density was 169 cpsi. In this example, graphite having a scaly particle shape was used as the carbonaceous solid, and the average particle diameter was evaluated as a diffraction scattering diameter by a laser diffraction scattering method.

  On the other hand, the silicon carbide porous body of the base of the control DPF (hereinafter referred to as “Filter-B”) is obtained by sintering a compression molded body of silicon carbide powder by evaporation condensation and surface diffusion mechanism. Yes (recrystallization method). Further, the size of Filter-B was the same as that of Filter-A, the thickness of the partition wall was 0.36 mm, and the cell density was 178 cpsi, which was almost the same as that of Filter-A.

The following evaluation was performed about Filter-A and Filter-B.
<Powder X-ray diffraction> Using a powder X-ray diffractometer (RINT III type) manufactured by Rigaku Corporation, a powder X-ray diffraction pattern was measured at an output of 40 kV, 40 mA and a scan speed of 6 ° / min. The crystal phase of the sintered body was identified.
<Pore diameter distribution by image analysis> A three-dimensional pore diameter distribution was analyzed using a tomographic image obtained by X-ray CT. L8321 manufactured by Hamamatsu Photonics was used as the microfocus X-ray tube, C7876 manufactured by Hamamatsu Photonics was used as the X-ray detector, and XVS manufactured by Uni-Height System was used as the CT data reconstruction system. As software used for the three-dimensional image analysis, TRI / 3D-BON manufactured by Ratok System Engineering was used.

<Thermal shock resistance test> A DPF is attached to a diesel engine (QD32 type manufactured by NISSAN), and the engine is operated at a rotational speed of 1400 rpm and a torque of 200 Nm to deposit 10 g of PM per liter of filter volume. Next, the engine was operated at a rotational speed of 3000 rpm and a torque of 190 Nm. When the temperature reached about 680 ° C., the engine was idling at once, and PM was burned in an oxygen excess state. Thereafter, the engine was cooled by idling, and the DPF was taken out at 100 ° C. or lower, and canned and cut, and the presence or absence of cracks was confirmed.
<Initial collection rate test> Similar to the thermal shock resistance test, DPF is attached to a diesel engine, and a sufficiently warmed engine is operated at a rotation speed of 1400 rpm and a torque of 200 Nm, and is included in the gas discharged from the DPF in the initial 2 minutes. The number concentration of PM to be measured was measured by EEPROM (Engine Exhaust Particle Sizer: TSI Model 3090).
<Pressure loss> Pressure caused by an increase in the amount of accumulated PM by allowing a gas containing PM to flow at a flow rate of 5 Nm ³ / min through a DPF installed in the gas flow path and measuring the pressure on the upstream side and the pressure on the downstream side. The change in loss was measured.

<Average pore diameter by mercury intrusion method> Using a mercury porosimeter (manufactured by Micromeritics, Autopore IV9500), the pore diameter distribution measured by the mercury intrusion method was used as the mode diameter (most frequent diameter, diameter).
<Apparent Porosity> In measuring the average pore diameter by the mercury intrusion method, the porosity was calculated from the volume of mercury pressed into the sample and the sample volume.
<Three-point bending strength at normal temperature> A test piece of 2 cells × 3 cells × 40 cm was cut out from the DPF and measured at a distance between supporting points of 30 mm and a crosshead speed of 0.5 mm / min in accordance with JIS R1601.
<Electron Microscope Observation> A scanning electron microscope (JXA-840 type, manufactured by JEOL Ltd.) was used to observe the fracture surface and the upstream surface after the initial collection rate test.

  The results of powder X-ray diffraction are shown in FIG. Filter-A was recognized as a crystal composed of a single phase of α-SiC, and it was confirmed that there was no unreacted silicon nitride or the like.

  As shown in Table 2, the average pore diameter (diameter) and apparent porosity determined by the mercury intrusion method were almost the same for Filter-A and Filter-B.

  FIG. 2 shows an observation image (hereinafter, simply referred to as “SEM image”) of the fracture surface with a scanning electron microscope. In Filter-A (FIG. 2A), it was observed that large pores were dispersed in a relatively dense matrix of small particles of uniform size. This is because, in Filter-A, since silicon carbide is reactively sintered, the sintering temperature is lower than that in the control example by the recrystallization method, and therefore abnormal particle growth is suppressed. it was thought. The large pores dispersed in the matrix were thought to be formed in the combustion traces of graphite used as a pore forming agent as well as a carbon source for reaction sintering. Then, scattered large-diameter pores were connected by small pores in the matrix, and it was observed that a so-called “ant nest-like” pore structure was formed.

  On the other hand, in Filter-B (FIG. 2 (b)), it is observed that the sizes of the matrix particles are uneven, including large particles that have grown abnormally, and pores of almost uniform size are observed therein. It was dispersed. The pore size of Filter-B was smaller than the large pores in Filter-A and larger than the small pores in the Filter-A matrix.

  The pore distribution as described above also appeared in the pore distribution obtained by image analysis. Here, the pore size distribution expressed by the number of pores is shown in FIG. 3, and the pore size distribution expressed by volume% with respect to the total pore volume is shown in FIG. As can be seen from FIG. 3, the mode diameter by image analysis is about 8 μm for both Filter-A and Filter-B, but Filter-A has a larger number of pores than Filter-B on the small diameter side of 5 to 20 μm. In addition, it had a characteristic peak around 15 μm. In addition, as can be seen from FIG. 4, Filter-A has a larger volume ratio of pores having diameters of 10 to 20 μm and 40 to 50 μm than Filter-B. Specifically, in Filter-A, the ratio of the total volume of pores having a diameter of less than 10 μm to the total pore volume is about 3.5%, and the total volume of pores having a diameter of 10 μm or more and less than 20 μm is occupied by the total volume of pores. The ratio is about 26%, the ratio of the total volume of pores having a diameter of 20 μm to less than 40 μm to the total pore volume is about 59%, and the ratio of the total volume of pores having a diameter of 40 μm to less than 50 μm to the total pore volume is about 11%. Met.

  On the other hand, as apparent from FIG. 4, the volume ratio of pores having a diameter of 20 to 40 μm was larger in Filter-B than in Filter-A. Specifically, the ratio of the total volume of pores having a diameter of less than 10 μm to the total pore volume is about 3.4%, and the ratio of the total volume of pores having a diameter of 10 μm to less than 20 μm to the total pore volume is about 22%. The ratio of the total volume of pores having a diameter of 20 μm to less than 40 μm to the total pore volume was about 69%, and the ratio of the total volume of pores having a diameter of 40 μm to less than 50 μm to the total pore volume was about 4.8%. .

  In summary, the silicon carbide based porous body of the base of Filter-A has a characteristic configuration in which a diameter of 40 to 40 is contained in a matrix of silicon carbide particles of almost uniform size without abnormal particle growth. 50 μm large pores (hereinafter referred to as “L-pore”) are scattered, and a plurality of small pores having a diameter of 5 to 20 μm (hereinafter referred to as “S-pore”) are used as a plurality. It can be considered to have an ant nest-like pore structure in which L-pores are connected.

  On the other hand, the basic structure of the silicon carbide porous body of the base of Filter-B is a medium of irregularly sized silicon carbide particles including abnormally grown particles with a diameter of 20 to 40 μm. It is considered that the pores having a certain size (hereinafter referred to as “M-pore”) are dispersed. That is, as described above with reference to Table 2, Filter-A and Filter-B have substantially the same average pore diameter and porosity, but are greatly different in pore distribution and pore structure.

  The results of the initial collection rate test are shown in FIGS. Here, FIG. 5 is a graph showing the change over time of the number of PM leaked without being collected by the DPF, and FIG. 6 is a graph showing the measurement result including the particle size distribution of the PM leaked without being collected. It is. In FIG. 6, the X axis indicates the particle diameter (diameter) of PM, the Y axis indicates the number of PMs, and the Z axis indicates the passage of time toward the front side of the page. As is clear from these figures, Filter-A has a smaller number of PM leaking without being collected in the initial stage than Filter-B. Specifically, the number of collection leakage PMs in Filter-A immediately after the start of use is about ½ of Filter-B, and the number of collection leakages does not decrease any more until it reaches about 2 million. The time was about 75 seconds for Filter-B, and about half that for Filter-A. In addition, the collected PM had many particle diameters of about 80 nm for both Filter-A and Filter-B.

  As described above, the reason for the difference in the initial collection rate between Filter-A and Filter-B is considered as follows. FIG. 7 shows an SEM image of the upstream surface of the DPF after the initial collection rate test. In Filter-A (FIG. 7A), most of the pores that are open on the surface are S-pores that are overwhelmingly larger in number than L-pores. A state where PM is adhered is observed. Therefore, in Filter-A, since the PM is collected by the small-diameter pores, the initial collection rate is high, and the number of PMs in the collection leakage is prematurely reduced by the clogging phenomenon of the small-diameter pores. It was. On the other hand, in the SEM image of Filter-B (FIG. 7B), it was observed that many M-pores were opened on the surface. Therefore, in Filter-B, PM passes through M-pore without being collected, and M-pore larger than S-pore takes time to be clogged. It was thought that it took time to decrease.

  In addition, the silicon carbide based porous body of the Filter-A base has an L-pore communicating with the S-pore inside, and the L-pore and the L-pore are complicatedly connected by a large number of S-pores. It is thought that a nest-like gas flow passage is formed. The speed of the fluid flowing through the flow path is high when the diameter of the flow path is small, and is slow when the diameter of the flow path is wide. Therefore, as schematically shown in FIG. 8, when the PM 5 transported to the gas flowing through the narrow flow path 2 of S-pore is decelerated by flowing into the large-diameter L-pore 3. It is thought that it is easy to adhere to the inner wall of L-pore3. And since the volume of L-pore3 is large, many PM5 can be made to adhere inside. After that, PM5 that has not been collected by the L-pore 3 is transported further downstream by the gas accelerating in the narrow flow path 2 of the S-pore communicating with the L-pore 3, and is captured by the L-pore 3 on the downstream side. Be collected. In addition, since the flow velocity of the gas in S-pore also decreases gradually and the diameter of the flow path 2 formed by S-pore is small in the first place, of course, PM is collected also in S-pore.

  In FIG. 9, the measurement result of the pressure loss accompanying PM collection is shown. Although Filter-A contained more pores (S-pore) with a smaller diameter than Filter-B, the degree of increase in pressure loss due to PM collection was about the same as Filter-B. From this, it was thought that the increase in pressure loss was suppressed because the large-diameter L-pore was dispersed in Filter-A.

  The measurement results of the three-point bending strength were 9.8 MPa for Filter-A and 7.6 MPa for Filter-B. That is, although Filter-A contains 10% by volume or more of a large diameter L-pore having a diameter of 40 to 50 μm, it is more mechanical than Filter-B in which M-pore having a smaller diameter than L-pore is almost uniformly dispersed. Strength was high. This is because the silicon carbide of the base of Filter-A is produced by the reaction product of silicon nitride and graphite, so even between relatively low sintering temperatures and short firing times, It was thought that the silicon carbide particles grew so fast that the neck was formed, and that a solid neck was formed.

  FIG. 10 shows a measurement chart in the thermal shock test, and Table 3 shows the measurement results. The maximum temperature of the DPF during combustion is slightly lower in Filter-A than in Filter-B, and the combustion rate (percentage of PM mass removed by combustion with respect to collected PM mass) is higher in Filter-A. It was. Moreover, generation | occurrence | production of the crack was not recognized after combustion with Filter-A and Filter-B.

  From the above, Filter-A can be used practically as a DPF that is used repeatedly by combustion, like commercial Filter-B, and has an initial collection rate, mechanical strength, combustion rate, etc. In several respects, it was considered superior to Filter-B as a DPF.

  The present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to the above-described embodiments, and various improvements can be made without departing from the scope of the present invention as described below. And design changes are possible.

  For example, by collecting a catalyst on a silicon carbide porous body as a DPF substrate, it is possible to more efficiently remove the collected PM by combustion.

It is a powder X-ray-diffraction pattern of an Example and a control example. It is an observation image by the scanning electron microscope of the torn surface of an Example and a control example. It is a pore diameter distribution represented by the number of pores for Examples and Control Examples. It is a pore diameter distribution represented by volume% with respect to the total pore volume for Examples and Control Examples. It is a graph which shows the time-dependent change of the number of PM which leaked without being collected by DPF in the initial collection rate test of an Example and a control example. It is a graph which shows the measurement result including the particle size distribution of PM which leaked without being collected by DPF in the initial collection rate test of an example and a control example. It is an observation image by the scanning electron microscope of the upstream surface of DPF after an initial collection rate test about an example and a control example. It is explanatory drawing which represented typically the ant nest-like pore structure. It is a graph which shows the change of the pressure loss accompanying PM collection about an Example and a control example. It is a measurement chart in the thermal shock test of an Example and a control example.

Explanation of symbols

2 S-pore (small diameter pores, pores) flow path 3 L-pore (large diameter pores, pores)
5 PM (particulate matter, particulate matter)

Claims (1)

A silicon carbide based porous material used as a base for a diesel particulate filter,
The mode diameter of the pore number distribution with respect to the pore diameter measured as a circle area equivalent diameter by the image analysis method is 8 ± 1 μm,
The total volume of pores having a pore diameter of 40 μm to 50 μm occupies 10% or more of the total pore volume ,
A large pore having a pore diameter of 40 μm to 50 μm is connected by a small pore having a pore diameter of 5 μm to 20 μm, and has a ant nest-like pore structure;
The matrix is a sintered body obtained by reactive sintering so that silicon carbide produced by reaction of silicon nitride as a silicon source and carbonaceous solid as a carbon source surrounds silicon carbide as an aggregate. A silicon carbide based porous material characterized by