JPS6191076A - Porous silicon carbide sintered body and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a porous silicon carbide sintered body made of plate-shaped crystals of silicon carbide and having low density, high strength and air permeability, and a method for producing the same.

Traditionally, silicon carbide is known for its chemical properties such as high hardness, soaked wear resistance, good oxidation resistance, good corrosion resistance, good thermal conductivity, low coefficient of thermal expansion, high thermal shock resistance as well as high strength at high temperatures. and have excellent physical properties, wear-resistant materials such as mechanical seals and bearings, refractory materials for high-temperature furnaces, heat exchangers, etc.
It is a material that can be widely used as a heat-resistant structural material such as combustion pipes, and as a corrosion-resistant material for pump parts for highly corrosive solutions such as acids and alkalis.

On the other hand, silicon carbide with these properties and its crystals form pores that have air permeability, that is, open pores (
A porous silicon carbide sintered body consisting of pores (hereinafter simply referred to as pores) is produced by taking advantage of the characteristics of silicon carbide in a high-temperature atmosphere.
Materials that can be used as filtration filters, catalysts or catalyst supports for oxidative exothermic reactions or chemical reactions at high temperatures in oxidizing and/or corrosive atmospheres, such as exhaust gas from internal combustion engines, especially diesel It is conceivable that it could be used as a filter to remove combustible particulate matter such as particulate carbon contained in high-temperature gas such as engine exhaust gas.

For the above-mentioned filter applications, it is not only necessary to have heat resistance and corrosion resistance, but also to have low resistance when fluid passes through, remove foreign particles with high efficiency, and have a long service life. The following characteristics are required. On the other hand, for applications such as catalysts, catalyst supports, or heat exchange, it is important that the surface area is large enough to effectively generate chemical reactions, heat transfer, or mass transfer, and that the surface is stable for long-term use. is required.

[Conventional technology]

Conventionally, as a method for producing porous silicon carbide sintered bodies, (1
) A method in which a binder such as vitreous 7 lux or clay is added to nylon carbide particles serving as aggregate, and the resulting product is then baked and solidified at a temperature at which the binder melts. (2) Coarse A method in which granular silicon carbide particles and fine silicon carbide particles are mixed, molded, and then fired at a high temperature of 2000°C or higher, or (8) JP-A-48-89515
Disclosed in the publication, "A carbonaceous binder is added to silicon carbide powder with or without carbon powder, and a stoichiometric amount of silicone powder is added to react with this carbon powder and free carbon from the binder produced during firing. Production of a homogeneous porous recrystallized silicon carbide body, characterized in that the carbon content in the molded body is silicified by heating the molded body to 1900 to 2400°C in carbon powder. method.'' etc. are known.

Glassy 7 lux is used as a bonding material as in (1) above.
The strength of the porous body manufactured by adding clay to the binding material is 1.
Since the porous material melts at temperatures between 000 and 1,400 degrees Celsius, it deforms in this temperature range, especially around the vitrification transition temperature, which not only significantly reduces its strength but also makes it difficult to use in fields that require chemical resistance and oxidation resistance. It has the disadvantage of being limited.

On the other hand, if the structure of the porous body produced by the above-mentioned methods (2) and (3) is illustrated as a model, it is shown in Fig. 8, in which the silicon carbide aggregate (4) and the aggregate are It consists of a silicon carbide binder or a carbonaceous binder which covers and binds the aggregates together) and a gap (0).

The gaps (C) or pores in the porous body are mostly determined by the arrangement of aggregate particles during molding, and the porosity in the sintered body is small, being 30 to 4 (l).

Therefore, the resistance when fluid passes through this porous body becomes extremely high. On the other hand, when the porosity of the sintered body is increased, the number of contact points between aggregate particles decreases, the strength of the porous body decreases significantly, and the contact area with fluid tends to decrease significantly.

On the other hand, the pore diameter in the porous bodies (2) and (3) is controlled by the particle size composition of the aggregate. According to this method, a large aggregate is required to create a porous body with pores with a relatively large cross-sectional area, which reduces the number of contact points between particles and reduces the bonding strength of the particles. The strength of the body is extremely low. On the other hand, in order to create a porous body with pores with a relatively small cross-sectional area, it is necessary to mix the aggregate particle size appropriately with coarse particles, medium particles, and/or fine particles, and then form the material. The porosity of the molded body becomes significantly small, and in extreme cases, some of the pores tend to become clogged. Therefore, the resistance when fluid passes through such a porous body is extremely high.

In addition, as a porous sintered body having a relatively large pore cross-sectional area, for example, according to Japanese Patent Application Laid-Open No. 58-122016, "a polymer foam material is impregnated with silicon carbide base slurry, The material is eliminated by heat treatment to form a silicon carbide skeleton structure, and the structure is
Firstly fired in argon at a temperature of 2,300°C, then secondarily fired at a temperature of 2,100°C in nitrogen gas of 1 to 200 atmospheres, and then heat resistant 1 on both ends.
A method for manufacturing a silicon carbide filter that can generate heat when energized by forming a pole and being energized. '', and according to Japanese Patent Application Laid-Open No. 48-81905, [an organic foam is impregnated with a slurry containing a finely ground ceramic material, and the impregnated foam is dried. , prior to firing and impregnating the foam with the slurry, the foam is layered such that the particulate material in the slurry adheres to the surface of the foam channel. A method for producing a ceramic material. ' has been disclosed.

Such a porous body is composed of large and small cellular skeletons called a so-called skeleton structure, as shown in FIG. Therefore, when the porous body is occupied by a relatively large cellular skeleton CD), the porosity of the porous body is 80 to 90 minus 0.
Although the resistance to passage of the fluid is small, the strength is 10 to 15 I9/c-, which means that from a practical point of view, the mechanical strength is poor, and the contact surface with the fluid is extremely small. . Furthermore, according to these packaging methods, the number of cells formed by polymeric foam such as polyurethane is 100.
sm or larger, and forming smaller pores is extremely difficult in terms of controlling the foamability of the polymer and dispersing it. Since the diameter of the continuous pores formed in the partition wall may become small, there is a drawback that passage resistance becomes large for allowing fluid to pass through.

[Problem that the invention seeks to solve]

The present invention eliminates and improves the drawbacks of the prior art, and provides a porous silicon carbide sintered body that is permeable to the outside and has arbitrary pore diameters and porosity according to various uses. We have developed a porous sintered silicon carbide body that has mechanical strength, a custom-made fluid passage, and can effectively perform mass transfer such as fluid separation, adsorption, and absorption, heat transfer, and chemical reaction purification, and a method for producing the same. This is what we provide.

For the above purpose, the present inventor molded a raw material composition containing silicon carbide powder as a main component, charged the molded body into a closed graphite crucible, and sintered it at 2000 to 230 O℃. It was discovered that a porous silicon carbide sintered body with a developed network of plate-like crystals with a significantly large ratio (low-temperature) and high porosity can be obtained, and the average length in the long sleeve direction is 0.5 to 1000 μm. porous, which has a three-dimensional network structure mainly composed of silicon carbide plate crystals with an average aspect ratio of 3 to 50, and in which the average cross-sectional area of open pores of the network is 0.01 to 250,000 μm2. A quality silicon carbide sintered body and its manufacturing method have been completed.

[Pause: Means for solving shell points]

Hereinafter, the porous silicon carbide sintered body of the present invention will be explained in detail.

FIG. 1 is an electron micrograph (X75) scanning the crystal structure of one porous silicon carbide sintered body of the present invention. As is clear from the drawings, the porous silicon carbide sintered body of the present invention has a three-dimensional A4 mesh structure in which silica carbide plate crystals with an aspect ratio of 10 to 20 and a length of approximately 500 μm are intricately intertwined in multiple directions. Furthermore, the pores are continuous and non-linear open pores, and are highly breathable. The length of the silicon carbide plate crystals herein refers to the maximum length of the orchid plate crystals observed in any cross section of the sintered body.
), and similarly the aspect ratio (R) of each individual plate crystal is
is expressed as the ratio of the maximum thickness (Y) of the plate crystal to the crystal length (X), that is, RwamX/Y.

The porous body of the present invention is characterized by having a three-dimensional network structure composed of silicon carbide plate crystals having an average aspect ratio of 3 to 50. The reason why the average aspect ratio of the porous body is set to 8 or more is that the pores formed by the silicon carbide plate crystals are larger than the volume occupied by the crystals, that is, the porous body has a high porosity. It's for a reason.

Note that the conventional porous silicon carbide sintered body is determined by the arrangement of aggregate during molding, as shown in Figure 3, and unlike the porous body in which plate-like crystals are developed as in the present invention, the crystals are The aspect ratio is only around 2 at most, and it does not have a high porosity or a large pore cross-sectional area.

By the way, conventionally, sintered bodies having a structure in which plate-like crystals are relatively developed are, for example, USP, A4QO49a4 and J
ouranxericanceramic
5ocity rs vol. 9 pp. 336-43 (19
76).

However, the sintered body is a relatively densified silicon carbide sintered body, and the plate-like crystals are generated as the sintered body becomes densified. Therefore, the structure is completely different from a sintered body in which only plate crystals are developed, such as the sintered body of the present invention.

On the other hand, the reason why the average aspect ratio of the porous body of the present invention is set to 50 or less is that a porous body composed of plate-shaped crystals with an average aspect ratio larger than 50 has few joints between the crystals, so the porous body This is because the strength itself is low. Among these, it is more preferable that the average aspect ratio of the plate crystals is 5 to 30, and the porous body of the present invention can be selected within this range depending on various uses.

Further, the average length of the plate crystals in the long sleeve direction is 0.5 to 1
000 μm. The reason for this is that when the average length in the major axis direction is smaller than 0.5 μm, the pores formed by the plate-like crystals are small, and in some cases, some of the pores may become independent pores, allowing fluid to pass through. This is because the resistance is large.

On the other hand, if the length is longer than 1000 μm, the strength of the joint between the plate crystals is low, and the strength of the porous chamber body itself is low. Among them, the average length of the plate crystals in the long sleeve direction is 1 to
More preferably, it is 800 μm, and the porous body of the present invention can be selected within this range depending on various uses.

Further, the average cross-sectional area of the open pores of the network structure is 0.01
It is necessary that the diameter is ~250,000μ♂.

The reason for this is that when the average cross-sectional area of the open pores is 0.01 μm or more, the resistance to passage of fluid is small.

On the other hand, if the average cross-sectional area of the open pores is larger than 250,000μ, the strength of the porous chamber body itself is low.
It is more preferable that the porous material of the present invention be within this range depending on various uses.

and 3 to 50 parts by weight of 100 parts by weight of crystals in the porous body.
It is preferable that the plate-like crystals having an aspect ratio of occupies at least 20 overlapping parts. Incidentally, the content of the plate crystals can be determined by analyzing a structural photograph of the crystals. Here, the reason why the porous body is preferably occupied by 20 parts by weight or more of plate crystals having an aspect ratio of 3 to 50 is that if the plate crystals are less than 20 parts by weight, the aspect ratio This is because a large number of small silicon carbide crystals are included, and the resistance to passage of fluid is large. In particular, it is advantageous for the plate crystals to account for at least 40 parts by weight of 100 parts by weight of the crystals in the porous body.

The open porosity of the porous silicon carbide sintered body is preferably 20 to 95% by volume based on the total volume of the sintered body. The reason for this is that when the open porosity is smaller than 20% by volume, some of the pores are independent, and the resistance when fluid passes through the sintered body is large, and the area in contact with the fluid is small. On the other hand, if the capacity is larger than 95 cm, the contact area with the fluid is large, but the strength of the porous sintered body is low, making it difficult to use, especially for heat-resistant structural materials, heat exchangers, filters. For such uses, it is advantageous that the open porosity of the porous body is 80 to 90% by volume based on the total volume of the sintered body.

The specific surface area of the silicon carbide sintered body is at least 0.
,05 wl/q. Here, the specific surface area is a value determined by the BET method using nitrogen adsorption. The reason why a specific surface area of 0.05 I11''/g or more is preferable is that in applications such as heat exchangers, catalyst carriers, or adsorbents, it is preferable to have a large contact area between the sintered body and the fluid. At least 0 for these applications
．． A specific surface area of 2♂/g can be most preferably used.

Next, a method for producing a porous sintered nium carbide body according to the present invention will be described in detail.

According to the present invention, (a) silicon carbide powder having an average particle size of 10 μm or less and containing at least 60% by weight of β-type, 2HfJ1 and amorphous silicon carbide is formed into a desired shape; and (b) the molded product obtained in step (a) is placed in a heat-resistant container and heated at 1900 to 200°C while blocking the intrusion of outside air.
It has a three-dimensional network structure mainly composed of silicon carbide plate-like crystals with an average length in the major axis direction of 10 to 1000 μm and an average aspect ratio of 3 to 50, which is obtained by firing within a temperature range of 300 ° C. A porous silicon carbide sintered body can be obtained in which the average cross-sectional area of the open pores of the network structure is within the range of 400 to 250,000 microns.

According to the invention, it is necessary that the starting material be one of the silicon carbide starting materials containing at least 60% by weight of type β, 2I (type) and amorphous silicon carbide sintered body.

The reason for this is that β-type crystals, 2H-type crystals, and amorphous silicon carbide crystals are low-temperature stable crystals that are synthesized at relatively low temperatures.
Not only does it easily undergo a phase transition to a high-temperature stable α-type crystal such as C1 plate crystals, but it also has excellent crystal growth properties. This is because the porous body targeted by the present invention can be produced by using the starting materials. Among these, it is preferable to use a starting material containing at least 70% by weight of β-type, 2H-type and amorphous silicon carbide.

The starting material needs to be a fine powder with an average particle size of 10 μm or less. Powders with an average particle size of less than 10 μm have a relatively large number of contact points between particles, and at the sintering temperature of silicon carbide, the thermal activity is large and the movement of atoms between silicon carbide particles is extremely large. , bonding between silicon carbide particles is extremely likely to occur. Therefore, the growth rate of plate crystals is extremely high. In particular, it is preferable that the average particle size of the starting material is 54 m or less, which gives more favorable results in the growth of plate crystals.

The silicon carbide cedar body molded into a desired shape from the starting materials is made of heat resistant 1.
1900 while blocking the intrusion of outside air by charging it in a raw container.
It is necessary to perform firing within a temperature range of ~2300"C.The reason why the firing is performed while blocking the intrusion of outside air by charging the container in a heat-resistant container is because the adjacent silicon carbide crystals This is because it is possible to fuse adjacent silicon carbide crystals and promote the growth of plate-shaped crystals.As mentioned above, by charging the silicon carbide crystals in a heat-resistant container and firing while blocking the intrusion of outside air, adjacent silicon carbide crystals can be fused together. The reason why the growth of plate-shaped crystals can be promoted through fusion is thought to be because the movement of silicon carbide atoms between silicon carbide particles by evaporation-recondensation and/or surface diffusion can be promoted. When we tried conventional pressureless sintering, atmospheric pressure sintering, or sintering under reduced pressure, we found that
Not only was it difficult to grow the plate-like crystals, but the joints of the silicon carbide particles had a constricted neck shape, and the strength of the sintered body was reduced. As the heat-resistant container, graphite
, silicon carbide, tungsten carbide.

It is more preferable to use a heat-resistant container made of at least one material selected from molybdenum and molybdenum carbide.

According to the present invention, by charging the formed body into a heat-resistant container that can block outside air and firing it,
It is advantageous that the volatilization rate of silicon carbide during firing is 5 times higher or lower.

In addition, in the porous body of the present invention, in order to obtain a porous body having open pores with a relatively large average cross-sectional area, the temperature increase rate during firing must be relatively slow, and the maximum temperature must be set relatively low. It is preferable to increase the temperature and/or to increase the holding time at the maximum temperature. Under these conditions, individual silicon carbide plate crystals can be grown to a large size, and as a result, a porous body having a large pore cross-sectional area can be obtained.

On the other hand, in order to obtain a porous body having open pores with a relatively small average cross-sectional area in the porous body of the present invention, the heating rate during firing must be relatively fast and the maximum temperature must be relatively low. And/or it is preferable to shorten the holding time at the maximum temperature, since this condition does not allow individual silicon carbide plate crystals to grow as much.

Further, according to the present invention, it is necessary to perform firing at a temperature range of 1900 to 2300°C. The reason for this is that if the firing temperature is lower than 1900°C, particle growth will be insufficient and it will be difficult to create a porous body with high strength.
This is because when the temperature is higher than 00°C, the sublimation of silicon carbide increases, and the developed plate-like crystals become thinner, making it difficult to obtain a porous body with high strength. Among these, firing at a temperature between 1950 and 2250°C is more preferable.

According to the present invention, (~ silicon carbide having an average particle size of 10 μm or less,
This powder is a starting material which is a carbon carbide powder consisting of α-type, β-type and/or amorphous silicon carbide and unavoidable impurities. .

Aluminum carbide, aluminum nitride, aluminum, aluminum oxide, boron, boron carbide, boron nitride, boron oxide,
Calcium oxide, calcium carbide, chromium, chromium boride, chromium nitride, chromium oxide.

Iron, iron carbide, iron oxide, lanthanum boride, lanthanum oxide,
(2) A step of uniformly mixing 28i or more of any one selected from lithium oxide, silicon, silicon nitride, titanium, titanium oxide, titanium dioxide, titanium trioxide, and yttrium oxide in an amount of 1θ weight or less; (a step of molding the mixture obtained in the step ~; and (C) the molded product obtained in the above step) is charged into a heat-resistant container and heated to 1700~2
By firing within a temperature range of 300°C, a three-dimensional network structure mainly composed of silicon carbide plate crystals with an average length in the long axis direction of 0.5 to 200 μm and an average aspect ratio of 3 to 50 is formed. It is possible to obtain a porous silicon carbide sintered body having an average cross-sectional area of open pores in the network structure within a range of 0.01 to 10,000 μm 2 .

According to the present invention, the starting material is required to be a fine powder with an average particle size of 10 μm or less. Average particle size is 10μ
Powders smaller than m have a relatively large number of contact points between particles, and C1 thermal activity is large at the sintering temperature of silicon carbide, and the movement of atoms between silicon carbide particles is extremely large, so silicon carbide particles Mutual coupling is extremely likely to occur.

Therefore, the growth rate of plate crystals is extremely high. In particular, it is preferable that the average particle size of the starting material is 5 μm or less, which gives more favorable results in the growth of plate-shaped crystals.

According to the invention, aluminum, aluminum diboride, aluminum carbide, aluminum nitride.

Aluminum oxide, boron, boron carbide, boron nitride,
Boron oxide, calcium oxide, calcium carbide, chromium, chromium boride, chromium nitride, chromium oxide, iron, iron carbide, iron trioxide, lanthanum boride.

It is necessary to add one or more selected from lanthanum oxide, lithium oxide, silicon, silicon nitride, titanium, titanium oxide, titanium dioxide, titanium trioxide, and yttrium oxide. The substance has the function of significantly increasing the rate of crystal growth of silicon carbide, and on the other hand, the substance has the effect of increasing the sintering temperature of the silicon carbide compact to 170°C.
At 0 to 2300°C, the vapor of the substance and/or the vapor of the decomposition product are generated and diffused throughout the silicon carbide molded body, forming a large number of plate-like crystal nuclei, and forming plate-like crystals in each part. This is because the development of plate-like crystals occurs, and as a result, the size of the plate-like crystals formed is restricted, resulting in a fine three-dimensional network structure.

Among said compounds, in particular boron, boron carbide, boron nitride, aluminum oxide, aluminum nitride.

Iron, aluminum carbide, aluminum diboride.

Aluminum can be used advantageously.

On the other hand, the amount of the substance added needs to be 10 parts by weight or less with respect to 100 parts by weight of the starting material mainly consisting of silicon carbide. The reason is that even if more than 10 parts by weight is added, the vapor partial pressure of the compound and/or its decomposition product hardly changes within the firing temperature range of the silicon carbide molded body. On the contrary, since the amount of the substance remaining in the molded body increases, the original properties of silicon carbide are lost. Further, the amount of the compound suitable for growth of plate crystals is preferably 5' parts or less per 1 part by weight of 100 parts by weight of silicon carbide starting material.

Furthermore, the silicon carbide used as the starting material may be any of α-type, β-type and/or amorphous silicon carbide.

According to the present invention, a charcoal JA source that leaves free carbon during firing can be added. As such a carbon source, any carbon source that exists in the carbon state at the start of sintering can be used, such as phenolic resin, lignin sulfonate, polyvinyl alcohol, corn starch, molasses, coal tar pitch, and alginate. Various organic substances such as carbon black, pyrolytic carbon such as acetylene black can be advantageously used.

When free carbon exists simultaneously with the above substances, it suppresses crystal growth and forms fine silicon carbide plate crystals, which is effective in obtaining a porous body having fine pores.

Further, it is advantageous that the free carbon content is 5 parts by weight or less based on 100 parts by weight of the starting material. The reason for this is that even if more than the 5-fold soft part is added, the effect will not change, but on the contrary, the amount remaining in the porous body will increase, reducing the oxidation resistance of the porous body. It is more effective that the amount is less than parts by weight.

According to the invention, the heat-resistant container is C1 graphite.

Use a container made of any one selected from silicon carbide, aluminum nitride, zirconium oxide, tungsten carbide, titanium carbide, magnesium oxide, molybdenum carbide, molybdenum, tantalum carbide, tantalum, zirconium carbide, and graphite-silicon carbide composite. can do.

These containers do not melt within the firing temperature range and can maintain their shape, and also prevent the vapors of the additives and/or decomposition products from leaking out of the system. However, the effect of the additive can be spread to every corner of the silicon carbide molded body. Among them, graphite and silicon carbide.

Graphite-silicon carbide composite, tungsten carbide, aluminum nitride, titanium carbide, molybdenum.

Molybdenum carbide can be used effectively.

In addition, in the porous body of the present invention, in order to obtain a porous body having open pores with a relatively large average cross-sectional area, the temperature increase rate during firing must be relatively slow, and the maximum temperature must be set relatively low. It is preferable to increase the temperature and/or to increase the holding time at the maximum temperature. Under these conditions, individual silicon carbide plate crystals can be grown to a large size, and as a result, a porous body having a large pore cross-sectional area can be obtained.

On the other hand, in order to obtain a porous body having open pores with a relatively small average cross-sectional area in the porous body of the present invention, the heating rate during firing should be relatively fast, the maximum temperature should be relatively low, and It is preferable to shorten the holding time at the maximum temperature. This is because, under these conditions, individual plate-like crystals of silicon carbide are not allowed to grow much.

Further, according to the present invention, it is safe to perform firing at a temperature range of 1700 to 2300°C. The reason for this is that the firing temperature is 1
If the temperature is lower than 700°C, particle growth will be insufficient and it will be difficult to obtain a porous body with high strength.
At temperatures higher than 2,300°C, silicon carbide sublimates rapidly, and the developed plate-like crystals become thin and thin, making it difficult to obtain a porous body with high strength. Among them, 1750~2250″C
It is more preferable to perform the firing between

Next, the present invention will be explained with reference to Examples and Comparative Examples.

Example 1 The silicon carbide fine powder used as a starting material contained 94.6% by weight of β-type crystals and the remainder substantially consisted of 2H crystals,
0.39' [quantity of free carbon, 0.17% by weight of oxygen,
It mainly contained 0.03% by weight of iron and 0.03% by weight of aluminum at °C, and had an average particle size of 0.28 μm.

5 parts by weight of polyvinyl alcohol and 300 parts by weight of water were blended with 100 parts by weight of the silicon carbide fine powder, mixed for 5:1 wI in a ball mill, and then dried.

An appropriate amount of this dry mixture was sampled, top granulated, and then molded at a pressure of 5019/cd using a press die made by Kanekata.

The resulting product had a density of 1.2 l/cJ and a dry weight of 21 l/cJ. - The resulting green body was placed in a graphite crucible that can be shut off from outside air, and fired in an argon gas atmosphere at 1 atm using a Tammann type furnace. The graphite crucible used was one with an internal volume of 50.

For firing, the temperature was raised to 2200°C at a rate of 2.5°C/min and maintained at the maximum temperature of 2200°C for 6 hours.

The weight of the obtained sintered body was 19.69, and its crystal groove structure had an average aspect ratio of 12 and an average of It has a three-dimensional groove structure in which plate crystals with a length of 380 μm are complicatedly intertwined in multiple directions, and the content of plate crystals with an aspect ratio of 3 to 50 is 98% of the total weight of the porous body: It. %Met. Further, the pores of this porous body were non-linear open pores, the open porosity accounted for 64% of the total volume, and the specific surface area was 1.2 rl/liter.

The bending strength of this sintered body is as high as 180 kg/crd, and the ventilation characteristics of this porous body were investigated using a test specimen with a wall thickness of 5 mm and air at 20°C passing through it at a flow rate of 1 m/SeC. When measured, the pressure loss was less than 480 columns of water.

Comparative Example 1 A method similar to Example 1 was used, but the molded body was not placed in a graphite crucible and sintered under normal pressure in an argon atmosphere. A sintered body of i s, sp was obtained. The crystal groove structure was made of mostly granular silicon carbide with an average aspect ratio of 1.8 and an average length in the long sleeve direction of 30 μm. The open porosity of this sintered body was 67% of the total volume, but the bending strength was 4 kg/c++f, which was extremely low.

Example 2.3 Same as Example 1, but 3000 kg/cJ.

The green bodies molded at a molding pressure of 1Q kg/cJ were charged into a tungsten carbide crucible and a silicon carbide crucible having a theoretical density of 95%, and fired. The results are shown in Table 1.

Example 4 and Comparative Example 2 A method similar to Example 1 was used, but silicon carbide powder was prepared by mixing the silicon carbide powder used in Example 1 and α-type silicon carbide powder as starting materials at the mixing ratio shown in Table 2. A porous sintered body was manufactured using the following method.

The α-type silicon carbide powder is obtained by pulverizing a commercially available α-type silicon carbide powder (GO #3000), further refining it, and classifying the particle size. jl and the amount of free carbon and 0
．． Contains 1% oxygen and has an average particle size of 8.4
It was μm.

Practical Examples 5 and 6 Same as Example 1, but as shown in Table 8, 'tjt
.

A porous silicon carbide sintered body was prepared using temperature rate, maximum firing temperature, and holding time at maximum temperature. ．．
6 tonnage units consist of β-type crystals and the remainder consists essentially of 2H-type crystals, 0.3 f) wt% free carbon, 0.17', Ii
il % of 1 finished element, l) , Oa 7fl jL1%
of iron, o, oai=s of aluminum, and had an average particle size of 0.28 μm.

1. For 100 parts by weight of silicon carbide imitation powder, 0.3 parts by weight of amorphous boron, 1 part by weight of polyethylene glycol as a molding binder, 4 parts by weight of polyacrylic normal ester, amount of penze/100 fi The mixture was mixed in a ball mill for 20 hours and then dried.

An appropriate amount of this dry mixture was taken, granulated, and then molded using a metal press mold at a pressure of 50 kg/cm.

The degree of precision of this product was 1.2 l/cr11 and the dry weight was 21 l.

The formed body was placed in a graphite crucible that can be shut off from outside air, and fired in an argon gas atmosphere at 1 atm using a Tammann type firing furnace. The graphite crucible used had an internal volume of 50.

For firing, the temperature was increased to 2200°C at a rate of 5°C/min and maintained at the optimum temperature of 2100″C for 4 hours.

The crystal structure of the obtained sintered body is a plate-shaped crystal with an average aspect ratio of 10 and an average length in the long direction of 13 μm, as shown in the scanning type micrograph (500x) in Figure 2. It has a three-dimensional structure that is intricately intertwined in multiple directions, and has three to
The content of plate crystals with an aspect ratio of 50 was 96% of the total weight of the porous chamber body. In addition, the pores of this porous material are non-linear open pores, and the open porosity occupies 61 ㎜ of the total volume, and the specific surface area is a, s+++''/
It was ri.

The bending strength of this sintered body is as high as 2870 kg/crl, and the ventilation characteristics of this porous body were tested using a test piece with a wall thickness of 5 mm and air at a temperature of 20°C passing through it at a flow rate of 1 m/sec. When measured, the pressure loss was less than 780 fat water columns.

'4...'m 19! I s Same as Example 7, but amorphous boron G is added in the direction of addition.
On the contrary, aluminum, aluminum diboride, aluminum nitride, aluminum nitride, boron carbide, boron oxide,! Chemistry R, 1'J
(Hycalcium, chromium chloride, chromium, chromium nitride, 1-chromium carbide, iron.

1 Inukachichi, iron oxide, lanthanum boride, 1 oxidized lanthanum.

, silicon, silicon nitride, titanium, titanium oxide, two-component titanium, titanium trioxide, and titanium oxide)
A porous sintered body was manufactured using IJum. All of these porous silicon carbide sintered bodies had a crystal structure in which plate crystals were well developed, and were extremely excellent in bending strength, air permeability, etc.

As described above, according to the present invention, the porous silicon carbide sintered body whose aspect ratio, pore diameter, etc. are uniform by controlling the atmosphere is more suitable for various filtration filters, dust collectors, or classifiers. It is possible to achieve precise separation efficiency, and it also enables efficient and reliable control in fields such as catalysts, catalyst supports, and heat exchangers in the chemical reaction industry.

[Brief explanation of the drawing]

Figure 1 is a scanning single micrograph (75x magnification) of the sintered body described in Example 1, and No. 21'W is a scanning single micrograph (500x magnification) of the sintered body described in Example 7. ), FIG. 8 is a schematic diagram showing the structure of a porous sintered body of silicon carbide obtained by a conventional method, and FIG. 4 is a schematic diagram showing the structure of a porous body having a skeleton structure. A...Silicon carbide aggregate, B...Binding material, C...
Gaps in porous body, D...Cellular skeleton.

Claims (1)

[Claims] 1. A sintered body mainly made of silicon carbide, having an average aspect ratio of 3 to 50 and an average length in the long axis direction of 0.5 to 1000 μm. It has a three-dimensional network structure mainly composed of crystals, and the average cross-sectional area of open pores in the network structure is 0.01 to 25,000.
Porous silicon carbide sintered body with a diameter of 0 μm^2. 2. 3 out of 100 parts by weight of the porous silicon carbide sintered body
Plate crystals with an aspect ratio of ~50 are at least 20
The sintered body according to claim 1, which is in parts by weight. 3. Claims 1 to 2, wherein the open porosity of the three-dimensional network structure is 20 to 95% by volume based on the total volume of the sintered body.
The sintered body according to any one of paragraphs. 4. The specific surface area of the sintered body is at least 0.05 m^2/
The sintered body according to any one of claims 1 to 3, which is g. 5. A three-dimensional network structure mainly composed of silicon carbide plate-like crystals with an average length in the major axis direction of 10 to 1000 μm and an average aspect ratio of 3 to 50, which consists of the following sequence of steps (a) to (b) A method for producing a porous silicon carbide sintered body having an average cross-sectional area of open pores in the network structure within the range of 400 to 250,000 μm^2: (a) having an average particle size of 10 μm or less; A step of molding a silicon carbide powder containing at least 60% by weight of β-type, 2H-type and amorphous silicon carbide into a desired shape; and (b) a step of forming the silicon carbide powder obtained in step (a) above. A process of charging the molded body into a heat-resistant container and firing it within a temperature range of 1900 to 2300°C while blocking the intrusion of outside air. 6. A three-dimensional silicon carbide crystal mainly composed of plate-shaped silicon carbide crystals having an average length in the major axis direction of 0.5 to 200 μm and an average aspect ratio of 3 to 50, consisting of the sequence of steps (a) to (c) below. A method for producing a porous silicon carbide sintered body having a network structure, in which the average cross-sectional area of open pores in the network structure is within the range of 0.01 to 10,000 μm^2; (a) Average particle size is silicon carbide with a diameter of 10 μm or less,
This powder is a starting material which is a silicon carbide powder consisting of α-type, β-type and/or amorphous silicon carbide and unavoidable impurities. , aluminum nitride, aluminum oxide, boron, boron carbide, boron nitride, boron oxide, calcium oxide, calcium carbide, chromium, chromium boride, chromium nitride, chromium oxide, iron, iron carbide, iron oxide, lanthanum boride, lanthanum oxide ( b) molding the mixture obtained in the step (a); and (c) placing the molded product obtained in the step (b) in a heat-resistant container for 1700 minutes while blocking the intrusion of outside air. Firing within a temperature range of ~2300°C.