KR101155549B1 - Manufacturing Methods of Porous Sintered Reaction-Bonded Silicon Nitride and Porous Sintered Reaction-Bonded Silicon Nitride Fabricated Thereby - Google Patents

Abstract

A method for producing a porous reactive silicon nitride and a porous silicon nitride sintered body produced thereby are provided. In the present invention, the sintered body is a step of granulating a raw material containing silicon and a sintering aid for producing a silicon nitride sintered body from the silicon, pressure-free molding the granulated raw material in a mold and the molded body in a nitrogen atmosphere Nitriding in the middle temperature region and sintering in the high temperature region. According to the present invention, the pore channel size is controlled so that coarse pores and fine pores coexist in a material, thereby providing a reactive silicon nitride sintered body which can simultaneously improve aeration performance and collection efficiency.

Porous, Silicon Nitride, Reaction Sintered, Granule, Pressureless Forming, Tapping, Coarse Pore, Pore Channel

Description

Manufacturing Method of Porous Sintered Reaction-Bonded Silicon Nitride and Porous Sintered Reaction-Bonded Silicon Nitride Fabricated Thereby

The present invention relates to a method for producing a porous reaction silicon sintered nitride and a porous reaction silicon nitride sintered body produced by the same, and more particularly, to control the pore structure to increase the specific surface area and the coarse pores for improving the air permeability. The present invention relates to a porous reactive silicon nitride production method and a porous reactive silicon nitride sintered body prepared thereby.

Silicon nitride materials have been widely used in fields requiring good thermal and mechanical properties and chemical resistance due to their light weight and excellent strength, toughness, impact resistance, heat resistance, and corrosion resistance.

Conventionally, silicon carbide-based porous materials have been mainly used in fields requiring thermal, mechanical, and chemical resistance properties.Since silicon carbide has low thermal shock resistance and high hardness, the mold wears during molding, resulting in very short lifespan. Since the sintered at a high temperature of 2000 ℃ or more there is a problem that leads to an increase in manufacturing cost.

As described above, the porous silicon nitride-based material has excellent heat resistance, mechanical properties, corrosion resistance, and the like, and thus, instead of silicon carbide-based material, filters for filtration, catalyst carriers, heat insulating materials, filters for high-temperature high-pressure gas, and fine dust of diesel vehicles It is a promising material to be used as a filter for filtering.

However, most studies on existing silicon nitride materials have been focused on improving the mechanical and thermal properties by densifying microstructures, and research on methods of manufacturing porous silicon nitride materials is relatively insufficient.

As an example of a technique for preparing a porous body with silicon nitride ceramics, Korean Patent Laid-Open Publication No. 195-702510 discloses a compound of Si ₃ N ₄ and a rare earth element and / or a transition metal compound for use as a filter or catalyst carrier for removing foreign substances. There is provided a method for producing a silicon nitride ceramic porous body consisting of, according to this method to prepare a porous body having a porosity of 30% or more by heat-treating the molded body of the mixed powder at a temperature of 1500 ℃ or more.

In addition, Korean Patent No. 10-0311694 provides a method for manufacturing a porous silicon oxynitride sintered body for manufacturing a porous silicon oxynitride sintered body applied to a refractory tile of a space shuttle, etc. According to this method, Si3N4: 11-16 Agglomerated by mixing a low melting point powder of 3% by weight, AlN: 3-5% by weight, 35-45% by weight of Al2O3, and 35-45% by weight of Y2O3, and the solidified low melting point powder was Si3N4: 57-100. 10-25% by weight of β-sialon silicon oxynitride powder in weight%, Al2O30-9 weight% and AlN: 0-33 weight%, followed by molding and sintering at a temperature of 1600-1700 ° C. for 1-8 hours A method for producing a porous silicon oxynitride sintered compact is provided.

On the other hand, Japanese Patent Application Laid-open No. Hei 9-100179 discloses a method for producing a silicon nitride porous body which can be used as a filtration filter or a catalyst carrier. This method makes contact with a silicon nitride-based porous body with an acid and / or an alkali to make silicon nitride. Some or all of the other components are dissolved to produce a porous body.

However, since all of the above methods use expensive silicon nitride as a raw material, there is a fundamental limitation in practical use itself, and the method used for forming pores is also impractical. For example, in the case of Korean Patent No. 10-311694, in order to form pores in the sintered compact, the low melting point composition powder is formed into a mass and then the molded body is mixed with the high melting point composition powder to secure the pores depending on the size of the mass compact. However, it is difficult to maintain the shape of the molded body in the mixing process, if you want to maintain it can not ensure sufficient mixing, it is difficult to control a consistent process and accompanied by increased costs. In addition, the method of forming pores by chemically treating the porous body prepared as Japanese Patent Application Laid-Open No. 9-100179 also requires a separate process called chemical treatment, and when the components present between silicon nitride are dissolved, the skeleton of the silicon nitride skeleton There is no guarantee that it will remain.

In order to solve the above-mentioned problems, the present inventors prepare a molded body after mixing rare earth oxide or rare earth oxide / alumina or rare earth oxide / magnesia as a sintering aid in silicon (Si), and the molded body is nitrogen atmosphere. It has been proposed a method for producing a silicon nitride filter for automobiles by firing in the medium temperature region of the silicon nitride by the reaction sintering and then sintering the silicon nitride in the high temperature region (Patent Application No. 10-2008-0040395).

According to this method, using cheap silicon as a starting material, it has excellent thermal shock resistance, mechanical properties such as strength, and stability at high temperature, so that it can be used as a soot filtration device and can be used as a particulate filter while optimizing its aspect ratio. The fine dust, which could not be filtered in the soot filtration device, was able to be filtered, and the sintering was possible at a lower temperature, thereby lowering the manufacturing cost.

However, the above-described invention has a problem in that the pore channel cannot be formed as large as desired because the pore size is limited by the particle size of the gas-solid nitride reaction mechanism and the silicon nitride of the post-sintered body.

In order to solve the above-mentioned problems, an object of the present invention is to provide a silicon sintered porous body and a method for producing the same to secure a pore channel of a sufficient size.

On the other hand, according to the preceding invention is formed a fine pore channel of a relatively uniform size, when the porous body having a uniform pore size of the micropore channel in the soot filtration device has a high particle capture efficiency, This can lead to a lack of breathability, which creates a large back pressure during operation, which can contribute to the degradation of the system in which the filter is mounted.

Accordingly, an object of the present invention is to provide a reactive silicon nitride sintered body in which the pore channel size is controlled so that coarse pores and micropores coexist in the material, thereby simultaneously improving air permeability and collection efficiency.

In order to achieve the above technical problem, the present invention comprises the steps of granulating a raw material comprising silicon and a sintering aid for producing a silicon nitride sintered body from the silicon; Pressure-free molding the granulated raw material in a mold; And it provides a method for producing a porous reaction silicon nitride comprising the step of producing a reaction silicon nitride in the nitrogen atmosphere of the molded body.

In the present invention, the sintering aid may include yttria and alumina.

In addition, the reaction sintering step in the present invention, the step of nitriding the molded body; And

It may include the step of sintering the nitrided molded body, wherein the nitriding step may be performed at a temperature of 1300 ~ 1500 ℃.

In the present invention, the content of the sintering aid is preferably included 2 to 10% by weight based on the complete nitriding of the silicon.

In addition, in the present invention, the granular powder preferably has a maximum weight frequency in the range of 30 to 150 microns.

In order to achieve the above technical problem, the present invention is made of an array of granular regions having fine pore channels therein, porous reaction sintering characterized in that it comprises a coarse pore channel formed between the granular sintered regions A silicon nitride sintered body is provided.

In the present invention, the pore distribution of the silicon nitride sintered compact shows a bimodal distribution having a first peak and a second peak having a larger pore size than the first peak, wherein the first peak is attributable to the fine pore channel in the granules. The second peak is due to coarse pore channels between the granules. The first peak is at a pore size in the range of less than 1 micron and the second peak is at a pore size of 1 micron or more.

In addition, the first peak is preferably present in the pore size is less than 1 micron, the second peak is present in the pore size range of 5 to 20 microns.

In addition, in the present invention, the granular sintered region is preferably distributed in the range of 30 ~ 150 microns in average diameter, the maximum frequency diameter of the granular sintered region is preferably present in the range of 50 ~ 150 microns.

In the present invention, the granular sintered region is preferably composed of β-Si ₃ N ₄ as a main component.

According to the present invention, the pore channel size is controlled so that coarse pores and fine pores coexist in the material, thereby providing a reactive silicon nitride sintered body which simultaneously increases aeration performance and collection efficiency.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In the present invention, "pressure-free molding", in addition to the conventional meaning of molding the molding mold by the weight of the powder without applying pressure during powder molding, in addition to the tapping, such as shaking or shaking the molding mold for the filling arrangement of the powder It is used as a term that includes forming by.

In addition, in the present invention, "reaction-bonded" refers to a method of simultaneously producing a chemical reaction and sintering from a raw material to a desired compound by heat treatment. As described above, the reaction sintering was originally a term for expressing the characteristics of the process, but is currently used as a term for specifying a sintered body. For example, the reaction sintered silicon nitride refers to a sintered body produced by nitriding reaction and sintering from a silicon precursor.

Granulation of Si + Sintering Agent Raw Powder

In the present invention, granulated powder was prepared by spray drying. The granular powder contains a sintering aid that promotes nitriding reaction and sintering of silicon and silicon. The sintering aid is composed of a ternary high melting point sintering aid for sintering silicon nitride composed of yttria and alumina, as well as a ternary or higher low melting point sintering aid further comprising an alkaline earth metal such as MgO, CaO, SrO, BaO, etc. Can be. Further, in the conventional Si material surface there SiO ₂ film is formed, it is possible to secondary sintering in the subsequent sintering process, with the SiO ₂ film is a sintering aid other.

In the present invention, it is preferable that the amount of the sintering aid added to the sintering aid is 2 to 10 wt% based on Si ₃ N ₄ based on the assumption that Si is completely nitrided. As the amount of sintering aid added in the present invention increases, the strength of the sintered body preferably increases.

In the present embodiment, as shown in Table 1, a high melting point YA system (Y ₂ O ₃ -Al ₂ O ₃ , T _eu = 1370 ° C) and a low melting point YAC system (Y ₂ O ₃ -Al ₂ O ₃ -CaO, Granules with varying atomizer rotational speeds (1,000, 10,000 rpm) were prepared with respect to the Si mixed powder in which T _eu = 1170 ° C.) was added as a sintering aid.

The spray slurry was prepared by planetary milling. The ratio of solids and water was 1: 1, and the amount of sintering aid added was 3wt% based on Si ₃ N ₄ based on the assumption that Si was completely nitrided. Si + sintering aid) based on 0.1 ~ 0.8wt%, binder was 2 ~ 5wt% based on solid content (Si + sintering aid). During spray drying, the rotation speed of the stirrer was maintained at 100 rpm, and the temperatures of the inlet and the outlet were 150 to 300 ° C and 80 to 120 ° C, respectively.

division Sintering aid T _eu Sintering Granular strength Molding method YA series Y ₂ O ₃ -Al ₂ O _3- (SiO ₂ ) 1370 ^o C x weakness Tapping, Pressureless Molding YAC system Y ₂ O ₃ -Al ₂ O ₃ -CaO- (SiO ₂ ) 1170 ^o C O Strong Uniaxial, Extrusion

As a result of spray drying, coarse granules (50-250 μm) were formed under low speed atomizer (1,000 rpm), and the yield of granules was lower than 1% based on Si 100g batch. The yield was more than 40% at 10,000 rpm, and the size and recovery of granules increased with increasing batch and binder addition amount. 2).

Sample Name Sintering aid PVA
(wt%) Rotation speed
(rpm) Granule size
(μm) Si 100g batch yield
(%) SD4 YA 2 10,000 30-150 43.7 SD5 YA 5 10,000 30-150 57.1 SD6 YAC 2 10,000 30-250 69.8

Subsequently, SD4 (Y ₂ O ₃ : Al ₂ O ₃ = 2: 1; PVA 2.1 wt%) granules were classified by sieving and then examined by appearance using a scanning electron microscope (SEM). Figure 1 (a) is 45-63 μm of the particle size (called 'm54' as the median particle size), (b) the particle size 90-125 μm (m107.5) (c) particle size 125-150 μm (m137. It is classified as 5). It is observed from the photograph that the small granules remain spherical with little damage (Figs. 1 (a) and (b)), but the large granules are partially broken by the sieving impact (see arrow (c) in Fig. 1).

Figure 2 is an enlarged observation of the surface of the granules, it can be seen that it is composed of particles smaller than this compared to the average particle diameter of 2 μm of the starting Si. This is because not only the particle size of the added sintering aid is smaller than that of Si, but also the Si particles, which are the main raw materials, are also pulverized during the milling process, thereby decreasing the average particle size.

As a result of measuring the weight distribution according to the size of the granules after sieving, similar size distributions were shown without depending on the composition of the sintering aid and the amount of binder added under the same conditions of atomizer rotation speed (FIG. 3). As a result of sieving, most of the particles for each sample have a size of between 30 and 150 microns, and it can be seen that about 50% of the granules are present in the particle size of 90 μm or more and 106 μm or less.

Pressureless Filling Molding of Plasticized Granule Powder

Pressureless molding was performed using a high melting point sintering aid YA-based granule powder having a composition as shown in Table 3 below. In Table 3, the content of each composition is expressed on a basis of 100 g of silicon, and the amount of sintering aid added to the SD5 granules is 97wt% Si ₃ N ₄ -2wt% Y ₂ O ₃ -1wt% Al ₂ O ₃ is indicated. In the following table 3 SD51 is a composition is increased under the conditions of a sintering aid SD5 amount to 2 times _{(94wt% Si 3 N 4 -4wt} % Y 2 O 3 -2wt% Al 2 O 3).

To examine the characteristics and phase relationships of microstructures such as porosity, coarse pore channel size, and specific surface area of pores according to the size of granules, the median particle size was 38.5μm (particle size range 32-45μm). , 54μm (particle size range 45-63μm), 76.5μm (particle size range 65-90μm) and 107.5μm (particle size range 90-125μm), and classified into granules (as-SD) for comparison It was. In the following, each specimen is denoted by m38.5, m54, m76.5, m107.5 and as-SD. In the case of sifted granules, coarse granules with a particle size of 125 μm or more were not used in the experiment, and coarse granules of 125 μm or more were included in the unsieved as-SD.

Name of sample Si Y2O3 Al2O3 PAA PVA SD5 100 3.43 1.72 0.53 5.26 SD51 100 7.09 3.54 0.55 5.53

Pressureless molding was performed by tapping molding, which caused the powder to fill by tapping the molding mold.

As a molding mold, a cylindrical graphite mold having an internal diameter of 30 mm was used, and a plurality of holes were formed in the upper and lower plates of the mold to allow nitrogen gas in and out, and the thickness of the disk specimen was maintained uniformly by the two plates. About 2 grams of granules were charged and tapped to have a thickness of about 4 mm. The tapping molded body had a density of about 0.71 g / cm ³ and a filling rate of about 30%.

Nitriding and Sintering of Molded Granule Powder

The granulated powder (SD5, SD51) molded in the mold was nitrided. Nitriding was carried out using a tube furnace and at 1450 ^° C. Subsequently, the sintered specimens (called 'SD5-RBSN' and 'SD51-RBSN', respectively) were subjected to post-sintering at 1700 ^° C. for 2 hours under a nitrogen atmosphere of 0.1 MPa. And 'SD51-SRBSN').

4 is a graph showing the nitriding rate of SD5-RBSN. Nitriding is known to be completed when a nitriding rate of more than 90% is obtained due to volatilization loss during the nitriding reaction.In this experiment, residual Si was not detected by XRD analysis of the specimen showing the lowest nitriding rate. Therefore, it was confirmed that the nitriding reaction was completed in all specimens.

Figure 5 (a) is a graph showing the measured porosity of SD5-RBSN and SD5-SRBSN, Figure 5 (b) is a graph showing the shrinkage and mass change rate of SD5-SRBSN, Figure 6 (a) is A graph showing the porosity of SD51-RBSN and SD51-SRBSN by measuring the porosity, Figure 6 (b) is a graph showing the shrinkage and mass change rate of the SD51-SRBSN.

Referring first to Figure 5, it can be seen that all the specimens exhibit porosity of about 65 ~ 70% without depending on the size of the granules. In addition, although the shrinkage of SD5-SRBSN is almost zero, the porosity of SD5-SRBSN is smaller than that of SD5-RBSN, which is presumed to be due to the increase in weight due to the inflow of atmospheric powder into the porous specimen during post-sintering.

On the other hand, in the case of SD51-RBSN, which doubled the amount of sintering aid, the porosity was slightly higher than that of SD5-RBSN (FIG. 6). This is due to an increase in the amount of sintering aid, and low density k-phase (YSiO ₂ N, ρ = 0.714 g / cm ³ ) is attributed to the precipitation. In the case of SD51-SRBSN, the porosity is reduced by 4-6% shrinkage with little weight increase, and the porosity is around 65% by granule size.

Figure 7 is an electron microscope observation picture of the SD51-SRBSN, SD51-SRBSN it can be confirmed that the needle-shaped particles inherent to silicon nitride by post sintering. Such a microstructure is expected to contribute to improving the collection efficiency of fine dust by increasing the specific surface area of the pores and forming a complex pore channel structure.

8 shows the fracture surface of SD5-SRBSN observed by scanning electron microscopy (SEM) according to granule size. It was confirmed that a porous granule having a weak strength but having a spherical granular shape was formed by molding by tapping, reaction sintering and post sintering. On the other hand, what is observed with white contrast in the empty space between the granules is a whisker-type silicon nitride, which is believed to act advantageously in the collection of nanoparticles because it increases the specific surface area of the filter.

In order to directly observe the coarse pore channel formed between the spherical granules of SD5-SRBSN, the polishing surface was observed by optical microscope after SRBSN was impregnated with resin. FIG. 9 is a photograph of the observation result. It was observed from FIG. 9 that almost all of the granules maintained a spherical shape immediately after spray drying, and a continuous pore channel was developed in proportion to the size of the granules due to the predominant point contact between the granules. On the other hand, the white contrast in the granules represents the resin part impregnated in the pores in the granules, according to the present invention, because the microporous channels are present in the granules as well as the coarse pore channels formed between the granules, the nanoparticles are increased by increasing the specific surface area of the pores. It can be seen that it will act as a mechanism for improving the trapping performance of the particles.

10 is a graph showing the results of XRD analysis of the SD5-SRBSN specimen. α-Si ₃ N ₄ and the second phase were not detected, and it was confirmed that only the β-Si ₃ N ₄ peak (peaks indicated by □) was present by complete phase transition.

FIG. 11 is a graph showing the size distribution of the pore channel of the SD5-SRBSN specimen by the mercury porosimetry device, and FIG. 12 is a graph showing the specific surface area measured. The mercury porosity device used in this experiment was Micromeritics' Autopore IV 9510 equipment, and the measurement conditions were equilibration time 10 seconds and stem volume used more than 25%.

Referring to FIG. 11, it can be seen that the size of the pore channel in all specimens exhibits a bimodal distribution consisting of a peak represented by micropores of 1 μm or less and a peak represented by coarse pores of about 1 μm or more and 10 μm. . More specifically, in the case of micropores, the maximum peak exists in the range of 0.1 to 1 μm, and the maximum s peak of the coarse pores exists in the range of 1 to 20 microns.

Since micropores are formed in the interior space of the granules, they do not depend on the granule size and are considered to have relatively similar sizes in all specimens. However, the size of the coarse pore channel tends to be dependent on the size of the granules, and the unclassified raw granules (as-SD) showed the second largest pore size.

Relatively coarse particles are collected by an impact mechanism of size and weight, whereas fine nanoparticles are collected by a diffusion mechanism because of Brownian motion. Therefore, as the specific surface area of the porous pores increases, the collection efficiency of the nanoparticles increases. The specific surface area of the SiC filter material mounted on a commercial diesel particulate filter (DPF) is about 0.2 m ² / g, whereas the reaction sintering by the Si mixed powder granules of the present invention as shown in FIG. The specific surface area of the silicon nitride porous body is about 1.9 to 2.3 m ² / g, which is more than 10 times larger, and thus, excellent collection efficiency for nanoparticles is expected. On the other hand, it can be seen from the analysis of the graph that the specific surface area due to coarse pores between granules is 0.5 m ² / g or less in all specimens, so that the specific surface area due to micropores in the granules is absolutely large. It can be seen from the graph that the relationship between granule size and specific surface area tends to be opposite to granule size-coarse pore size. That is, the smallest specific surface area of the specimen with the coarser granules (m107.5) was measured. What is unusual is that the largest specific surface area is measured in the specimens by unsorted biogranules (as-SD), which is the smallest granule size m38.5 used in this study. This is because it contains a large number of granules smaller in size than the granules.

FIG. 13 is a graph illustrating the mercury porosity analysis results of SD5-SRBSN and SD51-SRBSN. In the case of SD51-SRBSN having a high content of sintering aid, the pore channel of the specimen was large, whereas the specific surface area of the pores was larger in SD5-SRBSN with less amount of sintering aid. This shows that the pore structure of the liquid phase sintering system is governed by the absolute amount of liquid phase produced. When the graph is strictly analyzed, it can be seen that in the SD51 specimen, the coarse pore channel between granules (~ 10 μm) and the microporous channel in the granule (<1 μm) are larger at the same time than the SD5 specimen. On the other hand, the pore specific surface area of the SD51 specimens of the acicular particles was lower than that of the SD5 specimens of the isotropic particles because the growth of the particles simultaneously with the change of the particle shape was increased. However, even in this case, the pore specific surface area is about 1.0 m ² / g, and a large pore specific surface area is realized as compared to a commercial SiC filter composed of coarse isotropic particles.

In order to determine the optimum sintering conditions of SD51 granules according to the sintering temperature, specimens having different sintering temperatures were prepared at 1700 ^o C, 1800 ^o C, and 1900 ^o C, and the sintered bodies were measured and shown in FIG. 14. The 1700 ^o C and 1800 ^o C sintered showed similar shrinkage and porosity, but in 1900 ^o C sintering, the decrease in porosity due to rapid shrinkage was remarkable. In particular, in the sintering of 1800 ^o C or less, the weight loss is almost zero, while in the 1900 ^o C sintering, despite the 0.9 MPa nitrogen pressurized atmosphere, the weight loss of about 10% is accompanied by the decomposition of silicon nitride. Appeared.

In the SD51 specimens, pore structures of the 1700 ^o C and 1800 ^o C sintered porous bodies were analyzed and shown in FIG. 15 except for the 1900 ^o C sintered body whose strength and shrinkage characteristics were not suitable as filter materials. As shown in FIG. 15, the size of the coarse pore channel is similar in the sintered body at the two temperatures where similar porosity and shrinkage are measured, but the microporous channel is 1 μm or less in the case of 1700 ^o C sintered body, but the 1800 ^o C sintered body is 1 μm or more Grew. The specific surface area of the pores was determined to be large in the 1700 ^° C sintered body with relatively small micropore size.

As can be seen in the above-described embodiment, it is possible to produce a sintered body having a pore structure in which coarse pores and fine pores coexist with the granular powder of the present invention.

16 is a view for schematically explaining the pore structure of the porous sintered body according to the present invention. First, as shown in the left side, when the granulated powder produced by the present invention is pressure-free molded, coarse pores of a predetermined size are formed between the sintered powders. These pores are connected between the stacked powders to form pore channels.

When nitriding and post sintering the thus formed Si granule powder, the sintering aid contained in the raw material powder forms a liquid phase during the temperature rising process, and the resulting liquid phase remains in the fine pores inside the granule powder according to the principle of the capillary tube. It helps sinter inside the powder but does not fill the coarse pores. As a result, it is possible to obtain a microstructure in which granular regions having fine pores therein are arranged by point contact, as shown in the drawing on the right. This formed microstructure can be obtained.

Eventually, the size of the coarse pores depends on the size of the granular powder. For example, assuming that the granules are composed of the same size of sintered granules and the granules are stacked in a dense structure, the minimum size of the coarse pores is about 0.077 * D (D is Powder diameter), and the pore diameter in terms of equivalent area is about 0.23 * D. As described in the examples, when the particle size of the granules is between 30 and 150 microns, coarse pore channels of 1 micron or more or 10 microns or more can be secured, and silicon nitride is generated by nitriding reaction inside the granules and sintering is performed. As it progresses, microporous channels of less than 1 micron can be formed.

Therefore, the Si granule powder of the present invention can provide a porous silicon nitride sintered body having a fine structure in which coarse pores and fine pores coexist by nitriding reaction and post sintering process.

1 is a photograph of the biogranules having various sizes by classifying the biogranules obtained according to an embodiment of the present invention.

Figure 2 is an enlarged photograph of the biogranules obtained in accordance with an embodiment of the present invention.

Figure 3 is a graph showing the weight distribution of the sifted and classified samples according to an embodiment of the present invention.

Figure 4 is a graph showing the measurement of the nitriding rate of the nitrided specimen in accordance with an embodiment of the present invention.

Figure 5 (a) is a graph showing the measured porosity of the SD5-RBSN and SD5-SRBSN specimens according to an embodiment of the present invention, (b) is a graph showing the shrinkage and mass change rate of the SD5-SRBSN.

Figure 6 (a) is a graph showing the measured porosity of the SD51-RBSN and SD51-SRBSN specimens, Figure 6 (b) is a graph showing the shrinkage and mass change rate of the SD51-SRBSN.

7 is an electron microscope photograph of the SD51-SRBSN specimen according to an embodiment of the present invention.

FIG. 8 is a photograph of the fracture surface of the SD5-SRBSN specimen according to an embodiment of the present invention, which is observed by scanning electron microscope (SEM), arranged by granule size.

9 is a photograph of an SD5-SRBSN specimen according to an embodiment of the present invention after the resin impregnation was polished by an optical microscope.

10 is a graph showing the results of XRD analysis of the SD5-SRBSN specimen according to an embodiment of the present invention.

11 is a graph showing the size distribution of the pore channel by the mercury porosimetry of the SD5-SRBSN specimen according to an embodiment of the present invention.

12 is a graph showing the measurement of the cumulative specific surface area for the particle size of the SD5-SRBSN specimen according to an embodiment of the present invention.

FIG. 13 is a graph illustrating the mercury porosity analysis results of SD5-SRBSN and SD51-SRBSN according to an exemplary embodiment of the present invention.

14 is a graph showing the shrinkage and porosity behavior of the SD51-SRBSN specimen according to the sintering temperature according to an embodiment of the present invention.

FIG. 15 is a graph showing a change in pore distribution and cumulative specific surface area according to pore size according to the sintering temperature of the SD51-SRBSN specimen according to the embodiment of the present invention.

16 is a view for schematically explaining the pore structure of the porous sintered body according to the present invention.

Claims (12)

Granulating a raw material comprising silicon and a sintering aid for producing a silicon nitride sintered body from the silicon; Pressure-free molding the granulated raw material in a mold; And Method for producing a porous reaction silicon nitride comprising the step of sintering the molded body in a nitrogen atmosphere. The method of claim 1, The sintering aid is a method for producing a porous reaction silicon nitride characterized in that it comprises yttria and alumina. The method of claim 1, The reaction sintering step Nitriding the molded body; And Sintering the nitrided molded body, The nitriding step is a method for producing a porous reaction sintered silicon nitride, characterized in that carried out at a temperature of 1300 ~ 1500 ℃. The method of claim 1, The content of the sintering aid is a method for producing porous reaction sintered silicon nitride, characterized in that 2 to 10% by weight based on the complete nitriding of the silicon. The method of claim 1, The granular powder is a method for producing porous reaction silicon nitride characterized in that the maximum weight frequency in the range of 30 to 150 microns. delete delete delete delete delete delete delete

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