KR100646212B1 - Producing method of highly porous, high strength ceramics materials and the materials the same - Google Patents

Abstract

The present invention relates to a porous ceramics used as a base material of various industries,

A starting material consisting of a polysiloxane powder, a reactive filler, and a strength enhancer is formed by uniformly mixing polymer microspheres or expandable polymer microspheres as a medium for pore formation, and curing or thermal expansion thereof. And after curing, pyrolysis and chemical reaction to produce various porous ceramic materials having high porosity and high strength.

Since the porous ceramic material of the present invention has a porosity of 60 to 93%, a compressive strength of 12 Mpa or more, a porosity of 10 ⁹ to 10 ¹⁰ / cm3, and a high porosity and high strength, it can be suitably used as various high temperature structural materials. .

Polysiloxane, porous ceramics, reactive filler, polymeric microspheres, expandable polymeric microspheres, strength enhancers, shaped bodies, pyrolysis, chemical reactions

Description

Manufacturing method of high-porosity high-strength porous ceramics and its ceramic materials {PRODUCING METHOD OF HIGHLY POROUS, HIGH STRENGTH CERAMICS MATERIALS AND THE MATERIALS THE SAME}

1 is a process chart showing a manufacturing method of the high porosity porous ceramics of the present invention,

2 is an electron micrograph of a high porosity high-strength silicon carbide porous ceramics produced by the production method of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to porous ceramics used as basic materials in various industries, and more particularly, to a method for producing porous ceramics having a high porosity and high strength, and a ceramic material thereof.

Porous ceramics include various high temperature structural materials, various filters, high temperature refractory materials, kiln furniture, impact absorbing materials, sound absorbing materials, lightweight structural materials, insulating materials, and preforms for composite materials manufactured by impregnation. It is a material widely used as an industrial base material.

However, when the porosity of the porous ceramics is low, the insulation and filtration characteristics are lowered, and the material saving effect in the porous ceramic material is also reduced.

Therefore, the porosity of the porous ceramics is good, but the higher the porosity has the disadvantage that the strength of the material is lowered. In addition, if the porosity of the porous ceramic material is low, it means that the porosity is lowered, or the pore size is relatively increased at a constant porosity, and thus the material having a low pore density also has a problem of low strength. When the porous ceramic material is low in strength, it is difficult to apply to a technical field requiring small and light weight because of its thick thickness when used as a structure that receives a constant load, and the manufacturing cost increases.

Therefore, it is desired to develop a porous material having high strength while achieving high porosity and high porosity at the same time.

On the other hand, the strength of the porous ceramics largely depends on the porosity, generally following the empirical formula.

σ _P = σ _O exp (-bP)

Σ _P is the strength of the porous ceramics, σ _O is the strength of the ceramic having a porosity of 0%, b is a constant, and P is the volume fraction of the pores. Since the strength of the porous ceramics decreases exponentially as the porosity increases, in order to prepare a high-porosity and high-strength porous ceramics at a porosity of 60% or more, (1) the stress concentration in the pores can be avoided. It is essential to create spherical pores, (2) to reduce the size of critical defects (ie to increase pore density), and (3) to increase the strength of the strut between the pores and the pores. to be.

On the other hand, generally, the manufacturing method of a porous ceramic material can be largely divided into four methods as follows.

First, after dipping the polymer sponge into a ceramic slurry of a desired ceramic composition, the polymer slurry coated with the ceramic slurry is compressed to remove excess slurry, followed by a drying and sintering process, and a porous composition having various compositions. It is a method of manufacturing ceramics. At this time, the polymer sponge is pyrolyzed during the sintering process to fly to the gas, leaving pores (where the strut of the sponge was located) inside the strut between the pores and the pores. The process has the advantage that the pore size of the porous ceramics can be easily controlled by controlling the pore size of the polymer sponge.

However, the strength of the porous ceramics depends on the pore size and the strength of the strut between the pores and the pores. The porous ceramics produced by the above process have a pore size of about 100 μm to 3 mm, Since pores are included in the posts between the pores, the strength of the porous ceramics is low.

Secondly, there is a method of manufacturing a porous ceramic material by adding and thermally decomposing a thermally decomposable substance or a volatile substance to the ceramics, and volatilizing the thermally decomposable component or the volatile component in the mixture. As such a method, a method disclosed in US Pat. Nos. 5,358,910 and 5,790,449 is representative. In summary, first, a polysiloxane and a silicon carbide (SiC) mixture is optionally added with a polysiloxane hardener and a sintering aid to prepare a molded body of a predetermined shape, and a porous ceramics is formed through a hardening process and a sintering process.

However, this method has a problem that the open porosity of the prepared porous ceramics is 25% or more and less than 40%, making it difficult to manufacture a high porosity material having a porosity of 60% or more.

Third, there is a method of producing a porous ceramic material by lowering the sinterability of ceramics.

This can be divided into two methods. First, there is a method of forming more pores by sintering conditions of ceramics, for example, by sintering the temperature below an appropriate sintering temperature to lower the relative density of ceramics. However, since the porous ceramics prepared by this method are not sintered under optimum sintering conditions, there is a problem that mechanical properties such as strength are significantly lowered.

In addition, as the invention disclosed in US Pat. No. 6,214,078, there is a method for producing a porous ceramic by lowering the sintering property by using a difference in particle size of a ceramic raw material. In detail, a large-size particle and a small particle ceramic raw material are mixed to prepare a molded article having a predetermined shape, and when sintered with heat, the particle surface energy acting as a driving force for sintering is relatively higher than that of the small-sized particle. Since small large particles interfere with sintering, the relative density of the ceramics is lowered and pores are formed to produce a porous ceramics. However, this method also has a disadvantage in that it is difficult to produce porous fine ceramics having a porosity of 50% or more, and has problems such as uneven pore size and distribution and difficulty in controlling pore size.

Fourthly, as a method disclosed in U.S. Patent No. 4,900,698, there is disclosed a method for obtaining porous ceramic materials of various composition by adding metal powder to a ceramic raw material. In this method, the molded body is made of a mixture of ceramic filler, metal powder, polyolefin and plasticizer, and during heating, the plasticizer and polyolefin are decomposed and burned to form pores, and the temperature at which the metal component is oxidized. It is composed of a process of obtaining a porous ceramics material by heating the metal powder and oxidizing the metal powder and combining the oxidized metal powder with a ceramic filler. However, this method has a problem in that the composition of the porous ceramic material is limited to oxide, so that it is difficult to manufacture non-oxide-based materials such as silicon carbide or silicon nitride.

Further, the ceramic materials of silicon carbide, silicon nitride, mullite, cordierite, etc. can be made of porous ceramic materials having high strength and high pore density targeted at high porosity of 60% or more by any of the methods described above. It was difficult to manufacture.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing a porous ceramic material and a material capable of achieving high porosity and high strength at the same time.

Method for producing a porous ceramic material of the present invention to achieve the above object,

Preparing a molded body by uniformly mixing and molding a starting material consisting of a polysiloxane powder, a reactive filler, a polymer microsphere, and a strength enhancer;

Curing the molded body;

And thermally decomposing and chemically reacting the components of the molded body by heating the cured molded body.

In addition, another method for producing a porous ceramic material of the present invention,

Preparing a molded body by uniformly mixing and molding a starting material consisting of a polysiloxane powder, a reactive filler, an expandable polymer microsphere, and a strength enhancer;

Thermally expanding the molded body;

Curing the expanded molded body;

And thermally decomposing and chemically reacting the components of the molded body by heating the cured molded body.

According to the above method, a porous porous ceramic material having a porosity of 60 to 93%, a compressive strength of 12 Mpa or more, a pore density of 10 ⁹ to 10 ¹⁰ particles / cm 3 or more, a porosity and a high porosity, and a high pore shape You can get it.

Hereinafter, the manufacturing method of the high porosity high strength porous ceramic raw material of this invention, and its raw material are demonstrated in detail.

In the present invention, polysiloxane and various kinds of reactive fillers reacting with the same are essentially added to the starting materials and chemically reacted with the reactants, such as silicon carbide, silicon nitride, mullite, cordierite, and the like. The main characteristic is to obtain a porous ceramic material of cargo type and oxide type.

In addition, by including the fine spherical particles (hereinafter referred to as microspheres) as a medium for pore formation in the starting material to form a large number of spherical pores having a uniform distribution by evaporation or expansion and evaporation of the microspheres, high porosity Another feature of the present invention is that it is possible to achieve a high strength and at the same time. In addition, in the present invention, a strength enhancing material having a predetermined content is essentially included in the starting material, thereby increasing the strength of the material.

Therefore, the starting material for producing the material of the present invention, polysiloxane powder, reactive filler, microspheres, strength enhancer is essentially included.

1 is a process chart showing a method for producing a microporous ceramic material of the present invention.

As shown in FIG. 1, a common process for producing a high porosity high strength porous ceramic material of the present invention is a mixed molding process of a starting material, a curing process, pyrolysis to form pores and to obtain a ceramic product of a desired component. It is a chemical reaction process.

The production method of the present invention can be classified into two types according to the pore forming mechanism of the microspheres used as a medium for pore formation.

First, in the case of using the polymer microspheres, as shown in Figure 1a, it is possible to produce a high porosity high-strength porous ceramic material by mixing molding, curing, thermal decomposition and chemical reaction process of the starting material. In this case, pores are formed in such a way that the polymer microspheres evaporate in the pyrolysis and chemical reaction processes and pores are formed at the evaporated sites (hereinafter, referred to as pore forming mechanism a).

Next, in the case of using expandable polymer microspheres as a pore-forming medium as shown in FIG. 1B, a step of heat-expanding the molded body after mixing molding of the starting material is added, and the subsequent curing step is performed by the pore forming mechanism a. Same as the case of using a polymeric microsphere of the type. In this case, the expandable polymer microspheres are expanded during the thermal expansion process to increase the volume of the entire molded body (ie, decrease the density), and thus are effective in further increasing the porosity. In the pyrolysis process, the expanded microspheres are evaporated to form pores (hereinafter, referred to as pore forming mechanism b).

Hereinafter, a method of manufacturing a porous ceramic material according to each pore forming mechanism will be described in detail.

First, the starting material should be mixed and molded into a shaped body by any pore forming apparatus.

The uniform mixing of starting materials is very important because it is closely related to the uniform distribution of pores. Therefore, the above starting materials are uniformly mixed for a sufficient time, either dry or wet, and are molded into a molded body having a predetermined shape by a conventional molding process. That is, the raw material mixture may be molded through both the uniaxial pressure molding process and the hydrostatic pressure molding process which are generally used, or may be selected by molding only the uniaxial pressure molding process or the hydrostatic pressure molding process. However, in addition to such a molding method, if necessary, a molding process such as extrusion molding or injection molding can be used.

The composition of the starting material can be variously adjusted within a range to have properties suitable for the use required by the ceramic material as the final product. However, the starting material composition ratio is preferably as follows in order to manufacture the material more stably and to produce a material having desirable properties (eg, meat porosity, meat porosity and high strength).

By weight polysiloxane is preferably included in the range of 9 to 50% of the starting material.

Since polysiloxanes function as molding aids in the molding process, if they are too small, the strength of the molded body is so weak that they will be destroyed in the subsequent expansion or curing process or the strength will be reduced so that the specimen cannot be handled. In addition, if the content is excessively high, the content of the microspheres, which are pore-forming agents, is relatively small, so that it is difficult to achieve a porosity of 60% or more.

In addition, the reactive filler is preferably included in the range of 3 to 51% by weight of the starting material.

Since the reactive filler chemically reacts with the pyrolysis residue of polysiloxane in the pyrolysis and chemical reaction process to form a predetermined porous ceramic material, it is preferably included at least 3% or more to form a stoichiometric compound in the reaction. In addition, if the content is too large, the content of the microspheres, which are pore-forming agents, is relatively small, so that it is difficult to achieve a porosity of 60% or more. Since the reactive filler reacts with the pyrolysis residue of the polysiloxane to form porous ceramic materials of various component compositions, the reactive filler can be appropriately selected and used from materials having good reactivity with the polysiloxane. As a preferable reactive filler, one or more or a mixture thereof selected from Al ₂ O ₃ , MgO, graphite, carbon black and phenol resin is preferable.

In addition, the content of the preferred starting material of the polymer microspheres included as the pore-forming medium is 30% to 75% by weight. If the content of the polymer microspheres is less than the above range, it is difficult to achieve a high porosity of 60% or more, and if it is above the above range, too many pores are formed to achieve a target compressive strength (eg, 12 MPa or more). In addition, the particle size of the polymer microspheres is directly related to the size of the pores generated after evaporation. If the variation in pore size is too large, there are disadvantages such as nonuniformity of strength as described above, and the particle size of the polymer microspheres may have a particle size range of 8 to 100 μm in terms of uniformity of pore size. The polymeric microspheres should be ones that can be easily evaporated under pyrolysis conditions without disturbing the reaction of the pyrolysis residue of the polysiloxane with the reactive filler. As a material meeting these conditions, spherical polymethylmethacrylate (poly (methylmethacrylate)) (hereinafter referred to as PMMA microspheres) or spherical polymethylmethacrylate ethylene glycol dimethacrylate (poly (methylmethacrylte-co-ethylene glycol) dimethacrylate)).

On the other hand, when using expandable polymer microspheres as pore-forming medium, the content of the starting material is preferably included in the range of 30 ~ 70%, the numerical limitation is the same as the reason for limiting the content of the polymer microspheres .

In addition, the expandable microspheres used as the pore-forming medium have an average diameter of 6 to 12 μm filled with isobutane or isopentane as a medium for expansion in the shell made of PMMA and the space inside the film. Is a spherical material of which is a commercially available material. When the microspheres are heated to 120 ~ 200 ℃ at atmospheric pressure, the film is softened, the internal gas phase volume is expanded and has the property of expanding to a spherical material having an average diameter of 10 ~ 50㎛.

On the other hand, the strength enhancer in the starting material is included to remain inert particles in the molding-curing process to maintain the shape of the molded body, and to enhance the strength of the product produced by the chemical reaction in the thermal decomposition and chemical reaction process. Preferred strength enhancers include at least one selected from Al ₂ O ₃ , Y ₂ O ₃ , and Y ₃ Al ₅ O ₁₂ , or mixtures thereof. The strength enhancer is preferably contained at least 0.5% by weight in the starting material to have a sufficient strength enhancing effect. In addition, when the amount is too large, the ceramic material becomes too dense and the target porosity cannot be obtained, so it is preferably added at 8% or less. The strength enhancer promotes a chemical reaction by forming a liquid phase in a chemical reaction process between a residue produced by thermal decomposition of polysiloxane and a reactive filler, and after completion of the reaction, promotes densification of the support site between the pores and the pores. By increasing the strength of the strut site contributes to the strength of the entire porous ceramics.

The molded product formed by mixing and molding the components of the above-described preferred composition is subjected to curing (for the pore forming mechanism a) or curing after heat expansion (for the pore forming mechanism b).

In the case of the pore forming mechanism b, the thermal expansion conditions are preferably heated at a range between the softening temperature and the melting temperature of the polysiloxane. In order for the expandable polymer microspheres to expand, the surrounding polysiloxane particles need to be softened, and when the polysiloxane is melted, it is difficult to maintain the shape of the molded body. In addition, after reaching the desired temperature in the heat expansion step, it is important to maintain the expanded molded body below the softening temperature of the polysiloxane to maintain the expanded volume as it is.

In the curing step, for example, in order to thermoset the polysiloxane, the molded body (for the pore forming mechanism a) or the expanded molded body (for the pore forming mechanism b) is heated to 130 to 190 ° C under atmospheric pressure. It is desirable to keep it within 48 hours at the heated maximum temperature. Even if the holding time at the maximum temperature is longer than 48 hours, no further curing occurs, so the holding time at the maximum temperature is preferably limited to within 48 hours. At this time, if the heating rate is too fast, there is a fear that the curing of the polysiloxane is insufficient, so the heating rate is preferably 2 ° C / min or less.

In the process of the invention, the core process is the last pyrolysis and chemical reaction process.

In the pyrolysis process, the polymer microparticles or the expanded polymer microspheres are pyrolyzed to evaporate into gas to form pores, and some components of the reactive filler (for example, a part of H and C in the phenol resin) are pyrolyzed to evaporate into gas to obtain pores. Form. In addition, polysiloxanes are pyrolyzed to leave a portion of H and C volatilized, leaving behind pyrolysis residues of SiO ₂ (when pyrolyzed under air or oxygen atmosphere) or SiO ₂ + C (when pyrolyzed under nitrogen or inert atmosphere). .

The pyrolysis residue of the polysiloxane is chemically reacted with the reactive filler or the pyrolysis residue of the reactive filler (e.g. carbon in the case of phenol resins) to form the desired porous ceramic material. At this time, according to the type and the reaction atmosphere of the reactive filler, various kinds of ceramic materials as follows can be produced.

2SiO ₂ + 3Al ₂ O ₃ → Al ₆ Si ₂ O ₁₃ (mullite). (One)

5SiO ₂ + 2Al ₂ O ₃ + 2MgO → Mg ₂ Al ₄ Si ₅ O ₁₈ (cordierite). (2)

SiO ₂ + ₃ C → SiC + 2CO... (3)

3SiO ₂ + 6C + 2N ₂ → Si ₃ N ₄ + 6CO... (4)

In the reactions of (1) and (2) above, when Al ₂ O ₃ or Al ₂ O ₃ and MgO are used as the reactive filler in an air or oxygen atmosphere, a mullite and cordierite porous ceramic material is produced, respectively.

In addition, in the reaction of (3), a porous silicon ceramic material is made under an inert atmosphere such as argon or helium, and in the reaction of (4), a silicon nitride porous ceramic material is produced in a nitrogen atmosphere. Part of the C component in the reactions of (3) and (4) is the pyrolysis residue of polysiloxane, and the other part is from graphite, carbon black or phenol resin added with reactive filler.

As described above, according to the present invention, a high porosity high strength porous ceramic material having various kinds and compositions can be produced by appropriately selecting the composition of the starting material and appropriately selecting the reactive filler and the reaction atmosphere.

The temperature of the pyrolysis and chemical reaction process is preferably in the range of 1300 ~ 1700 ℃. Polysiloxanes are pyrolyzed even when heat treated at temperatures below 1300 ° C, but the strength of the formed material is weak due to incomplete chemical reactions. Because of the size. If the temperature increase rate is increased too rapidly in the pyrolysis and chemical reaction process, the polysiloxane may be thermally decomposed rapidly and cracks may occur in the molded body. Thus, the temperature increase rate is lower than 5 ° C./min up to 800 ° C. when the thermal decomposition of the polysiloxane is completed. Good to do.

As described above, in the production of the porous ceramics, mixing molding, curing, pyrolysis and sintering of the starting materials are common processes. Although this common process is applied to the method of the present invention, since the chemical reaction of the components is completed during the pyrolysis process, a porous ceramic having desired characteristics can be obtained, and thus no additional sintering process is required, and thus the heating temperature during the pyrolysis process is also required. There is an advantage that it does not have to be a high temperature enough to sinter as in the conventional. In addition, the manufacturing process of the present invention does not need to use a pressure vessel other than the mixing molding process, almost all processes can be performed under atmospheric pressure. As such, the method of the present invention can be carried out at a relatively low temperature and low pressure as compared with the conventional method for producing porous ceramics, and therefore is more economical.

In addition, the porous ceramic material prepared by the present invention is a spherical shape of the pores, the pore size is small to 100㎛ or less, the pore density is 10 ⁹ ~ 10 ¹⁰ / cm ³ very high, between the pores and pores The strut portion of is sufficiently densified in the role of strength enhancer, and has the advantage that the strength is very excellent at the same porosity as compared to the porous ceramics manufactured by the prior art.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

As starting materials, polysiloxane powder having an average particle size of 44 μm or less, Al ₂ O ₃ (reactive filler) powder having an average particle size of 3 μm, PMMA microspheres having a diameter of 8 to 20 μm, and Y ₂ O having an average particle size of 1 μm ₃ (Strength Enhancer) Powder was prepared and charged into a polyethylene ball mill at the mixing ratio (weight ratio) shown in Table 1 and mixed by dry ball milling for 24 hours using a Teflon ball. Thereafter, the raw material mixture was uniaxially press-molded at a pressure of 150 kg / cm ² in a mold having a rectangular parallelepiped shape of 100 × 100 × 8 mm to prepare a molded body.

Specimen No. 12 and 13 were prepared as a comparative example by mixing and molding mullite powder having an average particle size of about 1 μm and PMMA microspheres having a diameter of 8 to 20 μm at the mixing ratios shown in Table 1. Same as the other psalms.

The molded body was cured and heat treated (pyrolysis and chemical reaction) under the conditions shown in Table 1 to prepare a porous mullite ceramics. However, in the case of Comparative Examples Nos. 12 and 13, no curing process was necessary and did not go through.

The compressive strength of the mullite-like invention examples 1 to 11 and Comparative Examples 12 and 13 prepared under the conditions of Table 1 were measured, and the pore size, pore density (number of pores per unit volume) and porosity (the entire material) were obtained from the electron micrograph. Volume fraction of pores to volume) is measured and the results are shown in Table 2. The pore size was measured using an electron micrograph using an image analyzer (ie, Image-Pro Plus, Medis Cybernatics, Inc., Silver Spring, Md, USA).

Example 2

As starting materials, polysiloxane powder having an average particle size of 37 μm or less, Al ₂ O ₃ powder having an average particle size of 1 μm and MgO powder (reactive filler) having an average particle size of 2 μm, expandable PMMA fine particles having a diameter of 6 to 12 μm Spheres (spherical particles filled with PMMA film and isopentane inside the film) and Y ₂ O ₃ (strength enhancer) powder having an average particle size of 1 μm were prepared, and the polypropylene was mixed at the mixing ratio (weight ratio) shown in Table 3. Charged in a ball mill and ethanol of the same weight as the above raw material was added as a solvent, followed by mixing by ball milling for 6 hours using a Teflon ball. Thereafter, the slurry of the raw material mixture was dried in a well-ventilated place, and uniaxially pressurized at a pressure of 180 kg / cm ^{2 in} a 50 × 50 × 5 mm rectangular parallelepiped mold to prepare a molded body. Samples 18 and 19 used SiO ₂ powder having an average particle size of about 1 μm in place of polysiloxane as a comparative example, and other starting materials were prepared using the same raw materials and processes as the above examples.

The molded article was thermally expanded, cured and heat treated (pyrolyzed and chemically reacted) under the conditions shown in Table 3 to prepare porous cordierite ceramics. At this time, the specimens 18 and 19, which are comparative examples, were all broken in the expansion process, so that subsequent experiments could not be performed. This is because there is no component (eg polysiloxane) that can accommodate the expansion of the expandable microspheres in the molded body. From these results, it can be seen that when using expandable microspheres as a medium for pore formation, polysiloxane, which is an essential component of the present invention, must be included in the starting material.

Compressive strength was measured for Inventive Examples 14 to 17 of cordierite produced under the conditions of Table 3, the pore size, pore density and porosity were measured from the electron micrograph, and the measured results are shown in Table 4.

Example 3

As starting materials, polysiloxane powder having an average particle size of 44 μm or less, Al ₂ O ₃ powder having an average particle size of 0.5 μm, MgO powder (reactive filler) having an average particle size of 1 μm, and spherical polymethylmethes having a diameter of 15 to 25 μm Acrylate coethylene glycol dimethacrylate (poly (methylmethacrylte-co-ethylene glycol dimethacrylate)) (polymer microspheres), Y ₂ O ₃ (strength enhancer) powder having an average particle size of 1㎛ was prepared, and Table 5 Charged into a polyethylene ball mill at the mixing ratio (weight ratio) shown in and mixed by dry ball milling for 24 hours using a Teflon ball. Thereafter, the raw material mixture was uniaxially press-molded at a pressure of 200 kg / cm ² in a mold having a rectangular parallelepiped shape of 50 × 50 × 5 mm to prepare a molded body.

Samples 24 and 25 used SiO ₂ powder having an average particle size of about 1 μm in place of polysiloxane as a comparative example, and other starting materials were prepared using the same raw materials and processes as the above examples.

The molded article was cured and heat treated (pyrolyzed and chemically reacted) under the conditions shown in Table 5 to prepare porous cordierite ceramics, and the characteristics (compressive strength, pore size, porosity, pore density) were measured. Indicated. However, in the case of specimens 24 and 25 as the comparative example, the curing process was not necessary and did not go through.

Example 4

As starting materials, polysiloxane powder having an average particle size of 44 μm or less, carbon black powder having an average particle size of 0.01 μm or graphite powder having an average particle size of 3 μm (reactive filler), PMMA microspheres having a diameter of 50 to 100 μm, Al ₂₁ O ₃ powder having an average particle size of 0.5 μm and Y ₂ O ₃ (above, strength enhancing material) powder having an average particle size of 1 μm were prepared, and charged into a polyethylene ball mill at a mixing ratio (weight ratio) shown in Table 7. Teflon balls were mixed by dry ball milling for 24 hours. Thereafter, the raw material mixture was uniaxially press-molded at a pressure of 200 kg / cm ² in a mold having a rectangular parallelepiped shape of 50 × 50 × 5 mm to prepare a molded body.

Samples No. 30-31 used SiC powder having an average particle size of about 0.27 μm in place of the polysiloxane and the reactive filler, and the microspheres were made of the same raw materials as the above examples, and the mixing and forming processes were the same as those of the above examples. Prepared using the process.

The molded article was cured and heat treated (pyrolysis and chemical reaction) under the conditions shown in Table 7 to prepare porous silicon carbide ceramics, and the compressive strength, pore size, porosity and pore density were measured using the electron micrograph. Represented by. However, in the case of specimens 30 and 31, which are comparative examples, the curing process was not necessary and did not go through.

Specimen No. 31, which is a comparative example, was broken after the heat treatment process, so that subsequent measurement of properties could not be performed. From these results, it can be seen that more than 50% of PMMA microspheres, which are mediators of pore formation, cannot be added by the general powder manufacturing process, not the chemical reaction process between the pyrolysis residue of the polysiloxane and the reactive filler. This means that it is difficult to achieve meat power.

Example 5

As starting materials, polysiloxane powder having an average particle size of 44 μm or less, phenolic resin powder (reactive filler) having an average particle size of 44 μm or less, expandable PMMA microspheres having a diameter of 6 to 12 μm, Y _{3 having an} average particle size of 1 μm An Al ₅ O ₁₂ (strength enhancer) powder was prepared, charged into a polypropylene ball mill at the mixing ratio (weight ratio) shown in Table 9, and ethanol having the same weight as the weight of the raw material was added as a solvent, followed by teflon ball. And mixed by ball milling for 4 hours. Thereafter, the slurry of the raw material mixture was dried and uniaxially press-molded at a pressure of 180 kg / cm ² in a mold having a rectangular parallelepiped shape of 50 × 50 × 5 mm to prepare a molded body.

Expanded, cured and heat treated (pyrolysis and chemical reaction) of the molded body under the conditions shown in Table 9 to prepare porous silicon carbide ceramics, and by using the electron micrograph to measure the compressive strength, pore size, porosity and pore density It is shown in Table 10.

Example 6

As starting materials, polysiloxane powder having an average particle size of 44 μm or less, phenolic resin powder (reactive filler) having an average particle size of 44 μm or less, expandable PMMA microspheres having a diameter of 6 to 12 μm, Y _{2 having an} average particle size of 0.3 μm Prepare an O ₃ (strength enhancer) powder, load it into a polypropylene ball mill at the mixing ratio (weight ratio) shown in Table 11, add ethanol having the same weight as the weight of the raw material as a solvent, and then use Teflon ball. Mix by ball milling for 4 hours. Thereafter, the slurry of the raw material mixture was dried and uniaxially pressurized at a pressure of 170 kg / cm ^{2 in} a 30 × 30 × 4 mm rectangular parallelepiped mold to prepare a molded body.

Specimen Nos. 42-43 used Si ₃ N ₄ powder having an average particle size of about 0.3 μm as a comparative example, and the microspheres were spherical polymethylmethacrylate coethylene glycol dimethacrylate having a diameter of 15 to 25 μm (poly (methylmethacrylte). -co-ethylene glycol dimethacrylate)) (polymer microspheres) was prepared using the same mixing and molding process as in the invention example.

The molded article was expanded, cured and heat treated (pyrolysis and chemical reaction) under the conditions shown in Table 11 to prepare porous silicon nitride ceramics, and the compressive strength, pore size, porosity and pore density were measured using the electron micrograph. 12.

In Comparative Example 42-43, the expansion and hardening process were not necessary because the expansion and hardening process were not performed, and the molded body was manufactured by heat treatment under the conditions shown in Table 11.

As can be seen above, the porous ceramic materials of mullite, cordierite, silicon carbide, and silicon nitride prepared by the method of the present invention all have a high porosity of 60% or more and a compressive strength of at least 12 MPa or more. Porosity It can be seen that the material of high strength. In addition, the pore density also has a high value of 10 ⁹ / cm 3 or more, and as shown in FIG. 2, it can be seen that the size and distribution of the pores are also relatively uniform.

As described above, according to the method of manufacturing the porous ceramic material of the present invention, it is possible to easily produce a high porosity high strength porous ceramic material of mullite, cordierite, silicon carbide and silicon nitride, which was difficult to achieve in the past. It is very economical in terms of manufacturing cost since no sintering process is required and all reactions are completed at relatively low temperature and low pressure.

In addition, the porous ceramic material according to the present invention can realize a high porosity and high strength at the same time, because the pores are spherical and uniform size distribution, it can be used suitably for various high-temperature structural materials.

Claims (9)

By weight, polysiloxane powder 9 to 50%, reactive filler powder 3 to 51%, PMMA (poly (methylmethacrylate)) or polymethylmethacrylatecoethylene glycoldimethacrylate (poly ( methylmethacrylte-co-ethylene glycol dimethacrylate)) and a starting material consisting of 30 to 75% of fine spherical particles having a diameter of 8 to 100 µm and a strength enhancer of 0.5 to 8%, uniformly mixing and molding to prepare a molded article ; Curing the molded body; Heating the cured molded body to thermally decompose and chemically react constituents of the molded body; a method of manufacturing a high porosity high-strength porous ceramic material comprising a. 6 to 12 micron fine spherical particles 30 to 70 in weight%, having 9 to 50% of polysiloxane powder, 3 to 51% of reactive filler powder, and a PMMA coating and filled with isobutane or isopentane gas in the space inside the coating. %, The starting material consisting of 0.5 ~ 8% strength enhancer uniformly mixed and molded to produce a molded body; Thermally expanding the molded body; Curing the expanded molded body; Heating the cured molded body to thermally decompose and chemically react constituents of the molded body. The method according to claim 1 or 2, The hardening is a method for producing a high porosity high strength porous ceramic material, characterized in that the step of heating the molded body at 130 ~ 190 ℃ under atmospheric pressure to heat curing. The method according to claim 1 or 2, The pyrolysis and chemical reaction step, the method for producing a high porosity high-strength porous ceramic material, characterized in that the heating is carried out at 1300 ~ 1700 ℃ under a predetermined reaction atmosphere. The method of claim 2, The molded body is heated to a temperature in the range between the softening temperature and the melting temperature of the polysiloxane is expanded, the method of producing a high porosity high-strength porous ceramic material. The method according to claim 1 or 2, The reactive filler is Al ₂ O ₃ , MgO, graphite (graphite), carbon black, a phenol resin (phenol resin) at least one selected from or a mixture thereof, characterized in that the high porosity high-strength porous ceramic material. The method according to claim 1 or 2, The strength enhancer is at least one selected from Al ₂ O ₃ , Y ₂ O ₃ , Y ₃ Al ₅ O ₁₂ or a mixture thereof. A porous ceramic material produced by the method of claim 1 or 2, High porosity high strength porous ceramic material, characterized in that the porosity 60 ~ 93%, compressive strength 12Mpa or more, pore density 10 ⁹ ~ 10 ¹⁰ / cm 3 or more. The method of claim 8, The material is a high porosity high strength porous ceramic material, characterized in that the mullite, cordierite, silicon carbide, silicon nitride.

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