KR102149834B1 - A method for manufacturing of a porous silicon carbide sintered body by carbothermal reduction process - Google Patents

Abstract

The present invention relates to a method of manufacturing a silicon carbide sintered body by a thermal carbon reduction process, and more particularly, a sol-gel process using a liquid silicon compound and a carbon compound as a starting material and a metal compound for accelerating the thermal carbon reduction reaction. After preparing silicon dioxide and carbon composite powder to which a metal compound is added, a molded body is prepared using the silicon dioxide-carbon composite powder, and then heat-treated at a constant temperature to synthesize silicon carbide through thermal carbon reduction reaction. The present invention relates to a method for producing a porous silicon carbide sintered body in which micropores are uniformly distributed and excellent in mechanical strength.

Description

Manufacturing method of porous silicon carbide sintered body by thermal carbon reduction process {A METHOD FOR MANUFACTURING OF A POROUS SILICON CARBIDE SINTERED BODY BY CARBOTHERMAL REDUCTION PROCESS}

The present invention relates to a method of manufacturing a porous silicon carbide sintered body by a thermal carbon reduction process, and more particularly, to a method of lowering a heat treatment temperature for manufacturing a porous silicon carbide sintered body.

Silicon carbide has excellent properties such as abrasion resistance, thermal shock resistance, excellent thermal conductivity, and corrosion/chemical resistance.Silicone carbide porous material as a porous material is a catalyst carrier, water quality and dust filter material, adsorbent material, insulating material depending on the pore size. , Gas phase separation materials, artificial biomaterials, and shock absorbing materials.It is widely used as a core material in various industries, and recently, semiconductor, chemical, environmental and energy industries that require high temperature stability, chemical resistance, and high temperature mechanical properties. The range of applications is increasing significantly.

Until now, the production technology of porous silicon carbide having micro- or mesoporous pores has been reported to be manufactured in the form of porous silicon carbide powder for use as a catalyst carrier, but a technology for manufacturing a mesoporous silicon carbide sintered body having excellent mechanical strength Is reported very little.

According to the research results of MI Ledoux and Vix-Guterl, a liquid carbon raw material was added to silicon dioxide having nanometer-sized pores and reacted with gaseous silicon using a thermal carbon reduction method or a nanoporous carbon template, resulting in a specific surface area of 170. A silicon carbide powder having micro- or meso-sized pores of m ² /g was prepared, but the technology was not economically feasible using expensive starting materials, and no technology was proposed for a method of making a porous silicon carbide structure of a certain shape. .

According to XY GUO's and EP Simonenko's presentations, silicon dioxide-carbon gels are prepared by a sol-gel process using phenol resin and tetraethyl orthosilicate, and then heat treated under vacuum or inert atmosphere or through SPS (spark plasma sintering) process. A synthesis technique of a porous silicon carbide powder having a pore size of metric and a specific surface area of up to 200 m ² /g and 110 m ² /g has been reported.

In addition, in US 7,910,082, a technology for manufacturing microporous porous silicon carbide powder with a specific surface area of 400 to 900 m ² /g and an average pore size of 6 nm or less using a precursor manufactured using a phenol resin and TEOS (tetraethyl-orthosilicate) It has been reported, CN 001401564 A is obtained by dissolving a phenol resin in a solvent by adding a transition metal salt, ethyl silicate (or methyl or propyl silicate) and a salt of an inorganic acid, and then hydrolyzing and crosslinking the silicate and drying it at 1200 ~ 1400℃ A technique for preparing a mesoporous porous silicon carbide powder having a specific surface area of 60 to 120 m ² /g and a pore size of 3 to 50 nm by heat treatment at a temperature of 5 to 24 hours has been reported. The micro or mesoporous silicon carbide porous material technology that can be used as a catalyst carrier with a high specific surface area developed so far is mostly limited to a porous silicon carbide powder type manufacturing technology.

In WO2014/207096 A1, a technology for producing a catalyst carrier composed of a porous silicon carbide structure with mesoporous pores having a certain shape has been reported. In this patent, an organic carbon compound such as phenol resin is used as the main raw material to make a carbon structure having a mesoporous size, and a molded body is prepared by mixing it with silicon powder, and then heat treatment is performed under appropriate conditions and atmosphere to direct carbon and silicon. Silicon carbide was synthesized by reaction to prepare a porous silicon carbide structure having mesopores. In the present invention, a manufacturing process of a meso-macroporous silicon carbide porous body having a certain shape through a direct reaction between carbon and silicon was proposed, but precise control of the process is required to control the remaining silicon in the reaction process. The mechanical properties of the silicon structure were not shown.

As described above, since most of the manufacturing technology for manufacturing porous silicon carbide having a high specific surface area and micro or mesopores is in the form of porous silicon carbide powder, the application of the developed porous silicon carbide having a high specific surface area is common. It is limited to a catalyst carrier, and when porous silicon carbide powder is applied as a catalyst carrier in a reaction tank, porous silicon carbide has excellent thermal conductivity characteristics because of the air pockets (voids) formed between the porous silicon carbide powder particles filled in the reaction tank. Heat generated by catalytic reaction in the reaction tank cannot be effectively transferred. In addition, it is believed that the porous silicon carbide powder will have many difficulties in using it as a catalyst carrier under various conditions. Accordingly, in order to expand the application of a porous silicon carbide porous body having a high specific surface area, there is a demand for the development of an economical manufacturing technology for a porous silicon carbide sintered body having a high strength and a certain shape.

1.US 7,910,082 2.CN 001401564A 3. WO2014/207096A1

1.M.I.Ledoux et al, J. Catal. 114 (1988) 176 2. Vix-Guterl et al. J. European Ceram. SoC., 19 (1999) 427 3. E.P. Simonenko, J. Sol-Gel Sci. Technol, (2017) 82:748-759

The present invention is to solve the problems of the prior art as described above.

An object of the present invention is to produce a porous silicon carbide sintered body having a high specific surface area and a high porosity and excellent strength and high economic efficiency.

In other words, by using a liquid silicon source and a liquid carbon source as the starting materials, the starting materials are homogeneously mixed and a metal catalyst is added to increase the reactivity between the starting materials, thereby reducing the temperature and time of the thermal carbon reduction process, thereby reducing the process cost. It aims to provide a way to do it.

The object of the present invention is not limited to the object mentioned above. The object of the present invention will become more apparent from the following description, and will be realized by the means described in the claims and combinations thereof.

In the method of manufacturing a porous silicon carbide sintered body according to the present invention, the method comprising: preparing a mixture by mixing a liquid silicon compound, a liquid carbon compound, and a metal compound, and then gelling to prepare a gelling composition to which a metal compound is added; Drying the gelling composition to prepare a cured gel; First pulverizing the cured gel to obtain a gel powder; First heat-treating the gel powder to prepare a silicon dioxide-carbon composite; Secondary pulverization of the silicon dioxide-carbon composite to prepare a composite powder; Manufacturing a molded body using the composite powder; And secondary heat treatment of the formed body to produce a porous silicon carbide sintered body. Includes.

According to a preferred embodiment of the present invention, the gelling composition may be prepared by adding a catalyst to a mixture in which a liquid silicon compound and a liquid carbon compound and a trace amount of a metal compound are added.

According to another preferred embodiment of the present invention, the catalyst is an acid selected from the group consisting of nitric acid, hydrochloric acid, oxalic acid, maleic acid, acrylic acid, acetic acid, toluene sulfuric acid, and mixtures thereof; A base selected from the group consisting of aqueous ammonia, hexamethylene tetraamine, and mixtures thereof; And it may be one selected from the group consisting of a mixture thereof.

According to another preferred embodiment of the present invention, the liquid silicon compound may be selected from the group consisting of silicon alkoxide, polyethyl silicate, and mixtures thereof.

According to another preferred embodiment of the present invention, the liquid carbon compound may be prepared by dispersing a solid carbon source in a solvent selected from the group consisting of ethanol, methanol, isopropyl alcohol (IPA), and mixtures thereof. .

According to another preferred embodiment of the present invention, the solid carbon source may be selected from the group consisting of carbon black, carbon nanotubes, phenol resins, monosaccharides, disaccharides, and mixtures thereof.

According to another preferred embodiment of the present invention, the metal compound is selected from the group consisting of nitrates of alkali metals, alkaline earth metals, and transition metals, or carbonates of alkali metals, alkaline earth metals and transition metals, and the amount is 1 mol It may be 0.0001 mol to 0.05 mol relative to the silicon source of.

According to another preferred embodiment of the present invention, the liquid carbon compound is 30% to 100% by weight of the solvent; And within 70% by weight of a carbon source.

According to another preferred embodiment of the present invention, the mixture of the liquid silicon compound and the liquid carbon compound may have a carbon/silicon molar ratio (C/Si) of 1.0 to 4.0.

According to another preferred embodiment of the present invention, in the step of preparing the gelling composition, the liquid silicon compound and the liquid carbon compound are mixed by stirring at a temperature within 20°C to 60°C at a rate of 50RPM to 400RPM for 30 minutes or more. I can.

According to another preferred embodiment of the present invention, in the step of preparing the cured gel, drying of the gelling composition may be drying at a temperature of 40°C to 150°C for 2 to 72 hours.

According to another preferred embodiment of the present invention, the first heat treatment may be heat treatment of the cured gel powder at a temperature of 700° C. to 1000° C. for 0.5 to 4 hours in an inert or vacuum atmosphere.

According to another preferred embodiment of the present invention, the production of the molded body may be performed by at least one selected from uniaxial pressure molding, injection molding, and extrusion molding.

According to another preferred embodiment of the present invention, the secondary heat treatment may be heat treatment for 1 to 20 hours at a temperature of 1050°C to 1300°C in an inert atmosphere or a vacuum atmosphere.

According to another preferred embodiment of the present invention, the compressive strength of the porous silicon carbide sintered body is 10Mpa to 30Mpa, the porosity is 60% to 85%, and the specific surface area may be 50m ² /g to 130m ² /g.

According to another preferred embodiment of the present invention, the crystalline phase of the porous silicon carbide sintered body is a beta phase.

According to the manufacturing method for manufacturing the porous silicon carbide sintered body of the present invention, a silicon source and a carbon source are mixed in a liquid phase so that the starting material can be homogeneously mixed, and then a trace amount of a metal compound is added to perform a thermal carbon reduction reaction at a relatively low temperature. It can be generated to synthesize silicon carbide, thereby producing a porous silicon carbide sintered body having excellent strength, a large specific surface area, and a high porosity.

In addition, since the silicon carbide sintered body of the present invention has high specific surface area and porosity, as well as high strength and consists of a single structure, it is possible to achieve effective thermal conduction of heat generated even in gas-switching catalytic reactions in which heat generation is large. It is possible not only to prevent the destruction of the microporous structure due to, but also to minimize the destruction of the catalyst carrier due to thermal shock.

In addition, since the silicon carbide sintered body of the present invention can have various shapes, it can be applied as a filter material for removing foreign substances as well as a catalyst carrier.

The effects of the present invention are not limited to the effects mentioned above. It should be understood that the effects of the present invention include all effects that can be inferred from the following description.

1 is a schematic diagram of a method of manufacturing a porous silicon carbide sintered body by a thermal carbon reduction process according to the present invention.
Figure 2 shows the X-ray diffraction pattern of the porous silicon carbide sintered body according to the present invention.
Figure 3 shows the SEM microstructure of the porous silicon carbide sintered body according to the present invention.

The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments related to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed contents may be thorough and complete, and the spirit of the present invention may be sufficiently conveyed to those skilled in the art.

In describing each drawing, similar reference numerals have been used for similar elements. In the accompanying drawings, the dimensions of the structures are shown to be enlarged than actual for clarity of the present invention. Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are used only for the purpose of distinguishing one component from another component. For example, without departing from the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In the present specification, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance the possibility of being added. Further, when a part such as a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where the other part is "directly above" but also the case where there is another part in the middle. Conversely, when a part such as a layer, a film, a region, or a plate is said to be "under" another part, this includes not only the case where the other part is "directly below", but also the case where another part is in the middle.

Unless otherwise specified, all numbers, values, and/or expressions expressing quantities of ingredients, reaction conditions, polymer compositions, and formulations used herein are those that occur in obtaining such values, among other things essentially. Since they are approximations that reflect the various uncertainties of the measurement, it should be understood as being modified in all cases by the term "about". In addition, when numerical ranges are disclosed herein, these ranges are continuous and, unless otherwise indicated, include all values from the minimum value of this range to the maximum value including the maximum value. Furthermore, when this range refers to an integer, all integers from the minimum value to the maximum value including the maximum value are included, unless otherwise indicated.

In the present specification, when a range is described for a variable, it will be understood that the variable includes all values within the stated range, including the stated endpoints of the range. For example, a range of "5 to 10" includes values of 5, 6, 7, 8, 9, and 10, as well as any subranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc. Inclusive, and it will be understood to include any values between integers that are reasonable in the scope of the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5 and 6.5 to 9, and the like. Also, for example, the range of "10% to 30%" is 10% to 15%, 12% to 10%, 11%, 12%, 13%, etc., as well as all integers including up to 30%. It will be understood to include any subranges such as 18%, 20% to 30%, and the like, and include any values between reasonable integers within the scope of the stated range, such as 10.5%, 15.5%, 25.5%, and the like.

In the present specification, the terms "structure" and "sintered body" are sometimes used interchangeably. It can be used to refer to the same object. In addition, terms such as "porous", "porous material" and "porous material" can be considered to mean the same properties. In addition, when the terms "resin" and "resin" are used interchangeably, they can be understood as the same terms.

1 is a schematic diagram of a method of manufacturing a porous silicon carbide sintered body by a thermal carbon reduction process according to the present invention. Referring to this, the manufacturing method comprises the step of preparing a liquid silicon compound, a liquid carbon compound, and a metal compound as starting materials (S1), mixing the prepared liquid silicon compound and a liquid carbon compound, and a trace amount of the metal compound and the catalyst. The step of performing a sol-gel process (S2) of preparing a gelling composition to which a trace amount of a metal compound is added by causing a hydrolysis reaction and a gelation reaction of the liquid silicon compound to be added, drying the prepared gelling composition to cure Preparing a gel (S3), obtaining a gel powder by first grinding the cured gel (S4), preparing a silicon dioxide-carbon composite by subjecting the gel powder to a primary heat treatment (S5), silicon dioxide-carbon Secondary pulverization of the composite to prepare a composite powder (S6), the step of manufacturing a molded body using the composite powder (S7), the secondary heat treatment of the molded body to prepare a porous silicon carbide sintered body (S8). .

Hereinafter, the process for each step will be described in detail together with FIG. 1.

The starting material preparation step (S1) is a step of preparing a liquid silicon compound, a liquid carbon compound, and a metal compound.

The liquid silicon compound of the present invention may be selected from the group consisting of silicon alkoxide, ethyl silicate, and mixtures thereof.

The silicon alkoxide is a compound represented by SiH _a (OR) _b having 1 to 4 alkoxy groups having 1 to 8 carbon atoms (here, an integer of a=1 to 3, an integer of b=1 to 3, R=alkyl group, a+b=4) may be used, and a derivative compound substituted with a halogen element instead of H (hydrogen atom) may also be used. In addition, wherein R (alkyl group) is a methyl, ethylpropyl or butyl group.

The liquid carbon compound of the present invention may be a solution prepared by dispersing a solid carbon source in a solvent selected from the group consisting of ethanol, methanol, isopropyl alcohol (IPA), and mixtures thereof.

The solid carbon source can be dispersed by being added to a solvent within 70% by weight based on 100% by weight of the liquid carbon compound. Preferably it may be 3% by weight to 70% by weight. At this time, the solvent is 30% by weight to 100% by weight.

A method of dispersing the carbon source in a solvent is not particularly limited, and may be dispersed by, for example, a ball milling process or a sonication process. In addition, the dispersion time is not particularly limited, and it can be performed until the carbon source is sufficiently evenly dispersed.

The carbon source may be selected from the group consisting of carbon black, carbon nanotubes, phenol resins, monosaccharides, disaccharides, and mixtures thereof.

In addition, in the present invention, a liquid mixture solution may be prepared by dispersing a solid silicon source and a solid carbon source soluble in a solvent in a solvent to prepare a mixture. This is a method known in the art, and details will be omitted.

The metal compound may be made of at least one selected from alkali, alkaline earth metal, transition metal nitrate and carbonate.

In the present invention, the specific surface area, compressive strength, porosity, and the like of the porous silicon carbide structure can be easily controlled by adjusting the composition of the carbon source, which will be described later through examples.

In the step of performing the sol-gel process (S2), the prepared liquid silicon compound and the liquid carbon compound are mixed, and a trace amount of a metal compound and a catalyst are added to cause a hydrolysis reaction and a gelation reaction of the liquid silicon compound. It is a manufacturing step.

In the mixture of the liquid silicon compound and the liquid carbon compound, the molar ratio of carbon/silicon (C/Si) is preferably within the range of 1.0 to 4.0.

When the molar ratio of carbon/silicon is less than 1.0, the synthesis yield decreases rapidly when synthesizing silicon carbide, and when the molar ratio of carbon/silicon exceeds 4.0, the gelation reaction in the sol-gel process step decreases and the mechanical properties of the silicon carbide sintered body The strength is greatly reduced.

In addition, the amount of the liquid carbon compound to be used can be determined based on the amount of carbon remaining after the heat treatment reaction and the silicon element in the liquid silicon compound.

According to the present invention, the amount of the solvent used for dissolution of the solid carbon source required in the sol-gel process can be used in the range of 10 moles or less per 1 mole of silicon atoms in the liquid silicon compound.

According to a preferred embodiment of the present invention, the mixing of the liquid silicon compound and the liquid carbon compound is a Teflon-coated mixing device with little inflow of metals and metal compounds, such as a Teflon beaker, a Teflon-coated magnetic mixing device, and Teflon. It can be carried out using a coated household air conditioner and a Teflon-coated impeller, preferably by stirring at a temperature of 20°C to 60°C for 30 minutes or more at a rate of 50RPM to 400RPM to prepare a gelling composition consisting of a silicon compound and a carbon compound. can do. In the present invention, it is preferably stirred within 30 minutes to 10 hours to prepare a gelling composition.

According to a preferred embodiment of the present invention, a metal compound may be added as a catalyst for accelerating a chemical reaction between a silicon source and a carbon source, and the metal compound is an alkali metal, an alkali earth metal, and a nitrate or alkali metal of a transition metal, an alkaline earth metal. And it may be selected from the group consisting of carbonates of transition metals and the like. For example, a nitrate hydrate of nickel or chromium may be added in an amount of 0.05 moles or less relative to 1 mole of silicon element to accelerate the thermal carbon reduction reaction of silicon dioxide, thereby manufacturing a porous silicon carbide sintered body at a relatively low temperature. At this time, preferably, it may be added in an amount of 0.0001 to 0.01 mol relative to 1 mol of silicon element. More preferably, it is 0.001 mol-0.01 mol.

The metal compound added as described above is characterized by remaining as an oxide, carbide, or intermetallic compound in the prepared porous silicon carbide sintered body.

According to a preferred embodiment of the present invention, a liquid silicon compound and a liquid carbon compound are added to form an aqueous solution by mixing an acid or a base with a predetermined amount of distilled water as a catalyst for accelerating the hydrolysis reaction and gelation reaction of a liquid silicon compound. This uniformly mixed gelling composition can be prepared. Specifically, in the gelation composition, the liquid silicon compound becomes a gel state as the hydrolysis reaction and the gelation reaction proceed, and serves as a kind of matrix, and the liquid carbon compound is evenly distributed thereto.

The catalyst is one or more acids selected from nitric acid, hydrochloric acid, oxalic acid, maleic acid, acrylic acid, acetic acid and toluene sulfuric acid, or one or more bases selected from aqueous ammonia and hexamethylene tetraamine Can be used, and the acid or base is 0.2 molar ratio or less, preferably in the range of 0.001 to 0.2 molar ratio, relative to the silicon element (Si) in the liquid silicon compound, and water is compared to the silicon element (Si) in the liquid silicon compound. Thus, it is possible to prepare a gelling composition composed of a liquid silicon compound and a liquid carbon compound by using in a molar ratio of 20 or less, preferably 0.1 to 10 molar ratio.

The drying step (S3) is a step of preparing a cured gel by drying the prepared gelling composition.

According to a preferred embodiment of the present invention, a gelling composition prepared using a liquid silicon compound and a liquid carbon compound as starting materials is charged into a container made of Teflon, polyethylene, polyvinyl chloride, etc. A cured gel may be prepared by drying at a temperature for 1 hour or more, preferably 2 to 72 hours.

The first grinding step (S4) is a step of obtaining a gel powder by primary grinding the gel cured in the drying step.

The cured gel is first pulverized and classified through a sieve having a scale size of 1 mm or less to obtain a gel powder in which a silicon compound and a carbon compound are homogeneously distributed.

The first heat treatment step (S5) is a step of preparing a silicon dioxide-carbon composite by subjecting the gel powder to the first heat treatment.

Under preferred according to the embodiment, the gel powder such as silicon other than the metal impurity content of nitrogen and then charged into a low-purity quartz crucible and a high purity graphite crucible, argon, and vacuum (10 ⁰ Torr or lower) atmosphere of the present invention 1 ℃ / min to 10 ℃ A silicon dioxide-carbon composite can be prepared through the first heat treatment for 0.5 to 4 hours in a temperature range of 700°C to 1000°C by raising the temperature at a heating rate of /min.

The second grinding step (S6) is a step of producing a composite powder by secondary grinding the silicon dioxide-carbon composite.

According to the present invention, the average particle size can be reduced by pulverizing the silicon dioxide-carbon composite, and the particle size distribution can be controlled by classifying the pulverized composite powder. The average particle size adjusted here is preferably 45 μm or less.

The molded article manufacturing step (S7) is a step of manufacturing a molded article using the composite powder.

According to the present invention, a molded article having a predetermined shape can be manufactured by a conventional molding process using the composite powder.

The molding process includes uniaxial pressing, slip casting, and extrusion. The molding conditions in each molding method are not particularly limited.

According to a preferred embodiment of the present invention, after the composite powder is charged into a mold, a molded body may be manufactured by uniaxial pressure molding at a pressure within 5 MPa to 20 MPa.

The second heat treatment step (S8) is a step of producing a porous silicon carbide sintered body by secondary heat treatment of the molded body.

According to the present invention, after charging the prepared molded body into a graphite crucible or alumina boat, in a vacuum (10 ⁰ Torr or less) atmosphere or inert atmosphere in an alumina tube furnace or graphite vacuum furnace at a rate of 1°C/min to 10°C/min By raising the temperature, the secondary heat treatment at a temperature range of 1050° C. to 1250° C. for 5 to 20 hours may be performed to prepare a porous silicon carbide sintered body.

Here, the secondary heat treatment may be performed by a direct carbonization method as well as a carbothermal reduction reaction method.

Specifically, the thermal carbon reduction method is a method of producing silicon carbide by heat-treating silica mixed with carbon in an argon atmosphere, and during the heat treatment process, silica reacts with carbon and oxygen in the silica is formed as carbon monoxide (CO) gas and is lost. Is a method of reacting with carbon to form silicon carbide.

In addition, the direct carbonization method is the most economical and simplest method for producing β-SiC. However, in general, since the reaction proceeds at a temperature lower than the Si melting point (1412°C), there is a disadvantage in that the final product contains a large amount of unreacted silica, and it is difficult to manufacture high-purity silicon carbide powder. That's the way.

The sintered porous silicon carbide made according to the present invention, the compressive strength and an average mesopore size of 10MPa to 30MPa is having a 5nm to 30nm, and has a specific surface area characteristics of 50m ² / g to 130m ² / g.

Hereinafter, the present invention will be described in more detail through specific examples. The following examples are only examples to aid understanding of the present invention, and the scope of the present invention is not limited thereto.

The following physical properties were measured by the following method.

1) Compressive strength: Instron tensile tester

2) Porosity: Archimedes method

3) Specific surface area: BET specific surface area analysis

Examples 1 to 3

In order to prepare a porous silicon carbide sintered body having meso or macro-sized pores, ethyl silicate was used as the liquid silicon compound. As a liquid carbon compound, a phenol resin as a carbon source was added to ethanol as a solvent, and chromium nitrate was used as a metal compound to promote the thermal carbon reduction reaction. At this time, the amount of ethanol was used in an amount of 4 mol relative to 1 mol of silicon element in ethyl silicate, a liquid silicon compound, and the amount of the phenol resin was 1.0 mol, 1.6 mol, and 2.4 mol relative to 1 mol of silicon element in ethyl silicate, a liquid silicon compound. In addition, the amount of chromium nitrate was 0.001 mol compared to 1 mol of silicon element in chromium nitrate.

(C/Si=1.0 in Example 1, C/Si=1.6 in Example 2, C/Si=2.4 in Example 3)

And after adding 1 mol of ethyl silicate, the mixture was stirred at room temperature at a rate of 300 RPM to prepare a composite sol.

After adding 20 mol of distilled water and 0.001 mol of nitric acid relative to the silicon element to the prepared composite sol, the mixture was stirred for 2 hours, and then 0.003 mol of ammonia solution was added to the sol in which the hydrolysis of ethyl silicate was completed to prepare a gelling composition. The prepared gelling composition was dried at 80° C. and then pulverized to prepare a gel powder.

The gel powder was placed in a quartz crucible and charged in a quartz tube furnace, and then heated at a rate of 5°C/min under a nitrogen gas atmosphere, and subjected to primary heat treatment at 900°C for 3 hours to prepare a silicon dioxide-carbon composite. The prepared silicon dioxide-carbon composite was pulverized for 2 hours using a planetary mixer, and a classified composite powder was prepared using a sieve having a size of 32 μm.

The classified composite powder was charged into a mold and then uniaxially press-molded at a pressure of 5 MPa, and the prepared molded body was placed in a graphite crucible and charged into a graphite vacuum furnace. A porous silicon carbide sintered body was prepared by heating at a rate of 10° C./min in a vacuum atmosphere and secondary heat treatment at 1200° C. for 5 hours, and the residual carbon was removed by heat treatment at 600° C. in air for 2 hours.

The porosity and mechanical properties of the porous silicon carbide structures prepared in Examples 1 to 3 are summarized in Table 1 below.

division Example One 2 3 Starting material Carbon source Phenol resin Phenol resin Phenol resin Silicon source Ethyl silicate Ethyl silicate Ethyl silicate Cr/Si (molar ratio) 0.001 0.001 0.001 C/Si (molar ratio) 1.0 1.6 2.4 1st heat treatment temperature/time 900℃/3 hours 2nd heat treatment temperature/time 1200℃/5 hours SiC sintered body Specific surface area (m ² /g) 53 64 76 Strength (MPa) 23 16 7 Average pore size (nm) 11 13 18 Porosity (%) 75 78 80

According to Table 1, the compressive strength of the porous silicon carbide sintered body manufactured by the above method decreased from 23 MPa to 7 MPa as the molar ratio of carbon to silicon in the starting material increased to 1.0, 1.6 and 2.3, and apparent porosity and specific surface area. Increased to 75 to 80% and 53 to 76 m ² /g.

In addition, X-ray diffraction analysis was performed on the porous silicon carbide sintered bodies of Examples 2 and 3, and the results are shown in FIG. 2. Referring to this, it can be seen that the porous silicon carbide sintered body is a beta-phase silicon carbide, and since the amount of the added metal compound is small, it was not confirmed in the X-ray diffraction pattern analysis.

In addition, an SEM image of the porous silicon carbide sintered body of Example 3 observed at a magnification of x100,000 is shown in FIG. 3. Referring to this, it can be seen that the porous silicon carbide sintered body manufactured according to Example 3 contains evenly distributed mesopores.

Examples 4 to 6

Conducted in the same manner as in Example 3, but the molar ratio of carbon to silicon element was fixed to 2.4, and the secondary heat treatment of the molded body was heated at a rate of 10°C/min to 1050°C, 1200°C, and 1250°C in an argon atmosphere, respectively. It proceeded for 10 hours.

The porosity and mechanical properties of the porous silicon carbide sintered body prepared in Examples 4 to 6 are summarized in Table 2 below.

division Example 4 5 6 Starting material Carbon source Phenol resin Phenol resin Phenol resin Silicon source Ethyl silicate Ethyl silicate Ethyl silicate Cr/Si (molar ratio) 0.001 0.001 0.001 C/Si (molar ratio) 2.4 2.4 2.4 1st heat treatment temperature/time 900℃/3 hours 2nd heat treatment temperature/time 1050℃/10 hours 1200℃/10 hours 1250℃/10 hours SiC sintered body Specific surface area (m ² /g) 93 76 51 Average pore size (nm) 7 18 28 Strength (MPa) 8 18 23 Porosity (%) 78 78 78

According to Table 2, the compressive strength of the porous silicon carbide sintered body manufactured by the above method increased from 14 MPa to 23 MPa as the secondary heat treatment temperature increased from 1175°C to 1250°C, and the specific surface area was 93m ² /g to 51m ^It decreased to ² /g, and the mesopore size changed from 7nm to 28nm, but the porosity did not change significantly at 78%.

As described above, embodiments of the present invention have been described with reference to the accompanying drawings, but those of ordinary skill in the art to which the present invention pertains can be implemented in other specific forms without changing the technical spirit or essential features. You can understand that there is. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not limiting.

By homogeneously mixing each starting material in a liquid phase, the synthesis and sintering temperature of porous silicon carbide can be lowered, and the porous silicon carbide sintered body developed in the present invention has high thermal conductivity, excellent mechanical properties, and high specific surface area and porosity. It is applied to the chemical industry in which the direct catalytically active partial oxidation process of methane with high heat generation or the catalytic reforming of carbon dioxide of methane is used to manufacture the manufacturing process and synthesis gas, because it can improve catalyst efficiency and ensure durability and reliability of the catalyst carrier. can do.

In addition, the developed porous silicon carbide sintered body has a certain shape, has excellent mechanical properties, and has a meso-sized pore structure, so it can be used as a filter material for wastewater treatment where an oxide-based filter cannot be used.

Claims (16)

Preparing a mixture by mixing a liquid silicon compound, a liquid carbon compound, and a metal compound, and then gelling to prepare a gelling composition;
Drying the gelling composition to prepare a cured gel;
First pulverizing the cured gel to obtain a gel powder;
First heat-treating the gel powder to prepare a silicon dioxide-carbon composite;
Secondary pulverization of the silicon dioxide-carbon composite to prepare a composite powder;
Manufacturing a molded body using the composite powder; And
Preparing a porous silicon carbide sintered body by secondary heat treatment of the formed body; Including,
The liquid carbon compound includes a solvent and a solid carbon source,
The metal compound includes a nitrate hydrate of nickel or chromium,
The first heat treatment is a method of manufacturing a porous silicon carbide sintered body by a thermal carbon reduction process, wherein the cured gel powder is heat treated at a temperature of 700° C. to 1000° C. in an inert atmosphere or a vacuum atmosphere.
The method of claim 1,
The gelling composition is a method of manufacturing a porous silicon carbide sintered body, characterized in that it is prepared by adding a catalyst to a mixture of a liquid silicon compound, a liquid carbon compound, and a metal compound.
The method of claim 2,
The catalyst is an acid selected from the group consisting of nitric acid, hydrochloric acid, oxalic acid, maleic acid, acrylic acid, acetic acid, toluene sulfuric acid, and mixtures thereof;
A base selected from the group consisting of aqueous ammonia, hexamethylene tetraamine, and mixtures thereof; And
Method for producing a porous silicon carbide sintered body, characterized in that selected from the group consisting of a mixture thereof.
The method of claim 1,
The liquid silicon compound is a method of manufacturing a porous silicon carbide sintered body selected from the group consisting of silicon alkoxide, polyethyl silicate, and mixtures thereof.
delete The method of claim 1,
The liquid carbon compound is prepared by dispersing a solid carbon source in a solvent selected from the group consisting of ethanol, methanol, isopropyl alcohol (IPA), and mixtures thereof.
The method of claim 6,
A method for producing a porous silicon carbide sintered body selected from the group consisting of carbon black, carbon nanotubes, phenol resins, monosaccharides, disaccharides, and mixtures thereof as the solid carbon source.
The method of claim 6,
The liquid carbon compound is 30% to 100% by weight of the solvent; And a method for producing a porous silicon carbide sintered body containing within 70% by weight of a carbon source.
The method of claim 1,
The mixture of the liquid silicon compound and the liquid carbon compound has a carbon/silicon molar ratio (C/Si) of 1.0 to 4.0. A method of manufacturing a porous silicon carbide sintered body.
The method of claim 1,
In the step of preparing the gelling composition, the liquid silicon compound and the liquid carbon compound are stirred and mixed at a temperature within 20°C to 60°C at a rate of 50 to 400 RPM for 30 minutes or more.Preparation of a porous silicon carbide sintered body Way.
The method of claim 1,
In the step of preparing the cured gel, the drying of the gelling composition is performed at a temperature of 40°C to 150°C for 2 to 72 hours.
The method of claim 1,
The first heat treatment is a method of producing a porous silicon carbide sintered body by heat-treating the cured gel powder for 0.5 to 4 hours in an inert atmosphere or a vacuum atmosphere.
The method of claim 1,
The manufacturing method of the porous silicon carbide sintered body, characterized in that the production of the molded body is made by at least one selected from uniaxial pressure molding, injection molding, and extrusion molding.
The method of claim 1,
The secondary heat treatment is a method of manufacturing a porous silicon carbide sintered body by heat-treating the formed body at a temperature of 1050° C. to 1300° C. for 1 hour to 20 hours in an inert atmosphere or a vacuum atmosphere.
The method of claim 1,
The porous silicon carbide sintered body has a compressive strength of 10Mpa to 30Mpa, a porosity of 60% to 85%, and a specific surface area of 50m ² /g to 130m ² /g.The method of manufacturing a porous silicon carbide sintered body, characterized in that.
The method of claim 1,
The method of manufacturing a porous silicon carbide sintered body, characterized in that the crystal phase of the porous silicon carbide sintered body is a beta phase.

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