KR20200008701A - 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 for manufacturing a porous silicon carbide sintered body by a carbothermal reduction process. More specifically, metal compound added silicon dioxide and carbon composite powder is manufactured by using liquid silicon compound and carbon compound and a metal compound for promoting carbothermal reduction as starting materials and conducting a sol-gel process. A molded body is manufactured by using the silicon dioxide-carbon composite powder. The molded body is thermally treated at a predetermined temperature. Therefore, while silicon carbide is synthesized through carbothermal reduction, a porous silicon carbide sintered body which has uniformly distributed meso-sized fine pores and excellent mechanical strength can be manufactured.

Description

Method for manufacturing 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 characteristics such as abrasion resistance, thermal shock resistance, excellent thermal conductivity, and corrosion / chemical resistance.Since the silicon carbide porous material as a porous material has a catalyst carrier, water and dust filter material, absorbent material, and insulation material according to its pore size, It is widely used as a core material in various industries such as gas phase separation materials, artificial biomaterials and shock absorbing materials. Recently, the semiconductor, chemical, environmental and energy industries requiring high temperature stability, chemical resistance, and high temperature mechanical properties are required. The range of application is increasing significantly.

Until now, the manufacturing technology of porous silicon carbide having micro or meso-sized pores has been reported to be prepared in the form of porous silicon carbide powder for use as a catalyst carrier, but a technique for producing mesoporous silicon carbide sintered body having excellent mechanical strength Is extremely rarely reported.

According to the research results of MI Ledoux and Vix-Guterl, liquid carbon raw materials were added to silicon dioxide with nanometer-sized pores, and then reacted with gaseous silicon using the thermal carbon reduction method or nanoporous carbon template. Although silicon carbide powder having micro or meso-sized pores of m ² / g was prepared, this technique was not economical by using expensive starting materials and a technique for producing a silicon carbide porous structure having a uniform shape was not presented. .

According to XY GUO's and EP Simonenko's presentation, silicon dioxide-carbon gels were prepared by sol gel process using phenol resin and tetraethyl orthosilicate and then subjected to heat treatment under vacuum or inert atmosphere, or by water plasma sintering (SPS) process. Synthesis techniques for silicon carbide porous powders having a pore size of meters and specific surface areas of up to 200 m ² / g and 110 m ² / g have been reported.

In addition, US 7,910,082 discloses a technique for producing microporous porous silicon carbide powder having a specific surface area of 400 to 900 m ² / g and an average pore size of 6 nm or less using a phenol resin and precursor prepared using TEOS (tetraethyl-orthosilicate). It was reported that CN 001401564 A was dissolved 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 hydrolyzed and crosslinked the silicate and dried to 1200-1400 ° C. A technique for producing 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 body technology which can be used as a catalyst carrier with the high specific surface area developed until now is mostly limited to the manufacturing technology of porous silicon carbide powder form.

In WO2014 / 207096 A1, a technique for preparing a catalyst carrier in which meso-sized pores having a predetermined shape is made of a porous silicon carbide structure is reported. In this patent, organic carbon compounds such as phenol resin are used as main raw materials in order to make carbon structures having mesopore size, and the mixture is mixed with silicon powder to prepare a molded article, and then heat-treated under appropriate conditions and atmosphere to directly carbon and silicon. Silicon carbide was synthesized by the reaction to prepare a porous silicon carbide structure having mesopores. In the present invention, a process for producing a meso-macroporous silicon carbide porous body having a certain shape as a direct reaction between carbon and silicon is proposed, but precise control of the process is required to control silicon that can remain in the reaction process, and the manufactured porous carbonization Mechanical properties of the silicon structure are not shown.

As described above, since most of the conventional silicon carbide manufacturing techniques having high specific surface areas and micro or mesopores have been developed in the form of porous silicon carbide powder, the application of porous silicon carbides having high specific surface areas developed is common. It is limited to a catalyst carrier, and porous silicon carbide has excellent thermal conductivity because of the air pocket (pore) formed between the porous silicon carbide powder particles filled in the reaction tank when the porous silicon carbide powder is applied as a catalyst carrier in the reaction tank. It is not possible to effectively transfer the heat generated by the catalytic reaction in the reactor. In addition, the porous silicon carbide powder is considered to have a lot of difficulties in using as a catalyst carrier under various conditions. Therefore, in order to expand the application of the porous silicon carbide porous body having a high specific surface area, it is required to develop a manufacturing technique with high economical efficiency of the porous silicon carbide sintered body having a high strength and a certain shape.

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

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

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

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

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

The object of the present invention is not limited to the above-mentioned object. 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.

A method of manufacturing a porous silicon carbide sintered body according to the present invention, comprising: mixing a liquid silicon compound, a liquid carbon compound, and a metal compound to prepare a mixture, and then gelling to prepare a gelling composition to which the metal compound is added; Drying the gelling composition to produce a cured gel; First grinding the cured gel to obtain gel powder; Firstly heat treating the gel powder to produce a silicon dioxide-carbon composite; Secondary grinding the silicon dioxide-carbon composite to prepare a composite powder; Preparing a molded body using the composite powder; And forming a porous silicon carbide sintered body by performing secondary heat treatment on the molded body. It includes.

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

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 sulfonic acid and mixtures thereof; A base selected from the group consisting of ammonia water, hexamethylene tetraamine, and mixtures thereof; And it may be 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 and 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, 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 wt% to 100 wt% of the solvent; And it may be to include within 70% by weight 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 molar ratio of carbon / silicon (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 may be mixed by stirring at a temperature of 20 ° C. to 60 ° C. for 30 minutes or more at a rate of 50 RPM to 400 RPM. Can be.

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

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

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

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

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

According to another preferred embodiment of the present invention, the crystal 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, the silicon carbide and the carbon source are mixed in the liquid phase so that the starting materials can be homogeneously mixed, and then a trace metal compound is added to the thermal carbon reduction reaction at a relatively low temperature. It is possible to synthesize the silicon carbide by this, it is possible to produce a porous silicon carbide sintered body having excellent strength, high specific surface area and high porosity.

In addition, since the silicon carbide sintered body of the present invention not only has a high specific surface area and porosity, but also has a high strength and a single structure, it is possible to achieve an effective thermal conductivity of heat generated even in a gas conversion catalytic reaction with a large heat generation, It is possible to prevent the breakage of the microporous structure by the catalyst as well as to minimize the breakdown of the catalyst carrier by the thermal shock.

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

The effect of this invention is not limited to the effect mentioned above. It is to be understood that the effects of the present invention include all the effects deduced from the description below.

1 is a schematic diagram illustrating a method for producing 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 readily understood through the following preferred embodiments associated with 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 disclosure may be made thorough and complete, and to fully convey the spirit of the invention to those skilled in the art.

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

In this specification, terms such as "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described on the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, parts, or combinations thereof. In addition, 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 "right on" but also another part in the middle. Conversely, when a part of a layer, film, region, plate, etc. is said to be "below" another part, it includes not only the other part "below" but also another part in the middle.

Unless otherwise stated, all numbers, values, and / or expressions expressing the amounts of components, reaction conditions, polymer compositions, and combinations used herein, occur such that these numbers occur essentially to obtain these values among others. As these are approximations that reflect various uncertainties in the measurement, it should be understood that in all cases they are modified by the term "about." Also, where numerical ranges are disclosed herein, these ranges are continuous and include all values from the minimum to the maximum including the maximum, unless otherwise indicated. Furthermore, where such ranges refer to integers, all integers are included, including the minimum to the maximum including the maximum 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 described range including the listed endpoints of the range. For example, the range "5 to 10" includes any subrange such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, as well as values of 5, 6, 7, 8, 9, and 10. And any value between integers that fall within the scope of the described ranges such as 5.5, 6.5, 7.5, 5.5-8.5, 6.5-9, and the like. Also for example, the range of “10% to 30%” ranges from 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 any value between reasonable integers within the range of the stated range, such as 10.5%, 15.5%, 25.5% and the like.

In this specification, the term "structure" and the term "sintered body" may be used interchangeably. It can be used to refer to the same object. In addition, the terms "porous", "porous" and "porous" can be considered to mean the same properties. Also, when the terms "resin" and "resin" are used interchangeably, the same terms are understood.

1 is a schematic diagram illustrating a method for producing a porous silicon carbide sintered body by a thermal carbon reduction process according to the present invention. Referring to this, the manufacturing method is a step of preparing a liquid silicon compound and a liquid carbon compound and a metal compound as a starting material (S1), by mixing the prepared liquid silicon compound and the liquid carbon compound and a trace amount of the metal compound and catalyst Performing a sol-gel process for preparing a gelling composition to which a trace amount of a metal compound is added by adding a hydrolysis reaction and a gelling reaction of the liquid silicon compound (S2), and drying the prepared gelling composition to be cured. Step of preparing a gel (S3), the first step of pulverizing the cured gel to obtain a gel powder (S4), a first heat treatment of the gel powder to prepare a silicon dioxide-carbon composite (S5), silicon dioxide-carbon Second step of crushing the composite to produce a composite powder (S6), step of preparing a molded body using the composite powder (S7), the second heat treatment of the molded body to form a porous silicon carbide sintered body And a step (S8) for.

Hereinafter, the process for each step will be described in detail with reference to FIG.

Starting material preparation step (S1) is a step of preparing a liquid silicon compound and 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 alkoxides, ethyl silicates and mixtures thereof.

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

The liquid carbon compound of the present invention may use 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 may be dispersed in a solvent within 70% by weight based on 100% by weight of the liquid carbon compound. Preferably 3% to 70% by weight. At this time, the solvent is 30% by weight to 100% by weight.

The method of dispersing the carbon source in the solvent is not particularly limited, and can be dispersed, for example, by a ball milling process, a sonication process, or the like. In addition, the dispersion time is not particularly limited and may 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 solid silicon source and a solid carbon source soluble in a solvent may be dispersed in a solvent to prepare a liquid mixed solution to prepare a mixture. This is a method known in the art will not be described in detail.

The metal compound may be made of at least one selected from alkalis, alkaline earth metals, nitrates and carbonates of transition metals, and the like.

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

In the sol-gel process performing step (S2), the gelled composition is prepared by mixing the prepared liquid silicon compound with the liquid carbon compound and adding a trace amount of a metal compound and a catalyst to cause the hydrolysis reaction and gelation reaction of the liquid silicon compound. Manufacturing step.

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

Synthesis yield decreases rapidly when synthesizing silicon carbide in the range of less than 1.0 mole ratio of carbon / silicone, and the reduction of gelation reaction and mechanical mechanical sintering of silicon carbide in the sol-gel process step in the range of more than 4.0 mole ratio of carbon / silicon The strength is greatly reduced.

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

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

According to a preferred embodiment of the present invention, the liquid silicon compound and the liquid carbon compound are mixed with a Teflon-coated mixing device, such as a Teflon beaker, a Teflon-coated magnetic mixing device, or a Teflon with a low inflow of metals and metal compounds. It can be carried out using a coated collector, a Teflon-coated impeller, preferably a gelling composition consisting of a silicon compound and a carbon compound by stirring at a temperature of 20 ℃ to 60 ℃ at a rate of 50 RPM to 400 RPM for at least 30 minutes can do. In the present invention, the gelling composition is prepared by stirring within 30 minutes to 10 hours.

According to a preferred embodiment of the present invention, a metal compound may be added as a catalyst for promoting the chemical reaction between the silicon source and the carbon source, and the metal compound may be a nitrate or alkali metal, alkaline earth metal of alkali metal, alkaline earth metal and transition metal. And carbonates of transition metals. For example, a porous silicon carbide sintered body may be manufactured at a relatively low temperature by adding nitric acid hydrate of nickel or chromium to 0.05 mol or less with respect to 1 mol of silicon element to promote thermal carbon reduction reaction of silicon dioxide. In this case, preferably, it may be added in an amount of 0.0001 mol to 0.01 mol relative to 1 mol of the silicon element. More preferably, it is 0.001 mol-0.01 mol.

The metal compound added as described above is characterized in that it remains 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 as a catalyst to promote the hydrolysis and gelling reactions of the liquid silicon compound and mixed with a predetermined amount of distilled water to form an aqueous solution. This uniformly mixed gelling composition can be prepared. Specifically, in the gelling composition, the liquid silicon compound becomes a gel state as the hydrolysis reaction and the gelling reaction proceed, and serves as a kind of matrix, and the liquid carbon compound is evenly distributed therein.

The catalyst is at least one acid selected from nitric acid, hydrochloric acid, oxalic acid, maleic acid, acrylic acid, acetic acid and toluene sulfonic acid, or at least one base selected from ammonia water and hexamethylene tetraamine. The acid or base may be used in an amount of 0.2 mole or less relative to silicon element (Si) in the liquid silicon compound, preferably in a range of 0.001 to 0.2 mole ratio, and water is used in comparison to the elemental silicon (Si) in the liquid silicon compound. By using 20 mol ratio or less, preferably in the range of 0.1 to 10 molar ratio it can be prepared a gelling composition consisting of a liquid silicon compound and a liquid carbon compound.

Drying step (S3) is a step of drying the prepared gelling composition to prepare a cured gel.

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 to a container made of Teflon, polyethylene, polyvinyl chloride, etc. The cured gel can be prepared by drying at temperature for at least 1 hour, preferably 2 to 72 hours.

The first grinding step S4 is a step of first grinding the gel cured in the drying step to obtain gel powder.

The cured gel is first ground and classified into a sieve having a scale of 1 mm or less to obtain a gel powder in which silicon compounds and carbon compounds are homogeneously distributed.

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

According to a preferred embodiment of the present invention, the gel powder is charged into a high-purity quartz crucible and a high-purity graphite crucible having a low content of metal impurities other than silicon, for example, 1 ° C / min to 10 ° C under an atmosphere of nitrogen, argon and vacuum (10 ⁰ Torr or less). The silicon dioxide-carbon composite may be prepared by a first heat treatment for 0.5 to 4 hours in a temperature range of 700 ° C. to 1000 ° C. by heating at a temperature increase rate of / min.

Secondary 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 silicon dioxide-carbon composite may be pulverized to reduce the average particle size, and the pulverized composite powder may be classified to adjust the particle size distribution. The average particle size adjusted here is preferably 45 μm or less.

Molded body manufacturing step (S7) is a step for producing a molded body using the composite powder.

According to the present invention, it is possible to produce a molded article having a constant shape by a conventional molding process using the composite powder.

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

According to a preferred embodiment of the present invention, the composite powder may be charged into a mold mold and uniaxially press-molded at a pressure within a range of 5 MPa to 20 MPa to produce a molded body.

Secondary 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, the prepared molded article is charged to a graphite crucible or an alumina boat, and then, at a rate of 1 ° C./min to 10 ° C./min in a vacuum (10 ⁰ Torr or less) atmosphere or an inert atmosphere in an alumina tubular furnace or a graphite vacuum furnace. By heating the secondary heat treatment for 5 to 20 hours at a temperature range of 1050 ℃ to 1250 ℃ can be produced a porous silicon carbide sintered body.

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

Specifically, the thermal carbon reduction method is a method for producing silicon carbide by heat-treating silica mixed with carbon in an argon atmosphere.Since the silica reacts with carbon during the heat treatment process, 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, direct carbonization is the most economical and simple 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, which makes it difficult to manufacture high purity silicon carbide powder. 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 with reference to specific examples. The following examples are merely examples to help understanding of the present invention, but the scope of the present invention is not limited thereto.

Hereinafter, physical properties were measured by the following method.

1) Compressive Strength: Instron Tensile Tester

2) Porosity: Archimedes

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 a thermal carbon reduction reaction. At this time, the amount of ethanol was used as 4 mol compared to 1 mol of the silicon element in the liquid silica compound ethyl silicate, the amount of the phenol resin is 1.0 mol, 1.6 mol and 2.4 mol compared to 1 mol of the silicon element in the liquid silica compound ethyl silicate The amount of chromium nitrate was such that the amount of chromium in chromium nitrate was 0.001 mol relative to 1 mol of silicon.

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

Then, 1 mole of ethyl silicate was added, followed by stirring at a rate of 300 RPM at room temperature to prepare a composite sol.

20 mol of distilled water and 0.001 mol of nitric acid were added to the prepared composite sol, followed by stirring for 2 hours, and then 0.003 mol of ammonia solution was added to the sol in which hydrolysis of ethyl silicate was completed, thereby preparing a gelling composition. The gelling composition prepared above was dried at 80 ° C. and then ground to prepare gel powder.

The gel powder was placed in a quartz crucible, charged in a quartz tube furnace, and heated at a rate of 5 ° C./min under a nitrogen gas atmosphere, followed by primary heat treatment at 900 ° C. for 3 hours to prepare a silicon dioxide-carbon composite. The prepared silicon dioxide-carbon composites were 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 mold, and then uniaxially press-molded at a pressure of 5 Mpa, and the prepared molded body was put into a graphite crucible and charged into a graphite vacuum furnace. The porous silicon carbide sintered body was prepared by heating at a rate of 10 ° C./min in a vacuum atmosphere for 2 hours at 1200 ° C. to remove residual carbon by heat treatment at 600 ° C. for 2 hours in air.

The pore and mechanical properties of the porous silicon carbide structure prepared in Examples 1 to 3 are summarized in the following (Table 1).

division Example One 2 3 Starting material Carbon source Phenolic Resin Phenolic Resin Phenolic Resin Silicon 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 Primary heat treatment temperature / time 900 ℃ / 3 hours Secondary 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 the apparent porosity and specific surface area. Increased to 75-80% and 53-76 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 beta-phase silicon carbide, and since the added metal compound is small in amount, it was not confirmed in the X-ray diffraction pattern analysis.

In addition, the SEM image of observing the porous silicon carbide sintered body of Example 3 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 includes mesopores evenly distributed.

Examples 4-6

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

The pore 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 Phenolic Resin Phenolic Resin Phenolic Resin Silicon 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 Primary heat treatment temperature / time 900 ℃ / 3 hours Secondary 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 was increased from 14MPa to 23MPa as the secondary heat treatment temperature was increased from 1175 ° C to 1250 ° C, and the specific surface area was increased from 93m ² / g to 51m ^The mesopore size was reduced from 2nm to 28nm, but the porosity was not changed from 78%.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical idea or essential features thereof. You will understand that there is. Therefore, it is to be understood that the embodiments described above are exemplary in all respects and not restrictive.

By homogeneously mixing each starting material in the liquid phase, the synthesis and sintering temperature of the porous silicon carbide can be lowered. Applied to the chemical industry where the direct catalytically active partial oxidation process of methane with high heat generation or the carbon dioxide catalyst reforming method of methane is used for manufacturing process and synthesis gas, because it can improve catalyst efficiency and ensure durability and reliability of catalyst carrier. can do.

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

Claims (16)

Preparing a gelling composition by mixing a liquid silicon compound with a liquid carbon compound and a metal compound to prepare a mixture, followed by gelation;
Drying the gelling composition to produce a cured gel;
First grinding the cured gel to obtain gel powder;
Firstly heat treating the gel powder to produce a silicon dioxide-carbon composite;
Secondary grinding the silicon dioxide-carbon composite to prepare a composite powder;
Preparing a molded body using the composite powder; And
Preparing a porous silicon carbide sintered body by performing secondary heat treatment on the molded body; Method for producing a porous silicon carbide sintered body by a thermal carbon reduction process comprising a.
The method of claim 1,
The gelling composition is a method for producing a porous silicon carbide sintered body, characterized in that 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 may be an acid selected from the group consisting of nitric acid, hydrochloric acid, oxalic acid, maleic acid, acrylic acid, acetic acid, toluene sulfonic acid and mixtures thereof;
A base selected from the group consisting of ammonia water, hexamethylene tetraamine, and mixtures thereof; And
A 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,
Wherein said liquid silicon compound is selected from the group consisting of silicon alkoxides and polyethylsilicates and mixtures thereof.
The method of claim 1,
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, etc., and the amount thereof is 0.0001 mol to 0.05 mol relative to 1 mol of silicon source. A method for producing a sintered body of porous silicon carbide, characterized by the above-mentioned.
The method of claim 1,
The liquid carbon compound is a method for producing a porous silicon carbide sintered body, which 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,
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 wt% to 100 wt% of the solvent; And a carbon source containing 70 wt% or less of the porous silicon carbide sintered body.
The method of claim 1,
The method of manufacturing a porous silicon carbide sintered body in which the mixture of the liquid silicon compound and the liquid carbon compound has a molar ratio (C / Si) of 1.0 to 4.0 of carbon / silicon.
The method of claim 1,
Preparation of the porous silicon carbide sintered body characterized in that the liquid silicon compound and the liquid carbon compound in the step of preparing the gelling composition is stirred by mixing for at least 30 minutes at a temperature within 20 ℃ to 60 ℃ at a rate of 50RPM to 400RPM Way.
The method of claim 1,
Drying of the gelling composition in the step of preparing the cured gel is a method for producing a porous silicon carbide sintered body is dried for 2 to 72 hours at a temperature of 40 ℃ to 150 ℃.
The method of claim 1,
The primary heat treatment is a method for producing a porous silicon carbide sintered body is heat-treated for 0.5 hours to 4 hours at a temperature of 700 ℃ to 1000 ℃ 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 for producing a porous silicon carbide sintered body is heat treatment for 1 to 20 hours at a temperature of 1050 ℃ to 1300 ℃ in an inert atmosphere or a vacuum atmosphere.
The method of claim 1,
The porous silicon carbide sintered compact has a compressive strength of 10Mpa to 30Mpa, porosity of 60% to 85%, specific surface area of 50m ² / g to 130m ² / g method for producing a porous silicon carbide sintered body.
The method of claim 1,
The crystal phase of the porous silicon carbide sintered body is a beta phase manufacturing method of the porous silicon carbide sintered body.

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