KR101133097B1 - Silicon carbide ceramic compositions for high temperature hot gas filters by mullite-zirconia bonding and preparing method of hot gas filters using this - Google Patents

Abstract

The invention zirconia (zirconia, ZrO ₂₎ relates to a filter made of high-temperature exhaust gas purified mullite for bonding the silicon carbide material (3Al ₂ O ₃ o 2SiO _2, mullite), according to the present invention, silicon carbide (SiC) containing Mullite-zirconia-bonded silicon carbide for hot gas filter production comprising 100 parts by weight of powder, 5 parts by weight of mullite (3Al2O3 ?? SiO2) powder, 1 part by weight of calcium carbonate (CaCO3) powder and 1 to 5 parts by weight of zirconia (ZrO2) powder. As the quality ceramic composition is provided, the hot gas filter manufactured by molding, drying and sintering the ceramic composition has excellent mechanical strength and excellent oxidation resistance.

Silicon Carbide, Ceramic Filter, Mullite, Zirconia, Porosity

Description

Silicon carbide ceramic compositions for high temperature hot gas filters by mullite-zirconia bonding and preparing method of hot gas filters using this}

The present invention relates to the production of a silicon carbide ceramic composition for a high temperature exhaust gas dust collecting filter and a high temperature exhaust gas filter using the same, and more particularly sintering a composition comprising silicon carbide powder, mullite powder, zirconia powder and calcium carbonate source The present invention relates to a technique for manufacturing a hot gas filter. Silicon carbide powder constitutes a ceramic filter support layer, mullite and zirconia powder act as a sintering aid for bonding the particles constituting the silicon carbide support layer during sintering, and calcium carbonate reacts with mullite and zirconia sintering aid It relates to a technique for producing a filter having a strength and oxidation resistance superior to the ceramic filter of the clay-bonded silicon carbide material by acting to lower.

Recently, with the rise of energy and environmental problems, studies on liquefaction and gasification of coal have been actively conducted as technologies for solving energy efficiency and environmental problems at the same time. In addition, after the process of liquefaction or gasification of coal, the research on high-strength hot gas filter material having high temperature and high pressure precision dust collection performance required in the process of recombusting flammable coal gas in a turbine combustor is being actively conducted. In particular, there is an increasing need for an improvement in the next generation power generation ceramic hot gas filter for simultaneously treating fine particulate matter and pollutants contained in the synthesis gas under high temperature and high pressure conditions.

In general, in order to form a smooth flow of combustion flue gas in the filter material for high-temperature exhaust gas dust collection, the pore fraction of the filter is high and the air permeability is good, so that the pressure loss is low. There is a disadvantage in that cracks are generated or destroyed due to thermal shock and thermal fatigue during use. As such, the air permeability and strength characteristics of the filter have a mutually opposite relationship, there is a difficulty in improving the mechanical characteristics of the high temperature exhaust gas dust collecting filter while ensuring a constant air permeability.

Porous silicon carbide ceramics, on the other hand, have excellent characteristics such as corrosion resistance, abrasion resistance, thermal shock resistance, high temperature stability, and are used as hot gas filters, various refractory materials, diesel dust filters, and vacuum chuck materials. Pure sintered silicon carbide may be used for this purpose, but such products have a disadvantage that the manufacturing temperature is too high, such as 2000 ° C. or higher, and the manufacturing equipment cost is too expensive to manufacture large products.

Therefore, a silicon carbide material that can be fired at low temperature by adding an oxide or non-oxide binder to the silicon carbide starting material is used. Such binders include clay, silicon oxynitride, alumina, silicon nitride, and the like. However, these binders have a large difference in coefficient of thermal expansion with silicon carbide, and thus have low thermal shock resistance. The non-oxide silicon oxynitride and silicon nitride binders are oxidized to form silica (SiO ₂ ) phases when used at high temperatures, resulting in poor oxidation resistance and cracking. This has the disadvantage that the high temperature strength is lowered.

However, the mullite-zirconia binder of the present invention increases the mechanical strength after sintering by adding zirconia to the mullite binder, which has little difference in coefficient of thermal expansion. Use as a binder has the advantage of increasing oxidation resistance.

Korean Patent Registration No. 10-0419779 provides a method for producing a high strength silicon carbide ceramic filter for dust collection. In summary, 1.0 to 15.0 wt% of clay, 0.1 to 5.0 wt% based on 100 wt% of silicon carbide powder High strength silicon carbide ceramics for dust collection through mixing, aging and sintering of calcium carbonate, 1.0 to 5.0 wt% molding aid, 0.5 to 5.0 wt% dispersant, and 5.0 to 15.0 wt% water Provided is a method of making a filter. However, the silicon carbide filter manufactured by such a process has a disadvantage that the bending strength is not excellent as 31 MPa or less.

Meanwhile, Korean Patent Registration No. 10-0891956 provides a method for preparing a paste composition for sintering silicon carbide and a porous silicon carbide filter to which a mullite-based hollow sphere is added. In summary, the starting material comprises silicon carbide powder, organic binder, and mullite hollow spheres, which assist in the formation of the connection site between the silicon carbide particles during the sintering process and the porous structure of the sintered body Characterized in that the action to give. The patent is also a method for producing a silicon carbide filter, characterized in that the sintering at 1200 ~ 1600 ℃ by adding Y ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , CaO, MgO as an additive for lowering the melting temperature of the hollow spheres To provide. However, this method has a problem in that the mullite-based binder is present only at the bonding sites of the SiC particles, thereby deteriorating oxidation resistance, and excessive SiO ₂ formed by additional oxidation of SiC remains during sintering, resulting in phase transformation of SiO ₂ . It has the disadvantage that the strength is lowered during use due to cracking. The present inventors have completed the present invention as a result of research to solve the problems of the prior art.

Accordingly, an object of the present invention is to provide a zirconia-containing silicon carbide ceramic composition for producing a hot gas filter having excellent breathability and high mechanical strength.

Another object of the present invention is to provide a method for producing a high-temperature gas filter, which can be manufactured in air using the ceramic composition and has a low sintering temperature.

In order to achieve the above object, according to the present invention, 100 parts by weight of silicon carbide (SiC) powder, 5 parts by weight of mullite (3Al2O3 ?? SiO2) powder, 1 part by weight of calcium carbonate (CaCO3) powder and zirconia (ZrO2) powder 1 ~ Provided is a mullite-zirconia bonded silicon carbide ceramic composition for producing a hot gas filter comprising 5 parts by weight.

In addition, according to the present invention in order to achieve the above another object with respect to 100 parts by weight of the mullite-zirconia-bonded silicon carbide ceramic composition for producing a hot gas filter, 1 to 5 parts by weight of an organic binder and 5 to 20 parts by weight as a molding aid Mixing by shaping the solvent; Drying the molded filter; And it provides a method for producing a mullite-zirconia-bonded silicon carbide hot gas filter comprising the step of heating and drying the dried filter in air.

The organic binder may be used alone or in combination of two or more methyl cellulose (methylcellulose), ethyl cellulose (ethylcellulose), carboxymethyl cellulose (carboxymehylcellulose) or polyvinyl alcohol (polyvinyl alcohol).

As the solvent, any solvent may be used as long as it can dissolve the organic binder, but water is most preferably used.

The sintering is preferably made by heat treatment for 0.5 to 5 hours in the air at a temperature section of 1400 ~ 1450 ℃.

The filter manufactured by the method for producing a mullite-zirconia-bonded silicon carbide hot gas filter of the present invention uses a mixture of mullite, zirconia, and calcium carbonate in a silicon carbide powder, so that the silicon carbide powder is mullite in the air (air) during sintering. There is an advantage in that it is strongly bound by the eutectic phase produced by the reaction of zirconia-calcium carbonate to enable the manufacture of a filter of excellent strength.

Hereinafter, the present invention will be described in detail.

The mullite-zirconia-bonded silicon carbide ceramic composition for producing a hot gas filter includes 100 parts by weight of silicon carbide (SiC) powder, 5 parts by weight of mullite (3Al ₂ O ₃ ? SiO ₂ ) powder, and 1 weight of calcium carbonate (CaCO ₃ ) powder. Part and 1 to 5 parts by weight of zirconia (ZrO ₂ ) powder.

In the composition, mullite as an oxide binder, zirconia and calcium carbonate as sintering temperature regulators are added in an amount of 5 parts by weight of mullite, 1 part by weight of calcium carbonate, and 1 to 5 parts by weight of zirconia, based on 100 parts by weight of silicon carbide powder. It is preferable. If the mullite is less than 5 parts by weight or more than 6 parts by weight, the sinterability of the silicon carbide matrix is poor, and the sinter density and porosity cannot reach 20 MPa and 25% or more, respectively, and the sinter density is significantly lowered and the porosity is lower. Since silver becomes too high, it is preferable to limit to 5% by weight of mullite and 1% by weight of calcium carbonate, and to add an amount of zirconia raw material in an amount of 1 to 5% by weight.

In addition, according to an embodiment of the present invention method for manufacturing mullite-zirconia-bonded silicon carbide high temperature gas filter 1 to 5 parts by weight of the molding aid as a molding aid based on 100 parts by weight of the mullite-zirconia-bonded silicon carbide ceramic composition Molding by mixing an organic binder and 5 to 20 parts by weight of a solvent; Drying the molded filter; And sintering the dried filter by heating in air.

The organic binder may be used alone or in combination of two or more methyl cellulose (methylcellulose), ethyl cellulose (ethylcellulose), carboxymethyl cellulose (carboxymehylcellulose) or polyvinyl alcohol (polyvinyl alcohol). When the organic binder is added in less than 1 part by weight, there is a problem in that the bonding strength of the silicon carbide ceramic filter molded body is weakened, and when the organic binder content exceeds 5 parts by weight, a plurality of internal defects are caused during heat treatment of the filter. However, it is not preferable because a large amount of harmful gases by combustion are emitted.

As the solvent, any solvent may be used as long as it can dissolve the organic binder, but water is most preferably used in terms of economical efficiency. If the content of the solvent is added less than 5 parts by weight, the mixture is insufficient for molding due to lack of flexibility, and if the solvent is added more than 20 parts by weight, the viscosity of the raw material mixture is too low, difficult to mold, long time to dry It is not desirable because it takes.

The molding includes molding by pressing in a hydrostatic molding method, molding by ramming molding, or extruding the composition into a predetermined shape according to the shape of the desired filter.

Any method may be used in the drying step, and drying at less than 100 ° C. using hot air is effective to prevent defects such as cracking and warping which may occur during rapid drying.

The step of sintering the dried molded body is preferably made by heat treatment for 0.5 to 5 hours in the air at a temperature range of 1400 ~ 1450 ℃. At this time, the heat treatment process is carried out at a temperature range of 1400 ~ 1450 ℃, at a temperature of less than 1400 ℃ silicon carbide particles constituting the matrix because the mullite and zirconia react with calcium carbonate to form a eutectic liquid phase is not sufficient If the uniform bond between them is not formed, and if it exceeds 1450 ℃, the feedstock calcium carbonate begins to evaporate and swelling occurs on the surface of the molded body is not economically effective.

In addition, the sintering process is heat-treated for 0.5 to 5 hours in the temperature range of 1400 ~ 1450 ℃, when the heat treatment time is less than 0.5 hours silicon carbide particles due to the short time that the mullite and zirconia react with calcium carbonate to form a eutectic liquid phase This is because there is a weakness in that the binding strength between the weak and the strength is not expressed, when the heat treatment time exceeds 5 hours, calcium carbonate begins to evaporate, there is no additional strength increase due to the swelling phenomenon on the surface of the molded body.

The mullite-zirconia bonded silicon carbide material according to the present invention exhibits excellent strength properties for use as a filter material with a bending strength of 40 MPa or more at a porosity of 30% or more, and these physical properties further include zirconia in SiC and mullite bonding aids. It was obtained by addition.

Hereinafter, the present invention will be described in more detail with reference to Examples and Test Examples, but the present invention is not limited to the following Examples.

Examples 1-5 ceramic filter manufacturing

As shown in Table 1 below, a mullite-zirconia bond is obtained by mixing a silicon carbide (SiC) powder having an average particle size of 100 µm, a mullite powder having an average particle diameter of 44 µm, and a zirconia powder and a calcium carbonate powder having an average particle diameter of 50 µm. A silicon carbide ceramic material composition was prepared.

2 parts by weight of carboxymethylcellulose was added to 100 parts by weight of the ceramic composition, and 20 parts by weight of water were added as a solvent and mixed uniformly in a vibratory pot mill for 4 hours. After aging for 24 hours, the mixture was uniaxially press-molded at a pressure of 30 MPa to form a candle-filter shaped body. The molded product of the filter thus prepared was dried at room temperature for at least 12 hours and then completely dried at 80 ° C. for 24 hours using a hot air dryer. The dried molded body was sintered for 2 hours at a temperature range of 1400 ~ 1450 ℃ to prepare a filter of the present invention.

Comparative Example 1-2 Ceramic Filter Manufacturing

In Comparative Examples 1 and 2, 5 parts by weight of clay, 1 part by weight of calcium carbonate, 2 parts by weight of carboxymethyl cellulose are added to 100 parts by weight of silicon carbide powder, 100 parts by weight of an organic binder as the silicon carbide powder. 13 parts by weight of water was added as a solvent, followed by mixing, molding and drying in the same manner as in the above example. Comparative Example 1 was sintered at 1400 ° C. for 2 hours in air, and Comparative Example 2 was sintered at 1460 ° C. for 2 hours. In Comparative Example 3, 5 parts by weight of mullite instead of clay, 100 parts by weight of carboxymethyl cellulose were added to 100 parts by weight of silicon carbide powder, and 1 part by weight of calcium carbonate, 100 parts by weight of ceramic as an organic binder. Part by weight of water was added as a solvent, followed by mixing, molding, and drying in the same manner as in Example, and sintering was performed at 1400 ° C. As Comparative Example 4, a filter (commercially available for purifying the combustion gas as a German product (Schumacher, Dia-Schumalith 10-20)) was used.

division
(Parts by weight) Silicon Carbide
(SiC) Mullite
(3Al ₂ O ₃ SiO ₂ ) Zirconia
(ZrO ₂ ) clay Calcium carbonate
(CaCO ₃ ) Heat treatment condition Temperature
(℃) time
(h) atmosphere Example One 100 5 One - One 1400 2 air 2 100 5 2 - One 1400 2 air 3 100 5 3 - One 1400 2 air 4 100 5 4 - One 1400 2 air 5 100 5 5 - One 1400 2 air Comparative example One 100 - - 5 One 1400 2 air 2 100 - - 5 One 1450 2 air 3 100 5 - - One 1400 2 air 4 - - - - - - - -

Test Example 1 Mechanical Strength Test

In order to measure the porosity and bending strength of the filter, the sintered filter material was cut into 4 × 5 × 35 mm using a diamond wheel, and the tensile surface was polished with a diamond wheel when measuring the strength. The porosity of the specimens was calculated by using the Archimedes method after boiling each specimen in distilled water for 3 hours, measuring the suspension weight, catcher weight and dry weight.

In addition, the bending strength of each specimen was measured using a universal strength tester, the lower distance 30 mm jig and cross-head speed 0.5 mm / min. Three-point bending strength was used as the measuring method under conditions. The porosity and bending strength values of the filters thus measured are shown in [Table 2].

division Porosity (%) Breaking Strength (Mpa) Example One 35 35 2 35 40 3 35 45 4 33 40 5 30 38 Comparative example One 30 30 2 40 20 3 35 32 4 38 40

As shown in Table 2, the specimens to which the calcium carbonates of Comparative Examples 1 to 3, which were prepared by applying the prior art, exhibited strength values of up to 32 MPa, and are commercially available as the dust collection filter. Although the filter had a strength value of 40 MPa, the mullite-zirconia-bonded silicon carbide filter of the present invention exhibited an excellent strength value of 40 MPa or more.

This characteristic is a result confirming that the present invention can provide a silicon carbide filter with improved mechanical strength characteristics compared to the prior art.

Test Example 2 Observation of Microstructure of Sintered Body

In Comparative Example 3 and Example 3, the change of the support layer microstructure on the fracture surface was compared with respect to the specimen in which the bending strength was measured.

1A and 1B are photographs showing the microstructures of the sintered fracture surfaces of Comparative Examples 3 and 3, respectively, and in the case of the sintered fracture surfaces of Example 3, the areas where the support layer silicon carbide particles are connected are relatively large, and the bending strength It is shown that the surface where the fracture has progressed appears in the part where the particles were bonded by the applied load during the measurement. This shows well the reason that the bending strength values of the sintered specimens of Example 3 are excellent in the sintered specimens of Comparative Example 3 and Example 3 having the same porosity.

1A is a photograph showing a microstructure of a sintered compact of Comparative Example 3 of the present invention.

1B is a photograph showing a microstructure of a sintered compact of Example 3 of the present invention.

Claims (5)

100 parts by weight of silicon carbide (SiC) powder, 5 parts by weight of mullite (3Al ₂ O ₃ ? SiO ₂ ) powder, 1 part by weight of calcium carbonate (CaCO ₃ ) powder, and 1 to 5 parts by weight of zirconia (ZrO ₂ ) powder. Mullite-zirconia bonded silicon carbide ceramic composition for producing hot gas filters. A method for preparing a hot gas filter, the method comprising: mixing 1 to 5 parts by weight of an organic binder and 5 to 20 parts by weight of a solvent as a molding aid with respect to 100 parts by weight of the mullite-zirconia-bonded silicon carbide ceramic composition for preparing a hot gas filter; Drying the molded body; And heating and sintering the dried molded body in air to complete a filter. 12. A method of manufacturing a mullite-zirconia-bonded silicon carbide hot gas filter comprising a; 3. The method of claim 2, The organic binder is a mullite-bonded silicon carbide hot gas, characterized in that at least one selected from the group consisting of methyl cellulose (methylcellulose), ethyl cellulose (ethylcellulose), carboxymethyl cellulose (carboxymehylcellulose) and polyvinyl alcohol (polyvinyl alcohol) Method for producing a filter. 3. The method of claim 2, Method for producing a mullite-bonded silicon carbide hot gas filter, characterized in that the solvent is water. 3. The method of claim 2, The sintering is a method of manufacturing a mullite-bonded silicon carbide hot gas filter, characterized in that the heat treatment for 0.5 to 5 hours in the air at a temperature range of 1400 ~ 1450 ℃.

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