KR20090131111A - Cordierite/zirconia ceramic honeycomb and method for fabricating thereof - Google Patents

Abstract

PURPOSE: A porous cordierite/zirconia ceramic honeycomb, and its manufacturing method are provided to obtain the optimum porosity and the uniform distribution of pores. CONSTITUTION: A method for manufacturing a porous cordierite/zirconia ceramic honeycomb comprises the steps of (S10) mixing a cordierite powder with a zirconia powder, a PMMA (polymethyl methacrylate) powder for the formation of pores and an additive for molding aid to prepare a mixture; (S20) blending the mixture; (S30) extrusion molding the mixture to prepare a honeycomb molded product; and (S40) drying and sintering the honeycomb molded product to finish the ceramic honeycomb.

Description

Porous cordierite / zirconia ceramic honeycomb and its manufacturing method {CORDIERITE / ZIRCONIA CERAMIC HONEYCOMB AND METHOD FOR FABRICATING THEREOF}

The present invention relates to a porous cordierite / zirconia ceramic honeycomb and a method for manufacturing the same, and more particularly, it includes pore properties to remove harmful gases and dust, which is used for honeycomb carriers for purifying the air environment such as industrial and automobile fields. The present invention relates to a porous cordierite / zirconia ceramic honeycomb in which the ceramic honeycomb has excellent pore properties, mechanical properties and extrusion moldability, and a method of manufacturing the same.

In general, in order to use the ceramic porous material as a honeycomb filter, it is necessary to structurally increase the strength, formally increase the specific surface area to increase the activity, improve ventilation, lower the pressure loss, and increase the thermal insulation effect.

Ceramic materials used in the ceramic honeycomb include cordierite, spodumene, Al ₂ TiO ₄ , alumina, zirconia, Si ₃ N ₄ , SiC, and the like. In the case of the actual honeycomb molding process, the direction of the crystal can be arranged to minimize the thermal shock resistance.

In the case of the support using the polymer used in the past had a disadvantage that can not be used in a limited use environment, that is, conditions such as high temperature and strong acid. Accordingly, research on porous ceramics having excellent properties such as heat resistance and chemical resistance has been actively conducted in recent years. The support used as an environmental and energy material is used through a process such as surface treatment and coating, rather than being used as an environmental material as the support itself, and the support currently being studied is mainly alumina, cordierite, mullite, and SiC. Oxides such as and the like have been used, and various types of materials, such as a disk type, a candle type, and a multi hole type, have been studied.

In addition, in the case of honeycomb using silicon carbide (SiC), the silicon carbide is oxidized when used at 900 ° C or higher, so the honeycomb using the maximum temperature of 900 ° C or cordierite has high thermal shock resistance and low thermal expansion rate. It has excellent high temperature characteristics, so it can be used even at high temperature above 1,000 ℃.

The ceramic honeycomb provides very large filtration area due to the complex cross-sectional structure, and the filtration process using ceramic porous honeycomb consumes less energy than other processes, and the process is simple, so the water and wastewater treatment, desalination of seawater, ultrapure water materials, In addition to water quality, such as pharmaceutical and food manufacturing, gas condensation, and air pollution purification, it can be used in various fields, and it is a very important research field because various forms and materials are used depending on the field.

As described above, the reason why the ceramic porous honeycomb material according to the prior art is not widely used is that it is difficult to finely adjust the pore characteristics such as the pore shape and the pore size depending on the intended use, and accordingly, It can be said. Therefore, research on ceramic filters requires continuous research and development to analyze contamination factors, secure the reliability of ceramic porous carriers, and add additional functions. Pore property design research and industrial filter manufacturing technology should be combined.

The present invention has been made in view of the need to solve the above problems, and is intended to manufacture a porous cordierite / zirconia ceramic honeycomb having a uniform pore distribution and porosity suitable for a use, and having a constant mechanical property value.

The control technology of the pores present in the porous material represents a new technological advance, and the conditions that must be preceded in order to express the characteristic improvement not found in the dense crystalline material are the identification and composition of the basic pore properties in the manufacture of the porous ceramic honeycomb. The focus should be on optimizing the mixing ratio and increasing the physical properties compared to the base product. In other words, it is possible to increase the filtration efficiency and lower the pressure loss by identifying the change in the properties of the ceramic honeycomb according to the pore characteristics, pore size, pore shape, and pore distribution, and at the same time to minimize the thermal shock resistance due to the high temperature. The characteristics of the filter can be maximized.

The reasons for the use of porous ceramics in these applications are firstly the low self-load of the porous ceramics and excellent thermal shock resistance. The thermal shock coefficient representing the thermal shock resistance is proportional to the product of the bending strength and the thermal conductivity and inversely proportional to the product of the elastic modulus and the thermal expansion coefficient. By making the material porous, the elastic modulus can be lowered to increase the thermal shock resistance. In this process, it is important to suppress the decrease in strength as much as possible, so that the pores are introduced as much as possible while maintaining the strength to increase the thermal shock resistance. Specifically, for example, when the pores have an anisotropic shape, that is, fine needle or plate shape, and then control the directionality of these pores, the sintered body as a whole while maintaining high strength in the direction perpendicular to the pore orientation Having a large amount of pores, it is possible to obtain a material excellent in thermal shock resistance. Accordingly, the present invention provides a ceramic honeycomb having excellent pore properties, mechanical properties and extrusion moldability.

The porous cordierite / zirconia ceramic honeycomb according to the first embodiment of the present invention is a mixture of cordierite powder by adding zirconia powder, polymethyl methacrylate (PMMA) powder for forming pores, and an additive for molding aid. It is characterized by being produced by kneading and extrusion molding.

In the method for preparing a porous cordierite / zirconia ceramic honeycomb according to the second embodiment of the present invention, a cordierite powder is mixed with a zirconia powder, a polymethyl methacrylate (PMMA) powder for forming pores, and an additive for molding aid Preparing a honeycomb molded body by extruding the kneaded mixture; and drying and firing the honeycomb molded body to complete a ceramic honeycomb.

The present invention uses the poly methyl methacrylate (PMMA) as a pore forming agent, or by using a graphite (graphite) with the PMMA to prepare a ceramic honeycomb to establish the extrusion composition and extrusion composition of the ceramic honeycomb having an optimum porosity and uniform pore distribution It provides a porous body control technology that enables the process, the dispersion technology according to the pore-forming agent, the extrusion process control, and the size, shape, distribution and uniformity of the fine continuous pores, and the high efficiency porosity control technology with strength and heat resistance. It can secure the fluidity of the mixture during extrusion molding, give lubricating properties to the mixture, and control the extrusion process by simplifying the production process and establishing the composition so that it can be used as an important product in various environmental markets. Have

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

Porous cordierite / zirconia ceramic honeycomb according to the present invention is a cordierite powder (zirconia), zirconia (zirconia) powder, a mixture of the PMMA (Poly methyl methacrylate) powder for forming the pores and the additives for molding aid mixed It is prepared by kneading and extrusion molding.

The cordierite powder is preferably 99% or more in purity and has a particle size of several tens of micrometers.

Zirconia powder is a high-purity stabilized zirconia which does not occur in volume change, maintains a spherical shape, the particle size is preferably several micrometers, it is preferably contained in the range of 1 to 10wt% of the total mixture.

The PMMA powder is preferably contained in the range of 15 to 30 wt% based on the total mixture as the pore-forming agent, and in particular, the pores are formed by volatilization at a temperature lower than the sintering temperature of cordierite.

Meanwhile, in order to form pores in the mixture, it is preferable to mix or mix PMMA powder or graphite powder, respectively.

As an additive for the molding aid, a binder, for example, methyl cellulose is used.

Referring to the method for producing a porous cordierite / zirconia ceramic honeycomb according to the present invention.

1 is a flow chart illustrating a method of manufacturing a porous cordierite / zirconia ceramic honeycomb according to the present invention. As shown, the method for producing a porous cordierite / zirconia ceramic honeycomb according to the present invention is zirconia powder in cordierite powder, poly methyl methacrylate (PMMA) powder for forming pores and molding aid Mixing the additives to prepare a mixture (S10), kneading the mixture (S20), extruding the kneaded mixture to prepare a honeycomb molded body (S30), and drying and firing the honeycomb molded body to a ceramic Completing the honeycomb (S40).

In the step of preparing a mixture (S10), distilled water is mixed with cordierite powder, zirconia powder, PMMA powder and molding aid additives for a predetermined time, preferably 60 to 90 minutes, and these powders are mixed. Not only is the composition change of the powder and distilled water important, but also needs to be mixed so as to be evenly dispersed, preferably distilled water is contained in the range of 20 to 25wt% based on the mixture.

On the other hand, the step of preparing a mixture (S10) may be a graphite powder mixed with the PMMA powder to form pores in the mixture. That is, PMMA powder or graphite powder may be mixed in the cordierite powder, the zirconia powder, and the additive for molding aid to form pores. At this time, since the specific gravity is low in the case of PMMA powder or the mixed graphite powder for pore formation, the change in the content of distilled water should be appropriately controlled. In the case of PMMA powder, the hydrophobic property is used, so that surface modification through organic reaction is performed. Or sufficient dispersion during mixing.

In the step of kneading the mixture (S20), the powder mixed in the mixture preparation step (S10) is kneaded using a vacuum kneading extrusion molding machine, in which the mixture is kneaded several times, preferably two to five times. Done.

Step of preparing a honeycomb molded body (S30) is a step of extruding the kneaded mixture at a constant speed, it is important to control the extrusion rate according to the viscosity and humidity of the slurry, but the viscosity and humidity of the slurry is usually mixed ( In S10), it is preferable to start the extrusion molding according to the optimum conditions.

In the step of drying and firing the honeycomb molded body (S40), drying the honeycomb molded body at an appropriate temperature and humidity in a constant temperature and humidity chamber may prevent cracking or short-circuit of the honeycomb, and a firing temperature may be increased when firing the dried honeycomb molded body. It is preferable that it is 1,250-1,450 degreeC.

One embodiment according to the method for producing a porous cordierite / zirconia ceramic honeycomb according to the present invention will be described in more detail. After mixing, the mixture is sufficiently mixed with a mixer. At this time, the distilled water content is appropriately changed according to the amount of PMMA powder and graphite powder used as the pore-forming agent, and the mixed powder is kneaded three times using a vacuum kneading extruder and kneaded. Then, the honeycomb molded body is molded while adjusting the extrusion speed. The honeycomb molded body formed by this process has a temperature of 60 ° C. and a humidity of 40% in a constant temperature and humidity device in order to prevent rapid drying of surface moisture. After drying for 24 hours, the dried honeycomb molded body was sintered at 1,250 to 1,400 ° C. for 2 hours at 10 ° C./min at a rate of temperature increase, followed by furnace cooling.

Figure 2 is a diagram showing the composition change of the porous cordierite / zirconia ceramic honeycomb according to the present invention, a porous cordierite / zirconia ceramic honeycomb for exhaust gas purification having a uniform pore distribution and porosity, and a constant mechanical property value It is a mixing condition of starting materials for manufacturing ceramic honeycomb through the control of pore shape and size by adding spherical and plate-shaped pore-forming agents to the optimum composition developed in the prior research for manufacturing.

3 is a microstructure photograph of graphite (left) and PMMA (right) for forming spherical pores in the production of porous cordierite / zirconia ceramic honeycomb according to the present invention. It is a microstructure image of a raw material that is mixed with a pore-forming agent and used as an additive to form pores through a burn-out process.

FIG. 4 is a graph illustrating pyrolysis behavior due to thermogravimetric weight-loss of a pore-forming agent with increasing temperature in the method of manufacturing a porous cordierite / zirconia ceramic honeycomb according to the present invention. As the temperature increases, PMMA and methyl cellulose (5wt% Additive) indicates that the graphite burns out at around 1,350 ° C. at 412 ° C. and 1,250 ° C. or less. At this time, it can be observed that in the case of graphite, 10 wt% is finally remained in the weight ratio. The XRF quantitative qualitative analysis of the graphite, the impurities present in the graphite itself was analyzed that the main components are Fe ₂ O ₃ , B ₂ O _{3 and the like} .

In case of graphite, pyrolysis started at over 600 ℃ and reached about 48.2% of pyrolysis at 1,000 ℃. This is because the concentration of the reaction gas (O ₂ ) in the thermal decomposition of graphite is higher than the concentrations of the product gases (CO, CO ₂ ), the reaction gas is attached to the surface and reacts, and the pyrolysis reaction is caused by the surface reaction of desorption of the product gas. Dominated and the rate of pyrolysis increases as the reaction temperature increases.

On the other hand, the result of the curve inflection point around 1,100 ℃ is considered to be related to the change of the pyrolysis mechanism. Since the concentration of the product gas is higher than the concentration of the reaction gas from the temperature of 1,000 ° C. or more, pyrolysis is controlled by the diffusion reaction of the reaction gas passing through the product gas layer or the pore layer formed by pyrolysis.

PMMA (poly methyl methacrylate) shows pyrolysis behavior as the temperature is raised to 246 ~ 412 ℃. PMMA, which has the basic characteristics of the CH ₃ O ester group and has the formula (C ₅ H ₈ O ₂ ) _n , has a residue of less than about 1% after pyrolysis above 412 ° C., which is a carbon system. .

Methyl cellulose begins to exhibit about 4.5% pyrolysis behavior below 125 ° C. This is the behavior by adsorption water and shows the thermal decomposition behavior of 73.7% as the temperature increases from 246 to 355 ° C.

Methyl cellulose having the formula (C ₇ H ₁₂ O ₅ ) _n is thermally decomposed into H ₂ O, O _{2 with} increasing temperature. However, at a later temperature, the pyrolysis sharply decreased, and as the temperature increased to 1,257 ° C, the remaining 21.1% was pyrolyzed, and the pyrolysis behavior from 355 to 1,257 ° C burned out to the high temperature region under the influence of residual carbide as in graphite. burn-out).

5 is a particle size distribution graph of the pore-forming agent of the porous cordierite / zirconia ceramic honeycomb according to the present invention. (a) shows that the average particle size of graphite is 12 µm, and the particle size distribution of the structure having two modes from maximum 76 µm to 1 µm or less can be observed, and (b) particle size of PMMA. It is observed from the distribution that the average particle size is 46 µm and exhibits a uniform particle size from 63 µm up to 10 µm.

6 is a graph showing the results of X-ray diffraction analysis according to the sintering temperature change of the porous cordierite / zirconia ceramic honeycomb according to the present invention, the cordierite / zirconia composite heat-treated at a temperature from 1,250 ℃ to 1,400 ℃ As a result of X-ray diffraction analysis, only cordierite and Cubic ZrO ₂ exist at all sintering temperatures, and crystallization is enhanced with increasing temperature. In general, in the case of cordierite / zirconia composite, ZrSiO ₄ is produced by the reaction of SiO ₂ and ZrO ₂ of cordierite from the sintering temperature of 1,300 ° C., but ZrSiO ₄ could not be observed in the present invention, which is stable Cubic ZrO. This is because ₂ is used.

7 is a graph showing the pore distribution according to the number of kneading for the starting material of the porous cordierite / zirconia ceramic honeycomb according to the present invention, by repeating the number of kneading about 1 to 10 times a constant porosity in accordance with the object of the present invention The point having the pore distribution and is selected as the kneading condition. As a result of the kneading, four times, the most ideal pore distribution and a high porosity of 75% are shown. As the number of kneading times is five or more, the kneading is not performed smoothly due to the rapid evaporation of moisture.

8 is a graph showing the change in porosity of the porous cordierite / zirconia according to the pore forming agent composition of the porous cordierite / zirconia ceramic honeycomb according to the present invention, the shrinkage of the honeycomb sintered body according to the type and content of the pore forming agent As the sintering temperature increases, densification increases, and it can be seen that the sintered compact with graphite exhibits higher shrinkage at the same temperature than the sintered compact with PMMA. This is because densification proceeds rapidly by particle rearrangement and viscous flow due to liquid impurities of graphite added as pore-forming agent. The honeycomb shrinkage under all conditions showed a modest shrinkage behavior up to 1,300 ° C, while the shrinkage proceeded rapidly from 1,350 ° C.

9 is an image showing the microstructure of the honeycomb sintered body sintered at 1,350 ℃ according to the pore-forming agent of the porous cordierite / zirconia ceramic honeycomb according to the present invention, in the case of graphite-added honeycomb sintered body in the form of an elongated plate On the other hand, the honeycomb sintered body with PMMA has a spherical pore shape. In general, under the assumption that the pore size is uniform, the honeycomb having spherical pores has a higher specific surface area than the plate-shaped pores. Therefore, spherical pores by adding PMMA, a pore forming agent, can increase the efficiency of the honeycomb catalyst carrier. have.

10 is a graph showing the change in the extrusion pressure according to the pore-former composition and the compression rate change of the porous cordierite / zirconia ceramic honeycomb according to the present invention, the extrusion pressure increases as the extrusion rate increases under all conditions. However, the pore forming agent shows a significant difference depending on the presence or absence of the pore forming agent, and the extrusion pressure decreases when the pore forming agent is added. As such, the reason why the extrusion pressure decreases depending on the presence of the pore-forming agent is that spherical or plate-shaped particles of the pore-forming agent reduce the friction, yield strength, and shear stress between cordierite particles during extrusion. Because it increases. Also, when PMMA is added, the extrusion pressure is lower than that of graphite, since spherical particles, rather than plate-shaped particles, are easier to control the molding process during extrusion.

FIG. 11 is a graph showing the porosity and compressive strength of the porous cordierite / zirconia ceramic honeycomb according to the pore-forming agent composition of the porous cordierite / zirconia ceramic honeycomb according to the composition and the firing temperature. In the case of honeycomb sintered body in which no pore-forming agent is added at the temperature, it exhibits high strength and low porosity. The honeycomb sintered body using graphite as a pore-forming agent exhibits higher porosity and compressive strength than the honeycomb sintered body using PMMA, while the honeycomb sintered body containing PMMA and graphite exhibits high porosity but relatively low compressive strength. However, in the case of honeycomb sintered body, since the required properties are different depending on the intended use, high mechanical properties are not required for all honeycomb filters, but rather, the porosity is primarily required.

When PMMA is used as a pore-forming agent, it is important to change the surface of PMMA to hydrophilic because PMMA is hydrophobic. When hydrophobic PMMA is mixed with organic material and distilled water, organic matter surrounds PMMA, and ceramic inorganic material is settled around organic material. Therefore, PMMA is not easy to burn-out and at burn-out time. Generate fine cracks;

Considering that spherical pores have higher specific surface area and catalyst carrying characteristics than plate-shaped pores, the solution to solve these problems is urgently needed. Therefore, in this study, Poly (2-ethyl-2-oxazoline) was used to solve these problems through surface modification, and honeycomb filters having various physical properties can be manufactured according to the type and content of pore-forming agent.

According to a preferred embodiment of the present invention as described above, by using a poly methyl methacrylate (PMMA) as a pore forming agent, or by manufacturing a ceramic honeycomb using graphite with PMMA, ceramic honeycomb having an optimum porosity and uniform pore distribution It is possible to establish extrusion composition and extrusion process, and to obtain porous body control technology to control dispersion technology according to pore forming agent, to control extrusion process and to maintain size, shape, distribution and uniformity of micro continuous pores, and to have strength and heat resistance. It can secure high efficiency porosity control technology, improve the fluidity of the mixture during extrusion molding, impart lubrication characteristics to the mixture, and control the extrusion molding process by simplifying the production process and establishing the composition. It has the effect of being used as

As described above, specific embodiments have been described in the detailed description of the present invention, but it is obvious that the technology of the present invention can be easily modified by those skilled in the art, and such modified embodiments are defined in the claims of the present invention. It will be included in the technical spirit described.

1 is a flowchart illustrating a method of manufacturing a porous cordierite / zirconia ceramic honeycomb according to the present invention;

2 is a diagram showing the composition change of the porous cordierite / zirconia ceramic honeycomb according to the present invention,

3 is a microstructure photograph of graphite (left) and PMMA (right) for forming spherical pores in the production of porous cordierite / zirconia ceramic honeycomb according to the present invention.

Figure 4 is a graph of the thermal decomposition behavior of the pore-forming agent by the thermogravimetric weight-loss with increasing temperature in the method of manufacturing a porous cordierite / zirconia ceramic honeycomb according to the present invention,

5 is a particle size distribution graph of the pore-forming agent of the porous cordierite / zirconia ceramic honeycomb according to the present invention,

6 is a graph showing the results of X-ray diffraction analysis according to the sintering temperature of the porous cordierite / zirconia ceramic honeycomb according to the present invention,

7 is a graph showing the pore distribution according to the number of kneading for the starting material of the porous cordierite / zirconia ceramic honeycomb according to the present invention,

8 is a graph showing changes in porous cordierite / zirconia shrinkage according to the pore-forming agent composition of the porous cordierite / zirconia ceramic honeycomb according to the present invention;

9 is an image showing the microstructure change of the honeycomb sintered body sintered at 1,350 ℃ according to the pore-forming agent of the porous cordierite / zirconia ceramic honeycomb according to the present invention,

10 is a graph showing a change in extrusion pressure according to the pore-forming agent composition and compression rate of the porous cordierite / zirconia ceramic honeycomb according to the present invention,

11 is a graph showing the porosity and compressive strength of the porous cordierite / zirconia ceramic honeycomb according to the composition and the firing temperature of the porous cordierite / zirconia ceramic honeycomb according to the pore forming agent composition of the porous cordierite / zirconia ceramic honeycomb according to the present invention.

Claims (9)

A mixture obtained by adding zirconia powder, poly methyl methacrylate (PMMA) powder for forming pores, and additives for molding aid to cordierite powder is prepared by kneading and extrusion molding Porous cordierite / zirconia ceramic honeycomb, characterized in that. The method of claim 1, The zirconia powder, Contained in the range of 1 to 10 wt% based on the mixture Porous cordierite / zirconia ceramic honeycomb, characterized in that. The method of claim 1, The PMMA, Contained in the range of 15 to 30 wt% based on the mixture Porous cordierite / zirconia ceramic honeycomb, characterized in that. The method of claim 1, Graphite powder is mixed with the PMMA powder to form pores in the mixture Porous cordierite / zirconia ceramic honeycomb, characterized in that. Preparing a mixture by mixing cordierite powder with zirconia powder, poly methyl methacrylate (PMMA) powder for forming pores, and an additive for molding aid; Kneading the mixture; Extruding the kneaded mixture to produce a honeycomb molded body, Drying and firing the honeycomb molded body to complete a ceramic honeycomb; Method for producing a porous cordierite / zirconia ceramic honeycomb comprising a. The method of claim 5, wherein Preparing the mixture, Preparing the mixture by mixing distilled water for 60 to 90 minutes with the cordierite powder, the zirconia powder, the PMMA and the molding aid additive. Method for producing a porous cordierite / zirconia ceramic honeycomb, characterized in that. The method of claim 6, Preparing the mixture, The distilled water is contained in the range of 20 to 25wt% with respect to the mixture Method for producing a porous cordierite / zirconia ceramic honeycomb, characterized in that. The method of claim 5, wherein Preparing the mixture, Mixing graphite powder with the PMMA powder to form pores in the mixture Method for producing a porous cordierite / zirconia ceramic honeycomb, characterized in that. The method of claim 5, wherein Kneading the mixture, Kneading the mixture repeatedly 2-5 times Method for producing a porous cordierite / zirconia ceramic honeycomb, characterized in that.

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