KR101356382B1 - Method for fabrication cordierite/zirconia ceramic honeycomb - Google Patents

Abstract

The present invention relates to a process for producing porous cordierite / zirconia ceramic honeycomb.

Porous cordierite / zirconia ceramic honeycomb of the present invention, by mixing the zirconia powder, the graphite powder for forming the pores and the additives for molding aid to the cordierite powder to form a mixture and molding the mixture to honeycomb After the molded body is manufactured, the honeycomb molded body is dried and fired.

Therefore, the ceramic honeycomb having excellent pore properties, mechanical properties, and extrudability can be produced smoothly.

Cordierite, Zirconia, Graphite, Strength, Pore, Extrusion, Porous, Ceramic, Honeycomb, Filter

Description

Porous cordierite / zirconia ceramic honeycomb manufacturing method {METHOD FOR FABRICATION CORDIERITE / ZIRCONIA CERAMIC HONEYCOMB}

1 is a flow chart showing a method of manufacturing a porous cordierite / zirconia ceramic honeycomb according to the present invention,

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

3 is a graph showing the results of X-ray diffraction analysis according to the sintering temperature of the cordierite / zirconia composite according to the present invention,

4A and 4B are graphs showing changes in densification behavior according to composition and firing temperature of the porous cordierite / zirconia ceramic honeycomb according to the present invention;

5a and 5b are graphs showing porosity and compressive strength according to the composition and firing temperature of the porous cordierite / zirconia ceramic honeycomb according to the present invention, and the pore distribution according to the composition change,

Figure 6 is a graph showing the change in extrusion pressure according to the composition and extrusion rate of the porous cordierite / zirconia ceramic honeycomb according to the present invention,

7 is a table showing the coefficient of thermal expansion according to the composition change of the porous cordierite / zirconia ceramic honeycomb prepared through a firing temperature of 1,300 ℃ according to the present invention,

8 is a scanning electron microscope (SEM) photograph of a porous cordierite / zirconia ceramic honeycomb of C-7A10G2Z composition prepared at a firing temperature of 1,300 ° C. according to the present invention;

9 is a prototype photograph of a porous cordierite / zirconia ceramic honeycomb prepared under optimized process conditions in accordance with the present invention.

The present invention relates to a porous cordierite / zirconia ceramic honeycomb manufacturing method that can be used for a carrier filter for environmental purification, and more particularly, excellent pore properties, mechanical properties and extrusion molding. It relates to a porous cordierite / zirconia ceramic honeycomb manufacturing method having a property.

In general, ceramic honeycomb is a kind of porous material, which has high strength structurally, high specific surface area, high activity, low ventilation, low pressure loss, and excellent thermal insulation. It has been widely used as a three-way catalyst carrier for automobiles, a catalyst carrier for denitrification, a filter for molten metal, and the like, and has recently been used as a material for ceramic filters for various hot gases, including filters for removing smoke from diesel vehicles.

The catalyst-carrying ceramic filter is a structure that combines a porous ceramic support, a dust filter layer, and a catalyst capable of simultaneously performing dust filtration and a catalyst function, and the catalyst function reacts with various harmful gases to remove the catalyst. Is obtained by adhering to the porous support, and dust filtration is performed by a physical removal mechanism by the fine pores of the filtration layer formed on the surface of the support.

As such, the filter support serving as a support for the catalyst and the filtration layer is one of the important materials that are in the spotlight as the environment and energy material. There is a limitation in that it can not be used under the conditions, and recently, porous ceramic honeycomb excellent in heat resistance and chemical resistance is used.

Materials used in ceramic honeycomb include cordierite, spodumene, alumina, mullite, silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), and the like.

Among them, silicon carbide is oxidized when used at 900 ℃ or higher, so the maximum usable temperature is slightly lower than 900 ℃, but cordierite can be used even at high temperature of 1,000 ℃ or higher, and in the honeycomb molding process Since the crystal directions can be arranged, there is an advantage that the thermal shock resistance is high and the thermal expansion rate is small.

However, cordierite ceramics are a general brittle material and have a disadvantage in that mechanical properties are very bad because they are easily broken by an impact.

On the other hand, a variety of methods have been introduced and attempted as a method of manufacturing a ceramic honeycomb, but the extrusion molding method is known to be the best in terms of reliability and efficiency, and in fact, in the design and quality of the ceramic honeycomb after the introduction of the extrusion molding method. Considerable progress has been made.

The production by extrusion molding is performed by first mixing the raw powders and mixing additives for molding aid, such as a binder, followed by extrusion, followed by drying and firing.

However, since a large amount of additives for molding aid, such as lubricants and plasticizers, are used to secure smooth extrusion, the manufacturing cost is increased, the extrusion molding process is complicated, and the mechanical properties of the manufactured ceramic honeycomb are also reduced. There was a problem.

The present invention was devised to solve the above problems, and contains zirconia for the enhancement of mechanical properties, and by adding graphite as a pore forming agent, it has excellent pore properties and mechanical properties. It is an object of the present invention to provide a porous cordierite / zirconia ceramic honeycomb manufacturing method which can improve the lubrication characteristics of the added zirconia and graphite during extrusion molding and also reduce the amount of additives for molding aid.

The above objects and various advantages of the present invention will become more apparent from the preferred embodiments of the invention described below with reference to the accompanying drawings by those skilled in the art.

Porous cordierite / zirconia ceramic honeycomb of the present invention for achieving the above object, by mixing the cordierite powder with zirconia powder for enhancing mechanical properties, graphite powder for forming pores and additives for molding aid It is characterized in that the honeycomb molded body is manufactured by drying and firing the honeycomb molded body by molding the mixture.

In addition, the porous cordierite / zirconia ceramic honeycomb manufacturing method of the present invention for achieving the above object, quantitatively zirconia powder, graphite powder as a pore-forming agent and additives for molding aid to improve the mechanical properties to cordierite powder Mixing to obtain a mixture, kneading the mixture, extruding the mixture to produce a honeycomb molded body, and drying and firing the honeycomb molded body to complete a ceramic honeycomb. It is done.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flow chart showing a method of manufacturing a porous cordierite / zirconia ceramic honeycomb according to the present invention.

Method for producing a porous cordierite / zirconia ceramic honeycomb according to the present invention, the step of quantitatively mixing the additives for zirconia powder, pore-forming graphite powder and molding aid in the cordierite powder for the improvement of mechanical properties (100) And, the step of kneading the mixture using a vacuum kneading extruder (110), the step of extruding the kneaded mixture at a constant speed using a vacuum kneading extruder (120) to prepare a honeycomb molded body, and the honeycomb prepared Drying and firing the molded body to complete the ceramic honeycomb step (130).

First, in step 100 of mixing the raw materials, it is important to quantitatively combine the inorganic powders and the additives for molding aid, and then evenly mix them.

At this time, as cordierite powder, a purity of 99% and a particle size of several to several tens of micrometers are used.

The zirconia powder uses high purity stabilized or partially stabilized zirconia, and particles are spherical in shape and have a size of several μm.

Graphite powder, which is a pore-forming agent, uses particles in the form of a plate, and the graphite component is volatilized through plastic heat treatment to form pores.

Molding additives include lubricants, plasticizers, binders and ultrapure distilled water.

In the step of kneading the mixture (110), it is preferable to repeat the process several times in order to uniformly disperse the components in the mixture, and on average three to five times may be performed.

In the extrusion step 120, it is important to control the extrusion speed according to the viscosity and humidity of the mixture, but it is more preferable to adjust the viscosity and humidity of the mixture to the optimum conditions in the mixing step 100 before performing the extrusion. It may be desirable.

In the step of drying and firing 130, drying at an appropriate temperature and humidity can prevent cracking or short circuiting, and firing is preferably performed at a temperature range of 1,250 to 1,450 ° C.

<Examples>

After sufficiently mixing each of the various compositions as shown in the table of Figure 2, the mixture was kneaded three times using a vacuum kneading extruder, and then extruded while controlling the extrusion speed. In addition, the molded honeycomb molded body was dried at a temperature of 60 ° C. and a humidity of 40% for 12 to 24 hours in a constant temperature and humidity device to prevent rapid drying of the surface moisture. Thereafter, the dried molded body was calcined in air at a temperature rising rate of 10 ° C./min for 2 hours at 1,250˜1,400 ° C., and then cooled by furnace.

3 is a graph showing the X-ray diffraction analysis of the cordierite / zirconia composite heat-treated at a sintering temperature of 1,250 ℃ to 1,400 ℃.

Referring to the graph, it can be seen that only cordierite and cubic zirconia are present at all firing temperatures, and that crystallization is enhanced with increasing firing temperature.

Normally, it was expected that SiO ₂ and zirconia (ZrO ₂ ) of cordierite reacted with calcination to produce ZrSiO ₄ , but in practice ZrSiO ₄ could not be observed, which is considered to be due to the use of stable zirconia. .

4A and 4B are graphs showing shrinkage and density changes, respectively, which are changes in densification behavior according to composition and firing temperature of porous cordierite / zirconia ceramic honeycomb.

As a result, the shrinkage tends to increase with increasing firing temperature and zirconia content.

In addition, the addition of graphite shows a lower shrinkage at the same firing temperature than the addition of graphite, which is judged to be the result of the volatilization of the graphite component in accordance with the firing heat treatment to form pores smoothly.

In addition, under all conditions, the shrinkage shows a gentle shrinkage behavior up to a firing temperature of 1,300 ° C., but suddenly shrinks from 1,350 ° C.

Furthermore, there is almost no change in shrinkage and density depending on the content of the additive for molding aid, which means that the additive is an important process factor in extrusion molding and hardly affects the properties of honeycomb.

5A and 5B are graphs showing porosity, compressive strength, and pore distribution results according to the composition and the firing temperature of the porous cordierite / zirconia ceramic honeycomb.

As a result, it can be seen that as the zirconia content increases at the same firing temperature, the porosity decreases and the compressive strength increases, while the porosity increases and the compressive strength does not decrease or change according to the addition of graphite.

From this, it can be seen that the addition of zirconia greatly improves mechanical properties such as compressive strength, and the addition of graphite greatly improves the porosity.

Typically, pure cordierite honeycomb exhibits a porosity of 30 to 35% and a compressive strength of about 7 to 11 MPa. In the honeycomb added with zirconia and graphite according to the present invention, a porosity of 46% and a compressive strength of about 26 MPa are shown. Very good properties.

As a result, it is preferable to contain zirconia in the range of 1 to 5 wt%, and if it is contained below 1 wt%, the strength property is too low, and it is not preferable, while if it exceeds 5 wt%, it is helpful to improve the strength property. It is not preferable because the manufacturing cost is too high at a high point.

In addition, the graphite is preferably contained in the range of 5 to 30 wt%, and if it is contained below 5 wt%, the porosity is too low, which is not preferable. It may be undesirable.

In addition, it can be seen that the change in the content of the molding additive additive has little effect on the mechanical properties and pore properties.

On the other hand, referring to Figure 5b, the porous cordierite / zirconia ceramic honeycomb of the present invention has a good average pore size of about 7 ~ 8㎛ also showed excellent results in this respect.

6 is a graph showing a change in extrusion pressure according to a composition change of the porous cordierite / zirconia ceramic honeycomb according to the present invention.

Looking at the results, it can be seen that the extrusion pressure is increased as the extrusion velocity (extrusion velocity) increases as usual under all conditions.

And, above all, it can be seen that the extrusion pressure decreases as the content of zirconia and graphite increases, which means that the spherical zirconia particles and the plate-shaped graphite particles are subjected to friction, yield strength and shear stress between cordierite particles during extrusion. It is inferred that by decreasing the flow rate of the mixture, that is, the lubrication properties significantly increased.

That is, it can be concluded that the addition of zirconia and graphite not only ensures excellent pore properties and mechanical properties, but also additionally promotes extrudability, thereby reducing the amount of additives used in the molding aid.

7 is a table analyzing the coefficient of thermal expansion according to the composition change of the porous cordierite / zirconia ceramic honeycomb prepared by the firing temperature of 1,300 ℃ according to the present invention.

In general, zirconia has a high coefficient of thermal expansion, cordierite has a low coefficient of thermal expansion, and in the case of the cordierite used in the present invention, the coefficient of thermal expansion is 2.0 × 10 ⁻⁶ / ° C., according to the present invention. The coefficient of thermal expansion of the arite / zirconia ceramic honeycomb was slightly lowered with little change, which is thought to be a little lower due to the restraint of zirconia particles dispersed on the matrix of cordierite having low thermal expansion.

FIG. 8 is a scanning electron microscope (SEM) photograph of a porous cordierite / zirconia ceramic honeycomb of C-7A10G2Z composition prepared at a firing temperature of 1,300 ° C. according to the present invention, in which pores are uniformly dispersed in a honeycomb frame. You can see that.

Further, Figure 9 shows a prototype photograph of the porous cordierite / zirconia ceramic honeycomb prepared under the optimized process conditions according to the present invention, before the firing is black due to the added graphite component, It can be seen that the graphite component is volatilized and discolored.

Thus, according to the present invention, by adding an appropriate amount of zirconia and graphite to the cordierite, it is possible to ensure excellent pore characteristics, mechanical properties and extrusion molding.

It will be appreciated by those skilled in the art that changes may be made to the present invention without departing from the spirit and scope of the invention as defined by the appended claims.

According to the present invention, an effect of smoothly manufacturing a ceramic honeycomb having excellent pore properties, mechanical properties, and extrudability can be achieved.

Claims (6)

The cordierite powder is mixed with a stabilized or partially stabilized zirconia powder having a spherical particle shape to enhance mechanical properties, a graphite powder having a plate shape with a particle shape for forming pores, and an additive for molding aid to form a mixture. Method of manufacturing a porous cordierite / zirconia ceramic honeycomb, characterized in that by manufacturing a honeycomb molded body by molding and drying and firing the honeycomb molded body. The method of claim 1, The zirconia powder, Porous cordierite / zirconia ceramic honeycomb manufacturing method characterized in that it is contained in the range of 1 ~ 5wt%. 3. The method according to claim 1 or 2, The graphite powder, Porous cordierite / zirconia ceramic honeycomb manufacturing method characterized by containing in the range of 5 ~ 30wt%. delete delete delete

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