JP2000159570A - Production of compact cordierite sintered product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a compact cordierite sintered product, capable of producing the compact cordierite ceramic by a conventional molding and sintering method using natural raw materials without adopting a special method. SOLUTION: This method for producing a compact cordierite sintered product comprises using natural talc, natural kaolin, and alumina or aluminum hydroxide as raw materials, grinding and mixing the raw materials in an average particle size of a sub-micron value or smaller, if possible, <=0.6 μm, molding the obtained raw material particles by a conventional method and then sintering the molded product by a conventional method. In order to obtain the compact cordierite sintered ceramic, the mixed raw materials are ground and mixed in an average particle size of a sub-micron value or smaller, if possible, <=0.6 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to manufacturing a dense cordierite sintered body by an inexpensive method.

[0002]

2. Description of the Related Art Cordierite ceramics are known as low-expansion materials. At the beginning of development, they were widely used as thermal shock-resistant materials for heat-resistant tableware and electric industries, but recently, catalysts for purifying exhaust gas from automobiles. Cordierite honeycomb has been put to practical use as a carrier, and is widely used. The theoretical composition of cordierite is MgO: 13.
7 mass%, Al ₂ O ₃ : 34.9 mass%, SiO
₂ : 51.4% by mass, and Singer reports that the composition range of industrially usable cordierite is M
_{gO: 2.6~13.8mass%, Al 2 O} 3: 25.
5~38.8mass%, SiO _2: 51.4~64.
9 mass%.

[0003] Cordierite ceramics are industrially manufactured by solid phase reaction sintering using magnesium-containing raw materials such as talc and magnesite and kaolin, silica stone, alumina and aluminum hydroxide. However, since the temperature difference between the synthesis temperature and sintering temperature of cordierite and the melting decomposition start temperature is small, the sintering temperature range is narrowed, and it has been difficult to produce dense cordierite ceramics. For this reason, it is melted and vitrified, formed by the same method as glass, and then entirely crystallized by heat treatment to produce cordierite glass ceramics. In addition, dense cordierite ceramics are produced by using various additives as cordierite composition raw materials, or by producing high-purity cordierite fine powder by a new raw material preparation method such as the sol-gel method. Attempts have been made to do so.

[0004]

As described above, it is possible to produce dense cordierite ceramics by using raw materials by the sol-gel method or the like. It has a dense structure without pores, but all are expensive,
It does not become inexpensive and dense cordierite ceramics. In order to produce cordierite ceramics industrially at low cost, alumina is mixed with inexpensive natural materials such as talc and kaolin, and pulverized, molded, and fired to produce the same. However, since dense cordierite ceramics cannot be produced, addition of rare earth element oxides such as La ₂ O ₃ and CeO ₂ and aluminum titanate has been studied. However, there is a problem in that the additives are expensive and there is a problem in the addition method, and it has not yet been possible to stably produce dense cordierite ceramics.

On the other hand, potassium feldspar (10 mass) is added to a cordierite composition raw material calcined in advance, such as calcined talc.
%), Zirconia (20 to 30% by mass), zircon (5 to 20% by mass), and the like. However, since the additive forms a glass phase at the grain boundary of the sintered body, thermal expansion is performed. The disadvantage was that the coefficient was large. As described above, many attempts have been made to produce dense cordierite ceramics mainly using natural raw materials, but none has been industrially established as a production technique.

Accordingly, the present invention provides a method for producing dense cordierite ceramics by using conventional talc or kaolin and alumina or aluminum hydroxide as raw materials by a conventional molding and firing method instead of a special method. It is an object.

[0007]

The present invention uses talc or kaolin, which is a natural raw material, and alumina or aluminum hydroxide as raw materials, and reduces the mixed raw material powder to a submicron size or less, preferably an average particle size of 0.6 μm or less. Crushing
It is a method of preparing dense cordierite ceramics by the conventional molding and firing methods by preparing the raw materials by mixing, and in order to obtain dense cordierite ceramics, the mixed raw material is submicron or less, preferably an average It is constituted by pulverizing and mixing to a particle diameter of 0.6 μm or less. Therefore, the present invention is to reduce the raw material powder containing a natural raw material to submicron or less, preferably 0.6
The gist of the present invention is to provide a method for producing a dense cordierite sintered body, which is characterized by preparing a raw material to be pulverized and mixed to a size of μm or less.
Until now, it has not been possible to produce dense cordierite ceramics having extremely low porosity using a raw material obtained by mixing alumina or aluminum hydroxide with kaolin or talc, which is a natural raw material. When sintering cordierite ceramics by solid phase reaction sintering (sintering while synthesizing cordierite crystals by solid phase reaction) using kaolin, talc, alumina (or aluminum hydroxide) as raw materials, MgO The source talc melts and decomposes in the course of the reaction and melts and diffuses into the decomposed product of kaolin, thereby producing cordierite. However, the pores generated by melting and decomposing talc correspond to the particle diameter of talc to be used, so if the talc particle diameter is large, the pores become atmospheric pores and do not disappear in the sintering process and remain in the sintered body. . This is the reason why a dense sintered body cannot be obtained when cordierite ceramics are produced using the above-mentioned raw materials. In the method of the present invention, the natural raw material is talc and kaolin, and the talc and kaolin may be calcined talc and calcined kaolin. Therefore, the above raw material powder is obtained by mixing talc and kaolin with alumina or aluminum hydroxide.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION << Preparation of Raw Materials >> The average particle size of commercially available talc is several μm to several tens μm, and alumina having a particle size of 0.2 μm to several μm is commercially available. Things are cheaper. Each of these kaolin, talc, and alumina (or aluminum hydroxide) is 0.6
Even after pulverizing to a size of not more than μm, mixing, molding and sintering, it is difficult to form a dense cordierite ceramic. That is, since the three kinds of raw materials become finer powders, the more the powders are agglomerated, the more difficult it is to mix and disperse the powders. For this purpose, the above three types of mixed powder blended in the cordierite composition are mixed using a rolling (rotating) ball mill, a medium stirring mill, a vibration ball mill, or the like,
Pulverization to 0.6 μm or less is performed by wet pulverization / mixing using alcohol or water as a medium. In the embodiment of the preparation of the raw material to be pulverized and mixed according to the present invention, not only the embodiment in which the mixed powder of kaolin, talc and alumina is sufficiently mixed while being pulverized to submicron or less, And a mode in which wet mixing using a dispersant or the like or water or alcohol as a medium is performed over a long period of time so that the same effect as pulverization and mixing of the mixed powder can be obtained.

<Molding and sintering> The obtained mixed powder slurry is subjected to solid-liquid separation, dried, molded by a pressing method, an extrusion method or a casting method, and then sintered by a normal pressure sintering method. I do. At a sintering temperature of about 1150 ° C., a sintered body having almost zero apparent porosity is obtained. At 1250 to 1300 ° C., the amount of cordierite produced is maximized, and at 1350 ° C., the decomposition of cordierite starts. Therefore, the sintering temperature is 12
50-1300 degreeC is desirable.

<Natural Raw Materials> The natural raw materials kaolin and talc used may be used as they are, or may be calcined at a temperature of 800 to 1100 ° C.
Even if kaolin is used as amorphous calcined kaolin and talc is used as calcined talc composed of enstatite, dense cordierite ceramics can be produced by the above method.

When kaolin or talc is used without calcining, the cordierite formed in the sintering process is oriented in a direction perpendicular to the pressing direction in the molding process because the shape of the kaolin or talc is flat. The crystals are similarly oriented. Cordierite crystals have anisotropic thermal expansion coefficient in the crystal axis direction, and have a smaller thermal expansion coefficient on the c-axis than on the a and b axes. Microcracks occur in the cordierite ceramics in which the cordierite crystals are oriented, and the thermal expansion coefficient is reduced, but the strength is reduced.

On the other hand, when calcined kaolin and calcined talc are used, since the original flat shape is destroyed, compared with the case where kaolin and talc are used without calcining,
Since the degree of orientation of the formed body is low and the degree of orientation of the cordierite crystal after sintering is also low, microcracks do not occur and the ceramic becomes strong, but the thermal expansion coefficient increases. That is, even when using natural materials in any state of kaolin and talc, or calcined kaolin and calcined talc, fine cordierite having an apparent porosity of almost zero is obtained by performing the pulverization and mixing operation according to the present invention. It is possible to make ceramics,
When the calcined material is used, the strength is increased but the coefficient of thermal expansion is increased as compared with the case of using the mineral as it is. on the other hand,
When the mineral is used as it is, the thermal expansion coefficient becomes smaller, but the strength becomes lower than when it is used in a calcined state.

Regarding the type of raw material, first, talc is better as it contains less impurities. Even if the amount of impurities is large, it does not greatly affect the production of cordierite and the sintering for densification, but a glass phase is precipitated at the cordierite crystal grain boundary and the thermal expansion coefficient is increased. Kaolin has as little impurities as possible, especially the quartz content is 1 mass%.
Must be: This is because quartz particles present in the raw material have poor reactivity in the process of producing cordierite, and if the quartz content is large, it becomes impossible to produce dense cordierite ceramics. A dense cordierite sintered body can be produced using any of alumina and aluminum hydroxide as the alumina source.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to embodiments. The present invention is not limited by these examples.

Example 1 Georgia kaolin, which is a starting material, and 100% of talc
Calcination was performed at 0 ° C. to obtain calcined kaolin and calcined talc. First, a predetermined amount of calcined kaolin and calcined talc were separately wet-ground using a tumbling ball mill using ethanol as a solvent to obtain an average particle diameter of about 1 μm. The prepared calcined kaolin and calcined talc were mixed as a slurry, and the cordierite composition (MgO: 14.0 mass%, SiO ₂ : 4)
8.6 mass%, Al ₂ O ₃ : 37.4 mass%), and alumina having an average particle diameter of 0.5 μm was blended.
It was a mixed raw material. This mixed material is rolled with a rolling ball mill.
After crushing for 4, 72 and 120 hours, the mixture was dried to prepare three kinds of mixed powders having different particle diameters. These three types of mixed powders were uniaxially press-molded at a pressure of 30 MPa and then fired at 1250, 1300, and 1350 ° C. for 1 hour to obtain a sintered body. For these sintered bodies, the open porosity, bending strength, and coefficient of thermal expansion (normal temperature to 900 ° C.) were measured. Table 1 shows the physical properties of these sintered bodies and the average particle size of the pulverized mixed powder.

[0016]

[Table 1]

In Table 1 (physical properties of the cordierite sintered body prepared in Example 1), the average particle diameter of the mixed powder decreases as the pulverization time increases, as a matter of course. When a mixed powder having an average particle size of 0.44 μm or less was used, the open porosity was a value of 1.5% or less, and dense cordierite ceramics could be produced. The flexural strength shows a larger value as the average particle size of the mixed powder becomes smaller, and the flexural strength of a sintered body fired at 1300 ° C. using a raw material of 0.39 μm is 155M
Pa and a value equal to or higher than that of a sintered body using a raw material prepared by glass cordierite ceramics, a sol-gel method, or the like. The coefficient of thermal expansion of the sintered body produced under any condition is 1.80 to 2.21 × 10
^-6 / ° C., indicating an average value of the coefficient of thermal expansion of cordierite.

Example 2 Georgia kaolin and talc were calcined at 1000 ° C. for 5 hours, and then separately pulverized by a tumbling ball mill using water as a medium, and calcined kaolin and average particles having an average particle diameter of 0.49 μm were obtained. A calcined talc powder having a diameter of 1.16 μm was prepared. For the calcined kaolin and talc, a cordierite composition [(I, MgO: 13.7 mass%, S
iO ₂ : 51.4 mass%, Al ₂ O ₃ : 34.9 ma
ss%, theoretical composition), (II, MgO: 14.0 mass)
%, SiO ₂ : 48.6 mass%, Al ₂ O ₃ : 37.
4 mass%)] so that the average particle diameter is 0.5 μm
Was mixed to obtain a mixed raw material. These mixed raw materials were pulverized and mixed for 1 and 3 days by a rolling ball mill method using water as a medium, and then 3 mass% of a binder (polyvinyl alcohol) was added to the mixed raw material slurry, and dried using a spray drier. Granulated. Separately, uncalcined mineral talc was wet-pulverized by a rolling ball mill method using water as a medium to prepare a dry powder having an average particle diameter of 1.3 μm. The average particle size of the uncalcined mineral as-George Akolin was 0.87 μm, and kaolin was used without pulverization. The cordierite composition (I, MgO: 13.7 mass%, SiO ₂ : 51.
Alumina having an average particle size of 0.5 μm was blended so as to be 4 mass%, Al ₂ O ₃ : 34.9 mass%, theoretical composition) to obtain a mixed raw material. For these mixed raw materials, in the same way as when using calcined kaolin or calcined talc,
After pulverized and mixed, the mixture was granulated. The granules prepared as described above were pre-formed by uniaxial pressing at a pressure of 60 MPa, CIP-molded at a pressure of 300 MPa, fired at 1250, 1300, and 1350 ° C. for 1 hour, and sintered. Body. For these sintered bodies, the open porosity, bending strength, and coefficient of thermal expansion (normal temperature to 900 ° C.) were measured. Table 2 shows the physical properties of these sintered bodies and the average particle size of the pulverized mixed powder.

[0019]

[Table 2]

Table 2 (Cody prepared in Example 2)
Calcination of natural raw materials
If the material is used, the raw material of any grinding time
A dense cordierite sintered body with zero porosity
I have. In particular, the average particle size of the mixed powder for a grinding time of 24 hours
Is 0.54 μm, which is the average value of
Despite showing a large value compared to the average particle size
However, the sintered body is dense. This is compared to Example 1.
All with high molding pressure and high density
It is presumed to be caused by this. Flexural strength in each case
It shows a bending strength of 100 MPa or more,
The smaller the average particle size, the higher the value. Thermal expansion
The tension coefficient indicates a value in a range substantially similar to that of the first embodiment.
You. On the other hand, pores of a sintered body using uncalcined natural materials
The rate is slightly higher than when using calcined material
Cordierite sintering with uncalcined material
It suggests that the body can be made. Flexural strength is calcined
It is about 50% of the value when using
Despite being consolidated, cordierite sintered body
Shows low strength. However, the firing temperature and mixed powder
It depends on the average particle size, but when uncalcined material is used
The coefficient of thermal expansion is 0.96 to 1.43 × 10 ^-6/ ° C value
It is smaller than when calcined material is used. Unprovisional
When using porcelain, even if it is ground,
The material has a flat shape,
Cordierite firing due to large orientation of
In the compact, fine cracks are generated and it is a dense sintered body
Nevertheless, the bending strength is low and the coefficient of thermal expansion is low
It is presumed that it becomes. That is, the thermal expansion is slightly higher
But high bending strength and dense cordierite sintering
To make the body, use calcined material as a natural raw material and bend it
Cordierite sintered with low strength but low coefficient of thermal expansion
In order to produce the body, uncalcined materials should be used as a natural raw material.
It is.

Example 3 Gelatin akaolin as a starting material and talc in 100 parts
Calcined at 0 ° C, calcined kaolin and calcined talc separately,
Wet pulverization was performed using a tumbling ball mill with ethanol as a solvent to obtain an average particle diameter of 1 μm. The prepared calcined kaolin and calcined talc were mixed in a slurry state, and a cordierite composition (Mg: 14.0 mass%, SiO ₂ : 4)
Alumina having an average particle diameter of 0.5 μm or aluminum hydroxide having an average particle diameter of 0.64 μm is blended so as to be 8.6 mass% and Al ₂ O ₃ : 37.4 mass%.
It was a mixed raw material. This mixed raw material is rolled in a rolling ball mill for 12 hours.
After crushing for 0 hour, the mixture was dried to prepare two types of mixed powders having different alumina sources. These two types of mixed powders were subjected to uniaxial press molding at a pressure of 30 MPa, and then subjected to 125
It was fired at each temperature of 0, 1300 and 1350 ° C. for 1 hour to obtain a sintered body. For these sintered bodies, the open porosity, bending strength, and coefficient of thermal expansion (normal temperature to 900 ° C.) were measured. Table 3
The physical properties of these sintered bodies and the average particle size of the pulverized mixed powder are shown below.

[0022]

[Table 3]

As shown in Table 3 (physical characteristics of the cordierite sintered body prepared in Example 3), the open porosity was extremely small even when alumina or aluminum hydroxide was used as the alumina source. Values are shown, and a dense sintered body is obtained. The bending strength of the sintered body at 1300 and 1350 ° C. is 147 to 164MP.
a shows a high value. Therefore, a dense and high-strength cordierite sintered body can be produced using either alumina or aluminum hydroxide as the alumina source.

Example 4 Four kinds of kaolin and talc, Georgia kaolin, New Zealand kaolin, Chinese kaolin, and Kongo kaolin, were calcined at 1000 ° C. for 5 hours, and ground by a rolling ball mill method using water as a medium. Average particle size 0.
4 kinds of calcined kaolin of 49 μm and average particle size 1.1
6 μm calcined talc powder was prepared. For each of these four types of calcined kaolin and talc, a cordierite composition (Mg: 13.7 mass%, SiO ₂ : 5)
Alumina having an average particle diameter of 0.5 μm was blended so as to be 1.4 mass%, Al ₂ O ₃ : 34.9 mass%, theoretical composition) to obtain a mixed raw material. These mixed raw materials are pulverized and mixed for 3 days by a tumbling ball mill method using water as a medium, and then 3 mass% of a binder (polyvinyl alcohol) is added to the mixed raw material slurry, and dried and granulated using a spray drier. did.

With respect to the granules prepared as described above, 30
After molding by a uniaxial press method at a pressure of MPa, 125
It was fired at each temperature of 0, 1300 and 1350 ° C. for 1 hour to obtain a sintered body. The open porosity of these sintered bodies was measured. Table 4 shows the open porosity of these sintered bodies and the average particle size of the pulverized mixed powder.

[0026]

[Table 4]

In Table 4 (physical properties of the cordierite sintered body produced in Example 4), the average particle diameter of the mixed powder is 0.46 μm when using Kongo kaolin, which is larger than the others. It is about 0.4 μm. However, the open porosity of the sintered body using Georgia Kaolin shows a value of 1.0 to 1.6%, which is a dense sintered body. The union is
The X-ray diffraction profile of the kaolin raw material used in this example, which shows a large porosity at any firing temperature and is not a dense sintered body, was measured. The presence of α-quartz and cristobalite was confirmed in New Zealand kaolin, while the presence of α-quartz was confirmed in China and Kongo kaolin.
According to the results in Table 4, the reason why a dense sintered body cannot be obtained depending on the type of kaolin material used, despite the fact that the cordierite composition is the same, is whether or not impurities such as quartz exist in kaolin. It is thought to be due to.

Example 5 Georgia kaolin, which is a starting material, and talc were mixed with 100
Calcination was performed at 0 ° C. to obtain calcined kaolin and calcined talc. First, a predetermined amount of calcined kaolin and calcined talc were separately wet-ground using a tumbling ball mill using ethanol as a solvent to obtain an average particle diameter of about 1 μm. The prepared calcined kaolin and calcined talc were mixed as a slurry, and a cordierite composition (Mg: 13.7 mass%, SiO ₂ : 5)
Alumina having an average particle diameter of 0.5 μm is blended so as to be 1.4 mass% and Al ₂ O ₃ : 34.9 mass%).
mass% was added to obtain three types of mixed raw materials. These three
Each kind of mixed raw material was pulverized by a rolling ball mill for 120 hours, and then dried to produce three kinds of mixed powder. These three types of mixed powders were uniaxially press-molded at a pressure of 30 MPa, and then 1200, 1300, and 1350 ° C.
At each of the above temperatures for 1 hour to obtain a sintered body. The open porosity of these sintered bodies was measured. Table 5 shows the physical properties of these sintered bodies and the average particle size of the pulverized mixed powder.

[0029]

[Table 5]

In Table 5 (physical properties of the cordierite sintered body prepared in Example 5), the porosity of the sintered body without addition of quartz has a value close to zero at any firing temperature. And densification has been achieved. However, as the amount of added quartz powder increases, the open porosity of the sintered body increases at any firing temperature,
It is a porous body. In Example 4, it can be said that the reason why a dense sintered body cannot be produced depending on the type of the kaolin raw material is that even a small amount of quartz is contained. Therefore, it is considered that kaolin having a very low quartz content should be used as a raw material for producing a dense cordierite sintered body.

[0031]

As described above, since cordierite ceramics can be manufactured inexpensively by using a low-cost manufacturing method, the range of use can be expected to be expanded.

Claims (5)

[Claims] 1. A method for producing a dense cordierite sintered body, characterized in that a raw material powder containing a natural raw material is pulverized and mixed to a submicron size or less. 2. The method for producing a dense cordierite sintered body according to claim 1, wherein the compacted cordierite sintered body is pulverized and mixed to 0.6 μm or less. 3. The method for producing a dense cordierite sintered body according to claim 1, wherein said natural raw materials are talc and kaolin. 4. The method for producing a dense cordierite sintered body according to claim 3, wherein said talc and kaolin are calcined talc and calcined kaolin. 5. The method for producing a dense cordierite sintered body according to claim 1, wherein said raw material powder is obtained by mixing alumina or aluminum hydroxide with talc and kaolin.