JPH0582343B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a cordierite honeycomb structure catalyst carrier, particularly a honeycomb structure having low expansion and excellent thermal shock resistance, which is used as a catalyst carrier for purifying automobile exhaust gas. (Prior art and its problems) With the progress of industrial technology in recent years, the demand for materials with excellent heat resistance and thermal shock resistance has increased. In particular, thermal shock resistance is one of the important properties of ceramic honeycomb catalyst carriers used in automobile exhaust gas purification devices, and can prevent rapid heat generation due to the catalytic reaction of unburned hydrocarbons and carbon monoxide in the exhaust gas, and stop the engine from starting. High thermal shock resistance is required to withstand thermal stress caused by temperature differences that occur within the honeycomb structure due to temperature changes due to rapid heating and cooling. There are strong demands associated with driving. This thermal shock resistance is expressed by the rapid heating and cooling durability temperature difference, and it has been found that the durability temperature difference is inversely proportional to the thermal expansion coefficient among the characteristics of honeycomb, and the smaller the thermal expansion coefficient, the larger the durability temperature difference. It is known that in a honeycomb structure, the contribution ratio is particularly large in the direction perpendicular to the flow path (axis B in FIG. 4). It has been known that cordierite ceramics exhibit low expansion properties, for example, as described in U.S. Patent No.
Specification No. 3885977 (corresponding Japanese application: Japanese Patent Application Laid-open No. 1989-
As disclosed in Publication No. 75611), 25~
The coefficient of thermal expansion is at least 11 in one direction between 1000℃
Cordierite ceramics with an orientation smaller than ×10 ^-7 /℃ are described, and the planar orientation caused by plate clay and laminated clay is described as the cause of this orientation. discloses a composition that uses a silica raw material and exhibits a low expansion of 0.56 x 10 ^-6 /℃ between 25 and 1000℃.On the other hand, the characteristics of the system using silica here are also shown in the examples. As shown in the figure, the B axis thermal expansion coefficient is 1.01 to 1.08 x 10 ^-6 /°C, which is larger than the A axis thermal expansion coefficient of 0.62 to 0.78 x 10 ^-6 /°C, and B substantially contributes to thermal shock resistance. There was a problem in that it was not possible to achieve a low axial thermal expansion coefficient. Also, U.S. Patent No. 3950175 (Japanese Unexamined Patent Publication No.
-75612), by replacing part or all of the talc or clay in the raw material with silica or silica-alumina source raw materials such as pyrophyllite, kyanite, quartz, and fused silica. It is disclosed that cordierite porous ceramics having pores with a diameter larger than 10 μm can be obtained. On the other hand, this document discloses a composition that uses fused silica as a silica raw material and has many large pores of 10 μm or more, but there is no mention of low expansion.
It was not possible to achieve a low B-axis thermal expansion coefficient. Furthermore, in Japanese Patent Publication No. 57-28390, it is proposed that by setting the average particle diameter of talc to 5 to 150 μm,
It is disclosed that a low expansion of 1.6 × 10 ^-6 /℃ or less can be obtained between 1000℃, but between 25 and 1000℃
There is no description of a composition exhibiting low expansion of less than 0.9×10 ⁻⁶ /° C., and it was not possible to further reduce the thermal expansion coefficients in the A-axis and B-axis directions. Furthermore, the inventor's earlier patent application filed in 1983-
183904 describes a combination of high-purity amorphous silica and fine alumina based on the use of fine talc of 5 μm or less for the purpose of densification with a porosity of 30% or less. 0.3×10 ^-6 /℃
No low inflation was obtained. In the present invention, the coefficient of thermal expansion in the A-axis and B-axis directions is further reduced in a porosity range of more than 30% and less than 42%. The purpose of the present invention is to solve the above-mentioned problems and to reduce the A-axis and B-axis thermal expansion coefficients of the conventional cordierite honeycomb structure, thereby making cordierite excellent in heat resistance and thermal shock resistance. It is an object of the present invention to provide a method for manufacturing a cordierite honeycomb structure that can obtain a honeycomb structure. (Means for Solving the Problems) The method for producing a cordierite honeycomb structure of the present invention is characterized in that the chemical composition of the main components is SiO ₂ 42 to 56% by weight;
Talc with an average particle size of 5-100 μm, alumina with an average particle size of 2 μm or less, high-purity amorphous silica with an average particle size of 15 μm or less, and others so that Al ₂ O ₃ 30-45% by weight and MgO 12-16% by weight. A plasticizer and an organic binder are added to this mixture to form a plasticized and deformable batch by mixing and kneading, and this plasticized batch is formed by extrusion molding and then dried. , then this dried material was heated to 1350
By firing at a temperature of ~1440°C, the main component of the crystalline phase is cordierite, the porosity is more than 30% and 42% or less, and the flow path direction of the honeycomb structure (Fig. 4) is obtained. , A axis) 40~
Thermal expansion coefficient between 800℃ and 0.3×10 ^-6 /℃ or less, and the thermal expansion coefficient between 40 and 800℃ in the direction perpendicular to the flow path (Fig. 4, axis B) of 0.5×10 ^-6 /℃ or less The present invention is characterized in that a cordierite honeycomb structure is obtained. (Function) Low expansion can be achieved with the above-mentioned configuration because the reaction system is significantly different from the cordierite formation reaction system of talc, kaolin, and alumina due to the use of high-purity amorphous silica, and the cordierite crystallization stage is at a high temperature. This is because it is possible to obtain domains having a maximum diameter of 20 μm or more in which the preferable cordierite crystal orientation, that is, the C-axis crystallization direction of the cordierite crystals are aligned in the same direction. Furthermore, the average length of cordierite crystals in the C-axis direction is 1 to 5 μm.
A microstructure in which euhedral cordierite crystals with a C-axis/A-axis aspect ratio of 80% or more of the cordierite crystals is 1.5 or more is obtained. Furthermore, as a feature of this microstructure, the amount of microcracks is not significantly different from that of talc, kaolin, and alumina-based cordierite materials, but the microcracks develop along the C-axis direction of the cordierite crystals within the domain structure. Cordierite crystal A has positive expansion.
This is thought to be due to the fact that the microcracks make a greater contribution to low expansion because they absorb thermal expansion in the axial and B-axis directions, resulting in low expansion as a honeycomb structure. Low expansion is achieved by changing the chemical composition of the honeycomb structure.
42-56% by weight in _SiO2 , preferably 47-53% by weight,
30-45% by weight _{in Al2O3} , preferably 32-38% by weight, 12-16% by weight in MgO, preferably 12.5-15
It is preferable to set it as 2.5% by weight or less of unavoidably mixed components such as TiO ₂ , CaO, KNaO, and Fe ₂ O ₃ as a whole. It is preferable that the crystal phase consists essentially of cordierite crystals, and the amount of cordierite crystals is 90
At least % by weight of mullite and spinel (including saphirin) as other crystals contained. The porosity of the catalyst carrier is limited to more than 30% and no more than 42%, because if it is less than 30%, the conditions for supporting the catalyst will deteriorate, and if it exceeds 42%, the strength will decrease and the thermal shock resistance after supporting the catalyst will deteriorate. did. If the coefficient of thermal expansion exceeds 0.3×10 ^-6 /℃ in the A-axis direction and 0.5×10 ^-6 /℃ in the B-axis direction, the thermal shock resistance will deteriorate, so the coefficient of thermal expansion should be 0.3× in the A-axis direction.
It was limited to 10 ^-6 /°C or less and 0.5×10 ^-6 /°C or less in the B-axis direction. The coefficient of thermal expansion in the A-axis direction is 0.2×
More preferably, the temperature is 10 ^-6 /°C or less. When the average particle size of talc is less than 5 μm, the coefficient of thermal expansion increases and the porosity decreases.
If the average particle size exceeds 100μm, both the coefficient of thermal expansion and the porosity will increase, so the average particle size of 5~
It was limited to 100 μm. In addition, the average particle diameter is 7 to 50μ
It is preferable that it is m. The particle size of silica is limited to an average particle size of 15 μm or less because if the average particle size exceeds 15 μm, the coefficient of thermal expansion in the B-axis direction and the porosity increase. Regarding the type of silica, amorphous silica is used because crystalline silica increases the coefficient of thermal expansion and deteriorates thermal shock resistance, as well as increases the porosity. The average particle size of alumina is 2 μm because the coefficient of thermal expansion increases when the average particle size exceeds 2 μm.
Limited to the following. Furthermore, as this alumina,
It is preferable to use low soda alumina with a Na ₂ O content of 0.12% by weight or less because it allows for lower expansion. The average particle size of kaolin is 2 μm or less, and it is preferable to use one that is 1/3 or less of the average particle size of talc because it promotes the orientation of cordierite crystals and achieves low expansion. The aluminum hydroxide used as the alumina raw material preferably has an average particle diameter of 2 μm or less because it promotes cordierite crystal orientation and is very effective in reducing expansion. The amount of amorphous silica used is preferably 8 to 20% by weight because it is most effective in reducing swelling. (Examples) Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Example 1 Raw materials with chemical analysis values and particle sizes shown in Table 1 were
The mixtures were prepared according to the proportions of No. 1 to No. 36 in the table, and after adding methylcellulose, they were kneaded to form extrudable clay. Next, the clay of each batch was molded by a known extrusion method to form a square cell shape with a rib thickness of 152 μm and 62 cells per square centimeter, and a diameter of 93 mm.
It was molded into a cylindrical honeycomb structure with a length of 100 mm and a height of 100 mm. After drying the honeycomb structure, it was fired at the maximum temperature shown in Table 2, and the characteristics of the sintered body were evaluated for the coefficient of thermal expansion of the A and B axes, porosity, amount of cordierite crystals, and thermal shock resistance. The evaluation results are also shown in Table 2. In addition, from the above results, Fig. 1 shows the relationship between the coefficient of thermal expansion in the A-axis direction and the thermal shock resistance temperature, Fig. 2 shows the relationship between the coefficient of thermal expansion in the B-axis direction and the thermal shock resistance temperature, and Fig. 3 shows the relationship between the coefficient of thermal expansion in the A-axis direction and the thermal shock resistance temperature. Comparing the relationship between the talc average particle diameter and the thermal expansion coefficient in the A and B axis directions for batches No. 1 to No.
Figure 1 in Publication No. 28390 shows the relationship between the average particle diameter of talc and the coefficient of thermal expansion. In addition, the average particle diameter of the raw materials in Table 1 is talc.
(A), (B), and (C) were measured by a dry separation method using a JIS standard sieve, and the others were measured by an X-ray sedimentation method using a Sedigraph manufactured by Micromeritics.

【table】

【table】

【table】

[Table] * Uses low soda alumina ** Uses crystalline silica *1 Mercury intrusion method Total pore volume equivalent value (cordierite true specific gravity is 2.52)
*2 Quantitative value using X-ray diffraction ZnO internal standard *3 Durability temperature when put into electric furnace, held for 30 minutes, and taken out to room temperature From the results in Table 2, talc with an average particle size of 5 to 100 μm, and talc with an average particle size of 2 μm Test Nos. 2-6, 9-14, 16, 18 and 20-35 using the following alumina and high purity amorphous silica with an average particle size of 15 μm or less
was found to satisfy the thermal expansion coefficients of the A-axis and B-axis defined in the present invention. In addition, samples Nos. 1 and 7 whose talc particle size is outside the scope of the present invention,
Sample No. 8 with an alumina particle size outside the invention, sample No. 15 with a silica particle size outside the invention, and samples Nos. 17 and 19 using crystalline silica have thermal expansion along the A-axis and B-axis defined by the invention, respectively. It was also found that the coefficient was not satisfied. Furthermore, from FIG. 1 and FIG. 2, it can be seen that the thermal shock resistance temperature is inversely proportional to the coefficient of thermal expansion, and the correlation is remarkable with the coefficient of thermal expansion of the B axis. Although talc with the same particle size as the example used in Japanese Patent Publication No. 57-28390 was used, it was found that the coefficient of thermal expansion could be made extremely small by combining high-purity amorphous silica and fine alumina. Example 2 Several types of samples among the samples shown in Table 2 were prepared in the same manner as in Example 1, and the minimum domain major axis, average cordierite crystal length, crystal mass ratio with an aspect ratio of 1.5 or more, and honeycomb of each sample were prepared in the same manner as in Example 1. The ratio of cordierite crystals [(110)/{(110)+(002)}] on the wall surface (plane parallel to the honeycomb extrusion direction) was determined. The results are shown in Table 3. In Table 3, the minimum domain major axis of each sample is
It was determined from the length of the minimum domain that could be confirmed from the SEM photograph. In addition, the average length of cordierite crystals and the ratio of the amount of crystals with an aspect ratio of 1.5 or more were determined by randomly selecting cordierite crystals from the SEM photograph of each sample, measuring the length and width of each crystal, and calculating the aspect ratio. I asked for it.

[Table] Few.
From the results in Table 3, some samples of the present invention have a minimum domain major axis of 20 μm or more, an average cordierite crystal length of 1 to 5 μm, and an aspect ratio.
It was found that the crystal content ratio of 1.5 or more was in the range of 80% or more, and these ranges were found to be the preferred ranges in the present invention. Furthermore, it was found that a preferable range for the honeycomb wall ratio is 0.78 or more. In addition, Fig. 5 a and b show test No. 32 (this invention).
SEM photographs of Test No. 36 (reference example) are shown in Figures 6a and 6b. Furthermore, FIG. 7 shows a diagram for explaining each region of the SEM photograph shown in FIG. 5a. From Fig. 5a, b and Fig. 7, in the case of sample No. 32 of the present invention, long columnar cordierite euhedral crystals with an average length of 3.5 μm extending in the C-axis direction are extremely developed. It can be seen that domains with an elongated shape of 20 μm or more are formed. Also, the aspect ratio is 1.5
The above crystals account for 85% of the total, and many of the microcracks are also aligned in the C-axis direction of the crystal within the domain. If the SEM photograph shown in FIG. 5a is magnified 50 times, euhedral crystals and domains can be confirmed. In addition, large domains have a long axis of 100 μm or more, making it difficult to confirm with SEM. In contrast, sample No. 36 shown in Figure 6 a and b
In the reference example, cordierite euhedral crystals are not observed in most parts, and the average length of the euhedral crystals that can be confirmed is 0.8 μm. Therefore, the formation of relatively small domains (lengthwise diameter of 10 μm or more) is only observed in a small portion. The 2000x photograph shown in Figure 6b shows an area where euhedral crystals are relatively well-developed, but here too there are few crystals with an aspect ratio of 1.5 or more, and only 30% of the total are observed. Also,
Microcracks also exist, but their relationship with cordierite crystals is not clear. Further, FIGS. 8a and 8b show SEM photographs of Test No. 32 (invention) at room temperature and 800° C. in the same field of view. By comparing Figure 8a and b, it can be confirmed that the microcracks that are open at room temperature are almost completely closed at 800℃, which indicates that the microcracks contribute to the low expansion of the cordierite honeycomb. It shows that you are doing it. Furthermore, Fig. 9 shows Test No. 32 (present invention) and Test No.
The thermal expansion hysteresis curve of No. 36 (reference example) up to 1200℃ is shown. From Figure 9, the maximum hysteresis amount (the maximum value of the difference in coefficient of thermal expansion at the same temperature between the heating expansion curve and the cooling contraction curve) for Test No. 32 is 0.086%, and the maximum hysteresis amount for Test No. 36 is 0.068%. It is.
The magnitude of the maximum hysteresis amount is thought to represent the amount of microcracks and the magnitude of their contribution to low expansion, and no large difference in the amount of microcracks was observed in microstructure observation of No. 32 and No. 36. This shows that No. 32 has a greater effect of microcracks on reducing expansion. (Effects of the Invention) As is clear from the above detailed explanation, according to the present invention, the porosity is more than 30% and 42% or less, and the coefficient of thermal expansion A axis between 40 and 800°C is 0.3.
A honeycomb structure with excellent heat resistance and thermal shock resistance of 0.5× ^{10 -6 /} °C or less on the B axis can be obtained. Therefore, the present invention is extremely useful industrially, and is particularly useful for manifolding of automobile exhaust gas purification devices, which require high heat resistance and thermal shock resistance, and for ceramic catalyst carriers used in high-speed operation.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the A-axis thermal expansion coefficient and thermal shock resistance temperature, Figure 2 is a graph showing the B-axis relationship between the thermal expansion coefficient and thermal shock resistance temperature, and Figure 3 is the graph showing the relationship between the talc average particle diameter and thermal expansion. A graph showing the relationship with the coefficient, Fig. 4 is a perspective view showing an example of a honeycomb structure, and Fig. 5 a and b show the structure of the crystal of test No. 32.
50x and 2000x SEM photographs, Figure 6 a and b show the structure of the crystal of test No. 36.
SEM photographs. Figure 7 is a diagram for explaining each region of the SEM photograph shown in Figure 5 a. Figures 8 a and b show the crystal structures at room temperature and 800°C in the same field of view in Test No. 32. The SEM photo shown in Figure 9 is test No. 32.
It is a figure showing the thermal expansion hysteresis curve of No. 36 up to 1200°C.

Claims (1)

[Claims] 1. The chemical composition of the main component is SiO ₂ 42 to 56% by weight,
Talc with an average particle size of 5-100 μm, alumina with an average particle size of 2 μm or less, high-purity amorphous silica with an average particle size of 15 μm or less, and others so that Al ₂ O ₃ 30-45% by weight and MgO 12-16% by weight. A plasticizer and an organic binder are added to this mixture to form a plasticized and deformable batch by mixing and kneading, and this plasticized batch is formed by extrusion molding and then dried. , then this dried material was heated to 1350
By firing at a temperature of ~1440℃, a honeycomb structure whose main crystalline phase is cordierite, a porosity of more than 30% and 42% or less, and a porosity of 40 to 800% in the flow path direction of the honeycomb structure is produced. The coefficient of thermal expansion between ℃ and 0.3×10 ^-6 /℃ in the direction perpendicular to the flow path
A method for producing a cordierite honeycomb structure, the method comprising obtaining a cordierite honeycomb structure having a thermal expansion coefficient of 0.5×10 ^-6 /°C or less between 40 and 800°C. 2. The method for producing a cordierite honeycomb structure according to claim 1, which uses alumina containing 0.12% by weight or less of Na ₂ O among the raw materials for forming cordierite. 3 Average particle size of cordierite raw materials: 2μ
2. The method for manufacturing a cordierite honeycomb structure according to claim 1, using kaolin having a molecular weight of 10 m or less. 4 Average particle size of cordierite raw materials: 7~
A method for manufacturing a cordierite honeycomb structure according to claim 1, using 50 μm talc. 5. The method for producing a cordierite honeycomb structure according to claim 1, wherein the amount of high-purity amorphous silica added to the cordierite-forming raw material is 8 to 20% by weight.