JPH013067A - Manufacturing method of cordierite honeycomb structure - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a cordierite honeycomb structure catalyst carrier, particularly a honeycomb structure with low expansion and excellent thermal shock resistance used as a catalyst carrier for purifying automobile exhaust gas, and its production. It is about the method.

(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 characteristics of ceramic honeycomb catalyst carriers used in automobile exhaust gas purification devices, and it is important to avoid unburned hydrocarbons in exhaust gas. 2. Sudden heat generation due to catalytic reaction of carbon oxide or when starting or stopping the engine. Honey changes due to temperature changes due to heat and rapid cooling.

High thermal shock resistance is required to withstand thermal stress caused by temperature differences occurring within the cam structure, and this demand is particularly strong today as catalysts are installed near engines and operated at high speeds to improve catalyst activity.

This thermal shock resistance is expressed by the thermal quenching 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 higher the durability temperature difference. It is known that in honeycomb structures, the contribution rate 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. Pat. No. 3,885.977.
As disclosed in the specification (corresponding Japanese application: JP-A-50-75611), the coefficient of thermal expansion between 25 and 1000°C is 11XIO-7/'' in at least one direction.
Cordierite ceramics with an orientation smaller than C is described, and the planar orientation caused by plate clay and laminated clay is described as the cause of this orientation, and among them, silica raw material was used. A composition is disclosed that exhibits a low expansion of 0.56 x 10-6/''C between 25 and 1000C.

On the other hand, as shown in the examples, the characteristic of the system using silica is that the A-axis thermal expansion coefficient is 0.62 to 0.
．． 78×10-”/'c, the B-axis thermal expansion coefficient is 1.
01 to 1.08 x 10-'/''c, and there was a problem that a low expansion of the B-axis thermal expansion coefficient, which substantially contributes to thermal shock resistance, could not be achieved.

In addition, US Patent No. 3,950,175 (Japanese Patent Application Laid-open No. 75612/1983) discloses that a part or all of the talc or clay in the raw materials is replaced with pyroferrite, kyanite,
It is disclosed that cordierite-based porous ceramics having at least 20% of pores with diameters larger than 10 μm can be obtained by substitution with silica or silica-alumina source materials such as quartz, fused silica.

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, and a low expansion of the B-axis thermal expansion coefficient could not be achieved. .

Furthermore, Japanese Patent Publication No. 57-28390 discloses that by setting the average particle diameter of talc to 5 to 150 μm,
Although it is disclosed that a low expansion of less than 1.6X]O~6/°C is obtained between 00°C and a composition showing a low expansion of less than 0.9X10-67'C between 25 and 1000°C. There is no description of this, and it was not possible to further reduce the coefficient of thermal expansion in the A-axis and B-axis directions.

Furthermore, the inventor's earlier application, patent application No. 61-1839,
In 04, 5
It shows a combination of high-purity amorphous silica and fine alumina based on the use of fine talc of less than μm, but 4
A low expansion of less than 0.3 x 10-6/°C between 0 and 800°C has not been 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 improving the heat resistance and heat resistance of the cordierite honeycomb structure. It is an object of the present invention to provide a cordierite honeycomb structure and a method for manufacturing the same.

(Means for Solving the Problems) The cordierite honeycomb structure of the present invention has a chemical composition of main components of 42 to 56% by weight of SiOz, Al2O:
l 30-45% by weight, Mg0 12-16% by weight, 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 ( Figure 4 A-axis) (7) 40-800
The coefficient of thermal expansion of 'C nori; 1 is 0.3 x 10-6
/ 'C or below, 40 in the direction perpendicular to the flow path (Axis B in Figure 4)
Thermal expansion coefficient between ~800℃ is 0.5X10-b/'C
It is characterized by the following.

Further, in the method for producing a cordierite honeycomb structure of the present invention, the chemical composition of the main component is 5iOz 42 to 56% by weight.
, AIto:l 30-45% by weight, Mg012-16
Talc with an average particle size of 5 to 100 μm, alumina with an average particle size of 2 μm or less, and an average particle size of 15 μm so that the weight is 4%
m or less high-purity amorphous silica and other cordierite forming raw materials are prepared, a plasticizer and an organic binder are added to this preparation, mixed and kneaded to form a plasticized deformable batch, and this plasticized The process is characterized in that the resulting batch is formed by extrusion and then dried, and then this dried product is fired at a temperature of 1350 to 1440'C.

(Function) The reason why low expansion can be achieved with the above-mentioned configuration is that the reaction system is significantly different from the cordierite-forming reaction system of talc, kaolin, and alumina due to the use of high-purity amorphous silica. This is because the stage shifts to the high temperature side, and domains with a maximum diameter of 20 μm or more in which the preferred cordierite crystal orientation, that is, the C-axis crystallization direction of the cordierite crystals are aligned in the same direction, can be obtained. Furthermore, the average length of the cordierite crystal in the C-axis direction is 1 to 5 μm, and 8
A microstructure in which euhedral cordierite crystals with an aspect ratio of C axis/A axis of cordierite crystals of 0% or more is 1.5 or more is obtained.

Furthermore, as a feature of this microstructure, microcrack stars are not significantly different from those of talc, kaolin, and alumina-based cordierite materials, but microcranks develop along the C-axis direction of cordierite crystals within the domain structure. Cordierite crystals with positive expansion absorb thermal expansion in the A-axis and B-axis directions, so the contribution of microcracks to low expansion increases, resulting in low expansion as a honeycomb structure. it is conceivable that.

For low expansion, the chemical composition of the honeycomb structure is 42 to 56% by weight of SiO□, preferably 47 to 53% by weight of AI
30-45% by weight in to3, preferably 32-38% by weight, 12-16% by weight in MgO, preferably 12.5-
It is preferable to set the amount to 15% by weight, and components that are unavoidably mixed such as TiO2, CaO, KNaO1FezO
3 may be contained in an amount of 2.5% by weight or less as a whole.

It is preferable that the crystal phase consists essentially of cordierite crystals, and the amount of cordierite crystals is 90% by weight or more,
Other containing crystals include mullite and spinel (including sapphirine).

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 x 10-'/''c in the A-axis direction and 0.5 x 10-'/''c in the B-axis direction, the thermal shock resistance will deteriorate, so the A-axis Direction 0.
3×10-'/” C or less and B axis direction 0.5 x t
It was limited to o-'/'c or less. The coefficient of thermal expansion in the A-axis direction is more preferably 0.2XIO-'/''C or less.

If the average particle size of talc is less than 5 μm, the coefficient of thermal expansion will increase and the porosity will decrease, and the average particle size will be less than 1 μm.
If it exceeds 00 μm, both the coefficient of thermal expansion and the porosity increase, so the average particle diameter was limited to 5 to 100 μm. In addition,
The average particle diameter is preferably 7 to 50 μm.

The particle size of silica is limited to an average particle size of 15 μm or less, since if the average particle size exceeds 15 μm, the coefficient of thermal expansion in the B-axis direction and the porosity will 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 alumina particle size was limited to an average particle size of 2 μm or less since the coefficient of thermal expansion increases when the average particle size exceeds 2 μm. Note that it is preferable to use NazOlO, a low soda alumina containing 12% by weight or less, as the alumina, since this 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% 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.

1 test ±1 The raw materials with the chemical analysis values and particle size shown in Table 1 are converted to Nα in Table 2.
The mixtures were prepared according to the proportions of No. 1 to No. 36, and after addition of methyl cellulose, they were kneaded to obtain extrudable clay.

Next, each batch of clay was molded by a known extrusion method to form ribs with a thickness of 152 μm and a cell count of 6 per square centimeter.
2 pieces with square cell shape, straight 193+w+, height 10
It was molded into a 0 mm cylindrical honeycomb structure.

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.
1~l! By comparing the relationship between the average talc particle size and the coefficient of thermal expansion in the A and B axis directions in the batch of Iα7, the relationship between the average particle size of talc and the coefficient of thermal expansion in Figure 1 of the conventionally known Japanese Patent Publication No. 57-28390 was determined. show.

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.

From the results in Table 2, talc with an average particle size of 5 to 100 μm, alumina with an average particle size of 2 μm or less, and 15 μm with an average particle size of
Test No. 2 using high purity amorphous silica of m or less
~6.9~14+ 16+ 18 and 20~35 are
It was found that the A-axis and B-axis thermal expansion coefficients specified in the present invention were satisfied.

In addition, Sample No. 1.7 has a talc particle size outside the invention, Sample No. 8 has an alumina particle size outside the invention, Sample No. 15 has a silica particle size outside the invention, and Sample No. 17 uses crystalline silica. 19 is A defined in the present invention, respectively.
It was also found that the thermal expansion coefficients of the axis and B axis were 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. 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 length of each sample, Corgelai i/crystal average length, crystal amount ratio with aspect ratio of 1.5 or more, honeycomb ■Ratio (f(110) / (I
(110) + I(002) )] were calculated respectively. The results are shown in Table 3.

In Table 3, the minimum domain major axis is the SIEM of each sample.
It was determined from the length of the minimum domain that could be confirmed from the photograph. Also, cordierite crystal average length and aspect ratio 1
．． The crystal amount ratio of 5 or more was similarly 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.

From the results in Table 3, in some samples of the present invention, the minimum domain major axis is 20 μm or more, the average length of cordierite crystals is 1 to 5 μm, and the ratio of the amount of crystals with an aspect ratio of 1.5 or more is 80% or more. These ranges were found to be preferred ranges in the present invention. Furthermore, it was found that the preferable range of the ratio of the honeycomb wall surface is 0.78 or more.

In addition, FIGS. 5(a) and (b) show test results 32 (invention).
The 38M photographs at 50x and 2000x are shown in Figure 6 (a
), (6) is 50 times the test Nα36 (reference example) and 2
A 38M photograph at a magnification of 1,000 times is shown. Furthermore, FIG. 7 shows a diagram for explaining each region of the 38M photograph shown in FIG. 5(a).

From FIGS. 5(a), (b) and FIG. 7, it can be seen that in the sample Nα32 of the present invention, long columnar cordierite euhedral crystals with an average length of 3.5 μm extending in the C-axis direction It can be seen that the domains are very developed, forming elongated domains with a width of 20 μm or more. In addition, crystals with an aspect ratio of 1.5 or more account for 85% of the total. Many microcracks also occur in the direction of the intra-domain crystal C-axis. Figure 5(a)
When magnified with the 50x SFM photograph shown in Figure 1, euhedral crystals and domains can be confirmed. In addition, a large domain has a major axis of 100 μm or more, making it difficult to confirm by SEM.

On the other hand, sample N shown in FIGS. 6(a) and (b)
In reference example No. 36, cordierite euhedral crystals are not observed in most parts, and the average length of the euhedral crystals that can be observed is 0.8 μm. Therefore, the formation of relatively small domains (lengthwise diameter of 10 um or more) is only observed in a small portion. No. 6 [2000 shown in J(b)
The magnified photograph shows a relatively developed area of euhedral crystals, but here too there are few crystals with an aspect ratio of 1.5 or more, accounting for only 30% of the total. Microcracks also exist, but their relationship with cordierite crystals is not clear.

Furthermore, test No. 32 (
38M photographs at room temperature and 800° C. in the same field of view of the present invention) are shown. By comparing Figures 8(a) and (b), it was confirmed that the microcrank, which is open at room temperature, is almost completely closed at 800℃, which indicates that microcracks are responsible for the low expansion of the cordierite honeycomb. It shows that it is contributing.

Furthermore, FIG. 9 shows tests Nα32 (invention) and Nα3.
The thermal expansion hysteresis curve of No. 6 (Reference Example) up to 1200°C is shown. From FIG. 9, the maximum hysteresis amount (the maximum value of the difference in thermal expansion coefficient at the same temperature between the expansion curve during heating and the contraction curve during cooling) of test 32 is 0.086%, and the maximum hysteresis amount of test Nα36 is 0.086%. It is 068%.

The magnitude of the maximum hysteresis amount is considered to represent the amount of microcracks and the magnitude of their contribution to low expansion.
Microstructure observation revealed no significant difference in the amount of microcrank between Nα32 and Nα36, indicating that Nα32 has a greater effect of microcrank on low expansion.

(Effects of the Invention) As is clear from the detailed explanation above, according to the present invention, the porosity is more than 30% and less than 42%, and 4.
Thermal expansion coefficient between 0 and 800℃ A axis: 0.3XIO-
A honeycomb structure with excellent heat resistance and thermal shock resistance of 0.5X10-''/'C or less, B axis: 0.5X10-''/'C or less can be obtained. Therefore, the present invention is extremely useful industrially, and has particularly high heat resistance. It is useful as a manifold for automotive exhaust gas purification equipment, which requires high performance and thermal shock resistance, and as a ceramic catalyst carrier for high-speed operation.

[Brief explanation of drawings]

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. Figure 3 is the graph showing the relationship between talc average particle size 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), (b) show the structure of the crystal of test Nα3250
38M photographs at 50x and 2000x, Figures 6(a) and (b) show the structure of the crystal of test No. 36, 38M photographs at 50x and 2000x, Figure 7 is shown in Figure 5(a). Each area of the 38M photo
'Diagrams for explanation, Figures 8(a) and (b) are 38M photographs showing the structure of crystals at room temperature and 800°C in the same field of view of Test No. 32, Figure 9 is Test No. 32 and No. 36 1200℃
It is a figure showing a thermal expansion hysteresis curve until. Patent applicant: Nippon Insulator Co., Ltd. Representative patent attorney: Shudo Sugimura, Patent attorney: Sugi,
Made by Ko Mura Figure 1 850 QOOQ50 f00θ 1050
1f00Ifl! ! m 'l'逼１１('c)□
850 QOOQ50 1000 105θ f
f00 Heat resistance 118 degrees □ Fig. 3/ 23 5 40 2030 5θ foo
20θ Targ grain 44-) A axis B axis/r; y + y, 1.・L to J,'! , :shiE..., ・Power ~ ♀＾＼ ρ

Claims (11)

[Claims] 1. The chemical composition of the main component is SiO_242-56% by weight,
A honeycomb structure consisting of 330 to 45% by weight of Al_2O_, 12 to 16% by weight of MgO, and a main component of the crystalline phase being cordierite, with a porosity of more than 30% and less than 42%, and a porosity of 40% in the flow path direction of the honeycomb structure. The coefficient of thermal expansion between ~800℃ is 0.3 x 10^-^6/℃ or less, and the coefficient of thermal expansion between 40 and 800℃ in the direction perpendicular to the flow path is 0.5 x 1
A low expansion cordierite honeycomb structure characterized by a temperature of 0^-^6/°C or less. 2. The low expansion cordierite honeycomb structure according to claim 1, wherein the honeycomb structure has a thermal expansion coefficient of 0.2 x 10^-^6/C or less in the flow path direction between 40 and 800C. 3. The low expansion cordierite honeycomb structure according to claim 1, comprising cordierite aggregates (domains) having a maximum diameter of 20 μm or more and arranged in the same direction as the C-axis crystallization direction of the cordierite crystals. 4. The average length of the cordierite crystal in the C-axis direction is 1 to 5
The low expansion cordierite honeycomb structure according to claim 1, wherein the C-axis/A-axis length ratio (aspect ratio) of 80% or more of the cordierite crystals is 1.5 or more in μm. 5. The low expansion cordierite honeycomb structure according to claim 1, wherein the microcracks develop along the C-axis direction of the cordierite crystals within the domain structure. 6. Low expansion according to claim 1, wherein the cordierite crystal I ratio I = I (110) / [I (110) + I (002)] of the honeycomb wall surface (plane parallel to the honeycomb extrusion direction) is 0.78 or more. Cordierite honeycomb structure. 7. The chemical composition of the main component is SiO_242-56% by weight,
Talc with an average particle size of 5 to 100 μm so that Al_2O_330 to 45% by weight and MgO 12 to 16% by weight,
Alumina with an average particle size of 2 μm or less, average particle size of 15 μm
The following high-purity amorphous silica and other cordierite forming raw materials are prepared, a plasticizer and an organic binder are added to this preparation, mixed and kneaded to make a plasticized deformable batch,
A method for producing a low-expansion cordierite honeycomb structure, which comprises forming this plasticized batch by extrusion molding, drying it, and then firing the dried product at a temperature of 1,350 to 1,440°C. 8. Of the cordierite forming raw materials, Na_2O is 0.12
Claim 7 using alumina that is less than or equal to % by weight
A method for producing a low expansion cordierite honeycomb structure as described in . 9. 8. The method for producing a low-expansion cordierite honeycomb structure according to claim 7, which uses kaolin having an average particle diameter of 2 μm or less among the raw materials for forming cordierite. 10. Average particle size of cordierite raw materials: 7 to 50
8. The method for manufacturing a low expansion cordierite honeycomb structure according to claim 7, using talc of μm. 11. 8. The method for producing a low-expansion cordierite honeycomb structure according to claim 7, wherein the amount of high-purity amorphous silica added to the cordierite-forming raw material is 8 to 20% by weight.