JP3484756B2 - Aluminum titanate low thermal expansion porous ceramic body and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention has a small coefficient of thermal expansion,
High mechanical strength, no crystal decomposition at high temperature, excellent thermal shock resistance, particularly suitable for high temperature catalyst carriers, high temperature heat insulating agents, exhaust gas filters, etc. Aluminum titanate low thermal expansion porous ceramic body and production thereof It is about the method.

[0002]

2. Description of the Related Art In recent years, porous ceramics made of mullite, alumina, zirconia and mixtures thereof have been developed as materials for diesel engine exhaust gas filters and high temperature catalyst carriers. These are excellent in heat resistance and mechanical strength, but have a problem that they have high thermal expansion coefficients and poor thermal shock resistance. As a solution to these problems, Japanese Unexamined Patent Publication No. 2-255576 discloses cordierite porous ceramics.

On the other hand, as a method for manufacturing an exhaust gas filter for a diesel engine, for example, Japanese Patent Application Laid-Open No. 2-52
Japanese Laid-Open Patent Publication No. 015 discloses a technique for producing honeycomb-shaped ceramics by extrusion molding a cordierite material.

[0004]

However, in the above conventional structure, the cordierite-based porous ceramics are
It has a small thermal expansion coefficient and excellent thermal shock resistance, but its melting point is lower than that of mullite porous ceramics at 1420 ° C.
If the temperature exceeds 1 ° C, softening and melting abruptly and the shape change during firing tends to occur. On the other hand, if the temperature is lower than 1370 ° C, firing is still difficult and the optimum firing temperature range is very narrow, and the mechanical strength of the fired body is small. Had. Further, the honeycomb-shaped ceramics manufactured by extrusion molding has a mechanical strength higher than that of the cordierite porous ceramics,
Because of the extrusion molding by high pressure, the structure becomes dense, and at the same time the diameter of the internal pores decreases in inverse proportion to the extrusion pressure and the bulk density increases, and the porosity is low and the pressure loss is large when used as a filter. Had a problem of being heavy. Further, when this honeycomb ceramics is used as a high-temperature catalyst carrier, the porosity is low, so that the adhesion to the catalytically active substance and the catalytic substance is deteriorated, and there is a problem that peeling easily occurs during use. Furthermore,
In the production of honeycomb ceramics by extrusion molding, there is also a problem that cracks easily occur during the drying and firing steps and the production yield is poor.

The present invention solves the above-mentioned conventional problems. It has a small coefficient of thermal expansion, a large mechanical strength, no crystal decomposition at high temperatures, excellent thermal shock resistance and heat resistance, and an optimum firing temperature. An aluminum titanate low-thermal-expansion porous ceramic body having a wide range, which hardly causes shape change due to softening and melting during firing, and which has an optimal pore to function as a high-temperature catalyst carrier or a filter for diesel exhaust gas, and a method for producing the same. The purpose is to provide.

[0006]

In order to achieve this object, the aluminum titanate low thermal expansion porous ceramic body according to claim 1 of the present invention is aluminum titanate.
The mixing ratio of the rutile powder to the rutile powder is aluminum titanate.
Ru-based powder to 27.0 wt% to 67.0 wt%
Generated as a powder of 6.5 to 18.0 wt%
Aluminum Titanate Low Thermal Expansion Porous Cerami
And a rutile phase and a mullite phase as sub-components of the crystal phase, and the chemical composition of the aluminum titanate phase is Al ₂ O ₃ Is 49.0 to 56.0 wt%, TiO ₂
Of 35.0-46.0 wt% and SiO ₂ of 4.0-6.
0 wt%, Fe ₂ O ₃ is 1.0 to 3.0 wt%, and its coefficient of thermal expansion between 30 to 800 ° C. is 1.0 × 10 ⁻⁶ /
℃ or less, bending strength at room temperature is 200 Kg / cm ²
The above is the number of pores with a diameter of 3 to 29 μm.
It is composed of parts . Aluminum titanate porous low thermal expansion porous ceramic body according to claim 2, wherein the switch
Aluminum titanate low thermal expansion porous ceramic body
Therefore, it is used as a filter for diesel exhaust gas.
Has a configuration. The diameter according to claim 3 is 3 to 29 µ.
The method for producing an aluminum titanate low-thermal-expansion porous ceramic body having a large number of pores of m is 1
Al of 5.0～55.0Wt% mixing ratio ₂ O ₃ -SiO ₂
Based inorganic fiber, pulp, 27.0 wt% to 6
7.0 wt% aluminum titanate-based powder, 6.5
a slurry producing step of dispersing and mixing a wt% to 18.0 wt% rutile powder to obtain a slurry, and a cationic, anionic or nonionic polymer flocculant in the slurry or the polymer flocculant and a high electrolyte inorganic A flocculating step of adding a mixture of flocculants and aggregating the slurry, and after aggregating,
A sheet generation step of obtaining a sheet by a papermaking method, and a honeycomb-shaped molded body obtained by corrugating the sheet as required, or a molded body generation step of obtaining a laminated molded body by laminating rectangular sheets and rectangular sheets of the sheet, 1500 ℃ ~ 1550 ℃
And a firing step of firing the sheet, the honeycomb-shaped formed body, or the laminated formed body in the firing temperature range .

Here, as the aluminum titanate-based powder, a mixture of powders of aluminum oxide or aluminum hydroxide and titanium dioxide or a mixture thereof is calcined, and as the rutile-based powder, titanium dioxide powder is calcined. It is preferable to use the above. By using these as raw materials, it is possible to obtain an aluminum titanate-based low thermal expansion porous ceramic body having a small thermal expansion coefficient, excellent heat resistance and thermal shock resistance, and a wide optimum firing temperature range.
The compounding ratio of the aluminum titanate-based powder and the rutile-based powder is such that the aluminum titanate-based powder is 25.5 wt% to 7%.
2.5 wt%, preferably 27.0 wt% to 67.0 w
t% is used. If it is less than 27.0 wt%, the thermal expansion coefficient tends to increase, and if it exceeds 67.0 wt%, the bending strength tends to weaken, which is not preferable. Rutile powder is 5.1 wt% to 1
8.7 wt%, preferably 6.5 wt% to 18.0 wt
% Is used. If it is less than 6.5 wt%, the bending strength tends to be weakened, and if it exceeds 18.0 wt%, the thermal expansion coefficient tends to increase, which is not preferable.

The Al ₂ O ₃ —SiO ₂ type inorganic fiber is added in an amount of 15.0 wt% to 55.0 wt%, preferably 19.0 wt% to 53.0 wt%. 1
If it is less than 5.0 wt%, it is difficult to obtain a good floc and it becomes difficult to make a paper. As a result, the strength of the sheet tends to be weak, and if it is 53.0 wt% or more, the thermal expansion coefficient of the inorganic fiber itself is strong. However, the thermal expansion coefficient tends to increase, which is not preferable. The pulp is 0.3 wt% to 7.7 wt%, preferably 2.0 w
t% -7.5 wt% is used. When the amount is less than 2.0 wt%, the sheet produced by the papermaking method tends to be rigid and hard, and it tends to be difficult to produce a molded body.
As it exceeds 5 wt%, the distribution of pores tends to become non-uniform, which is not preferable. In the slurry forming step, it is preferable to add an aqueous solution of AlCl ₃ .6H ₂ O, NaOH or the like because good floc formation can be obtained. As the polymer flocculant, an amine-bonded polymer is used as a cation type, a polyacrylic acid salt is used as an anionic type, and polyacrylamide is used as a nonionic type, but nonionic is preferably used. This is because good floc formation can be obtained. As the high-electrolyte inorganic coagulant, NaOH, KOH, or the like is used. The mixing ratio of the polymer coagulant and the inorganic coagulant is such that the inorganic coagulant is 3 to 7, and preferably 4 to 6 with respect to the polymer coagulant. A strong floc can be obtained by using an inorganic coagulant together. The firing temperature is 1500 ° C to 1550 ° C, preferably 1520 ° C to 1540 ° C. If it is less than 1500 ° C, there is a tendency for insufficient firing, and if it exceeds 1550 ° C, there is a tendency for partial melting, which is not preferable.

[0009]

With this structure, since the Al ₂ O ₃ —SiO ₂ type inorganic fiber is used as the raw material, the change in shape due to the softening and melting during firing can be suppressed and the mechanical strength of the fired body can be increased. Since a mixture of 5.1 wt% to 18.7 wt% of rutile powder with aluminum titanate powder is used, the coefficient of thermal expansion can be reduced and the thermal shock resistance can be improved. Further, since the aluminum titanate-based powder synthesized from aluminum oxide or aluminum hydroxide and titanium dioxide is used, the optimum firing temperature can be widened. The aluminum titanate-based powder has a chemical composition of Al ₂ O ₃ and TiO _2.
In addition to ₂ , a small amount of SiO ₂ and Fe ₂ O ₃ are contained, so that decomposition of aluminum titanate crystals at high temperature can be prevented. Further, a part of the rutile powder can react with the Al ₂ O ₃ —SiO ₂ inorganic fiber during firing to form aluminum titanate. Furthermore, Al
_Since pulp was added together with ₂ O ₃ -SiO ₂ based inorganic fibers, it is possible to form a large number of uniformly dispersed pores, which can increase the porosity, reduce the bulk density, and reduce the weight of the ceramic body. .

[0010]

EXAMPLES An example of the present invention will be described in detail below.

(Example 1) Al ₂ O ₃ -SiO ₂ based inorganic fibers, pulp, aluminum titanate powder, and rutile powder were blended in the proportions shown in (Table 1),
Water was added and dispersed and mixed in a dedicated tank to obtain a slurry.

[0012]

[Table 1]

The resulting slurry was transferred to a dedicated dilution tank, water was added to make a predetermined volume, and then AlCl ₃ .6 was added.
7.4 The PH and H ₂ O added solution and NaOH solution
Adjusted to 7.8. Next, a cation, anion or nonionic polymer coagulant and a high electrolyte inorganic coagulant are added to coagulate the slurry, and Al ₂ O ₃ —SiO ₂ based inorganic fiber, pulp, aluminum titanate powder, and rutile powder are used. I got good flock.

Next, Al ₂ O ₃ --SiO _{2 is formed} by a papermaking method.
A sheet made of inorganic fiber, pulp, aluminum titanate powder, and rutile powder was prepared. Then, this sheet was fired within a temperature range of 1500 to 1550 ° C. to obtain a sample.

Then, for the obtained sample, the crystal layer was identified by powder X-rays, the thermal expansion coefficient was measured, and the bending strength as the mechanical strength was measured. The results are shown in (Table 2).

[0016]

[Table 2]

As is clear from this (Table 2), the sample of the first embodiment of the present invention has an aluminum titanate phase as the main component of the crystal phase, and a rutile phase and a mullite phase as sub-components. I understood it. Also, the 30-800
Coefficient of thermal expansion between ° C is 1.0 × 10 ^-6 / ° C or less,
Moreover, it was revealed that the bending strength at room temperature was 200 Kg / cm ² or more. On the other hand, the bending strength of the comparative example was only 60% to 83% of that of the working example, and it was found that all of them had a large coefficient of thermal expansion and were extremely problematic in practical use.

When the Al ₂ O ₃ —SiO ₂ type inorganic fiber is 15 wt% or less, the bending strength is lowered, and
It has become clear that the thermal expansion coefficient tends to increase at 5 wt% or more. Next, with respect to the samples of this example and the comparative example, the distribution of pores was confirmed by a scanning electron micrograph. In this example, it was found that a large number of uniformly dispersed pores were contained inside. On the other hand, in the comparative example, the size and distribution of the pores were non-uniform.

As described above, according to this embodiment, an aluminum titanate-based low thermal expansion porous ceramic body having a small thermal expansion coefficient, a large bending strength, and a large number of uniformly dispersed internal pores can be obtained. I understood it. This aluminum titanate low-thermal-expansion porous ceramic body has the excellent properties as described above, and is thus extremely useful as a diesel engine exhaust gas filter and a high-temperature catalyst carrier.

Example 2 In the same manner as in Example 1, A
A sheet made of l ₂ O ₃ —SiO ₂ based inorganic fiber, pulp, aluminum titanate powder, and rutile powder was prepared. Then, this sheet was corrugated to form a honeycomb-shaped formed body or a rectangular-shaped formed body to form a laminated formed body. This honeycomb-shaped molded body or laminated molded body
Firing was performed within a temperature range of 0 to 1550 ° C to obtain a diesel engine exhaust gas filter.

Then, an exhaust gas purification test of a diesel engine was conducted using the obtained filter. As a result, it has been found that the diameter of the inner pore is preferably 3 to 29 μm, particularly 4 to 25 μm in order to prevent the pressure loss from increasing.

The optimum firing temperature range was confirmed. The results are shown in (Table 3).

[0023]

[Table 3]

As is clear from the results shown in (Table 3), it was found that the shape change due to the softening and melting did not occur at the firing temperature of 1500 to 1550 ° C.

(Example 3) Described in Examples 1 and 2.
The aluminum titanate low thermal expansion porous cell of the present invention
Ramix and diesel engine exhaust gas filters
The chemical composition of the aluminum titanate phase, which is the crystal layer of
When identified and quantified by powder X-ray and fluorescent X-ray, Al
₂ O₃ Is 49.0-56.0 wt%, TiO₂ Is 35.
0-46.0wt%, SiO₂ Is 4.0-6.0 wt
%, Fe₂ O₃ Is 1.0 to 3.0 wt%
won. Also, Al₂ O₃ , TiO₂ Of the above chemical composition
If it is out of the range, the thermal expansion coefficient becomes large, which is not preferable.
Again, SiO₂ , Fe₂ O ₃ By adding
To prevent decomposition of aluminum titanate crystals at high temperature.
However, if it exceeds the above chemical composition range, the thermal expansion coefficient
It can be seen that heat resistance is impaired as the number increases.
It was.

[0026]

As described above, according to the present invention, Al ₂ O ₃ --S
It contains 15 to 55 wt% of io ₂ inorganic fiber, the main component of the crystal phase is an aluminum titanate phase, and the rutile phase and the mullite phase are sub-components of the crystal phase.
The coefficient of thermal expansion between 0 and 800 ° C is 1.0 × 10 ^-6 / ° C or less, and the bending strength at room temperature is 200 Kg / cm ²
As described above, the heat shock resistance and heat resistance are excellent, the optimum firing temperature range is as wide as 1500 to 1550 ° C., there is no shape change due to softening and melting during firing, and the product yield can be improved. Further, since it has a large number of uniformly distributed internal pores, it is possible to realize an aluminum titanate low thermal expansion porous ceramic body which is optimal for functioning as a high temperature catalyst carrier or a diesel exhaust gas filter. Is.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukinori Ikeda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Koichi Watanabe 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-4-26544 (JP, A) JP-A-6-56551 (JP, A) JP-A-63-236759 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/42-35/51 C04B 38/00-38/10

Claims (3)

(57) [Claims] 1. The compounding ratio of aluminum titanate powder and rutile powder is 27.0 for aluminum titanate powder.
wt% to 67.0 wt%, and the rutile powder to 6.5.
An aluminum titanate low-thermal-expansion porous ceramic body produced in an amount of 1% by weight to 18.0% by weight, wherein the main component of the crystal phase is the aluminum titanate phase, and the rutile phase and mullite are sub-components of the crystal phase. Phase, and the chemical composition of the aluminum titanate phase is Al ₂ O ₃ is 4
9.0-56.0 wt%, TiO ₂ is 35.0-46.
0 wt%, SiO ₂ 4.0 to 6.0 wt%, Fe ₂ O ₃
Has a thermal expansion coefficient of 1.0 × 10 ⁻⁶ / ° C. or less between 30 and 800 ° C., and a bending strength at room temperature of 200 Kg / cm ² or more. Yes, diameter 3
An aluminum titanate-based low thermal expansion porous ceramic body having a large number of pores of 29 μm inside. 2. The aluminum titanate low-thermal-expansion porous ceramic body according to claim 1, which is used as a diesel exhaust gas filter. . 3. Al having a compounding ratio of 15.0 to 55.0 wt%.
₂ O ₃ —SiO ₂ based inorganic fiber, pulp, 2
A slurry producing step of dispersing and mixing 7.0 wt% to 67.0 wt% aluminum titanate-based powder and 6.5 wt% to 18.0 wt% rutile-based powder, and a cation and anion in the slurry. Or a nonionic polymer coagulant or a mixture of the polymer coagulant and a high-electrolyte inorganic coagulant is added, and an aggregating step of aggregating the slurry, after aggregation, a sheet forming step of obtaining a sheet by a papermaking method, a molded body production step of obtaining the sheet corrugated honeycomb-shaped molded body or a sheet and rectangular processed by laminating rectangular sheet laminated molded body as necessary, 15
In the firing temperature range of 00 ° C. to 1550 ° C. and having a firing step of firing the sheet or the honeycomb molded body or the molded laminate, size 3
A method for producing an aluminum titanate low thermal expansion porous ceramic body having a large number of pores of 29 μm inside .