JPH03193336A - Heat-resistant honeycomb structural body - Google Patents

Abstract

PURPOSE:To enhance the heat resistance, by a method wherein a ceramic fiber is constituted of a polycrystalline alumina fiber having a fixed composition and ceramic fibers are joined to each other with mullite. CONSTITUTION:At least 50wt.% of a ceramic fiber is an alpha<->Al2O3 type polycrystalline alumina fiber and the ceramic fibers are joined to each other with mullite, in a honeycomb structural body made of paper comprised of the ceramic fiber or a mixture of the ceramic fiber and a heat-resistant filler. It is preferable that a mean crystal length of the mullite which is a binder of the alumina fiber and heat-resistant filler to be filled up at need is not exceeding 4mum, especially preferably not exceeding 1mum. The heat-resistant filler is selected out of matters having sufficient heat resistance in accordance with improved heat resistance to be expected for the honeycomb structural body. Corundum, the mullite, zirconia, zircon, silicon carbide and silicon nitride which are in a fine powdery state and possess a mean particle diameter of 0.2-10mum are available as the preferable filler.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a honeycomb structure having a high degree of heat resistance and useful as a catalyst carrier, a heat exchange element, etc. used at high temperatures of 1000°C or higher. be.

[Conventional technology]

A paper made from various ceramic fibers as the main raw material and processed into a honeycomb structure was disclosed in Japanese Patent Application Laid-open No. 52-12.
It is described in Publication No. 7663, Publication No. 56-136656, etc. Honeycomb structures made of ceramic fiber paper have excellent heat resistance (especially thermal shock resistance) and corrosion resistance, so they are lighter and have less pressure loss than extruded ceramic honeycomb structures, making them suitable for gas phase application catalyst carriers and heat exchange elements. This has attracted attention in recent years.

In these conventional honeycomb structures, the ceramic fibers are filled with inorganic powder such as colloidal silica and colloidal alumina within each paper and at the joints between the papers, along with inorganic powder filled in the gaps between the fibers as needed. They are bonded to each other by a cured adhesive, thereby ensuring the shape stability of the honeycomb structure.

[Problem that the invention seeks to solve]

Honeycomb structures made of ceramic fiber paper have excellent properties as described above, but as the development of their uses progresses, it has become desirable for some uses to have higher heat resistance.

In order to obtain a honeycomb structure with particularly good heat resistance, it is first necessary to use ceramic fibers that form the skeleton of the ceramic fiber paper and have as good heat resistance as possible. From this point of view, when a honeycomb structure having a particularly high degree of heat resistance is desired, alumina fiber, which exhibits the highest degree of heat resistance among ceramic fibers, has been selected as the fiber material.

However, although alumina fiber itself can withstand high temperatures of up to about 1600°C, conventional honeycomb structures made from it cannot withstand use at temperatures above about 1200'O. This is because the thermal deterioration of the binder, which plays an important role in maintaining the shape of the honeycomb structure, begins at a relatively low temperature, so even if fibers with a high heat-resistant temperature are used, their heat resistance is not fully utilized. It is. For example, those bonded with silicic acid gel are bonded by softening and melting of the silicic acid gel that starts at around 1000℃, and those bonded with alumina gel are bonded by embrittlement due to crystallization of alumina gel that starts around 1000℃. Since the strength decreases, the honeycomb structure becomes prone to collapse even though the fiber portions have not deteriorated.

The present invention aims to solve the above-mentioned problems in conventional honeycomb structures made of ceramic fiber paper and to provide a highly heat-resistant honeycomb structure in which the excellent heat resistance of alumina fibers is fully utilized.

[Means for solving problems]

Successfully achieving the above object, the present invention provides a honeycomb structure made from paper consisting of ceramic fibers or a mixture of ceramic fibers and a refractory filler, in which at least 50% by weight of the ceramic fibers contain α-A 1 ．． OS
The present invention provides a heat-resistant honeycomb structure that is made of polycrystalline alumina fibers and is characterized in that ceramic fibers are bonded together by mullite.

As is well known, alumina fiber contains α-A l x Os
In addition to the single crystalline type, there is also the microcrystalline type, and the latter also has α-A1.0! There are various crystal forms such as type, θ-AIto type, γ-A 1.0 S type, etc., but the alumina fiber in the heat-resistant honeycomb structure of the present invention is α-A 1.0 m at least 20
11-A 120 S type containing % by weight. α−
Even if the A I,0 type is single crystal, it is difficult to obtain the honeycomb structure of the present invention because it is rigid and difficult to corrugate. Further, even if the material is microcrystalline, it is not preferable because it often transforms into other crystal forms and becomes brittle when used at temperatures above about 1100°C.

Other fibrous materials that may be present in the heat resistant honeycomb structures of the present invention along with alumina fibers include polycrystalline mullite fibers, polycrystalline mullite-zirconia fibers, zirconia fibers, silicon carbide fibers, and the like. However, it is desirable that the total amount does not exceed the amount of α-AlzOs type alumina fibers.

Mullite (3AI!03・2Si02
) preferably has an average crystal length (according to the measurement method described below) of 4 μ or less, particularly preferably 1 μ or less.

Coarse crystals do not exhibit sufficient bonding force, so
To provide a nicum structure with inferior strength regardless of the high or low operating temperature.

Heat-resistant fillers are added to increase the strength of the paper and adjust its air permeability, as in the case of conventional heat-resistant/1 nicomb structures, but they do not have the high heat resistance expected of honeycomb structures. be selected from those that have sufficient heat resistance. Preferred fillers include corundum, mullite, zirconia, zircon, silicon carbide, and silicon nitride, which are in the form of fine powder with an average particle size of 0.2 to 10 μm.

The air permeability, that is, the porosity of the ceramic fiber paper constituting the honeycomb structure is not particularly limited in the present invention, but in the case of a honeycomb structure used as a catalyst carrier, the porosity is about 40 to 85%. things are appropriate,
In addition, in the case of those used as heat exchange elements, the porosity is 3.
It is preferably about 0 to 75%. The porosity is determined by the ratio of the mullite binder and filler to the fibrous material, so the amount of binder can be adjusted in the range of about 20 to 80% by weight, and the amount of O
It is desirable to select the amount of filler, respectively, in the range from about 70% by weight. The thickness of the paper is also appropriately selected depending on the intended use, but a thickness of about 0.2 to 0.8 mm is easy to manufacture.

The honeycomb structure of the heat-resistant honeycomb structure of the present invention is also not limited, and as shown in FIG. It can be of any configuration, such as a body.

The above heat-resistant honeycomb structure using mullite as a binder is
A honeycomb made of a sheet-like molded product of alumina fiber, easily reactive silicic acid raw material, easily reactive alumina, or a material obtained by adding a heat-resistant filler to these materials using the manufacturing method invented by the present inventors. It can be easily manufactured by a method in which a structure (raw honeycomb body) is manufactured and then fired at 1100 to 1500°C to generate mullite from a highly reactive silicic acid raw material and a highly reactive alumina.

When this manufacturing method is used, various modifications may be made to the steps up to obtaining the raw honeycomb body. Typical examples include alumina fibers, easily reactive silicic acid raw materials, easily reactive alumina, or materials in which other fibrous materials, heat-resistant fillers, organic binders, etc. are appropriately added to water. The resulting paper is corrugated and laminated with unprocessed flat paper to produce a raw honeycomb body. Alternatively, a method may be used in which paper is made from a fibrous material, further formed into a honeycomb structure, and then impregnated with an aqueous dispersion of a powdery material. In these manufacturing methods,
It is desirable to use a mixture of a highly reactive silicic acid raw material and a highly reactive alumina for bonding paper to obtain a honeycomb structure.

Raw material alumina fibers include α-AI20xW, θ-A 1.0 type, δ-A 1.0
, type, γ-A + , o 3 type, etc. can be used.

In addition, as easily reactive silicic acid raw materials, colloidal silica,
Alcoholic silica sol, other fine silica powder with an average particle size of 0.5μ or less, kaolin powder, etc. can be used, and when heated to about 1100°C or higher, silica (
Aluminosilicate fibers that release cristobalite) can also be used. As the easily reactive alumina, alumina sol, alumina fine powder with an average particle size of 0.5 μm or less, etc. can be used. The appropriate ratio of the easily reactive silicic acid raw material to the easily reactive alumina is 3 to 6:4 by weight. If the silica ratio is higher than this, excess silica will turn into cristobalite and reduce the heat resistance of the product.
On the other hand, if there is an excess of alumina, sufficient bonding strength cannot be obtained.
Product strength is insufficient. The easily reactive silicic acid raw material and the easily reactive alumina are used to the extent that the mullite produced therefrom accounts for 20 to 80% by weight in the product.

Suitable heat-resistant fillers include corundum, mullite, zirconia, zircon, silicon carbide, and silicon nitride in the form of fine particles with a particle size of 0.2 to 10 μm.

The raw honeycomb body is fired in an electric furnace at a temperature of 1100 to 1500
This is done by heating to ℃. As a result, mullite is generated from the silicic acid raw material and alumina, and the honeycomb structure is firmly fixed. Prior to firing, the raw honeycomb body is coated with up to about 3% boron oxide, sodium salt, lithium salt,
Absorbing magnesium salts, fluorides, etc. in the form of an alcohol solution promotes the formation of mullite, allowing firing to be performed at a lower temperature and in a shorter time, and also reduces shrinkage of the honeycomb structure during firing. The optimum firing conditions are approximately 1200-1400°C when approximately 1% boron oxide is added.
Approximately 3 to 10 hours, approximately 130 hours without boron oxide
It is about 6-20 hours at 0-1500°C. When boron oxide is added, it is desirable to pay attention to the maximum firing temperature, since if the firing temperature is too high, the mullite crystal particles will grow and become coarse, resulting in a product with low strength.

σ-A 1.0 as the raw material alumina fiber, α-A I2 depending on the firing conditions when using something other than a mold
Metastasis to type 03 progresses. In addition, when aluminosilicate fibers are used as a raw material for easily reactive silicic acid, mullite is produced along with silica from the aluminosilicate, so even after the silica reacts with easily reactive alumina, fibrous materials mainly consisting of mullite remain in the product. remain.

〔Example〕

The present invention will be described below with reference to Examples and Comparative Examples.

Example 1 A paper (thickness 0 .35■
, basis weight 100 (7 m pieces were made by a conventional method. Then,
Half of the obtained paper was corrugated using a corrugated pole processing machine (pitch 7.6 in, corrugation height 3.7 mm).
, unprocessed flat plates were alternately stacked and glued together to form a honeycomb structure as shown in Figure 1. For adhesion, 20 parts by weight of colloidal silica with a solid content of 20% by weight and 10% by weight of a solid content
A mixture of 60 parts by weight of alumina sol was used. The obtained raw honeycomb body was then immersed in an impregnating solution having the following composition for 20 minutes, dried and hardened at 110'O, and further 4
The organic matter was decomposed by heating at 50°C.

Colloidal silica (solid content 20% by weight) 35 parts by weight Alumina sol (solid content 10% by weight) 105 parts by weight Corundum powder (average particle size 2μ) 84 parts by weight Water
100 parts by weight of the above impregnated;
After applying each drying process again to obtain a raw honeycomb body in which the impregnating liquid component is fixed in the gaps between the fibers, this body is placed in an electric furnace and fired at 1450°C for 6 hours, so that one side is approximately 20011111 mm. A cubic honeycomb structure was obtained. The shrinkage rate due to firing is 2% in the stacking direction and 2% in the plane direction (vertical,
(both horizontally and horizontally) was 1.2%.

Figure 2 is an electron micrograph of the surface of this honeycomb structure (
The magnification is SOO times).

The crystal composition of this honeycomb structure was examined by powder X-ray diffraction, and as shown in FIG. 3, it was found to be composed of mullite and corundum (α-A 1.Os).

Comparative Example 1 The alumina fiber paper produced in Example 1 was corrugated in the same manner as in Example 1, and then laminated and immersed in an impregnating solution having the following composition for 20 minutes, and then dried at 110°C. Then, the mixture was further heated at 450° C. to decompose the organic matter.

Colloidal silica (solid content 20% by weight) 100 parts by weight Corundum powder (average particle size 2μ) 83 parts by weight Water
100 parts by weight The above-mentioned impregnation and drying treatments were performed again to obtain a honeycomb structure in which alumina fibers and corundum powder were bonded with silicic acid gel.

Example 2 45 parts by weight of the same alumina fibers as those used in Example 1 and 40 parts by weight of aluminosilicate fibers (average fiber diameter 4μ) having a composition of 0.48% by weight of A1 and 49% by weight of 5iOz were combined into an organic binder of 15% by weight. Paper-formed together with weight part, thickness 0
, 4 Ilk11 weight 00 (/tm) paper was manufactured.A raw honeycomb body was manufactured and impregnated in the same manner as in Example 1, and finally, it was fired at 1300°C for 10 hours.Shrinkage rate due to firing (3-way average value) was 1.3%.

The crystal composition of the obtained honeycomb structure consisted of mullite, corundum, and a small amount of cristobalite.

Comparative Example 2 Same aluminosilicate fiber 8 as used in Example 2
5 parts by weight are made into paper together with 15 parts by weight of an organic binder,
A paper having a thickness of 0.4 mm and a basis weight of 90 (7 m'') was produced.A raw honeycomb body was produced and impregnated in the same manner as in Example 1, and finally it was fired at 1300°C for 10 hours.

The shrinkage rate (average value in three directions) due to firing was 3.2%.

The crystal composition of the obtained honeycomb structure consisted of mullite and cristobalite. When observed under an electron microscope, in addition to the mullite produced by the reaction, a large amount of mullite and cristobalite precipitated from the aluminosilicate fibers were observed in this structure.

Example 3 In the same manner as in Example 1, a raw honeycomb body with fixed colloidal silica etc. was produced, and this was immersed in a saturated alcohol solution of boric acid to add 1% by weight of B to the raw honeycomb body.
, O, was absorbed. Thereafter, it was fired at 1200° C. for 6 hours to obtain a honeycomb structure having a crystal composition of mullite and corundum. The shrinkage rate (average value in three directions) due to firing was 0.3%.

Example 4 A honeycomb structure was manufactured in the same manner as in Example 3 except that immersion in a boric acid solution was not performed. The shrinkage rate (average value in three directions) due to firing was 0.6%. The crystal composition consisted of mullite, corundum and a small amount of cristobalite.

The honeycomb structure according to each side above and the following reference example 1.
The characteristic values and performance test results of No. 2 are shown in Table 1.

Reference example 1 Commercially available honeycomb structure carrier for automobile exhaust purification (cordierite extrusion molded product) Wall thickness 0.3 m + m, cell pitch 1.5 + am, opening ratio 7
9% Reference Example 2 Commercially available honeycomb structure carrier for denitrification (mullite extrusion molded product) Wall thickness 0.45 mm, cell pitch 4.25 mm, aperture ratio 7
9% The test methods for the load failure temperature and thermal shock test and the method for measuring the average crystal length of mullite are as follows.

Load failure temperature + 15K17cm2 load was applied to the test specimen (
30 x 3 Q x 30 mm) in the direction of the flute, the temperature is raised at 5° O/win, and the temperature at which the specimen breaks or softens and deforms is measured.

Thermal shock test: test specimen heated to 800°C
Place it in water at °C and inspect its appearance.

Average crystal length of mullite: Observe a representative part of the sample with a scanning electron microscope (magnification of 5000x to 20000x), and calculate the length of the acicular or columnar mullite crystals within the field of view (
measurement).

〔Effect of the invention〕

The honeycomb structure according to the present invention has extremely high performance, as shown by the data in Table 1. That is, 100
σ-A1□03 that does not transform to other crystal forms even above 0°C
1000 by consisting of type alumina fiber and mullite
It is significantly superior to conventional ceramic fiber paper-based honeycomb structures in terms of physical properties such as strength and durability at high temperatures of .degree. C. or higher. It also exhibits the highest performance in terms of thermal shock resistance due to its flexible structure with thin alumina fibers as its backbone and the strong bond between the surface of the alumina fibers and the mullite binder.

Due to the above-mentioned features, the honeycomb structure of the present invention exhibits far superior durability than conventional products when used as a catalyst carrier for high-temperature gas phase catalytic reactions or as a heat exchange element. It is also possible to use it under severe conditions that would otherwise be difficult to use, for example, as an element for catalytic catalytic combustion.

[Brief explanation of drawings]

Figure 1: A perspective view of an example of a honeycomb structure according to the present invention Figure 2: Electron micrograph of the surface of a honeycomb structure according to Example 1 Figure 3: X-ray diffraction diagram of a honeycomb structure according to Example 1

Claims (3)

[Claims] (1) In a honeycomb structure made from paper consisting of ceramic fibers or a mixture of ceramic fibers and a heat-resistant filler, at least 50% by weight of the ceramic fibers are α
- A heat-resistant honeycomb structure comprising Al_2O_3 type polycrystalline alumina fibers and ceramic fibers bonded together by mullite. (2) The heat-resistant honeycomb structure according to claim 1, wherein the mullite has an average crystal length of 4 μm or less. (3) The heat-resistant honeycomb structure according to claim 1, wherein the heat-resistant filler is particulate corundum.