JP2022129780A - Honeycomb structure and method of manufacturing honeycomb structure - Google Patents

Abstract

To provide a honeycomb structure in which strength degradation is prevented, the strength degradation being caused by a large cavity due to boehmite aggregate.SOLUTION: A honeycomb structure is formed of a honeycomb burned body in which multiple through-holes are provided side by side in a longitudinal direction while being separated from one another by partition walls. The honeycomb burned body is composed of: a composite oxide particle including a ceria-zirconia composite oxide particle and/or an alumina-ceria-zirconia composite oxide particle; an alumina particle; and alumina binder. In the honeycomb structure, an area ratio of a cavity including alumina aggregate to an area of the partition wall is 10% or less, the alumina binder aggregate existing 70% or more of an area of the cavity in a cavity having a diameter of 20 μm or larger in a cross-section of the partition wall of the honeycomb burned body in an electron microscopic image.SELECTED DRAWING: Figure 5

Description

The present invention relates to a honeycomb structure and a method for manufacturing a honeycomb structure.

Exhaust gases emitted from internal combustion engines such as automobiles contain harmful gases such as carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons (HC). Such an exhaust gas purifying catalyst that decomposes harmful gases is also called a three-way catalyst. things are common.

Patent Document 1 discloses a honeycomb fired body composed of an extruded body containing ceria-zirconia composite oxide particles (hereinafter also referred to as CZ particles) and alumina particles. A honeycomb structure having a pore size distribution curve peak in the range of 5 μm is disclosed.

WO2018/012565

Patent Document 1 describes that CZ particles, θ-alumina particles, boehmite, α-alumina fibers, methyl cellulose, acrylic resin, etc. are mixed to prepare a raw material paste, which is molded and fired to manufacture a honeycomb structure. It is

Boehmite sometimes agglomerates during the preparation of the raw material paste and forms aggregates (so-called “lumps”) in the raw material paste. In the honeycomb structure obtained by molding and firing the raw material paste containing the aggregates, the aggregates remained in the partition walls. It was found that since the shrinkage ratio of alumina is larger than that of other surrounding raw materials, voids are generated around aggregates, and voids of unintended size are present in partition walls.
Since the presence of such voids causes a decrease in the strength of the structure, it has been desired to reduce the voids to improve the strength of the structure.

The present invention has been made from such a point of view, and aims to provide a honeycomb structure in which strength reduction due to large voids caused by boehmite agglomerates is prevented, and a method for manufacturing the honeycomb structure. aim.

A honeycomb structure of the present invention for achieving the above object is a honeycomb structure comprising a honeycomb fired body in which a plurality of through holes are arranged in parallel in a longitudinal direction with partition walls interposed therebetween, wherein the honeycomb fired body comprises ceria -composed of composite oxide particles containing zirconia composite oxide particles and/or alumina-ceria-zirconia composite oxide particles, alumina particles, and an alumina binder, in the electron microscope image of the cut surface of the partition wall of the honeycomb fired body, The ratio of the area of the alumina aggregate-containing voids to the area of the partition walls is 10% or less, in which the aggregates of the alumina binder are present in the voids having a diameter of 20 μm or more at 70% or more of the area of the voids. Characterized by

In the honeycomb structure of the present invention, the aggregates of the alumina binder are present in the pores having a diameter of 20 µm or more in 70% or more of the area of the pores. % or less.
The alumina agglomerate-containing voids are portions in which alumina binder agglomerates (hereinafter referred to as alumina agglomerates) are present in the voids.
The diameter of the alumina agglomerate-containing voids is defined as the diameter of the entire void including the alumina agglomerates. A void in which the area of the alumina agglomerate accounts for 70% or more of the area of the entire void including the area of the alumina agglomerate is defined as an alumina agglomerate-containing void. That is, even if the diameter of the pores is 20 μm or more, the pores in which no alumina agglomerates are present or the pores in which the alumina agglomerates are small are distinguished from the alumina agglomerate-containing pores.

In the specification of the present application, the diameter of the void refers to the diameter of the area-equivalent circle (Heywood diameter) of the void in a cross-sectional view obtained by photographing the cross section of the partition wall with an electron microscope.

The ratio of the area of the alumina aggregate-containing voids to the area of the partition walls can be obtained by the following method.
1) First, a portion of the partition wall of the honeycomb structure is cut out as a measurement sample, and an enlarged image of the cut surface cut along the longitudinal direction is photographed with an electron microscope. At this time, the accelerating voltage of the electron microscope is 15 kV, and the magnification is 500 times.
2) Subsequently, a predetermined region of the obtained electron microscope image is separated into voids and portions other than voids using commercially available image analysis software or the like. After that, the diameter of the area-equivalent circle (pore diameter) is obtained from the area of each separated void. However, voids with an equivalent area diameter of less than 20 μm are excluded from this measurement.
3) The area of alumina agglomerates contained in voids with an area-equivalent diameter of 20 μm or more is determined, and the voids are separated into voids in which the area ratio of alumina agglomerates to the voids is 70% or more and other voids. Only voids in which the area ratio of alumina agglomerates to the voids is 70% or more are defined as alumina agglomerate-containing voids.
4) Find the ratio of the area of the alumina aggregate-containing voids contained in the electron microscope image.
The same measurement is performed on 10 electron micrographs to determine the ratio of the area of the alumina aggregate-containing voids to the area of the partition walls.

Since the alumina agglomerate-containing voids are voids of an unintended size, they may become fracture starting points, causing a decrease in the strength of the honeycomb structure.
In the honeycomb structure of the present invention, the ratio of the area of the voids containing the alumina aggregates is 10% or less with respect to the area of the partition walls. It becomes a honeycomb structure that is prevented from

The honeycomb structure of the present invention contains composite oxide particles containing ceria-zirconia composite oxide particles and/or alumina-ceria-zirconia composite oxide particles as its constituent components.
As described above, the ceria-zirconia composite oxide particles are also called CZ particles. Alumina-ceria-zirconia composite oxide particles are also called ACZ particles.

In the honeycomb structure of the present invention, the proportion of the area of the alumina aggregate-containing voids is preferably 5% or less with respect to the area of the partition walls.
When the ratio of the area of the alumina aggregate-containing voids is within the above range, the number of portions that cause a reduction in the strength of the honeycomb structure is reduced, resulting in a honeycomb structure in which the reduction in strength is further prevented.

In the honeycomb structure of the present invention, it is preferable that a precious metal is supported on the honeycomb fired body. By supporting precious metals on the honeycomb fired body, it becomes possible to use the honeycomb fired body for purification of exhaust gas.

A method for manufacturing a honeycomb structure of the present invention is a method for manufacturing a honeycomb structure comprising a honeycomb fired body in which a plurality of through-holes are arranged in parallel in the longitudinal direction with partition walls interposed therebetween, wherein boehmite and water are mixed and stirred. a stirring step of obtaining a paste-like material, and dry mixing of ceria-zirconia composite oxide particles and/or composite oxide particles containing alumina-ceria-zirconia composite oxide particles, alumina particles, and an organic binder to form a dry mixture; , a wet mixing step of obtaining a wet mixture by wet mixing the dry mixture and the paste-like material, and molding the wet mixture, so that a plurality of through holes are formed in the longitudinal direction across partition walls. It is characterized by including a forming step of producing honeycomb formed bodies arranged in parallel and a firing step of producing a honeycomb fired body by firing the honeycomb formed bodies.

In the above method, a stirring step is performed in which boehmite and water are mixed and stirred to obtain a paste. The boehmite and water are mixed in the stirring step, and a paste-like substance in which the boehmite is dispersed in the water is obtained at this stage. The paste is stirred so that boehmite aggregates (so-called "lumps") are reduced.

Thus, by first obtaining a paste-like material in which the generation of aggregates is prevented in advance and then mixing this paste-like material with other components, boehmite aggregates are formed in the partition walls of the honeycomb structure. It is possible to prevent the occurrence of large voids due to
That is, it is possible to manufacture a honeycomb structure whose strength is prevented from being lowered.

In the method for manufacturing a honeycomb structure of the present invention, it is preferable that the boehmite content in the paste is 25% by weight or more.
Since the paste used in the above production method contains boehmite in an amount of 25% by weight or more, it can be said that the paste has a relatively small water content. Use of such a paste is more preferable for obtaining a honeycomb structure whose strength is prevented from being lowered.

In the method for manufacturing a honeycomb structure of the present invention, it is preferable that the paste has a viscosity of 50.0 Pa·s or more.
When the viscosity of the paste-like material is 50.0 Pa·s or more, it can be said that the paste is sufficiently stirred and mixed and the amount of aggregates is further reduced. Use of such a paste is more preferable for obtaining a honeycomb structure whose strength is prevented from being lowered.

In the method for manufacturing a honeycomb structure of the present invention, it is preferable that the proportion of boehmite contained in the wet mixture is 10% by weight or more.
When the proportion of boehmite contained in the wet mixture is 10% by weight or more, the boehmite sufficiently functions as a binder after the firing step, and the strength of the obtained honeycomb structure can be improved.

FIG. 1 is a perspective view schematically showing an example of the honeycomb structure of the present invention. FIG. 2 is a schematic diagram showing an example of a cut surface of partition walls of a honeycomb fired body. 3 is a cross-sectional micrograph of partition walls of the honeycomb structure manufactured in Example 1. FIG. 4 is a cross-sectional micrograph of partition walls of the honeycomb structure manufactured in Example 2. FIG. 5 is a cross-sectional micrograph of partition walls of a honeycomb structure manufactured in Example 3. FIG. 6 is a cross-sectional micrograph of partition walls of a honeycomb structure manufactured in Comparative Example 1. FIG. FIG. 7 is a graph showing the measurement results of the A-axis bending strength of the honeycomb structures manufactured in Examples and Comparative Examples. FIG. 8 is a graph showing the measurement results of the B-axis bending strength of the honeycomb structures manufactured in Examples and Comparative Examples.

(Detailed description of the invention)
[Honeycomb structure]
First, the honeycomb structure of the present invention will be described.

FIG. 1 is a perspective view schematically showing an example of the honeycomb structure of the present invention.
A honeycomb structure 10 shown in FIG. 1 includes a single honeycomb fired body 11 in which a plurality of through holes 12 are arranged side by side in the longitudinal direction with partition walls 13 interposed therebetween. The honeycomb fired body 11 contains CZ particles and/or ACZ particles, alumina particles, and an alumina binder, and has the shape of an extruded body.
As shown in FIG. 1, when the honeycomb structure 10 is composed of a single honeycomb fired body 11, the honeycomb structure 10 is also the honeycomb fired body itself.

In the honeycomb structure of the present invention, the honeycomb fired body comprises composite oxide particles containing CZ particles and/or ACZ particles, alumina particles, and an alumina binder.
Whether or not the honeycomb structure of the present invention contains CZ particles and/or ACZ particles, alumina particles, and an alumina binder can be confirmed by X-ray diffraction (XRD).
Alumina binder is derived from boehmite used in manufacturing honeycomb structures.

In the electron microscope image of the cut surface of the partition walls of the honeycomb fired body, the ratio of the area of the alumina aggregate-containing voids, in which the alumina binder aggregates are present in the voids having a diameter of 20 μm or more to 70% or more of the void area, is is 10% or less with respect to the area of .
This will be described with reference to the drawings.

FIG. 2 is a schematic diagram showing an example of a cut surface of partition walls of a honeycomb fired body.
The partition 13 shown in FIG. 2 is made of porous ceramic. A large number of pores are present in the partition walls 13, and alumina aggregate-containing voids 15 are also present. Pores other than the alumina aggregate-containing voids present in the partition walls 13 are omitted from the drawing.
Alumina aggregate-containing voids 15 are voids in which aggregates 17 of alumina binder exist within voids 16 having a diameter of 20 μm or more.
Agglomerates of alumina binder are hereinafter referred to as alumina agglomerates.

The diameter of the alumina agglomerate-containing voids 15 is defined as the diameter of the entire voids 16 including the alumina agglomerates 17 . A void in which the area of the alumina agglomerate 17 is 70% or more of the area of the entire void 16 including the area of the alumina agglomerate 17 is defined as the alumina agglomerate-containing void 15 . That is, even if the diameter of the voids 16 is 20 μm or more, if the alumina aggregates 17 are not present in the voids 16 or if the size of the alumina aggregates 17 within the voids 16 is small, the voids 15 containing the alumina aggregates can be considered. distinguish.

The diameter of the void refers to the diameter (Heywood diameter) of the area-equivalent circle of the void in a cross-sectional view obtained by photographing the cross section of the partition with an electron microscope.

The ratio of the area of the alumina aggregate-containing voids to the area of the partition walls can be obtained by the following method.
1) First, a portion of the partition wall of the honeycomb structure is cut out as a measurement sample, and an enlarged image of the cut surface cut along the longitudinal direction is photographed with an electron microscope. At this time, the accelerating voltage of the electron microscope is 15 kV, and the magnification is 500 times.
2) Subsequently, a predetermined region of the obtained electron microscope image is separated into voids and portions other than voids using commercially available image analysis software or the like. After that, the diameter of the area-equivalent circle (pore diameter) is obtained from the area of each separated void. However, voids with an equivalent area diameter of less than 20 μm are excluded from this measurement.
3) The area of alumina agglomerates contained in voids with an area-equivalent diameter of 20 μm or more is determined, and the voids are separated into voids in which the area ratio of alumina agglomerates to the voids is 70% or more and other voids. Only voids in which the area ratio of alumina agglomerates to the voids is 70% or more are defined as alumina agglomerate-containing voids.
4) Find the ratio of the area of the alumina aggregate-containing voids contained in the electron microscope image.
The same measurement is performed on 10 electron micrographs to determine the ratio of the area of the alumina aggregate-containing voids to the area of the partition walls.

Since the alumina agglomerate-containing voids are voids of an unintended size, they may become fracture starting points, causing a decrease in the strength of the honeycomb structure.
In the honeycomb structure, since the ratio of the area of the voids containing the alumina aggregates is 10% or less with respect to the area of the partition walls, the portions that cause the strength reduction of the honeycomb structure are reduced, and the strength reduction is prevented. It becomes a honeycomb structure.

Also, the ratio of the area of the alumina aggregate-containing voids is preferably 5% or less of the area of the partition walls.
When the ratio of the area of the alumina aggregate-containing voids is within the above range, the number of portions that cause a reduction in the strength of the honeycomb structure is reduced, resulting in a honeycomb structure in which the reduction in strength is further prevented.

The honeycomb structure may have a single honeycomb fired body, or may have a plurality of honeycomb fired bodies, or may have a plurality of honeycomb fired bodies bonded together with an adhesive.

In the honeycomb structure, an outer peripheral coat layer may be formed on the outer peripheral surface of the honeycomb fired body.

In the honeycomb structure, the honeycomb fired body preferably has a porosity of 45 to 75% by volume.
When the honeycomb fired body has a porosity of 45 to 75% by volume, both high mechanical strength and exhaust gas purification performance can be achieved.

If the porosity of the honeycomb fired body is less than 45% by volume, the ratio of pores that can contribute to gas diffusion in the partition walls decreases, and the gas purification performance may deteriorate. On the other hand, when the porosity of the honeycomb fired body exceeds 75% by volume, the porosity becomes too high, so that the mechanical properties of the honeycomb structure deteriorate, and the honeycomb structure tends to crack or break during use. Become.

The porosity of the honeycomb fired body can be measured by the gravimetric method described below.
(1) Cut the honeycomb fired body into a size of 10 cells×10 cells×10 mm to obtain a measurement sample. After the measurement sample is ultrasonically cleaned using deionized water and acetone, it is dried at 100° C. using an oven. In addition, the measurement sample of 10 cells × 10 cells × 10 mm includes the outermost through-hole and the partition wall that constitutes the through-hole in a state in which 10 through-holes are arranged in the vertical direction and 10 in the horizontal direction, It refers to a sample cut out so that the length in the longitudinal direction is 10 mm.
(2) Using a measuring microscope (Measuring Microscope MM-40 manufactured by Nikon, magnification: 100 times), measure the dimensions of the cross-sectional shape of the measurement sample, and determine the volume from geometric calculations (geometric calculations If the volume cannot be obtained from the above, measure the weight in saturated water and the weight in water to measure the volume).
(3) From the calculated volume and the true density of the measurement sample measured with a pycnometer, calculate the weight of the measurement sample assuming that it is a completely dense body. The measurement procedure with the pycnometer is as shown in (4).
(4) Pulverize the honeycomb fired body to prepare 23.6 cc of powder. The powder obtained is dried at 200° C. for 8 hours. After that, the true density is measured according to JIS R 1620 (1995) using an Auto Pycnometer 1320 manufactured by Micromeritics. The evacuation time is 40 minutes.
(5) Measure the actual weight of the measurement sample with an electronic balance (HR202i manufactured by A&D).
(6) Obtain the porosity of the honeycomb fired body from the following equation.
(Porosity of honeycomb fired body) = 100 - (actual weight of measurement sample/weight assuming that measurement sample is a complete dense body) x 100 [%]
Even when the honeycomb structure supports the catalyst, the change in the porosity of the honeycomb fired body due to the catalyst support is so small that it can be ignored.

The shape of the honeycomb structure is not limited to a columnar shape, and may include a prismatic shape, a cylindric columnar shape, an elongated columnar shape, a chamfered prismatic shape (for example, a chamfered triangular columnar shape), and the like.

In the honeycomb structure, the shape of the through-holes of the honeycomb fired body is not limited to a quadrangular prism shape, and may be a triangular prism shape, a hexagonal prism shape, or the like.

In the honeycomb structure, the through-hole density in the cross section perpendicular to the longitudinal direction of the honeycomb fired body is preferably 31 to 155/cm ² .

In the honeycomb structure, the partition walls of the honeycomb fired body preferably have a thickness of 0.05 to 0.50 mm, more preferably 0.07 to 0.30 mm.

In the honeycomb structure, when an outer peripheral coat layer is formed on the outer peripheral surface of the honeycomb fired body, the thickness of the outer peripheral coat layer is preferably 0.1 to 2.0 mm.

In the honeycomb structure, it is preferable that the honeycomb fired body carries a noble metal.
In the honeycomb structure, if the honeycomb fired body carries a noble metal functioning as a catalyst, the honeycomb structure can be used as a honeycomb catalyst for exhaust gas purification.
Examples of noble metals include platinum, palladium, rhodium and the like.

In the honeycomb structure, the amount of noble metal supported is preferably 0.1 to 15 g/L, more preferably 0.5 to 10 g/L.
In the present specification, the supported amount of noble metal refers to the weight of the noble metal per apparent volume of the honeycomb structure. The apparent volume of the honeycomb structure is the volume including the volume of the voids, and includes the volume of the outer peripheral coat layer and/or the adhesive layer.

[Manufacturing method of honeycomb structure]
A method for manufacturing a honeycomb structure of the present invention is a method for manufacturing a honeycomb structure comprising a honeycomb fired body in which a plurality of through-holes are arranged in parallel in the longitudinal direction with partition walls interposed therebetween, wherein boehmite and water are mixed and stirred. a stirring step of obtaining a paste-like material, and dry mixing of ceria-zirconia composite oxide particles and/or composite oxide particles containing alumina-ceria-zirconia composite oxide particles, alumina particles, and an organic binder to form a dry mixture; , a wet mixing step of obtaining a wet mixture by wet mixing the dry mixture and the paste-like material, and molding the wet mixture, so that a plurality of through holes are formed in the longitudinal direction across partition walls. It is characterized by including a forming step of producing honeycomb formed bodies arranged in parallel and a firing step of producing a honeycomb fired body by firing the honeycomb formed bodies.

In the stirring step, boehmite and water are mixed and stirred to obtain a paste.
Boehmite is a solid alumina binder. In this production method, a solid material, such as alumina sol, which is different from a water-based alumina binder in which alumina is dispersed in water, is used. Boehmite is used as an alumina binder for that purpose.

The boehmite and water are mixed in the stirring step, and a paste-like substance in which the boehmite is dispersed is obtained at this stage. Stirring is carried out so as to reduce the amount of boehmite aggregates in the paste.

Thus, by first obtaining a paste-like material in which the generation of aggregates is prevented in advance and then mixing this paste-like material with other components, boehmite aggregates are formed in the partition walls of the honeycomb structure. It is possible to prevent the occurrence of large voids due to
That is, it is possible to manufacture a honeycomb structure whose strength is prevented from being lowered.

In the stirring step, it is preferable to mix boehmite and water so that the boehmite content in the paste is 25% by weight or more.
If the paste-like material prepared in the stirring step contains 25% by weight or more of boehmite, it can be said that the paste has a relatively small water content. Use of such a paste is more preferable for obtaining a honeycomb structure whose strength is prevented from being lowered.

The paste obtained in the stirring step preferably has a viscosity of 50.0 Pa·s or more.
The viscosity of the paste can be adjusted by stirring conditions (time, speed, etc.). If the stirring time is lengthened, the viscosity increases, and if the stirring progresses sufficiently, the viscosity does not increase even if the stirring time is extended. When the viscosity stops increasing, it can be said that the agglomeration of boehmite contained in the paste-like material has been sufficiently reduced due to sufficient stirring.
That is, when the viscosity of the paste-like material is 50.0 Pa·s or more, it can be said that the paste is sufficiently stirred and mixed and the amount of aggregates is further reduced. Use of such a paste is more preferable for obtaining a honeycomb structure whose strength is prevented from being lowered.
The viscosity of the paste is defined as the viscosity measured at 25°C with a rotary viscometer.

Further, a molding aid may be added to the paste that has undergone the stirring step, and the mixture may be stirred to obtain a paste containing the molding aid.

Examples of molding aids include, but are not limited to, ethylene glycol, dextrin, fatty acids, fatty acid soaps, polyalcohols, and the like, and two or more of them may be used in combination.

Next, a dry mixing step is performed to obtain a dry mixture by dry mixing composite oxide particles containing CZ particles and/or ACZ particles, alumina particles, and an organic binder.

Examples of organic binders include, but are not limited to, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, phenol resins, epoxy resins, and the like, and two or more of them may be used in combination.

Further, inorganic fibers or the like may be further mixed in the dry mixing step.
The material constituting the inorganic fiber is not particularly limited, but examples thereof include alumina, silica, silicon carbide, silica-alumina, glass, potassium titanate, and aluminum borate, and two or more of them may be used in combination. Among these, alumina fibers are preferred.

The aspect ratio of the inorganic fiber is preferably 5-300, more preferably 10-200, even more preferably 10-100.

Next, a wet mixing step is performed to obtain a wet mixture by wet mixing the dry mixture and the paste-like material.
It is preferable to adjust the ratio of the dry mixture and the paste so that the ratio of boehmite contained in the wet mixture is 10% by weight or more.
When the proportion of boehmite contained in the wet mixture is 10% by weight or more, the boehmite sufficiently functions as a binder after the firing step, and the strength of the obtained honeycomb structure can be improved.

In the wet mixing step, a mixer, an attritor or the like may be used for mixing, or a kneader or the like may be used for kneading.

When composite oxide particles containing CZ particles and/or ACZ particles, alumina particles, alumina fibers, and boehmite are used as the above raw materials, the blending ratio of these is Composite oxide particles: 40 to 60% by weight, alumina particles: 15 to 35% by weight, alumina fibers: 0 to 15% by weight, and boehmite: 10 to 20% by weight are preferable.

Next, by molding the wet mixture, a honeycomb molded body having a plurality of through holes arranged side by side in the longitudinal direction with partition walls therebetween is produced.
Specifically, a continuous honeycomb molded body having through holes of a predetermined shape is extruded by passing through a mold of a predetermined shape, and cut into a predetermined length to obtain a honeycomb molded body. can do.

Next, it is preferable to dry the molded body molded by the molding step.
At this time, the honeycomb molded body can be dried using a dryer such as a microwave dryer, a hot air dryer, a dielectric dryer, a reduced pressure dryer, a vacuum dryer, or a freeze dryer to produce a dried honeycomb body. preferable.

In this specification, the formed honeycomb body and the dried honeycomb body before the firing step are collectively referred to as a formed honeycomb body.

Next, a firing step of producing a honeycomb fired body is performed by firing the formed honeycomb body.
In the firing step, a fired honeycomb body is produced by firing the formed honeycomb body. Note that, since this step degreases and fires the formed honeycomb body, it can be called a "degreasing/firing step", but for the sake of convenience, it will be referred to as a "firing step".

The temperature of the firing step is preferably 800 to 1300°C, more preferably 900 to 1200°C. Also, the time for the firing step is preferably 1 to 24 hours, more preferably 3 to 18 hours. The atmosphere of the firing step is not particularly limited, but the oxygen concentration is preferably 1 to 20%.

Through the above steps, a honeycomb structure made of a honeycomb fired body can be manufactured.

The method for manufacturing a honeycomb structure may further include a supporting step of supporting a noble metal on the honeycomb fired body, if necessary.
As a method for supporting a noble metal on a honeycomb fired body, for example, a method of immersing a honeycomb fired body or a honeycomb structure in a solution containing noble metal particles or a complex, then pulling out and heating the body, or the like can be mentioned.
When the honeycomb structure has a peripheral coat layer, the noble metal may be carried on the honeycomb fired body before forming the peripheral coat layer, or the noble metal may be loaded on the honeycomb fired body or the honeycomb structure after forming the peripheral coat layer. You can carry it.

In the method for manufacturing a honeycomb structure, the amount of the noble metal supported in the supporting step is preferably 0.1 to 15 g/L, more preferably 0.5 to 10 g/L.

In the method for manufacturing a honeycomb structure, when forming the outer peripheral coat layer on the outer peripheral surface of the honeycomb fired body, the outer peripheral coat layer is applied to the outer peripheral surface excluding both end surfaces of the honeycomb fired body with a paste for the outer peripheral coat layer, and then dried. It can be formed by solidifying. The peripheral coating layer paste may have the same composition as the wet mixture.

(Example)
Examples that more specifically disclose the present invention are shown below. In addition, the present invention is not limited only to the following examples.

[Preparation of sample for evaluation]
(Example 1)
11.4 parts by weight of boehmite and 28.7 parts by weight of water were mixed and stirred by a planetary mixer to prepare a paste. The proportion of boehmite contained in the paste was 28% by weight.
The stirring time was set to 10 minutes, and the viscosity of the paste after stirring was measured to be 45.6 Pa·s.
Viscosity was measured at 25° C. with a rotary viscometer.
Furthermore, 3.7 parts by weight of oleic acid was added as a molding aid to the paste.

Separately from the preparation of the paste, 29.2 parts by weight of composite oxide particles consisting of a mixture of CZ particles and ACZ particles, 11.9 parts by weight of alumina particles, 5.5 parts by weight of alumina fibers, and 9.5 parts by weight of methyl cellulose. 6 parts by weight were dry mixed to prepare a dry mixture.

A wet mixture was prepared by mixing and kneading the paste-like material and the dry mixture.
The blending ratio of the paste-like material and the dry mixture is composite oxide particles: 53% by weight, alumina particles: 22% by weight, alumina fibers: 10% by weight, and boehmite: 15% by weight with respect to the total solid content remaining after the firing process. was made to be

The wet mixture was extruded using an extruder to produce a cylindrical honeycomb molded body.
Then, using a reduced pressure microwave dryer, the honeycomb molded body was dried at an output of 1.74 kW and a reduced pressure of 6.7 kPa for 12 minutes, and then degreased and fired at 1100° C. for 10 hours to prepare a honeycomb fired body. . This honeycomb fired body is the honeycomb structure manufactured in Example 1. ^The honeycomb structure had a cylindrical shape with a diameter of 103 mm and a length of 80 mm.

(Example 2)
The stirring time for preparing the paste was set at 20 minutes.
After the stirring, the viscosity of the paste was measured and found to be 50.1 Pa·s.
A honeycomb structure was produced in the same manner as in Example 1 except for the above.

(Example 3)
The stirring time for preparing the paste was 40 minutes.
After the stirring, the viscosity of the paste was measured and found to be 51.7 Pa·s.
A honeycomb structure was produced in the same manner as in Example 1 except for the above.

(Comparative example 1)
A wet mixture was prepared by mixing boehmite, water, composite oxide particles composed of a mixture of CZ particles and ACZ particles, alumina particles, alumina fibers, and methyl cellulose all at once.
A honeycomb structure was produced in the same manner as in Example 1 for the steps of molding and firing the wet mixture.
The weight ratios of the composite oxide particles, alumina particles, alumina fibers and boehmite to the total solid content remaining after the firing process were set to be the same as in Example 1.

Cross-sectional photographs of the partition walls of the honeycomb structures produced in each example and comparative example were taken, and the ratio of the area of the alumina aggregate-containing voids to the area of the partition walls was determined.
3 is a cross-sectional micrograph of partition walls of the honeycomb structure manufactured in Example 1. FIG.
4 is a cross-sectional micrograph of partition walls of the honeycomb structure manufactured in Example 2. FIG.
5 is a cross-sectional micrograph of partition walls of a honeycomb structure manufactured in Example 3. FIG.
6 is a cross-sectional micrograph of partition walls of a honeycomb structure manufactured in Comparative Example 1. FIG.

In the cross section of the partition wall of Comparative Example 1, there are many alumina aggregate-containing voids, and the sizes of the alumina aggregate-containing voids are large. The area percentage of voids containing alumina agglomerates was 13.5%.
Alumina agglomerate-containing voids exist in the cross section of the partition wall of Example 1, but they are few in number and small in size. The area percentage of alumina agglomerate-containing voids was 5.8%.
Alumina agglomerate-containing voids are also present in the cross-section of the partition walls of Example 2, but in fewer numbers and smaller sizes. The area percentage of alumina agglomerate-containing voids was 2.8%.
No alumina agglomerate-containing voids are seen in the cross-section of the partition walls of Example 3. That is, the ratio of the area of the alumina aggregate-containing voids was 0%.

[Measurement of bending strength]
The A-axis bending strength and B-axis bending strength of the honeycomb structures manufactured in each example and comparative example were measured.
The A-axis bending strength is the bending strength along the longitudinal direction of the honeycomb structure.
The sample for the A-axis bending strength test had a sample cross-sectional width of 5.5 mm, a sample cross-sectional height of 5.5 mm, and a length (longitudinal length of the honeycomb structure) of 40 mm.
Three-point bending strength was measured at a span distance of 30 mm and a measurement speed of 0.1 mm/min.

The B-axis bending strength is the bending strength along the direction perpendicular to the longitudinal direction of the honeycomb structure.
The sample for the B-axis bending strength test had a sample cross-sectional width of 10 mm, a sample cross-sectional height of 10 mm, and a length (the length in the direction perpendicular to the longitudinal direction of the honeycomb structure) of 35 mm.
Three-point bending strength was measured at a span-to-span distance of 25 mm and a measurement speed of 0.1 mm/min.

FIG. 7 is a graph showing the measurement results of the A-axis bending strength of the honeycomb structures manufactured in Examples and Comparative Examples.
FIG. 8 is a graph showing the measurement results of the B-axis bending strength of the honeycomb structures manufactured in Examples and Comparative Examples.

From FIG. 7, it was found that the A-axis bending strength increased as the ratio of the area of the alumina aggregate-containing voids decreased, and that the A-axis bending strength of Example 3 was improved by about 30% compared to Comparative Example 1.
From FIG. 8, it was found that the B-axis bending strength increased as the ratio of the area of the alumina aggregate-containing voids decreased, and that the B-axis bending strength of Example 3 was improved by about 40% compared to Comparative Example 1.
Moreover, it was found that the A-axis bending strength and the B-axis bending strength were particularly high in Examples 2 and 3 in which the ratio of the area of the alumina aggregate-containing voids was 5% or less.

From these results, when the ratio of the area of the alumina aggregate-containing voids to the area of the partition walls is 10% or less, the portion causing the strength reduction of the honeycomb structure is reduced, and the honeycomb structure in which the strength reduction is prevented. It turned out to be

Further, in the stirring step, the boehmite and water are mixed, and the paste-like material is stirred so that the amount of boehmite aggregates is reduced, and the honeycomb structure is manufactured using the paste-like material. It was found that it is possible to prevent the formation of large voids in the partition walls of the body due to boehmite agglomerates, and to manufacture a honeycomb structure in which the reduction in strength is prevented.

REFERENCE SIGNS LIST 10 honeycomb structure 11 honeycomb fired body 12 through-hole 13 partition wall 15 alumina aggregate-containing void 16 void 17 alumina binder aggregate (alumina aggregate)

Claims (7)

A honeycomb structure comprising a honeycomb fired body in which a plurality of through holes are arranged in parallel in the longitudinal direction with partition walls interposed therebetween,
The honeycomb fired body comprises composite oxide particles containing ceria-zirconia composite oxide particles and/or alumina-ceria-zirconia composite oxide particles, alumina particles, and an alumina binder,
In the electron microscope image of the cut surface of the partition wall of the honeycomb fired body, the area ratio of alumina aggregate-containing voids in which alumina binder aggregates are present in voids having a diameter of 20 μm or more in 70% or more of the void area. is 10% or less with respect to the area of the partition walls. 2. The honeycomb structure according to claim 1, wherein the ratio of the area of the alumina aggregate-containing voids is 5% or less with respect to the area of the partition walls. 3. The honeycomb structure according to claim 1, wherein the honeycomb fired body supports a noble metal. A method for manufacturing a honeycomb structure comprising a honeycomb fired body in which a plurality of through holes are arranged in parallel in the longitudinal direction with partition walls therebetween,
a stirring step of mixing and stirring boehmite and water to obtain a paste;
a dry mixing step of obtaining a dry mixture by dry mixing composite oxide particles containing ceria-zirconia composite oxide particles and/or alumina-ceria-zirconia composite oxide particles, alumina particles, and an organic binder;
a wet mixing step of obtaining a wet mixture by wet mixing the dry mixture and the paste-like material;
a forming step of forming a honeycomb formed body in which a plurality of through-holes are arranged in parallel in the longitudinal direction with partition walls separated by forming the wet mixture;
and a firing step of manufacturing a honeycomb fired body by firing the honeycomb formed body. 5. The method for manufacturing a honeycomb structure according to claim 4, wherein the boehmite content in the paste is 25% by weight or more. The method for manufacturing a honeycomb structure according to claim 4 or 5, wherein the paste-like material has a viscosity of 50.0 Pa·s or more. The method for manufacturing a honeycomb structure according to any one of claims 4 to 6, wherein the boehmite content in the wet mixture is 10% by weight or more.

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