JPH0217209B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas purifying structure for purifying exhaust gas discharged from an internal combustion engine of an automobile or the like.

Conventionally, a ceramic honeycomb structure is coated and then an oxidation catalyst is supported, but when this is installed, for example, in an exhaust gas passage,
Since the flow direction of exhaust gas and the through holes of the honeycomb structure are in the same direction, ventilation resistance is small, but interaction with the wall is also small. Therefore, there is a problem in that the mass transfer between the exhaust gas and the wall surface is reduced, and bubbling occurs, resulting in a poor purification rate of the exhaust gas. On the other hand, there are some that use ceramic foam. This is porous, has a large surface area, and has a good purification rate, but has the problem that it is extremely weak against mechanical forces such as vibrations compared to honeycomb.

Therefore, the present invention provides a first ceramic foam forming an exhaust gas purifying section, and a second ceramic foam provided around the outer periphery of the first ceramic foam and having a denser mesh than the first ceramic foam. The object of the present invention is to provide an exhaust gas purifying structure which has excellent mechanical strength and a high purification rate by co-firing a first ceramic foam and a second foam. shall be.

The present invention will be explained in detail below using specific examples. In Fig. 1, this figure shows a ceramic foam, which includes a coarse part 1 made of a first ceramic foam and a non-porous part 1 made of a second ceramic foam that surrounds the outer periphery and is integrated with the coarse part 1. It is composed of a flexible dense part 2. This coarse part 1 has a three-dimensional network cell structure with internal communication spaces. In addition, the densely woven portion 2 has a structure in which the communication space is clogged.
This ceramic foam supports a catalyst on its coarse part 1, which forms the exhaust purification section, and is housed in a metal case via a support element, thereby forming an exhaust gas purification structure.

Next, a method for producing the ceramic foam will be explained. Note that, for convenience, the reference numerals shown in FIG. 1 are used.

A cylindrical synthetic resin foam 1 having a three-dimensional network cell structure with internal communication spaces and an average mesh size of 13 meshes, and a plate-shaped synthetic resin foam 2 with the same cell structure and an average mesh size of 40 meshes. Prepare. In addition,
These foams 1 and 2 are made of polyurethane foam, for example, and have a cell structure as shown in FIG. 3, having a resin skeleton and an internal communication space communicating with the outside. Now, the first cylindrical foam 1
A plate-shaped second foam 2 with a thickness of 3 mm is placed around the 3 mm, and the ends are secured with tape or the like. This was immersed in cordierite slurry made by dissolving 1500 g of cordierite powder and 60 g of methyl cellulose in 2500 ml of water, and then the excess slurry was blown off with compressed air. Then, dry at 100℃ for 3 hours. After repeating the above operation several times,
Co-fire the first foam and the second foam at 1300°C to 1480°C for 5 hours. As a result, the foams 1 and 2 are burned away, leaving the cordierite attached to their skeletons. In addition to cordierite, ceramic materials include alumina, mullite, and the like. In the structure obtained by this method, the mesh in the foam 1 part is rough, so the slurry adheres only around the skeleton of the foam 1 and does not clog the ventilation holes. Since the foam 2 has a fine mesh, the slurry closes almost all of the air holes in the foam 2. Therefore, when this is fired, the foam 1 portion and the foam 2 portion have different apparent densities. Therefore, the more inflexible and dense portion 2 holds the relatively weaker portion 1, and becomes significantly stronger against mechanical strength such as vibration. Also,
In this method, foams 1 and 2 are impregnated and fired at the same time, so the composition is uniform, so there is almost no difference in thermal expansion coefficient, and the fired product does not have any deformation, cracks, or cracks. Ta.

The compressive strength of this structure made in this way is 150 to 200 Kg/cm ² in the axial direction, 50 to 100 Kg/cm ² in the radial direction,
It was 10 to 20 kg/cm ² in the diagonal direction. In addition, when these structures carrying Pt-Rh catalysts are installed in the exhaust gas to remove harmful substances such as NOx, CO, and HC, these components are reduced compared to conventional honeycomb structures. In all cases, the same purification rate could be obtained with a volume of about 60%. This is because the three-dimensional network structure of the foamed ceramic increases the contact interaction between the catalyst and the exhaust gas.

FIG. 2 shows another embodiment of the present invention in which a four-part ceramic foam body 1 is partitioned by a cross-shaped ceramic foam body 3, and the outer periphery of these is surrounded by a ceramic foam body 2. In this example, the apparent densities of the four ceramic foams 1 are approximately the same, but are coarser than the apparent densities of the other ceramic foams 2 and 3. Further, the other ceramic foams 2 and 3 have approximately the same apparent density. According to this embodiment, the strength of the ceramic foam 1 is that the ceramic foam 2 has a cross pillar shape.
The presence of this will further improve the performance.

FIG. 4 shows a modified embodiment of FIG. 1, in which a ceramic foam 4 (18 meshes on average) is provided in the center, and the apparent density of the foam 4 is set to be denser than the outer foam 1 and higher than the foam 2. It is a rough version. When the structure according to this embodiment is attached to the exhaust pipe of a car, the exhaust gas flow velocity passing through the center is slightly reduced and the flow velocity distribution within the exhaust pipe is eliminated, so it has a smaller volume than a conventional honeycomb structure. Equivalent purification performance can be obtained. Although the structure of the present invention has a cylindrical appearance, various shapes are possible.

In summary, according to the present invention, not only can the blow-through phenomenon be avoided compared to conventional ceramic honeycomb structures, but also the non-flexible second ceramic foam has a denser mesh than the first ceramic foam. Ceramic foam can significantly improve mechanical strength against vibrations, etc. Furthermore, since the first ceramic foam and the second ceramic foam have the same composition, there is no difference in coefficient of thermal expansion, and it is possible to prevent deformation, cracking, cracking, etc. of the fired product.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing one embodiment of the present invention;
FIG. 3 is a perspective view showing another embodiment of the present invention; FIG. 3 is a perspective view showing details of the ceramic foam shown in FIG. 1;
FIG. 4 is a perspective view showing still another embodiment of the present invention. 1... part with coarse mesh, 2, 3... part with dense mesh, 4... part with coarseness between 1 and 2.

Claims (1)

[Scope of Claims] 1. A first ceramic foam constituting an exhaust gas purifying section; and a foam formed on the outer periphery of the first ceramic foam, the opening of which is denser than that of the first ceramic foam. an exhaust gas purifying structure, characterized in that the first ceramic foam and the second ceramic foam are integrally formed by co-firing. thing.