Stock material or miscellaneous articles – Structurally defined web or sheet – Honeycomb-like
Reexamination Certificate
1999-01-29
2001-03-20
Lorin, Francis J. (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Honeycomb-like
Reexamination Certificate
active
06203882
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese Patent Application Nos. Hei. 10-64203 filed on Feb. 26, 1998 and 10-342374 filed on Nov. 16, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a catalytic converter for purifying an exhaust gas discharged from an internal combustion engine of a vehicle, and particularly to a producing method of a honeycomb-shaped catalyst carrier mainly made of cordierite.
2. Related Art
Conventionally, a cordierite honeycomb body made of cordierite and having a honeycomb shape is used as a catalyst carrier for carrying a catalyst for purifying an exhaust gas discharged from a vehicle engine. To produce the cordierite honeycomb body, source materials such as talc (Mg
3
Si
4
O
10
(OH)
2
), kaoline (Al
2
Si
2
O
5
(OH)
4
) and alumina (Al
2
O
3
) are mixed according to a desired cordierite composition. The mixture is formed into a desired honeycomb shape, and is sintered to become a cordierite honeycomb body.
Recently, it is necessary for the catalyst carrier for a vehicle to reduce a weight thereof and a pressure loss of exhaust gas flowing therethrough. Thickness of a cell wall of a cordierite honeycomb body consisting of the catalyst carrier may be decreased to meet this demand. However, when thickness of the cell wall is decreased, strength of the cordierite honeycomb body is also lessened. Thus, density of cordierite forming the cordierite honeycomb body needs to be increased so that strength of the cordierite honeycomb body is maintained even when thickness of the cell wall is decreased. For example, when thickness of the cell wall is decreased to 100 &mgr;m or less, porosity of cordierite forming the honeycomb body is preferably decreased to 20% or less so that the honeycomb body has sufficient strength.
It is known that cordierite material particles are finely grained or sintering aids are added to cordierite material so that density of cordierite is increased. However, these methods facilitate cordierite to be sintered, thereby increasing density of cordierite. Therefore, density of microcracks generated in cordierite and correlative with a coefficient of thermal expansion (hereinafter referred to as C.T.E.) of cordierite is also decreased. That is, in these methods, porosity of cordierite may be decreased, but the C.T.E. of cordierite may be increased. Thus, it is difficult to decrease porosity of cordierite so that density of cordierite is increased, while preventing the C.T.E. thereof from increasing. Further, when the cordierite honeycomb body having such a large C.T.E. is used as the catalyst carrier, a large thermal stress is generated by heat emitted while exhaust gas is purified by the catalyst carrier. As a result, cracks may occur in the catalyst carrier.
SUMMARY OF THE INVENTION
In view of the foregoing problems, it is an object of the present invention to provide a producing method of a cordierite honeycomb body which has sufficient strength even when thickness of a cell wall thereof is decreased, and has a low C.T.E. to be shock-resistant under heat.
According to the present invention, a cordierite honeycomb body is produced by mixing a cordierite material including kaoline, forming the mixed cordierite material into a honeycomb shape and sintering it. The kaoline is composed of at least partly kaolinite having a Hinckley crystallinity index of 0.5 or more. Therefore, the kaolinite particle has a less portion in an amorphous phase, and the number of micropores generated in the cordierite honeycomb body during the sintering process is decreased. When the kaolinite has the Hinckely crystallinity index of 0.5 or more, porosity of the cordierite honeycomb body is decreased to 20% and less. As a result, density of cordierite of the cordierite honeycomb body is increased without increasing a C.T.E. of cordierite. Thus, the cordierite honeycomb body has sufficient strength even when thickness of a cell wall thereof is decreased, while maintaining the low C.T.E. to be shock-resistant under heat.
Preferably, a ratio of the kaolinite with the Hinckley crystallinity index of 0.5 or more to the whole kaoline is in a range of 20-100% by weight.
Preferably, the cordierite material is sintered without sintering aides added thereto. The sintering aides facilitate the cordierite material to be sintered, thereby decreasing density of microcracks generated in the cordierite honeycomb body and increasing the C.T.E. thereof.
REFERENCES:
patent: 4755493 (1988-07-01), Takeuchi et al.
patent: 0 514 205 (1992-11-01), None
Koike Kazuhiko
Nakanishi Tomohiko
Tokuda Kojiro
Denso Corporation
Lorin Francis J.
Pillsbury Madison & Sutro LLP
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