1. Field of the Invention
The present invention relates to a honeycomb structure and a method for manufacturing thereof.
2. Discussion of the Background
In order to convert exhaust gases discharged from internal combustion engines of vehicles, such as buses or trucks, construction machines and the like, a honeycomb catalyst, which allows exhaust gases to pass through the inside thereof to convert the exhaust gases has been used, and conventionally, as the honeycomb catalyst, for example, such a honeycomb catalyst has been proposed in which a material having a high specific surface area such as active alumina, and a catalyst metal such as platinum, are supported on the surface of a cordierite-base honeycomb structure having an integral structure and a low thermal expansion property. Moreover, the honeycomb catalyst has been also proposed in which an alkali-earth metal such as Ba is supported thereon as a NOx absorbing agent, so as to be used for NOx treatment in an atmosphere with excessive oxygen, such as an atmosphere in a lean burn engine and a diesel engine.
Here, in order to improve the conversion performance, it is necessary to increase the probability of contact between exhaust gases and a catalyst noble metal as well as the NOx absorbing agent. For this purpose, the supporting carrier needs to have a higher specific surface area, and the particle size of the catalyst metal needs to be made smaller and dispersed in a high level.
As the supporting carrier having a high specific surface area, a honeycomb structure including honeycomb fired bodies, each of which is formed by bonding a high specific surface material such as active alumina as a main material with an inorganic fibers serving as a reinforcing material by an inorganic binder to be molded into a honeycomb shape, followed by firing, has been known (for example, see The contents of Japanese Unexamined Patent Application Disclosure Nos. 2005-218935 A, 2005-349378 A, and 5-213681 A). Moreover, in order to achieve a large-size honeycomb structure, such a structured body in which honeycomb fired bodies are bonded to one another by interposing adhesive layers has been known.
When using this honeycomb structure as a catalyst supporting carrier used for converting exhaust gases from an automobile, however, cracks tend to occur in the adhesive layers that combine the honeycomb fired bodies to one another due to repeated vibrations, sometimes resulting in coming off some of the honeycomb fired body from the honeycomb structure, and further the damage may be caused in the honeycomb structure.
In order to prevent such damages from occurring in the honeycomb structural body, examinations have been conducted so as to increase the mutual adhesive strength between honeycomb fired bodies forming the honeycomb structure, and Patent Document 4 has disclosed a honeycomb structure in which: a plurality of honeycomb fired bodies are integrally combined with one another by interposing adhesive layers made from a joining material, and among inorganic particles in the joining material, those inorganic particles having a particle diameter (μm) that is 1.1 times or more the surface roughness Ra (μm) of the outer wall of the honeycomb fired body are made not to be contained at a rate exceeding 30% by weight to the total weight of the joining material.
Japanese Unexamined Patent Application Disclosure No. 2004-130176 A discloses that, by determining the particle diameter of the inorganic particles contained in the joining material in this manner, the honeycomb fired bodies are mutually combined with one another more firmly to provide an integral honeycomb structure.
The contents of Japanese Unexamined Patent Application Disclosure Nos. 2005-218935 A, 2005-349378 A, 5-213681 A, and 2004-130176 A are incorporated herein by reference in their entirety.