Stock material or miscellaneous articles – Structurally defined web or sheet – Honeycomb-like
Reexamination Certificate
2002-06-17
2004-04-27
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Honeycomb-like
C428S034400, C055S523000, C422S180000, C422S222000, C427S284000, C427S287000, C427S244000, C427S443200, C264S631000, C264S340000
Reexamination Certificate
active
06726977
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a cordierite honeycomb structure suitably used as a catalyst carrier for purifying automobile exhaust gas and a manufacturing method thereof.
BACKGROUND ART
Catalysts for purifying automobile exhaust gas are generally used in the form in which they are carried on a carrier. As a catalyst carrier of this kind has been utilized a honeycomb structure made of cordierite. In particular, emission gas control has become increasingly strict year by year, and thus, to keep up with the situation, i.e., to improve purification performance of the catalyst, a honeycomb structure with extremely thin partition wall as compared with conventional one has been proposed.
Thin-walled honeycomb structures, in which the wall thickness is 100 &mgr;m or less and the open frontal area of the end surfaces are 83% or more in some cases, have a variety of favorable characteristics as a catalyst carrier; for example, (1) the catalyst can be activated in an early stage after engine start-up because of a low heat capacity and a high warming-up efficiency, and (2) a pressure loss during passage of exhaust gas through the catalyst carrier can be lowered due to a high open frontal area, and so utilization thereof can be expected in the future.
However, a thin-walled honeycomb structure presents a problem, due to the above described structural characteristics, of serious abrasion of the end surfaces of the frontal openings exposed to exhaust gas of high pressure discharged from the engine. In particular, a catalyst (i.e., catalyst carrier) has lately come to be placed in the immediate vicinity of an engine for the purpose of improving throughput, which becomes a factor in accelerating the abrasion of the end surfaces of the frontal openings.
As measures for solving such a problem have been studied a method of thickening only the partition walls in the vicinity of the end surfaces of the frontal openings of a honeycomb structure (JP-A-2000-51710), a method of applying and firing a glass component such as a glaze or water glass on the end surfaces of the frontal openings of the substrate of a honeycomb structure, and a method of similarly applying and firing a specific component of cordierite-forming raw materials (ibid.) and the like.
However, the method of thickening the proximities of the end surfaces of the frontal openings is not preferable because it lowers the open frontal area of the end surfaces of a honeycomb structure, although improving the abrasive resistance of the end surfaces of the frontal openings, thereby decreasing the merit of a small pressure loss of a thin-walled honeycomb structure. In addition, the method of applying and firing a glass component such as a glaze did not successfully provide sufficient abrasive resistance since the applied part was vitrified and became rather brittle, although making the part compact and increasing strength thereof.
Furthermore, the method of applying and firing a specific component of cordierite-forming raw materials (referring to raw materials, such as a mixture of talc, alumina and kaolin, which become cordierite by heat treatment such as firing) is not preferable because it causes the chemical composition of the applied part to deviate from the stoichiometrical composition of cordierite leading to a high coefficient of thermal expansion, thereby losing thermal shock resistance, although allowing compacting of the part to proceed. In addition, the method only made compact the proximities of the end surfaces of the frontal openings and was insufficient from the viewpoint of abrasive resistance as well.
The present invention was made in view of the problem of the prior art described above and it is an object of the invention to provide a honeycomb structure that does not decrease the merits of a thin-walled honeycomb structure, such as a small pressure loss, and is also excellent in the abrasive resistance of the end surfaces of the frontal openings, and manufacturing method thereof.
DISCLOSURE OF THE INVENTION
The inventors have carried out intensive studies, and found that the problem of the prior art described above can be solved by forming a reinforced part having been loaded with a cordierite powder at least on one end surface of the frontal openings of the substrate of a honeycomb structure made of cordierite thereby completing the invention.
In other words, the present invention provides a cordierite honeycomb structure characterized in that the structure has a reinforced part having been loaded with a cordierite powder at least on one end surface of the frontal openings of the substrate of a honeycomb structure made of cordierite.
A cordierite honeycomb structure of the present invention preferably has a reinforced part with which a cordierite powder has been loaded through a glass phase.
A cordierite honeycomb structure of the present invention preferably has reinforced parts only in portions of the end surfaces of the frontal openings of the substrate and of 10 mm or less from the end surfaces of the frontal openings of the substrate towards the cell-forming direction and it is effective when the thickness of the partition wall of the substrate is 100 &mgr;m or less.
In addition, the present invention provides a manufacturing method of a cordierite honeycomb structure characterized in that the drying and/or firing are carried out after slurry containing a cordierite powder is applied to at least one end surface of the frontal openings of the fired or unfired substrate of a honeycomb structure, made of cordierite or a cordierite-forming raw material.
In a manufacturing method of the present invention, the drying and/or firing are preferably carried out after slurry containing a cordierite powder and colloidal ceramic is made to adhere to the structure and the drying and/or firing are preferably carried out after slurry containing a cordierite powder and glaze is made to adhere to the structure.
BEST MODE FOR CARRYING OUT THE INVENTION
A cordierite honeycomb structure of the present invention has a reinforced part having been loaded with a cordierite powder at least on one end surface of the frontal openings of the substrate of a honeycomb structure made of cordierite.
The present invention provides a honeycomb structure that does not decrease the merits of a thin-walled honeycomb structure, such as a small pressure loss, and is excellent in the abrasive resistance of the end surfaces of the frontal openings.
A cordierite honeycomb structure of the present invention will be now described in detail.
A cordierite honeycomb structure of the present invention (hereinafter simply referred to as a “honeycomb structure”) is characterized in that it has a reinforced part having been loaded with a cordierite powder. This reinforced part fills atmospheric pores of the wall surface of a cordierite honeycomb structure of which substrate is made of a cordierite powder and is fused through a firing step, and therefore it becomes compact and its porosity is lowered, compared with other parts. As a result, in addition to the improvement of the abrasive resistance of the part, the thermal shock resistance is not decreased because the reinforced part is loaded with a cordierite powder, which is also a material used for the substrate, and so the difference in coefficients of thermal expansion between the reinforced part and the substrate is small and the thermal shock resistance does not decrease.
A “cordierite powder” in this invention literally refers to a powder of cordierite (2MgO.2Al
2
O
3
.5SiO
2
), the chemical composition is 48 to 54% by weight of SiO
2
, 32 to 38% by weight of Al
2
O
3
and 12 to 18% by weight of MgO, and its main crystalline phase is cordierite.
However, the effects of the present invention can not be attained, in the case that a material capable of being converted into cordierite by heat treatment after a “cordierite-forming raw material,” as is disclosed in JP-A-2000-51710, is adhered to a substrate and then the resultant is fired. This is because the resultant can not be called as one hav
Hamaguchi Kunikazu
Kumazawa Kazuhiko
Boss Wendy
Jones Deborah
NGK Insulators Ltd.
Parkhurst & Wendel L.L.P.
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