Stock material or miscellaneous articles – Structurally defined web or sheet – Honeycomb-like
Reexamination Certificate
2001-09-14
2004-04-06
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Honeycomb-like
C428S188000, C428S698000, C428S699000, C428S701000, C428S702000, C428S404000, C428S407000, C428S304400, C428S332000, C428S034500, C156S089220, C055S522000, C055S523000, C422S122000, C422S168000, C422S177000, C422S211000, C422S222000, C264S043000, C264S044000, C264S630000, C264S628000, C264S629000, C264S632000, C264S656000, C264S661000, C264S682000, C264S177120
Reexamination Certificate
active
06716512
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a honeycomb structure used in a filter for purification of automobile exhaust gas, a catalyst carrier, or the like.
BACKGROUND ART
Porous honeycomb structures are in wide use as a filter for capturing and removing the particulate substance present in a dust-containing fluid (e.g. exhaust gas emitted from diesel engine) or as a catalyst carrier for loading thereon a catalyst component to purify the harmful substances present in an exhaust gas. It is known that as a material constituting such a honeycomb structure, there are used refractory particles such as silicon carbide (SiC) particles or the like.
As a specific technique related thereto, there is disclosed, in, for example, JP-A-6-182228, a porous, silicon carbide-based catalyst carrier of honeycomb structure, obtained by using, as a starting material, a silicon carbide powder having a given specific surface area and a given impurity content, molding the material into a desired shape, drying the molded material, and firing the resulting material at a temperature of 1,600 to 2,200° C.
Meanwhile, there are disclosed, in JP-A-61-26550, a process for producing a vitrifying material-containing refractory, which comprises adding a vitrifying material to an easily oxidizable material or a refractory composition containing an easily oxidizable material, mixing and kneading them together with a binder, molding the kneaded material, and open-firing the molded material in a furnace under a non-oxidative atmosphere; and, in JP-A-8-165171, a silicon carbide molded material obtained by adding, to a silicon carbide powder, an organic binder and inorganic binders of clay mineral series, glass series and lithium silicate series and molding the resulting material.
Also, in JP-A-6-182228 is introduced a process for producing a conventional porous, silicon carbide-based sintered material, which comprises adding, to silicon carbide particles as an aggregate, a binder such as vitreous flux, clay or the like, molding them, and firing the molded material at a temperature at which the binder melts.
Further, there are reported, in JP-B-61-13845 and JP-B-61-13846, the preferred average particle diameter of refractory particles, particle size distribution of refractory particles, porosity of cylindrical material, average pore diameter of cylindrical material, pore volume of cylindrical material, wall thickness of cylindrical material, etc as to a high-temperature use ceramic filter produced by molding refractory particles which consists of silica sand, a ground pottery, a metal oxide such as Al
2
O
3
, TiO
2
or ZrO
2
, silicon carbide, nitride, boride, or other refractory material adjusted to a given grain size, to a porous, bottomed cylindrical material using a refractory binder such as water glass, flit, glaze or the like.
In the sintering (necking between particles) owing to the recrystallization of silicon carbide powder per se, shown in JP-A-6-182228, porosity is obtained but the silicon carbide powder per se is allowed to give rise to recrystallization; therefore, a very high firing temperature need be used which invites a high cost and, moreover, a material of high thermal expansion coefficient need be fired at a high temperature which invites a reduced yield in firing.
Meanwhile, the technique of binding a silicon carbide powder (as a raw material) with a vitreous material, shown in JP-A-61-26550 and JP-A-6-182228 uses a low firing temperature of 1,000 to 1,400° C.; however, the binder once melts during the firing, making it very difficult to obtain a porous material.
Further, the filter shown in JP-B-61-13845 and JP-B-61-13846 is porous but a bottomed cylindrical material having a large wall thickness of 5 to 20 mm: therefore, it was unusable under the condition of high space velocity (SV) experienced by a filter for purification of automobile exhaust gas.
The present invention has been made in view of the above-mentioned situation of the prior art, and is intended to provide a honeycomb structure which contains refractory particles (e.g. silicon carbide particles) and yet can be produced at a relatively low firing temperature at a low cost, which has a sufficiently high porosity and a high specific surface area, and which can be suitably used, for example, as a filter for purification of automobile exhaust gas by a treatment such as plugging of through-channel at its inlet or outlet, or as a catalyst carrier even under a high SV condition.
DISCLOSURE OF THE INVENTION
According to the present invention, there is provided a honeycomb structure having, in the axial direction, a number of through-channels separated by partition walls, which honeycomb structure contains refractory particles and a vitreous component and is porous.
According to the present invention, there is also provided a process for producing a honeycomb structure, which comprises adding a vitrifying material and an organic binder to refractory particles as a raw material, mixing and kneading them to obtain a readily formable bullet, extruding the readily formable bullet into a honeycomb shape, calcinating the extruded material to remove the organic binder contained therein, and then firing the calcinated material.
BEST MODE FOR CARRYING OUT THE INVENTION
The honeycomb structure of the present invention contains refractory particles and a vitreous component binding the refractory particles. Therefore, in its production, a relatively low firing temperature can be used for sintering; a low production cost is made possible; and a high yield can be obtained. The present invention is not directed to a bottomed cylindrical material of thick wall such as disclosed in JP-B-61-13845 or JP-B-61-13846 but directed to a porous honeycomb structure; accordingly, the present honeycomb structure can be used under a high SV condition, as a filter for purification of automobile exhaust gas, a catalyst carrier, or the like.
The honeycomb structure of the present invention preferably has a microstructure wherein the refractory particles are bound by the vitreous component in such a state that the particles used as a raw material for the refractory particles retain their shapes. Also, the honeycomb structure of the present invention preferably has a porosity of 30 to 90% when it is used as a filter for capturing and removing the particulate matter present in a dust-containing fluid. When the porosity of the honeycomb structure is less than 30%, the filtration rate is insufficient; when the porosity is more than 90%, the strength of the structure is insufficient. The porosity is preferably 40% or more when the present honeycomb structure is used in an application for such as for example as a filter for purification of automobile exhaust gas wherein there is a fear of pressure loss.
When the honeycomb structure of the present invention is used also as a filter, the honeycomb structure preferably has an average pore diameter determined depending upon the target substance to be filtered. For example, when the honeycomb structure is used as a diesel particulate filter (DPF) for capturing and removing the particulates contained in the exhaust gas emitted from a diesel engine, the average pore diameter is preferably set at 2 to 50 &mgr;m. When the average pore diameter is less than 2 &mgr;m, a very large increase in pressure loss appears even when the accumulation amount of particulates is small. When the average pore diameter is more than 50 &mgr;m, particulates pass through the DPF. Therefore, such average pore diameters are not preferred.
In the honeycomb structure, the thickness of the partition walls separating the through-channels (cells) is preferably 4 mil or more (102 &mgr;m or more). When the thickness of the partition walls is less than 4 mil (102 &mgr;m), the honeycomb structure has an insufficient strength. Generally in honeycomb structures, the strength has a close connection with the porosity. In the case of the present honeycomb structure, it was found out that when the thickness of the partition walls is set so as to have the following re
Harada Takashi
Noda Naomi
Yamamoto Yoshinori
NGK Insulators Ltd.
Parkhurst & Wendel L.L.P.
LandOfFree
Honeycomb structure and process for production thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Honeycomb structure and process for production thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Honeycomb structure and process for production thereof will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3274463