Stock material or miscellaneous articles – Structurally defined web or sheet – Honeycomb-like
Reexamination Certificate
2002-10-01
2004-07-20
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Honeycomb-like
C428S034400, C428S188000, C422S177000, C422S180000, C422S222000, C055S523000, C264S628000, C264S630000, C264S639000, C264S662000, C264S669000, C264S670000
Reexamination Certificate
active
06764742
ABSTRACT:
TECHNICAL FIELD
The present invention relates to honeycomb structure bodies used in filters for purifying automobile exhaust gas, catalyst carriers, and the like.
BACKGROUND ART
Porous honeycomb structure bodies are widely used as filters for collecting and removing particulate materials contained in such particulate dust containing fluid as exhaust gas discharged from diesel engines, or used as catalyst carriers for supporting catalytic components which purify harmful substances contained in the exhaust gas. In addition, it is well known that such a refractory granular powder as composed of the silicon carbide (SiC) grains and the like is used as a material composing such a honeycomb structure body.
As a specific related technique, for example, in JP-A-6-182228, there is disclosed a catalyst carrier of porous silicon carbide which has a honeycomb structure, obtained by using as the starting material a silicon carbide powder having a prescribed specific surface area and a prescribed impurity content, and by molding the material into a desired shape and drying, and subsequently firing in the temperature range of 1600 to 2200° C.
On the other hand, in JP-A-61-26550, there is disclosed a production method of a refractory substance containing a vitrifiable raw material which method is characterized in that a vitrifiable raw material is added to an easily oxidizable raw material or a refractory composite containing easily oxidizable raw materials, and the mixture obtained is mixed with a bonding material, and this mixture is kneaded and molded, and the molded body obtained is fired without crusible in a furnace having a nonoxidizing atmosphere, while in JP-A-8-165171, there is disclosed a silicon carbide molded body which is molded by adding an organic binder and inorganic binders based on clay minerals, glass, and lithium silicate to the silicon carbide powder.
In addition, in JP-A-6-182228 described above, there is also introduced, as a prior production method of sintered body based on porous silicon carbide, a production method in which a bonding material such as a glass-based flux or a clay material is added to silicon carbide grains working as filler, the mixture thus obtained is molded, and subsequently fired and compacted at the temperature at which the bonding material is melted.
Furthermore, in JP-B-61-13845 and JP-B-61-13846, there are disclosed the suitable average grain size of the refractory granular powder, the grain size distribution of the refractory granular powder, the porosity ratio of a tubular body, the average pore diameter of a tubular body, the pore volume of a tubular body, and the partition wall thickness of a tubular body, and the like, with respect to a high temperature ceramic filter formed in a porous, bottomed tubular shape in which the refractory granular powder, composed of silica sand, ceramic pulverized substances, metal oxide such as Al
2
O
3
, TiO
2
, ZrO
2
, and the like, silicon carbide, nitrides, borides, or other refractory materials and the like, is graded in grain size to a prescribed grain size, and used as mixed with a refractory bonding material such as liquid glass, flit, glaze, and the like.
Furthermore, in JP-A-10-29866, JP-A-2-6371, and JP-A-61-97165, there are disclosed the methods, compositions, and the like for silicon carbide based brick bonded with sialon which is an oxynitride of Si and Al.
As for a sintered form (necking) based on the recrystallization reaction of silicon carbide powder itself, disclosed in JP-A-6-182228 as described above, the silicon carbide component is evaporated from the surfaces of the silicon carbide grains, the evaporated component is condensed in the contact portions (neck portions) between grains, and thus the neck portions grow to yield the bonded state; in this connection, there is a problem that the cost increase is caused by the very high temperature required for the silicon carbide evaporation and the firing process yield is degraded owing to the high temperature firing needed for a material of high thermal expansion coefficient.
On the other hand, a technique for bonding the raw material of silicon carbide powder with glass material, disclosed in JP-A-61-26550 and JP-A-6-182228, requires a temperature between 1000 and 1400° C. which is low for the firing temperature, but it is very difficult to obtain porous substances because the bonding material undergoes once a melted state.
Furthermore, the filters disclosed in JP-B-61-13845 and JP-B-61-13846 are porous, but are of the bottomed tubular shape with partition walls of thickness as thick as 5 to 20 mm, and hence they cannot be applied under the high SV (spatial velocity) condition for the filters for purifying automobile exhaust gas.
In addition, furthermore, the silicon carbide based bricks bonded with sialon, as disclosed in JP-A-10-29866, JP-A-2-6371, and JP-A-61-97165, are used for a liner for furnaces and shelf boards, and the porosity is as small as 20% or below, but is absolutely inappropriate for being used as filters for purifying automobile exhaust gas in view of the pressure loss.
The present invention has been made in view of the above described circumstances, and takes as its object the provision of a honeycomb structure body and the production method thereof which honeycomb structure body contains such refractory grains as the silicon carbide grains, but can be produced at a relatively low firing temperature and at a low cost, is sufficiently porous, has a high specific surface area, and can be used suitably even under the high SV condition as a filter for purifying automobile exhaust gas, a catalyst carrier, or the like, by being subjected to plugging and the like.
DISCLOSURE OF THE INVENTION
According to the present invention, there is provided a honeycomb structure body which has a large number of passages penetrating along the axial direction and being partitioned with partition walls, and which is characterized in that the honeycomb structure body contains refractory grains as filler and one or more kinds of elements selected from the group consisting of the rare earth elements, the alkaline earth elements, Al, and Si; and the honeycomb structure body has a crystal containing at least one or more than one kinds of these elements, and is porous.
In addition, according to the present invention, there is provided a production method of a honeycomb structure body which method is characterized in that a puddle is obtained by adding one or more kinds of raw materials containing one or more kinds of elements selected from the group consisting of the rare earth elements, the alkaline earth elements, Al, and Si as well as an organic binder to a refractory granular raw material, and by successively mixing and kneading; and the obtained puddle is molded into a honeycomb shape, and the obtained molded body is calcined to remove the organic binder and subsequently fired for finishing.
BEST MODE FOR CARRYING OUT THE INVENTION
The honeycomb structure body of the present invention is an article in which refractory grains are bonded to each other by applying the mechanism of melt precipitation, in contrast to the production method described in JP-A-6-182228 in which the mechanism of evaporation condensation is employed in the sintering mechanism. In the melting precipitation mechanism, proper sintering aids are selected, added to and mixed with a refractory granular powder, which is a filler, and fired, when the aids are allowed to react with the refractory grains, and at that time the surfaces of the grains are melted to form liquid phase. The melted component, as it is in the liquid phase while containing the added aid components, moves to the neck portions low in energy state to be precipitated, and thus the substance transferred to the neck portions bonds the grains to each other.
As for the liquid phase, in the firing process, in some cases, the aids react mutually to form the liquid phase at the beginning, and the liquid phase reacts with the refractory grains, while in some other cases the reaction between the aids and the refractory
Ichikawa Shuichi
Kawasaki Shinji
Sakai Hiroaki
Tomita Takahiro
Boss Wendy
Jones Deborah
NGK Insulators Ltd.
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