Electrically heatable catalytic converter

Details Electrically heatable catalytic converter Electrically heatable catalytic converter

2000-08-14

2003-05-13

Tran, Hien (Department: 1764)

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

Waste gas purifier

C422S177000, C422S179000, C422S180000, C060S300000

Reexamination Certificate

active

06562305

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to an electrically insulating supporting structure being mechanically loadable in all directions and being capable of metallic bonding to electrically conductive components being electrically separated from one another.
Often such components must nevertheless be held together mechanically, and therefore a large number of electrically insulating supporting structures are known. In general, plastics or ceramic components are used for purposes of electrical insulation.
However, problems always occur whenever the electric insulations are at the same time exposed to considerable mechanical strains. For instance, ceramic structures can withstand loads but not major tensile forces. Moreover, if tensile forces are to be withstood, ceramic structures must be secured to the electrically conductive components, which again presents problems. Although metallized ceramics are known that can be brazed on, for instance, nevertheless once again the tensile strain that can be withstood is only that which the ceramic itself allows.
International Patent Application WO 92/02714, corresponding to U.S. Pat. No. 5,411,711 discloses an electrically heatable honeycomb body with internal support structures, in which individual components or partial regions or areas must be electrically insulated from one another. At the same time, extreme temperature strains and extreme mechanical loads because of thermal expansion also occur.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an electrically heatable catalytic converter and an electrically conductive honeycomb body using the same, which overcome the herein afore-mentioned disadvantages of the hereto fore-known devices and methods of this general type, in which the supporting structure is capable of bearing high mechanical loads in all directions, and in particular tensile loads and wherein the supporting structure is particularly suitable for use in an electrically heatable honeycomb body, for which extreme loads are typical.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electrically insulating supporting structure being mechanically loadable in all directions for metallic bonding to electrically conductive components being electrically separated from one another, comprising a first metallic structure; a second metallic structure; and an electrically insulating, ceramic material being disposed between the first and second metallic structures and being three-dimensionally pressed-in from substantially all sides; the first and second metallic structures being shaped to exert pressure from substantially all sides onto the ceramic material, without touching one another.
A decisive factor for the present invention is that two metallic structures are disposed in such a way that while they do not touch each other, nevertheless they practically completely surround a ceramic layer located between them and do not allow it to escape in any direction. It is unimportant whether the ceramic layer is a powdered material or is a molded part. The structures must be shaped in such a way that neither a powder nor fragments of a molded part crumbling in response to mechanical loads can fall out. The outstanding insulating properties of ceramic powder are well known, for instance in the field of thermocouples and jacket measuring conductors. The ceramic and metal materials which are suitable for such purposes are also suitable for the present invention. It is important that the supporting structure have a capability of metallic bonding to components that are electrically separated from one another. The first metallic structure must be connectable to a first component, and the second metallic structure to a second component being electrically insulated from the first.
In accordance with another feature of the invention, a simple and especially highly suitable construction provides that the first metallic structure is a continuous wire or a continuous band, and the second structure includes individual portions that encompass the wire or the band, wherein ceramic material is pressed-in between the two metallic structures. In this way, one component can be joined metallically to the wire or band, while another component, being electrically insulated from it, can be connected to the outer portions. Regardless of the direction in which forces are exerted on the two components, the ceramic material between the two metallic structures is only under compressible strain, because it is enclosed on practically all sides. The load bearing capacity of the supporting structure is therefore determined by that of its metallic parts, not by that of the ceramic material.
In accordance with a further feature of the invention, the ceramic material includes individual ceramic beads or small tubes, or may be in powder form. Nor does it play any role if initially compact ceramic beads or small ceramic tubes should breakdown over time, under alternating thermal strains, into fragments or powder, since the fragments cannot be lost.
In accordance with an added feature of the invention, it is especially advantageous and suitable for larger-surface-area supporting structures if the first metallic structure is form-lockingly connected to the second metallic structure by one or two bulges having at least one bottleneck, for instance in the manner of pushbuttons, wherein ceramic material, especially a thin metal oxide film, is present between the structures. In the region of the bulging features and the bottleneck, the ceramic intermediate layer cannot escape, and just as in the examples described above, regardless of the direction of the forces acting on the structure, it is always subject to pressure only. A form-locking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a force-locking connection, which locks the elements together by force external to the elements.
In accordance with an additional feature of the invention, it is especially advantageous to initially join the first and second metallic structures form-lockingly to one another, and only after that to form an insulating layer between them. This can be performed by oxidation or chemical treatment of the surface, or by a special coating of one of the surfaces between the two structures.
With the objects of the invention in view, there is also provided a method for producing an electrically insulating supporting structure being mechanically loadable in all directions for metallic bonding to electrically conductive components being electrically separated from one another, which comprises pressing-in an electrically insulating ceramic material, preferably in powdered form, on substantially all sides between a first metallic structure and a second metallic structure; and shaping the first and second metallic structures to be both accessible, at least in partial regions, and to exert pressure from substantially all sides onto the ceramic material, without touching one another, for metallic bonding to further structures.
Once again it is important that both the first and the second metallic structures be accessible for metallic bonding to further structures, yet nevertheless not touch one another and between them press-in a ceramic material which is always subject to pressure, regardless of the direction of the forces occurring at the metallic structures.
In accordance with another mode of the invention, the first metallic structure is surrounded by a ceramic layer and a metal envelope, and the surrounding metal envelope is subdivided into a plurality of individual segments. It is important in this respect that the end of the individual segments of the outer metal structure not be simply open but rather be shaped on the inside in such a way that they press-in the ceramic material between them on practically all sides. For instance, a supporting structure according to the invention can be made from a conventional jacket conductor

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