JP7594544B2 - Electrically heated carrier and exhaust gas purification device - Google Patents

Description

The present invention relates to an electrically heated carrier and an exhaust gas purification device.

In recent years, electrically heated catalysts (EHCs) have been proposed to improve the deterioration of exhaust gas purification performance immediately after engine start. EHCs are, for example, made by connecting metal electrodes to a columnar honeycomb structure made of conductive ceramics, and by passing electricity through the honeycomb structure itself to generate heat, allowing the temperature to be raised to the catalyst's activation temperature before the engine is started. In EHCs, it is desirable to reduce temperature unevenness within the honeycomb structure and achieve a uniform temperature distribution in order to fully obtain the catalytic effect.

To pass current through the EHC, metal electrodes connected to external wiring must be joined to the EHC. Methods for joining include fixing by thermal spraying, laser welding, or brazing.

Patent Document 1 also discloses a technique for applying heat energy from the metal terminal (metal electrode) side to join a metal electrode by welding onto the electrode layer of a honeycomb structure. It also describes that such a configuration can provide a conductive honeycomb structure with improved joining reliability with the metal electrode.

JP 2018-172258 A

In Patent Document 1, a stress relief layer (underlayer) is provided on the electrode layer to reduce breakage during welding and repeated fatigue of the ceramic honeycomb structure due to thermal cycles. However, EHCs are usually used at high temperatures (800-1000°C) in an exhaust gas atmosphere from automobiles, etc., and the physical properties of joints such as welded parts change due to the energy generated during joining. Therefore, if these joints are exposed to exhaust gas from automobiles, etc., their oxidation resistance is likely to decrease. As a result, although the underlayer can relieve stress, the material strength decreases due to oxidation, which can cause problems such as breakage of the joints.

The present invention was created in consideration of the above circumstances, and aims to provide an electrically heated carrier and an exhaust gas purification device that can effectively suppress oxidation of the joint portion that connects the base layer and the metal electrode. Another aim of the present invention is to provide an electrically heated carrier and an exhaust gas purification device that can effectively suppress oxidation of the fixing layer that fixes the metal electrode to the electrode layer.

As a result of intensive research, the present inventors have found that the above-mentioned problems can be solved by providing an anti-oxidation layer for protecting the joint portion connecting the underlayer and the metal electrode from exhaust gas. That is, the present invention is specified as follows.
(1) A columnar honeycomb structure made of ceramics having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and defining a plurality of cells that form flow paths penetrating from one end face to the other end face;
An electrode layer disposed on a surface of an outer peripheral wall of the columnar honeycomb structure;
a conductive underlayer provided on the electrode layer;
a metal electrode connected to the underlayer by a bonding site;
an anti-oxidation layer for protecting the joint from exhaust gas;
Electrically heated carrier comprising:
(2) A columnar honeycomb structure made of ceramics having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and defining a plurality of cells that form flow paths penetrating from one end face to the other end face;
An electrode layer disposed on a surface of an outer peripheral wall of the columnar honeycomb structure;
a metal electrode provided on the electrode layer;
a fixing layer provided to cover the metal electrode and fixing the metal electrode to the electrode layer;
an antioxidant layer provided so as to cover the fixing layer;
Electrically heated carrier comprising:
(3) An electrically heated carrier according to (1) or (2),
A metallic tubular member for holding the electrically heated carrier;
An exhaust gas purification device having the above structure.

According to the present invention, it is possible to provide an electrically heated carrier and an exhaust gas purification device capable of effectively suppressing oxidation of the joint portion connecting the base layer and the metal electrode. Also, according to the present invention, it is possible to provide an electrically heated carrier and an exhaust gas purification device capable of effectively suppressing oxidation of the fixing layer that fixes the metal electrode to the electrode layer.

FIG. 2 is a schematic cross-sectional view perpendicular to the extension direction of cells of an electrically heated carrier according to an embodiment of the present invention. 2 is a schematic view showing the appearance of a columnar honeycomb structure and an electrode layer according to the embodiment of the present invention. FIG. FIG. 2 is a schematic plan view showing an example of the arrangement of a base layer of an electrically heated carrier in an embodiment of the present invention. 1 is a cross-sectional schematic diagram of a columnar honeycomb structure, an electrode layer, a base layer, a bonding portion, a metal electrode, and an antioxidant layer in an embodiment of the present invention. 1 is a cross-sectional schematic diagram of a columnar honeycomb structure, an electrode layer, a base layer, a bonding portion, a metal electrode, and an antioxidant layer in an embodiment of the present invention. 1 is a cross-sectional schematic diagram of a columnar honeycomb structure, an electrode layer, a base layer, a bonding portion, a metal electrode, and an antioxidant layer in an embodiment of the present invention. 1 is a cross-sectional schematic diagram of a columnar honeycomb structure, an electrode layer, a base layer, a bonding portion, a metal electrode, and an antioxidant layer in an embodiment of the present invention. 1 is a cross-sectional schematic diagram of a columnar honeycomb structure, an electrode layer, a base layer, a bonding portion, a metal electrode, and an antioxidant layer in an embodiment of the present invention. 1 is a cross-sectional schematic diagram of a columnar honeycomb structure, an electrode layer, a base layer, a bonding portion, a metal electrode, and an antioxidant layer in an embodiment of the present invention. 1 is a cross-sectional schematic diagram of a columnar honeycomb structure, an electrode layer, a base layer, a bonding portion, a metal electrode, and an antioxidant layer in an embodiment of the present invention. 3 is a schematic diagram showing how a base layer and a metal electrode of a columnar honeycomb structure according to an embodiment of the present invention are joined by laser welding or the like. FIG. 2 is a cross-sectional schematic view of a columnar honeycomb structure, an electrode layer, a fixing layer, a metal electrode, and an antioxidant layer in an embodiment of the present invention. FIG. 1 is a cross-sectional schematic diagram of a columnar honeycomb structure, an electrode layer, a base layer, a bonding portion, a metal electrode, and an antioxidant layer in an embodiment of the present invention.

Next, the embodiments for carrying out the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes, improvements, etc. may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

1. Electrically Heated Carriers
Fig. 1 is a schematic cross-sectional view perpendicular to the extension direction of the cells 18 of the electrically heated carrier 10 in the embodiment of the present invention. The electrically heated carrier 10 includes a columnar honeycomb structure 11, electrode layers 13a and 13b arranged on the surface of the outer wall 12 of the columnar honeycomb structure 11, a base layer 16 provided on the electrode layers 13a and 13b, metal electrodes 14a and 14b connected to the base layer 16 by a joint portion 20, and an oxidation prevention layer 21 for protecting the joint portion 20 from exhaust gas. In Fig. 1, the joint portion 20 and the oxidation prevention layer 21 for protecting the joint portion 20 from exhaust gas are simplified, but the electrically heated carrier 10 in the embodiment of the present invention has various forms, which will be described in detail in each embodiment described later with reference to the drawings.

(1-1. Pillar-shaped honeycomb structure)
2 is a schematic diagram showing the appearance of a columnar honeycomb structure 11 and electrode layers 13a, 13b according to an embodiment of the present invention. The columnar honeycomb structure 11 has an outer peripheral wall 12 and partition walls 19 disposed inside the outer peripheral wall 12 and defining a plurality of cells 18 that penetrate from one end face to the other end face and form flow paths.

The outer shape of the columnar honeycomb structure 11 is not particularly limited as long as it is columnar, and may be, for example, a columnar shape with a circular bottom surface (cylindrical shape), a columnar shape with an oval bottom surface, a columnar shape with a polygonal bottom surface (quadragonal, pentagonal, hexagonal, heptagonal, octagonal, etc.), etc. The size of the columnar honeycomb structure 11 is preferably such that the area of the bottom surface is 2000 to 20000 ^mm2 , more preferably 5000 to 15000 ^mm2 , for the reason of increasing heat resistance (suppressing cracks that enter the circumferential direction of the outer peripheral wall).

The columnar honeycomb structure 11 is made of ceramics and is electrically conductive. As long as the electrically conductive columnar honeycomb structure 11 can be electrically conductive and generate heat by Joule heat, there are no particular restrictions on the electrical resistivity of the ceramics, but it is preferably 1 to 200 Ωcm, and more preferably 10 to 100 Ωcm. In the present invention, the electrical resistivity of the columnar honeycomb structure 11 is a value measured at 400°C by the four-terminal method.

The material of the columnar honeycomb structure 11 is not limited, but can be selected from the group consisting of oxide ceramics such as alumina, mullite, zirconia, and cordierite, and non-oxide ceramics such as silicon carbide, silicon nitride, and aluminum nitride. Silicon carbide-metal silicon composites and silicon carbide/graphite composites can also be used. Among these, from the viewpoint of achieving both heat resistance and electrical conductivity, it is preferable that the material of the columnar honeycomb structure 11 contains a silicon-silicon carbide composite or a ceramic mainly composed of silicon carbide. When the material of the columnar honeycomb structure 11 is said to be mainly composed of a silicon-silicon carbide composite, it means that the columnar honeycomb structure 11 contains 90% or more by mass of silicon-silicon carbide composites (total mass) of the entire structure. Here, the silicon-silicon carbide composite material contains silicon carbide particles as aggregate and silicon as a binder for binding the silicon carbide particles, and it is preferable that a plurality of silicon carbide particles are bound by silicon so as to form pores between the silicon carbide particles. When it is said that the material of the columnar honeycomb structure 11 is mainly composed of silicon carbide, it means that the columnar honeycomb structure 11 contains silicon carbide (total mass) in an amount of 90 mass% or more of the entire material.

When the columnar honeycomb structure 11 contains a silicon-silicon carbide composite material, the ratio of the "mass of silicon as a binder" contained in the columnar honeycomb structure 11 to the sum of the "mass of silicon carbide particles as aggregate" contained in the columnar honeycomb structure 11 and the "mass of silicon as a binder" contained in the columnar honeycomb structure 11 is preferably 10 to 40 mass%, and more preferably 15 to 35 mass%. If it is 10 mass% or more, the strength of the columnar honeycomb structure 11 is sufficiently maintained. If it is 40 mass% or less, the shape is more easily maintained during firing.

There are no restrictions on the shape of the cells in a cross section perpendicular to the extension direction of the cells 18, but a square, hexagon, octagon, or a combination of these is preferable. Of these, square and hexagonal shapes are preferable. By making the cell shape like this, the pressure loss when exhaust gas flows through the columnar honeycomb structure 11 is reduced, and the purification performance of the catalyst is excellent. From the viewpoint of easily achieving both structural strength and heating uniformity, a square shape is particularly preferable.

The thickness of the partition walls 19 that define the cells 18 is preferably 0.1 to 0.3 mm, and more preferably 0.15 to 0.25 mm. When the thickness of the partition walls 19 is 0.1 mm or more, it is possible to suppress a decrease in the strength of the honeycomb structure. When the thickness of the partition walls 19 is 0.3 mm or less, it is possible to suppress an increase in pressure loss when exhaust gas flows through the honeycomb structure when the honeycomb structure is used as a catalyst carrier to support the catalyst. In the present invention, the thickness of the partition walls 19 is defined as the length of the portion that passes through the partition walls 19 among the line segments connecting the centers of gravity of adjacent cells 18 in a cross section perpendicular to the extension direction of the cells 18.

The columnar honeycomb structure 11 preferably has a cell density of 40 to 150 cells/cm ² , more preferably 70 to 100 cells/cm ² , in a cross section perpendicular to the flow direction of the cells 18. By setting the cell density in such a range, it is possible to improve the purification performance of the catalyst while reducing the pressure loss when exhaust gas flows. When the cell density is 40 cells/cm ² or more, a sufficient catalyst carrying area is ensured. When the cell density is 150 cells/cm ² or less, when the columnar honeycomb structure 11 is used as a catalyst carrier to carry a catalyst, the pressure loss when exhaust gas flows is prevented from becoming too large. The cell density is a value obtained by dividing the number of cells by the area of one bottom surface portion of the columnar honeycomb structure 11 excluding the outer peripheral wall 12 portion.

Providing the outer peripheral wall 12 of the columnar honeycomb structure 11 is useful in terms of ensuring the structural strength of the columnar honeycomb structure 11 and suppressing leakage of the fluid flowing through the cells 18 from the outer peripheral wall 12. Specifically, the thickness of the outer peripheral wall 12 is preferably 0.1 mm or more, more preferably 0.15 mm or more, and even more preferably 0.2 mm or more. However, if the outer peripheral wall 12 is made too thick, it becomes too strong, and the strength balance with the partition wall 19 is lost, resulting in a decrease in thermal shock resistance. Therefore, the thickness of the outer peripheral wall 12 is preferably 1.0 mm or less, more preferably 0.7 mm or less, and even more preferably 0.5 mm or less. Here, the thickness of the outer peripheral wall 12 is defined as the thickness in the normal direction to the tangent of the outer peripheral wall 12 at the measurement point when the portion of the outer peripheral wall 12 to be measured for thickness is observed in a cross section perpendicular to the extension direction of the cells.

The partition walls 19 may be porous. The porosity of the partition walls 19 is preferably 35 to 60%, and more preferably 35 to 45%. If the porosity is 35% or more, deformation during firing is more easily suppressed. If the porosity is 60% or less, the strength of the honeycomb structure is sufficiently maintained. The porosity is a value measured using a mercury porosimeter.

The average pore diameter of the partition walls 19 of the columnar honeycomb structure 11 is preferably 2 to 15 μm, and more preferably 4 to 8 μm. When the average pore diameter is 2 μm or more, the electrical resistivity is prevented from becoming too large. When the average pore diameter is 15 μm or less, the electrical resistivity is prevented from becoming too small. The average pore diameter is a value measured using a mercury porosimeter.

(1-2. Electrode Layer)
Electrode layers 13a, 13b are disposed on the surface of the outer wall 12 of the columnar honeycomb structure 11. The electrode layers 13a, 13b may be a pair of electrode layers 13a, 13b disposed so as to face each other across the central axis of the columnar honeycomb structure 11.

There are no particular restrictions on the formation area of the electrode layers 13a and 13b, but from the viewpoint of increasing the uniform heat generation of the columnar honeycomb structure 11, it is preferable that each electrode layer 13a and 13b extend in a band shape on the outer surface of the outer peripheral wall 12 in the circumferential direction of the outer peripheral wall 12 and in the extension direction of the cells. Specifically, it is desirable that each electrode layer 13a and 13b extend over 80% or more of the length between both bottom surfaces of the columnar honeycomb structure 11, preferably over 90% or more of the length, and more preferably over the entire length, from the viewpoint of facilitating the spread of current in the axial direction of the electrode layers 13a and 13b.

The thickness of each electrode layer 13a, 13b is preferably 0.01 to 5 mm, and more preferably 0.01 to 3 mm. By setting the thickness within such a range, uniform heat generation can be improved. When the thickness of each electrode layer 13a, 13b is 0.01 mm or more, the electrical resistance is appropriately controlled and more uniform heat generation can be achieved. When the thickness is 5 mm or less, the risk of breakage during canning is reduced. The thickness of each electrode layer 13a, 13b is defined as the thickness in the normal direction to the tangent at the measurement point on the outer surface of each electrode layer 13a, 13b when the part of the electrode layer 13a, 13b whose thickness is to be measured is observed in a cross section perpendicular to the extension direction of the cell.

By making the electrical resistivity of each electrode layer 13a, 13b lower than that of the columnar honeycomb structure 11, electricity flows preferentially through the electrode layers 13a, 13b, and electricity spreads in the flow direction and circumferential direction of the cell when current is applied. The electrical resistivity of the electrode layers 13a, 13b is preferably 1/10 or less of the electrical resistivity of the columnar honeycomb structure 11, more preferably 1/20 or less, and even more preferably 1/30 or less. However, if the difference in electrical resistivity between the two becomes too large, current will concentrate between the ends of the opposing electrode layers 13a, 13b, causing uneven heat generation in the columnar honeycomb structure, so the electrical resistivity of the electrode layers 13a, 13b is preferably 1/200 or more of the electrical resistivity of the columnar honeycomb structure 11, more preferably 1/150 or more, and even more preferably 1/100 or more. In the present invention, the electrical resistivity of the electrode layers 13a and 13b is a value measured at 400° C. by a four-terminal method.

The material of each electrode layer 13a, 13b may be a metal, a conductive ceramic, or a composite material (cermet) of a metal and a conductive ceramic. Examples of metals include, for example, a single metal such as Cr, Fe, Co, Ni, Si, or Ti, or an alloy containing at least one metal selected from the group consisting of these metals. Examples of conductive ceramics include, but are not limited to, silicon carbide (SiC), and metal compounds such as metal silicides such as tantalum silicide (TaSi ₂ ) and chromium silicide (CrSi ₂ ). Specific examples of composite materials (cermets) of metals and conductive ceramics include composite materials of metal silicon and silicon carbide, composite materials of metal silicides such as tantalum silicide and chromium silicide, and composite materials in which one or more insulating ceramics such as alumina, mullite, zirconia, cordierite, silicon nitride, and aluminum nitride are added to one or more of the above metals from the viewpoint of reducing thermal expansion. As the material for the electrode layers 13a, 13b, among the various metals and conductive ceramics mentioned above, a combination of a metal silicide such as tantalum silicide or chromium silicide with a composite material of metal silicon and silicon carbide is preferred because it can be fired simultaneously with the columnar honeycomb structure portion, which contributes to simplifying the manufacturing process.

(1-3. Base layer)
In the embodiment of the present invention, the electrically heated carrier 10 is provided with a base layer 16 on the electrode layers 13a and 13b. The base layer 16 can be formed on the surfaces of the electrode layers 13a and 13b, and is formed in a substantially flat shape (specifically, curved so as to follow the outer surfaces of the electrode layers 13a and 13b). The base layer 16 is conductive. The base layer 16 may have a thermal expansion coefficient between the thermal expansion coefficient of the electrode layers 13a and 13b (the linear expansion coefficient of the electrode layers 13a and 13b is relatively small) and the thermal expansion coefficient of the metal electrodes 14a and 14b (the linear expansion coefficient of the metal electrodes 14a and 14b is relatively large). In this case, the base layer 16 has a function of absorbing the thermal expansion difference generated between the electrode layers 13a and 13b and the metal electrodes 14a and 14b.

The underlayer 16 can be made of conductive ceramics. The ceramics constituting the underlayer 16 include, but are not limited to, silicon carbide (SiC), metal compounds such as metal silicides such as tantalum silicide (TaSi ₂ ) and chromium silicide (CrSi ₂ ), and further include composites (cermets) consisting of a combination of one or more ceramics and one or more metals. Specific examples of cermets include composites of metal silicon and silicon carbide, composites of metal silicides such as tantalum silicide and chromium silicide, metal silicon and silicon carbide, and further composites in which one or more insulating ceramics such as alumina, mullite, zirconia, cordierite, silicon nitride, and aluminum nitride are added to one or more of the above metals from the viewpoint of reducing thermal expansion.

The number and arrangement of the underlayers 16 are not limited and can be set appropriately within the range required to fix the metal electrodes 14a and 14b. The shape of the underlayers 16 can be formed into any shape, such as a circle, an ellipse, or a polygon, in a plan view. From the viewpoints of productivity and practicality, it is preferable that the shape of the underlayers 16 is a circle or a rectangle.

(1-4. Metal electrode)
The metal electrodes 14a, 14b are connected to the base layer 16 by a joint 20. The metal electrodes 14a, 14b are connected to the base layer 16 by a joint 20. The metal electrodes 14a, 14b are connected to the base layer 16 by a joint 20. The metal electrodes 14a and 14b may be a pair of metal electrodes arranged to face each other across the central axis. When a voltage is applied through the electrode layers 13a and 13b, the metal electrodes 14a and 14b are energized and heated by Joule heat to form a columnar honeycomb structure. It is possible to heat the structure 11. Therefore, the electrically heated carrier 10 can be suitably used as a heater. The voltage to be applied is preferably 12 to 900 V, more preferably 64 to 600 V. The voltage to be applied can be changed as appropriate.

There are no particular restrictions on the material of the metal electrodes 14a, 14b, so long as it is a metal, and simple metals and alloys can be used, but from the standpoint of corrosion resistance, electrical resistivity, and linear expansion coefficient, for example, an alloy containing at least one selected from the group consisting of Cr, Fe, Co, Ni, and Ti is preferable, and stainless steel and Fe-Ni alloys are more preferable. The shape and size of the metal electrodes 14a, 14b are not particularly limited, and can be designed appropriately depending on the size and electrical conductivity of the electrically heated carrier 10.

Metal electrodes 14a, 14b may have two or more electrode portions 15. Each electrode portion 15 may be fixed to the outer surface of base layer 16. Here, electrode portion 15 may be fixed to base layer 16 by welding, or may be fixed to electrode layers 13a, 13b with a fixing layer formed by thermal spraying.

In the embodiment shown in Fig. 3, each of the metal electrodes 14a, 14b has three comb-shaped electrode portions 15, and each electrode portion 15 is fixed to two base layers 16. In this manner, the electrical connection between the comb-shaped electrode portions 15 and the electrode layers 13a, 13b may be realized by two or more base layers 16 spaced apart from each other.

Although the electrode portion 15 is shaped like a comb in FIG. 3, any shape can be adopted as long as it can be fixed to the base layer 16 and electrically connected to the electrode layers 13a, 13b, or as long as it can be fixed to the electrode layers 13a, 13b by thermal spraying.

(1-5. Antioxidant Layer)
The electrically heated carrier 10 in the embodiment of the present invention includes an anti-oxidation layer 21 for protecting the joint portion 20 from exhaust gas. In the present invention, the joint portion 20 and the anti-oxidation layer 21 for protecting the joint portion 20 may have various configurations. Each embodiment will be described in detail below with reference to the drawings.

[Embodiment 1]
4 shows a cross-sectional schematic diagram of the columnar honeycomb structure 11, the electrode layers 13a and 13b, the base layer 16, the joint portion 20, the metal electrodes 14a and 14b, and the oxidation prevention layer 21a in the first embodiment of the present invention. In the first embodiment shown in FIG. 4, a second base layer or a second electrode layer 17 for further relaxing thermal stress is provided between the electrode layers 13a and 13b and the base layer 16. The second base layer or the second electrode layer 17 may not be provided, or a third layer for further relaxing thermal stress may be further provided on the second base layer or the second electrode layer 17.

The joints 20 connecting the underlayer 16 and the metal electrodes 14a and 14b are joints formed between the underlayer 16 and the metal electrodes 14a and 14b by melting a part of the metal electrodes 14a and 14b when, for example, the metal electrodes 14a and 14b are provided on the underlayer 16 and laser welding or the like is performed from the metal electrodes 14a and 14b side. The example shown in FIG. 4 shows a schematic configuration in which columnar joints 20 are provided at three locations between the underlayer 16 and the metal electrodes 14a and 14b, each spaced apart. The joints 20 in this form can be formed, for example, by spot welding three locations by laser welding from the metal electrodes 14a and 14b side with the metal electrodes 14a and 14b provided on the underlayer 16. The size, shape, number, etc. of the joints 20 are not particularly limited.

The oxidation prevention layer 21a of the columnar honeycomb structure 11 in embodiment 1 of the present invention is provided continuously from the side of the metal electrodes 14a, 14b, sealing the gap 22, to the base layer 16, and further to the surface of the electrode layers 13a, 13b, as in the example of Figure 4. The oxidation prevention layer 21a is not limited to this, and may be provided from the side of the metal electrodes 14a, 14b to the middle of the side of the base layer 16, sealing the gap 22, as shown in Figure 5. In this way, the oxidation prevention layer 21a may be in any form as long as it is provided to seal the gap 22 between the base layer 16 and the metal electrodes 14a, 14b.

In addition, when the metal electrodes 14a, 14b are provided on the base layer 16 and ultrasonic welding is performed from the metal electrodes 14a, 14b side to connect the base layer 16 and the metal electrodes 14a, 14b, a joint portion 20a is formed over the entire surface between the base layer 16 and the metal electrodes 14a, 14b, as shown in Figure 6. In this case as well, the oxidation prevention layer 21a is provided so as to seal the gap 22 between the base layer 16 and the metal electrodes 14a, 14b.

The portion of the oxidation prevention layer 21a that seals the gap 22 between the underlayer 16 and the metal electrodes 14a, 14b is particularly susceptible to load due to thermal expansion of the metal electrodes 14a, 14b. For this reason, in order to increase the strength and suppress the occurrence of cracks, it is preferable to form the oxidation prevention layer 21a with a thickness of 10 μm or more. Furthermore, it is more preferable that the thickness of the oxidation prevention layer 21a is 10 to 100 μm.

The anti-oxidation layer 21a of the columnar honeycomb structure 11 in embodiment 1 of the present invention is provided from the outer surface of the electrode layer 13a, 13b to the outer surface of the metal electrodes 14a, 14b so as to seal the gap 22 between the base layer 16 and the metal electrodes 14a, 14b. Here, the gap 22 between the base layer 16 and the metal electrodes 14a, 14b is a gap of, for example, about several tens of μm between the base layer 16 and the metal electrodes 14a, 14b. In general, the joint parts 20, 20a may be oxidized by being exposed to exhaust gas diffusing from the gap 22 between the base layer 16 and the metal electrodes 14a, 14b. In contrast, in the columnar honeycomb structure 11 according to the first embodiment of the present invention, the anti-oxidation layer 21a is provided from the outer surfaces of the electrode layers 13a, 13b to the outer surfaces of the metal electrodes 14a, 14b so as to seal the gaps 22 between the base layer 16 and the metal electrodes 14a, 14b. This prevents the exhaust gas from entering through the gaps 22, and as a result, the oxidation of the joints 20, 20a can be effectively prevented.

The material of the oxidation prevention layer 21a may be ceramics, glass, or a composite material of ceramics and glass. The composite material may be, for example, a material containing 50 volume % or more of glass, more preferably 60 volume % or more, and even more preferably 70 volume % or more. Examples of the ceramics constituting the oxidation prevention layer 21a include SiO2 _- based, _{Al2O3 -} based, _SiO2 - _{Al2O3 -} based, _{SiO2 -} ZrO2 _- based, and SiO2- _Al2O3 - _{ZrO2 -} based ceramics. In addition, examples of glasses that may be used to form the antioxidant layer 21a include lead-free B ₂ O ₃ -Bi ₂ O _3- based, B ₂ O ₃ -ZnO-Bi ₂ O _3- based, B ₂ O ₃ -ZnO-based, V ₂ O ₅ -P ₂ O _5- based, SnO-P ₂ O _5- based, SnO-ZnO-P ₂ O ₅ -based, SiO ₂ -B ₂ O ₃ -Bi ₂ O _3- based, SiO ₂ -Bi ₂ O ₃ -Na ₂ O-based, and SiO ₂ -Al ₂ O ₃ -MgO-based glasses.

[Embodiment 2]
FIG. 7 is a cross-sectional schematic diagram showing the columnar honeycomb structure 11, the electrode layers 13a, 13b, the base layer 16, the bonding portion 20, the metal electrodes 14a, 14b and the oxidation prevention layer 21b in the second embodiment of the present invention.

The oxidation prevention layer 21b of the columnar honeycomb structure 11 in embodiment 2 of the present invention is provided on the surface of the joint portion 20. In this way, by providing the oxidation prevention layer 21b on the surface of the joint portion 20, it is possible to prevent the joint portion 20 from being exposed to exhaust gas. As a result, oxidation of the joint portion 20 can be effectively prevented. Furthermore, with this configuration, since the oxidation prevention layer 21b is provided on the surface of the joint portion 20, it is possible to reduce thermal stress on the oxidation prevention layer 21b due to thermal expansion of the metal electrodes 14a, 14b, etc. As a result, it is possible to more effectively prevent the occurrence of cracks.

In the example shown in FIG. 7, the anti-oxidation layer 21b is provided to fill the space from the surface of the joint 20 to the ends of the metal electrodes 14a and 14b, but is not limited to this. For example, the anti-oxidation layer 21b may be provided to fill the space from the surface of the joint 20 to partway through the ends of the metal electrodes 14a and 14b, as shown in FIG. 8. The anti-oxidation layer 21b may be formed using the same material as the anti-oxidation layer 21a shown in embodiment 1 of the present invention. The joint 20 may also be a joint 20a formed by ultrasonic welding, as shown in FIG. 6.

[Embodiment 3]
FIG. 9 is a schematic cross-sectional view of the columnar honeycomb structure 11, the electrode layers 13a, 13b, the base layer 16, the bonding portion 20, the metal electrodes 14a, 14b and the oxidation prevention layer 21c in the third embodiment of the present invention.

The oxidation prevention layer 21c of the columnar honeycomb structure 11 in embodiment 3 of the present invention is provided between the base layer 16 and the metal electrodes 14a, 14b, spaced apart from the joint portion 20. In this way, by providing the oxidation prevention layer 21c between the base layer 16 and the metal electrodes 14a, 14b, spaced apart from the joint portion 20, it is possible to suppress exposure of the joint portion 20 to exhaust gas. As a result, it is possible to effectively suppress oxidation of the joint portion 20. In addition, with this configuration, since the oxidation prevention layer 21c is provided between the base layer 16 and the metal electrodes 14a, 14b, it is possible to reduce thermal stress on the oxidation prevention layer 21c due to thermal expansion of the metal electrodes 14a, 14b. As a result, it is possible to effectively suppress the occurrence of cracks.

The oxidation prevention layer 21c can be formed using the same material as the oxidation prevention layer 21a shown in embodiment 1 of the present invention. The joint portion 20 may be a joint portion 20a formed by ultrasonic welding as shown in FIG. 6.

[Embodiment 4]
FIG. 10 is a schematic cross-sectional view of the columnar honeycomb structure 11, the electrode layers 13a, 13b, the base layer 16, the bonding portion 20b, the metal electrodes 14a, 14b and the oxidation prevention layer 21d in the fourth embodiment of the present invention.

The oxidation prevention layer 21d of the columnar honeycomb structure 11 in embodiment 4 of the present invention is filled between the base layer 16 and the metal electrodes 14a, 14b. In this way, by filling the oxidation prevention layer 21d between the base layer 16 and the metal electrodes 14a, 14b, the joint portion 20b can be prevented from being exposed to exhaust gas. As a result, the oxidation of the joint portion 20b can be effectively suppressed. In addition, with this configuration, since the oxidation prevention layer 21d is provided between the base layer 16 and the metal electrodes 14a, 14b, the thermal stress on the oxidation prevention layer 21d due to the thermal expansion of the metal electrodes 14a, 14b can be reduced. As a result, the occurrence of cracks can be effectively suppressed.

Figure 11 shows a schematic diagram of the bonding of the base layer 16 and the metal electrodes 14a, 14b of the columnar honeycomb structure 11 in embodiment 4 of the present invention by laser welding or the like. As shown in the upper diagram of Figure 11, first, a coating layer 23 made of an oxidation prevention layer forming material is provided on the base layer 16. Next, the metal electrodes 14a, 14b are placed on the coating layer 23. Next, spot welding is performed by laser welding or the like from above the metal electrodes 14a, 14b. At this time, by applying energy by laser welding or the like, the metal electrodes 14a, 14b melt and form a mixture with the oxidation prevention layer forming material of the lower coating layer 23. The mixture becomes the bonding portion 20b. The oxidation prevention layer forming material constituting the coating layer 23 can be formed using the same material as the oxidation prevention layer 21a shown in embodiment 1 of the present invention. Therefore, the bonding portion 20b is a mixture of metal and inorganic material such as glass.

Furthermore, by forming the joint area 20b as shown in FIG. 11, even if there are tiny pores between the joint areas 20b, the pores are filled with the anti-oxidation layer forming material, thereby further improving the oxidation resistance of the joint areas 20b.

[Embodiment 5]
FIG. 12 is a schematic cross-sectional view of the columnar honeycomb structure 11, electrode layers 13a, 13b, fixing layer 24, metal electrodes 14a, 14b and antioxidant layer 21e of an electrically heated carrier according to the fifth embodiment of the present invention.

In the electrically heated carrier in embodiment 5 of the present invention, electrode layers 13a, 13b are disposed on the surface of the outer wall of the columnar honeycomb structure 11 shown in embodiment 1, and metal electrodes 14a, 14b are provided on the electrode layers 13a, 13b. In addition, a fixing layer 24 is provided to cover the metal electrodes 14a, 14b, and an oxidation prevention layer 21e is provided to cover the fixing layer 24. The fixing layer 24 fixes the metal electrodes 14a, 14b to the electrode layers 13a, 13b.

In this way, by providing the fixing layer 24 to cover the metal electrodes 14a, 14b and further providing the oxidation prevention layer 21e to cover the fixing layer 24, it is possible to prevent the fixing layer 24, which is the joining site, from being exposed to exhaust gas. As a result, oxidation of the fixing layer 24 can be effectively prevented. Furthermore, with this configuration, the oxidation prevention layer 21e is provided on the fixing layer 24 that covers the metal electrodes 14a, 14b, so that thermal stress on the oxidation prevention layer 21e due to thermal expansion of the metal electrodes 14a, 14b can be reduced. As a result, the occurrence of cracks can be effectively prevented.

The fixing layer 24 in the fifth embodiment can be formed, for example, by thermal spraying. After providing the metal electrodes 14a, 14b on the electrode layers 13a, 13b, the fixing layer 24 can be formed by providing a material composed of a mixed spray material of NiCrAlY and mullite, etc., by thermal spraying so as to cover the metal electrodes 14a, 14b. In addition, the oxidation prevention layer 21e can be formed so as to cover the fixing layer 24 using a material similar to the oxidation prevention layer 21a shown in the first embodiment of the present invention.

[Embodiment 6]
Figures 13(a), 13(b), 13(c) and 13(d) show schematic cross-sectional diagrams of the columnar honeycomb structure 11, electrode layers 13a, 13b, second base layer or electrode layer 17, base layer 16, bonding portion 20d, metal electrodes 14a, 14b and antioxidant layers 21f, 21g, 21h, 21i of an electrically heated carrier in embodiment 6 of the present invention.

In the electrically heated carrier in embodiment 5 of the present invention, electrode layers 13a, 13b are disposed on the surface of the outer wall of the columnar honeycomb structure 11 shown in embodiment 1, and a second base layer or electrode layer 17 and base layer 16 are provided on the electrode layers 13a, 13b. The base layer 16 is joined to the metal electrodes 14a, 14b at the joint portion 20d by brazing the metal electrodes 14a, 14b.

In the embodiment shown in FIG. 13(a), the oxidation prevention layer 21f is continuously provided from the side of the metal electrodes 14a, 14b to the outer surface of the electrode layers 13a, 13b, and is configured to seal the gap between the base layer 16 and the metal electrodes 14a, 14b. In the embodiment shown in FIG. 13(b), the oxidation prevention layer 21g is continuously provided from the bottom surface of the metal electrodes 14a, 14b to the outer surface of the electrode layers 13a, 13b, and is configured to seal the gap between the base layer 16 and the metal electrodes 14a, 14b. In the embodiment shown in FIG. 13(c), a gap not having a joint portion 20d is provided between the metal electrodes 14a, 14b and the base layer 16, and an oxidation prevention layer 21h is provided in the gap so as to contact the joint portion 20d. In the embodiment shown in FIG. 13(d), a gap having no bond portion 20d is provided between the metal electrodes 14a, 14b and the underlayer 16, and an anti-oxidation layer 21i is provided in the gap, spaced apart from the bond portion 20d.

13(a), 13(b), 13(c), and 13(d), the anti-oxidation layers 21f, 21g, 21h, and 21i are provided to prevent the joint portion 20d from being exposed to exhaust gas. As a result, oxidation of the joint portion 20d can be effectively prevented.

By supporting a catalyst on the electrically heated carrier 10, the electrically heated carrier 10 can be used as a catalyst body. A fluid such as automobile exhaust gas can be flowed through the flow paths of the multiple cells 18. Examples of the catalyst include precious metal catalysts and other catalysts. Examples of the precious metal catalyst include three-way catalysts and oxidation catalysts in which precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) are supported on the surface of alumina pores and which contain co-catalysts such as ceria and zirconia, or NO _x storage reduction catalysts (LNT catalysts) containing alkaline earth metals and platinum as storage components for nitrogen oxides (NO _x ). Examples of catalysts that do not use precious metals include NO _x selective reduction catalysts (SCR catalysts) containing copper-substituted or iron-substituted zeolite. In addition, two or more catalysts selected from the group consisting of these catalysts may be used. There is no particular restriction on the method of supporting the catalyst, and it can be performed in accordance with the conventional method of supporting a catalyst on a honeycomb structure.

(2. Method for manufacturing electrically heated carrier)
Next, a method for manufacturing the electrically heated carrier 10 according to the present invention will be described by way of example. In one embodiment, the method for manufacturing the electrically heated carrier 10 according to the present invention includes a step A1 of obtaining an unfired honeycomb structure part with an electrode layer forming paste, a step A2 of firing the unfired honeycomb structure part with an electrode layer forming paste to obtain a columnar honeycomb structure, and a step A3 of welding a metal electrode to the columnar honeycomb structure.

Step A1 is a step of preparing a honeycomb molded body, which is a precursor of the honeycomb structure, and applying an electrode layer forming paste to the side of the honeycomb molded body to obtain an unfired honeycomb structure with an electrode layer forming paste. The honeycomb molded body can be prepared in accordance with the method of preparing a honeycomb molded body in a known method of manufacturing a honeycomb structure. For example, first, a forming raw material is prepared by adding metal silicon powder (metal silicon), a binder, a surfactant, a pore former, water, etc. to silicon carbide powder (silicon carbide). It is preferable that the mass of metal silicon is 10 to 40 mass% with respect to the total mass of the silicon carbide powder and the mass of the metal silicon. The average particle diameter of the silicon carbide particles in the silicon carbide powder is preferably 3 to 50 μm, and more preferably 3 to 40 μm. The average particle diameter of the metal silicon (metal silicon powder) is preferably 2 to 35 μm. The average particle size of silicon carbide particles and metallic silicon (metallic silicon particles) refers to the arithmetic mean size based on volume when the frequency distribution of particle sizes is measured by a laser diffraction method. Silicon carbide particles are fine particles of silicon carbide that constitute silicon carbide powder, and metallic silicon particles are fine particles of metallic silicon that constitute metallic silicon powder. Note that this is the blending of the forming raw materials when the material of the honeycomb structure part is a silicon-silicon carbide composite material, and when the material of the honeycomb structure part is silicon carbide, metallic silicon is not added.

Examples of binders include methyl cellulose, hydroxypropyl methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, etc. Among these, it is preferable to use methyl cellulose and hydroxypropoxyl cellulose in combination. The content of the binder is preferably 2.0 to 10.0 parts by mass when the total mass of the silicon carbide powder and the metallic silicon powder is 100 parts by mass.

The water content is preferably 20 to 60 parts by mass when the total mass of the silicon carbide powder and the silicon metal powder is 100 parts by mass.

As the surfactant, ethylene glycol, dextrin, fatty acid soap, polyalcohol, etc. can be used. These may be used alone or in combination of two or more. The content of the surfactant is preferably 0.1 to 2.0 parts by mass when the total mass of the silicon carbide powder and the metallic silicon powder is 100 parts by mass.

The pore-forming material is not particularly limited as long as it becomes pores after firing, and examples thereof include graphite, starch, foamed resin, water-absorbent resin, silica gel, etc. The content of the pore-forming material is preferably 0.5 to 10.0 parts by mass when the total mass of the silicon carbide powder and the metal silicon powder is 100 parts by mass. The average particle diameter of the pore-forming material is preferably 10 to 30 μm. If it is smaller than 10 μm, pores may not be sufficiently formed. If it is larger than 30 μm, the die may be clogged during molding. The average particle diameter of the pore-forming material refers to the arithmetic mean diameter based on volume when the frequency distribution of particle size is measured by the laser diffraction method. When the pore-forming material is a water-absorbent resin, the average particle diameter of the pore-forming material refers to the average particle diameter after water absorption.

Next, the obtained molding raw materials are kneaded to form a clay, and the clay is then extruded to produce a honeycomb molded body. A die having the desired overall shape, cell shape, partition wall thickness, cell density, etc. can be used during extrusion molding. Next, it is preferable to dry the obtained honeycomb molded body. If the length of the honeycomb molded body in the central axial direction is not the desired length, both bottom portions of the honeycomb molded body can be cut to the desired length. The honeycomb molded body after drying is called a dried honeycomb body.

Next, an electrode layer forming paste for forming the electrode layer is prepared. The electrode layer forming paste can be formed by adding various additives to raw material powders (metal powders, ceramic powders, etc.) that are mixed according to the required characteristics of the electrode layer, and kneading them. When the electrode layer has a laminated structure, the bonding strength between the metal terminal and the electrode layer tends to be improved by making the average particle diameter of the metal powder in the paste for the second electrode layer larger than the average particle diameter of the metal powder in the paste for the first electrode layer. The average particle diameter of the metal powder refers to the arithmetic mean diameter based on volume when the frequency distribution of particle size is measured by laser diffraction method.

Next, the obtained electrode layer forming paste is applied to the side of a honeycomb formed body (typically a dried honeycomb body) to obtain an unfired honeycomb structure part with electrode layer forming paste. The method of preparing the electrode layer forming paste and the method of applying the electrode layer forming paste to the honeycomb formed body can be performed in accordance with known manufacturing methods for honeycomb structures, but in order to give the electrode layer a lower electrical resistivity than the honeycomb structure part, the metal content can be made higher than that of the honeycomb structure part, or the particle size of the metal particles can be made smaller.

As a modified example of the manufacturing method of the columnar honeycomb structure, in step A1, the honeycomb formed body may be fired once before applying the electrode layer forming paste. That is, in this modified example, the honeycomb formed body is fired to produce a honeycomb fired body, and the electrode layer forming paste is applied to the honeycomb fired body.

In step A2, the unfired honeycomb structure part with the electrode layer forming paste is fired to obtain a columnar honeycomb structure. The unfired honeycomb structure part with the electrode layer forming paste may be dried before firing. Also, degreasing may be performed before firing to remove binders and the like. As firing conditions, it is preferable to heat at 1400 to 1500°C for 1 to 20 hours in an inert atmosphere such as nitrogen or argon. Also, after firing, it is preferable to perform oxidation treatment at 1200 to 1350°C for 1 to 10 hours to improve durability. The method of degreasing and firing is not particularly limited, and firing can be performed using an electric furnace, a gas furnace, or the like.

In step A3, a conductive material paste for forming a base layer is applied to the surface of the electrode layer on the columnar honeycomb structure. The conductive material paste thus prepared is applied in a predetermined arrangement using a curved printing machine or the like, dried, and then fired to form the base layer. As the conductive material paste, first, a ceramic raw material is prepared by mixing metal powder (metal powder of NiCr-based material, stainless steel, etc.) and oxide powder (oxide powder of Cd, alumina, mullite, etc.) in a volume ratio of 20 to 85 volume % metal and 15 to 80 volume % oxide powder. Next, 1 mass % binder, 1 mass % surfactant, and 20 to 40 mass % water are added to this ceramic raw material to prepare a base layer forming paste. The base layer may also be formed in a predetermined arrangement and shape by thermal spraying the conductive material.

Next, a metal electrode is fixed onto the base layer by welding. The welding method is described in detail below. First, a comb-shaped electrode is placed on the honeycomb structure on which the base layer has been formed, and laser welding or ultrasonic welding is performed on the areas where each comb-shaped electrode overlaps the base layer. The laser spot diameter when performing laser welding can be in the range of 0.5 to 3.0 mm. The vibration frequency when performing ultrasonic welding can be 20 kHz to 40 kHz, and the pressure can be in the range of 10 N to 30 N.

At this time, by performing multiple spot welds by laser welding, it is possible to form a joint 20 as shown in Figure 4. Also, by performing ultrasonic welding, it is possible to form a joint 20a as shown in Figure 6.

Next, an oxidation prevention layer is provided from the outer surface of the underlayer to the outer surface of the metal electrode so as to seal the gap between the underlayer and the metal electrode, thereby forming the oxidation prevention layer 21a as shown in Figures 4 to 6. At this time, after bonding the underlayer and the metal electrode, an oxidation prevention agent is sprayed on them with a spray or the like, and the resulting material is baked, preferably in a vacuum atmosphere, at 800 to 1100°C for 4 to 8 hours, thereby forming the oxidation prevention layer 21a.

In addition, by performing multiple spot welding by laser welding, it is possible to form the joint portion 20 as shown in Figures 7 to 9, and then form the oxidation prevention layers 21b, 21c as shown in Figures 7 to 9. In this case, an antioxidant is applied to the portions of the base layer other than the joint portion, and after the metal electrodes are joined by a method such as laser welding, the oxidation prevention layers 21b, 21c can be formed by firing at 800 to 1100°C for 4 to 8 hours, preferably in a vacuum atmosphere.

In addition, as shown in Figure 11, a coating layer made of an oxidation prevention layer forming material is provided between the base layer and the metal electrode, and then laser welding is performed from the metal electrode side to form an oxidation prevention layer 21d as shown in Figure 10.

(3. Exhaust Gas Purification Device)
The electrically heated carrier according to the embodiment of the present invention described above can be used in an exhaust gas purification device. The exhaust gas purification device has an electrically heated carrier and a can body that holds the electrically heated carrier. In the exhaust gas purification device, the electrically heated carrier is installed midway through an exhaust gas flow path for passing exhaust gas from an engine. As the can body, a metallic cylindrical member that houses the electrically heated carrier can be used.

The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

Example 1
(1. Preparation of cylindrical clay)
A ceramic raw material was prepared by mixing silicon carbide (SiC) powder and metal silicon (Si) powder in a mass ratio of 80:20. Hydroxypropyl methylcellulose was added as a binder and a water-absorbent resin was added as a pore-forming material to the ceramic raw material, and water was added to prepare a molding raw material. The molding raw material was kneaded by a vacuum clay kneader to prepare a cylindrical clay. The binder content was 7 parts by mass when the total of the silicon carbide (SiC) powder and the metal silicon (Si) powder was 100 parts by mass. The pore-forming material content was 3 parts by mass when the total of the silicon carbide (SiC) powder and the metal silicon (Si) powder was 100 parts by mass. The water content was 42 parts by mass when the total of the silicon carbide (SiC) powder and the metal silicon (Si) powder was 100 parts by mass. The average particle diameter of the silicon carbide powder was 20 μm, and the average particle diameter of the metal silicon powder was 6 μm. The average particle size of the pore-forming material was 20 μm. The average particle sizes of the silicon carbide powder, the metallic silicon powder and the pore-forming material refer to the arithmetic mean diameter on a volume basis when the frequency distribution of particle size is measured by a laser diffraction method.

(2. Preparation of dried honeycomb body)
The obtained cylindrical clay was molded using an extrusion molding machine with a checkerboard die structure to obtain a cylindrical honeycomb molded body in which each cell shape in a cross section perpendicular to the flow direction of the cells is a square. This honeycomb molded body was dried by high-frequency dielectric heating, and then dried at 120°C for 2 hours using a hot air dryer, and both bottom surfaces were cut by a predetermined amount to produce a dried honeycomb body.

(3. Preparation of electrode layer forming paste)
Metallic silicon (Si) powder, silicon carbide (SiC) powder, methyl cellulose, glycerin, and water were mixed with a rotation and revolution agitator to prepare an electrode layer forming paste. The Si powder and the SiC powder were mixed so that the volume ratio of the Si powder to the SiC powder was 40:60. In addition, when the total of the Si powder and the SiC powder was 100 parts by mass, the methyl cellulose was 0.5 parts by mass, the glycerin was 10 parts by mass, and the water was 38 parts by mass. The average particle diameter of the metallic silicon powder was 6 μm. The average particle diameter of the silicon carbide powder was 35 μm. These average particle diameters refer to the arithmetic mean diameter based on the volume when the frequency distribution of the particle size was measured by the laser diffraction method.

(4. Application and Firing of Electrode Layer Forming Paste)
Next, this electrode layer forming paste was applied to the dried honeycomb body with an appropriate area and film thickness using a curved surface printing machine, and then dried at 120°C for 30 minutes in a hot air dryer. After that, it was fired together with the dried honeycomb body at 1400°C for 3 hours in an Ar atmosphere to form a columnar honeycomb structure.

(5. Preparation of Undercoat Layer Forming Paste)
A ceramic raw material was prepared by mixing metal powder (metal powder of NiCr-based material, stainless steel, etc.) and oxide powder (oxide powder of Cd, alumina, mullite, etc.) at a volume ratio of 20-85% metal and 15-80% oxide powder. A paste raw material was prepared by adding 1 mass% binder, 1 mass% surfactant, and 20-40 mass% water to this ceramic raw material. The average particle size of the metal powder measured by laser diffraction was 10 μm, and the average particle size of the oxide powder was 5 μm.

(6. Application and firing of undercoat layer forming paste)
The above-mentioned undercoat layer forming paste was applied to the electrode layer of the columnar honeycomb structure by a curved surface printing machine, and then dried at 120° C. for 30 minutes in a hot air dryer, and then fired at 1100° C. for 1 hour in an Ar atmosphere.

The honeycomb structure had a circular bottom with a diameter of 100 mm and a height (length of the cells in the flow path direction) of 100 mm. The cell density was 93 cells/ ^cm2 , the thickness of the partition walls was 101.6 μm, the porosity of the partition walls was 45%, and the average pore diameter of the partition walls was 8.6 μm. The thickness of the electrode layer was 0.3 mm, and the thickness of the base layer was 0.2 mm. When the electrical resistivity at 400° C. was measured by the four-terminal method using test pieces made of the same material as the honeycomb structure, the electrode layer, and the base layer, it was 5 Ωcm, 0.01 Ωcm, and 0.001 Ωcm, respectively.

(7. Fixation of the electrodes)
A comb-shaped electrode was placed on the honeycomb structure on which the base layer was formed, and the overlapping portions of each comb-shaped electrode and the base layer were laser-welded with a diameter of φ0.5 mm in Examples 1 to 6 and Comparative Example 1. Ultrasonic welding was performed in Examples 7 to 11 and Comparative Example 2. Joining was performed by brazing in Examples 12 to 16 and Comparative Example 3.
Next, for Examples 1 to 16, an antioxidant layer was formed in the following manner.
The antioxidant layers in Examples 1 to 3 were provided as shown in FIG. 4 (Embodiment 1), the antioxidant layers in Examples 7 to 9 were provided as shown in FIG. 6 (Embodiment 1), and the antioxidant layers in Examples 12 to 14 were provided as shown in FIG. 13(a).
The oxidation-preventing layers in Examples 4 and 10 were provided as shown in FIG. 7 (Embodiment 2), and the oxidation-preventing layer in Example 15 was provided as shown in FIG. 13(b).
The oxidation-preventing layers in Examples 5 and 11 were provided as shown in FIG. 9 (Embodiment 3), and the oxidation-preventing layer in Example 16 was provided as shown in FIG. 13(d).
The oxidation prevention layer of Example 6 was provided as shown in FIG. 10 (Embodiment 4).
SiO ₂ --Al ₂ O ₃ --MgO was used as the material for the oxidation-preventing layers in all of Examples 1 to 16. The thickness of each oxidation-preventing layer is shown in Table 1 below.

(8. Oxidation Resistance Evaluation Test)
The oxidation resistance evaluation test was performed on the honeycomb structure to which a pair of metal electrodes was fixed by the above method. In the oxidation resistance evaluation test, a sample in which a disk-shaped base layer having a diameter of 5 mm and a thickness of 0.3 mm was arranged in a 5 x 4 row with the center distance between adjacent base layers set to 5 mm was placed in a heating furnace and heated at 1000 ° C. for 50 hours in an air atmosphere. The resistance increase rate relative to the initial resistance value of the sample was used as an indicator of the oxidation state, and it was determined that the smaller the resistance increase rate, the greater the oxidation inhibition effect of the present invention. As the resistance value, the resistance between two points on the base layer was measured at a total of 12 points by a four-wire resistance measurement method using a Kelvin probe, and the average value of these was calculated. The conduction path of the sample was set in the order of (1) base layer surface, (2) base layer, (3) electrode layer, (4) base layer, and (5) base layer surface. The evaluation results are shown in Table 1.

(9. Discussion)
Regardless of the bonding method, an oxidation suppression effect was obtained at the bonding site connecting the underlayer and the metal electrode in all of Examples 1 to 16. Among them, the magnitude of the oxidation suppression effect differed depending on the form of the oxidation prevention layer, and further, the oxidation suppression effect differed among the forms of the oxidation prevention layer shown in embodiment 1 (Examples 1 to 3, 7 to 9, and 12 to 14).
Among the configurations of the antioxidant layer shown in embodiment 1 (Examples 1 to 3, 7 to 9, and 12 to 14), Examples 3 and 14, in which the antioxidant layer was 200 μm thick, had the smallest oxidation suppression effect, which is believed to be due to the fact that the antioxidant layer was so thick that cracks were generated in the antioxidant layer due to the difference in thermal expansion between the antioxidant layer and the underlayer and the metal electrode. For the same reason, when the crack state was checked, Examples 1 and 12, in which the antioxidant layer was 10 μm thick, had smaller cracks than Examples 2 and 13, in which the antioxidant layer was 100 μm thick. For this reason, it is believed that the difference in oxidation suppression effect depending on the thickness of the antioxidant layer is due to cracks.
Next, when the forms of the antioxidant layer shown in Embodiments 2 to 4 are compared in Examples 4 to 6, the oxidation suppression effect is as follows: form of the antioxidant layer shown in Embodiment 3 of Example 5 < form of the antioxidant layer shown in Embodiment 2 of Example 4 < form of the antioxidant layer shown in Embodiment 4 of Example 6. This is considered to be the result of the amount of the antioxidant film filled between the metal electrode and the underlayer affecting the oxygen blocking ability, since, as described above, the antioxidant layer is provided in the embodiment 2 of Example 4 as shown in Fig. 7 and the antioxidant layer is provided in the embodiment 3 of Example 5 as shown in Fig. 9.
As described above, in embodiment 4 of example 6, an anti-oxidation layer is provided as shown in FIG. 10 . Since the anti-oxidation layer covers the entire periphery of the joint, even if oxygen penetrates through a part of the anti-oxidation layer due to a crack or the like, the anti-oxidation effect can be maintained, and therefore, it is considered that this has the greatest anti-oxidation effect.

10 Electrically heated carrier 11 Columnar honeycomb structure 12 Outer peripheral wall 13a, 13b Electrode layer 14a, 14b Metal electrode 15 Electrode portion 16 Base layer 17 Second base layer or electrode layer 18 Cell 19 Partition wall 20, 20a, 20b, 20c, 20d Joint portion 21, 21a, 21b, 21c, 21d, 21e, 21f, 21g, 21h, 21i Antioxidant layer 22 Gap 23 Coat layer 24 Fixing layer

Claims (4)

A ceramic pillar-shaped honeycomb structure having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and defining a plurality of cells that form flow paths penetrating from one end face to the other end face;
An electrode layer disposed on a surface of an outer peripheral wall of the columnar honeycomb structure;
a conductive underlayer provided on the electrode layer;
a metal electrode connected to the underlayer by a bonding site;
an anti-oxidation layer for protecting the joint from exhaust gas;
Equipped with
An electrically heated carrier, in which the antioxidant layer is provided from at least midway along the side of the base layer over a portion of the outer surface of the metal electrode in a direction from the outer surface of the electrode layer to the outer surface of the metal electrode so as to seal the gap between the base layer and the metal electrode. A ceramic pillar-shaped honeycomb structure having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and defining a plurality of cells that form flow paths penetrating from one end face to the other end face;
An electrode layer disposed on a surface of an outer peripheral wall of the columnar honeycomb structure;
a conductive underlayer provided on the electrode layer;
a metal electrode connected to the underlayer by a bonding portion;
an anti-oxidation layer for protecting the joint from exhaust gas;
Equipped with
An electrically heated carrier, wherein the anti-oxidation layer is provided between the base layer and the metal electrode and spaced apart from the joint portion. An electrically heated carrier as described in claim 1 or 2, wherein the electrode layer arranged on the surface of the outer wall of the columnar honeycomb structure is a pair of electrode layers arranged on the surface of the outer wall of the columnar honeycomb structure so as to face each other across the central axis of the columnar honeycomb structure. An electrically heated carrier according to any one of claims 1 to 3 ;
A metallic tubular member for holding the electrically heated carrier;
An exhaust gas purification device having the above structure.

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