JP2022135885A - Honeycomb structure, electrically heated carrier, and exhaust gas purification device - Google Patents

Abstract

To provide a honeycomb structure, an electrically heated carrier, and an exhaust gas purification device capable of reducing a decrease in electrical resistance when the temperature rises, facilitating constant application of electric power over time, and suppressing a rapid temperature rise.SOLUTION: A honeycomb structure 20 according to the present invention includes a honeycomb structure portion 10 having an outer peripheral wall 12 and a partition wall 13 arranged inside the outer peripheral wall 12 and partitioning and forming a plurality of cells 16 forming a flow path extending from one end face to the other end face, and a pair of electrode layers 14a and 14b provided on the surface of the outer peripheral wall 12 of the honeycomb structure 10 so as to face each other across the central axis of the honeycomb structure 10, and the honeycomb structure 10 is made of ceramics having NTC properties, and the electrode layers 14a and 14b are made of materials having PTC properties.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a honeycomb structure, an electrically heated carrier, and an exhaust gas purification device.

Patent Document 1 below proposes the use of a honeycomb structure as an electrically heated carrier. A honeycomb structure includes a tubular honeycomb structure body having porous partition walls and an outer peripheral wall that partition and form a plurality of cells, and a pair of electrode parts disposed on side surfaces of the honeycomb structure body, and a catalyst carrier. In addition, it is configured to function as a heater by applying a voltage. The partition wall and the outer peripheral wall are mainly composed of a silicon-silicon carbide composite material or silicon carbide, and the electrode part is mainly composed of silicon carbide particles and silicon.

For example, as shown in Patent Literature 2 below, etc., silicon carbide is known to have a characteristic (NTC characteristic) that electrical resistance decreases as temperature increases. The honeycomb structure disclosed in Patent Document 1 contains silicon carbide in the honeycomb structure portion and the electrode portion, and has NTC characteristics.

WO2011/125815 JP-A-7-89764

In an electrically heated carrier that functions as a heater by applying a voltage, it is not preferable from the viewpoint of temperature control of the electrically heated carrier that the electrical resistance fluctuates due to temperature changes. On the other hand, if the electrical resistance fluctuation due to temperature change is small, it becomes easier to control the voltage and current applied for temperature control. In addition, when the electrical resistance of the electrically heated carrier is greatly lowered when the temperature of the electrically heated carrier rises, the electric current tends to flow, and the temperature of the electrically heated carrier may rise rapidly. In particular, when a honeycomb structure having NTC characteristics is used, an increase in the temperature of the honeycomb structure causes a decrease in electrical resistance, which may result in a partial excessive current flow and a rapid temperature rise.

The present invention has been made in consideration of the above problems, and is a honeycomb structure that can reduce the decrease in electrical resistance when the temperature rises, can easily apply electric power uniformly over time, and can suppress a rapid temperature rise. , to provide an electrically heated carrier and an exhaust gas purifier.

A honeycomb structure according to the present invention is a honeycomb structure part having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and partitioning and forming a plurality of cells forming a flow path extending from one end face to the other end face. and a pair of electrode layers provided on the surface of the outer peripheral wall of the honeycomb structure so as to face each other across the central axis of the honeycomb structure, wherein the honeycomb structure is made of ceramics having NTC characteristics, The electrode layer is made of a material having PTC characteristics.

An electrically heated carrier according to the present invention comprises the honeycomb structure described above and electrode terminals electrically connected to the electrode layers of the honeycomb structure.

An exhaust gas purifier according to the present invention has the above-described electrically heated carrier and a can holding the electrically heated carrier.

According to the honeycomb structure, the electrically heated carrier, and the exhaust gas purifying device of the present invention, the honeycomb structure is made of ceramics having NTC properties, and the electrode layers are made of material having PTC properties. It is possible to reduce the decrease in electrical resistance over time, making it easier to apply a constant power over time and suppressing a rapid temperature rise.

1 is a schematic external view of a honeycomb structure according to an embodiment of the present invention; FIG. FIG. 3 is a schematic cross-sectional view perpendicular to the extending direction of the cells of the electrode layer provided on the honeycomb structure portion of the electrically heated carrier and the electrode terminal provided on the electrode layer in the embodiment of the present invention.

Embodiments of a honeycomb structure, an electrically heated carrier, and an exhaust gas purifier according to the present invention will be described below with reference to the drawings. Various changes, modifications and improvements can be made based on the knowledge of those skilled in the art without departing from the scope of the invention.

<Honeycomb structure and electrically heated carrier>
FIG. 1 shows a schematic external view of a honeycomb structure 20 according to an embodiment of the present invention. FIG. 2 shows electrode layers 14a and 14b provided on the honeycomb structure portion 10 of the electrically heated carrier 30 in the embodiment of the present invention, and electrode terminals 15a and 15b provided on the electrode layers 14a and 14b. FIG. 3 shows a schematic cross-sectional view perpendicular to the extending direction of the cell 16. FIG.

(1. Honeycomb structure)
The honeycomb structure 20 includes a honeycomb structure portion 10 and a pair of electrode layers 14a and 14b. The honeycomb structure part 10 is a columnar member made of ceramics, and has an outer peripheral wall 12 and a plurality of cells 16 arranged inside the outer peripheral wall 12 and forming a flow path extending from one end face to the other end face. It has a partition wall 13 to form. A columnar shape can be understood as a three-dimensional shape having a thickness in the extending direction of the cells 16 (the axial direction of the honeycomb structure 10). The ratio (aspect ratio) between the axial length of the honeycomb structure 10 and the diameter or width of the end surface of the honeycomb structure 10 is arbitrary. The columnar shape may also include a shape (flat shape) in which the length in the axial direction of the honeycomb structure body 10 is shorter than the diameter or width of the end face.

The outer shape of the honeycomb structure part 10 is not particularly limited as long as it is columnar. Other shapes, such as pillars, octagons, etc., are also possible. In order to improve heat resistance (to suppress cracks entering the circumferential direction of the outer peripheral wall), the size of the honeycomb structure part 10 is preferably such that the area of the end face is 2000 to 20000 mm ² , more preferably 5000 to 15000 mm ² . is more preferable.

Although the shape of the cells in the cross section perpendicular to the extending direction of the cells 16 is not limited, it is preferably square, hexagonal, octagonal, or a combination thereof. Among these, when the honeycomb structure member 10 is used as a catalyst carrier to carry a catalyst, the pressure loss when exhaust gas is flowed is small, and the purification performance of the catalyst is excellent. A rectangular shape is more preferred. A hexagonal shape is even more preferable from the viewpoint that the purification performance of the catalyst can be improved.

The thickness of the partition walls 13 defining the cells 16 is preferably 0.1 to 0.3 mm, more preferably 0.1 to 0.2 mm. When the thickness of the partition wall 13 is 0.1 mm or more, it is possible to suppress the strength of the honeycomb structure portion 10 from decreasing. Since the partition wall 13 has a thickness of 0.3 mm or less, when the honeycomb structure 10 is used as a catalyst carrier to support a catalyst, it is possible to suppress an increase in pressure loss when exhaust gas is flowed. In the present invention, the thickness of the partition wall 13 is defined as the length of the portion of the line segment connecting the centers of gravity of adjacent cells 16 passing through the partition wall 13 in a cross section perpendicular to the extending direction of the cells 16 .

The honeycomb structure part 10 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 extending direction of the cells 16 . By setting the cell density within such a range, the purification performance of the catalyst can be enhanced while reducing the pressure loss when the exhaust gas flows. When the cell density is 40 cells/cm ² or more, a sufficient catalyst supporting area is ensured. When the cell density is 150 cells/cm ² or less, when the honeycomb structure 10 is used as a catalyst carrier to support a catalyst, it is possible to suppress an increase in pressure loss when exhaust gas is flowed. The cell density is a value obtained by dividing the number of cells by the area of one end face portion of the honeycomb structure 10 excluding the outer peripheral wall 12 portion.

Providing the outer peripheral wall 12 in the honeycomb structure 10 is useful from the viewpoint of ensuring the structural strength of the honeycomb structure 10 and suppressing leakage of the fluid flowing through the cells 16 from the outer peripheral wall 12 . Specifically, the thickness of the outer peripheral wall 12 is preferably 0.05 mm or more, more preferably 0.10 mm or more, and even more preferably 0.15 mm or more. However, if the outer peripheral wall 12 is too thick, the strength becomes too high, and the strength balance with the partition wall 13 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 measured in the direction normal to the tangential line of the outer peripheral wall 12 at the point of measurement when the portion of the outer peripheral wall 12 whose thickness is to be measured is observed in a cross section perpendicular to the extending direction of the cell. Defined as thickness.

The honeycomb structure part 10 has electrical conductivity. The volume resistivity of the honeycomb structure portion 10 is not particularly limited as long as it can generate heat by Joule heat when an electric current is applied. . In the present invention, the volume resistivity of the honeycomb structure body 10 is a value measured at 25° C. by a four-probe method.

The honeycomb structure portion 10 is made of ceramics having NTC characteristics (characteristics in which electrical resistance decreases as temperature increases). Having NTC characteristics means, for example, that the honeycomb structure portion, which will be described later, exhibits a negative electrical resistance increase rate. The material of the honeycomb structure 10 is not limited, but can be selected from non-oxide ceramics such as silicon carbide, silicon nitride and aluminum nitride. A silicon carbide-metal silicon composite material, a silicon carbide/graphite composite material, or the like can also be used. Among these, from the viewpoint of achieving both heat resistance and conductivity, the material of the honeycomb structure 10 preferably contains a silicon-silicon carbide composite material or ceramics containing silicon carbide as a main component. When it is said that the material of the honeycomb structure part 10 is mainly composed of the silicon-silicon carbide composite material, the honeycomb structure part 10 contains the silicon-silicon carbide composite material (total mass) in an amount of 90% by mass or more of the whole. means that it contains Here, the silicon-silicon carbide composite material contains silicon carbide particles as an aggregate and silicon as a binder that binds the silicon carbide particles, and a plurality of silicon carbide particles are interposed between the silicon carbide particles. It is preferably bonded by silicon so as to form pores. When it is said that the material of the honeycomb structure 10 contains silicon carbide as a main component, it means that the honeycomb structure 10 contains 90% by mass or more of silicon carbide (total mass). .

The honeycomb structure 10 preferably has an electrical resistance increase rate of -80 to -10%. The rate of increase in electrical resistance of the honeycomb structure portion 10 is obtained by measuring the volume resistivity (Ω cm) at two points at 50°C and 500°C by the four-probe method, and calculating the volume resistivity at 50°C from the volume resistivity at 500°C. It can be obtained by dividing the value derived by subtracting the modulus by the volume resistivity at 50° C. and multiplying by 100. If the rate of increase in electrical resistance is -80% or more, the change in electrical resistance during electrical heating can be reduced, making it easier to apply constant power over time during electrical conduction. When the electrical resistance increase rate of the honeycomb structure 10 is -10% or less, the honeycomb structure 10 exhibits NTC characteristics, and the honeycomb structure 10 uses a silicon-silicon carbide composite material or ceramics containing silicon carbide as a main component. can do. The honeycomb structure body 10 preferably has an electric resistance increase rate of -70 to -20%, and even more preferably -70 to -30%.

It is preferable that the porosity of the honeycomb structure body 10 is higher than that of the electrode layers 14a and 14b. When the porosity satisfies this relationship, when the honeycomb structure 20 is used as a catalyst carrier to support a catalyst, the honeycomb structure body 10 having a high porosity easily supports the catalyst, and the electrode layer 14a having a low porosity. It is difficult for the catalyst to be supported on 14b. As a result, the catalyst can be efficiently supported on the honeycomb structure 10 through which the exhaust gas passes, and the purification performance of the catalyst tends to be excellent. The honeycomb structure body 10 preferably has a porosity of 35 to 60%, more preferably 35 to 45%. The porosity is a value measured with a mercury porosimeter.

The honeycomb structure portion 10 preferably has a thermal expansion coefficient of 4.0 to 4.75 ppm/K, more preferably 4.0 to 4.6 ppm/K. The thermal expansion coefficient refers to a linear thermal expansion coefficient of 40 to 800°C measured by a method conforming to JIS R1618:2002. As a thermal dilatometer, "TD5000S (trade name)" manufactured by BrukerAXS can be used.

(2. Electrode layer)
A pair of electrode layers 14a and 14b are provided on the surface of the outer peripheral wall 12 of the honeycomb structure 20 so as to face each other with the central axis of the honeycomb structure 10 interposed therebetween. The electrode layers 14a and 14b are made of a material having PTC characteristics (characteristics in which electrical resistance increases as temperature increases). Having a PTC characteristic means, for example, that the electrical resistance increase rate of the electrode layer, which will be described later, exhibits a positive value.

In the honeycomb structure 20 and the electrically heated carrier 30 according to the embodiment of the present invention, the honeycomb structure 10 is made of ceramics having NTC properties, and the electrode layers 14a and 14b are made of materials having PTC properties. By controlling the electrical resistance between the honeycomb structure 10 and the electrode layers 14a and 14b, it is possible to control the balance of the electrical resistance of the entire electrically heated carrier. A honeycomb structure 20 and an electrically heated carrier 30 which are easy to obtain can be obtained.

It is preferable that the coefficient of thermal expansion of the electrode layers 14 a and 14 b is larger than the coefficient of thermal expansion of the honeycomb structure 10 . When the coefficient of thermal expansion satisfies this relationship, when the electrode terminals 15a and 15b are disposed on the electrode layers 14a and 14b to form the electrically heated carrier 30, the heat of the electrode layers 14a and 14b and the electrode terminals 15a and 15b is reduced. The difference in coefficient of expansion is reduced, and the electrically heated carrier 30 is excellent in thermal shock resistance. The thermal expansion coefficient of the electrode layers 14a, 14b is preferably 4.5-10 ppm/K, more preferably 4.5-7 ppm/K. The thermal expansion coefficients of the electrode layers 14a and 14b can be measured by the same method as the method for measuring the thermal expansion coefficient of the honeycomb structure 10 described above.

It is preferable that the electrode layers 14a and 14b have an electrical resistance increase rate of 2 to 40%. The electrical resistance increase rate of the electrode layers 14a and 14b is determined by the four-terminal method, similarly to the electrical resistance increase rate of the honeycomb structure portion 10 described above, by measuring the volume resistivity (Ω·cm) at two points at 50° C. and 500° C. is measured, and the value derived by subtracting the volume resistivity at 50°C from the volume resistivity at 500°C is divided by the volume resistivity at 50°C and multiplied by 100. When the rate of increase in electrical resistance is 2% or more, the electrical resistance of the electrode layers 14a and 14b during electrical heating increases due to the PTC characteristics, which compensates for the decrease in electrical resistance during electrical heating due to the NTC characteristics of the honeycomb structure portion 10. It is possible to make it easier to apply power uniformly over time. When the rate of increase in electrical resistance of the electrode layers 14a and 14b is 40% or less, Joule heating due to the increase in resistance of the electrode layers 14a and 14b during electrical heating can be reduced. More preferably, the electrical resistance increase rate of the electrode layers 14a, 14b is 5 to 35%, and even more preferably 10 to 30%.

The material of the electrode layers 14a and 14b can be a mixture of a metal or a metal compound and oxide ceramics. The metal may be either a single metal or an alloy, and includes silicon, aluminum, iron, stainless steel, titanium, tungsten, Ni--Cr alloys, and the like. Examples of metal compounds include materials other than oxide ceramics, such as metal oxides, metal nitrides, metal carbides, metal silicides, metal borides, and composite oxides. The metal or metal compound may be used singly or in combination of two or more. Examples of oxide ceramics include glass, cordierite, and mullite. The oxide ceramics may be used singly or in combination of two or more. Among these, a mixture containing at least stainless steel and glass is more preferable because the electrical resistance is easily adjusted and the durability is superior.

The electrode layers 14a and 14b may be made of a mixture of carbon and ceramics. Examples of ceramics include glass, cordierite, mullite, silicon carbide, silicon nitride, and zirconia. Ceramics may be used singly or in combination of two or more.

Although there are no particular restrictions on the regions where the electrode layers 14a and 14b are formed, from the viewpoint of improving the uniform heat generation property of the honeycomb structure body 10, the electrode layers 14a and 14b are formed on the outer surface of the outer peripheral wall 12 around the periphery of the outer peripheral wall 12. It is preferable to extend in a band shape in the direction and the extending direction of the cells. Specifically, each of the electrode layers 14a and 14b extends over 80% or more of the length between both end faces of the honeycomb structure body 10, preferably over 90% or more of the length, and more preferably over the entire length. From the viewpoint that the current is likely to spread in the axial direction of the electrode layers 14a and 14b, it is preferable that the electrodes 14a and 14b extend in the same direction. By forming the pair of electrode layers 14a and 14b in a strip shape in this way, it is easier to suppress a rapid temperature rise. The reason for this is that when the electrical resistance of a portion of the honeycomb structure 10 having the NTC characteristic decreases and the temperature of the portion rises locally, the electrode layer 14a near the region of the honeycomb structure 10, It is presumed that the temperature of a part of 14b rises and the electrical resistance rises. As a result, the current flows through the electrode layers 14a and 14b other than the electrode layers 14a and 14b whose electric resistance has increased, and then flows into the honeycomb structure 10, so that the honeycomb structure 10 as a whole has a uniform temperature. It is thought that

The thickness of each electrode layer 14a, 14b is preferably 0.01 to 5 mm, more preferably 0.01 to 3 mm. Uniform heat build-up can be enhanced by setting it to such a range. When the thickness of each of the electrode layers 14a and 14b is 0.01 mm or more, the electrical resistance is appropriately controlled, and heat can be generated more uniformly. If it is 5 mm or less, the risk of breakage during canning is reduced. The thickness of each of the electrode layers 14a and 14b is determined by observing the section of the electrode layers 14a and 14b whose thickness is to be measured in a cross section perpendicular to the extending direction of the cell. is defined as the thickness normal to the tangent at

(3. Electrode terminal)
The electrode terminals 15a and 15b may be formed in a columnar shape, or may be branched into a plurality of comb-tooth-shaped electrodes, and each of the branches is formed to have a contact point connected to the electrode layers 14a and 14b. good too. Electrode terminals 15a and 15b are disposed on and electrically connected to electrode layers 14a and 14b. Accordingly, when a voltage is applied to the electrode terminals 15a and 15b, it is possible to conduct electricity and heat the honeycomb structure 10 by Joule heat. Therefore, the honeycomb structure 10 can also be suitably used as a heater. The applied voltage is preferably 12 to 900 V, more preferably 48 to 600 V, but the applied voltage can be changed as appropriate.

The material of the electrode terminals 15a and 15b may be metal. As the metal, a single metal, an alloy, or the like can be used, but from the viewpoint of corrosion resistance, volume resistivity, and coefficient of linear expansion, for example, at least one selected from the group consisting of Cr, Fe, Co, Ni, and Ti. It is preferable to use an alloy containing the metal, more preferably stainless steel and an Fe—Ni alloy. The shape and size of the electrode terminals 15a and 15b are not particularly limited, and can be appropriately designed according to the size of the electrically heated carrier, current-carrying performance, and the like.

The electrode terminals 15a and 15b may be made of ceramics. Ceramics include, but are not limited to, silicon carbide (SiC), metal compounds such as metal silicides such as tantalum silicide ( _TaSi2 ) and chromium silicide ( _CrSi2 ), as well as one or more A composite material (cermet) containing a metal can be mentioned. Specific examples of cermets include composite materials of silicon and silicon carbide, composite materials of metal silicide such as tantalum silicide and chromium silicide, metal silicon and silicon carbide, and furthermore, one or more of the above metals are heat-treated. Composite materials to which one or more kinds of insulating ceramics, such as alumina, mullite, zirconia, cordierite, silicon nitride, and aluminum nitride, are added from the viewpoint of expansion reduction. The material of the electrode terminals 15a and 15b may be the same as the material of the electrode layers.

Moreover, when the electrode terminals 15a and 15b are terminals made of ceramics, metal terminals may be joined to the tips thereof. The connection between the ceramic terminal and the metal terminal can be performed by caulking, welding, a conductive adhesive, or the like. As a material for the metal terminal, a conductive metal such as an iron alloy or a nickel alloy can be used.

By supporting a catalyst on the electrically heated carrier 30, the electrically heated carrier 30 can be used as a catalyst body. Fluid, such as automobile exhaust gas, can flow through the flow paths of the plurality of cells 16 . Examples of catalysts include noble metal-based catalysts and other catalysts. As noble metal catalysts, noble metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) are supported on the surface of alumina pores, and three-way catalysts and oxidation catalysts containing co-catalysts such as ceria and zirconia, or alkali A NOx storage reduction catalyst (LNT catalyst) containing an earth metal and platinum as a nitrogen oxide (NOx) storage component is exemplified. Examples of catalysts that do not use precious metals include NOx selective reduction catalysts (SCR catalysts) containing copper-substituted or iron-substituted zeolites. Also, two or more catalysts selected from the group consisting of these catalysts may be used. The catalyst loading method is also not particularly limited, and can be carried out according to a conventional loading method for loading a catalyst on a honeycomb structure.

<Method for producing electrically heated carrier>
Next, a method for producing an electrically heated carrier according to the present invention will be exemplified. In one embodiment in which the electrode terminals are made of ceramics, the method for producing an electrically heated carrier of the present invention comprises a step A1 of obtaining an unfired honeycomb structure with electrode terminal forming paste; is fired to obtain a honeycomb structure with electrode terminals. Moreover, as another embodiment, the electrode layer forming paste and the electrode terminal forming paste may be pasted on the honeycomb structure after being pre-fired. In an embodiment in which the electrode terminals are made of metal, a step of obtaining a honeycomb structure by firing the unfired honeycomb structure with the electrode layer forming paste after obtaining the unfired honeycomb structure with the electrode layer forming paste. and fixing metal electrode terminals to the electrode layers of the honeycomb structure.

In step A1, a columnar honeycomb formed body that is a precursor of a honeycomb structure is produced, and an electrode layer forming paste is applied to the side surface of the columnar honeycomb formed body to obtain an unfired honeycomb structure with the electrode layer forming paste. 2) is a step of providing an electrode terminal forming paste on the electrode layer forming paste to obtain an unfired honeycomb structure with the electrode terminal forming paste.

To manufacture a columnar honeycomb formed body, first, a forming raw material is prepared by adding metallic silicon powder (metallic silicon), a binder, a surfactant, a pore-forming material, water, and the like to silicon carbide powder (silicon carbide). It is preferable that the mass of the metal silicon powder is 10 to 40% by mass with respect to the sum of the mass of the silicon carbide powder and the mass of the metal silicon powder. The average particle size of silicon carbide particles in the silicon carbide powder (silicon carbide) is preferably 3 to 50 μm, more preferably 3 to 40 μm. The average particle size of the metallic silicon particles in the metallic silicon powder (metallic silicon) is preferably 2 to 35 μm. The average particle size of silicon carbide particles and metal silicon particles refers to the volume-based arithmetic mean size when the frequency distribution of particle sizes is measured by a laser diffraction method.

Examples of binders include methylcellulose, hydroxypropylmethylcellulose, hydroxypropoxylcellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinyl alcohol. Among these, it is preferable to use methyl cellulose and hydroxypropoxyl cellulose together. 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 metal silicon powder is 100 parts by mass.

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

Ethylene glycol, dextrin, fatty acid soap, polyalcohol and the like can be used as surfactants. These may be used individually by 1 type, and may be used in combination of 2 or more types. 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 metal silicon powder is 100 parts by mass.

The pore-forming material is not particularly limited as long as it forms pores after baking, and examples thereof include graphite, starch, foamed resin, water-absorbing resin, silica gel, and the like. 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 size of the pore-forming material is preferably 10-30 μm. The average particle diameter of the pore-forming material refers to the volume-based arithmetic mean diameter when the frequency distribution of particle sizes is measured by a laser diffraction method. When the pore-forming material is a water absorbent resin, the average particle size of the pore-forming material means the average particle size after water absorption.

Next, after kneading the obtained forming raw material to form a clay, the clay is extruded to produce a columnar honeycomb formed body. For extrusion molding, a die having a desired overall shape, cell shape, partition wall thickness, cell density, etc. can be used. Next, it is preferable to dry the obtained columnar honeycomb molded body. When the length of the columnar honeycomb formed body in the central axis direction is not the desired length, the desired length can be obtained by cutting both bottom portions of the columnar honeycomb formed body. The columnar honeycomb molded body after drying is called a columnar honeycomb dried body.

Next, an electrode layer forming paste for forming an electrode layer is prepared. The electrode layer forming paste can be formed by appropriately adding various additives to raw material powder (metal powder, glass powder, etc.) blended according to the required properties of the electrode layer and kneading the mixture. Metal powder such as stainless steel can be used as the metal powder.

Next, the obtained electrode layer forming paste is applied to the side surface of the columnar honeycomb formed body (typically the columnar honeycomb dried body) to obtain an unfired honeycomb structure with the electrode layer forming paste. The method of applying the electrode layer forming paste to the formed columnar honeycomb body can be carried out according to a known method of manufacturing a honeycomb structure.

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

Next, when the electrode terminals are made of ceramics, an electrode terminal forming paste for forming the electrode terminals is prepared. The electrode terminal forming paste can be formed by appropriately adding various additives to ceramic powder blended according to the required characteristics of the electrode terminal and kneading the mixture. Next, the prepared electrode terminal forming paste is provided in a columnar shape on the surface of the electrode layer on the honeycomb structure.

In step A2, the unfired honeycomb structure with electrode terminal forming paste is fired to obtain a honeycomb structure with electrode terminals. The firing conditions may be an inert gas atmosphere or atmospheric pressure, a firing temperature of 1150 to 1350° C., and a firing time of 0.1 to 50 hours. The firing atmosphere can be, for example, an inert gas atmosphere, and the firing pressure can be normal pressure. In order to reduce the electrical resistance of the ^honeycomb structure body 10, it is preferable to reduce residual oxygen from the viewpoint of preventing oxidation. Baking with an active gas purge is preferred. Examples of the inert gas atmosphere include N ₂ gas atmosphere, helium gas atmosphere, argon gas atmosphere, and the like. The unfired honeycomb structure with the electrode terminal forming paste may be dried before firing. Moreover, before firing, degreasing may be performed to remove binders and the like. Thus, an electrically heated carrier is obtained in which the electrode terminals are electrically connected to the electrode layers.

When metal terminals are used as the electrode terminals, the metal electrode terminals are fixed on the electrode layer of the honeycomb structure 20 . Examples of fixing methods include laser welding, thermal spraying, and ultrasonic welding.

<Exhaust gas purification device>
The electrically heated carrier according to each embodiment of the present invention described above can be used in an exhaust gas purifier. The exhaust gas purifier has an electrically heated carrier and a can holding the electrically heated carrier. In the exhaust gas purification device, the electrically heated carrier is installed in the middle of the exhaust gas flow path for flowing the exhaust gas from the engine. As the can body, a metallic cylindrical member or the like that accommodates the electrically heated carrier can be used.

REFERENCE SIGNS LIST 10 honeycomb structure 12 outer wall 13 partition walls 14a, 14b electrode layers 15a, 15b electrode terminals 16 cells 20 honeycomb structure 30 electrically heated carrier

Claims (10)

a honeycomb structure portion having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and partitioning and forming a plurality of cells forming a flow path extending from one end face to the other end face;
a pair of electrode layers provided on the surface of the outer peripheral wall of the honeycomb structure so as to face each other across the central axis of the honeycomb structure;
with
wherein the honeycomb structure portion is made of ceramics having NTC characteristics, and the electrode layer is made of a material having PTC characteristics;
Honeycomb structure. The porosity of the honeycomb structure body is higher than the porosity of the electrode layer,
The honeycomb structure according to claim 1. Each of the pair of electrode layers is provided on the outer surface of the outer peripheral wall so as to extend in the extending direction of the cell,
The honeycomb structure according to claim 1 or 2. The honeycomb structure portion has an electrical resistance increase rate of -80 to -10%.
A honeycomb structure according to any one of claims 1 to 3. The thermal expansion coefficient of the electrode layer is larger than the thermal expansion coefficient of the honeycomb structure,
A honeycomb structure according to any one of claims 1 to 4. The electrical resistance increase rate of the electrode layer is 2 to 40%,
A honeycomb structure according to any one of claims 1 to 5. The material of the electrode layer is a mixture of a metal or a metal compound and an oxide ceramic,
A honeycomb structure according to any one of claims 1 to 6. The material of the electrode layer is a mixture of carbon and ceramics,
A honeycomb structure according to any one of claims 1 to 6. a honeycomb structure according to any one of claims 1 to 8;
an electrode terminal electrically connected to the electrode layer of the honeycomb structure;
An electrically heated carrier having An electrically heated carrier according to claim 9;
a can body holding the electrically heated carrier;
has a
Exhaust gas purification device.

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