Honeycomb structure, electrically heated carrier, and exhaust gas purification device

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

[0001] The present invention relates to a honeycomb structure, an electrically heated carrier, and an exhaust gas purification device.

Background Art

[0002] In Patent Document 1 below, it has been proposed to use a honeycomb structure as an electrically heated carrier. The honeycomb structure includes a cylindrical honeycomb structure portion having a porous partition wall and an outer peripheral wall that partition and form a plurality of cells, and a pair of electrode portions disposed on the side surface of the honeycomb structure portion. It is a catalyst carrier and 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 portion is mainly composed of silicon carbide particles and silicon.

[0003] For example, as shown in Patent Document 2 below, it is known that silicon carbide has a characteristic (NTC characteristic) in which its electrical resistance decreases as the 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.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] 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 a temperature change. On the other hand, if the electrical resistance fluctuation due to a temperature change is small, it becomes easier to control the voltage and current applied for temperature control. Further, when the decrease in electrical resistance when the temperature of the electrically heated carrier rises is large, the current easily flows, and there is a risk that the temperature of the electrically heated carrier will rise rapidly. In particular, when using a honeycomb structure portion having NTC characteristics, when the temperature of the honeycomb structure rises, the electrical resistance decreases, so that there is a risk that current will flow excessively in part and the temperature will rise rapidly.

[0006] The present invention has been made in consideration of the above problems, and an object thereof is to provide a honeycomb structure, an electrically heated carrier, and an exhaust gas purification device that can reduce the decrease in electrical resistance during temperature rise, can easily apply power constantly over time, and can suppress a rapid temperature rise.

Means for Solving the Problems

[0007] The honeycomb structure according to the present invention includes a honeycomb structure portion having an outer peripheral wall and a partition wall that is disposed inside the outer peripheral wall and partitions and forms a plurality of cells that form 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 portion so as to face each other with the central axis of the honeycomb structure portion interposed therebetween. The honeycomb structure portion is made of a ceramic having NTC characteristics, and the electrode layer is made of a material having PTC characteristics.

[0008] The electrically heated carrier according to the present invention includes the above-described honeycomb structure and an electrode terminal that is electrically connected to the electrode layer of the honeycomb structure.

[0009] The exhaust gas purification device according to the present invention includes the above-described electrically heated carrier and a can body that holds the electrically heated carrier.

Effects of the Invention

[0010] According to the honeycomb structure, the electrically heated carrier, and the exhaust gas purification device of the present invention, since the honeycomb structure portion is made of ceramics having NTC characteristics and the electrode layer is made of a material having PTC characteristics, it is possible to reduce the decrease in electrical resistance during temperature rise, easily apply a constant power over time, and suppress a rapid temperature rise.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the honeycomb structure, the electrically heated carrier, and the exhaust gas purification device of the present invention will be described with reference to the drawings. However, the present invention is not construed as being limited thereto, and 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 present invention.

[0013] <Honeycomb Structure and Electrically Heated Carrier> FIG. 1 shows a schematic external view of the honeycomb structure 20 according to an embodiment of the present invention. FIG. 2 shows a schematic cross-sectional view perpendicular to the extending direction of the cell of the electrode layers 14a and 14b provided on the honeycomb structure portion 10 of the electrically heated carrier 30 according to an embodiment of the present invention and the electrode terminals 15a and 15b provided on the electrode layers 14a and 14b.

[0014] (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 portion 10 is a columnar member made of ceramics, and has an outer peripheral wall 12 and a partition wall 13 that is disposed inside the outer peripheral wall 12 and partitions and forms a plurality of cells 16 that form a flow path extending from one end face to the other end face. The columnar shape can be understood as a three-dimensional shape having a thickness in the extending direction of the cells 16 (axial direction of the honeycomb structure portion 10). The ratio (aspect ratio) of the axial length of the honeycomb structure portion 10 to the diameter or width of the end face of the honeycomb structure portion 10 is arbitrary. The columnar shape may include a shape (flat shape) in which the axial length of the honeycomb structure portion 10 is shorter than the diameter or width of the end face.

[0015] The outer shape of the honeycomb structure portion 10 is not particularly limited as long as it is columnar. For example, it can be other shapes such as a columnar shape with a circular end face (cylindrical shape), a columnar shape with an oval end face, a columnar shape with a polygonal (quadrilateral, pentagonal, hexagonal, heptagonal, octagonal, etc.) end face, etc. Also, the size of the honeycomb structure portion 10 is preferably such that the area of the end face is 2000 to 20000 mm 2 in order to enhance heat resistance (suppress cracks entering in the circumferential direction of the outer peripheral wall), and more preferably 5000 to 15000 mm 2 .

[0016] There is no limitation on the shape of the cells in a cross-section perpendicular to the extending direction of the cells 16, but it is preferably a quadrilateral, hexagonal, octagonal, or a combination thereof. Among these, when the honeycomb structure portion 10 is used as a catalyst carrier and a catalyst is supported, the pressure loss when the exhaust gas flows is small, and the purification performance of the catalyst can be excellent. Quadrilaterals and hexagons are more preferable. From the viewpoint of making the purification performance of the catalyst more excellent, hexagons are even more preferable.

[0017] The thickness of the partition wall 13 that forms the compartments of the cells 16 is preferably 0.1 to 0.3 mm, and 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 a decrease in the strength of the honeycomb structure portion 10. When the thickness of the partition wall 13 is 0.3 mm or less, when the honeycomb structure portion 10 is used as a catalyst carrier and a catalyst is supported, it is possible to suppress an increase in the pressure loss when the exhaust gas flows. In the present invention, the thickness of the partition wall 13 is defined as the length of the portion passing through the partition wall 13 among the line segments connecting the centers of gravity of the adjacent cells 16 in a cross section perpendicular to the extending direction of the cells 16.

[0018] In a cross section perpendicular to the extending direction of the cells 16, the honeycomb structure portion 10 preferably has a cell density of 40 to 150 cells / cm 2 and more preferably 70 to 100 cells / cm 2 . By setting the cell density within such a range, it is possible to improve the purification performance of the catalyst while reducing the pressure loss when the exhaust gas flows. When the cell density is 40 cells / cm 2 or more, a sufficient catalyst support area is ensured. When the cell density is 150 cells / cm 2 or less, when the honeycomb structure portion 10 is used as a catalyst carrier and a catalyst is supported, it is possible to suppress an increase in the pressure loss when the exhaust gas flows. 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 portion 10 excluding the outer peripheral wall 12 portion.

[0019] Providing the outer peripheral wall 12 to the honeycomb structure portion 10 is useful from the viewpoints of ensuring the structural strength of the honeycomb structure portion 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 made too thick, it will become too high in strength, the strength balance with the partition wall 13 will be lost, and the thermal shock resistance will decrease. 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 with respect to the tangent line of the outer peripheral wall 12 at the measurement location when the location of the outer peripheral wall 12 where the thickness is to be measured is observed in a cross section perpendicular to the extending direction of the cells.

[0020] The honeycomb structure portion 10 has electrical conductivity. The honeycomb structure portion 10 has no particular limitation on the volume resistivity as long as it can generate heat by Joule heat when energized, but it is preferably 0.1 to 200 Ω·cm, and more preferably 1 to 200 Ω·cm. In the present invention, the volume resistivity of the honeycomb structure portion 10 is the value measured at 25°C by the four-terminal method.

[0021] The honeycomb structure part 10 is made of ceramics having NTC characteristics (characteristics in which the electrical resistance decreases as the temperature increases). Having NTC characteristics means, for example, that the electrical resistance increase rate of the honeycomb structure part described later shows a negative value. As the material of the honeycomb structure part 10, although not limited, it can be selected from non-oxide ceramics such as silicon carbide, silicon nitride, and aluminum nitride. Also, a silicon carbide-metal silicon composite material, a silicon carbide / graphite composite material, or the like can be used. Among these, from the viewpoint of achieving both heat resistance and conductivity, it is preferable that the material of the honeycomb structure part 10 contains a silicon-silicon carbide composite material or ceramics mainly composed of silicon carbide. When the material of the honeycomb structure part 10 is mainly composed of a silicon-silicon carbide composite material, it means that the honeycomb structure part 10 contains 90% by mass or more of the silicon-silicon carbide composite material (total mass) in the whole. Here, the silicon-silicon carbide composite material contains silicon carbide particles as aggregates 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 the material of the honeycomb structure part 10 is mainly composed of silicon carbide, it means that the honeycomb structure part 10 contains 90% by mass or more of silicon carbide (total mass) in the whole.

[0022] The electrical resistance increase rate of the honeycomb structure part 10 is preferably -80% to -10%. The electrical resistance increase rate of the honeycomb structure part 10 can be obtained by measuring the volume resistivity (Ω·cm) at two points of 50°C and 500°C by the four-terminal method, subtracting the volume resistivity at 50°C from the volume resistivity at 500°C, dividing the derived value by the volume resistivity at 50°C, and multiplying by 100. When the electrical resistance increase rate is -80% or more, the change in electrical resistance during energization heating can be reduced, and it becomes easier to apply power constantly over time during energization. When the electrical resistance increase rate of the honeycomb structure part 10 is -10% or less, the honeycomb structure part 10 exhibits NTC characteristics, and a silicon-silicon carbide composite material or ceramics mainly composed of silicon carbide can be used for the honeycomb structure part 10. The electrical resistance increase rate of the honeycomb structure part 10 is more preferably -70% to -20%, and even more preferably -70% to -30%.

[0023] It is preferable that the porosity of the honeycomb structure part 10 is higher than the porosities of the electrode layers 14a and 14b. When the porosity satisfies this relationship, when the honeycomb structure 20 is used as a catalyst carrier and a catalyst is supported, the catalyst is more likely to be supported on the honeycomb structure part 10 with a high porosity, and the catalyst is less likely to be supported on the electrode layers 14a and 14b with a low porosity. As a result, the catalyst can be efficiently supported on the honeycomb structure part 10 through which the exhaust gas passes, and the purification performance of the catalyst is likely to be excellent. The porosity of the honeycomb structure part 10 is preferably 35% to 60%, and more preferably 35% to 45%. The porosity is a value measured by a mercury porosimeter.

[0024] The thermal expansion coefficient of the honeycomb structure part 10 is preferably 4.0 to 4.75 ppm / K, and more preferably 4.0 to 4.6 ppm / K. The thermal expansion coefficient refers to the linear thermal expansion coefficient at 40 to 800°C measured by a method conforming to JIS R1618:2002. As the thermomechanical analyzer, "TD5000S (trade name)" manufactured by Bruker AXS can be used.

[0025] (2. Electrode layer) In the honeycomb structure 20, a pair of electrode layers 14a and 14b are provided on the surface of the outer peripheral wall 12 so as to face each other across the central axis of the honeycomb structure portion 10. The electrode layers 14a and 14b are made of a material having PTC characteristics (characteristics in which the electrical resistance increases as the temperature rises). Having PTC characteristics means, for example, that the electrical resistance increase rate of the electrode layer described later shows a positive value.

[0026] In the honeycomb structure 20 and the electric heating type carrier 30 according to the embodiment of the present invention, since the honeycomb structure portion 10 is made of ceramics having NTC characteristics and the electrode layers 14a and 14b are made of a material having PTC characteristics, it is possible to control the electrical resistance of the honeycomb structure portion 10 and the electrode layers 14a and 14b to control the balance of the electrical resistance of the entire electric heating type carrier, and it is possible to obtain the honeycomb structure 20 and the electric heating type carrier 30 to which a constant power can be easily applied over time.

[0027] It is preferable that the thermal expansion coefficients of the electrode layers 14a and 14b are larger than the thermal expansion coefficient of the honeycomb structure portion 10. When the thermal expansion coefficients satisfy this relationship, when the electrode terminals 15a and 15b are disposed on the electrode layers 14a and 14b to form the electric heating type carrier 30, the difference in the thermal expansion coefficients between the electrode layers 14a and 14b and the electrode terminals 15a and 15b becomes small, and the electric heating type carrier 30 having excellent thermal shock resistance is obtained. The thermal expansion coefficients of the electrode layers 14a and 14b are preferably 4.5 to 10 ppm / K, and more preferably 4.5 to 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 portion 10 described above.

[0028] The electrical resistance increase rate of the electrode layers 14a and 14b is preferably 2 to 40%. Similar to the electrical resistance increase rate of the honeycomb structure portion 10 described above, the electrical resistance increase rate of the electrode layers 14a and 14b is obtained by measuring the volume resistivity (Ω·cm) at two points at 50°C and 500°C by the four-terminal method, subtracting the volume resistivity at 50°C from the volume resistivity at 500°C, dividing the derived value by the volume resistivity at 50°C, and multiplying by 100. When the electrical resistance increase rate is 2% or more, the electrical resistance of the electrode layers 14a and 14b during energization heating increases significantly due to the PTC characteristics, compensating for the decrease in electrical resistance during energization heating due to the NTC characteristics of the honeycomb structure portion 10, and making it easier to apply a constant power over time. When the electrical resistance increase rate of the electrode layers 14a and 14b is 40% or less, the Joule heat generation due to the resistance increase of the electrode layers 14a and 14b during energization heating can be reduced. The electrical resistance increase rate of the electrode layers 14a and 14b is more preferably 5 to 35%, and even more preferably 10 to 30%.

[0029] As the material of the electrode layers 14a and 14b, it can be a mixture of a metal or metal compound, and an oxide ceramic. The metal can be either a single metal or an alloy, and examples include silicon, aluminum, iron, stainless steel, titanium, tungsten, Ni-Cr alloy, etc. Examples of the metal compound are substances other than oxide ceramics, such as metal oxides, metal nitrides, metal carbides, metal silicides, metal borides, and composite oxides. The metal or metal compound can be a single type or two or more types can be used in combination. Examples of the oxide ceramics include glass, cordierite, and mullite. The oxide ceramics can be a single type or two or more types can be used in combination. Among these, a mixture containing at least stainless steel and glass is more preferable in that the electrical resistance is easily adjusted and the durability is more excellent.

[0030] As the material of the electrode layers 14a and 14b, it can also be a mixture of carbon and ceramics. Examples of the ceramics include glass, cordierite, mullite, silicon carbide, silicon nitride, and zirconia. The ceramics can be a single type or two or more types can be used in combination.

[0031] There are no particular restrictions on the formation regions of the electrode layers 14a and 14b. However, from the perspective of enhancing the uniform heat generation property of the honeycomb structure portion 10, each of the electrode layers 14a and 14b preferably extends in a strip shape on the outer surface of the outer peripheral wall 12 in the circumferential direction of the outer peripheral wall 12 and in the extending direction of the cells. Specifically, each of the electrode layers 14a and 14b extends over a length of 80% or more, preferably 90% or more, and more preferably the entire length between both end faces of the honeycomb structure portion 10. This is desirable from the perspective that current easily spreads in the axial direction of the electrode layers 14a and 14b. By forming the pair of electrode layers 14a and 14b in a strip shape in this way, it is easier to further suppress a rapid temperature rise. The reason for this is that when the electrical resistance decreases in a part of the honeycomb structure portion 10 having NTC characteristics and a part thereof locally increases in temperature, a part of the electrode layers 14a and 14b close to a part of the region of the honeycomb structure portion 10 increases in temperature and the electrical resistance is presumed to increase. As a result, current flows through the electrode layers 14a and 14b other than the part of the electrode layers 14a and 14b where the electrical resistance has increased, and then the current flows into the honeycomb structure portion 10. Therefore, it is considered that the temperature is made uniform throughout the honeycomb structure portion 10.

[0032] The thickness of each of the electrode layers 14a and 14b is preferably 0.01 to 5 mm, and more preferably 0.01 to 3 mm. By setting it within such a range, the uniform heat generation property can be enhanced. When the thickness of each of the electrode layers 14a and 14b is 0.01 mm or more, the electrical resistance can be appropriately controlled and heat can be generated more uniformly. When 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 defined as the thickness in the normal direction with respect to the tangent line at the measurement location on the outer surface of each of the electrode layers 14a and 14b when observing the location of the electrode layer 14a or 14b where the thickness is to be measured in a cross section perpendicular to the extending direction of the cells.

[0033] (3. Electrode Terminals) The electrode terminals 15a and 15b may be formed in a columnar shape, or may be formed to branch into a plurality of comb-like teeth, and each of the branched portions may have a contact point for connecting to the electrode layers 14a and 14b. The electrode terminals 15a and 15b are disposed on the electrode layers 14a and 14b and are electrically joined. Thereby, when a voltage is applied to the electrode terminals 15a and 15b, current flows and the honeycomb structure portion 10 can be heated by Joule heat. Therefore, the honeycomb structure portion 10 can also be suitably used as a heater. The voltage to be applied is preferably 12 to 900 V, more preferably 48 to 600 V, but the applied voltage can be changed as appropriate.

[0034] The material of the electrode terminals 15a and 15b may be metal. As the metal, single metals and alloys can be adopted, but from the viewpoints of corrosion resistance, volume resistivity, and linear expansion coefficient, for example, it is preferable to use an alloy containing at least one selected from the group consisting of Cr, Fe, Co, Ni, and Ti, and stainless steel and Fe-Ni alloy are more preferable. 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, the current-carrying performance, etc.

[0035] The electrode terminals 15a and 15b may be made of ceramics. Examples of the ceramics include, but are not limited to, silicon carbide (SiC), and metal compounds such as tantalum silicide (TaSi 2 ) and chromium silicide (CrSi 2 ), etc. Furthermore, composite materials (cermets) containing one or more metals can be mentioned. Specific examples of cermets include a composite material of silicon and silicon carbide, a composite material of a metal silicide such as tantalum silicide or chromium silicide, metal silicon, and silicon carbide, and furthermore, from the viewpoint of reducing thermal expansion, one or more insulating ceramics such as alumina, mullite, zirconia, cordierite, silicon nitride, and aluminum nitride are added to the above-mentioned one or two or more metals. The material of the electrode terminals 15a and 15b may be the same as that of the electrode layer.

[0036] Also, when the electrode terminals 15a and 15b are ceramic terminals, metal terminals may be joined to their tips respectively. The joining of the ceramic terminal and the metal terminal can be performed by caulking, welding, a conductive adhesive, or the like. As the material of the metal terminal, a conductive metal such as an iron alloy or a nickel alloy can be adopted.

[0037] By supporting a catalyst on the electrically heated carrier 30, the electrically heated carrier 30 can be used as a catalyst body. For example, a fluid such as automotive exhaust gas can flow through the flow paths of the plurality of cells 16. Examples of the catalyst include noble metal-based catalysts or catalysts other than these. As the noble metal-based catalyst, a three-way catalyst or an oxidation catalyst containing a noble metal such as platinum (Pt), palladium (Pd), or rhodium (Rh) supported on the surface of alumina pores and containing a promoter such as ceria or zirconia, or a NOx storage reduction catalyst (LNT catalyst) containing an alkaline earth metal and platinum as a NOx storage component is exemplified. Examples of a catalyst that does not use a noble metal include a NOx selective reduction catalyst (SCR catalyst) containing copper-substituted or iron-substituted zeolite. Also, two or more catalysts selected from the group consisting of these catalysts may be used. Note that there is no particular limitation on the method of supporting the catalyst, and it can be carried out in accordance with the conventional method of supporting a catalyst on a honeycomb structure.

[0038] <Manufacturing method of electrically heated carrier> Next, a method for manufacturing the electric heating carrier according to the present invention will be exemplarily described. In one embodiment where the electrode terminals are made of ceramics, the method for manufacturing the electric heating carrier of the present invention includes a step A1 of obtaining an unfired honeycomb structure with electrode terminal forming paste, and a step A2 of firing the unfired honeycomb structure with electrode terminal forming paste to obtain a honeycomb structure with electrode terminals. Further, as another embodiment, after pre-firing the electrode layer forming paste and the electrode terminal forming paste, they may be attached to the honeycomb structure. In an embodiment where the electrode terminals are made of metal, after obtaining an unfired honeycomb structure with electrode layer forming paste, a step of firing the unfired honeycomb structure with electrode layer forming paste to obtain a honeycomb structure, and a step of fixing metal electrode terminals to the electrode layer of the honeycomb structure are included.

[0039] Step A1 is a step of producing a columnar honeycomb formed body which is a precursor of the honeycomb structure, applying an electrode layer forming paste to the side surface of the columnar honeycomb formed body to obtain an unfired honeycomb structure with electrode layer forming paste, and then providing an electrode terminal forming paste on the electrode layer forming paste to obtain an unfired honeycomb structure with electrode terminal forming paste.

[0040] Regarding the production of the columnar honeycomb formed body, first, a molding raw material is produced by adding silicon carbide powder (silicon carbide), silicon metal powder (silicon metal), a binder, a surfactant, a pore former, water, etc. to the silicon carbide powder. It is preferable that the mass of the silicon metal powder is 10 to 40% by mass with respect to the total of the mass of the silicon carbide powder and the mass of the silicon metal powder. The average particle diameter of the 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 diameter of the silicon metal particles in the silicon metal powder (silicon metal) is preferably 2 to 35 μm. The average particle diameters of the silicon carbide particles and the silicon metal particles refer to the arithmetic average diameter based on volume when the frequency distribution of the particle size is measured by the laser diffraction method.

[0041] Examples of the binder include methyl cellulose, hydroxypropyl methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, and the like. Among these, it is preferable to use a combination of methyl cellulose and hydroxypropoxyl cellulose. 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.

[0042] The water content 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.

[0043] Examples of the surfactant include ethylene glycol, dextrin, fatty acid soap, polyalcohol, and the like. 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 metal silicon powder is 100 parts by mass.

[0044] The pore former is not particularly limited as long as it becomes pores after firing, and examples thereof include graphite, starch, foamed resin, water-absorbing resin, silica gel, and the like. The content of the pore former 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 former is preferably 10 to 30 μm. The average particle diameter of the pore former refers to the arithmetic mean diameter based on volume when the frequency distribution of the particle size is measured by the laser diffraction method. When the pore former is a water-absorbing resin, the average particle diameter of the pore former is the average particle diameter after water absorption.

[0045] Next, after kneading the obtained molding raw material to form clay, the clay is extruded to produce a columnar honeycomb molded body. When performing 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 in the central axis direction of the columnar honeycomb molded body is not the desired length, both bottom portions of the columnar honeycomb molded body can be cut to obtain the desired length. The columnar honeycomb molded body after drying is referred to as a columnar honeycomb dried body.

[0046] 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 powders (such as metal powders and glass powders) compounded according to the required characteristics of the electrode layer and kneading them. As the metal powder, metal powders such as stainless steel can be used.

[0047] Next, the obtained electrode layer forming paste is applied to the side surface of the columnar honeycomb molded body (typically a columnar honeycomb dried body) to obtain an unfired honeycomb structure body with an electrode layer forming paste. The method of applying the electrode layer forming paste to the columnar honeycomb molded body can be carried out according to a known method for manufacturing a honeycomb structure body.

[0048] As a modified example of the method for manufacturing a honeycomb structure body, in step A1, the columnar honeycomb molded body may be fired once before applying the electrode layer forming paste. That is, in this modified example, the columnar honeycomb molded body is fired to produce a columnar honeycomb fired body, and the electrode layer forming paste is applied to the columnar honeycomb fired body.

[0049] Next, when the electrode terminal is made of ceramics, an electrode terminal forming paste for forming the electrode terminal is prepared. The electrode terminal forming paste can be formed by appropriately adding various additives to ceramic powders compounded according to the required characteristics of the electrode terminal and kneading them. Next, the prepared electrode terminal forming paste is provided in a columnar shape on the surface of the electrode layer on the honeycomb structure body.

[0050] In Project A2, the green honeycomb structure with the electrode terminal forming paste is fired to obtain a honeycomb structure with electrode terminals. The firing conditions can be an inert gas atmosphere or an air atmosphere, below atmospheric pressure, a firing temperature of 1150 to 1350 °C, and a firing time of 0.1 to 50 hours. Note that the firing atmosphere can be, for example, an inert gas atmosphere, and the pressure during firing can be normal pressure or the like. In order to reduce the electrical resistance of the honeycomb structure portion 10, it is preferable to reduce the residual oxygen from the viewpoint of oxidation prevention, and after making the atmosphere during firing into a high vacuum of 1.0×10 -4 Pa or more, it is preferable to purge with an inert gas and then fire. Examples of the inert gas atmosphere include an N 2 gas atmosphere, a helium gas atmosphere, an argon gas atmosphere, and the like. Before firing, the green honeycomb structure with the electrode terminal forming paste may be dried. Also, before firing, degreasing may be performed to remove a binder or the like. In this way, an electrically heated carrier in which the electrode terminal is electrically connected to the electrode layer is obtained.

[0051] When using a metal terminal as the electrode terminal, the metal electrode terminal is fixed on the electrode layer of the honeycomb structure 20. Examples of the fixing method include laser welding, thermal spraying, ultrasonic welding, and the like.

[0052] <Exhaust gas purification device> The electrically heated carriers according to the respective embodiments of the present invention described above can each be used in an exhaust gas purification device. The exhaust gas purification device includes 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 in the middle of an exhaust gas flow path for flowing exhaust gas from an engine. As the can body, a metal cylindrical member that houses the electrically heated carrier or the like can be used.

Explanation of reference numerals

[0053] 10 Honeycomb structure portion 12 Outer peripheral wall 13 Partition wall 14a, 14b Electrode layer 15a, 15b Electrode terminal 16 cells 20 honeycomb structure 30 electrically heated carrier

Claims

1. A honeycomb structure part having an outer peripheral wall and a partition wall that is disposed inside the outer peripheral wall and partitions and forms a plurality of cells that form a flow path extending from one end face to the other end face, A pair of electrode layers, each consisting of a single layer, provided on the surface of the outer peripheral wall of the honeycomb structure part so as to face each other across the central axis of the honeycomb structure part, Comprising: The honeycomb structure part is made of ceramics having NTC characteristics, and the electrode layer is made of a material having PTC characteristics. Honeycomb structure.

2. The porosity of the honeycomb structure part is higher than the porosity of the electrode layer. The honeycomb structure according to claim 1.

3. Each of the pair of electrode layers is provided so as to extend in the extending direction of the cells on the outer surface of the outer peripheral wall. The honeycomb structure according to claim 1 or 2.

4. The electrical resistance increase rate of the honeycomb structure part is -80 to -10%, The electrical resistance increase rate of the honeycomb structure part is obtained by measuring the volume resistivity (Ω·cm) at two points of 50°C and 500°C by the four-terminal method, subtracting the volume resistivity at 50°C from the volume resistivity at 500°C, dividing the derived value by the volume resistivity at 50°C, and multiplying by 100. The honeycomb structure according to any one of claims 1 to 3.

5. The thermal expansion coefficient of the electrode layer is larger than the thermal expansion coefficient of the honeycomb structure part. The honeycomb structure according to any one of claims 1 to 4.

6. The electrical resistance increase rate of the electrode layer is 2 to 40%, The electrical resistance increase rate of the electrode layer is obtained by measuring the volume resistivity (Ω·cm) at two points of 50°C and 500°C by the four-terminal method, subtracting the volume resistivity at 50°C from the volume resistivity at 500°C, dividing the derived value by the volume resistivity at 50°C, and multiplying by 100. The honeycomb structure according to any one of claims 1 to 5.

7. The material of the electrode layer is a mixture of a metal or a metal compound and oxide ceramics. The honeycomb structure according to any one of claims 1 to 6.

8. The material of the electrode layer is a mixture of carbon and ceramics. The honeycomb structure according to any one of claims 1 to 6.

9. The 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.

10. The electrically heated carrier according to claim 9, a can body that holds the electrically heated carrier, and an exhaust gas purification device.

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