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

Abstract

Provided are a honeycomb structure, an electrically heated carrier, and an exhaust gas purification device, which can reduce the decrease in electrical resistance at a temperature increase, easily apply power constantly over time, and suppress a sharp temperature increase. A honeycomb structure (20) of the present application includes a honeycomb structure portion (10) having outer peripheral walls (12) and partition walls (13) provided on the inner side of the outer peripheral walls (12) and dividing a plurality of cells (16) to form flow paths extending from one end face to the other end face, and a pair of electrode layers (14a, 14b) provided on the surface of the outer peripheral walls (12) of the honeycomb structure portion (10) so as to face each other across the central axis of the honeycomb structure portion (10), wherein the honeycomb structure portion (10) is composed of a ceramic having NTC characteristics, and the electrode layers (14a, 14b) are composed of a material having PTC characteristics.

Description

Technical Field

[0001] This invention relates to honeycomb structures, electrically heated carriers, and exhaust gas purification devices. Background Technology

[0002] Patent Document 1 below proposes a scheme using a honeycomb structure as an electrically heated carrier. The honeycomb structure comprises: a cylindrical honeycomb section having an outer peripheral wall and porous spacer walls dividing it into multiple compartments; and a pair of electrode sections disposed on the sides of the honeycomb section. This honeycomb structure serves as a catalyst carrier and is configured to function as a heater when a voltage is applied. The spacer walls and outer peripheral wall are primarily composed of a silicon-silicon carbide composite material or silicon carbide, while the electrode sections are primarily composed of silicon carbide particles and silicon.

[0003] For example, as shown in Patent Document 2 below, silicon carbide is known to have the characteristic that its resistance decreases with increasing temperature (NTC characteristic). The honeycomb structure disclosed in Patent Document 1 contains silicon carbide in both the honeycomb structure portion and the electrode portion, thereby possessing the NTC characteristic.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2011 / 125815

[0007] Patent Document 2: Japanese Patent Application Publication No. 7-89764 Summary of the Invention

[0008] For electrically heated carriers that function as heaters by applying voltage, from the viewpoint of temperature control, resistance changes due to temperature variations are not preferable. On the other hand, if the resistance change caused by temperature variations is small, the applied voltage and current for temperature control are easier to control. Furthermore, if the resistance decreases significantly when the temperature of the electrically heated carrier rises, current flows easily, potentially causing a rapid increase in the temperature. In particular, if a honeycomb structure with NTC characteristics is used, the resistance decreases when the temperature of the honeycomb structure rises; therefore, excessive current flow may occur, leading to a rapid temperature increase.

[0009] The present invention was made in consideration of the above problems. Its objective is to provide a honeycomb structure, an electrically heated carrier, and an exhaust gas purification device that can reduce the rate of decrease in resistance when the temperature rises, can easily and constantly apply power over time, and can suppress rapid temperature rises.

[0010] The honeycomb structure according to the present invention comprises: a honeycomb structure portion having an outer peripheral wall and a partition wall, the partition wall being disposed on the inner side of the outer peripheral wall and dividing to form a plurality of compartments, the plurality of compartments extending from one end face to another end face to form a flow path; and a pair of electrode layers disposed on the surface of the outer peripheral wall of the honeycomb structure portion facing each other across the central axis of the honeycomb structure portion, the honeycomb structure portion being made of ceramic having NTC properties, and the electrode layers being made of a material having PTC properties.

[0011] The electrically heated carrier of the present invention comprises: the aforementioned honeycomb structure; and an electrode terminal electrically connected to the electrode layer of the honeycomb structure.

[0012] The exhaust gas purification device according to the present invention includes: the above-mentioned electrically heated carrier; and a tank that holds the electrically heated carrier.

[0013] Invention Effects

[0014] According to the honeycomb structure, electrically heated carrier, and exhaust gas purification device of the present invention, since the honeycomb structure is made of ceramic with NTC characteristics and the electrode layer is made of material with PTC characteristics, the resistance reduction when the temperature rises is reduced, and it is easy to apply electricity constantly over time, thus suppressing a sharp rise in temperature. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the appearance of a honeycomb structure according to an embodiment of the present invention.

[0016] Figure 2 This is a cross-sectional schematic diagram of the electrode layer and electrode terminals disposed on the honeycomb structure of the electrically heated carrier according to an embodiment of the present invention, perpendicular to the extending direction of the compartment.

[0017] Explanation of reference numerals in the attached figures

[0018] 10…Honeycomb structure, 12…Outer peripheral wall, 13…Spacer wall, 14a, 14b…Electrode layers, 15a, 15b…Electrode terminals, 16…Combine, 20…Honeycomb structure, 30…Electrically heated carrier. Detailed Implementation

[0019] Hereinafter, with reference to the accompanying drawings, embodiments of the honeycomb structure, electrically heated carrier, and exhaust gas purification device of the present invention will be described. The present invention is not 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.

[0020] <Honeycomb Structure and Electrically Heated Carrier>

[0021] Figure 1 A schematic diagram showing the appearance of a honeycomb structure 20 according to an embodiment of the present invention. Figure 2 This is a cross-sectional schematic diagram perpendicular to the extending direction of the compartment 16, showing 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.

[0022] (1. Honeycomb structure)

[0023] 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 component made of ceramic, having an outer peripheral wall 12 and a spacer wall 13. The spacer wall 13 is disposed on the inner side of the outer peripheral wall 12 and divides into multiple compartments 16, which extend from one end face to the other to form a flow path. "Columnar" can be understood as a three-dimensional shape having thickness in the extending direction of the compartments 16 (axial direction of the honeycomb structure portion 10). The ratio (longitudinal-to-transverse dimension 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. A columnar shape may include a shape where the axial length of the honeycomb structure portion 10 is smaller than the diameter or width of the end face (flat shape).

[0024] The honeycomb structure portion 10 can be cylindrical in shape, and is not particularly limited. For example, it can be a cylindrical shape with rounded end faces, an elliptical end face, or a polygonal shape (quadrilateral, pentagonal, hexagonal, heptagonal, octagonal, etc.). Furthermore, regarding the size of the honeycomb structure portion 10, for the purpose of improving heat resistance (suppressing cracks in the outer peripheral wall in the circumferential direction), the area of ​​the end face is preferably 2000 to 20000 mm². 2 More preferably, it is 5000–15000 mm. 2 .

[0025] The shape of the compartments in the cross-section perpendicular to the extending direction of compartment 16 is not limited, but quadrilaterals, hexagons, octagons, or combinations thereof are preferred. When the honeycomb structure 10 is used as a catalyst carrier and carries the catalyst, quadrilaterals and hexagons are more preferred as they reduce pressure loss during exhaust gas flow and improve the catalyst's purification performance. From the viewpoint of further improving the catalyst's purification performance, hexagons are even more preferred.

[0026] The thickness of the partition wall 13 that divides the compartments 16 is preferably 0.1 to 0.3 mm, more preferably 0.1 to 0.2 mm. A thickness of 0.1 mm or more for the partition wall 13 can suppress the reduction in strength of the honeycomb structure portion 10. A thickness of 0.3 mm or less for the partition wall 13 can suppress the increase in pressure loss during exhaust gas flow when the honeycomb structure portion 10 is used as a catalyst carrier and carries the catalyst. In this invention, the thickness of the partition wall 13 is defined as the length of the portion of the line segment connecting the centroids of adjacent compartments 16 in a cross-section perpendicular to the extending direction of the compartment 16, passing through the partition wall 13.

[0027] For the honeycomb structure portion 10, in a cross-section perpendicular to the extending direction of the compartments 16, the compartment density is preferably 40 to 150 compartments / cm². 2 More preferably, it is 70 to 100 compartments / cm². 2 By setting the compartment density within this range, the catalyst's purification performance can be improved while minimizing pressure loss during exhaust gas flow. For example, if the compartment density is 40 compartments / cm²... 2 The above ensures sufficient catalyst loading area. If the compartment density is 150 compartments / cm² 2 The following method enables the suppression of increased pressure loss during exhaust gas flow when the honeycomb structure 10 is used as a catalyst carrier and carries the catalyst. The compartment density is the value obtained by dividing the area of ​​one end face of the honeycomb structure 10 (excluding the outer peripheral wall 12) by the number of compartments.

[0028] From the viewpoint of ensuring the structural strength of the honeycomb structure 10 and suppressing leakage of fluid flowing in the compartment 16 from the outer peripheral wall 12, it is useful to provide an outer peripheral wall 12 in the honeycomb structure 10. 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, resulting in a strength imbalance with the partition wall 13 and reduced 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 relative to the tangent of the outer peripheral wall 12 at the measurement location 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 compartment.

[0029] The honeycomb structure portion 10 is conductive. The honeycomb structure portion 10 only needs to be able to conduct electricity and generate heat using Joule heating; its volume resistivity is not particularly limited, but is preferably 0.1 to 200 Ω·cm, more preferably 1 to 200 Ω·cm. In this invention, the volume resistivity of the honeycomb structure portion 10 is set to a value obtained by measuring at 25°C using the four-terminal method.

[0030] The honeycomb structure 10 is made of ceramic with NTC characteristics (the characteristic that resistance decreases with increasing temperature). Examples of NTC characteristics include a negative resistance increase rate, as described later. The material of the honeycomb structure 10 is not limited and can be selected from non-oxide ceramics such as silicon carbide, silicon nitride, and aluminum nitride. Alternatively, silicon carbide-silicon composite materials, silicon carbide / graphite composite materials, etc., can also be used. From the viewpoint of balancing heat resistance and electrical conductivity, the material of the honeycomb structure 10 preferably contains ceramics with silicon-silicon carbide composite materials or silicon carbide as the main component. When the material of the honeycomb structure 10 is mainly composed of silicon-silicon carbide composite materials, it means that the honeycomb structure 10 contains more than 90% by mass of silicon-silicon carbide composite materials (total mass). Here, the silicon-silicon carbide composite material contains silicon carbide particles as aggregates and silicon as a bonding material for binding the silicon carbide particles. Preferably, multiple silicon carbide particles are bonded together by means of silicon in a manner that forms fine pores between the silicon carbide particles. When the material of the honeycomb structure part 10 is mainly silicon carbide, it means that the honeycomb structure part 10 contains more than 90% by mass of silicon carbide (total mass).

[0031] The resistance rise rate of the honeycomb structure portion 10 is preferably -80% to -10%. The resistance rise rate of the honeycomb structure portion 10 can be calculated by measuring the volume resistivity (Ω·cm) at two points at temperatures of 50°C and 500°C using the four-terminal method. 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. If the resistance rise rate is -80% or higher, the resistance change during heating is reduced, allowing for a constant application of power over time. If the resistance rise rate of the honeycomb structure portion 10 is -10% or lower, the honeycomb structure portion 10 exhibits NTC characteristics. A silicon-silicon carbide composite material or a silicon carbide-based ceramic can be used for the honeycomb structure portion 10. More preferably, the resistance rise rate of the honeycomb structure portion 10 is -70% to -20%, and even more preferably -70% to -30%.

[0032] Preferably, the porosity of the honeycomb structure portion 10 is higher than that of the electrode layers 14a and 14b. If this relationship is satisfied, when the honeycomb structure 20 is used as a catalyst carrier and the catalyst is supported thereon, it is easier to support the catalyst in the honeycomb structure portion 10 with its high porosity, and difficult to support the catalyst in the electrode layers 14a and 14b with their low porosity. As a result, the catalyst can be effectively supported in the honeycomb structure portion 10 through which the exhaust gas passes, easily forming a structure with excellent catalyst purification performance. The porosity of the honeycomb structure portion 10 is preferably 35-60%, more preferably 35-45%. The porosity is a value measured using a mercury porosimeter.

[0033] The coefficient of thermal expansion of the honeycomb structure 10 is preferably 4.0 to 4.75 ppm / K, more preferably 4.0 to 4.6 ppm / K. The coefficient of thermal expansion refers to the linear coefficient of thermal expansion at 40 to 800°C, measured according to the method of JIS R1618:2002. As a thermal expansion meter, the "TD5000S (trade name)" manufactured by BrukerAXS can be used.

[0034] (2. Electrode layer)

[0035] For the honeycomb structure 20, a pair of electrode layers 14a and 14b are provided on the surface of the outer peripheral wall 12, facing each other across the central axis of the honeycomb structure portion 10. The electrode layers 14a and 14b are made of a material with PTC characteristics (the characteristic that the resistance increases with increasing temperature). Examples of having PTC characteristics include, for instance, that the resistance increase rate of the electrode layers, described later, is positive.

[0036] In the honeycomb structure 20 and the electrically heated carrier 30 of the embodiments of the present invention, the honeycomb structure 10 is made of ceramic with NTC characteristics, and the electrode layers 14a and 14b are made of material with PTC characteristics. Therefore, the overall resistance balance of the electrically heated carrier can be controlled by controlling the resistance of the honeycomb structure 10 and the electrode layers 14a and 14b, thereby obtaining a honeycomb structure 20 and an electrically heated carrier 30 that can easily apply constant power to the electrically heated carrier over time.

[0037] Preferably, the coefficients of thermal expansion of electrode layers 14a and 14b are greater than those of the honeycomb structure portion 10. If this relationship is satisfied, when an electrically heated carrier 30 is formed by arranging electrode terminals 15a and 15b on electrode layers 14a and 14b, the difference in the coefficients of thermal expansion between the electrode layers 14a and 14b and the electrode terminals 15a and 15b is reduced, resulting in an electrically heated carrier 30 with excellent thermal shock resistance. The coefficients of thermal expansion of electrode layers 14a and 14b are preferably 4.5 to 10 ppm / K, more preferably 4.5 to 7 ppm / K. The coefficients of thermal expansion of electrode layers 14a and 14b can be measured using the same method as the method for measuring the coefficient of thermal expansion of the honeycomb structure portion 10 described above.

[0038] The resistance rise rate of electrode layers 14a and 14b is preferably 2% to 40%. Similar to the resistance rise rate of the honeycomb structure 10 described above, the volume resistivity (Ω·cm) at two points at temperatures of 50°C and 500°C can be measured using the four-terminal method. The resistance rise rate of electrode layers 14a and 14b is obtained by subtracting the volume resistivity at 50°C from the volume resistivity at 500°C, dividing the result by the volume resistivity at 50°C, and multiplying by 100. If the resistance rise rate is 2% or more, the resistance of electrode layers 14a and 14b increases due to PTC characteristics during heating, thereby compensating for the decrease in resistance of the honeycomb structure 10 due to NTC characteristics during heating, thus allowing for easy and constant application of power over time. If the resistance rise rate of electrode layers 14a and 14b is 40% or less, the Joule heating caused by the resistance rise of electrode layers 14a and 14b during heating can be reduced. The resistance increase rate of electrode layers 14a and 14b is more preferably 5 to 35%, and even more preferably 10 to 30%.

[0039] The materials for electrode layers 14a and 14b can be a mixture of metal and oxide ceramic, or a mixture of metal compound and oxide ceramic. The metal can be any elemental metal or alloy, including silicon, aluminum, iron, stainless steel, titanium, tungsten, and Ni-Cr alloys. The metal compound is a metal oxide other than oxide ceramic, including metal oxides, metal nitrides, metal carbides, metal silicides, metal borides, and composite oxides. The metal or metal compound can be a single material or a combination of two or more. The oxide ceramic can be glass, cordierite, or andalusite. The oxide ceramic can be a single material or a combination of two or more. For ease of resistance adjustment and superior durability, a mixture containing at least stainless steel and glass is more preferable.

[0040] The electrode layers 14a and 14b can also be made of a mixture of carbon and ceramic. Examples of ceramic materials include: glass, cordierite, andalusite, silicon carbide, silicon nitride, and zirconium oxide. The ceramic material can be a single type or a combination of two or more types.

[0041] The formation areas of electrode layers 14a and 14b are not particularly limited. From the viewpoint of improving the uniformity of heat generation in the honeycomb structure 10, it is preferable that each electrode layer 14a and 14b extends in a strip along the circumferential direction of the outer peripheral wall 12 and the direction of the compartment extension on the outer surface of the outer peripheral wall 12. Specifically, from the viewpoint that current easily propagates axially to the electrode layers 14a and 14b, each electrode layer 14a and 14b extends to at least 80% of the length between the two end faces of the honeycomb structure 10, preferably at least 90%, and more preferably throughout the entire length. By forming a pair of electrode layers 14a and 14b in this strip-like manner, it is easier to further suppress a rapid increase in temperature. The reason for this is speculated to be that in a portion of the honeycomb structure 10 with NTC characteristics, the resistance decreases; if the temperature of that portion increases, the temperature and resistance of a portion of the electrode layers 14a and 14b in the region near that portion of the honeycomb structure 10 will also increase. Accordingly, current flows through electrode layers 14a and 14b other than the portion of electrode layers 14a and 14b where the resistance is increased, and then current flows to the honeycomb structure portion 10. Therefore, it can be considered that the temperature of the entire honeycomb structure portion 10 is homogenized.

[0042] The thickness of each electrode layer 14a, 14b is preferably 0.01 to 5 mm, more preferably 0.01 to 3 mm. Setting it within this range improves uniform heating. If the thickness of each electrode layer 14a, 14b is 0.01 mm or more, the resistance is appropriately controlled, allowing for more uniform heating. If the thickness of each electrode layer 14a, 14b is 5 mm or less, the possibility of breakage during canning is reduced. The thickness of each electrode layer 14a, 14b is defined as the thickness in the normal direction relative to the tangent at the measured location on the outer surface of each electrode layer 14a, 14b in a cross-section perpendicular to the extension direction of the compartment.

[0043] (3. Electrode terminals)

[0044] The electrode terminals 15a and 15b can be formed in a columnar shape, or they can be formed into multiple branches in a comb-like shape, each branch having a contact point for connection with the electrode layers 14a and 14b. The electrode terminals 15a and 15b are disposed on the electrode layers 14a and 14b and electrically connected. Accordingly, if a voltage is applied to the electrode terminals 15a and 15b, the honeycomb structure 10 can be heated by Joule heating through the energization. Therefore, the honeycomb structure 10 can also preferably be used as a heater. The applied voltage is preferably 12 to 900V, more preferably 48 to 600V, and the applied voltage can be appropriately varied.

[0045] The electrode terminals 15a and 15b can be made of metal. As the metal, elemental metals and alloys can be used. From the viewpoints of corrosion resistance, volume resistivity, and linear expansion rate, alloys containing at least one element selected from the group consisting of Cr, Fe, Co, Ni, and Ti are preferred, and stainless steel and Fe-Ni alloys are more preferred. 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, its electrical conductivity, etc.

[0046] Electrode terminals 15a and 15b can be made of ceramic. The type of ceramic is not limited, and examples include: silicon carbide (SiC); metal compounds such as tantalum silicide (TaSi2) and chromium silicide (CrSi2); and composite materials containing one or more metals (cermets). Specific examples of cermets include: composite materials of silicon and silicon carbide; composite materials of metal silicides such as tantalum silicide and chromium silicide with metal silicon and silicon carbide; and, from the viewpoint of reducing thermal expansion, composite materials obtained by adding one or more insulating ceramics such as alumina, andalusite, zirconium oxide, cordierite, silicon nitride, and aluminum nitride to one or more of the aforementioned metals. The material of electrode terminals 15a and 15b can be the same as the material of the electrode layer.

[0047] Furthermore, when electrode terminals 15a and 15b are ceramic terminals, metal terminals can be joined to their respective front ends. The ceramic terminals and metal terminals can be joined by riveting, welding, or using conductive adhesives. Conductive metals such as iron alloys and nickel alloys can be used as the material for the metal terminals.

[0048] By supporting the catalyst on the electrically heated carrier 30, the electrically heated carrier 30 can be used as a catalyst. For example, fluids such as automobile exhaust can flow through the flow path of the multiple compartments 16. Examples of catalysts include, for example, noble metal-based catalysts or catalysts other than noble metal-based catalysts. Examples of noble metal-based catalysts include, for example, three-way catalysts, oxidation catalysts, or NOx storage and reduction catalysts (LNT catalysts) that support noble metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) on the surface of alumina micropores and contain co-catalysts such as cerium oxide and zirconium oxide, containing alkaline earth metals and platinum as NOx storage components. Examples of catalysts that do not use noble metals include, for example, NOx selective reduction catalysts (SCR catalysts) containing copper-substituted zeolites or iron-substituted zeolites. In addition, two or more catalysts selected from the group consisting of these catalysts can be used. It should be noted that the catalyst support method is not particularly limited and can be based on conventional methods of supporting catalysts on honeycomb structures.

[0049] <Manufacturing Method of Electric Heating Carrier>

[0050] Next, an example of a method for manufacturing the electrically heated carrier according to the present invention will be described. In one embodiment where the electrode terminals are made of ceramic, the method for manufacturing the electrically heated carrier of the present invention includes: step A1, in which an unfired honeycomb structure with electrode terminal forming paste is obtained; and step A2, in which the unfired honeycomb structure with electrode terminal forming paste is fired to obtain a honeycomb structure with electrode terminals. Alternatively, as another embodiment, the electrode layer forming paste and the electrode terminal forming paste can be pre-fired and then adhered to the honeycomb structure. In another embodiment where the electrode terminals are made of metal, the method includes: a step of firing the unfired honeycomb structure with electrode layer forming paste after obtaining the unfired honeycomb structure with electrode layer forming paste to obtain a honeycomb structure; and a step of fixing the metal electrode terminals to the electrode layer of the honeycomb structure.

[0051] Step A1 is as follows: a columnar honeycomb molded body is made as a precursor of the honeycomb structure; an electrode layer is coated on the side of the columnar honeycomb molded body to form a paste, thereby obtaining an unfired honeycomb structure with electrode layer forming paste; and then electrode terminals are set on the electrode layer forming paste to form a paste, thereby obtaining an unfired honeycomb structure with electrode terminal forming paste.

[0052] To fabricate a columnar honeycomb structure, firstly, metallic silicon powder, binder, surfactant, pore-forming material, water, etc., are added to silicon carbide powder (silicon carbide) to prepare a molding raw material. The mass of the metallic silicon powder is preferably 10-40% by mass relative to the total mass of the silicon carbide powder and the metallic silicon powder. The average particle size of the silicon carbide particles in the silicon carbide powder (silicon carbide) is preferably 3-50 μm, more preferably 3-40 μm. The average particle size of the metallic silicon particles in the metallic silicon powder (metallic silicon) is preferably 2-35 μm. The average particle size of the silicon carbide particles and the metallic silicon particles refers to the arithmetic mean particle size under a volume reference when the frequency distribution of particle size is measured by laser diffraction.

[0053] Examples of binders include methylcellulose, hydroxypropyl methylcellulose, hydroxypropoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinyl alcohol. Preferably, both methylcellulose and hydroxypropoxycellulose are used simultaneously. When the total mass of silicon carbide powder and metallic silicon powder is set to 100 parts by mass, the binder content is preferably 2.0 to 10.0 parts by mass.

[0054] When the total mass of silicon carbide powder and metallic silicon powder is set to 100 parts by mass, the water content is preferably 20 to 60 parts by mass.

[0055] Surfactants such as ethylene glycol, dextrin, fatty acid soaps, and polyols can be used. These surfactants can be used alone or in combination of two or more. When the total mass of silicon carbide powder and metallic silicon powder is set to 100 parts by mass, the surfactant content is preferably 0.1 to 2.0 parts by mass.

[0056] As a pore-forming material, it is not particularly limited as long as pores are formed after firing. Examples include graphite, starch, foaming resin, water-absorbing resin, and silica gel. When the total mass of silicon carbide powder and metallic silicon powder is set to 100 parts by mass, the content of the pore-forming material is preferably 0.5 to 10.0 parts by mass. The average particle size of the pore-forming material is preferably 10 to 30 μm. The average particle size of the pore-forming material refers to the arithmetic mean particle size under a volume basis when the frequency distribution of particle size is determined by laser diffraction. When the pore-forming material is a water-absorbing resin, the average particle size of the pore-forming material is the average particle size after water absorption.

[0057] Next, the obtained molding raw materials are mixed to form a billet, and then the billet is extruded to produce a columnar honeycomb molded body. During extrusion molding, a die with the desired overall shape, cell shape, cell wall thickness, cell density, etc., can be used. Next, the obtained columnar honeycomb molded body is preferably dried. If the central axial length of the columnar honeycomb molded body is not the desired length, the two bottoms of the columnar honeycomb molded body can be cut off to form the desired length. The dried columnar honeycomb molded body is called a dried columnar honeycomb body.

[0058] Next, an electrode layer forming paste is prepared to form the electrode layer. Various additives can be appropriately added to raw material powders (metal powders, glass powders, etc.) formulated according to the required characteristics of the electrode layer, and then the mixture is kneaded to form the electrode layer forming paste. As the metal powder, stainless steel powder or similar metal powders can be used.

[0059] Next, the obtained electrode layer forming paste is applied to the side of the columnar honeycomb molded body (typically a dried columnar honeycomb body), thereby obtaining an unfired honeycomb structure with the electrode layer forming paste. The method of applying the electrode layer forming paste to the columnar honeycomb molded body can be based on known methods for manufacturing honeycomb structures.

[0060] As a modification to the manufacturing method of the honeycomb structure, in step A1, the columnar honeycomb molded body can be temporarily fired before the electrode layer is coated to form paste. That is, in this modification, the columnar honeycomb molded body is fired to produce a columnar honeycomb fired body, and the electrode layer is coated to form paste on the columnar honeycomb fired body.

[0061] Next, when the electrode terminals are made of ceramic, an electrode terminal forming paste is prepared for forming the electrode terminals. Various additives can be appropriately added to ceramic powder formulated according to the required characteristics of the electrode terminals, and the paste is then kneaded to form the electrode terminal forming paste. Next, the prepared electrode terminal forming paste is columnarly disposed on the surface of the electrode layer on the honeycomb structure.

[0062] In step A2, the unfired honeycomb structure with electrode terminals formed into paste is fired to obtain a honeycomb structure with electrode terminals. The firing conditions can be set to an inert gas atmosphere or atmospheric atmosphere, below atmospheric pressure, a firing temperature of 1150–1350°C, and a firing time of 0.1–50 hours. It should be noted that the firing atmosphere can be, for example, an inert gas atmosphere, and the firing pressure can be set to atmospheric pressure, etc. To reduce the resistance of the honeycomb structure portion 10, from the viewpoint of preventing oxidation, it is preferable to reduce residual oxygen, and preferably the atmosphere during firing should be set to 1.0 × 10⁻⁶. -4 After entering a high vacuum of Pa or higher, inert gases are removed before firing. Examples of inert gas atmospheres include N2, helium, and argon. Before firing, the unfired honeycomb structure with the electrode terminal paste can be dried. Additionally, degreasing can be performed before firing to remove adhesives and the like. This allows for the production of an electrically heated carrier with electrical connections between the electrode terminals and the electrode layer.

[0063] When metal terminals are used as electrode terminals, the metal electrode terminals are fixed to the electrode layer of the honeycomb structure 20. Examples of fixing methods include laser welding, spraying, and ultrasonic welding.

[0064] <Exhaust Gas Purification Device>

[0065] The electrically heated carriers described in the various embodiments of the present invention can be used in exhaust gas purification devices. These devices include an electrically heated carrier and a container for holding the carrier. In the exhaust gas purification device, the electrically heated carrier is positioned midway through the exhaust gas flow path for allowing exhaust gas from the engine to pass through. The container can be a cylindrical metal component or the like that used to house the electrically heated carrier.

Claims

1. A honeycomb structure, wherein, The honeycomb structure has the following features: A honeycomb structure has an outer peripheral wall and a partition wall, the partition wall being disposed on the inner side of the outer peripheral wall and dividing to form a plurality of compartments, the plurality of compartments extending from one end face to the other end face to form a flow path; as well as A pair of electrode layers, each consisting of a single layer, are disposed on the surface of the outer peripheral wall of the honeycomb structure portion, facing each other across the central axis of the honeycomb structure portion. The honeycomb structure is made of ceramic with NTC properties, and the electrode layer is made of a material with PTC properties. The electrode layer is made of a mixture of metal and oxide ceramic, or a mixture of metal compound and oxide ceramic. The oxide ceramic contains at least one of glass, cordierite, and andalusite.

2. A honeycomb structure, wherein, The honeycomb structure has the following features: A honeycomb structure has an outer peripheral wall and a partition wall, the partition wall being disposed on the inner side of the outer peripheral wall and dividing to form a plurality of compartments, the plurality of compartments extending from one end face to the other end face to form a flow path; as well as A pair of electrode layers, each consisting of a single layer, are disposed on the surface of the outer peripheral wall of the honeycomb structure portion, facing each other across the central axis of the honeycomb structure portion. The honeycomb structure is made of ceramic with NTC properties, and the electrode layer is made of a material with PTC properties. The electrode layer is made of a mixture of carbon and ceramic, wherein the ceramic comprises at least one of glass, cordierite, andalusite, silicon carbide, silicon nitride, and zirconium oxide.

3. The honeycomb structure according to claim 1 or 2, wherein, The porosity of the honeycomb structure is higher than that of the electrode layer.

4. The honeycomb structure according to claim 1 or 2, wherein, The pair of electrode layers are respectively arranged to extend along the extension direction of the compartment on the outer surface of the outer peripheral wall.

5. The honeycomb structure according to claim 1 or 2, wherein, The resistivity rise rate of the cellular structure is -80% to -10%.

6. The honeycomb structure according to claim 1 or 2, wherein, The coefficient of thermal expansion of the electrode layer is greater than that of the honeycomb structure.

7. The honeycomb structure according to claim 1 or 2, wherein, The resistivity increase rate of the electrode layer is 2-40%.

8. An electrically heated carrier, wherein, The electrically heated carrier has: The honeycomb structure according to any one of claims 1 to 7; and An electrode terminal is electrically connected to the electrode layer of the honeycomb structure.

9. A tail gas purification device, wherein, The exhaust gas purification device has the following features: The electrically heated carrier as described in claim 8; and The tank holds the electrically heated carrier.

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