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

Abstract

The present application provides a honeycomb structure, an electrically heated carrier, and an exhaust gas purification device. The honeycomb structure is less likely to develop cracks when housed in a metal tube and subjected to temperature changes. The honeycomb structure includes: a honeycomb structure portion having electrical conductivity, having an outer peripheral wall and a partition wall disposed inside the outer peripheral wall and dividing a plurality of cells, the plurality of cells forming flow paths from one end surface to the other end surface; and a pair of electrode layers disposed on the outer surface of the outer peripheral wall in a manner of facing each other with the center axis of the honeycomb structure portion interposed therebetween, the linear expansion coefficient of the honeycomb structure portion measured in accordance with JIS R1618:2002 when the temperature changes from 40°C to 300°C is 4.1 x 10 ‑6 / °C or more, the linear expansion coefficient of the honeycomb structure portion measured in accordance with JIS R1618:2002 when the temperature changes from 300°C to 800°C is 4.2 x 10 ‑6 / °C or more and 4.8 x 10 ‑6 / °C or less.

Description

Technical Field

[0001] This invention relates to a honeycomb structure, an electrically heated carrier having a honeycomb structure, and a waste gas purification device having an electrically heated carrier. Background Technology

[0002] In recent years, to improve the reduced exhaust gas purification performance after engine startup, the electrically heated catalytic converter (EHC) has been proposed. An EHC is a system in which a pair of electrodes are placed in a conductive ceramic honeycomb structure. By applying electricity, the honeycomb structure itself heats up, thereby raising the catalyst loaded within it to its activation temperature before engine startup. Typically, the honeycomb structure is housed (canned) in a metal canister (hereinafter referred to as a "metal tube") and positioned midway through the vehicle's exhaust gas flow path.

[0003] High-temperature exhaust gas flows through the waste gas flow path; therefore, the honeycomb structure is required to have thermal shock resistance. To improve thermal shock resistance, the preferred coefficient of thermal expansion of the ceramic used as the constituent material of the honeycomb structure was investigated. Patent Document 1 specifies that the coefficient of linear expansion at 25–800°C is preferably 3.5–6.0 ppm / K, more preferably 3.5–4.5 ppm / K. Patent Document 2 specifies that the coefficient of linear expansion at 40–800°C is preferably 2.0 × 10⁻⁶. -6 / K~4.6×10 -6 / K.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-181457

[0007] Patent Document 2: Japanese Patent Application Publication No. 2014-189447 Summary of the Invention

[0008] By ensuring that the coefficient of linear expansion of the ceramic used as the constituent material of the honeycomb structure falls within the range taught in existing art literature, the thermal shock resistance of the honeycomb structure can be improved. However, examples have been observed where, even when a honeycomb structure made of ceramic with a coefficient of linear expansion within the range described in existing art literature is housed in a metal tube and placed in the middle of a vehicle's exhaust gas path, cracks still occur during actual use. If cracks form in the honeycomb structure, current flow is difficult to achieve through the cracked areas, leading to reduced heating performance or decreased mechanical strength. Therefore, it is desirable to further suppress crack formation. Furthermore, if the honeycomb structure vibrates during vehicle operation, its position within the metal tube may sometimes shift.

[0009] The present invention was created in view of the above circumstances. In one embodiment, the objective is to provide a honeycomb structure housed in a metal tube that is not easily cracked or displaced when subjected to temperature changes and vibrations. In another embodiment, the objective is to provide an electrically heated carrier having the aforementioned honeycomb structure. In yet another embodiment, the objective is to provide an exhaust gas purification device having the aforementioned electrically heated carrier.

[0010] In one embodiment, the present invention is a honeycomb structure, wherein it comprises:

[0011] A conductive honeycomb structure having an outer peripheral wall and partitions, the partitions being disposed on the inner side of the outer peripheral wall and dividing it into multiple compartments, the multiple compartments forming a flow path from one end face to the other; and

[0012] A pair of electrode layers are disposed on the outer surface of the outer peripheral wall, facing each other and sandwiching the central axis of the honeycomb structure.

[0013] The coefficient of linear expansion of the honeycomb structure, as measured according to JIS R1618:2002, is 4.1 × 10⁻⁶ when the temperature changes from 40°C to 300°C. -6 The coefficient of linear expansion of the honeycomb structure, as measured according to JIS R1618:2002, is 4.2 × 10⁻⁶ °C when the temperature changes from 300 °C to 800 °C. -6 / ℃ or above 4.8×10 -6 / ℃ below.

[0014] In another embodiment, the present invention is an electrically heated carrier, comprising:

[0015] The honeycomb structure; and

[0016] A metal terminal is attached to the outer surface of each of the pair of electrode layers.

[0017] In another embodiment, the present invention is a waste gas purification device, comprising:

[0018] The electrically heated carrier; and

[0019] A cylindrical metal tube that houses the electrically heated carrier.

[0020] Invention Effects

[0021] One embodiment of the present invention involves a honeycomb structure housed within a metal tube that is less prone to cracking when subjected to temperature changes. Therefore, for example, by applying this honeycomb structure to an EHC (Exhaust Gas Concentrate), an EHC with excellent thermal shock resistance can be provided, which is less prone to cracking even when suddenly heated by high-temperature exhaust gases. Furthermore, even if vibration occurs during high-temperature heating, the honeycomb structure housed within the metal tube is unlikely to shift position. Attached Figure Description

[0022] Figure 1 This is a schematic diagram showing an electrically heated carrier according to one embodiment of the present invention viewed from one end.

[0023] Figure 2 This is a three-dimensional schematic diagram of an electrically heated carrier according to one embodiment of the present invention.

[0024] Figure 3 This is a cross-sectional schematic diagram illustrating an embodiment of the exhaust gas purification device involved in the invention.

[0025] Symbol Explanation

[0026] 100: Electric heating carrier; 110: Honeycomb structure; 112a: Electrode layer; 112b: Electrode layer; 113: Partition wall; 114: Outer peripheral wall; 115: Compartment; 116: End face; 118: End face; 120: Base layer; 130: Metal terminal; 200: Waste gas purification device; 220: Metal pipe; 240: Wire; 260: Gasket. Detailed Implementation

[0027] Next, with reference to the accompanying drawings, the embodiments for carrying out the present invention will be described in detail. The present invention is not limited to the following embodiments, and it should be understood that appropriate modifications and improvements can be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the invention.

[0028] (1. Electric heating type carrier)

[0029] Figure 1 This is a schematic diagram showing the electrically heated carrier 100 according to one embodiment of the present invention as viewed from one end face 116. Figure 2 This is a perspective view of an electrically heated carrier 100 according to one embodiment of the present invention. The electrically heated carrier 100 includes a honeycomb structure 110 and metal terminals 130. By supporting a catalyst on the electrically heated carrier 100, the electrically heated carrier 100 can be used as a catalyst.

[0030] 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: three-way catalysts, oxidation catalysts, and 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; and NOx storage and reduction catalysts (LNT catalysts) that contain alkaline earth metals and platinum as NOx storage components. Examples of catalysts that do not use noble metals include: NOx selective reduction catalysts (SCR catalysts) including copper-substituted zeolites or iron-substituted zeolites. Furthermore, two or more catalysts selected from the above-mentioned catalysts can be used. It should be noted that there are no particular limitations on the catalyst support method, and known methods of supporting catalysts in honeycomb structures can be used.

[0031] (1-1. Honeycomb structure)

[0032] In one embodiment, the honeycomb structure 110 includes:

[0033] A conductive honeycomb structure has an outer peripheral wall 114 and a partition wall 113, the partition wall 113 being disposed on the inner side of the outer peripheral wall 114 and dividing it into a plurality of compartments 115, the plurality of compartments 115 forming a flow path from one end face 116 to another end face 118; and

[0034] A pair of electrode layers 112a and 112b are disposed on the outer surface of the outer peripheral wall 114 in such a way that they are opposite each other, sandwiching the central axis O of the honeycomb structure.

[0035] The shape of the honeycomb structure 110 is not particularly limited. For example, it can be a column with round, oval, elliptical, racetrack-shaped, or oblong end faces, or a polygonal end face such as a triangle or quadrilateral, or a column with other irregular end faces. The honeycomb structure 110 shown in the figure has a round end face and is cylindrical in shape overall.

[0036] There are no particular restrictions on the height of a cellular structure (the length from one end face to another); it can be set appropriately according to the application and performance requirements. There are also no particular restrictions on the relationship between the height of the cellular structure and the maximum diameter of each end face (the longest diameter passing through the centroid of each end face). Therefore, the height of a cellular structure can be longer than the maximum diameter of each end face, or it can be shorter than the maximum diameter of each end face.

[0037] Furthermore, regarding the size of the honeycomb structure 110, for the reason of improving heat resistance (suppressing cracks in the circumferential direction of the outer peripheral wall), the area of ​​one end face is preferably 2000 to 20000 mm². 2 More preferably, it is 5000–15000 mm. 2 .

[0038] Although the volume resistivity of the outer peripheral wall 114 and the partition wall 113 is higher than that of the electrode layers 112a and 112b, they are conductive. Regarding the volume resistivity of the outer peripheral wall 114 and the partition wall 113, there are no particular limitations as long as they can be heated by Joule heating when energized. When measured using the four-terminal method at 25°C, it is preferably 0.1 to 200 Ωcm, more preferably 1 to 200 Ωcm, and even more preferably 10 to 100 Ωcm.

[0039] Regarding the materials of the outer peripheral wall 114 and the partition wall 113, there are no particular restrictions as long as they can generate heat using Joule heating when electricity is applied. Metals, ceramics (especially conductive ceramics), etc., can be used alone or in combination. There are no limitations on the materials of the outer peripheral wall 114 and the partition wall 113; they can contain one or more of the following: oxide ceramics such as alumina, andalusite, zirconium oxide, and cordierite; and non-oxide ceramics such as silicon carbide, silicon nitride, and aluminum nitride. Alternatively, silicon carbide-silicon composite materials and silicon carbide-graphite composite materials can also be used. From the viewpoint of possessing both heat resistance and electrical conductivity, the materials of the outer peripheral wall 114 and the partition wall 113 are preferably silicon carbide-silicon composite materials or silicon carbide as the main component. When the materials of the outer peripheral wall 114 and the partition wall 113 are mainly composed of silicon carbide-silicon composite materials, it means that the outer peripheral wall 114 and the partition wall 113 each contain more than 90% by mass of silicon carbide-silicon composite materials (total mass). Here, the silicon carbide-silicon composite material contains silicon carbide particles as aggregate and silicon as a binder material to bond the silicon carbide particles. Preferably, multiple silicon carbide particles are bonded together by silicon in such a way that fine pores are formed between the silicon carbide particles. When the material of the outer peripheral wall 114 and the partition wall 113 is mainly composed of silicon carbide, it means that the outer peripheral wall 114 and the partition wall 113 each contain more than 90% by mass of silicon carbide (total mass).

[0040] When the outer peripheral wall 114 and the partition wall 113 contain a silicon carbide-silicon composite material, the ratio of the mass of silicon as a binder in the outer peripheral wall 114 and the partition wall 113 to the total mass of silicon carbide particles as aggregate in the outer peripheral wall 114 and the partition wall 113 as a binder is preferably 10 to 40% by mass, more preferably 15 to 35% by mass. If it is 10% by mass or more, the strength of the outer peripheral wall 114 and the partition wall 113 can be sufficiently maintained. If it is 40% by mass or less, the shape is easily maintained during firing.

[0041] When the electrically heated carrier 100 is used in an exhaust gas purification device, it is usually fixed by pressing it into a metal tube located midway through the exhaust gas flow path from the engine, thus securing it in place. Pressure is applied to the outer peripheral wall 114 of the honeycomb structure 110 from the metal tube side to stably fix the electrically heated carrier 100 within the metal tube.

[0042] When hot exhaust gas flows from the engine into compartment 115, the honeycomb structure 110 undergoes thermal expansion. If the thermal expansion of the honeycomb structure 110 is significant, tensile stress is generated on the outer peripheral wall 114, which is the cause of cracks. However, if the thermal expansion of the honeycomb structure 110 is suppressed by the pressure from the metal tubes, cracks are less likely to form in the honeycomb structure 110. However, the metal tubes also thermally expand at high temperatures. Therefore, the honeycomb structure 110's thermal expansion to a certain extent can suppress the pressure drop from the metal tubes, thus effectively suppressing cracks.

[0043] Based on the above viewpoint, the inventors of this invention explored the relationship between the thermal expansion of the honeycomb structure 110 and the suppression of cracks. The results showed that it is advantageous to make the thermal expansion in the low temperature region of 40°C to 300°C greater than before, and to make the thermal expansion in the region of 300°C to 800°C the same level as before.

[0044] Specifically, for the honeycomb structure, the coefficient of linear expansion, measured according to JIS R1618:2002, is 4.1 × 10⁻⁶ when the temperature changes from 40°C to 300°C. -6 The coefficient of linear expansion, measured according to JIS R1618:2002, is 4.2 × 10⁻⁶ °C when the temperature changes from 300 °C to 800 °C. -6 / ℃ or above 4.8×10 -6 It is effective in inhibiting cracking below / ℃.

[0045] The coefficient of linear expansion of the honeycomb structure, measured according to JIS R1618:2002, is 4.1 × 10⁻⁶ when the temperature changes from 40℃ to 300℃. -6 A temperature above ℃ can suppress the increase in the thermal expansion difference between the honeycomb structure and the metal tube at high temperatures, thus helping to suppress the pressure drop from the metal tube. The lower limit of the linear expansion coefficient of this honeycomb structure when the temperature changes from 40℃ to 300℃ is preferably 4.5 × 10⁻⁶. -6 / ℃ or higher, more preferably 5.0×10 -6 / ℃ or above.

[0046] However, a heat treatment for sintering the catalyst into the honeycomb structure 110 is typically performed before canning. Therefore, during the heat treatment for sintering the catalyst, the crack suppression effect resulting from the pressure drop from the metal tube cannot be obtained. Thus, it is desirable to avoid excessive thermal expansion of the honeycomb structure 110. Accordingly, the upper limit of the linear expansion coefficient of the honeycomb structure portion when the temperature changes from 40°C to 300°C is preferably 7.5 × 10⁻⁶. -6 Below / ℃, more preferably 6.0×10 -6 / ℃ below.

[0047] The coefficient of linear expansion of the honeycomb structure, measured according to JIS R1618:2002, is 4.2 × 10⁻⁶ when the temperature changes from 300℃ to 800℃. -6 A temperature above ℃ can suppress the increase in the thermal expansion difference between the honeycomb structure and the metal tube at high temperatures, thus helping to suppress the pressure drop from the metal tube. The lower limit of the linear expansion coefficient of this honeycomb structure when the temperature changes from 300℃ to 800℃ is preferably 4.3 × 10⁻⁶. -6 / ℃ or higher, more preferably 4.4×10 -6 / ℃ or above.

[0048] Furthermore, the coefficient of linear expansion of the honeycomb structure, measured according to JIS R1618:2002, was 4.8 × 10⁻⁶ when the temperature changed from 300°C to 800°C. -6 Below a certain temperature, excessive thermal stress generated inside the honeycomb structure at high temperatures can be prevented. The upper limit of the linear expansion coefficient of the honeycomb structure when the temperature changes from 300℃ to 800℃ is preferably 4.7 × 10⁻⁶. -6 Below / ℃, more preferably 4.6×10 -6 / ℃ below.

[0049] In a preferred embodiment, the coefficient of linear expansion of the honeycomb structure measured according to JIS R1618:2002 when the temperature changes from 40°C to 300°C is greater than the coefficient of linear expansion of the honeycomb structure measured according to JIS R1618:2002 when the temperature changes from 300°C to 800°C. Specifically, the coefficient of linear expansion of the honeycomb structure measured according to JIS R1618:2002 when the temperature changes from 40°C to 300°C is set as CTE. A The coefficient of linear expansion of the honeycomb structure, measured according to JIS R 1618:2002, when the temperature changes from 300℃ to 800℃, is set as CTE. B At that time, CTE A >CTE B Established.

[0050] CTE is preferred A / CTE B ≥1.1 is established, and CTE is more preferred.A / CTE B ≥1.2 is valid.

[0051] CTE A / CTE B There is no specific upper limit set; typically, it is 1.5 ≥ CTE. A / CTE B ≥1.1 is true. More typically, 1.4 ≥ CTE. A / CTE B ≥1.2 is valid.

[0052] The linear expansion coefficient of the honeycomb structure was measured in the following order. For the honeycomb structure, a prism-shaped sample of 3mm × 3mm × 20mm (length in the extension direction of the compartment) was cut from the center of the honeycomb structure in both the radial and height directions. The linear expansion coefficient of this sample was measured under the temperature change conditions described above, and the measured value was recorded.

[0053] There is no limitation to the method of varying the coefficient of linear expansion of the honeycomb structure when the temperature changes from 40°C to 300°C and when the temperature changes from 300°C to 800°C. For example, a method can be used to make the honeycomb structure (outer peripheral wall, partition wall) a material that expands significantly due to a phase change between 40°C and 300°C.

[0054] Cubic quartz is an example of a material that undergoes a phase transition and expands significantly between 40°C and 300°C. Cubic quartz undergoes a phase transition and expands significantly around 200–300°C. Therefore, a higher cubic quartz content increases the coefficient of linear expansion when the temperature changes from 40°C to 300°C. Cubic quartz can be added to the ceramic raw material used to form the outer peripheral wall 114 and the partition wall 113. When the ceramic raw material used to form the outer peripheral wall 114 and the partition wall 113 contains Si, a cubic quartz-containing oxide film is generated when high-temperature firing is performed in an oxidizing atmosphere. Therefore, the cubic quartz content can be controlled by adjusting the oxidation treatment conditions after firing (temperature, holding time, type of oxidizing atmosphere, heating rate, cooling rate, etc.). Therefore, in one embodiment, at least a portion of the surface of each of the outer peripheral wall 114 and the partition wall 113 is covered by an oxide film containing cubic quartz.

[0055] The shape of the compartments in the cross-section perpendicular to the extending direction of compartment 115 is not limited, but is preferably quadrilateral, hexagonal, octagonal, or a combination thereof. Among these, quadrilaterals and hexagons are preferred. By setting the compartment shape to the above-mentioned shape, the pressure loss when exhaust gas flows through the honeycomb structure 110 is reduced, and the purification performance of the catalyst is excellent. From the viewpoint of easily achieving both structural strength and heating uniformity, a hexagonal shape is particularly preferred.

[0056] The compartment 115 can extend from one end face 116 to the other end face 118. Alternatively, the compartment 115 can be a first compartment with one end face 116 sealed and the other end face 118 having an opening, and a second compartment with one end face 116 having an opening and the other end face 118 sealed, which are alternately arranged adjacent to each other with a partition wall 113.

[0057] The thickness of the partition wall 113 that divides the compartments 115 is preferably 0.1 to 0.3 mm, more preferably 0.15 to 0.25 mm. A thickness of 0.1 mm or more for the partition wall 113 helps to suppress the reduction in strength of the honeycomb structure 110. A thickness of 0.3 mm or less for the partition wall 113 helps to suppress the increase in pressure loss during exhaust gas flow when the honeycomb structure 110 is used as a catalyst carrier to support the catalyst. In this invention, the thickness of the partition wall 113 is defined as the length of the portion of the line segment connecting the centroids of adjacent compartments 115 in a cross-section perpendicular to the extending direction of the compartment 115, passing through the partition wall 113.

[0058] Regarding the honeycomb structure 110, in a cross-section perpendicular to the extending direction of the compartments 115, 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 such a range, the purification performance of the catalyst can be improved to minimize the pressure loss when exhaust gas flows through the honeycomb structure 110. 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 In the following, when the honeycomb structure 110 is used as a catalyst carrier and a catalyst is supported thereon, excessive pressure loss during exhaust gas flow is suppressed. The compartment density is the value obtained by dividing the number of compartments by the area of ​​one end face of the honeycomb structure excluding the peripheral wall portion.

[0059] The partition wall 113 can be dense, but is preferably porous. The porosity of the partition wall 113 is preferably 35-60%, more preferably 35-45%. If the porosity is 35% or higher, deformation during firing is more easily suppressed. If the porosity is 60% or lower, the strength of the honeycomb structure 110 can be adequately maintained. The porosity is a value measured using a mercury porosimeter. It should be noted that dense material refers to material with a porosity of 5% or lower.

[0060] The average pore size of the partition 113 is preferably 2 to 15 μm, more preferably 4 to 8 μm. If the average pore size is 2 μm or more, excessive volume resistivity is suppressed. If the average pore size is 15 μm or less, excessively low volume resistivity is suppressed. The average pore size is a value measured using a mercury porosimeter.

[0061] From the viewpoint of ensuring the structural strength of the honeycomb structure 110 and suppressing leakage of fluid flowing through the compartment 115 from the outer peripheral side, it is useful to provide an outer peripheral wall 114 in the honeycomb structure 110. In this regard, the thickness of the outer peripheral wall 114 is preferably 0.1 mm or more, more preferably 0.15 mm or more, and even more preferably 0.2 mm or more. However, if the outer peripheral wall 114 is too thick, the strength will be too high, resulting in a strength imbalance with the compartment wall 113 and reduced thermal shock resistance. Therefore, the thickness of the outer peripheral wall 114 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 114 is defined as: the thickness in the normal direction of the tangent to the outer surface of the outer peripheral wall 114 at the measurement location when the portion of the outer peripheral wall 114 to be measured is observed in a section perpendicular to the extending direction of the compartment 115.

[0062] Electrode layers 112a and 112b, with a volume resistivity lower than that of the outer peripheral wall 114, are provided on the outer peripheral wall 114. This facilitates current diffusion in the circumferential direction of the honeycomb structure 110 and the extending direction of the compartments 115, thereby improving the uniform heating performance of the honeycomb structure 110. In a cross-section perpendicular to the compartment 115, the angle θ (0°≤θ≤180°) formed by two line segments extending from the circumferential center of each pair of electrode layers 112a and 112b to the central axis O of the honeycomb structure 110 is preferably 150°≤θ≤180°, more preferably 160°≤θ≤180°, further preferably 170°≤θ≤180°, and most preferably 180°.

[0063] The formation areas of electrode layers 112a and 112b are not particularly limited. From the viewpoint of improving the uniform heating performance of the honeycomb structure 110, electrode layers 112a and 112b are preferably arranged in a strip shape on the outer surface of the outer peripheral wall 114, extending along the circumferential direction of the honeycomb structure 110 and the extending direction of the compartment 115, respectively. Specifically, from the viewpoint of improving uniform heating performance by diffusing current in the circumferential direction, in a cross section perpendicular to the extending direction of the compartment 115, the central angle α formed by the two line segments connecting the two circumferential ends of each electrode layer 112a and 112b to the central axis O is preferably 30° or more, more preferably 40° or more, and even more preferably 60° or more. However, if the central angle α is too large, the current passing through the interior of the honeycomb structure 110 will decrease, while the current passing through the vicinity of the outer peripheral wall 114 will increase. Therefore, from the viewpoint of uniform heating of the honeycomb structure 110, the central angle α is preferably 140° or less, more preferably 130° or less, and even more preferably 120° or less. Furthermore, the electrode layers 112a and 112b preferably extend over a length of 80% or more, more preferably 90% or more, and more preferably the entire length of the honeycomb structure 110 between its two end faces. The electrode layers 112a and 112b can be a single layer or a multi-layered structure.

[0064] The thickness of electrode layers 112a and 112b 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 electrode layers 112a and 112b is 0.01 mm or more, the resistance is properly controlled, resulting in more uniform heating. If the thickness of electrode layers 112a and 112b is 5 mm or less, the possibility of breakage during canning is reduced. The thickness of electrode layers 112a and 112b is defined as the thickness in the normal direction of the tangent to the outer surface of electrode layers 112a and 112b at the measurement location when the portion of electrode layers 112a and 112b to be measured is observed in a cross-section perpendicular to the extending direction of compartment 115.

[0065] By making the volume resistivity of electrode layers 112a and 112b lower than that of partition wall 113 and outer peripheral wall 114, current can preferentially flow through electrode layers 112a and 112b, and when energized, the current can easily diffuse in the circumferential direction of the honeycomb structure 110 and the extending direction of the compartment 115. The volume resistivity of electrode layers 112a and 112b is preferably less than 1 / 10 of the volume resistivity of partition wall 113 and outer peripheral wall 114, more preferably less than 1 / 20, and even more preferably less than 1 / 30. However, if the difference in volume resistivity between the two is too large, the current will concentrate between the ends of the opposing electrode layers 112a and 112b, causing a shift in the heating of the honeycomb structure 110. Therefore, the volume resistivity of electrode layers 112a and 112b is preferably more than 1 / 200 of the volume resistivity of partition wall 113 and outer peripheral wall 114, more preferably more than 1 / 150, and even more preferably more than 1 / 100. In this invention, the volume resistivity of the electrode layer, partition wall, and outer peripheral wall is set to the value obtained by measuring at 25°C using the four-terminal method.

[0066] The materials of electrode layers 112a and 112b are not limited, and composite materials of metal and ceramic (especially conductive ceramic) (cermet) can be used. Examples of metals include elemental metals such as Cr, Fe, Co, Ni, Si, or Ti, or alloys containing at least one metal selected from these metals. Examples of ceramics are not limited, and in addition to silicon carbide (SiC), examples include metal compounds such as tantalum silicide (TaSi2) and chromium silicide (CrSi2). Specific examples of metal-ceramic composite materials (cermet) include composites of silicon metal and silicon carbide, composites of tantalum silicide or chromium silicide and silicon metal or 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. Among the various metals and ceramics mentioned above, the preferred materials for electrode layers 112a and 112b are composite materials of metal silicides such as tantalum silicide or chromium silicide and metal silicon or silicon carbide, based on the reason that they can be fired simultaneously with the partition wall and the outer peripheral wall to simplify the manufacturing process.

[0067] (1-2. Metal terminals)

[0068] Metal terminals 130 are directly or indirectly bonded to the outer surfaces of each of a pair of electrode layers 112a, 112b. When a voltage is applied to the honeycomb structure 110 via the metal terminals 130, electricity can be supplied and Joule heating can be utilized to heat the honeycomb structure 110. Therefore, the honeycomb structure 110 can also preferably be used as a heater. Accordingly, the uniform heating of the honeycomb structure 110 can be improved. The applied voltage is preferably 12–900V, more preferably 48–600V, and the applied voltage can be appropriately varied.

[0069] Metal terminals 130 and electrode layers 112a, 112b can be directly bonded. However, to mitigate the thermal expansion difference between electrode layers 112a, 112b and metal terminals 130 and improve the bonding reliability of metal terminals 130, bonding can be performed with one or more base layers 120 in between. Therefore, in a preferred embodiment, the honeycomb structure 110 has a pair of electrode layers 112a, 112b arranged opposite each other on its outer peripheral wall 114, sandwiching the central axis of the honeycomb structure 110. One or more metal terminals 130 are bonded to each electrode layer 112a, 112b with respect to the base layer 120.

[0070] From the viewpoint of improving the reliability of the connection, it is preferable to make the coefficient of thermal expansion decrease in stages in the order of metal terminal 130 → (substrate layer 120) → electrode layers 112a, 112b → outer peripheral wall 114. It should be noted that the "coefficient of thermal expansion" here refers to the coefficient of linear expansion measured according to JIS R1618:2002 when the temperature changes from 25°C to 1000°C.

[0071] The material for the metal terminal 130 can be any metal, without particular restrictions. Elemental metals and alloys can be used. From the viewpoints of corrosion resistance, volume resistivity, and thermal expansion coefficient, alloys containing at least one element selected from the group consisting of Cr, Fe, Co, Ni, and Ti are preferred, with stainless steel and Fe-Ni alloys being more preferable. The shape and size of the metal terminal 130 are not particularly limited and can be appropriately designed according to the size of the honeycomb structure 110, its electrical conductivity, etc.

[0072] The material of the substrate 120 is not limited; a composite material of metal and ceramic (especially conductive ceramic) (cermet) can be used. The thermal expansion rate of the substrate 120 can be controlled by adjusting, for example, the mixing ratio of metal and ceramic.

[0073] The substrate 120 is not limited, but preferably contains one or more metals selected from Ni-based alloys, Fe-based alloys, Ti-based alloys, Co-based alloys, metallic silicon, and Cr.

[0074] The base layer 120 is not limited, but preferably contains one or more ceramics selected from oxide ceramics such as alumina, andalusite, zirconium oxide, glass and cordierite, and non-oxide ceramics such as silicon carbide, silicon nitride and aluminum nitride.

[0075] The thickness of the base layer 120 is not particularly limited, but from the viewpoint of suppressing cracks, it is preferably 0.1 to 1.5 mm, and more preferably 0.3 to 0.5 mm. The thickness of the base layer 120 is defined as the thickness in the normal direction of the tangent to the outer surface of the base layer 120 at the measurement location when the base layer 120 to be measured is observed in a section perpendicular to the extension direction of the compartment.

[0076] There are no particular limitations on the bonding method between the metal terminal 130 and the electrode layers 112a, 112b or the base layer 120, for example: spraying, welding and brazing.

[0077] (2. Waste gas purification device)

[0078] An embodiment of the present invention relates to an electrically heated carrier 100 that can be used in an exhaust gas purification device. (See reference...) Figure 3 The exhaust gas purification device 200 includes an electrically heated carrier 100 and a cylindrical metal tube 220 for housing the electrically heated carrier 100. A power supply wire 240 can be connected to the metal terminal 130 of the electrically heated carrier 100. The material of the metal tube 220 is not limited; for example, stainless steel can be used.

[0079] In the exhaust gas purification device 200, the electrically heated carrier 100 can be positioned midway through the flow path of fluids such as automobile exhaust. The electrically heated carrier 100 can be fixed within the metal tube 220 by, for example, by pressing it into the metal tube 220 with its extension direction aligned with the extension direction of the compartment. A gasket (also called a "buffer material") 260 can be disposed between the metal tube 220 and the electrically heated carrier 100. The material of the gasket 260 is not limited, but ceramic fibers such as alumina fiber and andalusite fiber are preferred for reasons of suppressing positional displacement of the electrically heated carrier and maintaining surface pressure between the metal tube and the electrically heated carrier.

[0080] For the purpose of preventing positional displacement caused by exhaust gas pressure, the lower limit of the pressure exerted on the electrically heated carrier 100 fixed in the metal tube by the metal tube is preferably 0.1 MPa or more at 25°C, and more preferably 0.2 MPa or more.

[0081] For the purpose of preventing damage to the honeycomb structure, the upper limit of the pressure exerted on the electrically heated carrier 100 fixed in the metal tube by the metal tube is preferably 1.0 MPa or less at 25°C, and more preferably 0.8 MPa or less.

[0082] The pressure exerted on the electrically heated carrier 100 fixed inside the metal tube by the metal tube can be determined as follows: based on the outer diameter of the honeycomb structure, the inner diameter of the metal tube, and the specific gravity per unit area of ​​the gasket (g / m²). 2 Calculate the GBD (Gap Bulk Density) value, and use the inherent characteristic curve (GBD-surface pressure curve) of each gasket to determine the pressure (surface pressure) corresponding to the calculated GBD value. GBD (Gap Bulk Density) [g / cm³] 3 This refers to the density of the gasket between the honeycomb structure and the metal tube, which is equal to the specific gravity per unit area [g / m²]. 2 ] / ((inner diameter of metal tube - outer diameter of honeycomb structure)[mm]×1000).

[0083] (3. Manufacturing method)

[0084] Next, an illustrative description will be given of a method for manufacturing an electrically heated carrier according to one embodiment of the present invention. The electrically heated carrier can be manufactured using a manufacturing method comprising: step 1, obtaining a honeycomb molded body; step 2, obtaining an unburned honeycomb structure with an electrode layer forming paste attached; step 3, burning the unburned honeycomb structure with the electrode layer forming paste attached to obtain a honeycomb structure; and step 4, bonding metal terminals to the electrode layer.

[0085] (Process 1)

[0086] Step 1 is the process of fabricating the precursor of the honeycomb structure, i.e., the honeycomb molded body. The honeycomb molded body can be fabricated according to the honeycomb molded body fabrication method in a known honeycomb structure manufacturing method. For example, firstly, metallic silicon powder, binder, surfactant, pore-forming material, water, etc., are added to silicon carbide powder (silicon carbide) to prepare the 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 is preferably 3-50 μm, more preferably 3-40 μm. The average particle size of the metallic silicon particles in the metallic silicon powder 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 basis when the frequency distribution of particle size is measured using laser diffraction. Silicon carbide particles are the silicon carbide microparticles constituting the silicon carbide powder, and metallic silicon particles are the metallic silicon microparticles constituting the metallic silicon powder. It should be noted that this refers to the formulation of molding materials when the material of the honeycomb structure is set as a silicon-silicon carbide composite material. When the material of the honeycomb structure is set as silicon carbide, no metallic silicon is added.

[0087] Examples of binders include methylcellulose, hydroxypropyl methylcellulose, hydroxypropoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinyl alcohol. Among these, the combination of methylcellulose and hydroxypropoxycellulose is preferred. The binder content is preferably 2.0 to 10.0 parts by weight when the total mass of silicon carbide powder and metallic silicon powder is set to 100 parts by weight.

[0088] Ethylene glycol, dextrin, fatty acid soaps, polyols, etc., can be used as surfactants. These surfactants can be used alone or in combination of two or more. The surfactant content is preferably 0.1 to 2.0 parts by mass when the total mass of silicon carbide powder and metallic silicon powder is set to 100 parts by mass.

[0089] As a pore-forming material, it only needs to form pores after firing, and there are no particular limitations. Examples include graphite, starch, foaming resin, water-absorbing resin, and silica gel. The content of the pore-forming material is preferably 0.5 to 10.0 parts by mass when the total mass of silicon carbide powder and metallic silicon powder is set to 100 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 reference when the frequency distribution of particle size is measured using 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.

[0090] The water content is preferably 20 to 60 parts by mass when the total mass of silicon carbide powder and metallic silicon powder is set to 100 parts by mass.

[0091] Next, the obtained molding raw materials are mixed to form a billet, which is then extruded to produce a columnar honeycomb molded body with outer peripheral walls and partitions. During extrusion molding, a die with the desired overall shape, compartment shape, partition thickness, and compartment density can be used. Next, the obtained honeycomb molded body is preferably dried. If the length along the central axis of the honeycomb molded body is not the desired length, the two ends of the honeycomb molded body can be cut off to achieve the desired length. The dried honeycomb molded body is called a dried honeycomb body.

[0092] As a variation of step 1, the honeycomb molded body can be temporarily fired. That is, in this variation, the honeycomb molded body is fired to produce a fired honeycomb body, and step 2 is performed on the fired honeycomb body.

[0093] (Process 2)

[0094] Step 2 involves coating an electrode layer onto the side of the honeycomb molded body to form a paste, thereby obtaining an unfired honeycomb structure with the electrode layer forming paste attached. Various additives can be appropriately added to raw material powders (such as metal powders and ceramic powders) formulated according to the required characteristics of the electrode layer, and then the powders are mixed to form the electrode layer forming paste. The average particle size of the raw material powder is not limited, but is preferably 5–50 μm, and more preferably 10–30 μm. The average particle size of the raw material powder refers to the arithmetic mean particle size under a volume reference when the frequency distribution of particle size is measured using laser diffraction.

[0095] Next, the obtained electrode layer forming paste is applied to the desired areas on the side of the honeycomb molded body (typically a dried honeycomb body) to obtain an unburned honeycomb structure with the electrode layer forming paste attached. The method for preparing the electrode layer forming paste and the method for applying the electrode layer forming paste to the honeycomb molded body can be carried out according to known methods for manufacturing honeycomb structures. However, in order to make the electrode layer have a lower volume resistivity than the outer peripheral wall and the partition wall, the metal content ratio can be increased or the particle size of the metal particles in the raw material powder can be reduced compared to the outer peripheral wall and the partition wall.

[0096] (Process 3)

[0097] Step 3 is a step of firing an unfired honeycomb structure with an electrode layer forming paste attached to it to obtain a honeycomb structure. The unfired honeycomb structure with the electrode layer forming paste attached can be dried before firing. Additionally, degreasing can be performed before firing to remove adhesives, etc. The degreasing and firing methods are not particularly limited; electric furnaces, gas furnaces, etc., can be used for firing. Firing conditions also depend on the material of the honeycomb structure; however, heating at 1400–1500°C for 1–20 hours in an inactive atmosphere such as nitrogen or argon is preferred. Furthermore, it is preferable to perform an oxidation treatment for 1–20 hours after firing, within the range of 800°C to the highest oxidation treatment temperature, to improve durability and form an oxide film containing quartz. Preferably, the average heating rate from 800°C to the highest oxidation treatment temperature is 20–400°C / h, and the average cooling rate from the highest oxidation treatment temperature to 800°C is 400–40°C / h. For example, the oxidation treatment can be performed in an oxygen atmosphere, an atmospheric atmosphere, or a water vapor atmosphere. When using metallic silicon as the molding material, the amount of quartzite formed can be adjusted by changing the oxidation treatment conditions. Specifically, if the heating and cooling rates are both slow above 800°C, the amount of quartzite formed increases. The higher the oxidation temperature and the longer the oxidation time, the greater the amount of quartzite formed. Furthermore, oxidation treatment in an oxygen atmosphere or a water vapor atmosphere is more conducive to increasing the amount of quartzite formed compared to an atmospheric atmosphere. If the amount of quartzite formed increases, the coefficient of linear expansion of the honeycomb structure section tends to increase when the temperature changes from 40°C to 300°C.

[0098] (Step 4)

[0099] Step 4 is the process of bonding the metal terminals to the electrode layer. There are no particular limitations on the bonding method; examples include spray plating, welding, and brazing. To improve the adhesion between the electrode layer and the metal terminals, methods such as spray plating can be used to form the base layer.

[0100] Example

[0101] The following examples illustrate embodiments for a better understanding of the invention and its advantages; however, the invention is not limited to these embodiments.

[0102] <Example 1>

[0103] (1. Production of cylindrical blanks)

[0104] A ceramic raw material was prepared by mixing silicon carbide (SiC) powder and silicon metal (Si) powder at a mass ratio of 80:20. Then, hydroxypropyl methylcellulose as a binder, a water-absorbing resin as a pore-forming material, and water were added to the ceramic raw material to prepare a molding raw material. The molding raw material was then kneaded using a vacuum ply mill to produce cylindrical blanks. The binder content was 7 parts by mass when the total mass of silicon carbide (SiC) powder and silicon metal (Si) powder was 100 parts by mass. The pore-forming material content was 3 parts by mass when the total mass of silicon carbide (SiC) powder and silicon metal (Si) powder was 100 parts by mass. The water content was 42 parts by mass when the total mass of silicon carbide (SiC) powder and silicon metal (Si) powder was 100 parts by mass. The average particle size of the silicon carbide powder was 20 μm, and the average particle size of the silicon metal powder was 6 μm. The average particle size of the pore-forming material was also 20 μm. The average particle size of silicon carbide powder, metallic silicon powder, and pore-forming materials refers to the arithmetic mean particle size under a volume reference when the frequency distribution of particle size is measured using laser diffraction.

[0105] (2. Preparation of honeycomb dried body)

[0106] Using an extrusion molding machine with a checkerboard die structure, the obtained cylindrical preform is shaped to obtain a cylindrical honeycomb molded body with hexagonal compartments in a cross-section perpendicular to the extension direction of the compartments. After high-frequency dielectric heating and drying, the honeycomb molded body is dried at 120°C for 2 hours using a hot air dryer. The two bottom surfaces are then cut off by a specified amount to produce a dried honeycomb body.

[0107] (3. Preparation of electrode layer paste)

[0108] Metallic silicon (Si) powder, silicon carbide (SiC) powder, methylcellulose, glycerol, and water were mixed using a rotary mixer to prepare an electrode layer paste. The Si powder and SiC powder were mixed in a volume ratio of 40:60. Additionally, when the total amount of Si and SiC powder was set to 100 parts by mass, methylcellulose was 0.5 parts by mass, glycerol was 10 parts by mass, and water was 38 parts by mass. The average particle size of the metallic silicon powder was 6 μm. The average particle size of the silicon carbide powder was 35 μm. These average particle sizes refer to the arithmetic mean particle size under a volume basis, measured using laser diffraction to determine the frequency distribution of particle size.

[0109] (4. Coating of the electrode layer with paste)

[0110] Using a curved surface printing machine, the electrode layer forming paste described above is applied to two portions of the outer surface of the outer peripheral wall of the honeycomb drying body in an opposing manner, sandwiched between the central axis. Each coating portion is formed in a strip shape along the entire length between the two bottom surfaces of the honeycomb drying body (angle θ = 180°, central angle α = 90°).

[0111] (5. Firing)

[0112] The honeycomb structure with the electrode layer forming paste was dried at 120°C and then degreased at 550°C for 3 hours in an atmospheric atmosphere. Next, the degreased honeycomb structure with the electrode layer forming paste was sintered and then oxidized to obtain a cylindrical honeycomb structure with a height of 65 mm and a diameter of 80 mm. Sintering was carried out at 1450°C in an argon atmosphere for 2 hours. Subsequently, the oxidation process was performed under the following conditions: an average heating rate from 800°C to the highest temperature listed in Table 1, the highest oxidation temperature, the holding time at the highest temperature, the average cooling rate from the highest temperature to 800°C, and the oxidizing atmosphere, to generate an oxide film containing quartz. Analysis of the partition wall sample using X-ray diffraction confirmed the formation of quartz.

[0113] <Example 2>

[0114] The oxidation treatment conditions were changed to those described in Table 1, and the honeycomb structure was otherwise manufactured under the same manufacturing conditions as in Example 1.

[0115] <Example 3>

[0116] Compared to Example 1, the mass ratio of metallic silicon (Si) powder was increased to prepare ceramic raw materials for blank production. In addition, the oxidation treatment conditions were changed to those described in Table 1. Otherwise, the honeycomb structure was produced under the same manufacturing conditions as in Example 1.

[0117] <Example 4>

[0118] Compared to Example 1, the mass ratio of silicon carbide (SiC) powder was increased to prepare ceramic raw materials for blank production. In addition, the oxidation treatment conditions were changed to those described in Table 1. Otherwise, the honeycomb structure was produced under the same manufacturing conditions as in Example 1.

[0119] <Example 5>

[0120] The oxidation treatment conditions were changed to those described in Table 1, and the honeycomb structure was otherwise manufactured under the same manufacturing conditions as in Example 1.

[0121] <Example 6>

[0122] Compared to Example 1, the mass ratio of silicon carbide (SiC) powder was increased to prepare ceramic raw materials for blank production. In addition, the oxidation treatment conditions were changed to those described in Table 1. Otherwise, the honeycomb structure was produced under the same manufacturing conditions as in Example 1.

[0123] <Comparative Examples 1-3>

[0124] The oxidation treatment conditions were changed to those described in Table 1, and the honeycomb structure was otherwise manufactured under the same manufacturing conditions as in Example 1.

[0125] <Comparative Examples 4-5>

[0126] In addition to silicon carbide (SiC) powder and metallic silicon (Si) powder, cordierite powder was added. These were mixed to prepare a ceramic raw material for green body fabrication. Furthermore, the oxidation treatment conditions were changed to those described in Table 1. Otherwise, a honeycomb structure was fabricated under the same manufacturing conditions as in Example 1. For test examples where cordierite powder was added to the ceramic raw material, "Contains Cd" is recorded as "Yes". For test examples where cordierite powder was not added to the ceramic raw material, "Contains No Cd" is recorded as "No".

[0127] <Characteristic Evaluation>

[0128] The honeycomb structures obtained under the above manufacturing conditions were subjected to the following characteristic evaluation. It should be noted that the number of honeycomb structures prepared for the characteristic evaluation was sufficient.

[0129] (1. Coefficient of linear expansion)

[0130] Using the method described above, samples were obtained from the center of the honeycomb structure in the radial and height directions of the honeycomb structure involved in the examples and comparative examples. The coefficient of linear expansion (CTE) of the honeycomb structure was measured according to JIS R1618:2002 when the temperature varied from 40°C to 300°C. A(40-300℃) and the coefficient of linear expansion (CTE) of the honeycomb structure as measured according to JIS R1618:2002 when the temperature changes from 300℃ to 800℃. B The measurements were performed at (300–800℃). The results are shown in Table 1.

[0131] (2. Catalyst pre-calcination simulation test)

[0132] Simulation experiments were conducted on the heating conditions during catalyst pre-calcination. Specifically, the honeycomb structures involved in the examples and comparative examples were held in an electric furnace at an internal temperature of 550°C for 20 minutes, then removed from the furnace and allowed to cool naturally for 15 minutes, followed by cooling to room temperature using a cooling fan. The sides and ends of the honeycomb structures were visually inspected for cracks. This simulation experiment was performed on five honeycomb structures, and the number of honeycomb structures without any detectable cracks was counted. The results are shown in Table 1.

[0133] (3. Cold and heat test)

[0134] A propane gas burner testing machine equipped with a metal tube and a propane gas burner capable of supplying combustion gas into the metal tube was used to conduct cold and hot tests on the honeycomb structures involved in the examples and comparative examples. Specifically, a canister was inserted into a metal tube with an inner diameter of 87 mm and fixed inside a stainless steel metal tube. At this time, a gasket (buffer material) made of ceramic (such as alumina fiber and andalusite fiber) was sandwiched between the metal tube and the honeycomb structure. It should be noted that, based on the outer diameter of the honeycomb structure, the inner diameter of the metal tube, and the specific gravity per unit area of ​​the ceramic gasket, the surface pressure of the honeycomb structure fixed inside the metal tube at 25°C was calculated to be 0.1 MPa using the method described above.

[0135] Next, the combustion gas produced by burning propane gas in a propane burner was allowed to flow from one end face of a honeycomb structure fixed inside a metal tube to the other. Within 10 minutes, the temperature of the combustion gas at the inlet side of the honeycomb structure was raised to 950°C and maintained at that temperature for 5 minutes. Then, air was circulated, and the temperature was cooled to 150°C within 3 minutes and maintained at 150°C for 10 minutes. Finally, the honeycomb structure was cooled to room temperature and removed from the metal tube. The sides and ends of the removed honeycomb structures were visually inspected for cracks. This hot-cold test was performed on five honeycomb structures, and the number of honeycomb structures without any detectable cracks was counted. The results are shown in Table 1.

[0136] (4. HVT test)

[0137] A propane gas burner testing machine equipped with a metal tube and a propane gas burner capable of supplying combustion gas into the metal tube was used to conduct cold and hot tests on the honeycomb structures involved in the examples and comparative examples. Specifically, a canister was inserted into a metal tube with an inner diameter of 87 mm and fixed inside a stainless steel metal tube. At this time, a gasket (buffer material) made of ceramic (such as alumina fiber and andalusite fiber) was sandwiched between the metal tube and the honeycomb structure. Based on the outer diameter of the honeycomb structure, the inner diameter of the metal tube, and the specific gravity per unit area of ​​the ceramic gasket, the surface pressure of the honeycomb structure fixed inside the metal tube at 25°C was calculated to be 0.1 MPa using the method described above.

[0138] Next, the combustion gas produced by burning propane gas in a propane burner was allowed to flow from one end face of a honeycomb structure fixed inside a metal tube to the other. The temperature of the combustion gas at the inlet side of the honeycomb structure was raised to 900°C within 10 minutes and maintained at that temperature for 5 minutes. Then, air was introduced, and the structure was cooled to 100°C within 3 minutes and maintained at 100°C for 10 minutes. This series of operations was considered one cycle, and 96 cycles were performed. Simultaneously, while the combustion gas was flowing, the honeycomb structure was subjected to vibration at an acceleration of 40G and a frequency of 150Hz using a vibration load device. Finally, the structure was cooled to room temperature, and the longitudinal displacement of the metal tube inside the honeycomb structure before and after the experiment was measured. The results are shown in Table 1.

[0139] Table 1

[0140]

[0141] (5. Site Visit)

[0142] As shown in Table 1: CTE A (40-300℃) and CTE B (300-800℃) The honeycomb structures of Examples 1-6, when appropriately housed in metal tubes, are less prone to cracking when subjected to temperature changes. It was also learned that: CTE A (40-300℃) and CTE B The honeycomb structures of Examples 1 to 4, which are more suitable (300-800°C), are less prone to cracking when subjected to temperature changes at relatively low temperatures, such as during catalyst pre-calcination.

Claims

1. A honeycomb structure, wherein, have: A conductive honeycomb structure having an outer peripheral wall and partitions, the partitions being disposed on the inner side of the outer peripheral wall and dividing it into multiple compartments, the multiple compartments forming a flow path from one end face to the other; and A pair of electrode layers are disposed on the outer surface of the outer peripheral wall, facing each other and sandwiching the central axis of the honeycomb structure. The coefficient of linear expansion of the honeycomb structure, as measured according to JIS R1618:2002, is 4.1 × 10⁻⁶ when the temperature changes from 40°C to 300°C. -6 The coefficient of linear expansion of the honeycomb structure, as measured according to JIS R1618:2002, is 4.2 × 10⁻⁶ °C when the temperature changes from 300 °C to 800 °C. -6 / ℃ or above 4.8×10 -6 / ℃ below.

2. The honeycomb structure according to claim 1, wherein, The coefficient of linear expansion of the honeycomb structure, as measured according to JIS R1618:2002, is 4.1 × 10⁻⁶ when the temperature changes from 40°C to 300°C. -6 / ℃Above 6.0×10 -6 / ℃ below.

3. The honeycomb structure according to claim 1 or 2, wherein, The outer peripheral wall and the partition wall are made of silicon carbide-silicon composite material as the main component.

4. The honeycomb structure according to claim 3, wherein, At least a portion of the surface of the outer peripheral wall and the partition wall is covered by an oxide film containing quartz.

5. The honeycomb structure according to claim 1 or 2, wherein, The coefficient of linear expansion of the honeycomb structure, as measured according to JIS R1618:2002, when the temperature changes from 40°C to 300°C is greater than the coefficient of linear expansion of the honeycomb structure, as measured according to JIS R1618:2002, when the temperature changes from 300°C to 800°C.

6. An electrically heated carrier, wherein, have: The honeycomb structure according to any one of claims 1 to 5; and A metal terminal is attached to the outer surface of each of the pair of electrode layers.

7. A waste gas purification device, wherein, have: The electrically heated carrier as described in claim 6; and A cylindrical metal tube that houses the electrically heated carrier.

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