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

Abstract

To provide a honeycomb structure difficult to generate cracks when receiving a temperature change housed in a metal tube.SOLUTION: A honeycomb structure comprises: a conductive honeycomb structure having an outer peripheral wall and a conductive honeycomb structure that is arranged inside the outer peripheral wall and has a partition wall that defines a plurality of cells forming a flow path from one end face to the other end face, and a pair of electrode layers provided on the outer surface of the outer peripheral wall so as to face each other across a central axis of the honeycomb, wherein a coefficient of linear expansion of the honeycomb structure measured according to JIS R1618:2002 when the temperature is changed from 40°C to 300°C. is 4.1 x 10-6 / °C or more, and the coefficient of linear expansion of the honeycomb structure measured according to JIS R1618:2002 when the temperature is changed from 300°C to 800°C. is 4.2×10-6 / °C or more and 4.8×10-6 / °C or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, electrically heated catalysts (EHCs) have been proposed to improve the decrease in exhaust gas purification performance immediately after engine startup. An EHC is a system in which a pair of electrodes are arranged on a honeycomb structure made of conductive ceramics, and by applying an electric current, the honeycomb structure itself is heated, thereby raising the catalyst supported on the honeycomb structure to its activation temperature before engine startup. In an EHC, the honeycomb structure is usually housed (canned) in a metal can (hereinafter referred to as "metal tube") and installed in the middle of the exhaust gas flow path of an automobile.

[0003] Since high-temperature exhaust gas flows through the exhaust gas passage, the honeycomb structure is required to have thermal shock resistance. To improve thermal shock resistance, suitable thermal expansion coefficients for ceramics, which are the constituent materials of the honeycomb structure, have been investigated. Patent Document 1 states that the linear expansion coefficient at 25 to 800°C is preferably 3.5 to 6.0 ppm / K, and more preferably 3.5 to 4.5 ppm / K. Patent Document 2 states that the linear expansion coefficient at 40 to 800°C is 2.0 × 10⁻⁶. -6 / K~4.6×10 -6 It is stated that / K is preferred. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-181457 [Patent Document 2] Japanese Patent Publication No. 2014-189447 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] By setting the linear expansion coefficient of the ceramics, which is a constituent material of the honeycomb structure, within the range taught by prior art documents, the thermal shock resistance of the honeycomb structure can be enhanced. However, even when a honeycomb structure made of ceramics having a linear expansion coefficient within the range described in prior art documents is housed in a metal pipe and installed in the middle of an exhaust gas flow path of an automobile and actually used, cases where cracks occur have been observed. When cracks occur in the honeycomb structure, it becomes difficult for electricity to flow through the cracked portion, resulting in a decrease in heat generation performance or a decrease in mechanical strength. Therefore, it is desirable to further suppress the occurrence of cracks. Further, when the honeycomb structure vibrates during the operation of the automobile, the honeycomb structure may be displaced within the metal pipe.

[0006] The present invention has been created in view of the above circumstances, and in one embodiment, an object is to provide a honeycomb structure that is housed in a metal pipe and is difficult to crack and is difficult to be displaced when receiving temperature changes and vibrations. In another embodiment of the present invention, an object is to provide an electrically heated carrier including such a honeycomb structure. In yet another embodiment of the present invention, an object is to provide an exhaust gas purification device including such an electrically heated carrier.

Means for Solving the Problems

[0007] In one embodiment of the present invention, a conductive honeycomb structure portion having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and partitioning and forming a plurality of cells that form a flow path from one end face to the other end face, and a pair of electrode layers provided on the outer surface of the outer peripheral wall so as to face each other across the central axis of the honeycomb structure portion, the linear expansion coefficient of the honeycomb structure portion measured according to JIS R1618:2002 when the temperature is changed from 40°C to 300°C is 4.1×10 -6 / °C or more, and the linear expansion coefficient of the honeycomb structure portion measured according to JIS R1618:2002 when the temperature is changed from 300°C to 800°C is 4.2×10 -6above 4.8×10 / ℃ -6 is below / ℃ is a honeycomb structure.

[0008] In another embodiment of the present invention, the honeycomb structure and metal terminals joined to the outer surfaces of each of the pair of electrode layers, constitute an electrically heated carrier.

[0009] In yet another embodiment of the present invention, the electrically heated carrier and a cylindrical metal tube that houses the electrically heated carrier, constitute an exhaust gas purification device.

Advantages of the Invention

[0010] The honeycomb structure according to an embodiment of the present invention is housed in a metal tube and is less likely to crack when subjected to temperature changes. Therefore, for example, by applying the honeycomb structure to an EHC, it is possible to provide an EHC with excellent heat shock resistance that is less likely to crack even when rapidly heated by high-temperature exhaust gas. Also, even when vibration occurs during high-temperature heating, displacement of the honeycomb structure housed in the metal tube is less likely to occur.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic diagram when observing the electrically heated carrier according to an embodiment of the present invention from one end face. [Figure 2] It is a schematic perspective view of the electrically heated carrier according to an embodiment of the present invention. [Figure 3] It is a schematic cross-sectional view showing an exhaust gas purification device according to an embodiment of the invention.

Modes for Carrying Out the Invention

[0012] Next, embodiments for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that appropriate design changes, improvements, etc., can be made based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the invention.

[0013] (1. Electrically heated carrier) Figure 1 is a schematic diagram of an electrically heated carrier 100 according to one embodiment of the present invention, as observed from one end face 116. Figure 2 is a schematic perspective view of the electrically heated carrier 100 according to one embodiment of the present invention. The electrically heated carrier 100 comprises 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.

[0014] Examples of catalysts include precious metal catalysts and other catalysts. Precious metal catalysts include ternary catalysts and oxidation catalysts in which precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) are supported on the surface of alumina pores and include co-catalysts such as ceria and zirconia, or alkaline earth metals and platinum are used to produce nitrogen oxides (NOx). x NO, which is contained as a storage component of ) x An example is a storage-reduction catalyst (LNT catalyst). As a catalyst that does not use precious metals, NO containing copper-substituted or iron-substituted zeolites is an example. x Examples include selective reduction catalysts (SCR catalysts). Furthermore, two or more catalysts selected from these catalysts may be used. There are no particular restrictions on the catalyst support method; known methods for supporting catalysts on honeycomb structures can be employed.

[0015] (1-1. Honeycomb structure) In one embodiment, the honeycomb structure 110 is A conductive honeycomb structure having an outer periphery wall 114 and partition walls 113 disposed inside the outer periphery wall 114, which divide and form a plurality of cells 115 that form a flow path from one end face 116 to the other end face 118, and A pair of electrode layers 112a and 112b are provided on the outer surface of the outer peripheral wall 114 so as to face each other across the central axis O of the honeycomb structure portion.

[0016] The outer shape of the honeycomb structure 110 is not particularly limited. For example, it can be a round column such as a column with an end face having a circular shape, an oval shape, an elliptical shape, a race track shape, or an oblong shape, a polygonal column such as a column with an end face having a triangular shape or a quadrangular shape, and a column with an end face having other irregular shapes. The illustrated honeycomb structure 110 has a circular end face shape and is generally cylindrical.

[0017] The height of the honeycomb structure (the length from one end face to the other end face) is not particularly limited and may be appropriately set according to the application and required performance. There is also no particular limitation on the relationship between the height of the honeycomb structure and the maximum diameter of each end face (the diameter that indicates the maximum length among the diameters passing through the center of gravity of each end face of the honeycomb structure). Therefore, the height of the honeycomb structure may be longer than the maximum diameter of each end face, or the height of the honeycomb structure may be shorter than the maximum diameter of each end face.

[0018] In addition, the size of the honeycomb structure 110 is preferably such that the area of one end face is 2000 to 20000 mm 2 due to the reason of enhancing heat resistance (suppressing cracks entering in the circumferential direction of the outer peripheral wall), and more preferably 5000 to 15000 mm 2 is further preferred.

[0019] The outer peripheral wall 114 and the partition wall 113 have conductivity although their volume resistivity is higher than that of the electrode layers 112a and 112b. The volume resistivity of the outer peripheral wall 114 and the partition wall 113 is not particularly limited as long as it can generate heat by Joule heat when energized, but when measured at 25°C by the four-terminal method, it is preferably 0.1 to 200 Ωcm, more preferably 1 to 200 Ωcm, and still more preferably 10 to 100 Ωcm.

[0020] The materials for the outer perimeter wall 114 and the partition wall 113 are not particularly limited as long as they can generate heat by Joule heating when an electric current is passed through them, and metals and ceramics (especially conductive ceramics) can be used alone or in combination. The materials for the outer perimeter wall 114 and the partition wall 113 are not limited, but may include one or more selected from oxide ceramics such as alumina, mullite, zirconia, and cordierite, and non-oxide ceramics such as silicon carbide, silicon nitride, and aluminum nitride. Silicon carbide-silicon composites and silicon carbide-graphite composites can also be used. Among these, from the viewpoint of achieving both heat resistance and conductivity, it is preferable that the materials for the outer perimeter wall 114 and the partition wall 113 consist mainly of silicon carbide-silicon composites or silicon carbide. When the material of the outer perimeter wall 114 and the partition wall 113 is said to be mainly composed of silicon carbide-silicon composite material, it means that the outer perimeter wall 114 and the partition wall 113 each contain silicon carbide-silicon composite material (total mass) of 90% or more of the total mass. Here, the silicon carbide-silicon composite material contains silicon carbide particles as aggregate and silicon as a binder to bind the silicon carbide particles together, and it is preferable that multiple silicon carbide particles are bound together by silicon in such a way that pores are formed between the silicon carbide particles. When the material of the outer perimeter wall 114 and the partition wall 113 is said to be mainly composed of silicon carbide, it means that the outer perimeter wall 114 and the partition wall 113 each contain silicon carbide (total mass) of 90% or more of the total mass.

[0021] When the outer perimeter wall 114 and partition wall 113 contain a silicon carbide-silicon composite material, the ratio of the "mass of silicon as a binder" contained in the outer perimeter wall 114 and partition wall 113 to the sum of the "mass of silicon carbide particles as aggregate" and the "mass of silicon as a binder" contained in the outer perimeter wall 114 and partition wall 113 is preferably 10 to 40 mass%, and more preferably 15 to 35 mass%, respectively. If it is 10 mass% or more, the strength of the outer perimeter wall 114 and partition wall 113 is sufficiently maintained. If it is 40 mass% or less, it becomes easier to maintain the shape during firing.

[0022] When the electrically heated carrier 100 is used in an exhaust gas purification device, it is often fixed by push-canning, which involves pushing and fitting it into a metal pipe installed in the middle of the exhaust gas flow path for the exhaust gas from the engine. Pressure is applied to the outer wall 114 of the honeycomb structure 110 from the metal pipe side, stably fixing the electrically heated carrier 100 inside the metal pipe.

[0023] When high-temperature exhaust gas flows from the engine to the cell 115, the honeycomb structure 110 expands due to heat. However, if the thermal expansion of the honeycomb structure 110 becomes large, tensile stress is generated in the outer wall 114, which can cause cracks. However, if the thermal expansion of the honeycomb structure 110 is suppressed by the pressure from the metal pipe, cracks are less likely to form in the honeycomb structure 110. However, the metal pipe also expands due to heat at high temperatures. Therefore, allowing the honeycomb structure 110 to expand to a certain extent is effective in suppressing cracks because it suppresses the decrease in pressure from the metal pipe.

[0024] From the above perspective, the inventors investigated the relationship between thermal expansion and crack suppression of the honeycomb structure 110 and found that it is advantageous to increase the thermal expansion in the low-temperature region from 40°C to 300°C compared to conventional structures, while keeping the thermal expansion from 300°C to 800°C at the same level as conventional structures.

[0025] Specifically, the honeycomb structure has a coefficient of linear expansion of 4.1 × 10⁻¹⁰ when subjected to a temperature change from 40°C to 300°C, as measured according to JIS R1618:2002. -6 The temperature is above / ℃, and the coefficient of linear expansion measured according to JIS R1618:2002 when the temperature is changed from 300℃ to 800℃ is 4.2 × 10⁻⁶. -6 / ℃ or higher 4.8×10 -6 Maintaining a temperature below / ℃ is effective in suppressing cracking.

[0026] The coefficient of linear expansion of the honeycomb structure, measured according to JIS R1618:2002 when the temperature is changed from 40°C to 300°C, is 4.1 × 10⁻⁶. -6A value of 4.5 × 10⁻⁶ or higher helps to suppress the widening of the thermal expansion difference with the metal tube at high temperatures, and contributes to suppressing the decrease in pressure from the metal tube. The lower limit of the linear expansion coefficient of the honeycomb structure when the temperature is changed from 40°C to 300°C is 4.5 × 10⁻⁶. -6 It is preferable that the temperature is above / ℃, 5.0 × 10 -6 A temperature of / ℃ or higher is more preferable.

[0027] However, the heat treatment to bake the catalyst onto the honeycomb structure 110 is usually performed before canning. Therefore, the crack suppression effect by suppressing the decrease in pressure from the metal tube during the heat treatment to bake the catalyst cannot be obtained. For this reason, 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 when the temperature is changed from 40°C to 300°C is 7.5 × 10⁻⁶. -6 It is preferable that the temperature is below / ℃, and 6.0 × 10 -6 It is more preferable that the temperature be below / ℃.

[0028] The coefficient of linear expansion of the honeycomb structure, measured according to JIS R1618:2002 when the temperature is changed from 300°C to 800°C, is 4.2 × 10⁻⁶. -6 A value of 4.3 × 10⁻⁶ or higher helps to suppress the widening of the thermal expansion difference with the metal tube at high temperatures, and contributes to suppressing the decrease in pressure from the metal tube. The lower limit of the linear expansion coefficient of the honeycomb structure when the temperature is changed from 300°C to 800°C is 4.3 × 10⁻⁶. -6 It is preferable that the temperature is above / ℃, 4.4 × 10 -6 A temperature of / ℃ or higher is more preferable.

[0029] Furthermore, the coefficient of linear expansion of the honeycomb structure, measured according to JIS R1618:2002 when the temperature is changed from 300°C to 800°C, is 4.8 × 10⁻⁶. -6 By keeping the temperature below / °C, it is possible to prevent excessive thermal stress from occurring inside the honeycomb structure at high temperatures. The upper limit of the coefficient of linear expansion of the honeycomb structure when the temperature is changed from 300°C to 800°C is 4.7 × 10⁻⁶. -6It is preferable that the temperature is below / ℃, 4.6 × 10 -6 It is more preferable that the temperature be below / ℃.

[0030] In a preferred embodiment, the coefficient of linear expansion of the honeycomb structure measured according to JIS R1618:2002 when the temperature is changed 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 is changed 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 is changed from 40°C to 300°C is greater than the coefficient of linear expansion of the honeycomb structure measured according to JIS R1618:2002. A The coefficient of linear expansion of the honeycomb structure, measured according to JIS R1618:2002 when the temperature is changed from 300°C to 800°C, is defined as CTE. B Therefore, CTE A >CTE B This is true. CTE A / CTE B It is preferable that ≥ 1.1 holds true, and CTE A / CTE B It is more preferable that ≥ 1.2 holds true.

[0031] CTE A / CTE B There is no specific upper limit set, but typically it is 1.5 ≥ CTE. A / CTE B The condition ≥ 1.1 holds true. More typically, 1.4 ≥ CTE. A / CTE B The condition ≥ 1.2 holds true.

[0032] The coefficient of thermal expansion of the honeycomb structure is measured using the following procedure: A prismatic sample measuring 3 mm × 3 mm × 20 mm (length in the cell stretching direction) is cut from the honeycomb structure from the center in the radial and height directions of the honeycomb structure. The coefficient of thermal expansion of this sample is measured under the temperature change conditions described above, and the measured value is recorded.

[0033] Regarding the honeycomb structure, one method, though not limited, for introducing a change between the coefficient of linear expansion when the temperature is changed from 40°C to 300°C and when the temperature is changed from 300°C to 800°C is to use a material that undergoes a phase transition and expands significantly between 40°C and 300°C for the honeycomb structure (outer walls, partitions).

[0034] Cristobalite is an example of a material that undergoes a phase transition and expands significantly between 40°C and 300°C. Cristobalite undergoes a phase transition and expands significantly around 200-300°C. Therefore, a high cristobalite content can increase the coefficient of linear expansion when the temperature is changed from 40°C to 300°C. Cristobalite may be added to the ceramic raw material for forming the outer periphery wall 114 and the partition wall 113. However, if Si is included in the ceramic raw material for forming the outer periphery wall 114 and the partition wall 113, a cristobalite-containing oxide film is formed when fired at high temperature in an oxidizing atmosphere. Therefore, the cristobalite content can be controlled by adjusting the oxidation treatment conditions after firing (temperature, holding time, type of oxidizing atmosphere, heating rate, cooling rate, etc.). Accordingly, in one embodiment, at least a portion of the surface of each of the outer periphery wall 114 and the partition wall 113 is coated with a cristobalite-containing oxide film.

[0035] There are no restrictions on the shape of the cell in a cross-section perpendicular to the extension direction of the cell 115, but it is preferably a square, hexagon, octagon, or a combination thereof. Among these, square and hexagonal are preferred. By shaping the cell in this way, the pressure loss when exhaust gas is passed through the honeycomb structure 110 is reduced, resulting in excellent catalyst purification performance. From the viewpoint of easily achieving both structural strength and heating uniformity, a hexagon is particularly preferred.

[0036] Cell 115 may extend from one end face 116 to the other end face 118. Alternatively, the cell 115 may consist of a first cell with one end face 116 sealed and the other end face 118 open, and a second cell with one end face 116 open and the other end face 118 sealed, arranged alternately adjacent to each other with a partition wall 113 in between.

[0037] The thickness of the partition walls 113 that divide the cell 115 is preferably 0.1 to 0.3 mm, and more preferably 0.15 to 0.25 mm. A partition wall thickness of 0.1 mm or more can suppress a decrease in the strength of the honeycomb structure 110. A partition wall thickness of 0.3 mm or less can suppress an increase in pressure loss when exhaust gas is passed through the honeycomb structure 110 when the catalyst is supported on the honeycomb structure 110. In the present invention, the thickness of the partition wall 113 is defined as the length of the portion of the line segment that passes through the partition wall 113, in a cross section perpendicular to the extension direction of the cell 115, connecting the centroids of adjacent cells 115.

[0038] The honeycomb structure 110 has a cell density of 40 to 150 cells / cm² in a cross section perpendicular to the stretching direction of the cells 115. 2 Preferably, the density is 70-100 cells / cm². 2 It is even more preferable that the cell density is within this range. By setting the cell density within this range, the pressure loss when exhaust gas is passed through the honeycomb structure 110 can be reduced while the purification performance of the catalyst can be increased. Cell density of 40 cells / cm 2 With the above conditions, a sufficient catalyst support area is ensured. The cell density is 150 cells / cm³. 2 The following conditions are met: When the honeycomb structure 110 is used as a catalyst support and the catalyst is supported on it, excessive pressure loss when exhaust gas is passed through it is suppressed. The cell density is a value obtained by dividing the number of cells by the area of ​​one end face of the honeycomb structure excluding the outer periphery wall.

[0039] The partition wall 113 may be dense, but it is preferable that it be porous. The porosity of the partition wall 113 is preferably 35-60%, and more preferably 35-45%. A porosity of 35% or more makes it easier to suppress deformation during firing. A porosity of 60% or less ensures that the strength of the honeycomb structure 110 is sufficiently maintained. Porosity is a value measured by a mercury porosimeter. Note that dense refers to a porosity of 5% or less.

[0040] The average pore diameter of the septum 113 is preferably 2 to 15 μm, and more preferably 4 to 8 μm. If the average pore diameter is 2 μm or more, excessive volume resistivity is suppressed. If the average pore diameter is 15 μm or less, excessive volume resistivity is suppressed. The average pore diameter is a value measured by a mercury porosimeter.

[0041] Providing an outer peripheral wall 114 to the honeycomb structure 110 is useful in ensuring the structural strength of the honeycomb structure 110 and in suppressing leakage of fluid flowing through the cells 115 from the outer peripheral side surface. 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 made too thick, it will become too strong, disrupting the strength balance with the partition wall 113 and reducing 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 direction normal to the tangent of the outer surface of the outer peripheral wall 114 at the measurement location when the location of the outer peripheral wall 114 to be measured is observed in a cross section perpendicular to the extension direction of the cells 115.

[0042] By arranging electrode layers 112a and 112b, which have a lower volume resistivity than the outer peripheral wall 114, on the outer peripheral wall 114, the current spreads more easily in the circumferential direction of the honeycomb structure 110 and in the extending direction of the cell 115, thereby improving the uniform heating performance of the honeycomb structure 110. In a cross section perpendicular to the cell 115, the angle θ (0°≦θ≦180°) between two line segments extending from the circumferential centers of the 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°, even more preferably 170°≦θ≦180°, and most preferably 180°.

[0043] While there are no particular restrictions on the formation regions of the electrode layers 112a and 112b, from the viewpoint of improving the uniform heating properties of the honeycomb structure 110, it is preferable that the electrode layers 112a and 112b extend in a strip shape on the outer surface of the outer peripheral wall 114 in the circumferential direction of the honeycomb structure 110 and in the stretching direction of the cell 115, respectively. Specifically, in a cross section perpendicular to the stretching direction of the cell 115, the central angle α formed by two line segments connecting both 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, from the viewpoint of spreading the current in the circumferential direction and improving uniform heating properties. However, if the central angle α is made too large, the current passing through the inside of the honeycomb structure 110 will decrease, and the current passing near the outer peripheral wall 114 will increase. Therefore, from the viewpoint of uniform heat generation 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, it is desirable that the electrode layers 112a and 112b each extend over a length of 80% or more of the length between the end faces of the honeycomb structure 110, preferably 90% or more, and more preferably over the entire length. The electrode layers 112a and 112b may be composed of a single layer, or they may have a laminated structure in which multiple layers are stacked.

[0044] The thickness of the electrode layers 112a and 112b is preferably 0.01 to 5 mm, and more preferably 0.01 to 3 mm. By setting the thickness within this range, uniform heating can be improved. If the thickness of the electrode layers 112a and 112b is 0.01 mm or more, the electrical resistance is appropriately controlled, and heating can be achieved more uniformly. If the thickness of the electrode layers 112a and 112b is 5 mm or less, the risk of damage during canning is reduced. The thickness of the electrode layers 112a and 112b is defined as the thickness in the direction normal to the tangent of the outer surface of the electrode layers 112a and 112b at the measurement point, when the location of the electrode layer 112a and 112b whose thickness is to be measured is observed in a cross section perpendicular to the stretching direction of the cell 115.

[0045] By making the volume resistivity of the electrode layers 112a and 112b lower than that of the partition wall 113 and the outer peripheral wall 114, electricity flows preferentially through the electrode layers 112a and 112b, and when energized, the electricity spreads more easily in the circumferential direction of the honeycomb structure 110 and in the extension direction of the cell 115. The volume resistivity of the electrode layers 112a and 112b is preferably 1 / 10 or less of the volume resistivity of the partition wall 113 and the outer peripheral wall 114, more preferably 1 / 20 or less, and even more preferably 1 / 30 or less. However, if the difference in volume resistivity between the two becomes too large, current will concentrate between the ends of the opposing electrode layers 112a and 112b, causing uneven heating of the honeycomb structure 110. Therefore, the volume resistivity of the electrode layers 112a and 112b is preferably 1 / 200 or more, more preferably 1 / 150 or more, and even more preferably 1 / 100 or more, of the volume resistivity of the partition wall 113 and the outer peripheral wall 114. In this invention, the volume resistivity of the electrode layers, partition wall and outer peripheral wall is the value measured at 25°C by the four-terminal method.

[0046] The material of the electrode layers 112a and 112b is not limited, but composite materials (cermets) of metal and ceramics (especially conductive ceramics) 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, but include silicon carbide (SiC), as well as metal compounds such as tantalum silicide (TaSi2) and chromium silicide (CrSi2). Specific examples of composite materials (cermets) of metal and ceramics include composite materials of metallic silicon and silicon carbide, composite materials of metallic silicides such as tantalum silicide and chromium silicide with metallic silicon and silicon carbide, and composite materials in which one or more of the above metals are combined with one or more insulating ceramics such as alumina, mullite, zirconia, cordierite, silicon nitride, and aluminum nitride from the viewpoint of reducing thermal expansion. As for the material of the electrode layers 112a and 112b, among the various metals and ceramics mentioned above, it is preferable to use a composite material of metal silicides such as tantalum silicide and chromium silicide, metal silicon, and silicon carbide, because it can be fired simultaneously with the partition wall and the outer periphery wall, thus simplifying the manufacturing process.

[0047] (1-2. Metal terminal) The metal terminals 130 are directly or indirectly bonded to the outer surfaces of the pair of electrode layers 112a and 112b. When a voltage is applied to the honeycomb structure 110 via the metal terminals 130, current flows and the honeycomb structure 110 is heated by Joule heating. For this reason, the honeycomb structure 110 can be suitably used as a heater. This makes it possible to improve the uniform heating performance of the honeycomb structure 110. The applied voltage is preferably 12 to 900V, and more preferably 48 to 600V, but the applied voltage can be changed as appropriate.

[0048] The metal terminals 130 and the electrode layers 112a and 112b may be directly joined, but they may also be joined via one or more layers 120 to mitigate the difference in thermal expansion between the electrode layers 112a and 112b and the metal terminals 130 and to improve the reliability of the joining of the metal terminals 130. Accordingly, in a preferred embodiment, the honeycomb structure 110 has a pair of electrode layers 112a and 112b arranged on the outer peripheral wall 114 so as to face each other across the central axis of the honeycomb structure 110, and one or more metal terminals 130 are joined to each electrode layer 112a and 112b via the layer 120.

[0049] From the viewpoint of improving bonding reliability, it is preferable to gradually decrease the coefficient of thermal expansion in the order of metal terminal 130 → (underlayment 120) → electrode layers 112a, 112b → outer wall 114. Here, "coefficient of thermal expansion" refers to the linear expansion coefficient measured according to JIS R1618:2002 when the temperature is changed from 25°C to 1000°C.

[0050] There are no particular restrictions on the material of the metal terminal 130 as long as it is a metal, and single metals and alloys can be used, but from the viewpoint of corrosion resistance, volume resistivity and thermal expansion coefficient, it is preferable to use an alloy containing at least one selected from the group consisting of Cr, Fe, Co, Ni and Ti, and stainless steel and Fe-Ni alloy are more preferable. The shape and size of the metal terminal 130 are not particularly limited and can be appropriately designed according to the size of the honeycomb structure 110 and the current-carrying performance, etc.

[0051] The material of the base layer 120 is not limited, but a composite material (cermet) of metal and ceramics (especially conductive ceramics) can be used. The thermal expansion coefficient of the base layer 120 can be controlled, for example, by adjusting the mixing ratio of metal and ceramics.

[0052] The base layer 120 preferably contains one or more metals selected from Ni-based alloys, Fe-based alloys, Ti-based alloys, Co-based alloys, metallic silicon, and Cr, although this is not limited to these metals.

[0053] The base layer 120 preferably contains one or more ceramics selected from oxide ceramics such as alumina, mullite, zirconia, glass, and cordierite, and non-oxide ceramics such as silicon carbide, silicon nitride, and aluminum nitride, although this is not limited to these materials.

[0054] There are no particular restrictions on the thickness of the base layer 120, but from the viewpoint of crack suppression, 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 direction normal to the tangent to the outer surface of the base layer 120 at the measurement point, when the base layer 120 whose thickness is to be measured is observed in a cross section perpendicular to the extension direction of the cell.

[0055] There are no particular limitations on the method of joining the metal terminal 130 to the electrode layers 112a, 112b, or the base layer 120, but examples include thermal spraying, welding, and brazing.

[0056] (2. Exhaust gas purification device) An electrically heated carrier 100 according to one embodiment of the present invention can be used in an exhaust gas purification device. Referring to Figure 3, the exhaust gas purification device 200 has an electrically heated carrier 100 and a cylindrical metal tube 220 that houses the electrically heated carrier 100. Electrical wires 240 for power supply can be connected to the metal terminals 130 of the electrically heated carrier 100. The material of the metal tube 220 is not limited, but stainless steel is one example.

[0057] In the exhaust gas purification device 200, the electrically heated carrier 100 can be installed in the middle of the fluid flow path, such as automobile exhaust gas. The electrically heated carrier 100 can be fixed inside the metal pipe 220 by push-in canning, for example, in which the cell's extension direction coincides with the extension direction of the metal pipe 220. A mat (also called a "cushioning material") 260 may be placed between the metal pipe 220 and the electrically heated carrier 100. The material of the mat 260 is not limited, but ceramic fibers such as alumina fibers and mullite fibers are preferred for reasons of suppressing displacement of the electrically heated carrier and maintaining surface pressure between the metal pipe and the electrically heated carrier.

[0058] The lower limit of the pressure that the electrically heated carrier 100, which is fixed inside the metal pipe, receives from the metal pipe is preferably 0.1 MPa or higher at 25°C, and more preferably 0.2 MPa or higher, in order to prevent displacement due to exhaust gas pressure. The upper limit of the pressure that the electrically heated carrier 100 fixed inside the metal pipe receives from the metal pipe is preferably 1.0 MPa or less at 25°C, and more preferably 0.8 MPa or less, in order to prevent damage to the honeycomb structure.

[0059] The pressure exerted by the electrically heated carrier 100, which is fixed inside the metal tube, from the metal tube is determined by the outer diameter of the honeycomb structure, the inner diameter of the metal tube, and the surface density (g / m²) of the mat. 2 The GBD (Gap Bulk Density) value is calculated from the mat's surface pressure, and the pressure (surface pressure) corresponding to the GBD value is determined using a characteristic curve (GBD-surface pressure curve) unique to each mat. 3 ] refers to the packing density of the mat between the honeycomb structure and the metal tube = surface density [g / m²]. 2 This refers to ] / ((inner diameter of the metal pipe - outer diameter of the honeycomb structure) [mm] × 1000).

[0060] (3. Manufacturing method) Next, an exemplary method for manufacturing an electrically heated carrier according to one embodiment of the present invention will be described. The electrically heated carrier can be manufactured by a manufacturing method that includes the steps of: step 1 for obtaining a honeycomb molded body; step 2 for obtaining an unfired honeycomb structure with electrode layer forming paste; step 3 for firing the unfired honeycomb structure with electrode layer forming paste to obtain a honeycomb structure; and step 4 for joining metal terminals to the electrode layer.

[0061] (Process 1) Step 1 is a step in which a honeycomb molded body, which is a precursor of the honeycomb structure, is produced. The honeycomb molded body can be produced in accordance with the method for producing a honeycomb molded body in known methods for producing honeycomb structures. For example, first, a molding raw material is produced by adding metallic silicon powder (metallic silicon), a binder, a surfactant, a pore-forming agent, water, etc. to silicon carbide powder (silicon carbide). It is preferable that the mass of metallic silicon powder be 10 to 40% by mass of the total mass of silicon carbide powder and metallic silicon powder. The average particle diameter of silicon carbide particles in silicon carbide powder is preferably 3 to 50 μm, and more preferably 3 to 40 μm. The average particle diameter of metallic silicon particles in metallic silicon powder is preferably 2 to 35 μm. The average particle diameter of silicon carbide particles and metallic silicon particles refers to the arithmetic mean diameter based on volume when the particle size frequency distribution is measured by laser diffraction. Silicon carbide particles are fine particles of silicon carbide that make up silicon carbide powder, and metallic silicon particles are fine particles of metallic silicon that make up metallic silicon powder. Note that this is the formulation of the molding raw materials when the material of the honeycomb structure is a silicon-silicon carbide composite material; metallic silicon is not added when the material of the honeycomb structure is silicon carbide.

[0062] Examples of binders include methylcellulose, hydroxypropylmethylcellulose, hydroxypropoxylcellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinyl alcohol. Among these, it is preferable to use methylcellulose and hydroxypropoxylcellulose in combination. The binder content is preferably 2.0 to 10.0 parts by mass when the total mass of silicon carbide powder and metallic silicon powder is 100 parts by mass.

[0063] As surfactants, ethylene glycol, dextrin, fatty acid soap, polyalcohol, etc., can be used. These may be used individually 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 100 parts by mass.

[0064] The pore-forming material is not particularly limited as long as it becomes pore after firing, and examples include graphite, starch, foamed resin, superabsorbent resin, silica gel, etc. The content of the pore-forming material is preferably 0.5 to 10.0 parts by mass when the total mass of silicon carbide powder and metallic silicon powder is 100 parts by mass. The average particle diameter of the pore-forming material is preferably 10 to 30 μm. The average particle diameter of the pore-forming material refers to the arithmetic mean diameter based on volume when the particle size frequency distribution is measured by laser diffraction. If the pore-forming material is a superabsorbent resin, the average particle diameter of the pore-forming material is the average particle diameter after water absorption.

[0065] The water content is preferably 20 to 60 parts by mass when the total mass of silicon carbide powder and metallic silicon powder is 100 parts by mass.

[0066] Next, the obtained molding raw material is kneaded to form a clay body, and then the clay body is extruded to produce a columnar honeycomb molded body having an outer wall and partitions. When extruding, a die having the desired overall shape, cell shape, partition thickness, cell density, etc., can be used. Next, it is preferable to dry the obtained honeycomb molded body. If the axial length of the honeycomb molded body is not the desired length, both ends of the honeycomb molded body can be cut to the desired length. The honeycomb molded body after drying is called a dried honeycomb body.

[0067] As a variation of step 1, the honeycomb molded body may be fired first. That is, in this variation, the honeycomb molded body is fired to produce a honeycomb fired body, and step 2 is performed on the honeycomb fired body.

[0068] (Process 2) Step 2 is a step of applying electrode layer forming paste to the side surface of the honeycomb molded body to obtain an unfired honeycomb structure with electrode layer forming paste. The electrode layer forming paste can be formed by mixing various additives appropriately with raw material powders (metal powders, ceramic powders, etc.) that are blended according to the required characteristics of the electrode layer. The average particle size of the raw material powder is not limited, but is preferably 5 to 50 μm, and more preferably 10 to 30 μm. The average particle size of the raw material powder refers to the arithmetic mean diameter on a volume basis when the particle size frequency distribution is measured by laser diffraction.

[0069] Next, the obtained electrode layer forming paste is applied to the required areas on the sides of the honeycomb molded body (typically a dried honeycomb) to obtain an unfired honeycomb structure with electrode layer forming paste. 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 in accordance with known methods for manufacturing honeycomb structures. However, in order to make the electrode layer have a lower volume resistivity than the outer wall and partitions, the metal content ratio can be increased compared to the outer wall and partitions, or the particle size of the metal particles in the raw material powder can be reduced.

[0070] (Step 3) Step 3 is a step of obtaining a honeycomb structure by firing the unfired honeycomb structure with electrode layer forming paste. Before firing, the unfired honeycomb structure with electrode layer forming paste may be dried. Also, before firing, degreasing may be performed to remove binders, etc. The method of degreasing and firing is not particularly limited, and firing can be performed using an electric furnace, gas furnace, etc. As for the firing conditions, although it depends on the material of the honeycomb structure, it is preferable to heat it in an inert atmosphere such as nitrogen or argon at 1400 to 1500°C for 1 to 20 hours. Furthermore, after firing, it is preferable to perform an oxidation treatment for 1 to 20 hours in the range from 800°C to the maximum oxidation temperature in order to improve durability and form an oxide film containing cristobalite. It is preferable to set the average heating rate from 800°C to the maximum oxidation temperature to 20 to 400°C / h, and the average cooling rate from the maximum oxidation temperature to 800°C to 40 to 40°C / h. Oxidation treatment can be carried out in an oxygen atmosphere, an air atmosphere, or a water vapor atmosphere, for example. When metallic silicon is used as the molding material, the amount of cristobalite produced can be adjusted by changing the oxidation treatment conditions. Specifically, slower heating and cooling rates above 800°C increase the amount of cristobalite produced. Higher temperatures and longer oxidation treatment times increase the amount of cristobalite produced. Furthermore, performing oxidation treatment in an oxygen or water vapor atmosphere is more advantageous than in an air atmosphere for increasing the amount of cristobalite produced. When the amount of cristobalite produced increases, the coefficient of linear expansion of the honeycomb structure tends to increase when the temperature is changed from 40°C to 300°C.

[0071] (Step 4) Step 4 is the step of joining metal terminals to the electrode layer. There are no particular restrictions on the joining method, but examples include thermal spraying, welding, and brazing. To improve the bonding between the electrode layer and the metal terminals, a base layer may be formed by methods such as thermal spraying. [Examples]

[0072] The following examples illustrate the present invention and its advantages, but the present invention is not limited to these examples.

[0073] <Example 1> (1. Preparation of cylindrical clay bowls) A ceramic raw material was prepared by mixing silicon carbide (SiC) powder and metallic silicon (Si) powder in a mass ratio of 80:20. Hydroxypropyl methylcellulose was added as a binder and a water-absorbing resin as a pore-forming agent, along with water, to the ceramic raw material to create a molding material. The molding material was then kneaded in a vacuum clay mixer to produce cylindrical clay blocks. The binder content was 7 parts by mass when the total amount of silicon carbide (SiC) powder and metallic silicon (Si) powder was 100 parts by mass. The pore-forming agent content was 3 parts by mass when the total amount of silicon carbide (SiC) powder and metallic silicon (Si) powder was 100 parts by mass. The water content was 42 parts by mass when the total amount of silicon carbide (SiC) powder and metallic silicon (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 metallic silicon powder was 6 μm. Furthermore, the average particle size of the pore-forming material was 20 μm. The average particle sizes of silicon carbide powder, metallic silicon powder, and pore-forming material refer to the arithmetic mean diameter based on volume, when the particle size frequency distribution was measured by laser diffraction.

[0074] (2. Preparation of honeycomb dried material) The obtained cylindrical clay was molded using an extrusion molding machine with a grid-like nozzle structure to obtain a cylindrical honeycomb molded body in which each cell shape in a cross section perpendicular to the cell stretching direction was hexagonal. This honeycomb molded body was dried using high-frequency dielectric heating, then dried in a hot air dryer at 120°C for 2 hours, and a predetermined amount was cut from both bottom surfaces to produce a dried honeycomb body.

[0075] (3. Preparation of electrode layer forming paste) An electrode layer forming paste was prepared by mixing metallic silicon (Si) powder, silicon carbide (SiC) powder, methylcellulose, glycerin, and water in a rotary-orbiting stirrer. The Si powder and SiC powder were blended in a volume ratio of Si powder:SiC powder = 40:60. When the total amount of Si powder and SiC powder was 100 parts by mass, the methylcellulose was 0.5 parts by mass, the glycerin was 10 parts by mass, and the 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 diameter based on volume when the particle size frequency distribution was measured by laser diffraction.

[0076] (4. Application of electrode layer forming paste) The electrode layer forming paste described above was applied to the outer surface of the outer wall of the honeycomb dried body in two locations using a curved surface printing machine, so as to be opposite each other with the central axis in between. Each applied area was formed in a band shape extending over the entire length between the two bottom surfaces of the honeycomb dried body (angle θ = 180°, central angle α = 90°).

[0077] (5. Firing) After drying the honeycomb structure with electrode layer forming paste at 120°C, it was degreased in an air atmosphere at 550°C for 3 hours. Next, the degreased honeycomb structure with electrode layer forming paste was fired and then oxidized to obtain a cylindrical honeycomb structure with a height of 65 mm and a diameter of 80 mm. The firing was carried out in an argon atmosphere at 1450°C for 2 hours. Subsequently, the oxidation treatment was performed under the conditions of the average heating rate from 800°C to the maximum temperature listed in Table 1, the maximum temperature of the oxidation treatment, the holding time at the maximum temperature, the average cooling rate from the maximum temperature to 800°C, and the oxidizing atmosphere to generate an oxide film containing cristobalite. The formation of cristobalite was confirmed by analyzing the partition sample with an X-ray diffractometer.

[0078] <Example 2> A honeycomb structure was fabricated under the same manufacturing conditions as in Example 1, except that the oxidation treatment conditions were changed to those listed in Table 1.

[0079] <Example 3> A honeycomb structure was fabricated under the same manufacturing conditions as in Example 1, except that the mass proportion of metallic silicon (Si) powder was increased compared to Example 1 to prepare the ceramic raw material for clay production, and the oxidation treatment conditions were changed to those described in Table 1.

[0080] <Example 4> A honeycomb structure was fabricated under the same manufacturing conditions as in Example 1, except that the mass proportion of silicon carbide (SiC) powder was increased compared to Example 1 to prepare the ceramic raw material for clay production, and the oxidation treatment conditions were changed to those described in Table 1.

[0081] <Example 5> The honeycomb structure was fabricated under the same manufacturing conditions as in Example 1, except that the oxidation treatment conditions were changed to those listed in Table 1.

[0082] <Example 6> A honeycomb structure was fabricated under the same manufacturing conditions as in Example 1, except that the mass proportion of silicon carbide (SiC) powder was increased compared to Example 1 to prepare the ceramic raw material for clay production, and the oxidation treatment conditions were changed to those described in Table 1.

[0083] <Comparative Examples 1-3> The honeycomb structure was fabricated under the same manufacturing conditions as in Example 1, except that the oxidation treatment conditions were changed to those listed in Table 1.

[0084] <Comparative Examples 4-5> A honeycomb structure was fabricated under the same manufacturing conditions as in Example 1, except that cordierite powder was added to silicon carbide (SiC) powder and metallic silicon (Si) powder, and these were mixed to prepare a ceramic raw material for clay production, and the oxidation treatment conditions were changed to those described in Table 1. For the test examples in which cordierite powder was added to the ceramic raw material, "Yes" is indicated in the "Cd Content" column of Table 1. For the test examples in which cordierite powder was not added to the ceramic raw material, "No" is indicated in the "Cd Content" column of Table 1.

[0085] <Characteristic Evaluation> The following characteristics evaluation was performed on the honeycomb structures obtained under the above manufacturing conditions. The necessary number of honeycomb structures were prepared for the characteristics evaluation.

[0086] (1. Coefficient of linear expansion) Samples were taken from the radial and vertical centers of the honeycomb structure of the honeycomb structure according to the examples and comparative examples using the method described above, and the coefficient of linear expansion (CTE) of the honeycomb structure was measured according to JIS R1618:2002 when the temperature was changed from 40°C to 300°C. A (40-300℃), and the coefficient of linear expansion (CTE) of the honeycomb structure measured according to JIS R1618:2002 when the temperature is changed from 300℃ to 800℃. B The temperature (300-800℃) was measured. The results are shown in Table 1.

[0087] (2. Catalyst or calcination simulation test) A test was conducted to simulate the heating conditions during catalyst firing. Specifically, honeycomb structures according to the examples and comparative examples were held in an electric furnace at a furnace 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 presence or absence of cracks on the sides and ends of the honeycomb structures was visually inspected. This simulation test was performed on five honeycomb structures for each example, and the number of honeycomb structures in which no cracks were observed was counted. The results are shown in Table 1.

[0088] (3. Cold and heat test) The honeycomb structures according to the examples and comparative examples were subjected to thermal tests using a propane gas burner test machine equipped with a metal tube and a propane gas burner capable of supplying combustion gas into the metal tube. Specifically, the honeycomb structures were fixed inside a stainless steel metal tube by canning them into a metal tube with an inner diameter of 87 mm. At this time, a mat (cushioning material) made of ceramics (alumina fiber and mullite fiber, etc.) was interposed between the metal tube and the honeycomb structure. The surface pressure exerted on the honeycomb structure fixed inside the metal tube at 25°C was calculated to be 0.1 MPa using the method described above, based on the outer diameter of the honeycomb structure, the inner diameter of the metal tube, and the surface density of the ceramic mat. Next, combustion gas generated by burning propane gas with a propane gas burner was flowed from one end face to the other of a honeycomb structure fixed inside a metal tube. The combustion gas temperature at the inlet side of the honeycomb structure was raised to 950°C in 10 minutes and held at that temperature for 5 minutes. After that, it was cooled to 150°C in 3 minutes by flowing air through it, and held at 150°C for 10 minutes. Finally, it was allowed to cool to room temperature and the honeycomb structure was removed from the metal tube. The sides and ends of the removed honeycomb structure were visually inspected for the presence of cracks. This thermal test was performed on five honeycomb structures each, and the number of honeycomb structures in which no cracks were found was counted. The results are shown in Table 1.

[0089] (4. HVT test) The honeycomb structures according to the examples and comparative examples were subjected to thermal testing using a propane gas burner test machine equipped with a metal tube and a propane gas burner capable of supplying combustion gas into the metal tube. Specifically, the honeycomb structures were fixed inside a stainless steel metal tube by canning them into a metal tube with an inner diameter of 87 mm. At this time, a mat (cushioning material) made of ceramics (alumina fiber and mullite fiber, etc.) was interposed between the metal tube and the honeycomb structure. The surface pressure at 25°C on the honeycomb structure fixed inside the metal tube was calculated to be 0.1 MPa using the method described above, based on the outer diameter of the honeycomb structure, the inner diameter of the metal tube, and the surface density of the ceramic mat. Next, combustion gas generated by burning propane gas with a propane gas burner was flowed from one end face to the other of a honeycomb structure fixed inside a metal tube. The combustion gas temperature at the inlet side of the honeycomb structure was raised to 900°C in 10 minutes and held at that temperature for 5 minutes. After that, air was flowed to cool it down to 100°C in 3 minutes and held at 100°C for 10 minutes. This series of operations constituted one cycle, and 96 cycles were performed. In addition, while flowing the combustion gas, a vibration load device was simultaneously applied to the honeycomb structure with an acceleration of 40G and a frequency of 150Hz. Finally, the structure was allowed to cool to room temperature, and the distance the honeycomb structure moved along the length of the metal tube before and after the test was measured. The results are shown in Table 1.

[0090] [Table 1]

[0091] (5. Discussion) From Table 1, CTE A (40-300℃) and CTE B The honeycomb structures of Examples 1-6, with the (300-800℃) temperature range optimized, are less prone to cracking when housed in a metal tube and subjected to temperature changes. A (40-300℃) and CTE BThe honeycomb structures of Examples 1-4, with their optimized (300-800℃) temperature range, are also less prone to cracking when subjected to relatively low temperature changes, such as during catalytic or calcination. [Explanation of Symbols]

[0092] 100: Electrically heated carrier 110: Honeycomb structure 112a: Electrode layer 112b: Electrode layer 113: Bulkhead 114:Outer wall 115: Cell 116: End face 118: End face 120: Base layer 130: Metal terminal 200: Exhaust gas purification device 220:Metal tube 240: Electric wire 260: Matt

Claims

1. A conductive honeycomb structure having an outer periphery wall and partition walls disposed inside the outer periphery wall, which divide and form a plurality of cells that form a flow path from one end face to the other end face, The honeycomb structure comprises a pair of electrode layers provided on the outer surface of the outer wall so as to face each other across the central axis of the honeycomb structure, The material of the outer perimeter wall and the partition wall mainly consists of a silicon carbide-silicon composite material, and at least a portion of the surface of each of the outer perimeter wall and the partition wall is coated with an oxide film containing cristobalite. The coefficient of linear expansion of the honeycomb structure, measured according to JIS R1618:2002 when the temperature is changed from 40°C to 300°C, is 4.1 × 10⁻⁶. -6 / ℃ or higher 7.5 × 10 -6 The temperature is below 1 / °C, and the coefficient of linear expansion of the honeycomb structure, measured according to JIS R1618:2002 when the temperature is changed from 300°C to 800°C, is 4.2 × 10⁻⁶. -6 / ℃ or higher 4.8 × 10 -6 It is below / ℃. Honeycomb structure.

2. The coefficient of linear expansion of the honeycomb structure, measured according to JIS R1618:2002 when the temperature is changed from 40°C to 300°C, is 4.1 × 10⁻⁶. -6 / ℃ or higher 6.0 × 10 -6 The honeycomb structure according to claim 1, wherein the temperature is less than or equal to / ℃.

3. The honeycomb structure according to claim 1 or 2, wherein the coefficient of linear expansion of the honeycomb structure measured according to JIS R1618:2002 when the temperature is changed 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 is changed from 300°C to 800°C.

4. A honeycomb structure according to any one of claims 1 to 3, A metal terminal bonded to the outer surface of each of the pair of electrode layers, An electrically heated carrier equipped with the following features.

5. The electrically heated carrier according to claim 4, A cylindrical metal tube housing the aforementioned electrically heated carrier, An exhaust gas purification device equipped with the following features.

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