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

Abstract

To provide a honeycomb structure of which thermal shock resistance is heightened by a novel means.SOLUTION: A honeycomb structure comprises: a honeycomb structure portion that has an outer peripheral wall and a partition wall that is arranged inside the outer peripheral wall and defines a plurality of cells forming a flow path extending from one end face to the other end face; and a pair of electrode layers extended in band toward a flow path direction of the cell on an outer surface of the outer peripheral wall across a central axis of the honeycomb structure, wherein the porosity PW of the partition wall is 30% to 55%, and a ratio (PW / Po) of the porosity PW of the partition wall to the porosity PO of the outer peripheral wall satisfies 1<PW / PO≤1.8.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 placed on the outer wall of a honeycomb structure made of conductive ceramics, and by applying an electric current, the honeycomb structure itself is heated, thereby raising the temperature of the catalyst supported on the honeycomb structure to its activation temperature before engine startup.

[0003] Because high-temperature exhaust gas flows through the exhaust gas passage, the honeycomb structure is required to have thermal shock resistance. Various technologies have been developed to improve thermal shock resistance. For example, Patent Document 1 discloses that by having a portion of the electrode section that is 0 to 70% of the maximum thickness of the electrode section, the rigidity of the electrode section is reduced, thereby improving the thermal shock resistance of the honeycomb structure. Patent Document 1 also describes that by making the sum of the heat capacities of a pair of electrode sections 2 to 150% of the total heat capacities of the outer wall, the amount of heat accumulated in the electrode section is reduced, improving the thermal shock resistance of the honeycomb structure. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2012 / 086815 [Overview of the project] [Problems that the invention aims to solve]

[0005] Patent Document 1 describes a technology aimed at improving the thermal shock resistance of a honeycomb structure by defining the electrode structure and the relationship between the electrode and the heat capacity between the electrode and the outer wall. However, there is still room to improve the thermal shock resistance of honeycomb structures by means other than those described above. Finding novel means to improve the thermal shock resistance of honeycomb structures would be useful in broadening the options for further technological development of EHC.

[0006] The present invention was created in view of the above circumstances, and in one embodiment, aims to provide a honeycomb structure with improved thermal shock resistance by novel means. In another embodiment, the present invention aims to provide an electrically heated carrier equipped with such a honeycomb structure. In yet another embodiment, the present invention aims to provide an exhaust gas purification device equipped with such an electrically heated carrier. [Means for solving the problem]

[0007] In one embodiment, the present invention is described as follows: A 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 extending from one end face to the other end face, and The honeycomb structure is provided with a pair of electrode layers extending in a strip-like manner in the direction of cell extension on the outer surface of the outer peripheral wall, with the central axis of the honeycomb structure in between. The porosity P of the partition wall W However, the percentage is between 30% and 55%. The porosity P of the outer wall O The porosity P of the partition wall relative to the porosity P W The ratio (P W / P o ) but, 1 <P W / P O Satisfying ≤ 1.8, It is a honeycomb structure.

[0008] In another embodiment of the present invention, the honeycomb structure and A metal terminal bonded to the outer surface of each of the pair of electrode layers, It is an electrically heated carrier equipped with [a specific feature].

[0009] In yet another embodiment, the present invention is described as follows: The aforementioned electrically heated carrier, A cylindrical metal tube housing the aforementioned electrically heated carrier, This is an exhaust gas purification device equipped with [specific features / features]. [Effects of the Invention]

[0010] A honeycomb structure according to one embodiment of the present invention has high thermal shock resistance by controlling the relationship between the porosity of the outer wall and the partition wall disposed inside it to a predetermined range. Further improvement in thermal shock resistance can be expected by combining this technology with existing thermal shock resistance improvement technologies. For this reason, it is possible to provide an EHC with excellent thermal shock resistance that is less prone to cracking even when rapidly heated by high-temperature exhaust gas, for example. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of an electrically heated carrier according to one embodiment of the present invention, as observed from one end face. [Figure 2] This is a schematic perspective view of an electrically heated carrier according to one embodiment of the present invention. [Figure 3] This is a schematic diagram showing the sampling locations for partition wall samples and outer wall samples for measuring the porosity of the partition wall and outer wall at each cross-section. [Figure 4] This is a schematic cross-sectional view showing an exhaust gas purification device according to one embodiment of the present invention. [Figure 5] This is a schematic diagram illustrating how a concave pattern is formed on the tip of a honeycomb molded body extruded from a molding machine. [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) FIG. 1 is a schematic view of an electrically heated carrier 100 according to an embodiment of the present invention as observed from one end face 116. FIG. 2 is a schematic perspective view of the electrically heated carrier 100 according to an 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 body.

[0014] Examples of the catalyst include noble metal-based catalysts or catalysts other than these. As noble metal-based catalysts, noble metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) are supported on the surface of alumina pores, and a three-way catalyst containing a promoter such as ceria or zirconia, an oxidation catalyst, or an alkaline earth metal and platinum as a storage component of nitrogen oxides (NO x ) A NO x storage reduction catalyst (LNT catalyst) is exemplified. As a catalyst that does not use noble metals, a NO x selective reduction catalyst (SCR catalyst) containing copper-substituted or iron-substituted zeolite is exemplified. Further, two or more catalysts selected from these catalysts may be used. In addition, there is no particular limitation on the method of supporting the catalyst, and a known method of supporting the catalyst on the honeycomb structure can be adopted.

[0015] (1-1. Honeycomb structure) In one embodiment, the honeycomb structure 110 has a honeycomb structure portion including an outer peripheral wall 114 and partition walls 113 that are disposed inside the outer peripheral wall 114 and define a plurality of cells 115 that form a flow path extending from one end face 116 to the other end face 118, and a pair of electrode layers 112a and 112b that are provided on the outer surface of the outer peripheral wall 114 in a strip shape in the extending direction of the cells 115 with the central axis O of the honeycomb structure portion interposed therebetween.

[0016] The external shape of the honeycomb structure 110 is not particularly limited. For example, it can be a column with round end faces such as circular, oval, elliptical, racetrack, and oblong shapes, a column with polygonal end faces such as triangular and square shapes, or a column with other irregular end faces. The honeycomb structure 110 shown in the figure has a circular end face shape and is cylindrical overall.

[0017] There are no particular restrictions on the height of the honeycomb structure (the length from one end face to the other), and it can be set appropriately according to the application and required performance. There are also no particular restrictions on the relationship between the height of the honeycomb structure and the maximum diameter of each end face (referring to the maximum length of the diameter passing through the centroid 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] Furthermore, the size of the honeycomb structure 110 is such that the area of ​​one end face is 2,000 to 20,000 mm², in order to enhance thermal shock resistance (suppress cracks that enter the circumferential direction of the outer wall). 2 Preferably, it is 5000~15000mm 2 It is even more preferable that this be the case.

[0019] The outer periphery 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 periphery wall 114 and the partition wall 113 is not particularly limited as long as they can be heated by Joule heating when energized, but it is preferably 0.1 to 200 Ωcm, more preferably 1 to 200 Ωcm, and even more preferably 10 to 100 Ωcm when measured at 25°C using the four-terminal method.

[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 energized, 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 thermal shock resistance and conductivity, it is preferable that the materials for the outer perimeter wall 114 and the partition wall 113 be silicon carbide-silicon composites or silicon carbide as the main component. Furthermore, by using the same material as the partition wall 113, thermal expansion and other properties can be matched, thereby suppressing cracking during firing. Therefore, it is preferable that the materials constituting the electrode layers 112a and 112b, in addition to the materials of the outer periphery wall 114 and the partition wall 113, also consist of silicon carbide-silicon composite material or silicon carbide as the main component.

[0021] When the materials of the outer perimeter wall 114, the partition wall 113, and the electrode layers 112a and 112b are said to be mainly composed of silicon carbide-silicon composite material, it means that the outer perimeter wall 114, the partition wall 113, and the electrode layers 112a and 112b 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, 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 materials constituting the outer perimeter wall 114, the partition wall 113, and the electrode layers 112a and 112b are said to be mainly composed of silicon carbide, it means that each of the outer perimeter wall 114, the partition wall 113, and the electrode layers 112a and 112b contains silicon carbide (total mass) of 90% or more of the total mass.

[0022] When the outer perimeter wall 114, partition wall 113, and electrode layers 112a and 112b contain a silicon carbide-silicon composite material, the ratio of the "mass of silicon as a binder" contained in the outer perimeter wall 114, partition wall 113, and electrode layers 112a and 112b to the sum of the "mass of silicon carbide particles as aggregate" contained in the outer perimeter wall 114, partition wall 113, and electrode layers 112a and 112b 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, partition wall 113, and electrode layers 112a and 112b is sufficiently maintained. If it is 40 mass% or less, it becomes easier to maintain the shape during firing.

[0023] The partition wall 113 may be dense, but it is preferable that it be porous. Specifically, the porosity P of the partition wall 113 W The porosity is preferably 30% to 55%, and more preferably 30% to 45%. A porosity of 30% or more makes it easier to suppress deformation during firing. A porosity of 55% or less ensures that the strength of the honeycomb structure 110 is sufficiently maintained. Note that dense material refers to a porosity of 5% or less. Furthermore, the porosity of the outer wall 114 is preferably 30% to 55%, and more preferably 30% to 40%.

[0024] When a high-temperature gas flows through the honeycomb structure 110, the flow rate of the gas within the honeycomb structure 110 tends to be higher in the center than in the outer periphery. Therefore, the porosity P of the partition wall W Setting the porosity of the partition wall 113 to 30% to 55% is desirable to lighten the entire honeycomb structure 110 and reduce its heat capacity, thereby improving the temperature difference between the outer periphery and the center of the honeycomb structure 110 and enhancing the thermal shock resistance of the honeycomb structure 110.

[0025] Furthermore, conventionally, the partition wall 113 and the outer wall 114 are usually manufactured by integral molding, so the porosity of the partition wall 113 and the porosity of the outer wall 114 are basically the same. On the other hand, the electrode layers 112a and 112b are usually made more densely than the partition wall 113 and the outer wall 114 in order to spread the current. For this reason, if the porosity of the outer wall 114 is the same as that of the partition wall 113, the rigidity of the electrode layers 112a and 112b is usually higher than that of the honeycomb structure 110 (outer wall), so a difference in rigidity occurs between the electrode layers 112a and 112b and the outer wall 114, and there is a risk that cracks will occur in the outer wall 114.

[0026] Therefore, in the honeycomb structure 110 according to one embodiment of the present invention, the porosity of the outer peripheral wall 114 is made smaller than that of the partition wall 113, thereby making the outer peripheral wall 114 relatively denser and improving the rigidity of the outer peripheral wall. Specifically, the porosity P of the outer peripheral wall 114 O Porosity P of partition wall 113 W The ratio (P W / P o ) but, 1 <P W / P O It is preferable that the following conditions be met. W / P O When the value is greater than 1, the outer periphery wall 114 becomes relatively denser, reducing the rigidity difference between the electrode layers 112a and 112b and the outer periphery wall 114, suppressing the occurrence of cracks in the outer periphery wall 114, and improving the thermal shock resistance of the honeycomb structure 110. W / P O 1.05≦P W / P O It is more preferable that the condition is met, and 1.1 ≤ P W / P O It is even more preferable that the following conditions be met. On the other hand, from the viewpoint of ease of manufacture, P W / P O Preferably, the condition ≤ 1.8 is met, and P W / P O It is more preferable that ≤ 1.5 be satisfied, P W / P O It is even more preferable that ≤ 1.45 be satisfied, P W / P OIt is even more preferable that ≤ 1.3 be satisfied. Therefore, in one embodiment, 1 <P W / P O The condition ≤1.8 is satisfied, and in a preferred embodiment, 1.05 ≤ P W / P O Satisfying ≤1.5, and in a more preferred embodiment, 1.1 ≤ P W / P O Satisfying ≤1.45, and in a more preferred embodiment, 1.1 ≤ P W / P O It satisfies ≤ 1.3.

[0027] In this specification, the porosity P of the partition wall of the honeycomb structure is defined as follows: w The measurement is performed using the following procedure. First, let H be the height of the honeycomb structure, and take the coordinate axis in the direction of that height. If the coordinate value of one end face is 0 and the coordinate value of the other end face is 1.0H, then cut the honeycomb structure perpendicular to the cell extension direction at coordinate values ​​of 0.2H, 0.5H, and 0.8H to obtain the first division section from 0 to 0.2H, the second division section from 0.2H to 0.5H, the third division section from 0.5H to 0.8H, and the fourth division section from 0.8H to 1.0H. Next, partition samples are taken that include the cross-section at the coordinate value of 0.2H in the first division section ("first cross-section"), the cross-section at the coordinate value of 0.5H in the second division section (or the coordinate value of 0.5H in the third division section) ("second cross-section"), and the cross-section at the coordinate value of 0.8H in the fourth division section ("third cross-section"). For each cross-section, let R be the length from the centroid (central axis O) to the inner surface 114i of the outer wall 114. With the coordinate axis taken radially, and assuming the coordinate value of the centroid (central axis O) is 0 and the coordinate value of the inner surface 114i of the outer wall 114 is 1.0R, partition wall samples 142 (size: the above cross-section (5mm × 5mm) × depth 5mm) containing coordinate values ​​of 0.2R, 0.4R, 0.6R, and 0.8R at their center are taken at 90° intervals, expressed by the central angle with respect to the centroid (central axis O) (see Figure 3).

[0028] Next, the cross-section of each sample is observed at 50x magnification (field of view: 1 mm × 1 mm) using a scanning electron microscope (SEM) to obtain SEM images of the septa. By analyzing the acquired SEM images, the solid portion of the sample and the void portion (pores) of the sample are binarized using the modal method. The percentage ratio of the void portion in the sample to the total area of ​​the solid portion and void portion is then calculated, and this value is defined as the porosity of the sample. The average value of the porosity of all septa samples is defined as the porosity P of the septa of the honeycomb structure. w The measured value shall be as follows. Note that when measuring porosity using an electrically heated catalyst carrier equipped with a catalyst supported on a honeycomb structure, the catalyst portion shall be considered as the void portion of the partition wall.

[0029] In this specification, the porosity P of the outer wall of the honeycomb structure is defined as follows: O The measurement is performed using the following procedure. First, let H be the height of the honeycomb structure, and take the coordinate axis in the direction of that height. If the coordinate value of one end face is 0 and the coordinate value of the other end face is 1.0H, then cut the honeycomb structure perpendicular to the cell extension direction at coordinate values ​​of 0.2H, 0.5H, and 0.8H to obtain the first division section from 0 to 0.2H, the second division section from 0.2H to 0.5H, the third division section from 0.5H to 0.8H, and the fourth division section from 0.8H to 1.0H. Next, outer wall samples are taken that include the cross-section at the coordinate value of 0.2H in the first division section ("first cross-section"), the cross-section at the coordinate value of 0.5H in the second division section (or the coordinate value of 0.5H in the third division section) ("second cross-section"), and the cross-section at the coordinate value of 0.8H in the fourth division section ("third cross-section"). For each cross-section, 144 outer wall samples (size: 5mm x 5mm x 5mm depth, may include parts other than the outer wall) are taken from four locations in the circumferential direction at 90° intervals, using the central angle relative to the centroid (central axis O) (see Figure 3).

[0030] Next, the cross-section of each sample is observed at 50x magnification (field of view: 1 mm × 1 mm) using a scanning electron microscope (SEM) to obtain an SEM image of the outer wall. By analyzing the acquired SEM image, the solid portion of the sample and the void portion (pores) of the sample are binarized using the modal method. The percentage ratio of the void portion in the sample to the total area of ​​the solid portion and void portion is then calculated, and this value is defined as the porosity of the sample. The average value of the porosity of all outer wall samples is defined as the porosity P of the outer wall of the honeycomb structure. O This will be the measured value.

[0031] 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 heat uniformity, a hexagon is particularly preferred.

[0032] 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.

[0033] 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. From this viewpoint, 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. In this specification, the thickness T of the outer peripheral wall 114 of the honeycomb structure 110 O The porosity P of the outer wall 114 mentioned above is O This is defined as the average value of the outer wall thickness measured for all outer wall samples taken during the measurement process. The outer wall thickness for each outer wall sample is defined as the thickness in the direction normal to the tangent to the outer surface of the outer wall at any measurement point on that outer wall sample.

[0034] The thickness of the partition walls 113 that divide the cells 115 is preferably 0.1 to 0.3 mm, and more preferably 0.15 to 0.25 mm. A thickness of 0.1 mm or more for the partition walls 113 can suppress a decrease in the strength of the honeycomb structure 110. A thickness of 0.3 mm or less for the partition walls 113 can suppress an increase in pressure loss when exhaust gas is passed through the honeycomb structure 110 when the catalyst is supported on it. In this specification, the thickness of the partition walls 113 is defined as the length of the portion of the line segment that passes through the partition walls 113, in a cross section perpendicular to the extension direction of the cells 115, connecting the centroids of adjacent cells 115.

[0035] 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. 2It 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 110, excluding the outer peripheral wall portion.

[0036] By arranging electrode layers 112a and 112b, which have a lower volume resistivity than the outer peripheral wall 114, on the outer surface of the outer peripheral wall 114, the current spreads more easily in the circumferential direction of the honeycomb structure 110 and in the stretching direction of the cell 115, thereby improving the uniform heating performance of the honeycomb structure 110. In a cross section perpendicular to the stretching direction of 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°.

[0037] 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.

[0038] 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.

[0039] The thickness of the electrode layers 112a and 112b is preferably 0.01 to 5 mm, and more preferably 0.01 to 3 mm. This range enhances uniform heating. If the thickness of the electrode layers 112a and 112b is 0.01 mm or more, electrical resistance is appropriately controlled, allowing for more uniform heating. If the thickness of the electrode layers 112a and 112b is 5 mm or less, the risk of damage during canning is reduced. In this specification, the thickness of the electrode layer of the honeycomb structure 110 (T e ) is the porosity (P) of the electrode layer, which will be described later. eThis is defined as the average value of the electrode layer thickness measured for all electrode layer samples taken when measuring the electrode layer thickness. The electrode layer thickness in each electrode layer sample is defined as the thickness in the direction normal to the tangent to the outer surface of the electrode layer at any measurement point in that electrode layer sample.

[0040] It is preferable that the electrode layers 112a and 112b be porous. Specifically, the porosity (P) of the electrode layers 112a and 112b is e The porosity is preferably 30% to 55%, and more preferably 30% to 40%. A porosity of 55% or less can prevent the electrode layer from becoming too difficult to conduct current or too weak. A porosity of 30% or more can prevent the electrode layer from becoming too dense and too rigid.

[0041] In this specification, the porosity (P) of the electrode layer of the honeycomb structure e The following procedure is used to measure the temperature. First, let H be the height of the honeycomb structure, and take the coordinate axis in the direction of that height. If the coordinate value of one end face is 0 and the coordinate value of the other end face is 1.0H, then cut the honeycomb structure perpendicular to the cell extension direction at coordinate values ​​of 0.2H, 0.5H, and 0.8H to obtain the first division section from 0 to 0.2H, the second division section from 0.2H to 0.5H, the third division section from 0.5H to 0.8H, and the fourth division section from 0.8H to 1.0H. Next, electrode layer samples are taken that include the cross-section at the coordinate value of 0.2H in the first division section (referred to as the "first cross-section"), the cross-section at the coordinate value of 0.5H in the second division section (or the coordinate value of 0.5H in the third division section) (referred to as the "second cross-section"), and the cross-section at the coordinate value of 0.8H in the fourth division section (referred to as the "third cross-section"). For each cross-section, electrode layer samples 146 (size: 5mm x 5mm x 5mm depth, may include parts other than the electrode layers) are taken from four equally spaced locations (a total of eight locations) along the circumferential direction of each pair of electrode layers 112a and 112b (see Figure 3).

[0042] Next, the cross-section of each sample is observed at 50x magnification (field of view: 1 mm × 1 mm) using a scanning electron microscope (SEM) to obtain an SEM image of the electrode layer. By analyzing the acquired SEM image, the solid portion of the sample and the void portion (pores) of the sample are binarized using the modal method. The percentage ratio of the void portion in the sample to the total area of ​​the solid portion and void portion of the sample is then calculated, and this value is taken as the porosity of the sample. The average value of the porosity of all electrode layer samples is taken as the porosity (P) of the electrode layer of the honeycomb structure. e The measured value is taken from this value.

[0043] To improve thermal shock resistance, the thickness T of the electrode layers 112a and 112b e (Unit: mm), porosity P of electrode layers 112a and 112b e (Unit: %), Thickness T of outer wall 114 O (Unit: mm), and the porosity P of the outer wall 114. O (Unit: %) is 0.25≦(P O / T O ) / (P e / T e It is preferable that the relationship ) ≤ 1.0 is satisfied. (P O / T O ) / (P e / T e This value is an index that indicates the balance of rigidity between the electrode layers 112a and 112b and the outer wall 114.

[0044] (P O / T O ) / (P e / T e By setting the upper limit of ) to 1.0 or less, preferably 0.75 or less, and more preferably 0.7 or less, the rigidity of the electrode layers 112a and 112b can be relatively lowered. By relatively lowering the rigidity of the electrode layers 112a and 112b, the stress generated in the honeycomb structure can be reduced even in the event of rapid temperature changes. As a result, the thermal shock resistance of the honeycomb structure is improved.

[0045] (P O / T O ) / (P e / Te The lower limit of ) is preferably 0.25 or higher, more preferably 0.3 or higher, and even more preferably 0.4 or higher.

[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 (the same as the "silicon carbide-silicon composite material" described above), composite materials of metallic silicon and silicon carbide with metal silicides such as tantalum silicide and chromium silicide, 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 metallic silicon and silicon carbide, or a composite material of metallic silicon and silicon carbide with a metallic silicide such as tantalum silide or chromium silide, 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. 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-based ceramics such as alumina, mullite, zirconia, glass, and cordierite, and non-oxide-based 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 4, 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 cushioning material 260 may be placed between the metal pipe 220 and the electrically heated carrier 100. The material of the cushioning material 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] (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.

[0059] (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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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. This makes it possible to provide the honeycomb structure as a single molded product. Methods to make the porosity of the partitions higher than that of the outer wall include relatively reducing the amount of porosity-forming material added to the outer periphery of the clay body that will form the outer wall, and reducing the flow velocity and amount of clay body in the partition portion relative to the outer wall portion of the honeycomb molded body during extrusion molding. 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 honeycomb dried body.

[0065] 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.

[0066] (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 powder, ceramic powder, pore-forming material, etc.) that are formulated according to the required characteristics of the electrode layer. The porosity of the electrode layer can be controlled by adjusting the amount of pore-forming material added to the electrode layer forming paste. 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 based on volume when the particle size frequency distribution is measured by laser diffraction.

[0067] 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.

[0068] (Step 3) Step 3 is a step in which the unfired honeycomb structure with electrode layer forming paste is fired to obtain a honeycomb structure. 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, a 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.

[0069] (Step 4) Step 4 is a step of joining a metal terminal to the electrode layer. The joining method is not particularly limited, and examples thereof include spraying, welding, and brazing. From the viewpoint of improving the joinability between the electrode layer and the metal terminal, an underlayer may be formed by a method such as spraying.

Example

[0070] Hereinafter, examples for better understanding of the present invention and its advantages are illustrated, but the present invention is not limited to the examples.

[0071] <I. Manufacture of honeycomb structure (Comparative Example 1, Examples 1 to 9)> (1. Preparation of cylindrical green body) Silicon carbide (SiC) powder and silicon (Si) powder were mixed at a mass ratio of 80:20 to prepare a ceramic raw material. Then, hydroxypropylmethylcellulose as a binder and a water-absorbing resin as a pore-forming material were added to the ceramic raw material, and water was added to obtain a molding raw material. Then, the molding raw material was kneaded by a vacuum kneader to prepare a cylindrical green body.

[0072] In this case, 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 in all examples and comparative examples. 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 in all examples and comparative examples. The pore-forming material content was 5 parts by mass when the total amount of silicon carbide (SiC) powder and metallic silicon (Si) powder was 100 parts by mass in all examples and comparative examples. Furthermore, in Examples 1 to 9, by controlling the uneven pattern at the tip of the honeycomb molded body 44 formed by extruding clay 42 from the molding machine 40, a difference in flow velocity in the extrusion direction was created within the honeycomb molded body 44 extruded from the molding machine 40. Specifically, referring to Figure 5, the flow velocity and volume of the clay 42 in the partition wall portion of the honeycomb molded body 44 extruded from the nozzle 41 were made lower than those in the outer wall portion, creating a concave molding pattern at the tip of the honeycomb molded body 44 extruded from the molding machine 40. The flow velocity and volume of the clay 42 in the partition wall portion were controlled by the hole diameter and the pitch between the holes in the back plate 43, which is provided upstream of the nozzle 41 in the path of the clay 42 inside the molding machine 40. By reducing the diameter of the numerous holes in the back plate 43 through which the clay 42 forming the partition wall portion passes, or by increasing the pitch between the holes, the flow velocity and volume of the clay 42 forming the partition wall portion can be reduced. 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. The average particle size of the pore-forming material was also 20 μm. The average particle sizes of the silicon carbide powder, metallic silicon powder, and pore-forming material refer to the arithmetic mean diameter based on volume, obtained by measuring the particle size frequency distribution using laser diffraction.

[0073] (2. Preparation of honeycomb dried material) The obtained cylindrical clay was molded using an extrusion molding machine having a predetermined die 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. After high-frequency dielectric heating and drying of this honeycomb molded body, it was 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.

[0074] (3. Preparation of electrode layer forming paste) An electrode layer forming paste was prepared by mixing metallic silicon (Si) powder, silicon carbide (SiC) powder, a pore-forming agent (water-absorbing resin), methylcellulose, glycerin, and water in a rotary-rotating stirrer. The Si powder and SiC powder were blended in a volume ratio of Si powder:SiC powder = 40:60. In all examples and comparative examples, the methylcellulose content was 0.5 parts by mass when the total amount of Si powder and SiC powder was 100 parts by mass. In all examples and comparative examples, the glycerin content was 10 parts by mass when the total amount of Si powder and SiC powder was 100 parts by mass. In all examples and comparative examples, the water content was 38 parts by mass when the total amount of Si powder and SiC powder was 100 parts by mass. In Comparative Example 1, Examples 1-4, and 7-9, the pore-forming agent content was 3 parts by mass when the total amount of Si powder and SiC powder was 100 parts by mass. The content of the pore-forming material was reduced in Examples 5 and 6 compared to Comparative Example 1. The average particle size of the metallic silicon powder was 6 μm. The average particle size of the silicon carbide powder was 35 μm. The average particle size of the pore-forming material was 20 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.

[0075] (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°).

[0076] (5. Firing) The honeycomb structure with an electrode layer forming paste was dried at 120°C and then degreased at 550°C for 3 hours in an air atmosphere. Next, the degreased honeycomb structure with an electrode layer forming paste was fired and then oxidized to obtain a columnar honeycomb structure. The firing was carried out in an argon atmosphere at 1450°C for 2 hours. The subsequent oxidation treatment was carried out at a temperature of 1050°C for 6 hours in an air atmosphere. The honeycomb structure had a columnar outer shape with a height of 60 mm and a diameter of 103 mm, excluding the electrode layer. The thickness of the partition wall was 0.2 mm (designed value), and the cell density was 100 cells / cm 2 It was.

[0077] <II. Characteristic Evaluation> For the honeycomb structure obtained under the above manufacturing conditions, the following characteristic evaluations were carried out. Note that the number of honeycomb structures required for the characteristic evaluation was prepared.

[0078] (1. Measurement of Porosity) For the honeycomb structure obtained under the above manufacturing conditions, the porosity P of the partition wall, the porosity P of the outer peripheral wall, and the porosity P of the electrode layer were determined by the method described above. The results are shown in Table 1. w , the porosity P of the outer peripheral wall O , the porosity P of the electrode layer e were determined respectively. The results are shown in Table 1.

[0079] (2. Measurement of Outer Peripheral Wall Thickness) For the honeycomb structure obtained under the above manufacturing conditions, the thickness (T O ) of the outer peripheral wall was determined by the method described above. The results are shown in Table 1.

[0080] (3. Measurement of Electrode Layer Thickness) For the honeycomb structure obtained under the above manufacturing conditions, the thickness (T e ) of the electrode layer was determined by the method described above. The results are shown in Table 1.

[0081] (4. P W / P o and (P O / T O ) / (P e / T e )) Based on the above measurement results, PW / P o and (P O / T O ) / (P e / T e ) was calculated. The results are shown in Table 1.

[0082] (5. Heat shock resistance evaluation) Using a propane gas burner tester equipped with a metal case for storing the honeycomb structure (sample) obtained under the above manufacturing conditions and a propane gas burner capable of supplying heated gas into the metal case, a heating and cooling test of the sample was conducted. The above heated gas was combustion gas generated by burning propane gas with a gas burner (propane gas burner). Then, the heat shock resistance was evaluated by visually checking whether cracks occurred in the sample by the above heating and cooling test.

[0083] Specifically, the obtained sample was first placed (canned) in a metal case of a propane gas burner test machine. A ceramic cushioning material (alumina fiber and mullite fiber, etc.) was placed between the metal case and the sample. Then, gas heated by the propane gas burner (combustion gas) was supplied into the metal case and passed through the sample. The temperature conditions of the gas flowing into the metal case (inlet gas temperature conditions) were set as follows: First, the combustion gas was passed through to raise the temperature to the specified temperature in 5 minutes, and then it was held at the specified temperature for 10 minutes. After that, air was passed through to cool it to 100°C in 5 minutes, and then it was held at 100°C for 10 minutes. This series of operations—heating, cooling, and holding—is called the "heating and cooling operation." Afterward, the sample was visually inspected for cracks. Then, the "heating and cooling operation" was repeated while increasing the specified temperature by 25°C increments starting from 825°C. The specified temperature was set in 14 steps, in 25°C increments starting from 825°C. In other words, the above "heating and cooling operation" was performed until the specified temperature reached 1150°C. As the specified temperature increases, the rate of heating increases, and tensile stress is generated at the boundary between the electrode layer and the outer wall where the electrode layer is not formed. The results are shown in Table 1. In Table 1, the "Thermal Shock Resistance" column shows the specified temperature at which cracks occurred in the honeycomb structure during the heating and cooling test.

[0084] [Table 1]

[0085] (6. Discussion) Table 1 shows the porosity P of the outer wall. O The porosity P of the septum W The ratio (P W / P o ) but, 1 <P W / P O Examples 1 to 9, which satisfy ≤1.8, show a higher crack initiation temperature and improved thermal shock resistance compared to Comparative Example 1, which does not satisfy this relationship. Furthermore, P W / P oIt can also be seen that the larger the value, the more likely the crack initiation temperature is to rise. Furthermore, from a comparison of Examples 1, 5, 6, 7, 8, and 9, (P O / T O ) / (P e / T e It can also be seen that the smaller the value, the higher the crack initiation temperature tends to be. [Explanation of Symbols]

[0086] 100: Electrically heated carrier 110: Honeycomb structure 112a: Electrode layer 112b: Electrode layer 113: Bulkhead 114:Outer wall 114i: Inner surface of the outer wall 115: Cell 116: End face 118: End face 120: Base layer 130: Metal terminal 142: Partition sample 144: Exterior wall sample 146: Electrode layer sample 200: Exhaust gas purification device 220:Metal tube 240: Electric wire 260: Cushioning material

Claims

1. A 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 extending from one end face to the other end face, and The honeycomb structure is provided with a pair of electrode layers extending in a strip-like manner in the direction of cell extension on the outer surface of the outer peripheral wall, with the central axis of the honeycomb structure in between. The materials constituting the outer peripheral wall and the electrode layer are mainly composed of silicon carbide-silicon composite material. The porosity P of the partition wall W However, the percentage is between 30% and 55%. The porosity P of the outer wall O The porosity P of the partition wall relative to the porosity P W The ratio (P W / P o ) is 1 < P W / P O Satisfying ≤ 1.8, Honeycomb structure.

2. The thickness T of the electrode layer e (unit: mm), the porosity P of the electrode layer e (unit: %), the thickness T of the outer peripheral wall O (unit: mm), and the porosity P of the outer peripheral wall O (unit: %) satisfy the relationship of 0.25 ≦ (P O / T O ) / (P e / T e ) ≦ 1.

0. The honeycomb structure according to claim 1

3. The porosity P of the electrode layer e However, the honeycomb structure according to claim 1 or 2, wherein the percentage is 30% to 55%.

4. A honeycomb structure according to any one of claims 1 to 3, wherein the material constituting the outer peripheral wall, the partition wall, and the electrode layer is mainly composed of a silicon carbide-silicon composite material.

5. The honeycomb structure according to any one of claims 1 to 4, wherein the honeycomb structure portion is an integrally molded product.

6. A honeycomb structure according to any one of claims 1 to 5, 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.

7. The electrically heated carrier according to claim 6, A cylindrical metal tube housing the aforementioned electrically heated carrier, An exhaust gas purification device equipped with the following features.

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