Electric heating type carrier

Abstract

To provide an electric heating type carrier that can make a resistance increasing rate of an electric heating type carrier more gradual.SOLUTION: An electric heating type carrier according to the present invention comprises: a honeycomb structure 1 equipped with a honeycomb structural part 10 having an outer peripheral wall 100, and a partition wall 101 which is arranged inside the outer peripheral wall 100 and partitions and forms a plurality of cells 102a forming flow channels extending from one end face to the other end face; and a pair of electrodes for applying a voltage to the honeycomb structure 1, where the outer peripheral wall 100 and the partition wall 101 are constituted of a ceramic porous body, and the ceramic porous body has a specific surface area of 0.01 m2 / g or more and 0.20 m2 / g or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrically heated carrier. [Background technology]

[0002] Generally, an electrically heated carrier (EHC) is known in which electrodes are arranged on a honeycomb structure made of conductive ceramics, and the honeycomb structure itself is heated by passing electricity through it, thereby raising the temperature of the catalyst supported on the honeycomb structure to its activation temperature before the engine starts, thereby purifying the exhaust gas emitted immediately after the internal combustion engine starts.

[0003] Electrically heated carriers use power supplies of various voltages. Therefore, the resistance value of the electrically heated carrier must be adjusted to a predetermined value to match the voltage used. However, deterioration of the electrically heated carrier in a high-temperature environment can cause the conductive path to be interrupted, increasing the resistance and making it impossible to heat up to the target temperature within the specified time. The interruption of the conductive path is thought to be caused by the conductive path being exposed to the air in a high-temperature environment, causing an oxide film to grow on the surface of the conductive path, narrowing the conductive path.

[0004] In the following Patent Document 1, in order to realize a honeycomb structure that has an excellent balance between oxidation resistance and thermal shock resistance in high-temperature environments, it is proposed to adjust the temperature and time of heat treatment of the honeycomb structure to adjust the thickness of the oxide film formed on the surface of the silicon ceramic that constitutes the outer wall and partition wall. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-145495 Summary of the Invention [Problem to be solved by the invention]

[0006] In the above Patent Document 1, the thickness of the oxide film is adjusted, but there is room for improvement in the rate of increase in the resistance of the electrically heated carrier.

[0007] The present invention has been made to solve the above-mentioned problems, and one of its objects is to provide an electrically heated carrier that can slow down the rate of increase in resistance of the electrically heated carrier. [Means for solving the problem]

[0008] Item 1. In one embodiment, the present invention provides a honeycomb structure including a honeycomb structure part having an outer peripheral wall and partition walls disposed inside the outer peripheral wall to define a plurality of cells forming flow paths extending from one end face to the other end face, and a pair of electrodes for applying a voltage to the honeycomb structure, wherein the outer peripheral wall and the partition walls are made of a porous ceramic body, and the porous ceramic body has a thickness of 0.01 m. 2 / g or more and 0.20m 2 The present invention relates to an electrically heated carrier having a specific surface area of ​​0.1 wt.

[0009] Item 2. The present invention may relate to the electrically heated carrier according to Item 1, wherein the ceramic porous body is a composite of metal silicon and silicon carbide, and the volume ratio of metal silicon in the ceramic porous body is 18 vol% or more.

[0010] Item 3. The present invention provides a ceramic porous body having a bulk density of 2.7 g / cm 3 This may relate to an electrically heated carrier according to item 1 or 2 below.

[0011] Item 4. The present invention relates to a ceramic porous body having a specific surface area of ​​0.05 m 2 / g or more and 0.16m 2 / g or less.

[0012] Item 5. The present invention relates to a ceramic porous body having a specific surface area of ​​0.08 m 2 / g or more and 0.14m 2 / g or less. [Effects of the Invention]

[0013] According to one embodiment of the electrically heated carrier of the present invention, the ceramic porous body has a thickness of 0.20 m 2 / g or less, the porous ceramic body has a specific surface area of ​​0.01 m / g or less, which reduces the area of ​​the porous ceramic body that is exposed to the atmosphere and reduces the area where the porous ceramic body is oxidized. This makes it possible to moderate the rate of increase in resistance of the electrically heated carrier. Furthermore, if the porous ceramic body becomes too dense, the weight of the honeycomb structure increases and the time required to heat the honeycomb structure to a predetermined temperature (heating time) tends to become longer. However, according to the present invention, the porous ceramic body has a specific surface area of ​​0.01 m / g or less, which reduces the area of ​​the porous ceramic body that is exposed to the atmosphere and reduces the area where the porous ceramic body is oxidized. 2 / g or more, the heating time can be prevented from becoming long. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view showing a honeycomb structure included in an electrically heated carrier according to an embodiment of the present invention; [Figure 2] FIG. 2 is an explanatory view showing a state in which electrodes are attached to the honeycomb structure of FIG. [Figure 3] FIG. 4 is an explanatory diagram showing conductive paths in a honeycomb structure section. [Figure 4] 4 is an explanatory diagram showing a state in which the conductive path in FIG. 3 is narrowed by an oxide film. [Figure 5] 2 is an explanatory view showing a porous ceramic body that constitutes the outer peripheral wall and partition walls of the honeycomb structure part of FIG. 1. FIG. [Figure 6] FIG. 6 is an explanatory view showing a ceramic porous body having a smaller specific surface area than the embodiment of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to each embodiment, and the components can be modified and embodied without departing from the spirit of the present invention. Furthermore, various inventions can be formed by appropriately combining multiple components disclosed in each embodiment. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components of different embodiments may be appropriately combined.

[0016] FIG. 1 is a perspective view showing a honeycomb structure 1 included in an electrically heated carrier according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing a state in which an electrode 2 is attached to the honeycomb structure 1 of FIG.

[0017] The electrically heated carrier according to the embodiment of the present invention has a honeycomb structure 1 and a pair of electrodes 2 (see FIG. 2) for applying a voltage to the honeycomb structure 1.

[0018] As shown in FIG. 1, the honeycomb structure 1 has a honeycomb structure part 10. The honeycomb structure part 10 has an outer peripheral wall 100 and partition walls 101 disposed inside the outer peripheral wall 100 and defining a plurality of cells 102 that form flow paths extending from one end face to the other end face. The honeycomb structure part 10 may be a columnar member. A columnar shape can be understood as a three-dimensional shape having a thickness in the extension direction of the cells 102 (the axial direction of the honeycomb structure part 10). The ratio (aspect ratio) of the axial length of the honeycomb structure part 10 to the diameter or width of the end face of the honeycomb structure part 10 is arbitrary. The columnar shape may include a shape (flat shape) in which the axial length of the honeycomb structure part 10 is shorter than the diameter or width of the end face.

[0019] The outer shape of the honeycomb structure 10 is not particularly limited as long as it is columnar, and can be other shapes such as a columnar shape with circular end faces (cylindrical shape), a columnar shape with oval end faces, a columnar shape with polygonal end faces (quadragonal, pentagonal, hexagonal, heptagonal, octagonal, etc.), etc. The size of the honeycomb structure 10 is set to 2000 to 65000 mm2 in order to increase heat resistance (suppress cracks in the circumferential direction of the outer peripheral wall 100).2 It is preferable that the thickness is 5000 to 25000 mm 2 It is more preferable that the end faces of the pillar-shaped honeycomb structures are polygonal. A plurality of pillar-shaped honeycomb structures each having a polygonal end face can be joined together and used.

[0020] Although there are no limitations on the shape of the cells 102 in a cross section perpendicular to the extending direction of the cells 102, a square, a hexagon, an octagon, or a combination thereof is preferred. Among these, a square and a hexagon are preferred. By using such a cell shape, the pressure loss when exhaust gas flows through the honeycomb structure portion 10 is reduced, and the purification performance of the catalyst is improved.

[0021] The thickness of the partition walls 101 that define the cells 102 is preferably 0.1 to 0.8 mm, and more preferably 0.1 to 0.6 mm. When the thickness of the partition walls 101 is 0.1 mm or more, it is possible to prevent a decrease in the strength of the honeycomb structure section 10. When the thickness of the partition walls 101 is 0.8 mm or less, it is possible to prevent an increase in pressure loss when exhaust gas flows through the honeycomb structure section 10 when the honeycomb structure section 10 is used as a catalyst carrier and a catalyst is loaded thereon. In the present invention, the thickness of the partition walls 101 is defined as the length of a portion that passes through the partition walls 101, of a line segment that connects the centers of gravity of adjacent cells 102, in a cross section perpendicular to the extension direction of the cells 102.

[0022] The honeycomb structure 10 has a cell density of 4 to 150 cells / cm in a cross section perpendicular to the extending direction of the cells 102. 2 It is preferable that the number of cells is 7 to 100. 2 By setting the cell density in this range, it is possible to increase the purification performance of the catalyst while minimizing the pressure loss when exhaust gas flows through it. 2 If the cell density is 150 cells / cm or more, a sufficient catalyst carrying area is ensured. 2When the honeycomb structure 10 is used as a catalyst carrier and a catalyst is carried thereon, excessive pressure loss during the flow of exhaust gas is suppressed if the honeycomb structure 10 is not more than this value. The cell density is a value obtained by dividing the number of cells by the area of ​​one end face portion of the honeycomb structure 10 excluding the outer peripheral wall 100 portion.

[0023] Providing the peripheral wall 100 of the honeycomb structure 10 is useful from the viewpoint of ensuring the structural strength of the honeycomb structure 10 and suppressing leakage of the fluid flowing through the cells 102 from the peripheral wall 100. Specifically, the thickness of the peripheral wall 100 is preferably 0.05 mm or more, more preferably 0.10 mm or more, and even more preferably 0.15 mm or more. However, if the peripheral wall 100 is too thick, the strength becomes too high, which disrupts the strength balance with the partition walls 101 and reduces thermal shock resistance. Therefore, the thickness of the peripheral wall 100 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 peripheral wall 100 is defined as the thickness in the direction normal to the tangent of the peripheral wall 100 at the measurement point when the portion of the peripheral wall 100 whose thickness is to be measured is observed in a cross section perpendicular to the extension direction of the cells 102.

[0024] The honeycomb structure part 10 is made of a conductive material and is heated by passing an electric current through it. The honeycomb structure part 10 may be made of a conductive ceramic. There are no particular restrictions on the volume resistivity of the honeycomb structure part 10 as long as it can generate heat by Joule heat when a current is passed through it, but it is preferably 0.1 Ωcm or more and 200 Ωcm or less, and more preferably 1 Ωcm or more and 200 Ωcm or less. In the present invention, the volume resistivity of the honeycomb structure part 10 is a value measured at 25°C by a four-terminal method.

[0025] When the honeycomb structure member 10 is made of ceramics, the conductive material of the honeycomb structure member 10 can be selected from the group consisting of oxide ceramics such as alumina, mullite, zirconia, and cordierite, and non-oxide ceramics such as silicon carbide, silicon nitride, and aluminum nitride, but is not limited thereto. 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 material of the honeycomb structure member 10 contains a metal silicon-silicon carbide composite or a ceramic containing silicon carbide as the main component. When the conductive material of the honeycomb structure member 10 is said to be mainly made of a metal silicon-silicon carbide composite, this means that the honeycomb structure member 10 contains 90% by mass or more of the metal silicon-silicon carbide composite (total mass) as the total mass. Here, the metal silicon-silicon carbide composite contains silicon carbide particles as an aggregate and metal silicon as a binder that bonds the silicon carbide particles, and it is preferable that a plurality of silicon carbide particles are bonded by the metal silicon so as to form pores between the silicon carbide particles. When the conductive material of the honeycomb structure part 10 is said to be mainly composed of silicon carbide, it means that the honeycomb structure part 10 contains silicon carbide (total mass) in an amount of 90 mass% or more of the entire material.

[0026] When the honeycomb structure 10 contains a metal silicon-silicon carbide composite, the ratio of the "mass of metal silicon as a binder" contained in the honeycomb structure 10 to the sum of the "mass of silicon carbide particles as aggregate" contained in the honeycomb structure 10 and the "mass of metal silicon as a binder" contained in the honeycomb structure 10 is preferably 10 to 40 mass%, and more preferably 15 to 35 mass%.

[0027] The outer peripheral wall 100 and the partition walls 101 may be porous. If they are porous, the porosity of the outer peripheral wall 100 and the partition walls 101 is preferably 35 to 60%, and more preferably 35 to 45%. The porosity is a value measured with a mercury porosimeter. Furthermore, the outer peripheral wall 100 and the partition walls 101 may be dense, and if they are dense, the porosity of the outer peripheral wall 100 and the partition walls 101 may be 10% or less, or 5% or less.

[0028] The average pore diameter of the outer wall 100 and the partition walls 101 of the honeycomb structure portion 10 is preferably 2 to 15 μm, and more preferably 4 to 8 μm. The average pore diameter is a value measured by a mercury porosimeter.

[0029] The honeycomb structure 1 may have at least one electrode layer 11 provided on the outer surface of the peripheral wall 100. The electrode layer 11 may extend from one end to the other end of the honeycomb structure part 10 in the extending direction of the cells 102. The electrode layer 11 may constitute the outer peripheral surface of the honeycomb structure 1 together with the peripheral wall 100.

[0030] Although one electrode layer 11 may be provided over the entire outer peripheral surface of the honeycomb structure 1, in this embodiment, a pair of electrode layers 11 are provided, which are spaced apart from each other in the circumferential direction of the honeycomb structure 10 and extend in strip-like shapes in the extension direction of the cells 102. In a cross section of the honeycomb structure 10 perpendicular to the extension direction of the cells 102, one of the pair of electrode layers 11 is disposed on the opposite side of the center of the honeycomb structure 10 from the other electrode layer 11. Only one of the pair of electrode layers 11 is shown in FIG. 1. In a cross section perpendicular to the extension direction of the cells 102, 0.5 times the central angle of each electrode layer 11 may be 15 to 89°. The central angle of the electrode layer 11 may be the angle formed by two line segments connecting both ends of the electrode layer 11 to the center of the honeycomb structure 10 in a cross section of the honeycomb structure 10 perpendicular to the extension direction of the cells 102. When the honeycomb structure 10 is cylindrical, this angle may be the interior angle of a sector formed by two line segments and the electrode layer 11.

[0031] The thickness of the electrode layer 11 is preferably 0.01 to 5 mm, more preferably 0.01 to 3 mm. By setting the thickness within this range, uniform heat generation is possible. If the thickness of the electrode layer 11 is thinner than 0.01 mm, the electrical resistance may be high, which may result in inconsistent heat generation. If the thickness is thicker than 5 mm, the honeycomb structure 1 may be damaged during canning. Furthermore, if the electrode layer 11 is too thin, the effect of adjusting the outer diameter when varying the outer diameter of the honeycomb structure 1 in the extension direction of the cells 102 due to variations in the thickness of the electrode layer 11 is reduced, as described below. If the electrode layer 11 is too thick, the holding force of the portions without the electrode layer 11 is reduced, making them more likely to fall off during a vibration test. Furthermore, if the electrode layer 11 is too thin, the resistance value of the electrode layer 11 is insufficient, which makes it easier for current to flow through the substrate (honeycomb structure portion 10), resulting in unstable heat generation distribution, reduced purification performance, and damage to the substrate. On the other hand, if the electrode layer 11 is too thick, current tends to flow through the electrode layer 11, which tends to cause the electrode layer 11 to generate heat, resulting in unstable heat distribution, which leads to a decrease in purification performance and damage to the substrate.

[0032] The pair of electrode layers 11 in this embodiment each includes a separator 110 and a first partial electrode layer 111 and a second partial electrode layer 112 separated by the separator 110. The separator 110 may be a slit provided between the first partial electrode layer 111 and the second partial electrode layer 112. The slit may be filled with a material having a higher volume resistivity than the first partial electrode layer 111 and the second partial electrode layer 112. The first partial electrode layer 111 and the second partial electrode layer 112 are strip-shaped with a predetermined width in the circumferential direction of the honeycomb structure section 10, and the separator 110 is linear and narrower than the first partial electrode layer 111 and the second partial electrode layer 112. However, the arrangement of the separator 110 and the first partial electrode layer 111 and the second partial electrode layer 112 is not limited to this form as long as they can be connected to the electrode 2.

[0033] As shown in FIG. 2, a pair of electrodes 2 may be attached to the outer peripheral surface of the honeycomb structure 1. More specifically, the electrodes 2 may be fixed on the electrode layer 11. The electrodes 2 may be made of metal. An external power source such as a battery may be connected to the electrodes 2 via a power cable. By applying a voltage to the honeycomb structure 1 through the electrodes 2, the honeycomb structure 1 can be made to generate heat. This allows the catalyst supported on the honeycomb structure 1 to be heated to an activation temperature before starting the engine.

[0034] The electrode 2 may have a connection portion 21 arranged on the outer peripheral surface of the honeycomb structure 1 (on the electrode layer 11) and a lead portion 22 led out from the connection portion 21. Although not shown in detail, the connection portion 21 may be configured in a comb shape having a plurality of teeth, and some of the plurality of teeth may be connected to the first partial electrode layer 111 (see FIG. 1) and the other teeth may be connected to the second partial electrode layer 112 (see FIG. 1). The connection portion 21 may be formed in an arc shape along the outer peripheral surface of the honeycomb structure 1. The lead portion 22 may be erected from one end of the connection portion 21, and a power cable may be connected to this lead portion 22.

[0035] From the viewpoint of making it easier for electricity to flow through the electrode layers 11, the volume resistivity of the electrode layers 11 is preferably 1 / 200 or more and 1 / 10 or less of the volume resistivity of the honeycomb structure portion 10.

[0036] The material of the electrode layer 11 can be a conductive ceramic, a metal, or a composite material (cermet) of a metal and a conductive ceramic. Examples of the metal include a single metal such as Cr, Fe, Co, Ni, Si, or Ti, or an alloy containing at least one metal selected from the group consisting of these metals. Examples of the conductive ceramic include, but are not limited to, silicon carbide (SiC), and metal compounds such as metal silicides such as tantalum silicide (TaSi2) and chromium silicide (CrSi2).

[0037] In a manufacturing method of the honeycomb structure 1 having the electrode layers 11, first, an electrode layer forming raw material containing ceramic raw materials is applied to the side surface of a dried honeycomb body, and then dried to form a pair of unfired electrode layers extending in a band shape in the extension direction of the cells 102 on the outer surface of the peripheral wall 100, sandwiching the central axis of the dried honeycomb body, thereby producing a dried honeycomb body with unfired electrode layers. Next, the dried honeycomb body with the unfired electrode layers is fired to produce a fired honeycomb body with a pair of electrode layers 11. In this way, a honeycomb structure 1 having the electrode layers 11 is obtained.

[0038] By supporting a catalyst on the honeycomb structure 10, the electrically heated carrier can be used as a catalyst body. Examples of catalysts include precious metal catalysts and other catalysts. Examples of precious metal catalysts include three-way catalysts and oxidation catalysts in which a precious metal such as platinum (Pt), palladium (Pd), or rhodium (Rh) is supported on the pore surface of alumina and a promoter such as ceria or zirconia is included, and NOx storage reduction catalysts (LNT catalysts) containing alkaline earth metals and platinum as nitrogen oxide (NOx) storage components are included. Examples of catalysts that do not use precious metals include NOx selective reduction catalysts (SCR catalysts) containing copper-substituted or iron-substituted zeolites. Two or more catalysts selected from these catalysts may also be used. The catalyst support method is not particularly limited, and can be performed in accordance with conventional methods for supporting a catalyst on a honeycomb structure 1.

[0039] Next, Fig. 3 is an explanatory diagram showing the conductive paths 3 in the honeycomb structure section 10, and Fig. 4 is an explanatory diagram showing a state in which the conductive paths 3 in Fig. 3 are narrowed by an oxide film 3a. Figs. 3 and 4 show, as an example, an embodiment in which the outer wall 100 and the partition walls 101 of the honeycomb structure section 10 are made of a composite material of metal silicon (Si)-silicon carbide (SiC).

[0040] 3 and 4, the silicon metal-silicon carbide composite contains silicon carbide particles as an aggregate and metal silicon as a binder that binds the silicon carbide particles. When a current I is applied to the honeycomb structure 10, the current I flows through the conductive paths 3 formed by the silicon carbide particles and the metal silicon.

[0041] As shown in FIG. 3, even in the initial state of the honeycomb structure 1, an oxide film 3a is formed on the surface of the conductive path 3. When the honeycomb structure 1 is exposed to a high-temperature environment during use, the oxide film 3a grows from the surface of the conductive path 3 toward the inside, as shown in FIG. 4. The electrical resistivity of the oxide film 3a is higher than the electrical resistivity of the conductive path 3 formed by silicon carbide particles and metal silicon. Therefore, when the oxide film 3a grows and the conductive path 3 becomes narrower as shown in FIG. 4, the resistance value of the conductive path 3 increases, and the current I flowing through the conductive path 3 decreases. When the current I decreases, the amount of heat generated by the honeycomb structure portion 10 decreases.

[0042] Next, Figure 5 is an explanatory diagram showing the ceramic porous body 4 that constitutes the outer wall 100 and partition wall 101 of the honeycomb structure portion 10 in Figure 1, and Figure 6 is an explanatory diagram showing the ceramic porous body 4 having a smaller specific surface area than the embodiment in Figure 5.

[0043] The outer peripheral wall 100 and the partition walls 101 of the honeycomb structure section 10 of this embodiment are made of the porous ceramic body 4. In the honeycomb structure 1 of this embodiment, the porous ceramic body 4 is 0.01 m 2 / g or more and 0.20m 2 / g or less.

[0044] As shown in FIG. 5, when the specific surface area of ​​the porous ceramic body 4 is relatively large, the area of ​​the porous ceramic body 4 that is in contact with the atmosphere is relatively large, the region where the porous ceramic body 4 oxidizes (the region where the oxide film 3a shown in FIGS. 3 and 4 is formed) is wide, and the rate of increase in resistance (the rate of increase in resistance value over time) due to the growth of the oxide film 3a is large. In contrast, as shown in FIG. 6, when the specific surface area of ​​the porous ceramic body 4 is relatively small, the area where the porous ceramic body 4 is in contact with the atmosphere can be made relatively small, the region where the porous ceramic body 4 oxidizes (the region where the oxide film 3a shown in FIGS. 3 and 4 is formed) can be narrowed, and the rate of increase in resistance due to the growth of the oxide film 3a can be suppressed. After various studies by the present inventors, it was found that when the specific surface area of ​​the porous ceramic body 4 is set to 0.20 m as described above, 2 / g or less, the area of ​​the porous ceramic body 4 exposed to the air can be reduced, the area of ​​the porous ceramic body 4 that oxidizes can be reduced, and it has been found that the rate of increase in the resistance of the electrically heated carrier can be made slower.

[0045] On the other hand, if the porous ceramic body 4 becomes too dense, that is, if the specific surface area of ​​the porous ceramic body 4 is made too small, the weight of the honeycomb structure 1 increases, and the time required to heat the honeycomb structure 1 to a predetermined temperature (heating time) tends to become longer. 2 It was found that by setting the SiO2 content to 1 / g or more, it is possible to prevent the temperature rise time from becoming long.

[0046] The specific surface area of ​​the ceramic porous body 4 may be a value measured by a mercury porosimeter. More specifically, when a plurality of samples each weighing 0.80±0.03 g are taken from the center of the partition wall 101 in the honeycomb structure portion 10 of the electrically heated carrier and the specific surface areas of the samples are measured using a mercury porosimeter in accordance with JIS R1655:2003, the average value of the specific surface areas is 0.01 m. 2 / g or more and 0.20m 2 / g or less, the ceramic porous body 4 of the electrically heated carrier is 0.01 m 2 / g or more and 0.20m2 It may be understood that the specific surface area is equal to or less than 1 / g. The specific surface area may be the average value of values ​​measured from two samples.

[0047] The specific surface area of ​​the ceramic porous body 4 can be adjusted by the amount of pore-forming material contained in the material of the honeycomb structure 1. The pore-forming material intentionally forms pores, thereby increasing the specific surface area. When the total mass of the silicon carbide powder and metal silicon powder is taken as 100%, the content of the pore-forming material may be adjusted within the range of 0% to 10%.

[0048] The specific surface area of ​​the ceramic porous body 4 is 0.05 m 2 / g or more and 0.16m 2 / g or less. 2 / g or less, the rate of increase in the resistance of the electrically heated carrier can be more reliably made gentle. 2 / g or more, it is possible to more reliably prevent the temperature rise time from becoming long.

[0049] The specific surface area of ​​the ceramic porous body 4 is 0.08 m 2 / g or more and 0.14m 2 It is more preferable that the specific surface area of ​​the ceramic porous body 4 is 0.14 m / g or less. 2 / g or less, the rate of increase in the resistance of the electrically heated carrier can be made more surely gentle. 2 / g or more, it is possible to more reliably prevent the temperature rise time from becoming long.

[0050] 5 and 6, the ceramic porous body 4 may be a composite of metal silicon (Si) and silicon carbide (SiC), and the volume fraction of metal silicon in the ceramic porous body 4 may be 18 vol% or more. A volume fraction of metal silicon of 18 vol% or more can more reliably suppress the rate of increase in resistance. From the viewpoint of more reliably suppressing the rate of increase in resistance, there is no particular upper limit to the volume fraction of metal silicon, but from the viewpoint of thermal shock resistance, the upper limit to the volume fraction of metal silicon can be 48 vol%.

[0051] The volume fraction of metallic silicon in the ceramic porous body 4 may be a numerical value obtained by calculating the area fraction of metallic silicon by SEM image analysis and converting this area fraction into a volume fraction. More specifically, a sample may be taken from the center of the partition wall 101 of the honeycomb structure portion 10 of the electrically heated carrier, and multiple cross-sectional observation photographs may be taken at a magnification of 500 times (as an example, the number of cross-sectional observation photographs may be four). The observation range is an observation area of ​​0.08 mm2 in actual size. 2 (For example, 0.1mm x 0.2mm x 4 sheets = 0.08mm) 2 In the SEM image (which may be a single image), the proportions of metallic silicon and silicon carbide may be calculated by image processing (binarization). When measuring metallic silicon (white), silicon carbide (gray), and pores (black) using binarization, a threshold may first be set between metallic silicon and silicon carbide, with metallic silicon colored white and everything else colored black, and the area ratio measured to obtain the metallic silicon area S1. Next, a threshold may be set between silicon carbide and pores, with metallic silicon + silicon carbide colored white and pores colored black, to obtain the pore area ratio S2. When the area of ​​the entire honeycomb structure in the SEM image is S, the silicon carbide area S3 can be calculated by S - S1 - S2. Using S1 and S3, the area ratios of metallic silicon and silicon carbide can be calculated by (S1 / S) × 100 and (S3 / S) × 100, and then converted to volume ratios. When the average value of the measurements from the four images is 18 vol% or more, it can be understood that the volume fraction of metallic silicon in the ceramic porous body 4 of the electrically heated carrier is 18 vol% or more. GIMP can be used as binarization software.

[0052] When manufacturing the honeycomb structure 1, auxiliary materials such as metal silicon powder, silicon carbide powder, and binders are mixed to prepare a molding raw material. The volumetric ratio of metal silicon in the ceramic porous body 4 can be adjusted by adjusting the ratio of metal silicon and silicon carbide added at this time. The above-mentioned volumetric ratio of metal silicon can be obtained by preparing the molding raw material so that the metal silicon accounts for 10-40% by mass of the total mass of silicon carbide and metal silicon. When manufacturing the honeycomb structure 1 by silicon impregnation and firing, the amount of metal silicon can also be adjusted by the amount of silicon used during impregnation and firing.

[0053] The bulk density of the ceramic porous body 4 is 2.7 g / cm 3 The bulk density of the ceramic porous body 4 may be 2.7 g / cm or less. 3 From the viewpoint of more reliably reducing the temperature rise time, there is no particular lower limit for the bulk density of the porous ceramic body 4, but from the viewpoint of ensuring the strength of the honeycomb structure 1, the lower limit for the bulk density of the porous ceramic body 4 is set to 1.4 g / cm 3 Examples include:

[0054] The bulk density of the porous ceramic body 4 may be a value calculated from the bulk density measured by the Archimedes method and the opening ratio of the honeycomb structure part 10. More specifically, a sample may be taken from the partition walls 101 of the honeycomb structure part 10 of the electrically heated carrier, the bulk density of the sample may be measured in accordance with JISR1634:1998, and the measured bulk density may be divided by the opening ratio to calculate the bulk density of the porous ceramic body 4. For example, if the bulk density of the sample is 3 g / cm 3 When the opening ratio of the honeycomb structure portion 10 is 50%, the bulk density of the ceramic porous body 4 is 3÷0.5=6 g / cm 3 The calculated bulk density is 2.7 g / cm 3 When the bulk density of the ceramic porous body 4 of the electrically heated carrier is 2.7 g / cm or less, 3It may be understood as follows. Here, the opening ratio of the honeycomb structure 10 is the ratio of the area of ​​the cells 102 (openings) at the end face of the honeycomb structure 10 to the area of ​​the end face of the honeycomb structure 10 including the cells 102 (openings), and the thickness of the partition walls 101 can be calculated from the pitch of the cells 102. These thicknesses and pitches may be average values ​​measured at the center of the honeycomb structure 10.

[0055] The bulk density of the ceramic porous body 4 can be adjusted by controlling the porosity through the content of the pore-forming material, in the same manner as the specific surface area.

[0056] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Example]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0058] The inventors measured the specific surface area and bulk density of the porous ceramic body 4, as well as the volume fraction of metallic silicon in the porous ceramic body 4, for a number of electrically heated carriers. They also measured the resistance increase rate (resistance value after use / initial resistance value) and temperature rise time for these electrically heated carriers. The results are shown in Table 1 below.

[0059] [Table 1]

[0060] The specific surface area of ​​the ceramic porous body 4 was measured by the following method. That is, multiple samples were taken from the center of the partition wall 101 in the honeycomb structure part 10 of the electrically heated carrier so that the weight was 0.80±0.03 g, and the specific surface area of ​​each sample was measured using a mercury porosimeter in accordance with JIS R1655:2003. The specific surface area was determined as the average value of the values ​​measured for two samples.

[0061] The volume ratio of metallic silicon in the ceramic porous body 4 was measured by the following method. That is, a sample was taken from the center of the partition wall 101 of the honeycomb structure part 10 of the electrically heated carrier, and multiple cross-sectional observation photographs were taken at a magnification of 500 times. At this time, the number of cross-sectional observation photographs was four. 2 The observation area was set to 0.1 mm x 0.2 mm (0.1 mm x 0.2 mm x 4 sheets = 0.08 mm) 2 ) The proportions of metallic silicon and silicon carbide were then calculated by image processing (binarization). In the SEM image, metallic silicon appeared white, silicon carbide appeared gray, and pores appeared black. First, a threshold was set between metallic silicon and silicon carbide, rendering metallic silicon white and everything else black, and the area ratio was measured to obtain the metallic silicon area S1. Next, a threshold was set between silicon carbide and pores, rendering metallic silicon + silicon carbide white and pores black, obtaining the pore area ratio S2. When the area of ​​the entire honeycomb structure in the SEM image is S, the silicon carbide area S3 was calculated by S - S1 - S2. Using S1 and S3, the area ratios of metallic silicon and silicon carbide were calculated by (S1 / S) x 100 and (S3 / S) x 100, and then converted to volume ratios. GIMP was used for the binarization software.

[0062] The bulk density of the porous ceramic body 4 was measured by the following method. Specifically, a sample was taken from the partition wall 101 of the honeycomb structure part 10 of the electrically heated carrier, and the bulk density of the sample was measured in accordance with JIS R1634:1998. The bulk density of the porous ceramic body 4 was calculated by dividing the measured bulk density by the opening ratio.

[0063] A sample was cut out from the honeycomb structure 1, and the volume resistivity R0 of the sample was measured as an initial resistance value using a four-terminal method. The measured sample was then subjected to a durability test in a water vapor atmosphere at 950°C for 200 hours, and the volume resistivity R200 of the sample after the durability test was similarly measured as a resistance value after use. Then, R200 / R0 was calculated as the resistance increase rate.

[0064] As the temperature rise time of the honeycomb structure 1, a voltage of 3 kW was applied to the honeycomb structure 1, and the time until the input heat quantity reached 120 kJ was measured.

[0065] In the "Overall Evaluation" column of Table 1, an "x" (cross mark) indicates that the resistance increase rate is 1.60 or more, or the temperature rise time is 60 seconds or more. "△" (triangle), "◯" (circle) and "◎" (double circle) indicate that the resistance rise rate is less than 1.60 and the temperature rise time is less than 60 seconds. In particular, "△" indicates that the resistance increase rate is 1.50 or more and less than 1.60, or the temperature rise time is 54 seconds or more and less than 60 seconds. "Good" indicates that the resistance increase rate is 1.40 or more and less than 1.50, or the temperature rise time is 50 seconds or more and less than 54 seconds. "◎" indicates that the resistance increase rate is less than 1.40 and the temperature rise time is less than 50 seconds. Electrically heated carriers rated as "△", "◯" and "◎" are regarded as having a suitable resistance increase rate and temperature rise time.

[0066] As shown in Table 1, the specific surface area is 0.251 m 2 In Comparative Example 2, the resistance increase rate was 1.67, and the specific surface area was 0.196 m 2 In Example 8, where the specific surface area of ​​the porous ceramic body 4 was 0.20 m / g, the resistance increase rate could be suppressed to 1.54. 2 / g or less, the area of ​​the porous ceramic body 4 exposed to the air can be reduced, the area of ​​the porous ceramic body 4 that is oxidized can be reduced, and it has been confirmed that the rate of increase in the resistance of the electrically heated carrier can be made slower.

[0067] In addition, the specific surface area is 0.008m 2 In Comparative Example 1, the temperature rise time was 63 seconds, and the specific surface area was 0.011 m 2 In Example 1, where the specific surface area of ​​the porous ceramic body 4 was 0.01 m / g, the temperature rise time could be reduced to 58 seconds. 2 It was confirmed that by setting the solubility of the polymer to 1 / g or more, it is possible to prevent the temperature rise time from becoming long.

[0068] From these results, the specific surface area of ​​the ceramic porous body 4 was set to 0.01 m 2 / g or more and 0.20m 2 It was confirmed that by setting the SiO2 content to 1 / g or less, the resistance increase rate and temperature rise time of the electrically heated carrier can be kept within a preferable range.

[0069] Looking at Examples 1 to 8 from a different perspective, it was found that in Examples 1 to 8, the volume fraction of metallic silicon in the porous ceramic body 4 was 18 vol% or more. From these results, it was confirmed that when the volume fraction of metallic silicon in the porous ceramic body 4 is 18 vol% or more, the rate of increase in resistance of the electrically heated carrier can be more reliably suppressed.

[0070] Looking at Examples 1 to 8 from another perspective, in Examples 1 to 8, the bulk density of the ceramic porous body 4 was 2.7 g / cm 3 From these results, the bulk density of the ceramic porous body 4 was determined to be 2.7 g / cm 3 It was confirmed that the temperature rise time could be more reliably reduced by setting the temperature as follows:

[0071] In particular, the specific surface area is 0.155m 2In Example 7, where the specific surface area was 0.054 m / g, the resistance increase rate was further suppressed to 1.44. 2 In Example 3, where the specific surface area of ​​the porous ceramic body 4 was 0.05 m / g, the temperature rise time could be further reduced to 50 seconds. 2 / g or more and 0.16m 2 It was confirmed that by setting the SiO2 content to 1 / g or less, the rate of increase in the resistance of the electrically heated carrier can be more reliably suppressed, and the temperature rise time can also be more reliably reduced.

[0072] In addition, the specific surface area is 0.131m 2 In Example 6, where the specific surface area was 0.087 m / g, the resistance increase rate was further suppressed to 1.38. 2 In Example 4, where the specific surface area of ​​the ceramic porous body 4 was 0.08 m / g, the temperature rise time could be further reduced to 48 seconds. 2 / g or more and 0.14m 2 It was confirmed that by setting the SiO2 content to 1 / g or less, the resistance increase rate of the electrically heated carrier can be more reliably suppressed, and the temperature rise time can be more reliably reduced. [Explanation of symbols]

[0073] 1: Honeycomb structure 10: Honeycomb structure 100: Outer wall 101: Bulkhead 102: Cell 2: Electrode 4: Porous ceramics

Claims

1. a honeycomb structure including a honeycomb structure part having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and defining a plurality of cells that form flow paths extending from one end face to the other end face; a pair of electrodes for applying a voltage to the honeycomb structure; Equipped with The outer peripheral wall and the partition walls are made of a porous ceramic body, and the porous ceramic body has a thickness of 0.01 m 2 / g or more and 0.20m 2 / g or less specific surface area, Electrically heated carrier.

2. the ceramic porous body is a composite material of metal silicon and silicon carbide, and the volume ratio of the metal silicon in the ceramic porous body is 18 vol% or more; 2. An electrically heated carrier according to claim 1.

3. The bulk density of the ceramic porous body is 2.7 g / cm 3 Below is the 2. An electrically heated carrier according to claim 1.

4. The specific surface area of ​​the ceramic porous body is 0.05 m 2 / g or more and 0.16m 2 / g or less, 4. An electrically heated carrier according to any one of claims 1 to 3.

5. The specific surface area of ​​the ceramic porous body is 0.08 m 2 / g or more and 0.14m 2 / g or less, 5. An electrically heated carrier according to claim 4.

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